November 3, 2005
Caribbean Reefs Bleached by Warm Water
SAN JUAN, Puerto Rico -- Unusually warm waters are bleaching coral reefs throughout the Caribbean, raising fears of a die-off of the important organisms, scientists and environmentalists said Wednesday.
Ocean temperatures have been slowly rising, threatening sea coral that can only live within a narrow temperature band, according to the experts. A slight increase in temperature can induce coral bleaching and eventually kill the coral.
Recent data gathered by the University of Puerto Rico shows that up to 95 percent of coral colonies off the island have had some bleaching.
"The concern is that we may be witnessing a massive die-off. Reports from Vieques (Puerto Rico), Barbados and many other Caribbean islands is grim," said Mary Ann Lucking, director of the Puerto-Rico-based conservation group Coralations.
The bleaching occurs when the microscopic plants, or zooxanthellae, which live in coral tissue stop working. The zooxanthellae provide corals with color and food.
Scientists say without them, corals usually die.
Worldwide, coral reefs cover about 110,000 square miles, less than one-tenth of 1 percent of the world's oceans. But they support more than 1 million species of marine life, sustain tourism industries and provide food for islanders throughout the tropics.
Since March, the northeast Caribbean has had higher than normal sea surface temperatures. The trade winds, which usually help cool the sea, were also not as strong as they have been in the past.
Prior to the 1980s, coral bleaching events were isolated and appeared to be the result of short-term events such as storms or pollution.
But in the past 20 years bleaching has become more common.
"This is probably the most severe bleaching event that Puerto Rico and the U.S. Virgin Islands has ever recorded," said Andy Bruckner, a scientist with the U.S. National Oceanic and Atmospheric Administration.
The bleaching process can begin when temperatures are as little as one or two degrees above 86F for an extended period of time.
Scientists in Puerto Rico say temperatures have been two degrees above normal since September, typically Puerto Rico's warmest month.
"We're seeing species of coral that have never been effected by bleaching now suffering a high mortality," Lucking said.
Some colonies of coral in the Caribbean, which include up to 42 species of the animal, have become completely white, according to University of Puerto Rico marine biologist Edwin Hernandez. Reefs off the island-nation of Grenada are also bleached with up to 70 percent of colonies suffering some impact.
"The threat from this is enormous, we may be losing an incredible resource," said Hernandez.