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In the western Caribbean, some coral reefs have turned into eerie white ghost towns.

Scientists with the Smithsonian Tropical Research Institute have documented a major bleaching event in the reefs near Panama and the island of Curaçao. Such bleaching occurs when a reef loses the tiny photosynthetic algae that typically live in the coral, providing it with food (and color). Bleaching occurs when coral is under stress, most typically due to higher ocean temperatures. And this was a hot summer.

Abnormally warm water since June appears to have dealt a blow to shallow and deep-sea corals that is likely to top the devastation of 2005, when 80% of corals were bleached and as many as 40% died in areas on the eastern side of the Caribbean. [ScienceNOW]

The rise in water temperature doesn’t have to be dramatic, just steady. In 2005, the water near the Virgin Islands was about 5 degrees Fahrenheit above average from August to November, and coral reefs in the eastern Caribbean suffered. This year, slightly higher ocean temperatures spread over a much broader area in the western and southern Caribbean. Near Panama, researchers reported that water temperatures reached a high of 7 degrees Fahrenheit above average in mid-September.

Hurricane season may be enhancing the current problem, resulting in low water circulation in the southwestern Caribbean and thus creating a “warm pocket” of water along the coasts of Panama and Costa Rica, the researchers speculate. [MSNBC]

Coral reefs can recover from bleaching, but there’s not guarantee–and as long as the reefs are pale shadows of their former selves, they’re in trouble. Bleaching impairs the coral’s ability to grow and reproduce, and the reefs can die altogether.

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