Coral Reefs

Status and outlook of coral reefs around the world

Coral reefs are wondrous, diverse, productive, valuable ecosystems, upon which millions of people around the world depend. Despite their importance and value, reefs are severely threatened by both local and global threats, including climate change. This global profile provides an overview of why coral reefs are important, what threats they are facing, what makes them resilient and what we can do to save them.

Photo: Steve Lindfield - Coral Reef Image Bank

Table of Contents

Reefs are Valuable

Coral reefs are one of the most biologically rich and productive ecosystems on earth. Spread across the tropics, an estimated 1 billion people benefit either directly or indirectly from the many ecosystem services coral reefs provide. These services include providing a source of food and livelihood, reducing wave energy and protecting shorelines, attracting tourism, providing a source of inspiration and cultural value, and offering tremendous potential for bio-pharmaceuticals through the rich biological diversity found on coral reefs.

Worldwide, approximately 1 billion people live within 100 km of reefs, many of whom are likely to derive some benefits from the ecosystem services reefs provide. More than 330 million people reside in the direct vicinity of coral reefs (within 30 km of reefs and less than 10 km from the coast), where livelihoods are most likely to depend on reefs and related resources. This number of people dependent on coral reefs is estimated to have increased by 20 percent over the last decade.


Coral reefs are an important magnet for both domestic and international tourism in over 100 countries and territories, generating jobs, revenue and foreign exchange. They provide on-reef recreation, such as diving and snorkeling, but also generate white sandy beaches and calm waters favored by tourists. Poorly managed tourism, however, can damage coral reefs. Prior to the abrupt decline in visitation due to COVID-19,coral reefs attracted an estimated 70 million visitors annually, with an associated expenditure of US$36 billion.


Coral reef-associated fisheries provide an important source of protein and livelihood across the tropics for an estimated 6 million reef fishers, many of whom are artisanal (small-scale and traditional subsistence fishers). The value of theselandings was estimated to be over US$6.8 billion in 2011. Women represent about50% of the workforce in the seafood sector and 80–90% in the post-harvest sectorof small-scale fisheries.

Shoreline Protection

Beyond their biological value, the physical structures of coral reefs reduce wave energy, wave heights, and associated erosion and storm damage. Reefs protect an estimated 150,000 km of shoreline in more than 100 countries and territories. On average, coral reefs reduce the annual expected damages from storms globally by more than US$4 billion. The protection provided by coral reefs will become even more important as sea level rises and coastal population and assets continue to grow.

Photo by Steve Lindfield
Photo: Steve Lindfield

Coral reefs’ ability to attenuate wave energy is greater for lower intensity, frequent storms (with smaller waves), but reefs also provide important protection during more extreme storm events—for both people and property. A recent global analysis of the average annual benefits (avoided damages) due to the presence of coral reefs evaluated the effect of a 1-m loss in reef height on the resulting flooding for multiple storm events (10, 25, 50, 100-yr return periods) and combined these to arrive at average annual avoided damages of US$4 billion. This is likely an underestimate of the value of protection provided by coral reefs.

Reefs are Threatened

Coral reefs face a wide and intensifying array of threats—from both local and global sources. The local threats include impacts from overfishing and destructive fishing (with explosives or poisons), coastal development, sewage discharge, poorly managed tourism, plastic and other pollution, agricultural runoff, and shipping (a source of invasive species, pollution, and physical damage). The global threats of warming and acidifying seas are driven by greenhouse gas emissions, and the dissolving of CO2 in ocean waters.This combination of threats has already resulted in the degradation and, in some cases, loss of more than half of the world’s coral reefs. Degradation is typified by reduced areas of living coral, increased algal cover, coral disease, reduced species diversity, and lower fish abundance. These changes will reduce the value of coral reefs for fisheries, tourism, shoreline protection, and other values, impacting dependent coastal communities.

