The mysterious coral bleaching phenomenon that swept through most of the Caribbean last summer seems to be over, and there are signs that the corals may be recovering without dying off.

Fears of a major ecological disaster arose when marine biologists found that the reef-building organisms had lost their normal color and turned white.

The living polyps that line the surfaces of coral formations normally contain brownish one-celled algae that live symbiotically inside their cells. The algae carry out photosynthesis and share some of their captured solar energy with the corals. In return, the corals keep them in a well-lighted environment and protect them against currents.

The algae give coral polyps their color, but it is known that if the coral becomes too warm -- water temperatures were unusually high last summer -- the polyps expel the algal cells and appear white. High temperatures can kill the algae, but the corals expel them before this happens -- an action that apparently saves the corals from the metabolic burden of coping with dead or dying algae. It was feared that without their beneficial algal guests, the corals would be vulnerable to disease or other threats. Some corals did die.

From the Florida Keys and the Bahamas south to the coasts of Colombia and Venezuela, from Jamaica east to Puerto Rico and the Virgin Islands, once colorful reefs turned a ghostly white. Now, however, the fears of permanent damage are abating. Peter Glynn, an expert at the University of Miami on the phenomenon, said there are signs that the corals are recovering, gradually reacquiring algae without dying.

"I'm optimistic that the corals -- most of them, probably 95 percent of them -- are on their way to recovery," Glynn said.