what is a good thesis statement for coral reefs

91 Coral Reef Essay Topic Ideas & Examples

🏆 best coral reef topic ideas & essay examples, 🥇 most interesting coral reef topics to write about.

• 🎓 Simple & Easy Coral Reef Essay Title

❓ Research Questions About Coral Reefs

• Coral Reef and Biodiversity in Ecosystems Coral reefs are formed only in the tropical zone of the ocean; the temperature limits their life – are from +18 to +29oS, and at the slightest deviation from the boundaries of the coral die.
• Biomes and Ecosystems: Aquatic & Coral Reefs In some of them, the protection is enhanced by the presence of anemones on the shell. Currently, under the influence of anthropogenic factors, there is a reduction in biological diversity due to the elimination of […]
• Divers Practices and Associated Effects on Coral Reefs However, in a bid to preserve the good marine life and the coral with excellent visibility in the Sharm el-Sheikh, it is necessary to control the crowding of divers because may damage the coral reefs. […]
• Coral Reefs Protection: Academic Sources Analysis The authors published the work on behalf of the United States Department of Commerce and provided only objective information in the form of statistical calculations; therefore, the level of bias is low.
• IMC Campaign Project of Hawaii Living Reef The Hawaii Living Reef Program will focus on the target audiences to aware them about the importance of the coral reef ecosystem, to change their behavior towards living reefs, to aware about the consequence of […]
• Hawaii Living Reef Program: Strategic Plan The Hawaii living reef program aims at sensitizing the communities living in the island of the importance of conserving the coral reefs.
• Hydrosphere: Coral Reefs and Their Protection The theme of this paper is to discuss the coral reefs ecosystem and the favorable environment required for the growth and maintenance of the corals.
• Biology. Coral Reef Disease as an Emerging Issue The disease affects the tissue of pink starlet coral and the blush star coral and to a lesser extent in Montastraea annularis.
• Biology: Coral Reef and Its Diseases The stresses that affect coral reefs can include changes in water temperature, differences in the amount of ultraviolet radiation they are exposed to and the amount of sedimentation and pollutants that settle in and around […]
• Importance of Coral Reefs The algae that is found in the sea also helps in reef building because they contain limestone and this is important in the integrity of the reefs.
• Protected Marine Areas: Great Barrier Reef To protect the Great Barrier Reef the administration has put in place several policies to protect this region. In this plan, A panel of scientists was to advise on the quality of waste.
• Ecology of Coral Reefs Review However, there are also places in the ocean such as the seafloor slopes up toward the continental shelf and the oceanic islands where the marine life is concentrated due to the availability of sunlight and […]
• Review of the Quaternary History of Reefs in the Red Sea With Reference to Past Sea-Level Changes Some of the changes have occurred on the very grandest of scales, such as the Merging and ensuing breaking up of huge supercontinents, or the decimation of the dinosaurs by extra-terrestrial impacts.reefs are not invulnerable […]
• Coral Bleaching on the Great Barrier Reef The economic implications of the inclusion of the large figures in this report may lead the reader to inquire why the losses are so significant in the case of coral reefs.
• Coral Reefs in Australia Following the ecological importance of the coral reefs, under the management of Australia and Queensland government, zoning of the coral area was done along the coastline, thus creating the Great Barrier Reef.
• The Great Barrier Reef The System Analysis Diagram of the Current Situation The first diagram indicates that the effects of human activities on the GBR may not be necessarily direct, and sometimes they are very difficult to trace.
• Great Barrier Reef: Flood Alleviation Solutions In the first presentation, solutions to protect the Great Barrier Reef, which is endangered from rising acidity levels due to methane extraction, were given while the second, third and fourth presentations focused on the measures […]
• Florida Keys National Marine Sanctuary Reefs This essay addresses some of the disturbances which have been experienced in the coral reefs of the Florida Keys National Marine Sanctuary together with measures which have been implemented to salvage the ecosystem.
• Global Warming and Coral Reefs The frightening evidence of the devastating tendencies in coral reef reduction can be illustrated by the case of the coral cover of the Rio Bueno, a coral reef site on the North East of Jamaica […]
• Coral Bleaching and Its Impact on Coral Reefs Ecosystems
• Improving Water Quality and Protect Coral Health in the Great Barrier Reef
• Coral Reef Ecosystems Under Climate Change and Ocean Acidification
• Coral Reef Bleaching and the Impact on the Marine Ecosystem
• Benefits and Related Threats of Coral Reef Ecosystem Services
• Coral Reef Monitoring, Reef Assessment Technologies, and Ecosystem-Based Management
• Benthic Oxygen and Nitrogen Exchange on a Cold-Water Coral Reef
• Coral Reef Building Organisms and Form the Reef Framework
• Beyond Reef Restoration: Next-Generation Techniques for Coral Gardening, Landscaping, and Outreach
• Coral Reef Pollution Can Hurt Bermuda’s Tourism Industry
• Building Coral Reef Resilience Through Spatial Herbivore Management
• Coral Reef Carbonate Chemistry Variability at Different Functional Scales
• Selectivity of Fishing Gears in a Multi-Species Indonesian Coral Reef Fishery
• Coast Guards Should Prevent Divers From Going Near a Living Coral Reef
• Co-management Strategy for the Sustainable Use of Coral Reef Resources
• Coral Reef Degradation Differentially Alters Feeding Ecology of Co-occurring Congeneric Spiny Lobsters
• Reconstructing Four Centuries of Temperature-Induced Coral Bleaching on the Great Barrier Reef
• Tropical Fish Diversity Enhances Coral Reef Functioning Across Multiple Scales
• Conserving Coral Reef Organisms That Lack Larval Dispersal
• Coral Biodiversity and Bio-Construction in the Mesoamerican Reef System

🎓 Simple & Easy Coral Reef Essay Titles

• Quantifying Coral Reef Resilience to Climate Change and Human Development
• Thermally Variable, Macrotidal Reef Habitats Promote Recovery From Mass Coral Bleaching
• Role of Larval Connectivity Among Coral Reef Islands in an Era of Global Change
• The Link Between Ecological Goods and Services of Coral Reef Ecosystems
• Analysis of Optics and Ecophysiology of Coral Reef Organisms
• Emerging Technologies and Coral Reef Conservation: Opportunities, Challenges, and Moving Forward
• Few Herbivore Species Consume Dominant Macroalgae on a Caribbean Coral Reef
• Fine-Scale Coral Connectivity Pathways in the Florida Reef Tract
• Great Barrier Reef: Impacts of Sea Temperature on Coral Bleaching
• Managing Local Stressors for Coral Reef Condition
• Multiple Stressors and Ecological Complexity Require a New Approach to Coral Reef
• The Importance of Partner Abundance in Reef Coral Symbioses
• The Effects of Climate Change on Coral Reef Ecosystems
• Science, Diplomacy, and the Red Seas Unique Coral Reef: Its Time for Action
• Small Scale Genetic Population Structure of Coral Reef Organisms
• The Analysis of the Great Barrier Reef of Australia’s Coral Reefs
• Time Preferences and the Management of Coral Reef Fisheries
• Warmer Water Affects Immunity of a Tolerant Reef Coral
• What Can Artificial Intelligence Offer Coral Reef Managers?
• What Is Happening to Coral Reefs as a Result of Ocean Acidification?
• How Does Human Overpopulation Affect Coral Reefs?
• Why Are Coral Reefs Dying?
• Are Coral Reefs Beneficial to the Ecosystem and Mankind?
• How Can People Prevent Coral Reefs From Disappearing?
• Why Is Coral Reef the Most Productive Ecosystem?
• How Does Climate Change Affect Coral Reefs?
• What Is the Impact of Humans on the Resilience of Coral Reefs?
• How Is Plastic Waste Linked to Diseases on Coral Reefs?
• What Is the Variety of Coral Reefs?
• How Far and How Often Do Fish on Coral Reefs Disperse?
• What Are the Effects of Coral Reefs on Populations in the Atlantic and Caribbean Region?
• How Are Coral Reefs Related to Shark Extinction?
• What Will Happen if the Coral Reefs Are Destroyed?
• What Threatens the Decomposition of Coral Reefs?
• Is It Correct to Believe That Coral Reefs Are the Source of Life in Our World?
• What Is the Impact of Coral Reefs on the Environment?
• What Problems Do Cruise Liners Cause for Coral Reefs?
• How Are Coral Reefs Formed?
• How Are Coral Reefs Related to Other Underwater Life Forms?
• Coral Reefs: Are They the Rainforests of the Sea?
• How Does Coral Bleaching Affect Coral Reefs?
• What Is the Current and Future Status of Coral Reefs in Malaysia?
• How Does the Sugar Industry Affect Florida’s Coral Reefs?
• Is There a Connection Between Global Warming and Coral Reefs?
• How Are Coral Reefs Classified?
• Can Restocking Herbivorous Fish Populations Be a Tool for Coral Reef Restoration?
• How Can We Save Them Coral Reefs?
• What Factors Play an Important Role in Fish Production in Coral Reefs?
• How Are Coral Reefs Managed in the South China Sea?
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Coral Reef Essay: Descriptive Writing How-to Guide

Coral reefs can be called one of the most amazing things created by nature. These structures can be found in tropical and temperate waters. Like many other unique natural phenomena, coral reefs are influenced by human activity these days. This negative impact is one of the significant issues to consider when talking about coral reefs.

By the way, it can be a crucial idea for discussion in your coral reef essay. Maybe, it is even one of the easiest ways to complete coral reef essays. For additional info, just keep reading – we also have some excellent suggestions for you on custom writing service .

• ❓ What Is a Coral Reef?
• 📃 Coral Reef Essay Structure
• 🐠 21 Coral Reef Essay Topics

1. ❓ What Is a Coral Reef?

When you write about coral reefs, you should have a clear understanding of what is a coral reef ecosystem, and what is a coral. We all saw corals on photos, videos or even live. But what exactly are corals? Are they plants or animals?

Let’s find out!

Corals neither are plants, nor a quaint stone, but living marine polyps that have a unique limestone skeleton structure growing about 15 mm every year. Corals are the lower coelenterate multicellular creatures in the world’s oceans.

Imagine a solid lime cylinder, surrounded from the inside and outside by a soft tissue of cells. In its center is the “mouth” of the coral and then it turns into the abdominal cavity. The coral feeds on plankton, capturing small marine organisms with its tentacles around the mouth, which have mucus that paralyzes the prey.

Corals in their structure are very different. Some corals have a solid skeleton (which is called madrepores), some don’t have it, and some have mixed type of skeleton, like tubular coral.

There are both solitary and colonial corals, which together form a complete barrier, shore reefs or atolls. Old corals die, and new living corals grow on top of them.

Corals, like plants, take energy from light, water and carbon dioxide. This happens because of the unicellular algae that live in their tissues. In the daytime the coral functions like a plant, and at night it lives the life of an animal. Another coral reef features are the abilities to glow when the coral gets under ultraviolet rays or illuminated by blue light.

2. 📃 Coral Reef Essay Structure

Well, now you know what corals and coral reef are. It’s time to think about your assignment and sketch the essay outline.

Whether you’re writing a descriptive or argumentative essay on coral reefs, the structure remains the same:

• In the coral reef introduction, you may present a short overview of what are coral reefs and point out the central thesis of your writing. A thesis statement generator for expository essay might help you to come up with an informative intro.
• The body of your essay must support the thesis statement by coral reef facts and research results. How can you defend the thesis statement of your paper? Remember, each body paragraph must present a particular idea to prove your essay thesis.
• In the essay conclusion, you have to summarize your body and present the essay topic. Avoid repeating the central thesis, but rather sum up all facts and arguments. Don’t forget to keep it short.

3. 🐠 21 Coral Reef Essay Topics & Research Ideas

Now comes the most exciting part of our article. We’ve prepared a bunch of essay topic ideas on coral reefs.

Keep reading!

3.1. Coral Reef Essay Topics: Basics

If you’re going to write a descriptive essay, you may try one of the suggested topic ideas below:

• Types of coral reefs. The barrier reef, fringing reef, atoll, and ribbon reef are all the types of coral reef. Give definitions to each type and describe their peculiarities in your coral reef essay.
• Famous coral reefs. What is the largest coral reef? Which one is the longest? Which coral reef is called the deepest photosynthetic reef? You can answer these questions if you investigate some of the most famous reefs in your coral reef essay.
• Coral reefs feeding. Are you surprised? In fact, they do eat, and you can learn more about it when covering this topic in the coral reef essay. When do corals eat? Find the answers and present them in your coral reef essay.
• Coral reef animals and plants . Discover what animals live in the coral reef? How do they feed? You may also want to create your own Great Barrier Reef animals list to find out more about the coral reef ecosystem.
• The corals and their place in the marine ecosystem. What is the importance of the Great Barrier Reef? Why are coral reefs important to the entire ocean ecosystem ?

• Cold-water corals. Did you know that corals can live in cold water? Find out more about these fantastic creatures.
• Importance of coral reefs for the environment. Provide some reasons why coral reefs are important for the environment and humanity.

3.2. Coral Reef Research Topics: Human Impact

Human impact on coral reefs is significant. That’s why we need to protect them. Check the topics on how are humans affecting coral reefs below:

• Overfishing. Coral reef animals are a significant food source for people. But some coral reef species play a significant role in its ecosystem . Find out how fishing impacts coral reefs.

• Marine pollution . Tons of garbage, plastic, and human waste is thrown every day into the ocean. Explore how the pollution affects coral reef destruction.
• Sewage. Discover how untreated wastewater impacts tropical coral reef ecosystem.
• Coral reefs and climate change. Examine how does temperature affect coral reefs?
• Coral preservation . Think, how you can help to save coral reefs?
• Ocean acidification . Find out how it impacts coral reef sands.
• Coral bleaching causes and consequences. How does coral bleaching affect marine life ? Explore why is coral bleaching bad for the environment .

• Destructive fishing. How do cyanide fishing, bottom trawling, blast or dynamite fishing, and muro-ami affect the Great Barrier Reef organisms ?
• Vacations and reefs. Everyone wants to spend their holiday in a picturesque place and try boating, snorkeling, fishing, and diving. Tourists touch and collect corals, drop anchors on reefs, etc. Explore how does tourism affect coral reefs? Explain why this threatens reefs and offer solutions to avoid it.
• Resorts and reefs. Explore the negative impact of a tourist resort on reef ecosystem.
• Sedimentation and its effects on coral reefs. Find out how construction, farming , mining and logging and deforestation cause erosion and its negative impact on coral reefs.
• What would happen if the Great Barrier Reef was destroyed? Express your opinion.
• Coral reefs and medicine. How do coral species can contribute to medicine and disease treatments?
• Sugar industry and coral reefs. Discover how does sugar industry affect coral reefs.

Definitely, human activity and its impact is not the only topic you can consider in coral reef essays. If you are really interested, you can look through scientific articles on coral reefs and find out the most burning issues.

If you want to write descriptive essays on a coral reef, we have additional tips for you. Our site will also be helpful if you need to write a geography essay.

Well, we’re all living on Earth, and we cannot just hide from global issues. Think of how everyone can make the world a better place for a living. Share your thoughts with Custom Writing team in comments below!

Learn more on this topic:

• Best Descriptive Essays That Win Top Marks
• Harriet Tubman Essay: How to Write, Prompts and Ideas
• Americanism Essay Writing: How-to Guide, Tips, Topics
• Halloween Essay: How to Write, Topics and Essay Ideas

🔗 References

• How to Write a Descriptive Essay: Jennifer Frost, GrammarCheck
• Descriptive Essays: Purdue Writing Lab
• Coral Reefs Essay: Bartleby
• Developing A Thesis: Harvard College Writing Center
• Corals and Coral Reefs: Smithsonian Ocean
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A scientific framework for evaluating coral reef resilience to climate change

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JOINT PROGRAM IN OCEANOGRAPHY/APPLIED OCEAN SCIENCE & ENGINEERING

• Coastal Studies
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• Marine geology/geophysics/tectonics
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• Program Requirements
• Questions and Clarity: Insights from Applying Computational Methods to Paleoclimate Archives

Coral Reefs in the Anthropocene Ocean: Novel Insights from Skeletal Proxies of Climate Change, Impacts, and Resilience

• Inferring the Thermomechanical State of the Lithosphere Using Geophysical and Geochemical Observables
• Structure and Mechanics of the Subducted Gorda Plate: Constrained by Afterslip Simulations and Scattered Seismic Waves
• The Heterogeneity and Volatile Content of Earth’s Mantle, Magmas and Crust
• Insights from Geodynamic Models Into Ice Flow, Mantle Magmatism, and Their Interactions
• Coastal Evolution on Earth and Titan
• U-Th Dating of Lacustrine Carbonates
• High Resolution Sedimentary Archives of Past Millennium Hurricane Activity in the Bahama Archipelago
• Reconstructing Atmospheric Changes in Monsoon Regions Using Eolian Dust
• Seismic and Numerical Constraints on the Formation and Evolution of Oceanic Lithosphere
• Greenlandic Ice Archives of North Atlantic Common Era Climate
• Investigating Mexican Paleoclimate with Precisely Dated Speleothems
• Wave-Driven Geomorphology of Pacific Carbonate Coastlines: From landscape to Wavelength Scale
• An inverse modeling approach to investigate deep ocean ventilation from radiocarbon records
• Geophysical and Geochemical Contraints on Submarine Volcanic Processes
• Storm Signatures in Coastal Ponds and Marshes Over the Late Holocene
• Water and Volatile Element Accretion to the Inner Planets
• Influence of Meltwater on Greenland Ice Sheet Dynamics
• Geophysical and Petrological Constraints on Ocean Plate Dynamics
• Trace Element Proxies and Mineral Indicators of Hydrothermal Fluid Composition and Seafloor Massive Sulfide Deposit Formation Processes
• Reconstructing Deglacial Ocean Ventilation Using Radiocarbon: Data and Inverse Modeling
• Geophysical and Geochemical Constraints on the Evolution of Oceanic Lithosphere From Formation to Subduction
• Coral Biomineralization, Climate Proxies and the Sensitivity of Coral Reefs to CO2-Driven Climate Change
• A Scientific Framework for Evaluating Coral Reef Resilience to Climate Change
• Little Ice Age Climate in the Western Tropical Atlantic Inferred from Coral Geochemical Proxies
• Seismic Constraints on the Processes and Consequences of Secondary Igneous Evolution of Pacific Oceanic Lithosphere
• Plan-View Evolution of Wave-Dominated Deltas
• Chemical, Isotopic, and Temporal Variations during Crustal Differentiation: Insights from the Dariv Igneous Complex, Western Mongolia
• Investigating the Evolution and Formation of Coastlines and the Response to Sea-Level Rise
• Mechanical and Geological Controls on the Long-Term Evolution of Normal Faults
• Exploring the Climate Change Refugia Potential of Equatorial Pacific Coral Reefs
• Lithospheric Dynamics of Earth’s Subduction Zones and Martian Tectonic Provinces
• Quaternary Morphology and Paleoenvironmental Records of Carbonate Islands
• Amundsen Sea Sea-Ice Variability, Atmospheric Circulation, and Spatial Variations in Snow Isotopic Composition from New West Antarctic Firn Cores
• Evolution of Oceanic Margins: Rifting in the Gulf of California and Sediment Diapirism and Mantle Hydration During Subduction
• Deep Explosive Volcanism on the Gakkel Ridge and Seismological Constraints on Ahallow Recharge at TAG Active Mound
• Climate Controls on Coral Growth in the Caribbean
• The CAFE Experiment: A Joint Seismic and MT Investigation of the Cascadia Subduction System
• Investigation of the Effect of a Circular Patch of Vegetation on Turbulence Generation and Sediment Deposition Using Four Case Studies
• Advanced Geophysical Studies of Accretion of Oceanic Lithosphere in Mid-Ocean Ridges Characterized by Contrasting Tectono-Magmatic Settings
• Earthquake Behavior and Structure of Oceanic Transform Faults
• Aridification of the Indian Subcontinent During the Holocene: Implications for Landscape Evolution, Sedimentation, Carbon Cycle and Human Civilizations
• Determining Timescales of Natural Carbonation of Peridotite in the Samail Ophiolite, Sultanate of Oman
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• Hydrological and Biogeochemical Cycling Along the Greenland Ice Sheet Margin
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• Low-Latitude Western North Atlantic Climate Variability During the Past Millennium: Insights from Proxies and Models

Nathaniel Mollica, Ph.D., 2021 Anne Cohen, Co-Advisor Weifu Guo, Co-Advisor

and rapid ocean acidification (OA). Ensuring survival of coral reefs will require a new management approach that incorporates robust understanding of reef-scale climate change its impact on corals, and their potential for adaptation. In this thesis, I extract information from within coral skeletons to 1) Quantify the changes occurring on coral reefs and the effects on coral growth, 2) Identify differences in the sensitivity of coral reefs, and 3) Evaluate their adaptation potential. First, I develop a model to show coral that skeletal density is vulnerable to OA and that, 21 st century OA projections will reduce coral skeletal density globally. Second, I use a skeletal bleaching proxy to quantify coral responses to heatwaves in the central equatorial Pacific (CEP) revealing a long history of bleaching in the region and reef-specific differences in thermal tolerance. Third, I improve the Sr-U paleo-thermometer to generate monthly-resolved sea surface temperatures (SST) using laser ablation ICPMS. Finally, I reconstruct the past 100 years of SST at Jarvis Island in the CEP, and show that a coral population on Jarvis Island has not yet adapted to the pace of anthropogenic climate change.

