Coral Reefs are Vanishing Faster than Rainforests

Coral reefs in the Indo-Pacific are disappearing twice as fast as tropical rainforests, say researchers. They have completed the first comprehensive survey of coral reefs in this region, which is home to 75% of the world's reefs.

John Bruno and Elizabeth Selig of the University of North Carolina at Chapel Hill in the US compiled data from 6000 studies that between them tracked the fate of 2600 reefs in the Indo-Pacific between 1968 and 2004. They used the extent to which reefs were covered by live coral as an indication of their health.

"The corals themselves build their limestone foundation, so if the surface of the reef is not covered with live tissue that is continually secreting it, the reef can erode fairly quickly," explains Selig.
She and Bruno found that coral cover declined by 1% per year on average between 1968 and 2004. For comparison, tropical rainforests declined by 0.4% per year between 1990 and 1997.

Steep decline

In the early 1980s about 40% of reefs were covered with live coral, but that number had halved by 2003. Today only 2% of Indo-Pacific reefs have the same amount of live coral as they did in the 1980s.

That's much less than expected, says Selig. She explains that it was generally thought that Indo-Pacific reefs were faring much better than Caribbean reefs, a bias she believes stems from the fact that Caribbean reefs have been studied more extensively. Caribbean reefs are declining by 1.5% a year (Science vol 301p 929).

The researchers found little difference between protected and unprotected reefs. "Well-managed reefs are definitely doing better in terms of fish population but not in terms of coral cover," Selig told New Scientist.

This uniformity has led Selig and Bruno to conclude that warming seas as a result of climate change are likely to be driving the rapid decline. Warmer oceans cause coral bleaching because higher temperatures kill their symbiotic algae. They also help diseases spread across reefs.

International effort

Selig and Bruno say local policies – for instance to limit harmful fishing methods and reduce continental run-off – can do much to help maintain the corals in the short-term, but long-term conservation will require an international effort to tackle global warming.

"There certainly are local problems that [reef] managers can and are addressing," says Bruno. "But there are problems that are happening at regional and global scales that no single manager, or even federal authority can cope with. Managers can't manage ocean temperatures."

In 2004, research led by Andrew Baker of Columbia University in New York, US, suggested that coral reefs might adapt to live in warmer oceans (see Corals adapt to cope with global warming).

Bruno says some reefs in their survey were recovering from previous damage – sometimes thanks to effective protection, sometimes independently of human intervention. But overall the reefs do not appear to be adapting fast enough to stem their decline.

Baker believes more research is needed to explore whether anything can be done to boost corals' natural ability to adapt to change. “This might include attempts to inoculate the largest and oldest colonies on reefs with heat-tolerant symbiotic algae that might help them survive bleaching events,” he says. Journal reference: PLoSONE (DOI: 10.1371/journal.pone.0000711)

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NewScientist.com news service
Catherine Brahic