This is the VOA Special English Environment Report.

A new study shows an eighty percent decrease of hard coral in the Caribbean Sea over the past thirty years. Scientists from the University of East Anglia and the Tyndall Center for Climate Change Research, both in Britain, did the study. They published their findings in Science.

Coral is made up of hundreds to hundreds of thousands of organisms called polyps. Each is covered with cells filled with poison. The coral uses the poison to defend itself and to capture its food.

Hard coral is what covers reefs. Soft coral, like sponges and sea fans, live on hard coral.

In the nineteen-seventies, hard coral covered about fifty percent of the average reef in the Caribbean. Today, the researchers say, the cover is down to ten percent. They say it appears nothing like this has happened before for at least three-thousand years.

Ocean biologist Isabelle Cote took part in the study. She says the scientists knew there were serious problems with the Caribbean reef system, but what they found surprised them. They based their findings on sixty-five earlier studies that examined more than two-hundred-sixty areas of reef in the Caribbean Sea.

At first, the scientists were trying to learn the amount of destruction that ocean storms had caused to coral reefs over the years. But the researchers decided they had to widen their study. Mizz Cote says they needed to be able to compare storm damage with damage from other forces.

The study found that weather conditions have played a part in the decrease of Caribbean coral. But the scientists say human activity has been at least as equally destructive.

Overfishing is one problem. Fish eat plants that live on coral. The fish help keep a balance in the plant life. When too many fish are caught, some plants may spread too fast and kill the coral.

Pollution is also a problem. So too, they say, is the flow of soil into rivers that feed the sea. This includes soil from forests that have been cut down.

For coral cells to build a reef takes tens of thousands of years. Scientists say healthy reefs are not only important for nature. The many different kinds of marine life may also provide materials for new medicines.

The scientists who did the study say there are signs of recovery in some areas of the Caribbean. But they say they do not know if this new coral will be able to survive any better.

This VOA Special English Environment Report was written by Caty Weaver.