A critical moment for coral reef survival

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The mass coral bleaching occurring on enormous scales globally is a startling and accurate indicator of how much our climate is changing Dr Melita Samoilys

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How does climate change affect coral reefs?

The varied effects of climate change are changing the ocean ; these changes dramatically affect coral reef ecosystems ..

Climate change poses a major threat to coral reefs. Download this infographic | Infographic Text

Climate change is the greatest global threat to coral reef ecosystems. Scientific evidence now clearly indicates that the Earth's atmosphere and ocean are warming, and that these changes are primarily due to greenhouse gases derived from human activities.

As temperatures rise, mass coral  bleaching  events and infectious disease  outbreaks are becoming more frequent. Additionally, carbon dioxide absorbed into the ocean from the atmosphere has already begun to reduce calcification rates in reef-building and reef-associated organisms by altering seawater chemistry through decreases in pH. This process is called  ocean acidification .

Climate change will affect coral reef ecosystems, through sea level rise, changes to the frequency and intensity of tropical storms, and altered ocean circulation patterns. When combined, all of these impacts dramatically alter ecosystem function, as well as the goods and services coral reef ecosystems provide to people around the globe.

Infographic Text

Threats to coral reefs: climate change.

Increased greenhouse gases from human activities result in climate change and ocean acidification. Climate change = ocean change. The world's ocean is a massive sink that absorbs carbon dioxide (CO 2 ). Although this has slowed global warming, it is also changing ocean chemistry.

Climate change dramatically affects coral reef ecosystems

Contributing factors that increase greenhouse gases in the atmosphere include burning fossil fuels for heat and energy, producing some industrial products, raising livestock, fertilizing crops, and deforestation. Climate change leads to:

• A warming ocean: causes thermal stress that contributes to coral bleaching and infectious disease.
• Sea level rise: may lead to increases in sedimentation for reefs located near land-based sources of sediment. Sedimentation runoff can lead to the smothering of coral.
• Changes in storm patterns: leads to stronger and more frequent storms that can cause the destruction of coral reefs.
• Changes in precipitation: increased runoff of freshwater, sediment, and land-based pollutants contribute to algal blooms and cause murky water conditions that reduce light.
• Altered ocean currents: leads to changes in connectivity and temperature regimes that contribute to lack of food for corals and hampers dispersal of coral larvae.
• Ocean acidification (a result of increased CO 2 ): causes a reduction in pH levels which decreases coral growth and structural integrity.

How you can help

Shrink your carbon footprint to reduce greenhouse gases.

• Drive less.
• Reduce, reuse, or recycle.
• Purchase energy-efficient appliances and lightbulbs.
• Print less. Download more. Use less water.

Do your part to help improve overall coral reef condition.

• Reduce the use of lawn and garden chemicals.
• DO NOT dump household chemicals in storm drains.
• Choose sustainable seafood. Visit FishWatch.gov .
• Learn about good reef etiquette and practice it when in the water.
• Volunteer for beach and waterway clean ups.

CORAL REEF THREATS Land-based Pollution

Many serious coral reef ecosystem stressors originate from land-based sources, most notably toxicants, sediments, and nutrients.

CORAL REEF THREATS Overfishing

Many coastal and island communities depend on coral reef fisheries, but overfishing can deplete key reef species and damage coral habitat.

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Last updated: 01/20/23 Author: NOAA How to cite this article

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Decoding Coral Reefs: Exploring Their Status, Risks and Ensuring Their Future

• coral reefs
• climate change

Coral reefs are an undeniably critical part of the ocean. Although these ecosystems only occupy 0.01% of the ocean floor, they support 25% of all marine life, providing crucial habitat for a myriad of fish and invertebrate species. Coral reefs also have a significant impact on coastal communities, with one billion people benefiting from their existence. They provide food and livelihoods , reduce storm surge and flood risk to coastlines across the tropics,  protect against erosion and attract tourists to over 100 countries and territories.

Despite their importance, coral reefs face local and global threats including nutrient runoff from land sources like agriculture or deforestation, overfishing and climate change. Without immediate action to protect and restore coral reefs, they could cease to provide the essential goods and services valued by communities worldwide. Addressing these issues requires an understanding of what coral reefs are, relevant trends, threats and reasons for optimism about the future of these incredible ecosystems.

Answering Common Coral Queries

The ins and outs of coral reefs can be confusing. Here’s a deep dive into what makes a coral reef, why they’re threatened and how they’re doing now:

What Are Coral Reefs?

Coral reefs are vast, three-dimensional structures comprised of coral animal colonies that secrete calcium carbonate, also known as limestone. Over time, these limestone secretions build up and create structures, some of which can be seen from space. Reefs are built by a variety of hard corals, of which there are 800 different species . The coral colonies that form these structures can take on a multitude of shapes and sizes. These colonies grow close together on the reef to create vibrant underwater cities for thousands of invertebrate species and over 4,000 fish species .

A coral animal, or "polyp," has a simple, transparent, tubular body with a ring of stinging tentacles. While they have a central mouth that filters food, 90% of their nutrition comes from microscopic algae within a polyp's tissues, known as "zooxanthellae." Zooxanthellae photosynthesize sugars, which the coral animal depends on for the energy it does not get from filtering food. This algae also provides coral reefs with their notoriously vivid colors.

What Are the Main Threats to Coral Reefs?

Coral reefs are threatened by both local and global threats , including overfishing; sediment, nutrient and marine pollution; and increasing ocean warming and acidification.

Overfishing is the most pervasive local threat to coral reefs. It can alter the ecological balance on the reef through removing herbivorous fish that control the macroalgae growing on coral. Sedimentation from land clearing also poses a major threat, as sediments within the water column can bury the corals and reduce the amount of sunlight that reaches the zooxanthellae, therefore limiting their access to nutrients from photosynthesis. Additionally, nutrient pollution from agriculture and sewage can increase nutrient levels that promote algal cover at the expense of corals. Ships can damage reefs with anchors or chains, discharge pollutants or introduce invasive species that can disrupt the ecosystem.

Globally, ocean warming due to climate change is a rapidly growing threat. The zooxanthellae within corals’ tissues are sensitive to ocean temperature, and ocean warming can cause the corals to expel their colorful algae — a process known as “coral bleaching.” This leaves behind the appearance of a bright white skeleton and deprives the polyps of an important source of nutrition. The corals eventually die if the symbiotic algae don’t return, if there is inadequate time between bleaching for corals to recover or if other threats impede their recovery.

On top of that, increasing carbon dioxide in sea water is slowly causing oceans to become more acidic. This decreases the availability of aragonite, a mineral which corals need to build their skeletons. A lack of aragonite slows coral growth and results in less dense, weaker structures that are more prone to erosion and damage. Aragonite saturation levels have consistently decreased in the last century, and this trend is projected to continue over the next century under current CO 2 emissions.

How Are the World’s Coral Reefs Doing Now?

Unfortunately, there is no simple answer on the state of coral reefs. The extent of damage to the world’s coral reefs vary, and some have recovered . However, most present a grim outlook. Around half of the world’s reefs are likely degraded from climate change, pollution and overfishing . Hard coral cover has declined significantly in some regions, and there has been a clear change in coral community structure, with loss of susceptible coral species and loss of diversity .

A recent report by the Global Coral Reef Monitoring Network (GCRMN ) paints a more nuanced chronology of coral decline. The report utilizes data from 35,000 coral reef surveys collected in 73 countries over the past 40 years to reflect fluctuation in live hard coral cover and algal cover, two key indicators of coral reef condition. Although the findings are based on limited data, they suggest that average live hard coral cover was reasonably stable prior to the first mass coral bleaching event in 1998. That event prompted an 8% loss of coral cover globally, but most coral reefs recovered during the subsequent decade.

Between 2009 and 2018, coral cover progressively declined by 14%, primarily due to recurring large-scale coral bleaching events and inadequate time between events for coral to recover. Local disturbances and threats also contribute to coral decline and hinder recovery after coral bleaching, creating an opportunity for algae to occupy the space. As a result, algal cover increased by 20% over that period. Transition from coral to algae dominance in a reef community reduces the physical and biological complexity of coral habitat, which is essential to support important ecosystem services.

What is the Outlook for Coral Reefs?

The decline in live hard coral cover over the past 40 years isn’t the end of the story. Projections of future ocean warming and the associated increased frequency of coral bleaching make coral reefs highly susceptible to further declines. By the 2030s, most coral reefs are projected to experience coral bleaching at least twice per decade , and possibly every year by the 2040s. This frequency would prevent coral recovery between episodes. Without drastic change, coral reefs could disappear by 2100 .

While this may look bleak, there are signs of hope. Reef resilience, better understanding of these ecosystems and improved reef management can help prevent the worst-case-scenario.

The GCRMN report, among other studies, show that coral reefs can recover under certain conditions. In some cases, coral reefs with particularly high coral cover and diversity show evidence of natural resistance to higher ocean temperatures. Reducing local and global pressures on coral reefs is also critical to help reefs recover and maintain their resilience. This includes preventing destructive fishing practices and overfishing, minimizing pollution and sedimentation, managing dredging and preventing direct physical damage to reefs.

Networks of scientists, coastal managers and conservation professionals are also mobilizing to better understand the factors which aid coral persistence and recovery. Approaches are being tested, including:

• Amplification of alerts of impending elevated sea surface temperatures . These alerts show when corals are expected to experience stress, which better enables coastal managers to reduce local threats.
• The strategic development of marine protected areas (MPAs). When reefs in protected areas are able to survive and reproduce, their coral larvae can drift into degraded reefs and help them repopulate, as well. This can also disperse more heat-tolerant algae to bleached reefs.
• The development of more successful coral restoration techniques.

Furthermore, coral reefs are becoming increasingly protected through their inclusion in new and expanded MPAs. More coral reefs are also in “ fully and highly protected areas ,” which typically include zones where fishing is prohibited. Good management practices — like the implementation of “no take” zones from which the removal of resources, living or dead, is restricted, as well as practices that reduce pollution and physical disturbance within these areas — can help to reduce local threats and promote coral resilience. Meanwhile, global actions to reduce global greenhouse gas emissions and control warming will also help reduce threats to reefs.

Tools that help increase knowledge on coral reefs and address local and global threats are also critical to reef protection. Data and visualization platforms, such as the Global Coral Reef Profile , are especially valuable in providing this knowledge and increasing understanding of the complexity of coral reefs, the threats they face, their enormous values and what is needed to help them persist.

Tools that provide insight into interactions on a regional scale have additional utility to stakeholders on the ground. The Coral Reef Regional Dashboards includes some of the most requested data to support decision-making relevant to coral reefs. The regional dashboards provide an overview of the value of coral reefs for fisheries, tourism and shoreline protection values; reef dependent populations; and the relative social and economic vulnerability of people within the region to coral degradation. They also provide information on the extent of coral reef and mangrove habitat, as well as how many are within MPAs and fully protected areas. Finally, the dashboards include mapping and indicators of current and future threats, locally and globally, and summarizes current knowledge about changes in the extent of live coral cover and algal cover within the region.

What Must Be Done to Ensure a Future for Coral Reefs?

There is no one solution to saving coral reefs — many coordinated steps must be taken toward a future where corals persist.

On a local level, threats to coral reefs can be addressed by managing fisheries sustainably, eliminating destructive fishing and addressing all sources of pollution. Moreover, management and financial support for MPAs and other area-based conservation measures must become more connected and efficient, with different departments recognizing potential areas for coordination.

On a global scale, efforts to keep warming within 1.5 degrees C are paramount to lessen the risk of coral bleaching and acidification. While talks about the ocean are becoming more prominent at international climate events like the United Nations Framework Convention on Climate Change, progress is slow. The importance of ocean environments like coral reefs must gain momentum and take a more central role in climate mitigation strategies.

Finally, tools that help regional policy makers and global leaders make informed decisions can offer new hope to protect coral reefs. These changes will not come easy, but they must come now to save coral reefs and those that depend on them.

Relevant Work

What is kelp and why is it vital to people and the planet, release: 85 percent of reefs in the coral triangle are threatened, new report finds, climate change poses an existential risk to ocean industries. here’s how they can respond., press release: 75% of world’s coral reefs currently under threat, new analysis finds, how you can help.

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Coral Reefs

Learn the risks our world's coral reefs are facing and what they mean for our future and the future of the ocean.

Biology, Ecology, Health, Earth Science, Oceanography, Experiential Learning

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Coral reefs are important ocean habitats and offer a compelling case of the risks of climate change . Reefs provide a large fraction of Earth’s biodiversity —they have been called “the rain forests of the seas.” Scientists estimate that 25 percent of all marine species live in and around coral reefs, making them one of the most diverse habitats in the world. Paulo Maurin, education and fellowship coordinator for NOAA’s Coral Reef Conservation Program, says the reefs are invaluable to our planet’s biodiversity. “They act as productive nurseries to many fish species, giving the small fish a home and a chance to grow,” he says. “Coral reefs’ diversity is so rich that we do not have a firm count on all the species that live within it and every year discover new species.” Reefs provide a variety of economic benefits, including recreational activities, tourism , coastal protection, habitat for commercial fisheries, and preservation of marine ecosystems . “Corals are important to us for many reasons,” Maurin says. “From a practical point of view, they can help protect coastlines from storm events, for instance, and help maintain fisheries that are essential to a lot of people. And complex compounds found in coral reefs hold promises in modern medicine . These are what we call ecosystem services that would be very difficult and expensive to replace. “They also have a unique ability to inspire us to explore and visit the ocean. Can you think of any other invertebrate that people would come from afar just to see?” Corals live with algae in a type of relationship called symbiosis . This means the organisms cooperate with each other. The algae, called zooxanthellae, live inside the corals, which provide a tough outer shell made from calcium carbonate . In return for that protection, the algae provide their host with food produced through photosynthesis . Zooxanthellae also provide corals with their striking colors. This symbiotic relationship is strongly dependent on the temperature of the surrounding water. As the water warms, zooxanthellae are expelled from a coral’s tissue, causing it to lose its color and a major source of food. This process is known as “ coral bleaching .”

Coral bleaching does not always mean the death of a coral reef. Corals can recover their zooxanthellae in time, but the process requires cooler temperatures. Warmer ocean water also becomes more acidic . Ocean acidification is making it more difficult for corals to build their hard exoskeletons . In Australia’s Great Barrier Reef , coral calcification has declined 14.2 percent since 1990—a large, rapid decline that hasn’t been seen for 400 years. Ocean acidification also occurs because of rising carbon dioxide (CO2) levels. The ocean absorbs carbon dioxide released into the atmosphere . Carbon dioxide alters the chemistry of seawater by reducing pH , a measure of acidity. Water that has a lower pH is more acidic. “When the pH of seawater is lowered as a result of CO2, the availability of carbonate ions—one of the main building blocks in their calcium-carbonate skeletons—is reduced, and corals have a tougher time building up, or even maintaining, their skeleton,” Maurin says. The combination of rising ocean temperatures and increased acidity will likely cause major changes to coral reefs over the next few decades and centuries. New research suggests that corals may begin to dissolve at atmospheric CO2 concentrations as low as 560 parts per million, which could be reached by the middle of this century if emissions are not curbed. In 2010, atmospheric carbon dioxide levels were around 390 parts per million. Maurin believes there are several ways people can help preserve these valuable resources. “Over the long term, we need to reduce the amount of CO2 that is up in the atmosphere that is causing both increased bleaching and acidification,” he says. “But in the more immediate time, there are other ways to help. By understanding that bleaching and acidification stress corals, we can help by building up what we call ‘reef resiliency.’ That is, making sure that reefs have this capacity to bounce back. “For instance, ensuring that there is less pollution entering the ocean can help far-away corals. Also, people can help by making sure that the seafood consumed is sustainable and not contributing to a depletion of fish species that keep algae in check, following fishing regulations when fishing, as well as supporting marine protected areas in key conservation sites .”

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• Open access
• Published: 12 March 2024

Systematic review of the uncertainty of coral reef futures under climate change

• Shannon G. Klein   ORCID: orcid.org/0000-0001-8190-3188 1 , 2 , 3 ,
• Cassandra Roch   ORCID: orcid.org/0000-0001-6712-2318 1 , 2 , 3 &
• Carlos M. Duarte   ORCID: orcid.org/0000-0002-1213-1361 1 , 2 , 3  

Nature Communications volume  15 , Article number:  2224 ( 2024 ) Cite this article

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• Climate-change ecology
• Climate-change impacts
• Marine biology

Climate change impact syntheses, such as those by the Intergovernmental Panel on Climate Change, consistently assert that limiting global warming to 1.5 °C is unlikely to safeguard most of the world’s coral reefs. This prognosis is primarily based on a small subset of available models that apply similar ‘excess heat’ threshold methodologies. Our systematic review of 79 articles projecting coral reef responses to climate change revealed five main methods. ‘Excess heat’ models constituted one third (32%) of all studies but attracted a disproportionate share (68%) of citations in the field. Most methods relied on deterministic cause-and-effect rules rather than probabilistic relationships, impeding the field’s ability to estimate uncertainty. To synthesize the available projections, we aimed to identify models with comparable outputs. However, divergent choices in model outputs and scenarios limited the analysis to a fraction of available studies. We found substantial discrepancies in the projected impacts, indicating that the subset of articles serving as a basis for climate change syntheses may project more severe consequences than other studies and methodologies. Drawing on insights from other fields, we propose methods to incorporate uncertainty into deterministic modeling approaches and propose a multi-model ensemble approach to generating probabilistic projections for coral reef futures.

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Introduction.

Anthropogenic climate change is anticipated to propel large components of the Earth’s system beyond critical climate tipping points (CTPs), initiating feedback-driven change and impacts across biophysical systems 1 . These components, known as ‘tipping elements,’ are distinguished by their significance in Earth’s system functioning, their substantial contributions to human well-being, and their unique value 1 . A notable example is the projected dieback of the Amazon rainforest that could release gigatons of carbon into the atmosphere and accelerate global warming 1 , 2 , 3 . Although the concept of CTPs has been subject to debate 4 , 5 , a recent synthesis delivered a shortlist of nine global and seven regional elements at risk 1 . Global tipping elements, such as the Amazon rainforest and West Antarctic Ice Sheet, refer to components spanning subcontinental scales that could alter the operation of Earth’s system 1 . Regional tipping elements represent biospheres expected to exhibit perpetual feedback at confined scales that have the potential to occur synchronously across subcontinental scales, including for example, the simultaneous melting of alpine glaciers 1 , 6 . Among the shortlisted regional elements at risk are warm-water coral reefs, which are deemed vulnerable to exceedance if global warming surpasses 1.5 °C above preindustrial levels 1 , 4 , 7 .

Low-latitude reefs, as some of Earth’s most biodiverse ecosystems 8 , have reached a critical juncture where further deterioration could compromise global food supply, coastline protection, economic revenue, and the livelihoods of up to one billion people 9 , 10 , 11 . Their inclusion as a regional tipping element was based upon historical evidence of near-synchronous coral bleaching events spanning >1000 km scales 12 , 13 and projections indicating progressive degradation of reefs under modest levels of global warming 14 , 15 , 16 , 17 . Although coral bleaching is regarded as a localized process, near-synchronous bleaching events on many of the world’s reefs have occurred as a result of concomitant increases in ocean temperatures across the tropics 13 . These phenomena are expected to become more frequent, intense, last longer, and affect wider geographic areas with future warming 18 , 19 , 20 .

The most recent CTP synthesis followed the same confidence rating system used by the Intergovernmental Panel on Climate (IPCC) 1 , 21 . It identified a CTP of 1.5 °C (1–2 °C, high confidence) for tropical coral reefs, with an estimated timescale of 10 years for dramatic change (with medium confidence) 1 . In high agreement with findings of the IPCC 22 , 23 , the synthesis cited several modeling efforts using similar ‘excess heat’ modeling approaches as the basis of the assessment 14 , 15 , 16 , 17 . These approaches apply thresholds – in the form of degree heating weeks or months – that represent an accumulation of excess heat above baseline summer conditions. These thresholds are then applied to sea surface temperatures (SSTs) and forced by different emissions scenarios in an effort to retrieve the likelihood of future bleaching events 14 , 15 , 16 , 17 . Such models analyze the frequency of bleaching events and estimate the proportion of reef locations at risk of ‘long-term degradation’ or ‘severe bleaching events’, producing estimates with high coherence among studies 14 , 15 , 16 , 17 . The resulting CTP of 1.5 °C (1–2 °C) places warm-water reefs among the six elements at risk of exceeding their tipping points within the global warming range set by the Paris Agreement (1.5–<2 °C) 1 . This finding aligns with the conclusions of Working Group II’s contribution to the IPCC’s 6th Assessment Report (AR6) 22 and raises concerns over imminent impacts to marine biodiversity, human livelihoods, and the effectiveness of interventions to alleviate further coral reef degradation.

