Coral Reefs Feel the Heat

School of Fish in Kenya Photo
Reef stability is essential to the balance of marine ecosystems
©R Graham

Climate change affects life in every biome, from the apex of the Arctic food chain to the tropical sea floor. The tiny creatures that are the building blocks of coral reefs are particularly vulnerable to rising ocean temperatures. During prolonged periods of surface warming, many coral species discharge the algae that live within their tissues—the same organisms that give them their stunning colors—and “bleach.” This leaves the reefs white and sickly. If the stress is not too severe and lessens, the affected corals can regain their algae and recover. But if it persists, the corals will die. Researchers still have much to learn about the long-term impacts of this phenomenon.


Because reefs contain some of the most diverse life on the planet, including tropical fish, marine turtles, and sharks, their stability is essential to the balance of marine ecosystems. But both rising sea temperatures and overfishing have wrought havoc on reefs from Belize to Madagascar, in Fiji, and throughout the Coral Triangle. Reefs located in waters with stable but high temperatures are most susceptible to fatal bleaching. Those subject to overfishing will lose their zooplankton, an essential coral food, and can also bleach.


  • Continue to determine which corals are most sensitive to climate change and likely to be eliminated or go extinct.
  • Study how corals adapt to climate change through their relationship with symbiotic algae.
  • Identify sites that may survive climate change without big disturbances.
  • Map the global stress on corals throughout their range.
  • Determine which types of fishing methods will exacerbate climate change disturbances to reefs, and conversely which types can be tolerated by reefs.

What WCS is Doing

WCS scientists studying the reefs in the Indian Ocean off Africa’s east coast have found that corals with the best chances of survival live in seas with wide-ranging seasonal temperatures. These hardier reefs tend to be located in the “shadow” of islands, protected from the oceanic currents that keep temperatures stable in more fragile reef ecosystems. Our scientists are now mapping the global stress on corals in the Indo-Pacific Ocean.

WCS researchers are also determining how human communities living adjacent to reefs in southern Kenya, Tanzania, Seychelles, Mauritius, and Madagascar adapt to the impacts of climate change. When reefs die off, their valuable fish stocks disappear and tourism dollars dry up. WCS is working to improve coral reef fishery management to relieve stress on these ecosystems. Ultimately, conservationists hope to help provide wider economic opportunities to local communities dependent on reef fishing.

In addition, WCS researchers are finding ways to help reduce the negative impacts of climate change and potentially increase the resilience of marine ecosystems by managing fishing gear. Different types of equipment used by artisanal fishers target fish with various effects on the coral reef ecosystem. At our study sites in Papua New Guinea and Kenya, WCS has observed that traps and spear guns target many species that are highly susceptible to coral mortality, based on their role in the food chain and their reliance on the reef for shelter and other needs. Conservationists hope that by selectively banning or restricting certain fishing gear that damage coral reef ecology, they can develop a powerful tool to combat the detrimental effects of climate change.

From the Newsroom

Helping Corals Survive a Changing ClimateApril 22, 2013

Coral reef fisheries expert Dr. Tim McClanahan highlights the resilience of coral reefs and the conservation efforts that will help them adapt to changing conditions.

Fishing Communities Put the Heat on Climate Change TalksDecember 8, 2011

As global leaders convene in Durban, South Africa to tackle climate change, WCS coral reef fisheries expert Dr. Tim McClanahan and his colleague Dr. Joshua Cinner urge action on behalf of the world’s fishing communities dependent upon the increasingly threatened bounty of warming tropical seas.

A Countdown to Coral CollapseSeptember 28, 2011

A new study identifies a better way to determine if coral ecosystems are in danger of collapse.

A Map for Reef ReliefAugust 12, 2011

WCS marine scientists provide a color code for coral conservation by mapping out the stress loads of the world's reefs.

A Stress Test for Corals on EdgeMarch 22, 2011

WCS has developed a stress test to map out which coral reefs will have the best chance of surviving through the climate change era.


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