LONDON — The world's coral reefs are far smaller than scientists thought and are shrinking fast under a deadly combination of pollution, climate change, and dynamite fishing, according to a United Nations study released on Tuesday.

The most comprehensive mapping yet of the "rainforests of the oceans," prepared by the United Nations Environment Program (UNEP), showed the world's reefs covered between a half and one-tenth of the area of previous studies. The study showed coral reefs covered just 284,300 square km (110,000 square miles), or less than one-tenth of a percent of the world's seabed.

UNEP Executive Director Klaus Toepfer said the "Coral Atlas" showed that the fragile beauty and precious ecosystems of the reefs were in retreat right across the planet. "They are rapidly being degraded by human activities. They are over-fished, bombed, and poisoned," he said in a statement accompanying publication of the atlas. "They are damaged by irresponsible tourism and are being severely stressed by the warming of the world's oceans. Each of these pressures is bad enough in itself, but together, the cocktail is proving lethal."

Scattered under the waters of 101 countries and territories, corals are vital for fisheries, coastal protection, tourism, and wildlife, hosting up to 2 million marine plants and animals.

Often compared to the equally endangered tropical rainforests as a source of biodiversity, some of their compounds are used in drugs such as AZT, a treatment for the HIV virus.

WORLDWIDE DAMAGE

Damage is being inflicted on coral around the world, but some regions are suffering disproportionately.

In Indonesia, the world's largest coral nation, the study found that 82 percent of corals were "at risk" from illegal blast fishing in which explosives are thrown at the reef.

Some parts of the Indian Ocean have lost 90 percent of their coral reefs — or five percent of the total world reef area — as a result of the 1998 El Niño weather phenomenon, an unusual warming in the waters of the eastern Pacific Ocean.

In the Caribbean, entire coral reefs have been decimated by disease, the report said.

Many of the world's 660 protected marine areas fail to defend corals from the ravages of pollution, it added. "Often remote from reefs, deforestation, urban development, and intensive agriculture are now producing vast quantities of sediments and pollutants which are pouring into the sea and rapidly degrading coral reefs in close proximity to many shores," Toepfer said.

The report said there is a powerful economic as well environmental case for saving the coral. Hundreds of millions of people have no other source of animal protein, and well-managed diving programs could provide major tourism revenue.

"One of the saddest facts about the demise of reefs is that it is utterly nonsensical," said Mark Spalding, lead author of the study. "Protecting and managing reefs is not just for the good of the fishes. In every case it also leads to economic and social benefits for local communities."