Coupled with a recent bleaching event that whitened and weakened coral on Australia's Great Barrier Reef, the Caribbean epidemic has biologists fearing for the future of the habitats that serve as spawning grounds, nurseries, tourist attractions and, some believe, alarm systems for the health of the oceans.

A catastrophic loss of corals, which grow in vivid colonies often likened to flower gardens, could be a body-blow to the Caribbean islands' multibillion-dollar tourism industry, which sells scuba, snorkeling and fishing along with sun and sand.

The unprecedented assault started last summer with some of the highest water temperatures on record in the Caribbean, which caused coral to bleach from Panama to the Virgin Islands. Hot water stresses corals, causing the tiny animals to expel their symbiotic algae, which give corals their bright colors.

Scientists believe bleaching weakens corals, leaving them susceptible to disease. In some Caribbean locations, 90 percent of corals were bleached, according to reef monitors.

Coral can recover from bleaching when the water cools and the algae return to their hosts. But last year's bleaching event was followed by a devastating attack of black band disease, white plague and other ailments.

"It's one of the worst we've ever seen in the Caribbean," said Dr. Mark Eakin, coordinator of the US National Oceanic and Atmospheric Administration's Coral Reef Watch.

SITUATION COULD WORSEN

Researchers are uncertain how widespread the disease outbreak is and they fear it could get worse as the waters warm again this summer. Some preliminary observations in the British Virgin Islands show mortality of 20 percent to 25 percent, Eakin said.

In the US Virgin Islands, disease has killed some of the slow-growing corals, like brain and star corals, that build a reef's foundation, said Jeff Miller, a biologist with the National Park Service.

"At one of the study sites near St. John ... the preliminary results show about a 30 percent loss of coral cover," he said.

The Caribbean contains two of the longest reefs in the world -- the Belize reef, which ranks behind only the Great Barrier Reef, and the Florida Keys reef, which stretches beyond the length of the 110-mile (177-km) US island chain.

Billy Causey, superintendent of the Florida Keys National Marine Sanctuary, said bleaching was less severe on the Keys reefs because the area was hit by a swarm of hurricanes, which gain their power by drawing energy from warm sea water.

Divers have seen some plague and black band disease on the Keys reefs but it has caused less damage than on the Caribbean reefs, he said.

While some scientists decline to link record high water temperatures to human-induced global warming because they have relatively few years of good records from which to draw conclusions, others are less reticent.

"I'm calling it heat stroke. I'm calling it an underwater nightmare," said marine pathologist James Cervino, a professor at Columbia and Pace universities.