We could see horrific change becoming more frequent year by year

Mark Spalding, lead author

The reefs are being damaged faster than researchers can collect data about them and their ecosystems.

But countries which look after their reefs can expect handsome returns from tourism.

The atlas is the work of the United Nations Environment Programme's World Conservation Monitoring Centre (Unep-WCMC), based in Cambridge, UK.

Its estimate of the worldwide extent of coral reefs is 284,300 sq km, an area the size of the UK and Ireland combined - under one tenth of one per cent of the oceans.

The lead author of the atlas, Mark Spalding, said: "Previous estimates had suggested over double or up to 10 times the area that our calculations have now shown to exist.

Scientists outpaced

"It is not that other reefs have disappeared, but rather that these earlier estimates were somewhat crude extrapolations.

"Less than 10% of an estimated 1-2 million reef species have been identified.

Hawksbill turtles have been devastated globally

"The reefs are degrading faster than data can be collected. An estimated 58% are under threat from human activities, whilst we have no idea how much has already gone.

"Coral reefs are highly sensitive to changes in water temperature - an increase of one to two degrees in the El Nino event of 1998 destroyed 90% of coral in the central Indian Ocean.

"Mass bleaching (a stress response of corals) was unknown before 1979. In 1998 it affected every region where there are reefs, leading to widespread death of corals.

"Current sea temperature models suggest such events could be repeated every year within 30 years."

Dr Klaus Toepfer, executive director of Unep, said: "Coral reefs are under assault. They are rapidly being degraded by human activities.

Fatal combination

"They are over-fished, bombed and poisoned. They are smothered by sediment, and choked by algae growing on nutrient-rich sewage and fertilizer run-off.

"They are damaged by irresponsible tourism and are being severely stressed by the warming of the world's oceans.

They are over-fished, bombed and poisoned. They are smothered by sediment, and choked by algae growing on nutrient-rich sewage and fertilizer run-off

Dr Klaus Toepfer, Unep

"Each of these pressures is bad enough in itself, but together, the cocktail is proving lethal."

Indonesia has most reefs, followed by Australia and the Philippines. France is fourth, and the UK twelfth, ahead of the US because of its overseas territories.

The Coral Reef Alliance said the atlas was important for highlighting the abundance of life found on the reefs.

It said: "Several important drugs have already been developed from chemicals found in coral reef organisms. The most famous of these is AZT, a treatment for people with HIV infections, which is based on chemicals extracted from a Caribbean reef sponge.

"Unique compounds from coral reefs have also yielded treatments for cardiovascular diseases, ulcers, leukaemia and skin cancer."

And countries like Egypt and Australia are earning huge amounts from tourism to well-managed reefs.

No refuge

Mark Spalding told BBC News Online: "The atlas gives us the best picture yet, far and away the most comprehensive assessment.

Some of Sinai's reefs are very well managed

"There's damage almost everywhere. People are going to the most remote reefs after the really valuable fish, like sharks and groupers.

"The scale of the 1998 bleaching caught everybody unawares. But scientists still don't know how quickly corals can adapt.

"Perhaps they will adapt to what's happening. At the worst, we could see horrific change becoming more frequent year by year."

Images courtesy of Unep-WCMC. Anemonefish copyright 2001 Stuart Westmorland/Stone; hawksbill M Spalding/WCMC; Sinai Earth Sciences and Image Analysis Laboratory, Nasa, Johnson Space Center