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Last Updated: Friday, 13 February, 2004, 23:38 GMT
Action needed to save coral reefs
By Jonathan Amos
BBC News Online science staff, in Seattle

coral reef
The report says reefs are suffering from the so-called "bleaching" effect
More than half of the world's coral reefs will be damaged beyond repair by the year 2100 unless action is taken to halt the many threats they now face.

Scientists have issued a report saying that reefs are being assaulted by high temperatures, pollution, overfishing, disease, and soil run-off from land.

The report has been written for the Pew Center on Global Climate Change.

"These events are unprecedented on centennial and millennial scales," said US coral expert Dr Richard Aronson.

The report is a synthesis document that reviews all the latest data on coral reef impacts - more than 150 pieces of research.

It was released here in Washington State at the annual meeting of the American Association for the Advancement of Science.

Slow growth

The report's key focus is the damage now being wrought by climate change.

Its authors say human emissions of carbon dioxide (CO2) and other greenhouse gases, blamed for global warming, are endangering reefs in two ways.

The first is to increase the incidence of "bleaching" events, in which warmer waters weaken or kill corals and other reef-building species by causing them to eject the vital algae that live within their tissues.

These elevated water temperatures are also thought to be a factor in the recent increase in coral diseases in the Caribbean.

The second damaging effect of CO2 rises is to change the chemistry of the ocean.

As the gas builds up in the atmosphere, more of it is dissolved into the ocean, lowering concentrations of the carbonate ion, a building block of the calcium carbonate that corals and other organisms use to grow their skeletons and build up reefs.

"We are making the oceans more acidic and we know that corals and many other organisms that secrete the calcium carbonate - limestone - that forms their skeletons grow more slowly under these conditions," said Dr Joan Kleypas, from the US National Center for Atmospheric Research and a co-author on the Pew report.

Moving coral

The authors say more than a tenth of the world's coral reefs have been damaged beyond repair. Further destruction had major implications for human communities that lived close to reefs, said Dr Aronson, from the Dauphin Island Sea Lab in Alabama.

"Tens of millions of people depend on reefs to provide them with food and to protect tropical shorelines from erosion," he told the Seattle meeting.

"In economic terms, a conservative estimate puts the total annual income from the world's coral reefs at $30bn - a huge amount of money.

"Coral reefs also have great aesthetic value and support a huge biodiversity with some estimates running into the millions of species."

He said one interesting side-effect of the warming waters could be seen in the way elkhorn and staghorn corals, two important and temperature-sensitive species on Caribbean reefs, were now expanding their populations northward along the east coast of the Florida Peninsula.

These species last lived at this location 6,000 years ago when the climate was warmer.

Marine parks

But Dr Aronson cautioned that it was simply not possible for all of the world's coral to change latitude in response to global warming. The pace of change witnessed in the past few decades was simply too fast for systems to adapt, he said.

Measures to restrain global warming are urgently needed, the authors say, as are marine reserves to protect reefs from the other threats they face.

The situation is particularly serious in the Indian Ocean, where certain areas could be totally devoid of living coral in 20 years; and the Caribbean, where the amount of reef covered by live coral has shrunk by 80% in the last three decades.

"Coral reefs are striking, complex, and important features of the marine environment," said Eileen Claussen, president of the Pew Center.

"If we fail to act, the destruction of these rare and important ecosystems will continue unabated, threatening one of our world's most precious natural resources."

Dr Terry Done, from the Australian Institute of Marine Science, commented: "We need to slow the rate of global warming, clean up the watersheds that drain into coral reef waters, stop overfishing and start an ecosystem-based management approach to coral reefs and their fisheries.

"This includes people in the picture. It's easy to say but very hard to do."

The BBC's Christine McGourty
"Even a slight increase in water temperature can disrupt this delicate ecosystem"

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