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Reef-building corals most vulnerable to extinction

July 10, 2008 |  1:20 pm

Staghorn_coral_in_trouble2_2Nearly one-third of the small animals that build the most massive and elaborate structures in coral reefs face elevated risk of extinction from global warming and various local problems, an international group of scientists reported today.

The worldwide assessment of more than 700 species of corals showed that 32.8% of them are now threatened with extinction, especially those that form large mounds or intricate branches resembling antlers.

Some of the threats are global in scope, such as elevated ocean water temperatures that have stressed corals to the extent that they have "bleached" bone-white. A massive bleaching episode in 1998 resulted in a vast decline of the world's reefs.

Corals also face problems from excessive and destructive fishing, polluted runoff that buries them under sediment or bathes them in nutrients that fuel out-of-control growth of algae and bacteria. Compounding the problem are outbreaks of various diseases that kill corals when they are under stress.

Using criteria established by the International Union for the Conservation of Nature, the team of scientists determined that  loss of reefs and mounting threats have nudged them into the  "critically endangered," "endangered" or "vulnerable" categories, leapfrogging over other groups of animals threatened with extinction.

"That makes corals the most threatened animals on Earth," said Greta Aeby, a coral disease expert with the Hawaii Institute of Marine Biology. Corals, as a group, are followed closely by frogs and related amphibians, which have also been on steep decline in recent decades due to pollution, loss of habitat and climate change.

The results, released online today by the journal Science, was presented at the International Coral Reef Symposium  in Fort Lauderdale, Fla. Nearly 3,000 scientists and managers have congregated here to learn about the latest scientific discoveries and figure out ways to save the world's coral reefs.

Read on...

Kent Carpenter, director of IUCN's Global Marine Species Assessment and lead author of the Science article, stressed the importance of coral reefs beyond their majesty and beauty to tourists donning snorkels and masks. Coral reefs, he said, house 25% of the diversity of marine life.

"Corals make up the very framework of the coral reef ecosystem," said Aeby, one of the 38 scientists who co-authored the study. If they disappear, she said, "we can expect to lose the fish and crabs and other critters that depend on these corals."

Loss of coral reefs could have profound impact on more than 500 million poor, subsistence fishermen in the tropics who rely on coral reefs to feed themselves and their families, said David Obura, a marine biologist and East Africa coordinator for the Coastal Oceans Research and Development in the Indian Ocean.

"People rely on coral reefs every day," said Obura, another co-author. "In places like the Indian Ocean," he said, "we need to work with fishermen and help people decide not to fish in a destructive way."

The decline in reef-building corals has been led by the loss of the two major branching corals in the Caribbean in recent decades. William F. Precht, manager of damage assessment and restoration for the Florida Keys National Marine Sanctuary, noted that 95% to 98% of the elkhorn and staghorn corals in the Keys and elsewhere in the region have been lost to disease, toppled by hurricanes or crowded out by algae and bacteria.

Both of these species are also listed as "threatened" with extinction under the U.S. Endangered Species Act.

Yet it's the rich diversity of corals in the tropical waters of the West Pacific, a place called the Coral Triangle that includes Malaysia, Indonesia and the Philippines, that presents the potential greatest loss of species.

-- Kenneth R. Weiss, in Ft. Lauderdale, Fla.

Photo of staghorn coral by Cathie Page