The earliest studies to project coral reef responses to future global warming utilized ‘excess heat’ threshold approaches 24 , 25 , 26 , 27 . Put simply, these methods operate under the notion that widespread bleaching predictably occurs when temperatures accumulate beyond a specific threshold. While many investigations show that ‘excess heat’ threshold metrics have strong predictive relationships with bleaching events 12 , 28 , 29 , others have found these metrics to have weak predictive power when applied to historical bleaching records 24 , 30 , 31 . These inconsistencies indicate that the effectiveness of ‘excess heat’ threshold metrics may depend on the specific context 24 . In the mid to late-2000s, a consensus emerged that differences in bleaching susceptibility between locations were best explained by multiple modifying variables 24 , which eventually led to development of alternative model-based approaches. Since then, various approaches, such as species distribution models, ecology-evolutionary models, and models of reef population dynamics have been applied. However, influential syntheses of climate change impacts largely overlook these later developments, relying on projections derived exclusively from ‘excess heat’ threshold approaches that apply similar assumptions and parameterizations 1 , 4 , 22 , 23 , 32 .

Despite the growing body of literature projecting coral reef futures and their prominent role in assessments of climate change impacts, a comprehensive evaluation of available projections is lacking. Here, we address this requirement by conducting a systematic review of published projections of coral reef futures under climate change in isolation or in combination with other pressures. We first review existing approaches to project coral reef futures and their use in the scientific literature, and then identify key gaps in knowledge that currently contribute to uncertainties. We also disarticulate how lessons from the field of climate change science can provide pathways for improving coordination of modeling efforts toward greater certainty in projections of coral reef futures.

Results and discussion

Approaches for projecting coral reef futures.

A search of articles in the peer-reviewed literature found 79 studies published between 1999 and 2023 that modeled coral reef responses to future climate change (Supplementary Data  1 ). While most studies delivered projections for distinct geographical regions (59% of the studies), a considerable proportion offered global-scale predictions (41%) (Supplementary Data  1 & Supplementary Table  1 ). We found six studies in our literature search that provided projections for individual reef ecosystems 33 , 34 , 35 , 36 , 37 , 38 . However, these studies were excluded to ensure a comparable synthesis with most other assessments at regional and global scales. The majority of articles in our database (76 of 79) could be classified into five broad categories of methodologies: ‘excess heat’ threshold models, population dynamic models, species distribution models (SDMs), ecological-evolutionary models, and projective meta-analyses of published data.

‘Excess heat’ threshold models

‘Excess heat’ threshold models integrate thermal threshold metrics assumed to predict the likelihood of severe coral bleaching with future sea surface temperature (SST) projections to forecast future instances of bleaching events. These models usually adopt a specific frequency of events exceeding the thresholds, such as two severe bleaching events per decade 14 , 39 , 40 , that is estimated to preclude long-term recovery. This assumption permits the estimation of reef cells (e.g., 0.5° × 0.5° pixels on the Earth’s surface) that are at risk of ‘long-term degradation’ 14 , 15 or ‘severe bleaching events’ 41 , 42 , 43 , according to the threshold and frequency of events set. Although these models have the advantage of utilizing a method that can be applied to broad geographical scales and incorporate other moderating factors without the need for detailed in situ data, they rarely perform any direct assessments of biological or ecological processes 14 , 15 , 44 , 45 , 46 . This approach was the most prevalent model type in our analysis (32%) (Fig.  1a ) and attracted a disproportionately higher number of cumulative citations (68%) than all other model types (Fig.  1b ). This trend can be partly attributed to this method’s dual role as the foundation for satellite products that are used to alert the risk of coral bleaching 47 , 48 , and its widespread adoption as the primary method for global-scale projections in the field (Supplementary Data  1 & Supplementary Table  1 ).

Cumulative frequency of a all published articles ( n  = 79) and articles classified into five broad categories of methodologies, and b citations of all published articles and articles classified into the same five categories. Citations were extracted from the Thomson Reuters Web of Science database. Source data are provided as a Source Data file.

Population dynamic models

Articles examining the consequences of climate change on the dynamics of coral reef populations accounted for 23% of the analyzed studies (18 of 79) (Fig.  1a ). Population dynamic models typically employ a process-based approach to simulate the impacts of warming on crucial ecological and biological processes. They consider factors such as coral recruitment 49 , 50 , colony growth 51 , 52 , coral basal mortality 53 , predation 52 , 54 , herbivory 55 , and the interactions between coral and algal populations 53 , including competition for space 55 , 56 . By incorporating such mechanisms, population dynamic models provide detailed mechanistic frameworks of how coral reef states could change with warming. These models have been used to simulate connectivity between reef ecosystems, by considering alterations in the physical transport of coral larvae and the expected physiological impacts of warming on larvae 49 , 53 , 57 . They have also been used to evaluate the efficacy of management strategies, such as increased control of crown-of-thorns starfish (CoTS) and reductions in local nutrient inputs 54 , 55 , 58 . However, a significant drawback of these approaches is their reliance on detailed ecological and biological data, which are available only for a few taxa and locations 54 . As a result, the majority of population dynamic studies (17 out of 18) focused on regional geographical scales (Supplementary Data  1 & Supplementary Table  1 ). Despite accounting for nearly one-quarter of the studies in our database, these models received only 13% of the cumulative citations (Fig.  1b ).

Species distribution models

Species distribution models (SDMs), also known as niche models, establish correlations between the occurrence or abundance of species and environmental data in geographic space. In turn, they project changes in the distribution of suitable habitat under future environmental conditions 59 , 60 . Nearly one-quarter of the studies in our database (23%) applied SDMs to forecast the effects of climate change on coral reefs. Despite the equal contribution of SDMs and population dynamic models to our database (Supplementary Data  1 & Supplementary Table  1 ), they received even fewer cumulative citations than population dynamic models, accounting for <7% of the total cumulative citations (Fig.  1b ). The SDMs primarily focused on assessing changes in suitable areas for coral reefs under future climate change scenarios (78% of the SDMs) and accounted for 25% of studies offering global-scale projections (Supplementary Data  1 ). By identifying the conditions that support historical or present-day coral reefs and simulating future changes in environmental variables, the models project shifts in suitable habitats 61 , 62 , 63 . This approach permits large-scale projections that consider multiple physical parameters, even with limited field sampling 63 , 64 , 65 , making SDMs cost-effective tools. Although the widespread adoption of SDMs amplifies their value for comparing a diverse range of responses across marine and terrestrial ecosystems 66 , 67 , a recent systematic review showed that SDMs may have significant limitations in accurately predicting the biology of real-world populations 68 .

While climate-related data (e.g., mean SST) are used in SDMs applied to coral reefs, other physical parameters such as light availability, current speed, and water depth can also be included 63 , 65 , 69 . The most common physical parameters employed in the SDMs within our database were SST and aragonite saturation 64 , 65 , 70 , 71 , which were commonly represented by their means (Supplementary Data  2 ). By primarily relying on means of physical parameters, such models overlook the well-recognized importance of environmental variability in influencing coral reef responses to climate change, which includes capturing the shapes and distributions of these parameters 72 , 73 . Another major limitation arises from the assumption that the physical environment alone largely governs the natural distribution of warm-water reefs. This key assumption overlooks key biological and ecological processes, such as the influential role of larval dispersal and retention in shaping reef distributions 74 , 75 , as well as the role of top-down controls in the food web 76 , 77 , 78 , 79 . Significantly, the biogeographic approach of inferring past ecology largely disregards the potential for species’ niches to evolve through adaptive processes. This limitation can lead to an underestimation of future distributions 80 .

Ecology-evolutionary models

Simulating the potential role of eco-evolutionary processes in helping coral reefs to adapt to changing ocean conditions has gained attention in this field (12% of the studies) (Fig.  1 ). Eco-evolutionary models simulate the interplay between ecological dynamics and evolutionary processes in response to changing climatic conditions. The earliest eco-evolutionary models 81 , 82 (published in 2009 and 2013) examined how heat-tolerant symbionts – the phototrophic component of reef-building corals — could improve coral heat tolerance through changes in the symbiont community and/or evolutionary adaptation. Building upon similar frameworks used in population dynamic models, more recent studies 83 , 84 , 85 incorporate species interactions and their abilities to adapt and disperse across diverse environments. While nearly a third of these studies generated global-scale projections (Supplementary Table  1 & Supplementary Data  1 ), a significant challenge lies in the requirement for knowledge of taxa-specific traits, genetic adaptation, and ecological dynamics, which is lacking for most coral species and locations. As with population dynamic models, the reliability of their projections for non-focal taxa and regions can be influenced by the parameter estimations and assumptions incorporated 85 .

While these studies do not aim to achieve spatial or ecological realism, they provide essential insights into the potential role of adaptation and key environmental drivers that help to inform conservation planning at local and regional scales 85 . For instance, recent eco-evolutionary models reveal the importance of protecting networks of reefs to facilitate the migration of heat-tolerant larvae to cooler waters, thereby facilitating evolutionary adaptation 84 , 85 , 86 . Despite the rising demand for conservation strategies that prioritize the adaptive capacity of coral reefs and a deeper understanding of the underlying mechanisms 87 , 88 , these models attracted a minor proportion of the cumulative citations (Fig.  1b ).

Meta-analyses

Another approach to project coral reef futures consolidates data from published experimental manipulations. Representing a minority of the reviewed studies (5%) (Fig.  1 ), the identified meta-analyses 20 , 89 , 90 , 91 shared a common aim of projecting the dual impacts of ocean warming and acidification on biological processes within reefs. They compile data from experiments that measure how corals and other coral reef taxa respond to conditions that simulate future warming and acidification scenarios. These data are then utilized to parameterize models for estimating future coral responses under various representative concentration pathway (RCP) scenarios. The specific purposes of these meta-analyses range from estimating changes in numerous biological responses of corals 20 to those that exclusively focused on alterations in coral calcification processes 91 or reef-wide calcium carbonate production 89 , 90 . Although data from coral reef monitoring, rather than controlled experiments, arguably offer more realistic insights into how reefs will respond to further warming, our understanding of how reef organisms will react to ocean acidification is primarily based on manipulative experiments 92 , 93 . Thus, one significant advantage of these approaches is their capacity to consolidate the wealth of data derived from experiments to estimate how future warming and acidification will interact and impact the biological responses of reef organisms.

By aggregating data from numerous independent studies, meta-analyses can help to resolve discrepancies among experimental designs, locations, and species by uncovering overall patterns across studies 94 . However, the data underlying the projections from meta-analyses originate from short-term experiments 20 , 89 , 90 , 91 , which fail to measure important elements of resilience such as genetic adaptation 20 and the complex ecological feedbacks that operate in natural reef environments 95 . It is important to acknowledge, however, that other model types similarly rely on results from short-term acidification experiments to parameterize their models 14 , 15 , 96 . Overall, the cumulative frequency of citations based on these meta-analyses aligned with their rarity in the field, equating to <3% (Fig.  1b ).

Other emerging approaches

There are several other approaches to examine coral reef vulnerability to future climate change. In addition to the five approaches outlined above, one study adopted a spatial modeling approach to project the combined effects of warming and sea-level rise on the future coral reef growth rates in the South China Sea 97 . Another integrated linear extension rates of corals from three different islands in the same region with future SSTs to forecast coral growth rates 98 . One study used historical bleaching and sea surface temperature records to project future bleaching probabilities in the Indo-Pacific 99 , while another regional-scale study focused on larval connectivity and identified conservation areas with lower risks of coral bleaching in the Amani Islands of southern Japan 100 .

A standardized method for assessing the risk of ecosystem collapse, the International Union for Conservation of Nature (IUCN) Red List of Ecosystems (RLE), represents an emerging method 101 , 102 , 103 , 104 . The RLE offers a standardized classification system that utilizes thresholds for key variables to integrate diverse data 101 , 105 , 106 . One study applying this method used various coral reef datasets to model interactions within western Indian Ocean reefs under future warming 104 . The study reported varying levels of regional vulnerability to ecosystem collapse, ranging from ‘critically endangered’ to ‘vulnerable’ across the 11 eco-regions examined 104 . However, the ecosystem model’s assessment excluded data on fishing pressure and rates of sedimentation, among other variables, due to data scarcity across countries and regions. There are at least four studies applying this method to coral reefs in the Caribbean 101 , 102 , meso-America 103 , and the western Indian Ocean 104 . Together, they emphasize the need for improvements in the consistency of monitoring efforts and advocate for the development of a unifying framework to enable more conclusive risk assessments.

In summary, the discussed approaches span a spectrum from simplistic models that minimize complexity to those incorporating detailed mechanistic frameworks that address complex ecological and evolutionary processes. While the latter approaches provide a deeper understanding of the effects of climate change on essential ecological and biological processes in warm-water reefs, their practical utility is constrained by limited data availability.

How heat stress is modeled

Severe marine heatwaves that trigger mass coral bleaching events are expected to become more intense, frequent, last longer, and affect wider geographical areas as the planet continues to warm 18 , 20 , 107 . While the approaches discussed thus far encompass five distinct approaches for forecasting coral reef futures, the underlying procedures for modeling heatwaves and their impacts on reefs can be classified into two overarching techniques ( sensu 24 ). The first technique utilizes thermal stress thresholds, which are defined as metrics requiring a variable, such as SST, to surpass a pre-determined value 24 . For studies to be classified as threshold techniques, the use of these metrics had to form the primary framework of the models that delivered projections. The second technique represents approaches that abandon the central threshold concept to focus on empirical relationships between continuous variables. Articles classified as using this approach could use thermal stress thresholds, however, they had to be included as one of numerous variables examined 24 . Only one study in our database could not be classified as using either technique. The study integrated various data sources, environmental variables, and analytic techniques, including regression and association methods for projecting future coral cover 72 .

Our analysis revealed that more than half of all the studies (53%) employed thermal threshold techniques as the primary basis for their projections (Supplementary Data  2 ). Besides the exclusive use of this method in ‘excess heat’ threshold models, around 40% of population dynamic and eco-evolutionary models also relied on thresholds as the basis for their projections (Fig.  2 ). Across the five major approaches (Fig.  2 ), the most common threshold metrics applied were degree heating weeks (DHWs) or months (DHMs), which calculate values representing both the intensity and duration of heat stress events in singular metrics.

Proportion of studies classified as using either a thermal threshold or continuous variable technique across the five broad categories of methodologies ( n  = 74 articles). Note: one article could not be classified as using either of the threshold or continuous variable techniques 72 and four studies could not be classified as one of five major methodologies. These five studies were excluded to enable a meaningful analysis, but see Supplementary Data  2 . Source data are provided as a Source Data file.

One explanation for variations in the efficacy of thresholds metrics in explaining realized coral bleaching is their inability to capture different marine heatwave characteristics, such as peak temperatures, duration, and rates of heating. For instance, a historical assessment spanning from 1985 to 2017 examined variations in SST and showed that increases in accumulated heat stress, as measured by two common threshold metrics, were predominantly attributed to longer heating events affecting wider areas 108 . However, the study could not detect changes in peak temperatures or event frequencies during the analyzed period, indicating the limitations of the metrics in capturing changes in different heating variables 108 . A study by McClanahan et al. 73 evaluated the effectiveness of heatwave variables in explaining bleaching severity on 226 coral reefs and found that the DHW metric explained 9% of the model variance. In contrast, peak temperatures, the duration of cool temperatures, and temperature bimodality were found to be stronger predictors of bleaching severity. Several empirical studies have also reported that variables representing different marine heatwave characteristics were best at predicting changes in coral cover 72 , 109 , 110 . For example, a study investigating the power of 27 environmental factors in explaining changes in coral cover on Indian Ocean reefs reported that temperature anomalies, temperature variation, and the duration of cyclones were the best predictors 109 .

We found only one study projecting impacts on coral reefs that directly compared model outputs derived from both thermal threshold and continuous variable techniques 72 . This study revealed that a DHW-based model projected more severe declines in coral cover in the Indian Ocean compared to the multivariate approach that integrated variables characterizing historical and future patterns of stressors. The findings suggested that patterns of acute and chronic stressors could be more influential than cumulative heat stress in predicting future coral cover in certain regions 72 , further highlighting the importance of variable selection procedures in the modeling process. Although there is substantial uncertainty in how climate change will morph future thermal regimes, global databases of marine environmental data provide many useful exposure and modifying variables for this purpose 72 , 111 .

While thermal threshold metrics have acknowledged limitations, they remain vital for established programs forecasting coral bleaching risk using satellite-based products. Work has already been done to test how well different degree heating algorithms explain coral bleaching patterns at local, regional, and global scales in an effort to improve their efficacy (e.g. refs. 112 , 113 , 114 , 115 ). New configurations of the operational DHW algorithm hold promise in improving their ability to predict instances of observed bleaching 112 , 113 , 116 , although the extent to which adapted algorithms improve predictability depends on the focal region and spatial scale of the test. This suggests that researchers could consider adapting different degree heating algorithms to pinpoint the most appropriate stress metric for their geography. Subsequently, these customized algorithms could be confidently applied to projection models for the focal region. Several studies in our database have shown how threshold choice affected their model outputs 26 , 40 , 46 , 112 , 117 , 118 . For example, one study reported divergent estimates of bleaching onset timing when different inter-annual variation thresholds were used 117 .

Another major consideration is the future efficacy of threshold-based metrics in reliably approximating instances of coral bleaching or changes in other coral reef metrics. This is because most coral reefs have already experienced a complex legacy of exposure to disturbance and it is presently unclear by how much and to what extent organisms have adapted or will adapt in future 119 , 120 . A recent study examined intrapopulation variability of heat tolerance in corals from the western Pacific Ocean 121 . The study demonstrated that the most heat-tolerant corals in their study required double the heat stress to induce bleaching compared to their least-tolerant corals. When these differences in heat tolerance were translated into contrasting DHW thresholds and applied to an ambitious emissions scenario (SSP2 −4.5), the study reported that the most heat-tolerant corals could potentially experience annual bleaching events up to 17 years later than their less-tolerant counterparts 121 . Overall, greater confidence in coral reef projections will depend on an increased number of projections derived from methods that incorporate robust variable selection procedures and a deeper understanding of how the thermal tolerances of corals and other coral reef taxa may evolve under escalating stress levels over time.

Addressing uncertainty through more coordinated modeling efforts

Uncertainties in coral reef projections stem from various sources that compound in the steps involved in generating the projections 122 . The sources range from variations in the climate system that impact various modeling tools, such as General Circulation Models (GCMs) 122 , 123 , to uncertainties in how future socioeconomic policies and technologies will affect future emissions trajectories 124 . Uncertainties related to the models themselves pertain to the model structure and parameter settings used 122 , 125 , which both rely on knowledge of the specific physical and ecological processes affecting how coral reefs will respond in the future.

While the models reviewed here vary in their complexity and underlying methodologies, most rely on deterministic rules to establish cause-and-effect relationships (Supplementary Data  2 ). Such deterministic models do not directly incorporate uncertainty 126 and are inherently limited in their ability to account for uncertainties stemming from interactions between physical and ecological factors inherent to coral reefs. In contrast, models employing probabilistic relationships can accommodate natural variation and uncertainty in model input values and parameters by considering potential value ranges and associated probabilities 127 . While probabilistic models may be deemed most suitable for capturing uncertainties in how coral reefs will respond in the future 127 , 128 , 129 , this field still faces significant issues in establishing robust connections between key coral reef metrics and satellite-derived data 72 , 73 , 109 , 110 . These difficulties ultimately hinder the reliability and utility of probabilistic models.

The question of how to account for uncertainty of deterministic models poses a significant challenge. Uncertainty associated with the model structure, specifically uncertainty about the cause-and-effect relationships, is often difficult to quantify because this requires the comparison of model outputs with real-world observations 127 . However, it is possible to evaluate and then use uncertainty caused by the model’s input values and parameters. The probable range of model outputs can be examined by analyzing how these outputs behave when model input values are changed within plausible ranges 127 , 130 . Some studies have evaluated how choices in model inputs and different assumptions affect the outputs of coral reef models (e.g. refs. 55 , 72 , 130 , 131 , 132 , 133 ), though differences in model outputs are seldom used to produce formal estimates of uncertainty arising from model inputs. One approach to doing this is to conduct a formal uncertainty analysis of different model outputs. A straightforward method for conducting such an analysis is by applying Monte Carlo methods, where variations in model inputs are drawn randomly, and the resulting model outputs are treated as a random sample of the model output distribution 127 (e.g. refs. 55 , 130 ). Although effective in helping to incorporate uncertainty into deterministic models, this approach requires a substantial number of model runs.

