...That's how we are treating the the reefs and seas, says one expert on coral bleaching. Linda Vergnani reports on scientists' alarm about the state of our oceans.

Just off Heron Island, Australia, stingrays flip out of the water and sharks cruise with their fins sticking out cartoon-style above the reef flats. In a nearby forest of lime-green Pisonia trees is Heron Island Marine Research Centre, where wetsuits drip outside bungalows and staff are busy fixing boats. The main building looks more like a run-down resort than the largest research centre on the Great Barrier Reef. Each year, it is visited by more than 1,000 students and researchers from all over the world. Its director, Ove Hoegh-Guldberg, is an expert on coral bleaching.

This August morning, he dons a wetsuit and - carrying a camera, a yellow builders' tape measure and what looks like a rectangular home-made clothesline - he heads for a whitened area on the reef crest. There he lays down his quadrant on the staghorn coral and begins taking photographs.

"This coral bleached snow-white after exceptionally cold water temperatures a week ago," says Hoegh-Guldberg, director of the University of Queensland's Centre for Marine Studies. The unusual mid-winter bleaching is the latest symptom of a problem that is devastating corals worldwide. It is hard to believe, looking at the high-rise coral city teeming with fish, that this intricate ecosystem could be largely obliterated.

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The problem, Hoegh-Guldberg says, is that sea temperatures are rising 200 times faster than the fastest rate in prehistory and animals and plants cannot respond quickly enough. The energetic Australian researcher, who, even out on the reef, manages to juggle research demands, my interview and a TV documentary crew, is among 17 scientists who published one of two lead papers in Science last week on the decline of coral reefs. Heogh-Guldberg's paper estimates that 30 per cent of reefs are already severely damaged. By 2030, it predicts, close to 60 per cent "may be lost". The group wants vigorous implementation of international management strategies that support "reef resilience".

The authors, led by Terry Hughes of Australia's James Cook University, include US, Australian, British and Swedish experts. To limit the damage, they recommend that at least 30 per cent of the world's coral reefs be declared no-take areas - to prevent people removing anything from the reef - with greater protection of adjacent habitats. These strategies should be complemented by "strong international policy decisions to reduce the rate of global warming". Overfishing and pollution are seen as the "major drivers of massive and accelerating decreases in the abundance of coral reef species, causing widespread changes in reef ecosystems in the past two centuries". These effects have been compounded by global climate change, leading to a projected "massive loss of all corals" within 50 years.

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The paper notes that although coral reefs are unlikely to disappear entirely because some species show greater tolerance to climate change and coral bleaching, they will undergo huge changes. Hoegh-Guldberg, who chairs the joint World Bank and Unesco Intergovernmental Oceanographic Commission working group on coral bleaching, says that with a minimum sea temperature rise of 2C certain by the end of this century, coral reefs will become "unrecognisable". The reefs will no longer be dominated by coral but by seaweeds and other organisms he describes as "brown scuzz", and biological diversity will decline.

"Of course, reefs will bounce back in 10,000 years after we have gone," he adds. "This isn't the question. It's what quality reefs we will have in the near future - the human future." Hardest hit would be the 100 million people around the world who need reefs for subsistence fishing. "If you change coral reefs, you have to feed those people on something else," Hoegh-Guldberg says.

Tourism would be hurt. A World Wide Fund for Nature paper to be published in September shows that Australia will lose A$3 billion to A$8 billion in tourism revenue over 20 years if half the Great Barrier Reef corals were lost. It predicts that by 2010, there will be a 2C-5C rise in sea temperature along the Great Barrier Reef and that by 2050 corals will cover less than 5 per cent of it.

Hoegh-Guldberg, who wrote the study with his economist father, Hans, says:

"Over 80 per cent of tourists identify Australia with the Great Barrier Reef before anything else."

The Australian government has put forward a re-zoning proposal to increase the no-take area in the Great Barrier Reef Marine Park from the current 4.5 per cent to 32.5 per cent. Hoegh-Guldberg applauds this "visionary first step". But he and others agree that protection has to extend across the globe. A network of no-take areas and marine reserves is essential if reef fish and other organisms are to stand a chance of surviving this super-heated century.

Hoegh-Guldberg is worried that millions of reef species, possibly of great benefit to humans, could disappear without ever being documented.

