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HALIFAX - Coral reefs in the Caribbean are being destroyed by ever-growing human populations, according to a new study that goes so far as to recommend controls over how many people can live near the imperilled species.

Scientists studied 322 coral sites around 13 countries and found for the first time that the greatest pressure on the valuable marine life forms is heavy concentrations of people.

"In the Caribbean, 50 to 80 per cent of coral reefs have been lost and only 20 per cent of the reefs remain in a healthy state," said Camilo Mora, a Dalhousie University biologist who led the study published Tuesday in the Proceedings of the Royal Society of London, B.

"Where you see a lot of people, you don't see larger fish and all the biomass of these reefs have been reduced. It's like a cascade. Having humans there is going to create a broad range of factors that are going to be bad for corals."

Mora said researchers have long known that corals are being decimated around the world, but have rarely pinpointed the cause of the damage in the Caribbean until now.

Science has focused on specific factors that have damaged corals, such as overfishing, increased sedimentation and warming water temperatures. But Mora said looking too closely at those influences is too narrow and doesn't identify the real problem of intense human pressure.

"Focusing on overfishing and sedimentation is like looking at the branches of the problem because underneath all of these things is the amount of people causing these factors," he said in an interview.

Using survey data from 1999 to 2001, scientists found that where there were greater concentrations of people in areas such as the Florida Keys, Cuba, Belize and Mexico, fish stocks were depleted and there were higher amounts of algae that prevent the growth of corals.

Mora said they also measured the effect of coastal development on corals, finding that chemical runoffs and sewage-contaminated waters kill reefs.

Corals provide vital habitats for a range of marine species and are important spawning grounds, leading researchers to believe that if they disappear so too could a host of other life forms.

"The coral is a structure being used by many, many other animals so when the coral is not able to grow all this biodiversity, it is going to be lost," he said.

Mora said governments - particularly those responsible for the 121 million people living in Caribbean coastal areas - have to introduce strict measures to limit the effect people are having on corals.

Fishing should be reduced, water quality should be improved by limiting sewage runoff, and greater controls should be imposed on the use of land for agriculture to stem chemical leaching, the paper states.

But most importantly, Mora said the size of populations near corals should be controlled through controversial means like family planning.

"We have to start thinking on how to regulate the size of the human population," he said, citing countries such as China and India. "We have to start proposing some serious family planning."

The findings come in the wake of a major report last month that warned the world's coral reefs could be wiped out in the next 10 decades if nothing is done to stem the effects of warming water temperatures and increased acidification.

Mora's study estimates that coral reefs are worth more than $4 billion annually in tourism, fisheries and other services.