04 November 2005

Caribbean coral reefs under pressure

A bleaching phenomenon caused by unusually warm waters is whitening coral reefs throughout the Caribbean, raising fears of a large-scale die-off of the vital organisms, scientists said on Wednesday.

Global atmospheric temperatures have been slowly raising ocean temperatures, threatening sea coral that can only live within a narrow temperature margin, according to scientists. A slight increase in sea surface temperature can induce coral bleaching, killing the coral.

Recent data gathered by the University of Puerto Rico shows that up to 95 percent of coral colonies off the island have been bleached in some areas.

"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 colour and food.

Without them, corals usually die.

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.

"When the trade winds blow, they usually blow across the surface of the water, and cause water from the bottom, cooler water, to rise up to the surface, which keep the Caribbean cooler. That didn't happen this year and we don't know why," said Lucking.

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 and more severe.

"This is probably the most severe bleaching event that Puerto Rico and the US Virgin Islands has ever recorded," said Andy Bruckner, a scientist with the US National Oceanic and Atmospheric Administration.

The bleaching process can begin when temperatures are as little as one or two degrees above 30°C for an extended period of time during summer months.

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 scientists in Puerto Rico, 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.

Worldwide, coral reefs cover about 280 000 square kilometres - which is less than one-tenth of one percent of the world's oceans. But they support more than a million species of marine life, sustain tourism industries and provide food for islanders throughout the tropics.

Healthy reefs are like undersea rain forests that naturally draw in carbon dioxide, helping pull harmful greenhouse gases from the air. They also provide medication. AZT, a drug for HIV patients, is derived from a Caribbean reef sponge.

Possibly the most severe bleaching happened during El Nino in 1998, which raised ocean temperatures and changed currents, causing bleaching that devastated reefs worldwide. Parts of the Indian Ocean lost up to 90 percent of its corals.

Source: www.iol.co.za


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