Hoegh-Guldberg and his wife, marine biologist Sophie Dove, recently took out a patent on a pigment that occurs naturally in coral. Among the first species to vanish will be his favourite fish, the exquisite turquoise and orange-spotted filefish.

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Hoegh-Guldberg's passion for reefs was ignited when he was first taken snorkelling on the Great Barrier Reef by his Danish grandfather, a medical doctor, noted lepidopterist and a leader of the Danish resistance. His grandfather pointed out a butterfly fish. "It was a copper-banded butterfly fish, which is a bit like a gazelle because it is a very delicate creature with a long nose. It picks out the coral polyps and the little creatures living among the coral. It was burned into my mind as if it was a sacred moment when I first focused on reefs."

In his first year at Sydney University, he visited Heron Island Research Centre. "I went off the reef crest and I didn't come back for five hours.

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People thought I had drownedI There were those garish parrotfish, the sharks and rays and turtles. This was a dream come true."

His PhD on the causes of coral bleaching was done at the University of California at Los Angeles. Hoegh-Guldberg says that although other scientists had attributed coral bleaching to a rise in sea temperature above a certain threshold, he was the first to prove the link in laboratory experiments. In a 1999 research paper, he calculated that "the sea temperature under even mild climate change would be several degrees above that threshold by 2050". His colleagues nicknamed him Dr Gloom, but his alarming predictions are now broadly accepted.

Hoegh-Guldberg says developed countries need to show leadership. "America's position is untenable because it now produces 25 per cent of the emissions on the planet, andI it will be environmentally and economically disastrous if we go into the higher levels of climate change than are predicted."

His concerns are shared by John Pandolfi, curator in the department of palaeobiology at the Smithsonian Institution and lead author of Science's other lead paper last week. "Given the inertia involved in governments, the history of our consumption and the acceleration of our consumption, it seems imperative that we act as soon as possible," he says.

Pandolfi and 11 other scientists examined the global trajectories of change of coral reefs over thousands of years in different areas and concluded that reefs would not survive for more than a few decades "unless they are promptly and massively protected from human exploitation". They found that degradation of reefs began long before the current episodes of coral bleaching and was linked directly to overfishing and pollution.

Once large marine herbivores such as seacows, green turtles and bump-head parrotfish disappeared, there was an "an almost inexorable march to decline". Losing these is equivalent to losing the top predators in the Serengeti with the effects cascading right down the ecosystem, Pandolfi says.

Of the 14 reef sites studied, those in west Panama and Jamaica are 80 per cent of the way to ecological extinction. Pandolfi says that without intervention and attempts at restoration, these reefs are "the ghosts of Christmas future".

His group will now research what percentage of reefs will survive under different management strategies. Pandolfi believes that coral bleaching and, to a lesser extent, coral disease get a lot of publicity because they are so dramatic and important, but it is human pressures such as overfishing and pollution that have weakened the reefs, leaving the coral susceptible to bleaching and disease. He likens this to "kicking around a cancer patient".

The drastic consequences have been seen in the Caribbean. Pandolfi's group studied historical records, including ship captains' logs and found that early European explorers found the Caribbean swarming with turtles.

Pandolfi says: "They were so abundant that the ship could navigate by the sound of turtles hitting their hulls." Sailors knew they were too close to islands when the impacts increased. The turtles, manatees, parrotfish and other large herbivores of the Caribbean were destroyed. But even in the late 1970s and 1980s, it looked as if the reefs were flourishing. "We didn't realise what a tenuous thread they were on," Pandolfi says. A few years later, a mass die-off of starfish and other species followed hurricanes. There were not enough herbivores to keep down the algae. When the last herbivore, the sea urchin, disappeared, "the reefs simply collapsed right across the Caribbean", Pandolfi says. They have not recovered in 20 years.

Pandolfi recalls that the Caribbean used to be dominated by "towering forests" of two species of staghorn coral. "Now it looks like a battlefield in which all the trees have been knocked down, and all you see is the occasional rock in a barren wasteland."

On the far side of the Pacific, Hoegh-Guldberg echoes his gloomy prognostic. He says: "It's like a very bad science-fiction novel that we've got to the point where humans can and are rapidly killing off entire ecosystems."

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