Local Threats


Overexploitation of reefs—both for markets and for local consumption, affects more than half of the world’s coral reefs. This threat includes both the overfishing of high value target species for the live reef food fish trade (e.g. groupers, snappers, sharks, sea cucumbers, and lobsters), as well as fishing for smaller, often herbivorous fish, for local consumption. The use of destructive techniques (explosives and poisons) and reef gleaning (gathering and collecting seafood at low tide) can also directly damage coral reefs. Heavily fished reefs are prone to algal overgrowth, without herbivorous fish to graze the algae as it grows. Such overfished reefs appear to be generally less resilient to stressors and may be more vulnerable to disease and slower to recover from other human impacts. Although well-managed, small-scale coastal fisheries can be a sustainable resource, growing human populations, more efficient fishing methods, and increasing demands from tourism and international markets have significantly increased pressure on vulnerable fish stocks.

The following map shows overfishing threat to coral reefs by default, but users can also view layers reflecting threats from coastal development, watershed-based pollution, marine-based pollution, and an integration of these local threats. All data are from Reefs at Risk Revisited, published in 2011. These data, though dated, are still the best available global mapping of local threats to coral reefs. The coral reef conservation community should consider a collaboration to revise and improve these threat maps—either region-by-region or globally.

Coastal Development

Development of human settlements, industry, aquaculture, and infrastructure in the coastal zone can impact coral reefs—either directly through physical damage from dredging or land filling, or indirectly through increased runoff of sediment and pollution. Elevated nutrient levels in sewage encourage blooms of plankton that block light and encourage growth of seaweeds that compete for space on the reef, while the bacteria promote coral disease. Many countries with coral reefs have little to no sewage treatment, with an estimated 80 percent of discharged wastewater inadequately treated. In addition, the removal of coastal vegetation such as mangroves takes away a critical sediment and pollutant trap. Poorly managed tourism also threatens coral reefs.

Photo: Steve Lindfield

Watershed-based Pollution

Pollution from inland activities includes erosion due to land clearing, sewage from tourists and residents, and runoff of livestock waste, fertilizers, and pesticides from agricultural lands. These all can be transported by rivers to the sea where they impact coastal waters and coral reefs—sometimes extending more than 100km from river mouths. In high quantities, sediments can smother, weaken, and kill corals, while in lower quantities, they reduce sunlight reaching corals, slowing coral growth. Excessive levels of nutrients (nitrogen and phosphorus) in shallow coastal waters can encourage blooms of phytoplankton, which reduce light reaching the corals, can cause growth of algae and seaweeds which can overgrow corals. Mangroves and seagrass habitats can help trap sediments and remove nutrients.

Marine-based pollution and damage

Commercial, recreational, and passenger vessels bring with them a host of potential threats to coral, including contaminated bilge water, fuel leakages, raw sewage, solid waste, and invasive species, which can promote coral disease and alter ecological balance by displacing native species. Vessels cause physical damage through groundings, anchors, and oil spills. Cruise ships are a significant source of pollution in many areas. The widespread accumulation of plastics in the ocean is also an important (and growing) threat to coral reefs and marine life in general. 

Global Threats/Climate Change

Warming Seas

Rising concentrations of greenhouse gases in the atmosphere have led to warming of the atmosphere and, as a result, an increase in sea surface temperatures (SST). Prolonged episodes of elevated temperature are prompting coral bleaching, the stress response whereby corals lose their colorful symbiotic algae, exposing their white skeletons. Corals die if the heat stress is extreme and/or prolonged. We examine past, current, and future ocean warming.

Bleached staghorn coral (foreground)
Photo: The Ocean Agency - Coral Reef Image Bank

Past Warming and Bleaching

Mass coral bleaching has occurred around the globe, increasing in frequency and severity as sea temperatures have risen over time. Extreme bleaching events often kill corals outright, while less extreme events can weaken corals, reducing growth and reproduction, and leaving them vulnerable to disease. The time between heat stress events is critical for coral recovery. In addition, areas with low levels of local threats tend to be more resilient. Between 1985 and 2018, 87.4% of the world’s reefs experienced bleaching level heat stress, while 42.5% underwent severe heat stress.

