Threats to corals

Corals and reefs are among the most threatened of all marine ecosystems.They are perhaps the most vulnerable ecosystems on the planet to human-caused pressures.

The main threats to corals are:

Greenhouse gas emissions

The biggest threat to corals is the unprecedented increase in atmospheric greenhouse gases, particularly CO2. Warmer ocean temperatures stemming from atmospheric greenhouse gases have led to mass coral bleaching, greater spread and intensity of coral disease, and catastrophic coral mortality around the world.

Change in land use

Intensifying agriculture, coastal development, and loss of coastal and riparian vegetation lead to increased pollutants and sediments from land, resulting in loss of coral reef, mangrove, and seagrass habitats that serve as nurseries and natural filters.

Direct exploitation

Corals are highly susceptible to illegal, unreported, and unregulated fishing, leading to the reduction of biomass production and other important processes. Destructive fishing reduces habitat and reproductive potential, and impairs reef recovery.

Pollution

Increasing imports of nutrients, pesticides, plastics, and sediments from unsustainable land use, untreated sewage, and poor waste management increase growth of algae and other nuisance organisms, anoxia, smothering, coral disease, and mechanical damage.

Invasive species

Non-native pathogens and species (such as lionfish in the Caribbean), introduced through releases, escapes, and ballast water of ships, disrupt food webs and cause disease or mortality of corals and other important reef species.

A double punch

The world’s corals also face thousands of individual local threats—overfishing, pollution, and trawling, among others. The special vulnerability of corals comes from their sensitivity to global and local human activity.

This double assault has led to the loss of between one third and one half of the world’s tropical coral reefs, and to major losses of cold-water corals.

The threats to corals often compound each other. Pollution, physical damage, and heat stress can weaken corals, making them more susceptible to disease.

Heat stress makes already unhealthy corals even more prone to bleaching. And overfished reefs are usually less resistant to overgrowth by algae or other nuisance organisms.

When added together, these injuries have reduced the resilience of corals and increased their vulnerability to bleaching, disease, and invasive species. The resulting rapid loss of biodiversity, critical habitat, and ecosystem services are now jeopardizing the livelihoods of hundreds of millions of people—and may result in the extinction of many marine species.

The window is closing—we must act now

We are now at an inflection point. The coming five to 10 years likely offer the last chance to change the trajectory of corals from a descent toward worldwide collapse to a slow but steady recovery. And because coral is so widespread, and because the biggest threat to corals is global, no single nation can reverse this course.

We must act now

References

Rebuilding Coral Reefs: A Decadal Grand Challenge. ICRS Science to Policy Paper 2021 [Paper]

Status of Coral Reefs of the World: 2020 Report. GCRMN, ICRI, Australian Government, and Australian Institute of Marine Science. [Report]

G20 Environment Ministers Communiqué. Virtual Meeting – September 16, 2020. Communiqué. [Paper]

Discover more

Deep-water corals
UNEP’s 2020 Projections of Future Coral Bleaching report says that global bleaching events may become the norm over the coming decades due to climate change.

Read the Status of Coral Reefs of the World: 2020 Report by the GCRMN and ICRI.

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Images: © Morgan Bennett-Smith. Infographic: Rebuilding Coral Reefs: A Decadal Grand Challenge. ICRS Science to Policy Paper 2021