Another approach is to apply a sensitivity analysis – a common method to understand how changes in input values and/or parameters of a model affect its output 127 . Essentially, these analyses aim to pinpoint the input parameters to which the model output is most sensitive. For example, if plausible changes in an input parameter value induce large variations in the model output, this indicates that the parameter value is highly uncertain. Conversely, if model outputs remain stable, the analysis will indicate that the parameter value has low uncertainty. These analyses can become computationally expensive when all possible parameter values and their interactions are tested in a step-wise manner. However, there are techniques to reduce the number of model runs 127 , 130 . For instance, sensitivity analyses have been applied to coral reef models by testing only the highest and lowest plausible values of the biological parameters and adjusting single parameter values by ±10% 130 , 131 .

While the model sensitivity analyses described above offer ways to account for uncertainty caused by the model’s input values and parameters within an individual study, it is possible to address system and model uncertainty using multiple independent models in an ensemble approach 127 . For instance, in the field of climate change science, atmospheric scientists initially faced issues with fragmented data and disparate deterministic models when modeling the Earth’s response to increasing greenhouse gas emissions 134 . By the 1980s, coordinated data collection from weather stations and satellites improved the accuracy of atmospheric-ocean GCM models 135 . By 1988, the IPCC formed and used the Coupled Model Inter-comparison Project (CMIP) to coordinate simulations using the same emissions scenarios and model outputs 136 . This ensemble approach combined diverse deterministic model types across research groups to generate reliable probabilistic statements 134 . While acknowledging that climate scientists only model a single system compared to the thousands of interdependent and locally-adapted species comprising coral reefs, adopting a multi-model ensemble approach to generate probabilistic projections for coral reef futures is feasible 123 , 134 , 137 . This, in turn, would help to highlight major sources of variation and better characterize the extent of uncertainty of coral reef futures under climate change. However, applying an IPCC ensemble-like approach would initially necessitate improved coordination among modelers and the selection of common output metrics and emission scenarios.

Despite the growing body of studies forecasting coral reef futures, there is presently no broad consensus on the optimal variables for projecting coral reef vulnerability 102 , 103 , 104 . This is reflected in the diversity of variables used and the large proportion of studies delivering projections with metrics that prove challenging to translate to real-world observations (Supplementary Data  1 ). Establishing a connection between model outputs and real-world observations is not only crucial for enhancing the practicality and usefulness of modeled projections but also enables future assessments of the models’ ability to simulate past conditions. More than half of the studies employing ‘excess heat’ thresholds presented their projections in terms of fractions of reef cells at risk (52%), while SDMs typically provided estimates in terms of fractions of reef cells with suitable habitats or relative changes in habitat suitability (69%) (Supplementary Data  1 ). Although coral cover serves as a widely used and accessible indicator for this purpose 104 , 138 , projections of coral cover were delivered in less than a third of all published studies in our database (29%).

While coral cover represents the most frequently simulated metric directly linked to real-world observations, its effectiveness as a singular measure is constrained 104 . The simplicity and accessibility it provides comes with trade-offs, as it fails to encompass other crucial aspects of reef health, including changes in community compositions of corals, algae, and other key taxa essential for ecosystem functioning. Transitions in coral communities in the western Indian Ocean and the Great Barrier Reef have marked significant ecological shifts in response to climate change 139 , 140 , highlighting the requirement for coordinated simulations of numerous common reef variables to better capture future coral reef vulnerability. Present coral reef assessment and monitoring efforts, however, suffer from differences in methods and the resulting datasets 104 . Recommendations for unifying frameworks to select common metrics to capture different dimensions of ecosystem integrity and risk of collapse across ecosystems already exist 141 . However, coordination to select key metrics specific to coral reef ecosystems for this purpose is still lagging. This recommendation is further emphasized by studies utilizing the IUCN RLE classification system to evaluate the risk of coral reef ecosystem collapse, which call for enhanced coordination in monitoring coral reefs and improved data quality and quantity 102 , 103 , 104 .

There is currently no formal consensus on the most suitable emissions scenarios for modeling coral reef futures. While the number and type of emissions scenarios varied, the most frequently used scenario in our database was RCP8.5 (CMIP5), representing a high-emission scenario of ~4.5 °C global warming by the end of the 21st century (Supplementary Data  2 ). Most studies applied two emissions scenarios, typically comparing RCP8.5 (CMIP5) with a scenario of lower radiative forcing such as RCP2.6 or RCP4.5 (CMIP5) (Supplementary Data  2 ). Though subject to debate, recent analyses show that observed trends in global CO 2 emissions are substantially lower than those simulated by high-emission baseline scenarios such as RCP8.5 (CMIP5) 142 , 143 , 144 , 145 . These studies suggest that this divergence could widen throughout this century and conclude that such scenarios should no longer serve as reference high-emission scenarios 142 , 143 , 144 , 145 . Given these developments and the release of the IPCC’s AR6 report 22 , there is a pressing need for coordination to select the common emissions pathways for modeling coral reef futures. This urgency is underscored by the introduction of new socioeconomic pathways representing novel levels of radiative forcing (1.9, 3.4, 7.0 W m −2 ), already incorporated into recent projections for coral reefs (e.g. refs. 17 , 146 ).

Comparison with a prevailing diversity in methodologies

A major challenge in synthesizing existing projections stems from the diversity of coral reef metrics simulated and emissions scenarios used. In other fields, meta-analyses have been employed to compile published projections and compare the direction and extent of modeled impacts across studies using diverse metrics 147 , 148 . These syntheses adopt standardized effect-size metrics such as Hedges’ g . Calculated based on relative differences between impacted and baseline (or control) scenarios and weighted for variance, these metrics offer a uniform measure for assessing the magnitude of anticipated effects 147 , 149 . We focused on the three most commonly projected coral reef metrics (fractions of reef cells at risk, fractions of reef cells deemed habitable, and changes in coral cover). However, due to reporting limitations in most published articles, we could extract requisite data from only 39 modeled scenarios across eight studies (Fig.  3 & Supplementary Data  3 ). We therefore consider this analysis to be exploratory in nature to encourage future efforts, rather than providing definitive or conclusive results.

Calculated mean effect sizes (Hedges’ g  ± 95% CIs) represent the magnitude of projected impacts on model outputs (i.e., coral reef metrics) across three global warming scenarios (1.5–2 °C, 2–4 °C, and >4 °C). Model outputs (mean ± 1 Std) used in this analysis were extracted from n  = 39 individual modeled scenarios across eight published studies, and represented in Fig.  4 . Mean effect sizes were derived from differences between projected estimates of coral reef metrics for the end-of-century (2090–2100) and the baseline period (2000–2015) (cf. “Methods” section). Hedges’ g, a common effect-size metric ranging from −∞ to +∞, signifies no impact at zero, positive values indicate ecological benefits, and negative values signify adverse effects. The 95% CIs represent variability among scenarios within each study and warming scenario (Supplementary Data  3 ). Analyzed coral reef metrics include percent reef cells at risk (black), percent habitat change (blue), and percent coral cover change (red). Circles and triangles denote studies using thermal threshold and continuous variable techniques for modeling heat stress, respectively. Open symbols represent global-scale projections, while closed symbols denote regional-scale projections. Source data are provided as a Source Data file.

Figure  3 illustrates mean effect sizes representing the direction and magnitude of expected impacts on coral reef metrics across the selected studies. The distribution of effect sizes among the studies is influenced by a combination of factors: (1) varying assumptions on key drivers, such as choices in future emissions scenarios, (2) methodological differences, including the choice of simulated coral reef metric and the type and parameterization of the model, and (3) how the results were reported, such as the number of, and agreement among individual scenarios within each study. To help disentangle these factors, we aligned model outputs to baselines years between 2000 and 2015 (0.86–0.96 °C) and three end-of-century warming scenarios (1.5–2 °C, 2–4 °C, and >4 °C), which categorized the various emissions scenarios used (Supplementary Data  3 ). We further categorized each study based on whether it employed a thermal threshold or continuous variable technique in modeling heat stress and whether it presented global or regional-scale projections (Fig.  3 ).

Nearly all studies projected negative impacts on the coral reef metrics, but the relative sizes of these effects differed (Fig.  3 ). Articles that used thermal threshold techniques tended to yield more negative effect sizes than alternative methods (Fig.  3 ). Among the threshold studies in the 2–4 °C scenarios, Teneva et al. 117 produced a relatively small effect size, aligning with the study’s less severe and more variable projections of reef cells at risk (Figs.  3 & 4 ). The projections by Teneva et al. 117 cannot be easily compared with other threshold studies reviewed here because of various methodological differences. In contrast to the other studies 14 , which applied global temperature thresholds to estimate future bleaching frequencies, Teneva et al. 117 used bleaching observations from Reef Base to test prediction methods in which thermal thresholds were determined by historical SST variability. Accounting for historical climate experience might explain why the projections by Teneva et al. 117 deviated from most other threshold studies in the analysis (Fig.  4 ). Importantly, Teneva et al. 117 also defined reef cells at risk as grid cells characterized by at least a 50% probability of experiencing 5-year mild or severe bleaching events by 2100.

Percent change in mean estimates (±1 standard deviation) of model outputs (i.e., coral reef metrics) used in the analysis presented in Fig.  3 . Model outputs were extracted from n  = 39 modeling scenarios across eight published studies and converted into percent change for ease of interpretation. Mean estimates of coral reef metrics for historical global warming levels of 0.86–0.96 °C represent the baseline period of the years 2000–2015. Mean estimates of coral reef metrics categorized into for future warming scenarios of 1.5–2 °C, 2–4 °C, and >4 °C represent projections at the end of the century (years 2090–2100). Negative values for percent reef cells at risk (black), percent habitat change (blue), and percent coral cover change (red) signify adverse ecological impacts compared to a baseline of 0% (no effect), while positive values indicate a positive effect direction, such as projections estimating increases in reef cell habitat availability. Circles and triangles denote studies using thermal threshold and continuous variable techniques for modeling heat stress, respectively. Open symbols represent global-scale projections, while closed symbols denote regional-scale projections. Supplementary Data  3 provides a comprehensive list of individual scenario descriptions. Source data are provided as a Source Data file.

In future scenarios characterized by >4 °C warming, articles applying thermal threshold techniques consistently projected that >93% of global reef cells will be at risk by the end of the century 14 , 42 , 55 (Fig.  4 ). However, the study by Maynard et al. 42 generated a notably smaller effect size than Frieler et al. 14 and Anthony et al. 55 (Fig.  3 ). Given that the effect sizes were based on relative differences between the baseline and end-of-century scenarios and weighted for variance, this discrepancy may be explained by the more severe and variable baseline impacts modeled by Maynard et al. 42 (Fig.  4 ). The relatively large effect size for Frieler et al.’s 14 projections occurred because of the absence of any variance with the study’s drastic projections of reef cells at risk (−100%, ±0 Std) (Fig.  4 ). In contrast to the threshold studies, articles employing continuous variable techniques produced effect sizes that were relatively modest, but variable (Fig.  3 ). This can be attributed to the high variability in model outputs across the individual scenarios, reflecting the distinct characteristics of different coral reef provinces (Fig.  4 ). For example, projected changes in suitable habitats under >4 °C ranged from −99.9% (±3.1 Std) to +36.8% (±3.1 Std), and changes in coral cover varied from −100% ( ± 25.4 Std) to −19.2 (±25.8 Std) (Fig.  4 ).

How do our findings relate to the IPCC’s projections for coral reefs? The IPCC’s AR6 Summary for Policy Makers anticipates that coral reefs will decline by 70–90% at 1.5 °C global warming, exceeding 99% at 2 °C (with high confidence) 22 , 150 . Although the IPCC reports lack a definition for coral reef “decline,” their assessments draw on projections from Schleussner et al. 15 and Frieler et al. 14 . The two studies exhibit high agreement, collectively estimating that between 69.7% (±42.2 1 Std) and 100% (±15.2 1 Std) of coral reef cells will be at risk under scenarios of 1.5−2 °C (Fig.  4 ). We find that these projections generated effect sizes similar to those generated by alternative methodologies under even the most pessimistic warming scenario (Fig.  3 ). This suggests that the studies serving as a basis for recent climate change impact assessments 1 , 22 , 23 might project more severe consequences for coral reefs than other approaches.

The main reason for the high coherence between Schleussner et al. 15 and Frieler et al. 14 is the minimal differences in their approaches to modeling the frequency of bleaching events across global reef cells. Both articles used the same model type and made analogous assumptions, including their selection of global thermal thresholds and frequency of heating events expected to impede reef recovery. Overall, there are several factors that may explain the high variation in expected outcomes for coral reefs. In contrast to Schleussner et al. 15 and Frieler et al. 14 , differences in model types, model parameterization, and assumptions are likely important factors explaining differences in the extent of expected impacts. While our analysis has limitations, it underscores the importance of exercising caution when drawing conclusions from a limited number of key studies and emphasizes the need for enhanced coordination to transition toward a multi-model ensemble approach.

Reporting uncertainty and metrics of model outputs

One of the fundamental, yet basic steps toward improving future syntheses of modeled projections is the adherence to essential reporting standards. While all studies in our database provided ample data to facilitate interpretation of the study outcomes, most (89% of studies) failed to report basic metrics for model outputs or sufficient extractable data for measures of variation to be converted into the same units. In many cases, challenges arose from the display of results in figures and geographical maps that were not accompanied by adequate supplemental information reporting extractable values. While there is an increasing emphasis on depositing empirical data into online repositories (e.g., Dryad, Figshare, and Zenodo), this is rarely required for model outputs. Recognizing the necessity for reporting and metadata availability standards, other fields focused on projecting climate change impacts to biological systems have implemented agreed-upon standards 66 , 67 , 134 . For instance, the IUCN established preliminary reporting standards for species threat assessments based on SDMs 151 , which have been further refined in subsequent publications 66 , 67 .

Another vital component of studies projecting coral reef futures is clarity over units of the metrics projected. Modeling studies simulate changes using a diverse set of metrics that vary according to the purpose of the study and ultimately communicate the extent and nature of expected impacts on coral reefs. However, a lack of clarity over the ecological or biological meaning of the projected variable and the exact outcomes anticipated for coral reefs constrains the usefulness of projections in guiding effective decision making, management, and conversation efforts.

While the vast majority explicitly define the metrics simulated, some earlier studies provide indistinct descriptions (Supplementary Data  2 ). For instance, several ‘excess heat’ threshold models simulate the frequency of severe bleaching events to deliver projections as the proportion of coral reef cells (e.g., 1° × 1° grid cells on the Earth’s surface) at risk of ‘long-term degradation’ or ‘severe bleaching events’  14 , 15 , 16 , 17 . However, there is presently no agreed nomenclature of such states for coral reefs, raising uncertainty as to their exact meaning and the consequences involved. In some cases, subjective terms affect the communication of projections in influential assessments of climate change impacts, where terms like ‘losses of coral reefs’ 152 , ‘corals being lost’ 23 , and ‘coral reefs at risk’ 23 are used interchangeably without accompanying definitions. These terms could, in theory, be understood to imply a range of outcomes for coral reefs, ranging from reductions in live coral to the ecological collapse of entire reef ecosystems. Clear and well-defined nomenclature is especially important to in the context executive summaries addressing policymakers and other stakeholders. In summary, establishing and adhering to standards for the comprehensive reporting and communication of projections, including associated uncertainties, would facilitate more conclusive syntheses of coral reef projections in the future. This may also involve setting standards for publishing metadata.

Toward ecologically relevant and restoration-compatible spatial scales

The recent establishment of ambitious goals to restore biodiversity (Kunming–Montreal biodiversity framework) has ignited a race to identify effective strategies assisting decision-makers in implementing successful mitigation and intervention efforts for coral reefs 153 . The capacity of projection models to guide these strategies, however, is challenged by the difficulties they face in detecting changes at practical scales 17 , 154 . Almost half of the studies in our database (49%) provided projections at geographical resolutions lower than 0.25° latitude × 0.25° longitude (Supplementary Data  2 ). In practical terms, this roughly corresponds to grid cells with an area of 770 km² at the equator — a size that is orders of magnitude larger than a typical coral reef.

There are two main approaches to improve the spatial resolution of global and regional models: statistical and dynamical downscaling procedures 155 (Table  1 ). Statistical downscaling estimates local-scale climate variables from larger-scale climate models using statistical methods, whereas dynamical downscaling uses regional numerical models to simulate local conditions at a higher spatial resolution based on global climate model outputs 156 . Among the 19 studies in our database that applied downscaling techniques, the majority (85%) used statically downscaled models to formulate their projections (Supplementary Data  2 ). While statistical techniques are computationally inexpensive, one major drawback is their inherent assumption that patterns between large- and local-scale climates observed today will remain unchanged in the future 157 (Table  1 ). This assumption introduces substantial uncertainty across decadal time frames 157 . On the other hand, dynamical techniques explicitly model ocean dynamics and are more likely to capture the key processes involved 156 (Table  1 ). These dynamical procedures, however, can still inherit biases present in the large-scale climate models and face challenges in considering how ocean dynamics may change over time 157 , 158 (Table  1 ).

We found only one study that compared the performance of statistical and dynamical downscaling procedures. The study by Hooidonk and colleagues compared models of annual coral reef bleaching in the Caribbean that were downscaled using either statistical or dynamical procedures 156 . While there was a high level of agreement between the projections produced by the two techniques, the dynamically downscaled model detected an earlier onset of annual severe bleaching linked to future changes in regional currents. In contrast, the statistical procedure failed to detect these changes due to its inability to capture local-scale features, such as eddies, which influence warming levels leading to coral bleaching 156 . Although these results suggest that dynamical downscaling may outperform statistical methods, further assessments of the relative costs and benefits of the two techniques are warranted (Table  1 ). Downscaling techniques, however, ultimately introduce an additional source of uncertainty. Fortunately, the spatial resolution of global models is expected to improve in the near term with the introduction of new data streams, including higher-resolution satellites (e.g., Himawari 159 ) coming online. This enhancement will improve sea surface temperature (SST) data resolution and reduce the reliance on downscaling approaches 160 .

Geographical bias in modeled projections

It is well-documented that coral reef responses to climate change vary across major coral reef provinces 13 , 161 , 162 . However, when analyzing the landscape of climate projections, it becomes evident that there are substantial geographic gaps that require attention (Fig.  5 ) 163 , 164 . A significant portion of the research provides global-scale projections, which offer a broad perspective on climate patterns and anticipated changes across coral reefs worldwide. While these global-scale projections provide valuable insights into overall trends, they lack the necessary resolution and accuracy to provide detailed and reliable information at more practical scales for management and intervention purposes 17 , 154 . In contrast, regional-scale models usually benefit from region-specific data and typically offer projections with finer spatial detail, addressing the need for more localized information to inform conservation efforts 156 .

a represents the distribution of modeling approaches used at a global-scale, and b represents the association between coral reef provinces and the main methodologies used. The specific flow width is proportional to the number of research articles applying each of the five main methods, while the numbers in parentheses indicate the total count of articles that generated projections for global reefs ( a ) or each reef province ( b ). See Supplementary Data  1 for a full description of the focal geographic regions for each study included in database ( n  = 74). This diagram has been generated using the online tool: Visual Paradigm ( https://online.visual-paradigm.com ). Source data are provided as a Source Data file.

Our analysis shows that the availability of regional-scale models is inconsistent across the world’s coral reefs. Provinces such as eastern Australia and the Caribbean have received considerable attention and have well-documented projections using various modeling approaches (Fig.  5 ). However, other equally important coral reef provinces, including the eastern Pacific (Costa Rica, Ecuador, and Mexico), the western Atlantic (Brazil’s northeastern coast), the Indian Ocean, and the Arabian Seas, lack regional-scale models (Fig.  5 165 ). These understudied regions thus heavily rely on less-tailored global assessments for projections of future reef impacts in these locations. Many of these provinces also suffer from a limited number of studies and diversity of modeling approaches (Fig.  5 ). For example, projections for the Arabian seas, the western Atlantic, and the eastern Pacific are exclusively based on SDMs, which involve key assumptions and limitations. Coral reef scientists are increasingly aware of this issue. Addressing these gaps necessitates targeted efforts to enhance the resolution and accuracy of global-scale projections, while simultaneously expanding the scope and diversity of regional and local-scale projections and monitoring efforts. Such efforts are already underway and essential in providing decision-makers with actional information to manage climate change impacts on coral reefs at global, regional, and local scales 166 , 167 .

Beyond the impact of warming

Although climate change is acknowledged as a dominant driver of coral reef degradation, it is clearly not the only threat. The extensive list of pressures includes ocean acidification 168 , sea-level rise 169 , deoxygenation 170 , cyclones 171 , pollution 172 as well as numerous biotic pressures such as disease 42 , pest species 173 , and overfishing 174 . However, the vast majority of studies in this review modeled the impacts of warming alone or warming in combination with only one other stressor (76% of studies) (Supplementary Data  1 ). In reality, coral reefs are subject to ongoing climate change and a complex interplay of numerous interacting pressures that operate across various temporal and spatial scales.

