A Third of Reef-Building Corals at Risk of Extinction

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"Caribbean reefs appear to be the worst off in terms of numbers of important species that have a very high risk of extinction," Carpenter reported.

By contrast the "Coral Triangle" region of the Indo-Malay Philippine Archipelago—an area of high marine biodiversity—has the highest number of species appearing on the list, but many are at a lower level of extinction risk.

"It's potentially the next big problem area," Carpenter said. "If conditions worsen, we're talking about the most important marine biodiversity area in the world potentially becoming a big problem."

Meanwhile, areas of the Pacific Ocean stood out as regions where corals are faring better. Reefs among the Pacific's tens of thousands of isolated islands are scattered and relatively unaffected by human activity.

What is Killing Coral?

Experts generally agree that large scale die-offs from bleaching and disease have increased in frequency during recent decades—due at least in part to warming sea-surface temperatures linked to global climate change.

(Related story: "Soft Corals 'Melting' Due to Warming Seas, Expert Says" [July 13, 2007])

When sea temperatures rise for a sustained period of time by even a small amount, corals may expel their symbiotic food-producing algae, which turns reefs a sickly white.

A massive bleaching event in 1998 related to the El Niño weather phenomenon was the worst coral die-off ever observed. In the succeeding years such events have occurred with increasing frequency and severity.

The impact of disease or bleaching events is even worse when corals are weakened by local impacts such as overfishing, which sometimes targets species that protect reefs. Sedimentation and pollution from coastal development also harm coral health.

Corals do show some capacity to bounce back from bleaching and other destructive events. But if their overall declines are to be reversed, people must address the threats that have landed so many species on the IUCN list, scientists stress.

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