But because the exoskeletons remain, hard corals can sometimes regenerate after a bleaching event.
For soft corals, which are much more sensitive, bleaching usually wipes them out for good.
"Once soft corals disappear, the entire ecosystem is threatened," Benayahu said.
"Many organisms [such as reef fish] are associated with the corals, and once the host disappears, all the associated organisms will disappear as well."
In addition, harmful macro-algae—which compete with corals—can settle on the barren reefs, preventing coral larvae from regrowing the colonies.
Soft corals once covered 50 to 60 percent of some of the sites Benayahu studies. This figure has now dropped to an average of five percent.
"I'm afraid we've already lost knowledge of the real diversity of some sites," he said.
"There is such a huge gap in our knowledge of soft corals …. But it's too late, we have now actually missed the boat."
Ounce of Prevention
Benayahu and other experts agree that bleaching events, such as the one that caused the worst coral die-off on record in 1998, have been intensifying as the world's climate changes.
(Related news: "Global Warming Has Devastating Effect on Coral Reefs, Study Shows" [May 16, 2006].)
Nick Polunin, a marine scientist at the U.K.'s Newcastle University, said continuing damage to coral reefs due to bleaching could affect food webs and cause the localized extinction of fish species.
He also raised the possibility that the loss of just one pivotal species in a given reef environment—a so-called keystone species—could dramatically affect the entire ecosystem.
"When you lose one of those, then you could be on much more difficult ground" in terms of recovery, Polunin said.
Maoz Fine, of the Interuniversity Institute for Marine Sciences at Eilat, Israel, said global warming will subject most reefs to deadly temperature increases by the year 2030.
Preparing reefs now for dramatic climate change should be the most important task, he said.
"If we want to see reefs in the near future, we must remove all other disturbances such as overfishing, increased pressure from tourists, sewage, and so on," he said.
"Many acute disturbances can be prevented, and this will definitely increase the resilience of reefs."
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