Coral reef research has allocated significant effort to projecting and understanding the combined impacts of climate change and ocean acidification on coral reefs (Supplementary Data  1 & Supplementary Table  2 ). On the other hand, our analysis revealed that 16 studies in the database considered pollution to some extent, and four studies considered fishing pressure in their projections (Supplementary Data  1 & Supplementary Table  2 ) Although ocean acidification will undoubtedly have discernable effects on coral reefs 175 , there are no practical solutions available to mitigate ocean acidification, apart from the urgent reduction of greenhouse gas emissions 176 , 177 . In contrast, elevated nutrients and fishing pressure are now well recognized to increase the susceptibility of coral reefs to heatwaves 172 , 178 , 179 , and measures to address these pressures are effective and practical 180 , 181 . Local-scale management actions to minimize pollution and regulate fishing have already demonstrated success in reducing cumulative impacts to coral reefs 180 , 181 , 182 , 183 , particularly in Pacific nations where actions to manage reefs have been implemented for centuries 184 .

A similar pattern exists for evaluating how pest species and disease will interact with climate change to shape the future of coral reefs. In our analysis, we found only two investigations that delved into the role of coral disease outbreaks in influencing coral reef futures under climate change (Supplementary Data  1 & Supplementary Table  2 ) 34 , 42 , with one of these studies being limited to a simulation of a single reef. The global study highlighted that future warming is likely to heighten coral susceptibility to disease and identified specific locations where targeted management could be implemented 42 . Although excluded from our analysis due to the absence of future climate change projections, numerous predictive models serving as early warning systems for coral diseases exist 185 , 186 , 187 . These early warning system models have identified crucial drivers of disease outbreaks in various regions, which could prove useful for refining existing models projecting coral disease outbreaks under future climate change scenarios. Similarly, we identified only one study that simulated the impact of a pest species in climate change scenarios for coral reefs (Supplementary Data  1 & Supplementary Table  2 ). This study assessed the potential effectiveness of management strategies in addressing outbreaks of CoTS and reducing cumulative impacts on the Great Barrier Reef 54 . The urgency to address this area of uncertainty is underscored by the ongoing coral disease outbreak in the Gulf of Mexico, which poses a severe threat to coral reefs in the region 188 , 189 . Disease outbreaks are becoming increasingly concerning, affecting not only coral reefs but also other marine life 190 , 191 , highlighting the need for urgent attention and action.

With the growing recognition of the need for intervention measures, particularly in line with the Kunming–Montreal biodiversity framework’s objective of restoring 30% of degraded habitats by 2030, projection models are likely to play a crucial role in guiding these endeavors. Our analysis points toward a possible need to shift the focus of future modeling experiments to better guide actions to manage and restore coral reefs. This does not imply that modeling studies should neglect stressors like ocean acidification, which are expected to have long-term impacts with limited practical solutions. Instead, modelers could consider prioritizing the inclusion of management and intervention scenarios, including coral reef restoration, that integrate the modeled effects of global and regional pressures. Just three of the 79 studies reviewed here included potential intervention scenarios. Two of these studies explored unconventional geoengineering solutions 96 , 192 , while one simulated the potential benefits of demographic restoration and assisted evolution in enhancing reef resilience 83 .

In summary, projections of coral reef futures at global, regional, and local scales play a crucial role in informing discussions and policy-making at various levels of governance. While recognizing the diverse objectives and methods employed in the reviewed articles, there is a clear need for greater coordination in efforts to project coral reef futures. Robust projections are vital for decision-makers and policymakers to implement effective strategies for coral reef management and restoration, helping us achieve our climate, biodiversity, and sustainable development goals. The recommendations presented here propose tangible steps toward a greater understanding of the uncertainty surrounding coral reef futures while also promoting transparency in reporting projections and communicating them to decision-makers. Crucially, the success of these endeavors will depend on interactive communication between the scientific community, policymakers, and local end-users.

Literature search and study selection

We searched the Thomson Reuters Web of Science database ( http://www.webofknowledge.com ) to identify studies projecting the impact of climate change on shallow tropical and sub-tropical coral reefs. The search was performed on March 6, 2023, and retrieved 2705 peer-reviewed articles. Our literature search strategy followed the guidelines of PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-analyses) 193 (Supplementary Fig.  1 ). To synthesize the initial database, we screened the title, abstract, and display items of each article, resulting in the identification of 2073 potentially eligible articles to be included in our database (Supplementary Fig.  1 ). Publications were then selected based on the following criteria: (1) projections represented the responses of tropical and/or sub-tropical coral reefs to future levels of warming alone or in combination with any other drivers, (2) future emissions pathways and/or warming scenarios used to force the simulations were stated, and (3) projections were modeled across more than one reef site to be included in the database. The final database consisted of 79 peer-reviewed articles published between 1999 and 2023.

Data extraction

We initially extracted the key characteristics of each study, including the focal variable(s) simulated, model inputs, spatial scale, and focal geographic area. We classified the models into five broad categories of methodologies: (a) ‘excess heat’/threshold models, (b) population dynamic models, (c) species distribution models, (d) ecological-evolutionary models, and (e) meta-analyses of published data (see the Main text for definitions). In a few cases where studies could not be categorized, the model type was recorded as ‘other’ (Supplementary Data  1 ). We further classified the studies according to the underlying techniques used to simulate heat stress on reefs, as either threshold techniques or continuous variable techniques (see the Main text for definitions). We recorded each study’s purpose, underlying methodological approach, key assumptions, spatial resolution, and application of downscaling techniques (Supplementary Data  2 ). Finally, we acknowledged the diverse range of approaches used to simulate coral reef futures by summarizing the key advantages and limitations of each study (Supplementary Data  2 ).

Study criteria and data analysis

A major objective of our study was to examine and compare the magnitude of projected impacts and estimated uncertainties across different model types. Meta-analyses offer a valuable approach to aggregate evidence from multiple studies to provide a comprehensive overview of current modeled projections 149 . The database of 79 studies was considered for inclusion in the exploratory meta-analysis based on specific criteria (view supplementary methods for detailed list and Supplementary Fig.  1 ). Briefly, to enable a meaningful analysis, we identified the three most common coral reef metrics used as model outputs in our database. The first unit, usually expressed as a percentage of reef cells at risk of repeated severe bleaching events (or ‘long-term degradation’ 14 , 15 ), was a common model output of ‘excess heat’ threshold models (Supplementary Data  1 ). Both population dynamic and ecological-evolutionary model types frequently projected changes in percent coral cover, whereas species distribution/niche models usually simulated fractional changes in habitat suitability (Supplementary Data  1 ). Among those, only studies that provided: (1) sufficient data for projection estimates and uncertainty measures to be reliably extracted or calculated, (2) reported end-of-century projections, and (3) used a baseline period between 2000 and 2015, were selected for the exploratory meta-analysis. In cases where projection and uncertainty estimates were only presented in figures, values were extracted using PlotDigitizer (plotdigitizer.com), where possible. When projection estimates and uncertainties were reported as proportional values between 0 and 1, we converted these values to percentages ranging from 0 to 100.

Among the initial pool of 79 studies, eight studies were identified as containing quantitative data that could be extracted and compared in our analysis. As such, due to the low number of studies included, we consider this analysis to be exploratory in nature. For each study, we calculated Hedges’ g effect sizes and variance for all individual scenarios/trajectories (39 scenarios in total) (Supplementary Data  3 ). The signs of the effect sizes (positive or negative) were adjusted to align with the effect direction reported by the individual studies. In this adjustment, a negative effect size denotes a negative ecological response, while a positive effect size indicates a positive ecological response (Supplementary Methods). Hedges’ g quantifies the difference between the means of two groups divided by the pooled standard deviations and was calculated as follows:

where X P and X B are the estimate of end-of-century projections and baseline data, respectively. J corrects for bias attributed to different sample sizes by differentially weighting studies as follows:

Where N P and N B are the number of models used for projections and baselines.

The s.d . pooled was calculated as follows:

Variance for each scenario was calculated as:

All calculations were computed using the metafor package (v. 4.2-0) in R (v. 4.3.0) 194 .

Reporting summary

Further information on research design is available in the  Nature Portfolio Reporting Summary linked to this article.

Data availability

The source data supporting Figs.  1 – 5 are available in the Source Data file. Supplementary Data Files  1 – 3 provide a summary of all other data generated by this study, and the complete database is deposited in Dryad ( https://doi.org/10.5061/dryad.4f4qrfjkp ) 195 .  Source data are provided with this paper.

Code availability

The R script needed to produce the analysis has been deposited in Dryad ( https://doi.org/10.5061/dryad.4f4qrfjkp ) 195 .

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Human Impacts on Coral Reef Ecosystem

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Healthy, Coral reefs are the most spectacular, diverse and economically valuable marine ecosystems on the planet, Complex and productive, coral reefs are extremely important for biodiversity, providing a home to 35,000–60,000 species of plants and animals (over 25% of all marine life), many of which are not described by science. They are also vital for people and business. They provide nurseries for many species of commercially important fish, protection of coastal areas from storm waves. They are providing hundreds of billions of dollars in food, jobs and significant attraction for the tourism industry. Yet coral reef ecosystems have undergone phase shifts to alternate, degraded assemblages because of the combined human activates of unsustainable overfishing, intensive tourism, urbanization, sedimentation, declining water quality, pollution and primarily from the direct and indirect impacts of climate change. Most coral ecologists confirm that coral reef degradation has increased dramatically during the last three decades due to enhanced anthropogenic disturbances and their interaction with natural stressors. So, it is necessary to recognize the threats facing coral reefs from anthropogenic activities and try to minimize and mitigate these impacts.

• coral reef ecosystem
• anthropogenic activities
• natural threats
• climate change
• coral protection
• proposed solutions

Author Information

Hussein a. el-naggar *.

• Zoology Department, Faculty of Science, Al-Azhar University, Cairo, Egypt

*Address all correspondence to: [email protected]

1. Introduction

Coral reefs are extraordinary living geological diverse underwater ecosystems held together by calcium carbonate structures secreted by corals. They represent the most conspicuous and magnificent community in the tropical and subtropical regions. Coral reefs are built by colonies of tiny living animals found in shallow subtidal marine waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that live together in groups. The polyps belong to a group of animals known as Cnidaria, which also includes sea anemones and jellyfish. The polyps secrete a hard carbonate exoskeleton which support and protect their bodies. Most reefs grow best in warm, shallow, clear, sunny and agitated waters. The oldest coral reefs on the earth occurred about 500 million years ago, as well as the first relatives of recent corals developed in the south of Europe from about 230 million years ago. Most corals get their color from the symbiotic single-celled algae called zooxanthellae. Millions of these single-celled algae are living as symbionts within polyp tissues, intercellular in the gastrodermis layer. Zooxanthellae produce organic nutrients and oxygen through photosynthesis thus helping the coral in the growth and the process of producing limestone or calcium carbonate. Corals grow much faster with the help of the zooxanthellae. Corals get up 90% of their nutrients from their zooxanthellae. Zooxanthellae produce pigments visible through the clear body of the polyp and give the coral its beautiful color [ 1 , 2 ].

Coral reefs provide a home for at least 25% of marine origin fauna, including fishes, echinoderms, crustaceans, mollusks, sponges, tunicates, and other cnidarians and so on. Coral reefs ecosystem (CRE) provides many services to tourism, fisheries in addition to coastline protection from wave action. The global economic value of coral reefs ecosystem is estimated between US $29.8 and 375 billion per year. However, coral reef is a fragile ecosystem, because it is very sensitive to elevations of water temperature. Coral reef ecosystems are exposed to many threats most of them resulting from humans such as global warming, oceanic acidification, climate change, water pollution, Irrational tourism, blast fishing, overfishing, illegal fishing for aquarium fish, overuse of reef resources, harmful land-use practices including urbanization and agricultural runoff which may be harmful for reefs by enhancing algal overgrowth [ 3 , 4 ].

Coral reef ecosystem degradation has increased dramatically during the last three decades due to enhanced anthropogenic disturbances and their interaction with natural stressors [ 5 ]. These stressors are thought to cause coral diseases and bleaching leading to a loss of coral cover. Unfortunately, very little is currently known about the prevalence, distribution and pathology of coral diseases in the Red Sea [ 1 , 6 ].

The annihilation of the reef ecosystem will lead to the disappearance of 25% of marine habitats, and a quarter of marine life that needs to productive and diversified this three-dimensional building to stay alive. Graham et al. [ 7 ] found a serious decline in coral reef fish populations as a result of climate change. Coral reefs provide food and are a source of income for hundreds of millions of people scattered in many countries. The loss of this ecosystem will lead to unexpected effects with serious damages already beginning to appear. It has been estimated that the volume of services and natural resources offered by the coral reefs to humanity from 10 years ago to be about US $30 billion per year, through benefits such as fisheries, tourism and shore protection; it is perhaps greatly increased now [ 8 ]. The mass coral bleaching and death of CRE is one of the most obvious effects of climate changes which warn the world that we should take global warming seriously. The loss of the oceans to most if not all effective CREs could lead to unexpected disasters. We are on the verge of these disasters, but they can be avoided if the necessary international efforts are combined for adverse impact mitigation [ 9 ].

2. The main components of the coral reef ecosystem

Algae: Coral reefs are chronically at risk of algal encroachment. Overfishing and excess nutrient supply from onshore can enable algae to outcompete and kill the coral. There are three groups of algae, these are:

The coralline algae: These groups are very important in constructing and maintaining reef. They belong to the red algae, and can precipitate calcium carbonate as do corals, but tend to be encrusting and spreading out in thin layers over the reefs, cementing the various pieces of calcium carbonate together. These algae form what is called “the algal ridge” on reef which is the most rapidly calcifying zone on reef.

Calcareous green algae: These algae include certain species of green algae, such as Halimeda, which grow erect and secrete calcium carbonate, giving much of reef sand by breaking up.

Other free living algae: They include the free living algae that exist just below the surface layers of calcium carbonate in the coral colonies themselves but are inconspicuous on the reef.

Members of phylum Cnidaria

The stony corals: These groups belong to the Order Scleractinia (Madreporaria) and form the major structure of reefs.

Order Gorgonacea: Its members are commonly called sea fan and sea whip, which have an internal skeleton of spicules. They are abundant in Atlantic Ocean.

Order Alcyonacea: This order comprises the soft corals, which may be abundant in some Indo-Pacific regions than the stony corals, but very rare in Atlantic. Several species of soft corals have internal spicules of calcium carbonates.

Order Hydrocorallina: It includes the hydrocorals, which belong to the class hydrozoa, and called “Fire corals,” for their powerful nematocysts. The hydrocorals are conspicuous in the Atlantic Ocean.

Mollusca: Mollusks have significant role in reef formation due to the ability of their species for calcium carbonate deposition. The most important of mollusk are the giant clam, Tridacna spp. and Hippopus spp. which may be up to 2200 individuals per square meter. Also there is a prominent role of other gastropods and bivalves in deposition of CaCO 2 at the coral reefs.

Echinodermata: Some species of echinoderms have adverse effects on coral reef, particularly the sea star, Acanthaster planci , which predates the coral polyp and cause coral bleaching. However, other species of sea urchin, sea cucumbers, starfish and feather stars are found but their role in reef ecosystem is understood.

Crustaceans and Polychaetes: Members of these groups are very abundant on coral reefs but there is little information about their role in reef formation.

Sponges: They are essential for the functioning of the coral reefs ecosystem. Algae and corals produce organic material. This is filtered through sponges which convert this organic material into small particles which in turn are absorbed by algae and corals. It was recorded that, some species of Siliceous sponges (class: Demospongiae) may be important in holding coral and rubble together, and prevent loss from reef until it can be fused together by coralline algae. Other sponges have symbiotic blue green algae responsible for net primary productivity.

Coral reef fishes : Fishes are very conspicuous and abundant and many of them may have an adverse effect on coral structure due to their feeding regime.

Bacteria: The role of these organisms is very important in reefs structures. This group is very abundant and is responsible for the decomposition and quick cycling of organic matter.

Other communities: Sea eels and snakes as well as marine birds; such as boobies, pelicans, gannets and herons, all feed on fish and other coral reef components’. Land-based reptiles such as monitor lizards, marine crocodile and semiaquatic snakes such as Laticauda colubrina can be intermittently associated with reefs and feed on some of their components. Sea turtles, such as hawksbill sea turtles, feed on sponges between reefs.

3. The importance of the coral reef ecosystem

Coral reef ecosystems are one of the most diverse and beautiful natural environments on earth. Coral reefs have an important role in the marine and coastal environments. They provide valuable habitat (food and shelter) for a great diversity of plants and animals, including important breeding and nursery grounds for many marine organisms [ 10 ].

Coral reefs also provide protection from coastal erosion by acting as natural breakwaters for big waves and storms. Also, the breakdown of corals and other organisms living in the reef habitat creates beaches, which are an important resource for the survival of many coastal organisms, including endangered sea turtles and monk seals. Coral reefs are an important environmental and economic resource for people. In addition to shoreline protection, reefs provide food, recreational and employment opportunities, and are a potential source for new medicines [ 11 , 12 ]. Coral reefs also provide economic benefits to coastal communities from tourism. The major benefits from coral reef ecosystem will be described as follows:

3.1 Reef as a source of income

The diversity of marine life and coasts protected and supported by coral reefs supply attractive conditions and ambience for visitors, reef lovers, divers and snorkelers. Actually, there are more than 8.5 million certified divers in the USA who spend money on diving during each year. The coral reef destruction generates a considerable loss of tourism employment, marine recreation industries and fishing activities. These can have huge impacts on inhabitants of coral reef areas that essentially rely on income from tourism [ 13 , 14 ].

The coral reefs ecosystem provides a significant protein source for millions of people, and is considered as part of their lives. The people inhabiting coral reef areas madly love it, because the coral reef is considered a part of their lives, providing them with the major part of their food through fishing and tourism services. Coral reefs are also strongly linked with cultural, spiritual and traditional values of many people who live in areas nearest to reefs [ 10 ].

3.2 Coral reefs act as protector from storm and wave action

Another benefit to people from coral reefs is that they act as the guards of our coast. They serve as a buffer and protection for the shore areas from the pounding of ocean waves. In the absence of coral reefs, many of beaches and coastal cities would become vulnerable to storm damage and wave action. In the Maldives, when the coral reef and sand were mined away along the coast, it cost $10 million American dollars for each kilometer to construct a wall for coastline protection. In Indonesia, the value of this protective service of coral reefs is estimated at 314 million American dollars [ 15 ].

3.3 Coral reefs save our lives

Just as in the rain forest, plant and animal life in reef ecosystem contain promising medicinal components, several of which are just being detected. Already, many important drugs have been developed from chemicals extracted from coral reef organisms. AZT is the most famous of these drugs, it is a treatment for HIV infections, which relies on chemicals extracted from sponge inhabiting Caribbean reef [ 16 ].

Several unique compounds extracted from coral reefs have also produced the treatments for skin cancer, leukemia, ulcers and cardiovascular diseases. In addition, the unique skeletal structures produced from reef have been used to produce the advanced forms of bone grafting materials. Surprisingly, more than half of all new research related cancer drug discovery focuses on marine organisms. The fragile and beautiful organisms of coral reefs have the potent to make even huge contributions to our lives through providing new treatments for diseases that are threats to our lives [ 11 , 12 ].

3.4 Coral reefs serve as a home for fishes

Over the last 350 million years, coral reefs have developed to become one of the most and largest complex ecosystems on the earth planet. Coral reefs provide shelter for about 25% of all known marine species. They serve as a home to 4000 fish species, 700 corals species and thousands of other forms of flora and fauna. Ecologists estimate that more than one million of biota species are associated with the coral reef ecosystem [ 15 , 17 ].

4. Global threats facing reef ecosystems

Coral Reef ecosystems are facing many natural and anthropogenic threats. Many human impacts are resulting in the destruction and degradation of coral reefs ecosystem to cause loss in biodiversity, fundamental supplies for food and reef economic revenue. Combined with threats from nature in the form of diseases, earthquakes, climate change, typhoons and storms, coral reefs are struggling to survive. Natural stressors are made worse by human disturbances. For example, the diseases may be present at a higher level in corals stressed by human influences such as pollution and mechanical damage [ 18 ].

A majority of the problems threatening coral reefs are the direct (and indirect) result of human activities on land, and in the marine environment. Marine debris, water pollution, sedimentation, overfishing, careless recreation, and global warming are some examples of human-caused threats to the coral reef habitat. Each of these threats has a significant impact on the health of coral reefs. Coral reefs grow very slowly and can take hundreds of years to form. If damage to coral reefs continues at the current rate, over half of all reefs in the world could disappear in our lifetimes. Currently, millions of acres of reef have already been severely damaged or destroyed. Through education, awareness, and action, people can help to preserve and protect coral reefs [ 15 ]. The threats facing coral reef ecosystems can be summarized as below:

4.1 Natural Impacts

4.1.1 earthquakes and storms.