Current SST and Bleaching Risk

Bleaching-level conditions occur when the SST exceeds the normal high temperature (for the hottest month) for an extended period (usually several weeks). This combines deviation from the normal high and duration. The U.S. National Oceanic and Atmospheric Administration (NOAA) Coral Reef Watch (CRW) program has developed a daily global 5km resolution product to monitor thermal stress on coral reefs and alert coral reef managers to impending threats.

Projections of SST and Bleaching Risk

As greenhouse gas emissions continue to rise, the atmosphere and ocean will continue to warm. Projections suggest that severe bleaching will occur with increasing frequency in the decades ahead, and virtually all reefs will experience severe bleaching annually by the end of the century. The time between bleaching events is critical for coral recovery. When bleaching exceeds twice per decade corals are less likely to recover, resulting in increased mortality and reduced structural complexity. These changes will become more sever when bleaching events begin to occur annually. Hence, the continued emission of greenhouse gases gives rise to a dire outlook for coral reefs.

Tropical Cyclones

Patterns of tropical storms vary considerably around the world, with low occurrence near the equator and higher occurrence near the edges of the tropics. Warming ocean temperatures are increasing the frequency of the strongest cyclones, which generate extreme waves that can damage coral reef communities, even up to several hundred kilometers from storm tracks. Recovery from damage can take up to a decade and can be hindered by other pressures on the reef.

Ocean Acidification

Increasing CO2 in sea water is slowly causing the world’s oceans to become more acidic and is decreasing the availability of aragonite, the form of calcium carbonate that corals use to build their skeletons. This slows coral growth and results in less dense, weaker coral structures, making them more prone to erosion and damage. Aragonite saturation levels have fallen dramatically within the past century and will continue to decline due to increasing CO2.

The map below presents projections of suitability of areas for coral reefs (from 2010 until the end of the century) based on projections of aragonite saturation from NOAA Coral Reef Watch. Users can adjust the displayed year using the slider below the legend. This mapping assumes that an aragonite saturation level of 4.0 or greater is favorable for coral growth; above 3.5 is adequate; while a level of 3.0 or less is considered very poor for supporting coral reefs. 

Coral Reef Condition

Estimates of the extent of damage to the world’s coral reefs vary, but most present a grim outlook for these magnificent ecosystems. Globally, it is likely that over half of the world’s reefs have already been degraded– by climate change, pollution and other human activities - resulting in loss of live coral cover, reduced coral diversity and increased algal cover. Hard coral cover has declined significantly in some regions, and there has been a shift toward coral species less able to support diverse coral reef habitats. Both the global 2011 Reefs at Risk Revisited report and a 2017 paper in Frontiers in Marine Science project that by 2050, virtually all of the worlds reefs will be at high risk from a combination of local threats and ocean warming.

A global compilation of data on live coral cover and algal cover by the Global Coral Reef Monitoring Network (GCRMN), however, finds considerable resilience on many reefs. Status of Coral Reefs of the World: 2020 is based on data collected by more than 300 scientists over the past 40 years, from nearly 35,000 coral reef surveys at over 12,000 sites, though for many sites data are only available for a single year. The report finds that large-scale coral bleaching events caused by ocean warming are the greatest disturbance to the world’s coral reefs, but also identifies examples of coral recovery between disturbances. It recommends reducing local pressures on reefs to maintain their resilience, while global threats posed by climate change are addressed. (Results are available for ten regions within the report.) The figures below reflect global trends for live, hard coral cover and algal cover.

Photo: Daniel Stephen Pendygrasse

Live Hard Coral Cover

Prior to 1998, the global average cover of live hard coral was high (>30% of area) and stable, although the sparsity of data prior to 1998 increases uncertainty around this estimate. The first mass coral bleaching event in 1998 killed approximately 8% of the world’s coral. Between 2002 and 2009, the average global cover of hard coral recovered to pre-1998 levels, but between 2009 and 2018, there was a progressive loss amounting to 14% of the coral from the world’s reefs. This decline was primarily due to recurring large-scale coral bleaching events, with a frequency that prevented coral cover from recovering in many areas. While the influences of smaller scale disturbances and threats, such as coral disease, crown-of-thorns starfish outbreaks, tropical storms, overfishing, sediment, and pollution have undoubtedly played a role in the decline of coral reefs, their specific contributions were not assessed.

