Warm Caribbean, Gulf seas threaten corals

updated 4:39 p.m. ET July 23, 2009

WEST PALM BEACH, Florida - Warm ocean temperatures predicted to persist through October in the Caribbean and the central Gulf of Mexico could mean the loss of huge swaths of corals across those regions, U.S. scientists warned Wednesday.

The National Oceanic and Atmospheric Administration's Coral Reef Watch network said the conditions may lead to coral disease outbreaks and bleaching, when the stressed organisms expel the colorful algae living in their tissues, leaving a whitish color.

Coral bleaching that lasts more than a week can kill the organisms, since they rely on the algae for sustenance, leading to the loss of reef habitat for numerous marine species.

Sea surface temperatures in parts of the Caribbean are already at levels typically not seen until late summer months when the water is hottest, said C. Mark Eakin, coordinator of NOAA's Coral Reef Watch.

Bleaching can occur when sea temperatures rise just a few degrees above the average of the warmest summer months in these areas where coral reefs live. The general average for the hottest summer months in the Caribbean is about 84 degrees Fahrenheit, Eakin said.

Slide show   Corals in crisis View images taken by researcher John Bruno and others of coral reefs stressed by disease, warming seas and other factors. more photos

He noted that sea temperatures in some parts of this region already are at the higher threshold, around 86 degrees, and that some bleaching has already begun. Those temperatures are expected to hold through October.

Scientists fear the bleaching could exceed what was seen in 2005 in the Caribbean, the worst coral bleaching event in the region's recorded history. In parts of the eastern Caribbean four years ago, up to 90 percent of corals suffered bleaching, with more than half dying.

"Just like any climate forecast, local conditions and weather events can influence actual temperatures. However, we are quite concerned that high temperatures may threaten the health of coral reefs in the Caribbean this year," Eakin said.

NOAA also warned of potential high sea temperatures stressing corals near the central Pacific islands of Kiribati, and between the Northern Mariana Islands and Japan.

Scientists hope the early warnings of potential coral stress will lead governments to take protective steps, including establishing temporary restrictions on users of coral reefs in the areas, such as divers, boaters and anglers.

Corals around the world are being stressed by rising sea temperatures, causing bleaching events that expose the organisms to disease and death. Carbon dioxide released by burning fossil fuels is absorbed by the oceans, making the waters more acidic and corrosive on corals. Land-based pollution, such as sewage, beach erosion, coastal development and overfishing also are to blame, experts say.

About 25 percent of all marine species need coral reefs to live and grow, while 40 percent of fish caught commercially and consumed worldwide use reefs to breed.

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