Disasters such as earthquakes and storms occur periodically and naturally and devastate massive areas of coral reefs. These natural events can be more severe if the communities of coral reef are already weakened by other influences and recovery is inhibited by algal overgrowth due to the lack of grazing organisms, removed by fishing.

4.1.2 Climate change and acidification

Climate change impacts have been identified as one of the greatest global threats to coral reef ecosystems. If the temperatures of sea water stay higher than the usual for some weeks, the symbiotic algae “zooxanthellae” that corals rely on for their food leave the coral tissue. Actually, without zooxanthellae the corals turn to white color, because it gives corals their color. Unhealthy white corals are called bleached. Bleached corals are weak and lose their ability to combat diseases and then die [ 18 ]. As climate change continues, bleaching will become more common, and the overall health of coral reefs will decline [ 19 , 20 ].

Since the late nineteenth century, the global temperature of oceans has risen by 1.3°F (0.74°C), causing more frequent and severe corals bleaching around the world. At the recent increasing emissions rate of greenhouse gases, the global temperature could rise up to 7.3°F (4.1°C). These changes in global temperature already have harmful effects on coral reef ecosystems and will continue to impact on coral reef ecosystems over the world during the next century. The decline and loss of coral reef ecosystems have significant social, cultural, economic, and ecological bad impacts on people and communities around the world [ 21 ].

As water temperature rises, infectious diseases and huge bleaching may likely become more frequent. In addition, carbon dioxide absorbed into the sea water from the atmosphere has begun to reduce the calcification rates in reef-building corals and organisms associated with coral throughout change of water chemistry by decreases in pH (ocean acidification). In the long term, the failure in addressing carbon emissions and the impacts of rising water temperatures and ocean acidification could make the several efforts to coral reef ecosystems managements futile. In summary, climate change and ocean acidification have been identified as the most important threats to CRE on a global basis [ 22 ].

In the last decades, 33–50% of corals were significantly degraded, because of the negative impacts that accompanied climate change [ 10 ]. Recently, some areas have lost about half or more of their living coral and more deterioration can occur over the next two decades due to continued temperature rise. Because of the destruction of the CRE, 25% of marine species would be in danger while the economic losses will showcase hundreds of millions of people to the lack of food security and increasing poverty [ 23 ]. Wilkinson [ 10 ] recorded bleaching and death of about 16% of the global reefs communities together with high average of surface temperature in 1998. Since then, the bleaching and death of coral occur on a large scale, with increasing severity of these effects over the successive decades [ 24 ].

Other reasons for coral bleaching are the extreme lowering in tides levels, increased UV radiation and changes in salinity and nutrient levels. Coral reefs may recover but this extreme incident is generally presumed to weakened it. The death may be occurring largely due to starvation, although it is thought that some autolysis (tissue destruction) occurs. The physiological mechanisms involved with bleaching are not fully understood and are currently a source of investigation.

4.1.3 Crown-of-Thorns

Historically, tropical cyclones and poor water quality that cause outbreaks of crown of thorns starfish have been the major causes of coral loss. Current increases in the Crown-of-Thorns starfish populations that eat corals are considered as another natural threat to reefs. When present in huge numbers, these stars are able to destroy massive areas of coral reef. Recovery of the coral reef from the outbreaks of Crown-of-Thorns may take up to 20–40 years, where the damage is not severe. However, coral recovery in some world areas may never occur when the coral is being taken over by sponge, algal cover and other coral species. Acanthaster planci can produce many million babies during 1 year. People have contributed to their population increase through increase of the nutrients from sewage and over harvesting of their natural predator Triton Trumpet and so on. Crown-of-Thorns babies gave more plant food (seaweed) to survive and become devastating adults for coral [ 25 ].

4.1.4 Coral diseases

Coral reefs when are under stress, suffer many bacterial infections as a result of growing production of protective mucus. The coral production for excessive mucus due to natural and man-made influences (e.g., global warming, toxic chemicals, increased sedimentation and so on) can also promote the growth of many blue green algae; this algae is thought to be responsible for black band disease (Intense black band of filaments across coral colonies). This disease kills the Coral polyps and the black band advances then leaving the reef as a white limestone behind it [ 16 ].

Although this disease is rare, the pathogenic bacteria and parasites resulting from fecal contamination may cause some diseases in coral reefs, particularly if corals are stressed by unfavorable environmental conditions. Naturally, the diseases occur for corals in healthy ecosystems, but the pathogen-containing pollution inputs could exacerbate the intensity and frequency of disease outbreaks [ 16 ].

A change of environmental conditions such as higher temperatures or a change in salinity but also disease can cause the polyps to expel the zooxanthellae algae. The coral becomes totally white (= coral bleaching). If the coral regains some algae it might survive, but bleaching can be irreversible and then the coral dies. Coral bleaching is the loss of intracellular endosymbionts (zooxanthellae) from coral tissue, when corals are stressed by changes in conditions such as temperature, light, or nutrients, they expel the symbiotic algae living in their tissues, causing them to turn completely white [ 2 ].

4.1.5 Invasive alien species

Invasive alien species are non-native (exotic) species that may cause huge environmental damages and can have effects on fisheries stock, economy and even on human health. They should not be confused with introduced spe-cies which are also non-native and have been deliberately introduced for a benefit or purpose within the limits imposed on them. It is estimated that of the several of the introduced species to different habitats and different climes have threats to native ecosystems. These invasive alien species have the ability to rapidly grow, vigorously compete with the native species. These species in the absence of their natural preda-tors can lead to the pushing out native species and finally to ecological havoc. They can be able to change and threaten native biodiversity and contribute to economic hardship and social instability, placing constraints on environmental conservation, economic growth and sustainable development [ 26 ]. Actually, the threat to global biodiversity from Invasive Alien Species is the second after habitat destruction. Ballast water is the major channel of spreading Invasive Alien Species in marine habitats. Ships discharge their cargo of ballast water at ports; with this discharge, they also release organisms that were taken in accidentally with the ballast water from other ports [ 27 ].

4.2 Anthropogenic impacts

4.2.1 use the coral reefs in construction and curio trade.

Coral reefs are used as a construction tool for many purposes. They may be used for the construction of house foundations, canals, streets, embankment of fish ponds and lime kilns. Large businesses also are keen on collecting coral reefs for selling them as souvenirs or in the aquarium trade.

4.2.2 Chemical pollution

Coastal waters suffer from huge amounts of a variety of agricultural and industrial chemicals that are released into them. Fertilizers and pesticides used in agricul-tural development projects are discharged into the sea and might lead to coral reef destruction. Pesticides pollution may destroy or harm to reef communities. They lead to further deterioration through accumulating in tissues and may affect physi-ological processes of animals. Herbicides may impact the basic food chain; they can destroy and damage symbionts zooxanthellae algae in coral reef, other algal, sea grass and even free living phytoplankton communities.

The chemical spillage from oil tankers, harbors and pipelines have heavy impacts on feeding, growth rate, reproduction, defensive responses and even on cell structure in coral reefs. Industrial activities such as dredging, mining and refining produce heavy metals and hydrocarbon pollutants that are released into coastal waters. Many coral species are more sensitive to these pollutants, which can damage the ecosystem of coral [ 28 ]. Herbicides and pesticides can affect coral reproduction, growth, and other physiological processes, in particular, can affect the symbiotic algae (plants). This can damage their partnership with coral and result in bleaching.

4.2.3 Nutrients loading/sewage

The discharge of aquacultural and agricultural inputs such as fertilizers, herbicides, pesticides, feed waste and other materials can result in more nutrients loading into coastal areas. These organic compounds lead to increases of eutrophi-cation status of coastal areas and subsequent oxygen depletion. When the nutrient loading into coastal areas and eutrophication occur, the community becomes dominated by algae and seaweed, to the limit transcend grazing organisms’ capacity to control. These can leads to light reduction, oxygen depletion and perhaps death of the communities living there. When coral reef ecosystems are subjected to huge quantities of nutrients, they are easily taken over by algae and may be severely damaged, if not killed.

4.2.4 Fishing and overfishing

Illegal fishing such as blast “dynamite,” cyanide or poison (duva) fishing and hunting by gum boots, are all destructive of any ecosystem. Other injurious practices of fishing include reef structure disintegration in order to remove hiding places, weight traps and herd fish into nets by beating coral surfaces. Accidental grounding of boats and anchor damage may be significant threat to coral reef ecosystem. Such practices lead to annihilation and degradation of habitat of coral reef ecosystem. For instance, 3150 km 2 of coral reef were destroyed when one cruise ship anchored on one occasion [ 29 ].

Overfishing may alter food-webs structure of coral reef ecosystem and cause cascading impacts, such as decrease of the grazer fish numbers that remove algal overgrowth and keep corals clean. Blast fishing (kill fish by explosives) may create physical damage to coral reefs [ 30 ].

The vast majority of the world’s reefs are affected by over exploitation of resources. This may lead to decrease of average size of the fish and reduction of target predatory fish. Removal of main predator and herbivores species may result in change of large scale reef ecosystem. When grazers are removed from reef ecosystem, the algae quickly take over and dominate, particularly if the ecosystem is also suffering from organic pollution [ 31 ].

4.2.5 Construction and sedimentation

Sedimentation is an extremely important cause of destruction of coral reef ecosystem. Predominating, coastal development and construction can lead to heavy amounts of sediment. There are other effects caused by inadequate land management and deforestation, where sediment run off from farms and land and settling on the reefs. In this context, Watersheds that are cleared of their vegetation cover are vulnerable to flooding and erosion and can lead to increase of sedimentation levels reaching coral reefs. Agriculture chemicals also make their way reaching coral reefs through run off from land, streams and rivers [ 32 ].

Dredging has several serious impacts on coral reefs ecosystem. The most spectacular effects are produced by sedimentation, turbidity, silt suspension, reduction of oxygen and release of bacteria and toxic substances. Great quantities of either fine or coarse particles can cover corals, which are unable to withstand cover for more than 1 or 2 days [ 33 ].

The corals secrete protective mucus in a bid to rid themselves of the sedi-mentation. This process requires high energy levels, which have to be diverted away from essential processes. If this problem is exacerbate by other stresses, for example, temperature change, then the reefs become extra stressed and may die. The mucus secretion for sediment clearing makes the reefs more susceptible to infection by bacteria and therefore more probable to suffer from diseases [ 15 ]. The higher level of sedimentation that exceeds the clearing capacity of mucus secretion of coral reefs can reduce light breakthrough and may change the vertical distribu-tion of plants and animals on coral reefs [ 34 ].

4.2.6 Cutting of mangroves

Mangroves destruction by obvious cutting or pollution has resounding con-sequences on reef ecosystem. Mangroves destruction leads to the removal of the main source of leaf litter, a food resource for the set of reef animals. Also, mangroves provide the nutrient rich feeding grounds for several marine species. Moreover, mangroves protect the shoreline against storms and cyclones and give it stability against land loss by erosion.

4.2.7 Rubbish/litter

Trash such as discarded fishing gear, bottles and plastic bags that get to the coast may settle on reefs and prevent the sunlight required for photosyn-thesis or decomposition and kill reef organisms and damage or break corals. Degraded plastics and small pieces of plastic can be ingested by coral, turtles, fish and other reef animals, which can block their digestive tracts and kill them.

Litter and rubbish are one of the groups of largest problems facing any ecosystem. The decomposition of this artificial rubbish takes a very long time. Plastic bottles decomposed in 150 years, plastic bags 50 years, batteries in 200 years, paper in 1 year and cigarette in 75 years. A turtle facing a plastic bag similar to jellyfish may swallow it and can choke it. Batteries leak poisons as they breakdown and can con-taminate the fish we eat, as well as kill corals and other marine life. Rubbish should be disposed of properly, by recycling or taking it back to the mainland dump. If rubbish is left lying around, it can easily get blown into the sea.

4.2.8 Tourism

Tourism has a large potential to contribute to sustainable socio-economic devel-opment and environmental conservation. It can support the protection of natural resources, as local residents realize the value of their assets and try to preserve it. Tourism can also provide another form of land use (other than agriculture) which supports land conversion. It can also contribute to maintaining livelihoods and preserving cultural practices. Opportunities arise for education and awareness-raising to understand and respect cultural diversity along with biodiversity. All these benefits can be derived from the tourism if optimally used and controlled in the required form to preserve the environment, biological diversity and natural habitats. The uncontrol and misuse of tourism can lead to the degradation and collapse of ecosystems and biodiversity that are essentially the real attraction of tourism [ 4 , 14 , 35 ].

Tourism and biodiversity are closely linked both in terms of impacts and dependency. Many types of tourism rely directly on ecosystem services and biodiversity (ecotourism, agritourism, wellness tourism, adventure tourism, etc.). Tourism uses recreational services and supply services provided by ecosystems. Tourists are looking for cultural and environmental authenticity, contact with local communities and learning about flora, fauna, ecosystems and their conservation. On the other hand, too many tourists can also have a negative, degrading effect on biodiversity and ecosystems. Therefore, the tourism sector has both a strong influence on biodiversity loss and a role to play in its conservation [ 36 ]. Regrettably, the tourism-environment relationship is unbalanced; tourism is depending on an environment that is vulnerable to the tourism impacts [ 37 ]. Yet it’s not easy to achieve sustainable development in many developing countries that heavily rely on tourism income, particularly in ecologically sensitive areas. Other influences come from the tourists services area such as domestic wastes, garbage and many bad practices from site visitors. The main harmful human activities that can destroy the biodiversity stock in any area result from uncontrolled tourism and fishing activity [ 1 ].

4.2.9 Coral harvesting for the aquarium trade

Coral harvesting for the aquarium trade, jewelry, and curios can lead to over-harvesting of specific species, destruction of reef habitat, and reduced biodiversity. The practice of keeping marine aquaria as a hobby has increased in the last decade. It is reported that, globally, between 1.5 and 2 million people keep saltwater aquaria [ 38 , 39 ]. Murray et al. [ 40 ] confirmed that the areas of southern California rocky shores which have been used by humans intensely for recreational activities such as fishing, exploration, walking, enjoyment of the out-of-doors, and educational field trips had suffered from reduction of species abundance and diversity due to visitors collection of intertidal organisms for consumption, fish bait, home aquariums and other purposes. The most direct effects of intensive collection are decreased abundances of exploited species and because humans preferentially collect larger individuals, altered population size structures. El-Naggar et al. [ 4 ] attributed the reduction of certain gastropod shells (Cypraeidae) from Aqaba Gulf to their intensive collection by visitors because they have beautiful shells.

4.2.10 Fish-feeding

The feeding behavior of reef fishes, eels, sharks and even rays has come to a “selling point” through commercial fish feeding dive tours and “interactive diving.” However, many do not realize the harmful effects this activity has on these animals. Studies done around the world have indicated that fish feeding significantly alters behavioral patterns by “training” these wild creatures with human food handouts. In addition, fish feeding causes health problems for the fed animals and disrupts the natural processes within the marine community. Here in the Mamanucas, particularly at sites where fish feeding occurs, there has been an increase in aggressive behavior within schools of surgeonfish, fighting amongst themselves and causing injury, even to the point of destroying their own reef habitat by breaking hard corals. Triggerfish have also been observed biting and destroying the reef structure. Sergeant Damselfish swarm around snorkelers or divers expecting to be fed. The fish that are fed often “peck’ at the snorkelers or divers entering the water, taking away the pleasure of observing the reef and its inhabitants in a calm and inoffensive manner. By feeding the algae eaters that control algae growth, they become handout feeders that soon neglect their important role of eating algae, which in turn can overgrow corals. Major conservation organizations, including UNEP, DAN, WWF and Environmental Defense, encourage passive interaction with marine life and avoiding feeding and petting, which may lead to accidental injury.

5. Proposed solutions to mitigation of the coral reef threats (methods for conserve the coral reef)

The aggregate effects of these stressors can decrease resilience of the reef overall and increase susceptibility to disease and invasive species. The anthropogenic stressors on coral reef ecosystem are suggested potential factors respon-sible for the degradation and instability of any ecosystem. Any bad practices from human; directly and indirectly can have effects on coral reef ecosystem. So, it is necessary to create new strategies to protect coral reef ecosystems. Given that 20% of the coral reefs in the world have already been destroyed much has to be done in the future for the preserve of coral reef ecosystem.

5.1 Establishment of marine protected areas

One of the key techniques of conserving coral reef ecosystem is the establishment of Marine Protected Areas (MPAs). Marine Protected Areas (MPAs) are important tools for marine conservation and management. Although there are many types of MPAs, in all them, there are areas set aside for unlimited human activities. When the MPAs restriction is highest, they are considered as “no-take” areas, where the deal-ing with all forms of marine life is prevented; even recreation, research and educa-tion are restricted. Many of MAPs were constructed specifically for management of a special purpose (for instance, for biodiversity preservation, as a refuge of a certain species to breed, for conservation of a historical site or even for recreation). Multiple use management protected areas are zones to permit for complete limitation on dealing in some areas and managed use in others [ 41 ]. However, a main problem in MPAs is that they fail to achieved their management objectives and become parks on paper only [ 42 ]. Even though MPAs may be gazetted legally, enforcement of relevant laws (zoning, prohibiting certain activities) is often poor.

5.2 Prevention of over-harvesting through legislation

Many species are protected under general species protection laws across the region. Most of this protection is afforded to marine vertebrates, but some countries–such as India and Sri Lanka–have laws protecting several species of coral, mollusks and echinoderms. In India, all Stony corals, all Black corals, all Fire corals, and all Sea fans are protected by law [ 43 ]. In Sri Lanka, all Stony corals are protected by law [ 44 ].

5.3 Monitoring

Coral reefs monitoring is a substantial process for developing efficacious strategies of management. Only through monitoring only, is it possible to assess patterns and trends of coral reefs health and use. There are many worldwide organizations specializing in monitoring of coral reefs status. The Global Coral Reef Monitoring Network (GCRMN) devote their efforts and coordinates in order to improve coral reefs management in the whole world, this through capacity building and knowledge sharing and works closely with Reef Base (Global database about coral reef related information) and Reef Check. After the coral bleaching event in 1998 and with the continuous threat of coral degradation as a result of other anthropogenic activities, Coastal Ocean Research and Development in the Indian Ocean (CORDIO) commenced in 1999. CORDIO supports and funds the scientists and organizations in the Indian Ocean Region, for assurance of monitoring of coral reefs status in the region with focus on both socio-economic and ecological impacts of coral reef degradation. Monitoring plays a critical role in managing Marine Protected Areas. The importance of monitoring and research is in guiding management of the fisheries and biodiversity resources. It is necessary to develop a long term monitoring plan for management of abundance and diversity of biota coupled with an assessment of fishing and habitats quality including coral reef [ 1 ].

5.4 Building awareness

Building awareness about coral reef ecosystems, their biodiversity, services they provide and their business are highly supportive of mitigation of the threats that are facing these fragile ecosystem of coral reefs. Awareness at the community levels is extreme efficient as it may help to encourage coral reefs users to change their behavior to sustainable use of these ecosystems. On the other hand, the awareness at national level through conservation education by the media and other means is necessary to guarantee that decision makers integrate coral reef preser-vation into all development stages. It is also important to ensure that some envi-ronmental issues, such as poorly planned or unplanned inland development and pollution, are prevented in order to protect coastal ecosystems such as coral reefs. Worldwide, 1997 was designated as International Year of the Coral Reef Because of growing threats to coral reefs in the whole world. Also, 2008 was designated as International Year of the Coral Reef.

5.5 Support of sustainable livelihoods and participation in reef dependent communities

The relationship between reef ecosystems and poverty is very significant, whereas 67% of all countries having reef areas are developing countries and about 25% of these countries are least developed countries [ 45 ].

Coral reef ecosystems contribute to the national economies and provide signifi-cant resources for poor people. The current direction of growing threats to coral resources is projected to impact poor communities dependent on reef ecosystem. To make matters worse, the predominating objectives of reef ecosystem management for preservation restrict community access to their resources thus reducing liveli-hood options for these communities. Oftentimes, these restrictions are not followed by communities which may have weak understanding or low participation in the process of reef management.

It is now well recognized that these communities need to be offered alternates for livelihoods in order to assure that reefs are not further damaged, as well as to mitigate poverty for these communities. Therefore, managers of coastal areas are highly switching toward more integrated as well contributory approaches for coral reefs conservation and management. These approaches include identifying and supporting alternate livelihoods for reducing reliance on reef components, in addi-tion to promoting the activities of current livelihood to make them more cost and resource use effective . Rather than comprehensive restrictions on reefs resources use, recently, limited and controlled uses of these resources are advocated in certain circumstances. The reef access rights, resolution of struggles over resource uses, local community involvement and cooperative reef management are now being integrated in to reefs resources management [ 46 ].

5.6 New management initiatives

It is now understood that the standard approaches of management of coastal zones have not been successful in realizing sustainable development and reef preservation aims and there is need for change in approaches [ 16 ].