Algal Cover

Prior to 2010, the global estimated average cover of algae was low (approximately 16% of area) and relatively stable. Since 2010, algae cover has increased by about 20%, mirroring the decrease in hard coral cover. Prior to 1998, there was, on average, over twice as much coral on the world’s reefs as algae, but that ratio has decreased to closer to 1.5. Transition from coral to algae dominance in a reef community reduces the complex 3-dimensional habitat that is essential to support high biodiversity and important ecosystem services—fisheries habitat and the rugged coral structure which is critical to reducing wave energy and protecting shorelines. 

Modeled cover of live hard coral (left) and algae (right) for the world. The solid line represents the predicted marginal mean while the ribbons represent 80% (lighter shade) and 95% (darker shade) confidence intervals.


Coral reefs are likely to continue to decline due to the combined pressures of warming and acidifying seas, coupled with the more local pressures of overfishing, destructive fishing, direct physical damage, sedimentation, pollution, and disease. Even if the most ambitious global temperature target of the Paris Agreement is met (limiting warming to 1.5°C), reefs are projected to decline by 70-90%. But coral reefs have proven to be resilient and can recover if conditions permit. While the world works to limit global warming, it is critical that local pressures be limited – to increase resilience and the prospect of coral recovery. 

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A Blue Sea Star (Linckia laevigata) resting on hard Acropora coral at Lighthouse, Ribbon Reefs, Great Barrier Reef
Photo: Richard Ling

Select Global and Regional Reports

Global Report

Regional Reports

  • Australia (2019/2020) 
  • French Territories (2020) – Guadeloupe, Martinique, Iles du Nord, Mayotte, Iles Eparses, Réunion, Nouvelle-Calédonie, Polynésie Française, Wallis et Futuna, and Clipperton (summary in English)
  • Mesoamerican Reef (2020) – Mexico, Belize, Guatemala, Honduras
  • US States and Territories (2020) – US summary report, and individual state and territory reports (Florida, Puerto Rico, US Virgin Islands, Flower Garden Banks, American Samoa, Northern Mariana Islands, Guam, and Hawaii)
  • Multiple country reports from the Global Reef Expedition(The Bahamas, St. Kitts and Nevis, Jamaica, Navassa, Columbia, Galapagos, Fiji, French Polynesia, Tonga, Cook Islands, New Caledonia, Solomon Islands, and Palau) 

Coral Disease

Coral diseases could be considered a threat to coral reefs, but they are also an indicator of reef condition, as a diseased reef is damaged and vulnerable. Diseases are a natural feature in any ecosystem and are present in background populations of most species. Both in terms of prevalence and geographic distribution, coral diseases have increased over the last 40 years. Corals have become more susceptible to disease as a result of degraded water quality and climate change, which may cause some pathogens to become more virulent and may reduce a coral’s resilience. There is strong evidence that disease outbreaks have followed coral bleaching events.

Stony Coral Tissue Loss Disease in Florida
Photo: The Nature Conservancy

Although many scientists and organizations monitor coral reefs and capture information on coral disease, no global database on disease has been updated since 2010. This is a significant gap in our understanding of coral threats, condition, and trends. A concerted effort is needed to address this gap. There are, however, local and regional efforts to track specific disease outbreaks, such as this dashboard on the Stony coral tissue loss disease (SCTLD) in the Caribbean.

Management, Resilience and Other Mitigating Factors

Though threats to reefs are near-ubiquitous, the degree of threat is variable world-wide and coral reefs show varied levels of resilience, or the ability to recover from perturbations. Coral reef resilience is influenced by natural factors but can also be enhanced by the reduction and removal of local threats through management interventions. Some reefs are in geographically advantaged locations, such as with high levels of ocean circulation or large amounts of coral larvae available to aid recovery. Management of coastal and marine areas can also reduce threats to reefs by restricting activities that harm reefs, which can help increase resilience of coral reefs in warming and acidifying oceans.

