The World Conservation Union (IUCN), meeting in Geelong, west of Melbourne, heard yesterday that half of the world's reefs could be lost in the next 40 years unless measures were taken to protect them against climate change and pollution.
Carl Gustaf Lundin, head of the IUCN's marine programme, said that up to 20 per cent of reefs had, in effect, already been destroyed. A principal reason, he said, was rising sea temperatures, which can cause coral bleaching - a phenomenon that results from the loss of microscopic algae that live inside coral and help it survive.
Achim Steiner, IUCN's director general, said a conservation plan for the unregulated high seas - involving a network of marine parks - would be produced by 2008, for adoption by governments four years later. "We've had a good century of developing ... national parks on land," he said.
"But in the face of big challenges such as habitat loss, pollution of coastal zones, and species loss, and the high seas collapse of fish stocks, the whole marine realm is becoming rapidly more important. The situation in oceans around the world is deteriorating, and at an escalating pace."
Mr Steiner said 15 of the world's 17 largest fisheries were already being exploited to the maximum.
There are hundreds of marine parks in the world, but most were set up in the past 15 to 20 years. Australia has the World Heritage-listed Great Barrier marine park, which was established in 1975 and is bigger than Italy, covering 87 million acres. There are also marine-protected areas in the US, Europe and Africa.
Scientists say parks could help save reefs by preventing over-fishing, which can decrease coral cover or deplete fish populations that are important for the ecosystem. Mr Lundin said another 30 per cent of the world's reefs would be seriously affected if no action was taken in the next 20 to 40 years.