The Deputy Prime Minister, John Prescott, very sensibly combines pleasure with business whenever he can.

BBC Correspondent Roger Harrabin: Damage to coral described as 'spectacular'

So during his current visit to the Maldives for high-level political talks on climate change, he enjoyed some diving in the warm waters of the Indian Ocean.

But the sight that greeted Mr Prescott under water is likely to have depressed and alarmed him.

The Maldives

The world's coral reefs - described by scientists as "the rainforests of the sea" - are under attack.

A voluntary group, Reef Check, conducted the first global assessment of coral damage in 1997.

It repeated the survey in 1998, and found cause for serious concern:

• Reefs more than 1,000 years old had died.
• In some parts of the Indian Ocean, more than 90% of the coral was dead.
• Many reefs were almost devoid of fish.

Stocks and stress

Overfishing proved to be far worse than the scientists had expected, and remote reefs were just as liable to have been damaged as coastal ones.

Illegal and destructive fishing methods using poison and explosives were employed by many Far Eastern boats.

Reef Check found that lobsters had disappeared from 85% of reefs where they had once been abundant, and groupers from 63%.

Many fish were being caught as juveniles, before they had reached spawning age.

Possibly even more serious is the problem of coral bleaching, the process in which coral literally loses its colour and turns a pallid white.

Fish stocks are rapidly decreasing

The great barrier reef off Australia's east coast has undergone widespread inshore bleaching, with up to 88% of coastal coral affected.

The US National Oceanic and Atmospheric Administration (NOAA) says the first half of 1998 saw the problem at a record high.

"Coral bleaching is a sign that reefs are under severe stress and may be seriously damaged", says NOAA's James Baker.

The stresses can include pollution, changes in salinity levels, or silt. And rising water temperatures compound the other factors.

Wider implications

Corals usually live at the upper edge of their temperature tolerance, and 1998 was the hottest year since records began.

An increase of even one degree above the usual maximum temperature at a site can be fatal.

Many corals usually recover from a short spell of bleaching. But longer periods, or recurrent bouts, can leave them severely weakened and more susceptible to disease and damage.

Coral reefs have a wide ecological value

NOAA found that a rise in water temperature of one degree for more than a month was often enough to cause extensive bleaching.

It is not clear what role the El Nino phenomenon in the Pacific played in raising ocean warmth last year.

But climatologists believe global water temperatures could rise by about two degrees over the next half century as climate change takes hold.

So John Prescott's dives may not have been very happy ones. But more important than the role of the reefs as tourist attractions is their wider ecological value.

In NOAA's words, they are "some of the oldest and most biologically diverse eco-systems on earth".

They produce fisheries for food, materials for new medicines, and protect coastal communities from storms.

President Clinton says the reefs' disappearance "would destroy the habitat of countless species, and unravel the web of marine life".