In the first attempt to place dollar values on these havens of biodiversity, the UN Environment Programme (UNEP) said the bill from disasters such as the 2004 Asian tsunami and the record 2005 US hurricane season could have been slashed by preserving coastal buffers.

"Reefs and mangroves play an important role in shore protection under normal sea conditions and during hurricanes and tropical storms," it said in a report issued at a conference hosted by UNESCO in Paris on the state of the world's oceans.

"At least 70-90 percent of the energy of wind-generated waves is absorbed, depending on how healthy these ecosystems are and their physical and ecological characteristics."

As for tsunamis, coral and mangroves can also absorb much of the sting from giant waves, although the degree of cushioning depends how and where the initial quake occurs, the gradient of the shoreline and type and thickness of vegetation.

The report hammers out the message that the accelerating destruction of corals and mangroves is economically senseless as well as environmentally damaging.

Wisely used for small-scale fishing, as sightseeing for intelligent tourism or for selling aquarium fish, coral reefs are annually worth between 100,000-600,000 dollars per square kilometer (259,000-1.554 million dollars per square mile), depending on location, it said.

Mangroves are worth between 200,000-900,000 dollars per sq. km. (526,000-2.36 million dollars per sq. mile) each year, mainly as a fishing resource.

Corals and mangroves also play a key role in preventing erosion of the coast, preserving beaches, roads and homes.

UNEP cited the example of Sri Lanka, which earns around 5.5 million dollars a year and employs around 50,000 people by exporting aquarium fish to Europe and the United States.

"A kilo of aquarium fish was worth nearly 500 dollars (227 dollars a pound) in 2002, compared with a kilo of food fish, which sold for about six dollars (2.7 dollars a pound)," it noted.

A 440-sq.-km. (167.-sq.-mile) managed mangrove forest in Matang, Malaysia, supports a fishery worth 100 million dollars a year, and forestry products worth 10 million dollars annually.

"Day in and day out and across the oceans and seas of the world, nature is working to generate incomes and livelihoods for millions, if not billions of people," said UNEP Executive Director Klaus Toepfer.

Yet the true value of such ecosystems is rarely noted because of short-term methods of estimating profit, the report said.

As a result, coral reefs are being destroyed by abusive fishing, anchor damage and reckless tourism, and mangroves are being degraded by destructive aquaculture and timber extraction. Both are threatened by pollution and climate change.

Some 30 percent of coral reefs are already seriously damaged and 60 percent could be lost by 2030. An estimated 35 percent of the world's original mangrove cover has already disappeared, and some countries have lost up to 80 percent.

The cost of preserving them is minimum -- 775 dollars per sq. km. (2,040 dollars per sq. mile), to set up and police a protected marine area -- but the cost of losing them is very high, said the report.

It gave the example of the Maldives, which had to spend 10 million dollars per kilometer (16 million dollars per mile) to install artificial breakwaters made of concrete tetrapods to protect its shores after its natural reef was degraded.

And in Indonesia, a hotel in West Lombok is spending 125,000 dollars each year in a seven-year bid to restore its 250-metre (300-yard) beach after coral mining eroded an offshore reef, allowing ocean currents to sweep the precious sand away.

The document was produced by UNEP's World Conservation Monitoring Centre, in collaboration with the International Coral Reef Action Network and the World Conservation Union (IUCN).

The figures are based on studies carried out in Sri Lanka, Samoa, Thailand, Indonesia and the West Indies.

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