Coastal development, destructive fishing practices that include cyanide poisoning and dynamiting, and pollution from both land and marine sources are all threatening reefs across the globe, according to the two-year study carried out by the Cambridge-based World Conservation Monitoring Centre, and two other conservation bodies in the US and the Philippines.
Coral reefs are often thought of as "the rainforests of the sea" both for the huge numbers of species they contain, and their vulnerability to degradation.
Occupying less than a quarter of one per cent of the marine environment, they nevertheless shelter more than 25 per cent of all known fish species; more than 4,000 have so far been described, along with 800 species of reef-building corals.
Until now, the only information on the status of coral reefs worldwide was a 1993 estimate, much quoted but based on guesswork and anecdotal evidence, which indicated that 10 per cent of the world's reefs were dead and 30 per cent were likely to die within 10 to 20 years.
The new study, the first systematic global assessment, confirms that reefs are seriously threatened in most parts of the world: just under 60 per cent in total are believed to be at risk.
South-east Asia is the worst region, with more than 80 per cent of the reefs in the Philippines and Indonesia in jeopardy, followed by the Caribbean, where two thirds are in danger. In the Indian Ocean, and in the Red Sea and the Arabian Gulf, more than half are threatened. Only the Pacific is in relatively good shape - more than 60 per cent of its reefs are thought to be "low risk".
"What is particularly saddening about all of this is that it is totally unnecessary," said Mark Spalding, the WCMC's coral reef expert and UK co-author of the review. "Studies from around the world are now showing that protecting reefs isn't just an exercise in pleasing the environmentalists, but that it makes sound economic sense. Good management of these resources has shown booming and sustainable fish-yields and huge revenues from tourism, while leaving an economically crucial heritage for future generations."
The report estimates global revenues arising from coral reefs at $375bn (pounds 245bn) and says that more than 100 countries stand to benefit from tourism- related income derived from their reefs.
But in too many, destruction is continuing. The growth of coastal cities and towns generates a series of threats: outright destruction from the building of airports and harbours, dredging to keep shipping channels open, and mining for construction materials. Most damaging are the indirect effects of development: sewage and agricultural pollution produce algae that block out the sunlight that corals need to survive.
Unregulated tourism produces trampling, destruction of coral for souvenirs and the sewage discharge and overfishing associated with resorts. Overfishing is a problem in many places, often taking out several key fish species, upsetting the ecological balance and leading again to destructive algal blooms. Destructive fishing with poisons and explosives damages reefs directly, and oil spills are another threat.
Despite the bad news, however, there are a number of success stories, such as the Great Barrier Reef in Australia, which has been kept healthy, the study says, by careful management.
'Reefs at Risk: A Map-Based Indicator of Potential Threats to the World's Coral Reefs'. World Conservation Monitoring Centre, World Resources Institute #and the International Center for Living Marine Aquatic Resources.
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