Reef coral in Caribbean is dying off, study finds

Coral reefs across the Caribbean have suffered an 80 percent decline in cover during the past three decades, a far more devastating loss than scientists had expected, according to a study released yesterday.

"It's depressing," said marine biologist Isabelle Cote, one of the authors of the study, which appeared in this week's Science. "We all knew that we had a bad situation on our hands. But nobody expected it to be this bad."


The researchers gathered information from 65 previous studies of 263 sites and analyzed it to construct a regional picture.

They discovered a sharp drop in the coral almost everywhere in the Caribbean, from Florida to South America. Coral covered about 50 percent of the average reef in the early 1970s but only 10 percent now.


Other researchers were surprised by the findings.

"Everybody sees a bit of the problem in their area. For someone to say the whole Caribbean is in a downward slide, that's a shock," said Clive Wilkinson, who runs the Global Coral Reef Monitoring Network. Caribbean reefs cover almost 10,000 square miles, about 10 percent of the world's reef total.

He said 10 percent coverage indicates a reef that's not healthy. Reefs consist of dead coral, which serves as a foundation for living coral, algae and other organisms. On healthy reefs, living coral covers 60 percent or more of the surface.

Like their counterparts around the world, Caribbean coral reefs are subject to a variety of threats, most of which stem from humans.

For example, overfishing in Jamaica has sharply decreased the number of parrotfish and surgeonfish, which feed on seaweed. In turn, that leaves more seaweed to compete with coral for space on the reefs. On many Caribbean reefs, seaweed has largely choked off coral.

Increased water temperatures due to El Nino and global warming have also killed coral, scientists say. Coral exists in a symbiotic relationship with microscopic algae, which produce energy for their hosts. But when the water temperature rises too high for more than a week or so, the algae produce free radicals that damage the coral.

In response, the coral expels the algae. But without algae, the coral starves. This is known as "bleaching" because, without the colorful algae, the coral turns white. In 1998, warm water killed about 10 percent of the world's coral, the report said.

Over the past 20 years, several diseases have killed Caribbean coral species. Pollution has taken its toll, too, including agricultural runoff, mud and silt from cleared forests and raw sewage that can smother coral, according to Cote, a professor at the University of East Anglia in Britain.


Because of the Caribbean's geography, its coral is particularly sensitive to pollution.

"The problem with the Caribbean is it's a big lake," said Wilkinson. "So everything that comes into there from the Mississippi, from Mexico, Central America, South America and even as far as the Amazon, all this runoff and pollution doesn't drain out quickly."

Another problem: Compared with other reef regions, the Caribbean has a large human population, which catches more fish and produces more pollution.

The disappearance of coral could have wide-ranging implications. Reefs provide habitat for millions of species, some of which might prove useful to humans, Cote said.

The anti-AIDS drug AZT, for example, is derived from a Caribbean sponge that lives on reefs. But there are other more immediate concerns, including drops in tourism and fish harvests. Healthy reefs also serve as a wave break, protecting shores from tropical storms.

The current decline is "unprecedented," according to Caribbean coral researcher Bill Precht, who has studied the region for 25 years in Belize, Jamaica, Florida and the Bahamas. Precht has done historical research, drilling cores of ancient reefs going back 3,000 years. "What is going on with Caribbean reefs, this is the first time this has happened," he said.


The key now is to pinpoint which problems are causing the worst harm, Precht said: "Humans are clearly the vector. The question is how are we the vector."

Although Wilkinson said extinction was unlikely, some researchers do not rule out the possibility. Without help, some of the Caribbean's 70 to 100 coral species could easily disappear altogether, said University of Kansas coral researcher Bob Buddemeier.

"It's grim. The people aren't going to go away. The climate is going to get worse. A lot of these countries don't have the wherewithal to protect the reefs. If we're lucky, we can stabilize things where they are now."