A Third of Reef-Building Corals at Risk of Extinction

Brian Handwerk
for National Geographic News
July 10, 2008
A third of the world's major reef-building coral species are in danger of extinction, an international team of scientists warns in a study published today.

Because coral reefs are home to more than a quarter of all marine species, their loss could be devastating for biodiversity in the world's oceans.

"If corals themselves are at risk of extinction and do in fact go extinct, that will most probably lead to a cascade effect where we will lose thousands and thousands of other species that depend on coral reefs," said the study's lead author Kent Carpenter, a zoologist at Old Dominion University in Norfolk, Virginia.

The rate at which reefs have been besieged is most troubling, the scientists say.

Of the 704 corals classified in the study, 231 were listed as "vulnerable," "endangered," or "critically endangered" according to the International Union for Conservation of Nature's Red List.

A decade ago just 13 species met the same criteria.

The study appears in the online journal Science Express.

On The Brink?

Studies around the globe have made the news of coral reef declines distressingly commonplace, the researchers say.

"What we did was use that information about decline to ask the question, What is the consequence of this on the potential loss of biodiversity?" Carpenter said.

"It's easy for people to understand that coral reefs are at risk, but it's gotten to the point now where the risk of extinction is a reality for the actual species that form the coral reefs. That could be devastating to biodiversity in the ocean."

Some reef locales are faring worse than others, the paper said.

"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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