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More than one-quarter of the world’s coral reefs have been lost, and while over-fishing and landclearing are a threat and a focus of attention, the largest single cause of this loss was the climate-related coral bleaching event of 1998. This damaged about 16 percent of the world’s coral reefs in 9 months. Only about half of these reefs are expected to recover (Wilkinson, 2000).
Mass coral bleaching has occurred on several occasions in Australia’s World Heritage listed Great Barrier Reef since the 1970s. A particularly intense year of bleaching occurred in 1997-1998 caused by human induced global warming, in association with a major El Nino event and record high sea surface temperatures (Pittock and Wratt 2001).The Great Barrier Reef is struggling to cope with sea temperatures that have been increasing steadily since early this century (Pittock and Wratt 2001). Tropical sea temperature has increased by almost 1oC over the past 100 years and is continuing to increase at the rate of 1 - 2oC per century (Hoegh-Guldberg, 1999). Water only a degree or two warmer than usual can damage the symbiotic algae living in corals (zooxanthellae), causing these important organisms to leave the coral host. Without zooxanthellae to enable photosynthesis, corals usually die immediately following coral bleaching events (Hoegh-Guldberg 1999). While coral reefs can recover from bleaching, it is extremely unlikely if bleaching conditions continue year after year. The Great Barrier Reef, the world’s largest continuous coral reef, could face severe bleaching events every year by the year 2030. The reef south of Cooktown is likely to be severely affected by sea temperature rise within the next 20-40 years (Hoegh-Guldberg, 1999). Mass bleaching, leading to death of corals, will become a more frequent event on Australian coral reefs in the coming decades. Tourism on the Great Barrier Reef had a financial value of $682 million in 1991-92. Other uses include commercial fishing, private boating and research and the total value of all uses is estimated at close to $1 billion per year directly spent and earned in the GBR World Heritage Area and adjacent mainland regions (Driml 1994).
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Great Barrier Reef Great Barrier Reef, Image courtesy of World Wide Fund For Nature
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