Photo: Jayne Jenkins

Coral reef resilience refers to a reef ecosystem's ability to recover from a disturbance and restore towards a coral-rich and diverse state, as opposed to shifting to an algal-dominated state or a single coral morphology. Reefs with broad size and age range, high biodiversity, healthy herbivorous fish populations, low local threats, little coral disease, and a history of surviving past thermal stress events tend to be more resilient.

Adjacent Habitats

Coral reefs, mangroves, and seagrass areas are interconnected habitats which thrive adjacent to each other and provide nurseries and habitat for fish. Coral reefs reduce wave energy and create calmer conditions which suit mangroves and seagrass, while the plants filter pollutants and sediment, creating cleaner water favored by reefs. Unfortunately, both mangrove and seagrass habitats have suffered widespread losses—often for coastal development or aquaculture.

Mangrove in Belize
Photo: Lauretta Burke
Seagrass - TNC - Benjamin Jones, Project Seagrass.jpg
Seagrass meadow
Photo: Benjamin Jones, TNC

Coral Connectivity

Corals spawn larvae which drift in ocean currents and are important for seeding new reef locations and helping to restore damaged or recovering areas. Reefs with large or multiple “upstream” sources of larvae and close proximity to the sources are considered to have high “connectivity”.

Marine Protected Areas

Marine Protected Areas (MPAs) are an important tool for controlling activities and associated pressures inside legally defined zones—typically for protection of economic resources, biodiversity conservation or species protection. MPAs can come in many forms including strictly controlled marine reserves, wildlife refuges, research areas, multiple-use areas, and locally managed marine areas, among others. When all types of MPAs are considered, 42 percent of the world’s reefs are located inside designated MPAs. Only a minority of MPAs are highly protected marine reserves, which prohibit fishing, or include such zones. Based on available information, an estimated ten percent of coral reefs are within mapped "no take" areas.

The map above shows MPAs as recorded in the World Database of Protected Areas, which is maintained by Protected Planet. MPAs can range from strictly controlled marine reserves which prohibit extractive activities, through to “paper parks” which lack a management plan, regulations, or means of enforcement. MPAs can include limitations on development, fishing practices, fishing seasons and catch limits, moorings, and removal of marine life. The effectiveness of protection afforded by MPAs varies considerably, depending on the management objectives, level of restrictions on extractive activities, adequacy of resources for enforcement of regulations, and maturity of the MPA, among other factors.

There are excellent ongoing efforts to compile up-to-date information on MPAs, including the type of MPA, year of establishment, existence of a management plan, and the extent of fully or highly protected (no take) areas. Statistics on MPAs and protection will constantly evolve, as MPAs are established or expanded and management plans and zoning advance. 

Islands in Mayotte
Photo: Gaby Barathieu

Signs of Hope

Coral reefs are important and valuable but are threatened and in decline in many locations around the globe. There are, however, signs of hope including healthy, resilient, and recovering reefs in many locations.

Photo: Matt Curnock - Coral Reef Image Bank

An analysis of “Bright Spots” identified 15 areas where reefs were found to be healthier and coral reef fisheries more productive than expected given local environmental and socioeconomic conditions. These areas were characterized by strong sociocultural institutions (such as customary tenure), high levels of engagement in local management, high dependence on marine resources, and beneficial environmental conditions such as proximity to deep-water refuges. (The contrasting “dark spot” areas were characterized by intensive capture and storage technology and a recent history of environmental shocks.) The bright spots analysis approach can be used to inform the types of investments and governance structures that can help to sustain coral reefs (e.g. participatory management and improved property rights).

Hope Spots are places that are scientifically identified as critical to the health of the ocean, in an effort coordinated by Mission Blue. Some Hope Spots are already formally protected, while others still need defined protection. The areas vary in size, and are often included due to one or more of several characteristics: a special abundance or diversity of species; unusual, rare, threatened or endemic species; importance as a migration corridor or spawning ground; significant historical, cultural or spiritual value; or particular economic importance to the community. Hope Spots are championed by local conservationists, with communications, expeditions, and scientific advisory support from Mission Blue.

