WASHINGTON --A one-two punch of bleaching from record hot water followed by disease has killed ancient and delicate coral in the biggest loss of reefs that scientists have seen in Caribbean waters.
Researchers from around the globe are trying to figure out the extent of the loss. Early conservative estimates from Puerto Rico and the US Virgin Islands have found that about one-third of the coral in official monitoring sites has died recently.
''It's an unprecedented die-off," said a National Park Service fisheries biologist, Jeff Miller, who checked 40 stations last week in the Virgin Islands. ''The mortality that we're seeing now is of the extremely slow-growing reef-building corals. These are corals that are the foundation of the reef . . . We're talking colonies that were here when Columbus came by have died in the past three to four months."
Coral reefs are the basis for a multibillion-dollar tourism and commercial fishing economy in the Caribbean. Key fish species use coral as habitat and feeding grounds. Reefs limit the damage from hurricanes and tsunamis. More recently, they have been touted as possible sources for new medicines.
If coral reefs die, ''you lose the goose with golden eggs" that are key parts of small island economies, said Edwin Hernandez-Delgado, a biology researcher at the University of Puerto Rico.
On Sunday, Hernandez-Delgado found a colony of 800-year-old star coral, more than 13 feet high, that had died in the waters off Puerto Rico.
''We did lose entire colonies," he said. ''This is something we have never seen before."
On Wednesday, Tyler Smith, coordinator of the US Virgin Islands Coral Reef Monitoring program, dived at a popular spot for tourists in St. Thomas and saw an old chunk of brain coral, about 3 feet in diameter, that was at least 90 percent dead from a disease called ''white plague."
''We haven't seen an event of this magnitude in the Caribbean before," said Mark Eakin, coordinator of the National Oceanic and Atmospheric Administration's Coral Reef Watch.
The Caribbean is better off than areas of the Indian and Pacific oceans, where mortality rates, mostly from warming waters, have been in the 90 percent range in past years, said Tom Goreau of the Global Coral Reef Alliance. Goreau called the events ''an underwater holocaust."
And with global warming, scientists have voiced pessimism about the future of coral reefs.
''The prognosis is not good," said a biochemistry professor, M. James Crabbe, of the University of Luton, near London.
In early April, he will investigate coral reef mortality rates in Jamaica.
''If you want to see a coral reef, go now, because they just won't survive in their current state," Crabbe said.
For the Caribbean, it started with hot sea temperatures, in Panama in the spring and early summer, and it got worse.
New NOAA sea-surface temperature figures have found that the sustained heating in the Caribbean last summer and fall was by far the worst in 21 years of satellite monitoring, Eakin said.
The heat causes algae that provides food for the coral to die and turn white. That puts the coral in critical condition.
In the past, only some species bleached during hot water spells, and the problem occurred only at certain depths. But in 2005, bleaching struck far more of the region, at all depths and in most species.
A NOAA report issued in February calculated that 96 percent of lettuce coral, 93 percent of the star coral, and almost 61 percent of the brain coral in St. Croix had bleached.
''The big problem for coral is the question of whether they can adapt sufficiently quickly to cope with climate change," Crabbe said. ''I think the evidence we have at the moment is: No, they can't.
''It'll not be the same ecosystem," he said. ''The fish will go away. The smaller predators will go away. The invertebrates will go away."