The shifting from small and isolated efforts of management to large-scale networks using cooperative management is a new trend. Increasing reefs area under high conservation is a main propulsion for this shifting, thus now 33% of Great Barrier Reef has been declared as a highly protected areas or as no-take zones, where no activity is permitted except in the narrowest limits. The cooperation for creating greater network of Marine Protected Areas is another meth - od that has been favored by main Non-governmental organizations (NGOs) such as Conservation International, the Nature Conservancy and the World Wildlife Fund who are developing training modules to identify and develop a network of Marine Protected Areas in Asia depending on zones of highest biodiversity. Another shift is in the effort to focus research on real-life problems that resource managers face [ 16 ].

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Perspectives

How Tourism Can Be Good for Coral Reefs

Data highlights opportunities for the tourism industry to support better conservation outcomes

April 25, 2017

View The Study

Coral reefs could be considered the poster child of nature-based tourism. People come specifically to visit the reefs themselves, to swim over shimmering gardens of coral amongst hordes of fish. But even if you aren’t snorkeling or diving on a reef, your tropical beach vacation was likely made possible by a coral reef.

The world’s coral reefs perform many essential roles. They are home to the fish that provide the food - and often livelihoods - for nearly 100 million people. They also act as barriers against the worst impacts of storms, protecting the beaches and the millions of people who live around and rely upon them. By modelling the economic contributions of coral reefs to global and local economies, this work can be used to persuade governments of the importance of investing in their protection.

Quote : Source: Mapping Ocean Wealth

The global economic value of coral reefs for tourism is $36 billion/year

Source: Mapping Ocean Wealth

In a  study published in the Journal of Marine Policy , The Nature Conservancy’s Mapping Ocean Wealth (MOW) initiative and partners, used an innovative combination of data-driven academic research and crowd-sourced and social media-related data to reveal that 70 million trips are supported by the world’s coral reefs each year, making these reefs a powerful engine for tourism.

In total, coral reefs represent an astonishing $36 billion a year in economic value to the world. Of that $36 billion, $19 billion represents actual “on-reef” tourism like diving, snorkeling, glass-bottom boating and wildlife watching on reefs themselves. The other $16 billion comes from “reef-adjacent” tourism, which encompasses everything from enjoying beautiful views and beaches, to local seafood, paddleboarding and other activities that are afforded by the sheltering effect of adjacent reefs.

There are more than 70 countries across the world that generate more than 1 million dollars per square mile.

In fact, there are more than 70 countries and territories across the world that have million dollar reefs—reefs that generate more than one million dollars per square kilometer. These reefs support businesses and people in the Florida Keys, Bahamas, Mexico, Indonesia, Australia, and Mauritius, to name a few. Demonstrating this value creates a powerful incentive for local businesses and governments to preserve these essential ecosystems.

The Conservancy’s  Atlas of Ocean Wealth , and the accompanying  interactive mapping tool , serves as a valuable resource for managers and decision makers to drill down to determine not just the location of coral reefs or other important natural assets, but how much they’re worth, in terms of their economic value as well as fish production, carbon storage and coastal protection values. By revealing where benefits are produced and at what level, the MOW maps and tools can help businesses fully understand and make new investments in protecting the natural systems that underpin their businesses.

The Methodology

Along with traditional data-driven academic research, and research from the emerging fields of crowd-sourced and social media-related data, a combination of tourism datasets that included hotel rooms, general photographs, underwater photographs, dive centers and dive site were used to render and improve crude national statistics, and also to cross-validate with independent datasets – for example, using hotel locations alongside number of photos taken in a location to independently show tourism spread at national levels, and using dive-sites and locations of underwater photographs to distinguish between tourism activities that take place directly on the reef (e.g., snorkeling, diving) versus tourism activities that indirectly benefit from the presence of coral reefs (e.g., enjoying pristine beaches, calm waters, and fresh seafood).

The data is available in the  mapping application , which allows users to view and compare economic and visitation values of coral reef tourism around the world. Users can also focus on specific geographies, such as Florida, the Bahamas, the Eastern Caribbean, and Micronesia, to view a more fine-scale distribution of values in these regions.

Armed with concrete information about the value of these important natural assets, the tourism industry can start to make more informed decisions about the management and conservation of the reefs they depend on—and thus become powerful allies in the conservation movement.

The concept of valuing nature isn’t a new one, but the detailed, targeted knowledge of the MOW initiative presents an opportunity for the travel and tourism industry to lead both in the private sector, institutionalizing the value of nature into business practices and corporate sustainability investments, and in the sustainability movement more broadly by capturing the business opportunities that exist when we realize that we need nature.

Quote : Dr. Robert Brumbaugh

It’s clear that the tourism industry depends on coral reefs. But now, more than ever, coral reefs are depending on the tourism industry."

Dr. Robert Brumbaugh

For those interested in learning more, or if you have questions or feedback, contact us at  [email protected] .

Atlas of Ocean Wealth

This Atlas represents the largest collection to date of the economic, social and cultural values of coastal and marine habitats globally. View Atlas

Mapping Ocean Wealth

Understanding in quantitative terms all that the ocean does for us today, so that we make smarter investments and decisions for the ocean of tomorrow. Visit Site

Recreation and Tourism Data Portal

Dig in to visualize and simplify global, regional and local ecosystem benefits for use in natural resource planning and policy decisions. Explore the Data

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There’s A Crisis Unfolding In Florida's Waters. DeSantis Hasn’t Said A Word.

Senior Reporter, HuffPost

Typically, when an environmental and economic disaster strikes a state, its leader takes the time to address the threat, look for solutions, maybe even show up in person.

But as coral reefs throughout the Florida Keys have turned ghost white and perished in recent weeks amid a record-breaking, relentless marine heat wave, Florida Gov. Ron DeSantis (R) has remained completely silent — at least publicly.

HuffPost was unable to identify a single comment from DeSantis about the crisis, which is forecast to persist for months and threatens to devastate not only the remaining corals in the Keys but also the region’s tourism-based economy. A spokesperson for DeSantis did not respond to a request for comment Friday, instead forwarding HuffPost’s questions to the Florida Department of Environmental Protection.

Brian Miller, a spokesperson for the environmental agency, told HuffPost in an email that the state has “taken many preemptive actions to safeguard Florida’s Coral Reef for generations to come” under DeSantis’ leadership. Since 2019, Florida has spent more than $50 million for coral reef recovery and restoration, he noted.

“The Governor’s forward-thinking funding priorities ― including coral reef restoration and recovery initiative grants ― provide crucial financial resources to tackle current and future environmental issues, including those currently affecting Florida’s Coral Reef,” Miller wrote.

Of course, funneling money to reef restoration does nothing to confront the main threat to corals. Planet-warming greenhouse gas emissions are driving up ocean temperatures and fueling mass coral die-offs.

“No matter what we do regarding restoration, local sources of pollution, marine protected areas — if we don’t get our hands around global climate emissions, anything we do is a rear guard action that will only put things off for the future,” said Bill Precht, a veteran coral scientist based in Miami. “And that’s not good enough.”

When corals are exposed to prolonged spells of hot water, they become stressed and expel their zooxanthellae ― the symbiotic algae that they rely on for most of their food ― and turn white, a phenomenon known as coral bleaching. If temperatures return to normal, bleached corals can recover. If not, they can die.

Water temperatures in the Keys have been in the low- and mid-90s since early July. Already, scientists there have documented widespread bleaching and coral mortality. And the threat of heat stress is far from over. The Keys and much of the Caribbean are under the National Oceanic and Atmospheric Administration’s highest alert level for bleaching, which means reefs there have a 90% chance of severe bleaching and mortality over the next several months.

The situation is so dire that scientists have mobilized to relocate corals from offshore nurseries and into labs in a desperate effort to preserve their genetic diversity.

DeSantis, now a 2024 Republican presidential candidate, often touts Florida as an economic powerhouse. Early in the COVID-19 pandemic, he lifted lockdown restrictions, citing the effect those safety measures were having on the state’s economy.

“Our economy is the envy of the nation,” he said during his State of the State address last year. “And the state is well-prepared to withstand future economic turmoil.”

Yet for the last month, DeSantis has ignored environmental and economic turmoil in the Keys, apparently too focused on waging his never-ending political war on “woke ideology.” This week, for example, his Department of Education “effectively banned AP Psychology in the state by instructing Florida superintendents that teaching foundational content on sexual orientation and gender identity is illegal under state law,” the College Board said in a statement . And at a GOP primary campaign stop in New Hampshire, he promised to “start slitting throats” in the federal government on “Day One” if elected to the White House.

Coral reefs are vital ecosystems, providing habitat for more than 25% of the planet’s marine species and generating goods and services valued at an estimated $375 billion each year . Ocean recreation and tourism in the Keys support approximately 33,000 jobs and account for $2.3 billion in annual sales, according to NOAA. Reefs are the backbone of the area’s economy.

Precht called coral reefs the “major breadwinner for South Florida” and said he’s been troubled by DeSantis’ silence on the unfolding disaster.

“I’ve been surprised with the lack of leadership on an issue that has tremendous ramifications not just for the reefs of Florida but for the economy of Florida, which includes ecotourism — No. 1 dive destination in the world — commercial fishing, sport fishing and everything that goes with all of those things,” he said. “Lodging, hotels, gasoline stations, restaurants. The number is billions of dollars a year in importance to the state of Florida.”

Precht has been studying corals since 1978 and said he’s always been an optimist. But the devastation to reefs over the last decade, in particular this summer, has left him feeling shocked and depressed. He noted that Florida entered this year’s bleaching event with already historically low coral cover. Upwards of 90% of corals in the Keys have vanished since the 1970s due to warming temperatures, disease and other threats.

“We’ve had continual declines from disease and past bleaching events, and the reefs in Florida have never recovered,” Precht said. “If we lose 50-plus or 90-plus percent [of remaining corals], depending on how bad this thing gets, what’s left? There’s nothing left.”

“I don’t want to say it’s over” for the reefs, Precht added. “But there are going to be places in the Keys that are going to see mortality levels we’ve never seen before. And there might not be much left in those spots.”

In unveiling his proposed state budget earlier this year, DeSantis declared that “conserving Florida’s beauty, protecting Florida’s beauty, has been a staple of our administration from the very start.”

Yet like many Republicans, he has largely ignored the mounting effects of climate change in his own backyard.

“I’ve always rejected the politicization of the weather,” DeSantis told Fox News in May shortly after announcing his presidential bid.

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How to Write a Good Conclusion (With Examples) 

• Smodin Editorial Team
• Published: May 31, 2024

Students often spend a great deal of time crafting essay introductions while leaving the conclusion as an afterthought. While the introduction is one of the most vital aspects of an essay, a good conclusion can have just as much of an impact on its effectiveness. Knowing how to write a good conclusion is crucial, as it encapsulates your main points and leaves a lasting impression on the reader.

A well-crafted conclusion should serve as the final pitch for your arguments. Your reader should walk away with a clear understanding of what they just read and how it applies to the core of your thesis. With the right approach, your conclusion can transform a good essay into a great one, making it both memorable and impactful.

This article will guide you through four simple steps of writing compelling conclusions. Each step is designed to help you reinforce your thesis and articulate your final thoughts in a way that will resonate with your teacher or professor. With a bit of practice, you can learn how to stick the landing and give every essay the finale it deserves.

What Is the Purpose of the Conclusion Paragraph?

Understanding the purpose of the conclusion paragraph is essential for effective essay writing. The conclusion paragraph should be more than just a summary of your essay. It should consolidate all your arguments and tie them back to your thesis.

Remember, all good writing inspires emotion. Whether to inspire, provoke, or engage is up to you, but the conclusion should always leave a lasting impression.

If in doubt, Smodin’s AI Chat tool can be handy for gauging the emotional impact of your conclusion.

By mastering the art of writing a powerful conclusion, you equip yourself with the tools to ensure your essays stand out. Whether it’s the first or last essay you’re writing for the class, it’s your chance to leave a definitive mark on your reader.

How to Write a Good Conclusion

This approach ensures your conclusion adds value and reinforces your arguments’ coherence. Here are three simple and effective practices to help you craft a solid conclusion.

Restating Your Thesis

Restating your thesis in the conclusion is a common practice in essay writing, and for good reason. It helps underscore how your understanding has deepened or shifted based on the evidence you provided.

Just understand that a restatement of your original thesis doesn’t mean a complete word-for-word repeat. You should rephrase your original thesis so that it elucidates the insights you touched on throughout the essay. Smodin’s AI Rewriter can help refine your restatement to ensure it is fresh and impactful.

Here are a few tips to effectively restate your thesis

• Show Complexity : If your essay added layers or nuances to the original statement, be sure to articulate that clearly.
• Integrate Key Findings : Incorporate the main findings of your essay to reinforce how they supported or refined your thesis.
• Keep It Fresh : Again, you want to avoid repeating the same things twice. Use different wording that reflects a nuanced perspective.

Finally, always ensure that the restated thesis connects seamlessly with the rest of your essay. Always try to showcase the coherence of your writing to provide the reader with a strong sense of closure.

Using AI tools like Smodin’s Outliner and Essay Writer can ensure your writing flows smoothly and is easy to follow.

Providing an Effective Synthesis

Providing an effective synthesis should enhance your original thesis. All good arguments should evolve and shift throughout the essay. Rather than simply summarizing these findings, you should integrate critical insights and evidence to demonstrate a deeper or more nuanced understanding.

Draw connections between the main points discussed and show how they collectively support your thesis. Also, reflect on the implications of these insights for the broader context of your subject. And once again, always use fresh and engaging language to maintain the reader’s interest.

The last thing you want is for your reader to view your essay as a collection of individual points. A good essay should read as a unified whole, with all the pieces tying together naturally. You affirm your argument’s significance when you tie all the pieces together in your conclusion.

Providing New Insights

Also, think of this step as your opportunity to propose future research directions based on your findings. What could a student or researcher study next? What unanswered questions remain? If you’re having trouble answering these questions, consider using Smodin’s research tools to expand your knowledge of the topic.

That isn’t to say you can leave open-ended or unanswered questions about your own thesis. On the contrary, your conclusion should firmly establish the validity of your argument. That said, any deep and insightful analysis naturally leads to further exploration. Draw attention to these potential areas of inquiry.

(Optional) Form a Personal Connection With the Reader

Forming a connection with the reader in the conclusion can personalize and strengthen the impact of your essay. This technique can be powerful if implemented correctly, making your writing more relatable, human, and memorable.

That said, slime academics discourage using “I” in formal essays. It’s always best to clarify your teacher’s or professor’s stance before submitting your final draft.

If it is allowed, consider sharing a brief personal reflection or anecdote that ties back to the main themes of your essay. A personal touch can go a long way toward humanizing your arguments and creating a connection with the reader.

Whatever you choose, remember that your conclusion should always complement the analytical findings of your essay. Never say anything that detracts from your thesis or the findings you presented.

Examples of Good Conclusions

Let’s explore some examples to illustrate what a well-crafted conclusion looks and sounds like. The following are two hypothetical thesis essays from the fields of science and literature.

• Thesis Topic: The Impact of Climate Change on Coral Reefs
• Introduction: “Coral reefs act as the guardians of the ocean’s biodiversity. These underwater ecosystems are among the most vibrant and essential on the entire planet. However, the escalating impact of climate change poses a severe threat to their health and survival. This essay aims to dissect specific environmental changes contributing to coral degradation while proposing measures for mitigation.”
• Conclusion: “This investigation into the impact of climate change on coral reefs has revealed a disturbing acceleration of coral bleaching events and a significant decline of reef biodiversity. The findings presented in this study establish a clear link between increased sea temperatures and coral reef mortality. Future research should focus on the resilience mechanisms of coral species that could influence conservation strategies. The fate of the coral reefs depends on humanity’s immediate and concentrated action to curb global emissions and preserve these vital ecosystems for future generations.”

Notice how the conclusion doesn’t simply restate the thesis. Instead, it highlights the definitive connection between climate change and coral health. It also reiterates the issue’s urgency and extends a call of action for ongoing intervention. The last sentence is direct, to the point, and leaves a lasting impression on the reader.

If you’re struggling with your closing sentence (or any sentence, for that matter), Smodin’s Rewriter can create hundreds of different sentences in seconds. Then, choose the sentences and phrases that resonate the most and use them to craft a compelling conclusion.

• Thesis Topic: The Evolution of the American Dream in 20th-Century American Literature
• Introduction: “The American Dream was once defined by prosperity and success. However, throughout the 20th century, the representation of the American Dream in popular literature has undergone significant changes. Are these representations indicative of a far-reaching sentiment that lay dormant among the American public? Or were these works simply the result of disillusioned writers responding to the evolving challenges of the times?”
• Conclusion: “Works by F. Scott Fitzgerald, John Steinbeck, and Toni Morrison illustrate the American Dream’s evolution from unbridled optimism to a more critical examination of the American ethos. Throughout modernist and post-modernist literature, the American Dream is often at odds with core American values. These novels reflect broader societal shifts that continue to shape the national consciousness. Further research into contemporary literature could provide greater insight into the complexities of this concept.”

You will know exactly what this essay covers by reading the introduction and conclusion alone. It summarizes the evolution of the American Dream by examining the works of three unique authors. It then analyzes these works to demonstrate how they reflect broader societal shifts. The conclusion works as both a capstone and a bridge to set the stage for future inquiries.

Write Better Conclusions With Smodin

Always remember the human element behind the grading process when crafting your essay. Your teachers or professors are human and have likely spent countless hours reviewing essays on similar topics. The grading process can be long and exhaustive. Your conclusion should aim to make their task easier, not harder.

A well-crafted conclusion serves as the final piece to your argument. It should recap the critical insights discussed above while shedding new light on the topic. By including innovative elements and insightful observations, your conclusion will help your essay stand out from the crowd.

Make sure your essay ends on a high note to maximize your chances of getting a better grade now and in the future. Smodin’s comprehensive suite of AI tools can help you enhance every aspect of your essay writing. From initial research to structuring, these tools can streamline the process and improve the quality of your essays.

What’s the meaning behind World Oceans Day?

M ore than 70% of the planet’s surface is covered by oceans, and to highlight their importance, the United Nations observes World Oceans Day every June 8th.

Every year, the agency proclaims a new theme, with this year’s being "awaken new depths."

"The UN is joining forces with decision-makers, indigenous leaders, scientists, private sector executives, civil society, celebrities, and youth activists to showcase how our relationship with the ocean needs to urgently change, since our efforts to date have only skimmed the surface. To motivate widespread momentum for the ocean, we need to awaken new depths," the agency said in a statement.

SHARK ATTACKS FORCE SOME FLORIDA BEACHES TO CLOSE TO SWIMMERS

Biologists estimate that oceans produce at least 50% of the planet’s oxygen and are in need of humans’ support.

"With 90% of big fish populations depleted and 50% of coral reefs destroyed, we are taking more from the ocean than can be replenished. We need to work together to create a new balance with the ocean that no longer depletes its bounty but instead restores its vibrancy and brings it new life," the U.N. stated.

In recent decades, climate change has garnered greater interest as increasing water temperatures have led to the destruction of ecosystems, including coral reefs.

During the summer of 2023, reefs along the Florida Keys experienced an extreme heat wave that led to some reefs being completely bleached.

WILL THE ANNUAL SEAWEED INVASION THREATEN FLORIDA BEACHES IN 2024?

In addition to the warming waters, the U.N. says oceans are literally choking on plastic waste.

It’s estimated that every day, the equivalent of over 2,000 garbage trucks full of plastic are dumped into waterways.

Some nations have started to crack down on plastic usage, but efforts have yet to yield meaningful results.

"As we bump up against planetary boundaries, less bad is simply not good enough. Now is the time for governments, cities, businesses, and other organizations to unite around a just transition to a circular economy for plastic," Csaba Kőrösi, the former president of the United Nations General Assembly, previously stated.

Original article source: What’s the meaning behind World Oceans Day?

How to have an eco-friendly holiday on the Great Barrier Reef

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Coral Expeditions' annual Citizen Science Cruise engages travellers in coral science and reef monitoring. Photo / Coral Expeditions

We all want to do our part to future-proof the planet but we don’t always know where to start. Here, travel writer Jessica Wynne Lockhart hops on board Coral Expeditions’ annual Citizen Science Cruise to do her bit.

As the sun set over Queensland’s coastline, I stood on the sun deck of the 72-passenger Coral Discoverer and waved goodbye.

In the distance, the Sunshine Coast’s Glass House Mountains drifted past, their silhouettes dark against the orange-pink simmer—a perfect colour match for the aperol spritz I sipped.

With the bon voyage cocktail cool in my hand, it was easy to forget that the trip I was embarking on from Brisbane to Cairns wasn’t just another pleasure cruise. As a passenger on Coral Expeditions’ annual Citizen Science Cruise, I’d be spending the next 10 days learning about coral science, observing reef restoration, and helping to monitor the health of the reef at snorkel and dive sites along the way.