Photo: Gregory Pipe - Coral Reef Image Bank
Photo: Matt Curnock - Coral Reef Image Bank

Although coral reefs are threatened by many factors, climate change is a dominant and rapidly growing threat. The 50 Reefs initiative used modern portfolio theory in an analysis to identify coral reef locations globally that, in the absence of other impacts, are likely to have a heightened chance of surviving projected climate changes relative to other reefs. These locations constitute important opportunities for novel conservation investments to secure less vulnerable yet well‐connected coral reefs that may, in turn, help to repopulate degraded areas in the event that the climate has stabilized.

Social and Economic Vulnerability

Degradation and loss of reefs cause significant social and economic impacts, and these impacts vary widely based on local circumstances. A country’s vulnerability to reef loss is influenced by its level of dependence on coral reefs for food, livelihoods, exports, tourism revenue, and shoreline protection, as well as the adaptive capacity of the population (ability to cope with the effects of degradation). Adaptive capacity is influenced by social and economic factors including education, health, governance, access to markets, and availability of economic and agricultural resources.


Coral reefs provide vitally important goods and services in countries around the globe but are besieged by an array of threats. For coral reefs to survive in the coming decades we need to:

  1. reduce local threats to coral reefs – manage fisheries sustainably, eliminate destructive fishing, lessen pollution entering the ocean, manage costal development sustainably
  2. decrease emissions of greenhouse gases in order to try to keep warming to the 1.5 degree C target, thereby lessening the risk of coral bleaching and acidification
  3. increase investment in coastal management and restoration, with emphasis on resilience-based management and the use of data and information to understand and reduce risk
  4. establish and effectively manage marine protected areas and other effective area-based conservation measures
  5. ensure that management decisions are inclusive and participatory, based on data, and examine equity implications
  6. manage tourism sustainably to lessen impacts and benefit local communities 
  7. raise awareness of the value of coral reefs and other coastal ecosystems, including the cost of degradation and loss
Photo: Gaby Barathieu - Coral Reef Image Bank

Key Resources

Regional Coral Reef Dashboards

For coral reef maps and indicators focused on the individual GCRMN regions, click the links below the map:

GCRMN regions

Science and Management

  • The Reef Resilience Network consolidates information on science and management approaches for coral reefs. Resilience-based managementis an important management approach which addresses local threats within the context of global threats and the stakeholders / users of resources.
  • NOAA Coral Reef Watch provides near real-time data on sea surface temperature and modeled outlooks of bleaching risk.
  • Allen Coral Atlas is a partnership developing high resolution maps of coral reefs and other benthic habitat, geomorphology, and other tools, including identifying potential large coral bleaching events using satellite imagery.
  • Coral Restoration Consortium (CRC) is a community of practice comprised of scientists, managers, coral restoration practitioners, and educators developing and sharing tools, technologies and knowledge to help restore coral reefs.
  • Reef Restoration and Adaptation Program (RRAP) brings together Australia's leading experts to create an innovative suite of safe, acceptable interventions to help the Great Barrier Reef resist, adapt to, and recover from the impacts of climate change.

Protected Areas

  • Locally Managed Marine Area (LMMA) is an international network of natural resource management practitioners who share knowledge on best practices
  • Protect Planet provides data MPAs updated monthly with submissions from governments, non-governmental organizations, landowners and communities.   
  • Marine Protection Atlas (MPAtlas) augments spatial data on MPAs to attempt to distinguish MPAs by implementation status and by protection level (such as no-take, fully, and highly protected areas). This ongoing effort (updated monthly) uses (soon to be published), scientifically-based criteria for measuring an MPA’s protection level and associated conservation outcomes.
  • Ocean + Habitats is an evolving tool that provides insight into the known extent, protection and other statistics of ecologically and economically important ocean habitats, such as corals, mangroves, seagrasses and saltmarshes.
Photo: Hannes Klostermann - Coral Reef Image Bank
Photo: The Ocean Agency - Coral Reef Image Bank

Status and Trends

Government and Policy

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Photo: Jett Britnell - Coral Reef Image Bank
Photo: Krishna Desai

Ecosystem Values

Getting Involved: What you can do to help

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Photo: Jane Harris
Photo: Yen-Yi Lee, Coral Reef Photo Bank