Widespread bleaching of the world?s coral reefs has spread fear that global warming, and the subsequent warming of the oceans, may kill off the coral, which is essential to ocean ecology. But according to Andrew Baker, of the New York Aquarium in Brooklyn, the bleaching may be a risky gamble by corals to adapt to warmer seas.

Reef-building corals contain algae that interact with the sun and help feed the coral, in exchange for a place to stay. But if the light or temperature changes, corals often evict the algae. Since the algae contain the pigments that give corals their color, the reefs are left bleached.

To study the effects of bleaching, Baker moved corals around a reef in the San Blas Islands off Panama. He brought deep dwelling corals closer to the surface, where they would have more light and warmth, and moved corals from shallow sites to deeper locations.

About half the corals he shifted into shallower water were partially or severely bleached after 8 weeks, while all those moved to deeper water kept their algae. A year later, he was surprised to find that all the coral in shallow water still survived, despite the bleaching, while some of the corals moved to deeper water had died.

The corals that lived after moving to shallower water took on shallower strains of algae after bleaching. Baker feels that, by finding partners that were better adapted to the new water conditions, this move enabled them to save themselves.

?It is an interesting and somewhat controversial hypothesis,? says Simon Cripps of the World Wide Fund for Nature?s International Marine Program in Geneva. ?If correct, it suggests the corals use a very risky strategy of out with the old and in with the new to survive.?

Last year the WWF and the World Conservation Union said that pollution and fishing needed to be reduced so that corals could recover. But ?climate change events are likely to cause more serious and frequent bleaching,? says Cripps.

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