Caribbean Reefs
Bleached by Warm Water
November 03, 2005 — By Associated Press
SAN JUAN, Puerto Rico — 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
organisms, scientists said Wednesday.
The warmer atmosphere has 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.
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 coral.
The bleaching occurs when the microscopic plants, or zooxanthellae,
which live in coral tissue stop working. The zooxanthellae provide
corals with color 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 was isolated and appeared to be the
result of short-term damage from things like 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 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 (30C) 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 affected 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 110,000 square miles (284,300 square
kilometers) -- which is 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.
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.
Source: Associated Press
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