FORT LAUDERDALE, Fla. — Nearly one-third of the small animals that build the most massive and elaborate structures in coral reefs face high risk of extinction from global warming and local problems, a team of scientists reported yesterday.

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

Using criteria established by the International Union for the Conservation of Nature, the 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 University of Hawai'i's Hawai'i Institute of Marine Biology, based at O'ahu's Coconut Island. 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 team's report, released online yesterday by the journal Science, were presented at the International Coral Reef Symposium in Fort Lauderdale, where nearly 3,000 scientists and managers from 114 countries have congregated to learn about the latest scientific discoveries and figure out ways to save the world's reefs.

Coral reefs provide hiding places and habitat for a quarter 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 Niño resulted in a vast decline of the world's reefs.

RISK IN ISLANDS

A new system to predict coral bleaching indicates there is a risk of widespread bleaching in the Northwestern Hawaiian Islands in August, but little bleaching elsewhere during the northern hemisphere summer, the National Oceanic and Atmospheric Administration announced yesterday.

The Northwestern Hawaiian Islands are a chain of small islands and atolls northwest of Kaua'i.

"The ability to predict coral bleaching events and provide advance warning is critically important to sustaining healthy reefs," said Tim Keeney, deputy assistant secretary of commerce for oceans and atmosphere and co-chair of the United States Coral Reef Task Force.

The new prediction system uses NOAA experimental sea surface temperature forecasts to develop maps of anticipated coral bleaching severity.

REEFS' IMPORTANCE

Kent Carpenter, director of the international union's Global Marine Species Assessment and lead author of the Science article on the threatened extinction of corals, emphasized the importance of coral reefs beyond their beauty to tourists.

"Corals make up the very framework of the coral reef ecosystem," said Aeby, one of the 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 poor subsistence fishermen in the tropics who rely on coral reef ecosystems 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 study collaborator. "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 percent to 98 percent 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 thick mats of algae and bacteria.

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

Advertiser staff writer David Waite and the Los Angeles Times contributed to this report.