"Corals make up the very framework of the coral reef ecosystem,"… (Rick Loomis / Los Angeles…)
FORT LAUDERDALE, FLA. — Nearly one-third of the small animals that make up the most massive and elaborate structures in coral reefs face an elevated risk of extinction from global warming and various local problems, an international group of scientists reported Thursday.
The worldwide assessment of more than 700 species of corals showed that 32.8% were threatened with extinction, especially those that formed large mounds or intricate branches resembling antlers.
Coral reefs provide hiding places and a habitat for 25% of all marine life and are a major source of food for the poor and of tourist revenue in tropical countries.
Some of the threats are global, including elevated ocean temperatures that have stressed corals so much that they are "bleached" bone-white. A massive bleaching brought on by warmer waters in the 1998 El Nino resulted in a vast decline of the world's reefs.
Corals also face excessive and destructive fishing and 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 various diseases that kill corals when they are under stress.
Using criteria established by the International Union for Conservation of Nature, the team of scientists determined that a loss of reefs and mounting threats had nudged the animals into the "critically endangered," "endangered" or "vulnerable" categories, leapfrogging other groups threatened with extinction.
"That makes corals the most threatened animals on Earth," said Greta Aeby, a coral disease expert at the Hawaii Institute of Marine Biology.
Close behind are frogs and related amphibians, which also have been on a steep decline in recent decades because of pollution, loss of habitat and climate change.
The results, released online Thursday by the journal Science, were presented at the International Coral Reef Symposium in Fort Lauderdale, where nearly 3,000 scientists and managers have gathered to learn about the latest scientific discoveries and try to figure out ways to save the world's reefs.
Kent Carpenter, director of the international union's Global Marine Species Assessment and lead author of the Science article, emphasized the importance of coral reefs beyond their majesty and beauty to tourists donning snorkels and masks.
"Corals make up the very framework of the coral reef ecosystem," said Aeby, one of 38 scientists who collaborated on 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 a profound effect on more than 500 million impoverished fishermen in the tropics who rely on them to feed themselves and their families, said David Obura, a marine biologist and East Africa coordinator for the Coastal Oceans Research and Development-Indian Ocean.
"People rely on coral reefs every day," said Obura, another coauthor. "In places like the Indian Ocean, we need to work with fishermen and help people decide not to fish in a destructive way."
The decline of reef-building corals can be blamed primarily on 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, said that 95% to 98% of the elkhorn and staghorn corals in the Keys and elsewhere in the region had been lost to disease, toppled by hurricanes or crowded out by thick mats of algae and bacteria.
Both are listed as threatened with extinction under the Endangered Species Act.
But it is 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.