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The 115, largely postcard perfect, islands of the Seychelles are found strung across a patch of the Indian Ocean 1,500 km off the coast of East Africa.

Around 90% of the population and practically all economic activity on the islands is located on narrow coastal strips, most around two metres above sea level and less than two kilometres wide.

The international airport, crucial to tourism - which accounts for 20% of GDP and one third of jobs - is built on land reclaimed from the sea, and no more than two to three metres above sea level. The same is true for the fishing port, the commercial port, a major power station, waste processing plants, fuel storage depots and major industrial zones.

It's not a widely known fact, but all of this is protected from storm surges and wave action by a network of coral reefs.

Coral reefs are not only spectacular biological baubles and playgrounds for divers; in many parts of the world, including Australia and most small tropical islands, they provide essential services that communities are totally dependent upon.

In Australia the Great Barrier Reef is responsible for protecting over 2,000 km of coastline from the ravages of the open sea, says Ove Hoegh-Guldberg a veteran marine biologist and director of the Global Change Institute at the University of Queensland. Here the reef encourages mangroves, seagrass and fisheries along the coast and protects against erosion, he says.

More than just a pretty face

On top of this, the reef contributes billions of dollars to the Australian economy each year. And world-wide, more than 500 million people rely on reefs for food and revenue. "Coral reefs are really important to this planet, they are not only beautiful and magical, but they support an enormous number of people," Hoegh-Guldberg says.

"Coral reef ecosystems are valuable to human communities because of the ecosystem services that they provide," agrees Ilsa Kuffner, a biologist at the US Geological Survey in St Petersburg, Florida. "These include shoreline protection, production of carbonate sand for beaches, habitat for economically important fisheries, and recreation for tourism industries."

Ronny Jumeau is the ambassador of the Republic of the Seychelles to the United Nations. He is the former environment minister of the Seychelles, and is the nation's leading diplomat on issues concerning climate change. "You cannot de-link the fate of coral reefs to the existence of small islands and low-lying areas which are protected by them," he says. "We hear a lot about sea level rise being a threat to small islands. The death of reefs poses the same threat."

Under global warming predictions for the next half century, many small islands such as those of the Seychelles and Maldives face a serious threat from rising sea levels. This is occurring not only because of melting glaciers and ice caps, but because the sea is expanding as it warms. In 2007 the UN's Intergovernmental Panel on Climate Change (IPCC) warned an increase in sea level of just 18 to 59 centimetres is likely by 2100. This could be enough to wipe the Maldives off the map.

Extinction

But even before sea level rise takes effect many coastal regions and island face another threat: the mass extinction of coral reefs. "Even without sea level rise if coral reefs were to die... small island states would be swept away," says Juneau.

A study by researchers at the University of Chapel Hill in North Carolina, US, published in the journal PLoS One in 2007, compared 6,000 other studies and showed that reefs in the Asia-Pacific region are declining at a remarkable rate. It estimated that between 1997 and 2003 corals were being lost at a rate of 3,168 km2 a year.

The main factors driving the decline of reefs are pollution and excessively warm water in the summer, which causes mass die-offs or bleaching. "Research has shown that temperatures only one or two degrees above normal in the late summer can cause bleaching, leading to mortality if the temperature anomaly persists for longer than a few weeks," says Kuffner.

A further serious threat is ocean acidification, caused by carbon dioxide dissolving in sea water. This is already having an effect, and is further likely to slow coral growth (or 'calcification') by 15 to 50% by 2050, she says.

"We've lost around 30 to 50 per cent of corals over the last 40 years, and are currently losing them at a rate of one to two per cent per year," says Hoegh-Guldberg. "The consensus among marine biologists is that coral reefs won't exist as the biodiverse and supportive ecosystem that they are today by the middle of this century."

Reefs are storehouses of ocean biodiversity. Some 25% of marine life is found in and around coral reefs - an estimated one million species. Despite this, they only cover 1% of the world's surface.

"We have a lot at stake in a tiny area," he says. "Coral reefs lie in heavily populated coastal regions of the world where people depend on reefs, mangroves and other ecosystems like seagrass for their food and income... this demonstrates that the changes in acidity and pH have huge implications for human livelihoods."

Putting a value on reefs

A report commissioned by Australia's Great Barrier Reef Marine Park Authority in 2005 estimated that the reef contributes about AUD$5.8 billion to the Australian economy each year. The vast majority of this comes from tourism, with a fishing component of only $119 million. "There has been a big swing towards protecting the reef, because fishing destroys populations and doesn't bring in that much money, whereas tourism brings in enormous amounts," adds Hoegh-Guldberg.

Another study, commissioned by the Great Barrier Reef Foundation, and produced by the firm Oxford Economics in August 2009, came up with a total value for the reef of AUD$51.4 billion and estimated that climate change could hit the Australian economy for AUD$37.7 billion if the reef was totally bleached.

Another surprising way in which the reef is bringing in money and other benefits is through the development of new medical treatments based on research on marine species. Hoegh-Guldberg says that a series of new biomedical companies have sprung up based around creating pharmaceuticals from the venom of cone snails (Conus spp), which show promise as a range of highly effective painkillers, with none of the addictive side effects of morphine.

The worrying thing is that all of the benefits we get from the reefs are under serious threat as carbon dioxide builds up in the atmosphere and the world warms. "The ecosystem services that reefs provide to humankind could be in jeopardy," Kuffner says.

Hoegh-Guldberg told the UN's Copenhagen Climate Conference in December 2009 that to retain diverse reefs of the kind we have today we ought to "bring greenhouse gasses like carbon dioxide to below 350 ppm in the long term," and minimise the extent of further rises in the meantime.

The failure of December's meeting showed that international agreement on climate is going to be difficult to come by, however. That, says Hoegh-Guldberg, is why it's so important to have studies that quantify the massive economic value reefs have to nations such as Australia.

The financial value of the Great Barrier Reef, was the major factor that led to its protection by the government as a marine park in 1975, which in turn led to it being listed as a World Heritage Site in 1981. With luck other countries and communities can be persuaded of the value of their reefs too, before it's too late.