Coral reefs across the Caribbean have declined by 80% in three decades, UK scientists say.
By Alex Kirby
BBC News Online environment correspondent
They believe the causes are both natural and human, but found no evidence of climate change damage.
The crest of a healthy reef
Reefs in some areas appear to be recovering, but there are doubts about how well new coral formations will cope.
The scientists say this "dramatic" rate of loss appears not to have slowed since 1975.
The team, from the University of East Anglia (UEA) and the Tyndall Centre for Climate Change Research, report their findings in the online journal Science Express.
They write: "We report a massive region-wide decline of corals across the entire Caribbean basin, with the average hard coral cover on reefs being reduced by 80%, from about 50% to 10% cover, in three decades."
Hard coral is the main component of a reef: it is the substance on which soft corals like sea fans, and other species, are able to grow.
The authors analysed the results of 65 separate studies of 263 sites. Their results showed patterns of change in coral cover varied across time periods, but were largely consistent across sub-regions.
They say this suggests that local causes have operated at more or less the same time across the region.
Suspected causes of the decline include natural factors like hurricanes and disease, and others of human origin, including overfishing, pollution, and smothering by sediments released by soil erosion and deforestation.
Coral loss can have serious consequences, including the collapse of reef fisheries, a reduction in tourism, and increased coastal damage from hurricanes.
A live coral display
Although most of the loss occurred in the 1980s, there is no evidence the rate of loss is slowing. There is obviously less coral to be lost, simply because most has gone already.
The team said: "The feeling among scientists and tourists has long been that Caribbean corals are doing badly, since many people have seen reefs degrade over the years.
"We are the first to pull information together from across the region and put a hard figure on coral decline. The end result has surprised us.
"The rate of decline we found exceeds by far the well-publicised rates of loss for tropical forests."
Dr Isabelle Cote, a tropical marine ecology specialist in UEA's School of Biological Sciences, said: "The good news is that there are some areas in the Caribbean that appear to be recovering.
"The bad news, however, is that the new coral communities seem to be different from the old ones.
"We don't know how well these new ones will be able to face the challenges of rising sea levels and temperatures that result from global warming."
While the authors say their analysis shows "a clear and dramatic decline in absolute coral cover", it also reveals significant variations from year to year.
All that's left: Dead coral
Dr Cote told BBC News Online: "The year-on-year changes provide a more fine-scale picture of what is happening.
"In 1983-84, for example, there was a massive sea urchin die-off across the Caribbean, which corresponded with a very rapid coral decline.
"We're fairly certain the death of the urchins, probably from a pathogen, caused the loss of the coral.
"Urchins eat the algae which normally compete with the coral in a very limited habitat, and without the urchins to control them the algae simply won."
The authors say there are suggestions this pattern of decline in many areas of the Caribbean "is unprecedented within the past few millennia".
The situation looks unlikely to improve in either the short or the long term, they believe.
They conclude: "The ability of Caribbean reefs to cope with future local and global environmental change may be irretrievably compromised."
Images courtesy and copyright of William F. Precht