Bleaching Hits Caribbean Corals

Widespread coral bleaching caused by abnormally high sea temperatures is hitting reefs throughout the Caribbean, according to reports from field researchers in the region. It’s just the latest development in what is shaping to be one of the worst years on record for the world’s coral reefs.

For the Caribbean, where ocean temperatures are only now reaching their yearly highs, the bleaching under way in some areas could match or exceed the damage done in 1998 and in 2005, years that were also extremely warm. In 2005 90 percent of coral in the area were damaged and 10 percent were destroyed.

“This is unusual,” Mark Eakin, an oceanographer who studies corals for the National Atmospheric and Oceanic Administration, said in an interview. “It’s hitting more areas, and it’s hitting some corals that were spared in 2005.”

Bleaching has already hit numerous reefs throughout the world this year, with areas in Thailand and Indonesia seeing up to 80 percent of some corals affected.

Reefs in the Flower Garden Banks National Marine Sanctuary, off the coasts of Texas and Louisiana, are also experiencing serious bleaching.

“We are concerned we could lose much of the fire corals this year,” Emma Hickerson, a sanctuary researcher, told Agence France-Presse this week. Fire corals are beautiful but also venomous to the touch.

Scientists believe that the increase in coral bleaching is largely a consequence of global warming, as Justin Gillis explained in an article in September.

Bleaching occurs when environmental stresses like excessive heat cause coral to expel the algae that live symbiotically inside them.
Coral lives a symbiotic life. Inside the sac of each coral polyp lives a one-celled algae called zooxanthellae (right). The algae gives off oxygen and other nutrients that the coral polyp needs to live and in return the polyp gives the algae carbon dioxide and other substances the algae needs. That is why coral reefs grow so near the surface of the water where it is the sunniest--the algae need sunshine for photosynthesis.

"High temperatures cause corals to force out the symbiotic algae that provide them with food. This makes the corals appear white or bleached and can increase outbreaks of infectious disease," said Mark Eakin, coordinator of NOAA’s Coral Reef Watch.

Reefs often recover after bleaching, but can die if the stress they experience is too extreme. During 1998, still the hottest year on record, about 16 percent of the world’s coral are thought to have died as a result of heat stress.

"Temperatures are high in the Caribbean, and we expect this to continue," Eakin stated, so "this season has the potential to be one of the worst bleaching seasons for some reefs."

Already this year, corals off the coast of Panama are experiencing high rates of mortality, a troubling sign given that sea temperatures are expected to remain elevated for some time. The coral die-offs are being caused not just by warming, but also by the heat-driven evaporation of shallow coastal waters, which is making the sea around the reefs abnormally salty.

“I’ve heard of lots of bleaching and lots of dead corals in Panama,” Dr. Eakin said. “The bleaching is really kicking in strong at this point.”

Reefs off the island of Guadeloupe, in the French Antilles, are also being hit hard, with up to 80 percent of some corals affected, field researchers say.

Reefs around Puerto Rico and the Florida Keys (left) appear to have been largely spared this year, however.

Source:
New York Times, "Bleaching Hits Caribbean Corals", accessed October 8, 2010
The Citizen, "Fears Mount of Massive Coral Damage", accessed October 8, 2010