June 2001

From Wildlife Conservation Society

Study says bleaching could be a hidden strength for corals

The global phenomenon of bleaching, in which reef-building corals lose their colorful algae and become white during times of stress, may actually allow some corals to adapt to global warming and other environmental change.The study, conducted by the New York-based Wildlife Conservation Society (WCS), will be published in the June 14th issue of the journal Nature.

The study counters conventional wisdom that bleaching is universally detrimental, instead suggesting that it represents a high-risk ecological strategy that allows corals to rid themselves of sub-optimal algae. By doing so, corals can become hosts to more suitable algal types that increase their chances of survival during times of stress.

Reef-building corals use different types of symbiotic algae called zooxanthellae for nutrients, which in turn live in the tissue of the coral polyps. Baker transplanted corals found off the coast of Panama from shallow water to deep water, and visa versa. He discovered that corals transplanted upwards generally bleached but ultimately survived by recovering with new algae.

In contrast, corals transplanted downwards did not bleach, and did not change their type of algae, though it was poorly adapted to the deeper environment. As a result, a significant number of these corals died.

"These findings indicate that bleaching can sometimes help corals respond quickly to environmental change," said the study's author, Dr. Andrew Baker of the Wildlife Conservation Society's Osborn Laboratories of Marine Sciences. "The same bleaching that makes corals so fragile may also, during times of extreme environmental stress, help some of them survive."

Baker was quick to point out that bleaching, particularly as a result of warmer sea temperatures in recent years, is still a major cause for concern, and will continue to cause high mortality among reef ecosystems in the foreseeable future.

"These findings do provide a glimmer of hope for the ability of coral reefs to survive the severe warming and environmental change projected over the next half century." Baker said. "However, Coral reefs are still under assault from global warming, poor water quality, and overfishing. Much more needs to be done to protect and understand these fragile ecosystems before we lose the ones we have left."

Copies of the study available through WCS telephone inteview opportunities with Dr. Baker available on June 13th between 10 am and 1 pm US EDT or by request.












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