READ MORE: How to preserve the Great Barrier Reef for future generations

Citizen science — which refers to when the general public makes observations or helps collect data for use by scientists, often submitted through apps — is far from a new concept.

However, it’s only been in the last decade that it’s been more widely embraced by tour operators, who are increasingly recognising the potential of travellers to help conduct research at scale. This is particularly true for expedition cruise companies like Coral Expeditions, which frequent waters that may be inaccessible to researchers due to funding constraints or resource limitations.

These citizen science programmes also give travellers greater insight and understanding into the natural world around them.

At our first stop outside Bundaberg, for example, we’re given an insider tour of Monsoon Aquatics. The aquaculture facility is currently conducting research to determine how corals spawn — and what species might be most heat tolerant as global water temperatures rise.

“We still don’t know so much about coral; we don’t know how old they have to be before they spawn or even how long certain coral live for,” explains our guide, Megan Combe.

Combe leads us between the rows of water tanks, each containing neon-coloured coral fragments. Their vivid colours are the result of the blue lights above and zooxanthellae algae within their polyps, which help them to photosynthesize.

These are the same algae that coral expel when they’re stressed, resulting in bleaching. But bleached coral is not dead coral. As Combe begins to feed coral from a dropper—their tentacles emerging and their mouths opening—she points out one fragment that’s less colourful than the rest.

“It was bleached, but you can see it’s already recovering,” she says.

At each stop over the next week, we, too, are drip-fed, our minds opening and hungry for knowledge. At Lady Elliot Island, we meet a manta ray researcher. At Daydream Island, where we get a chance to hand-feed stingrays and learn from on-staff marine biologists about how they’re perfecting their coral planting programme through trial-and-error — research that has implications for restoration elsewhere on the reef. And at each snorkel site we visit, we’re invited to submit our observations to apps, such as the Great Barrier Reef Marine Park Authority’s Eye on the Reef.

However, critics are increasingly concerned that the proliferation of these programmes is nothing more than “public relations citizen science”, as researchers from York University and the University of Hawaii phrased it in Social Studies of Science in 2021.

Part of the problem? Even though assessment tools — like the waterproof rapid monitoring surveys that we’re handed on our first day — are designed for laypeople, the average person is prone to biases and deviations from standard procedures. Research shows that citizen scientists are more likely to record significant sightings (like sharks) while ignoring the seemingly mundane (yet another parrotfish). The result is gaps, redundancies, and a vast ocean of data, much of it potentially unusable.

I have my own doubts. But I’m reminded of my purpose when I speak to one of my fellow passengers, a woman in her late 80s, about climate change.

“We look at our great grandchildren and wonder: What kind of a future is there for them?” she says.

There’s no future without more research. Even if the data we’re collecting as tourists isn’t usable, our presence is helping to make the work of the ship’s master reef guides — who are trained to collect data — possible.

The simple fact is that scientists would never be able to complete the amount of surveying necessary to properly assess the 2300km-long reef’s health without help, due to its sheer scale. That’s where tourism comes in.

In an April 2024 statement, the Great Barrier Reef Marine Park Authority credited tourism operators for doing the “heavy lifting” with monitoring in the latest mass bleaching event. They conducted over 15,000 reef health surveys, including submitting 65,000 images, which helped create an accurate snapshot of the reef’s health.

Citizen science may have its faults, but when we disembark in Cairns, I feel more knowledgeable and empowered. When it comes to the Great Barrier Reef, the only chance for its future is to foster this culture of hope — not one of helplessness.

How to get involved

Coral Expeditions’ next 10-day Citizen Science Cruise will be setting sail from Brisbane in March 2025. It’s just one of the many expedition cruise lines — including the newly B Corp-certified Aurora Expeditions — to offer a participatory science component on board, with passengers doing everything from counting penguins to taking water samples.

However, you don’t need to be aboard a cruise to get involved in citizen science efforts on the Great Barrier Reef. Here are three ways that any traveller can give back on their next visit to tropical north Queensland:

Report your sightings to Eye on the Reef

Before you head out on your next snorkel sesh, download the Eye on the Reef app. Developed by the Great Barrier Reef Marine Park Authority, the free program allows anyone out on the water to report sightings in real-time, including of coral-hungry Crown of Thorns starfish. The data is then used by the authority to inform its management decisions and actions, contributing to the long-term protection of the reef.

Become a marine biologist for a day

Apps like Eye on the Reef and iNaturalist are designed for the average person to use, without any training required. However, if you’re looking for further insight into how to interpret what’s happening under the water’s surface, then sign up for a guided snorkel or dive. Daily tours departing from Cairns and Port Douglas from the reef typically have trained marine biologists on board, and many tour operators are now offering citizen science excursions. In April, Passions of Paradise launched its Eco Reef Tour, with departures daily starting from A$410. On the full-day small group tour, you’ll assist master reef guides as they survey reef health and monitor the more than 9000 pieces of coral that have been planted by the tour operator at the Hastings Reef.

Learn about a living coral reef biobank

If you’re not a confident swimmer or snorkeller, you can witness the majesty and diversity of the Great Barrier Reef at the Cairns Aquarium. However, down a back hallway and behind the tanks is where you’ll find something truly extraordinary: the Forever Reef Project. This is where researchers analyse and house 179 of 400 species of coral from the Great Barrier Reef — some collected by Coral Expeditions on a previous Citizen Science Cruise — to help ensure coral biodiversity for future generations. Backstage access is available daily at 11.30am on the 30-minute Coral Conservation Tour.

coralexpeditions.com/au/destinations/great-barrier-reef/citizen-science-on-the-great-barrier-reef-brisbane-to-cairns-10-nights

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05 june 2024, secretary-general's special address on climate action "a moment of truth" [as delivered].

Dear friends of the planet,

Today is World Environment Day.

It is also the day that the European Commission’s Copernicus Climate Change Service officially reports May 2024 as the hottest May in recorded history.   

This marks twelve straight months of the hottest months ever. 

For the past year, every turn of the calendar has turned up the heat.

Our planet is trying to tell us something.  But we don't seem to be listening.

Dear Friends,

The American Museum of Natural History is the ideal place to make the point.

This great Museum tells the amazing story of our natural world. Of the vast forces that have shaped life on earth over billions of years. 

Humanity is just one small blip on the radar.

But like the meteor that wiped out the dinosaurs, we’re having an outsized impact.

In the case of climate, we are not the dinosaurs.

We are the meteor.

We are not only in danger.

We are the danger.

But we are also the solution.

So, dear friends,

We are at a moment of truth.

The truth is … almost ten years since the Paris Agreement was adopted, the target of limiting long-term global warming to 1.5 degrees Celsius is hanging by a thread.

The truth is … the world is spewing emissions so fast that by 2030, a far higher temperature rise would be all but guaranteed.

Brand new data from leading climate scientists released today show the remaining carbon budget to limit long-term warming to 1.5 degrees is now around 200 billion tonnes.  

That is the maximum amount of carbon dioxide that the earth’s atmosphere can take if we are to have a fighting chance of staying within the limit.

The truth is… we are burning through the budget at reckless speed – spewing out around 40 billion tonnes of carbon dioxide a year.

We can all do the math.

At this rate, the entire carbon budget will be busted before 2030.

The truth is … global emissions need to fall nine per cent every year until 2030 to keep the 1.5 degree limit alive. 

But they are heading in the wrong direction. 

Last year they rose by one per cent.   The truth is… we already face incursions into 1.5-degree territory.

The World Meteorological Organisation reports today that there is an eighty per cent chance the global annual average temperature will exceed the 1.5 degree limit in at least one of the next five years.

In 2015, the chance of such a breach was near zero.

And there’s a fifty-fifty chance that the average temperature for the entire next five-year period will be 1.5 degrees higher than pre-industrial times.

We are playing Russian roulette with our planet.

We need an exit ramp off the highway to climate hell. 

And the truth is… we have control of the wheel.

The 1.5 degree limit is still just about possible.

Let’s remember – it’s a limit for the long-term – measured over decades, not months or years.

So, stepping over the threshold 1.5 for a short time does not mean the long-term goal is shot.

It means we need to fight harder.

The truth is… the battle for 1.5 degrees will be won or lost in the 2020s – under the watch of leaders today. 

All depends on the decisions those leaders take – or fail to take – especially in the next eighteen months.

It’s climate crunch time. 

The need for action is unprecedented but so is the opportunity – not just to deliver on climate, but on economic prosperity and sustainable development.

Climate action cannot be captive to geo-political divisions.

So, as the world meets in Bonn for climate talks, and gears up for the G7 and G20 Summits, the United Nations General Assembly, and COP29, we need maximum ambition, maximum acceleration, maximum cooperation - in a word maximum action.

So dear friends,

Why all this fuss about 1.5 degrees?

Because our planet is a mass of complex, connected systems.  And every fraction of a degree of global heating counts. 

The difference between 1.5 and two degrees could be the difference between extinction and survival for some small island states and coastal communities.

The difference between minimizing climate chaos or crossing dangerous tipping points.

1.5 degrees is not a target.  It is not a goal.  It is a physical limit.

Scientists have alerted us that temperatures rising higher would likely mean:

The collapse of the Greenland Ice Sheet and the West Antarctic Ice Sheet with catastrophic sea level rise;

The destruction of tropical coral reef systems and the livelihoods of 300 million people;

The collapse of the Labrador Sea Current that would further disrupt weather patterns in Europe;

And widespread permafrost melt that would release devastating levels of methane, one of the most potent heat-trapping gasses.

Even today, we’re pushing planetary boundaries to the brink – shattering global temperature records and reaping the whirlwind.    

And it is a travesty of climate justice that those least responsible for the crisis are hardest hit: the poorest people; the most vulnerable countries; Indigenous Peoples; women and girls.

The richest one per cent emit as much as two-thirds of humanity. 

And extreme events turbocharged by climate chaos are piling up:

Destroying lives, pummelling economies, and hammering health;

Wrecking sustainable development; forcing people from their homes; and rocking the foundations of peace and security – as people are displaced and vital resources depleted. 

Already this year, a brutal heatwave has baked Asia with record temperatures – shrivelling crops, closing schools, and killing people.   

Cities from New Delhi, to Bamako, to Mexico City are scorching.  

Here in the US, savage storms have destroyed communities and lives.

We’ve seen drought disasters declared across southern Africa;

Extreme rains flood the Arabian Peninsula, East Africa and Brazil;

And a mass global coral bleaching caused by unprecedented ocean temperatures, soaring past the worst predictions of scientists.

The cost of all this chaos is hitting people where it hurts:

From supply-chains severed, to rising prices, mounting food insecurity, and uninsurable homes and businesses. 

That bill will keep growing.  Even if emissions hit zero tomorrow, a recent study found that climate chaos will still cost at least $38 trillion a year by 2050.

Climate change is the mother of all stealth taxes paid by everyday people and vulnerable countries and communities. 

Meanwhile, the Godfathers of climate chaos – the fossil fuel industry – rake in record profits and feast off trillions in taxpayer-funded subsidies.

Dear friends,

We have what we need to save ourselves. 

Our forests, our wetlands, and our oceans absorb carbon from the atmosphere.  They are vital to keeping 1.5 alive, or pulling us back if we do overshoot that limit.  We must protect them. 

And we have the technologies we need to slash emissions. 

Renewables are booming as costs plummet and governments realise the benefits of cleaner air, good jobs, energy security, and increased access to power.

Onshore wind and solar are the cheapest source of new electricity in most of the world – and have been for years.

Renewables already make up thirty percent of the world’s electricity supply.

And clean energy investments reached a record high last year – almost doubling in the last ten [years].

Wind and solar are now growing faster than any electricity source in history.

Economic logic makes the end of the fossil fuel age inevitable.

The only questions are:  Will that end come in time?  And will the transition be just? 

We must ensure the answer to both questions is: yes.

And we must secure the safest possible future for people and planet.

That means taking urgent action, particularly over the next eighteen months:

To slash emissions;

To protect people and nature from climate extremes;

To boost climate finance;

And to clamp down on the fossil fuel industry.

Let me take each element in turn. 

First, huge cuts in emissions.  Led by the huge emitters.   The G20 countries produce eighty percent of global emissions – they have the responsibility, and the capacity, to be out in front.

Advanced G20 economies should go furthest, fastest;

And show climate solidarity by providing technological and financial support to emerging G20 economies and other developing countries. 

Next year, governments must submit so-called nationally determined contributions – in other words, national climate action plans.  And these will determine emissions for the coming years.

At COP28, countries agreed to align those plans with the 1.5 degree limit. 

These national plans must include absolute emission reduction targets for 2030 and 2035.

They must cover all sectors, all greenhouse gases, and the whole economy.

And they must show how countries will contribute to the global transitions essential to 1.5 degrees – putting us on a path to global net zero by 2050; to phase out fossil fuels; and to hit global milestones along the way, year after year, and decade after decade.   That includes, by 2030, contributing to cutting global production and consumption of all fossil fuels by at least thirty percent; and making good on commitments made at COP28 – on ending deforestation, doubling energy efficiency and tripling renewables.

Every country must deliver and play their rightful part.

That means that G20 leaders working in solidarity to accelerate a just global energy transition aligned with the 1.5 degree limit.  They must assume their responsibilities.

We need cooperation, not finger-pointing.

It means the G20 aligning their national climate action plans, their energy strategies, and their plans for fossil fuel production and consumption, within a 1.5 degree future.

It means the G20 pledging to reallocate subsidies from fossil fuels to renewables, storage, and grid modernisation, and support for vulnerable communities.

It means the G7 and other OECD countries committing: to end coal by 2030; and to create fossil-fuel free power systems, and reduce oil and gas supply and demand by sixty percent – by 2035.   It means all countries ending new coal projects – now.  Particularly in Asia, home to ninety-five percent of planned new coal power capacity.

It means non-OECD countries creating climate action plans to put them on a path to ending coal power by 2040. 

And it means developing countries creating national climate action plans that double as investment plans, spurring sustainable development, and meeting soaring energy demand with renewables.

The United Nations is mobilizing our entire system to help developing countries to achieve this through our Climate Promise initiative.

Every city, region, industry, financial institution, and company must also be part of the solution.

They must present robust transition plans by COP30 next year in Brazil – at the latest:

Plans aligned with 1.5 degrees, and the recommendations of the UN High-Level Expert Group on Net Zero.

Plans that cover emissions across the entire value chain;

That include interim targets and transparent verification processes;

And that steer clear of the dubious carbon offsets that erode public trust while doing little or nothing to help the climate.

We can’t fool nature.  False solutions will backfire.  We need high integrity carbon markets that are credible and with rules consistent with limiting warming to 1.5 degrees.   

I also encourage scientists and engineers to focus urgently on carbon dioxide removal and storage – to deal safely and sustainably with final emissions from the heavy industries hardest to clean.  

And I urge governments to support them.

But let me be clear: These technologies are not a silver bullet; they cannot be a substitute for drastic emissions cuts or an excuse to delay fossil fuel phase-out.

But we need to act on every front.

The second area for action is ramping up protection from the climate chaos of today and tomorrow.

It is a disgrace that the most vulnerable are being left stranded, struggling desperately to deal with a climate crisis they did nothing to create.

We cannot accept a future where the rich are protected in air-conditioned bubbles, while the rest of humanity is lashed by lethal weather in unliveable lands.

We must safeguard people and economies. 

Every person on Earth must be protected by an early warning system by 2027. I urge all partners to boost support for the United Nations Early Warnings for All action plan.

In April, the G7 launched the Adaptation Accelerator Hub.

By COP29, this initiative must be translated into concrete action – to support developing countries in creating adaptation investment plans, and putting them into practice.

And I urge all countries to set out their adaptation and investment needs clearly in their new national climate plans.

But change on the ground depends on money on the table.

For every dollar needed to adapt to extreme weather, only about five cents is available.

As a first step, all developed countries must honour their commitment to double adaptation finance to at least $40 billion a year by 2025.

And they must set out a clear plan to close the adaptation finance gap by COP29 in November. 

But we also need more fundamental reform.

That leads me onto my third point: finance.

If money makes the world go round, today’s unequal financial flows are sending us spinning towards disaster.

The global financial system must be part of the climate solution.

Eye-watering debt repayments are drying up funds for climate action.

Extortion-level capital costs are putting renewables virtually out of reach for most developing and emerging economies.

Astoundingly – and despite the renewables boom of recent years – clean energy investments in developing and emerging economies outside of China have been stuck at the same levels since 2015.

Last year, just fifteen per cent of new clean energy investment went to emerging markets and developing economies outside China – countries representing nearly two-thirds of the world’s population.

And Africa was home to less than one percent of last year’s renewables installations, despite its wealth of natural resources and vast renewables potential. 

The International Energy Agency reports that clean energy investments in developing and emerging economies beyond China need to reach up to $1.7 trillion a year by the early 2030s.

In short, we need a massive expansion of affordable public and private finance to fuel ambitious new climate plans and deliver clean, affordable energy for all.

This September’s Summit of the Future is an opportunity to push reform of the international financial architecture and action on debt. I urge countries to take it.

And I urge the G7 and G20 Summits to commit to using their influence within Multilateral Development Banks to make them better, bigger, and bolder. And able to leverage far more private finance at reasonable cost.

Countries must make significant contributions to the new Loss and Damage Fund. And ensure that it is open for business by COP29.

And they must come together to secure a strong finance outcome from COP this year – one that builds trust and confidence, catalyses the trillions needed, and generates momentum for reform of the international financial architecture.

But none of this will be enough without new, innovative sources of funds.

It is [high] time to put an effective price on carbon and tax the windfall profits of fossil fuel companies.

By COP29, we need early movers to go from exploring to implementing solidarity levies on sectors such as shipping, aviation, and fossil fuel extraction – to help fund climate action.

These should be scalable, fair, and easy to collect and administer. 

None of this is charity.

It is enlightened self-interest.

Climate finance is not a favour. It is fundamental element to a liveable future for all.

Dear friends,   Fourth and finally, we must directly confront those in the fossil fuel industry who have shown relentless zeal for obstructing progress – over decades. 

Billions of dollars have been thrown at distorting the truth, deceiving the public, and sowing doubt.

I thank the academics and the activists, the journalists and the whistleblowers, who have exposed those tactics – often at great personal and professional risk.

I call on leaders in the fossil fuel industry to understand that if you are not in the fast lane to clean energy transformation, you are driving your business into a dead end – and taking us all with you.

Last year, the oil and gas industry invested a measly 2.5 percent of its total capital spending on clean energy.

Doubling down on fossil fuels in the twenty-first century, is like doubling down on horse-shoes and carriage-wheels in the nineteenth.

So, to fossil fuel executives, I say: your massive profits give you the chance to lead the energy transition. Don’t miss it.

Financial institutions are also critical because money talks.

It must be a voice for change.

I urge financial institutions to stop bankrolling fossil fuel destruction and start investing in a global renewables revolution;

To present public, credible and detailed plans to transition [funding] from fossil fuels to clean energy with clear targets for 2025 and 2030;

And to disclose your climate risks – both physical and transitional – to your shareholders and regulators. Ultimately such disclosure should be mandatory.

Many in the fossil fuel industry have shamelessly greenwashed, even as they have sought to delay climate action – with lobbying, legal threats, and massive ad campaigns. 

They have been aided and abetted by advertising and PR companies – Mad Men – remember the TV series - fuelling the madness.

I call on these companies to stop acting as enablers to planetary destruction. 

Stop taking on new fossil fuel clients, from today, and set out plans to drop your existing ones.

Fossil fuels are not only poisoning our planet – they’re toxic for your brand.

Your sector is full of creative minds who are already mobilising around this cause. 

They are gravitating towards companies that are fighting for our planet – not trashing it.

I also call on countries to act.

Many governments restrict or prohibit advertising for products that harm human health – like tobacco. 

Some are now doing the same with fossil fuels.

I urge every country to ban advertising from fossil fuel companies.  

And I urge news media and tech companies to stop taking fossil fuel advertising.

We must all deal aso with the demand side.  All of us can make a difference, by embracing clean technologies, phasing down fossil fuels in our own lives, and using our power as citizens to push for systemic change. 

In the fight for a liveable future, people everywhere are far ahead of politicians.

Make your voices heard and your choices count. 

We do have a choice. 

Creating tipping points for climate progress – or careening to tipping points for climate disaster. 

No country can solve the climate crisis in isolation.

This is an all-in moment.

The United Nations is all-in – working to build trust, find solutions, and inspire the cooperation our world so desperately needs.

And to young people, to civil society, to cities, regions, businesses and others who have been leading the charge towards a safer, cleaner world, I say: Thank you.

You are on the right side of history.

You speak for the majority.

Keep it up.  

Don’t lose courage. Don’t lose hope.

It is we the Peoples versus the polluters and the profiteers. Together, we can win.  

But it’s time for leaders to decide whose side they’re on.

Tomorrow it will be too late.

Now is the time to mobilise, now is the time to act, now is the time to deliver.

This is our moment of truth.

And I thank you.

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