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Bloomberg.com: Australia & New Zealand: "Reef Corals Face Extinction Due to Global Warming, Over-Fishing

By Alex Morales

Reef Corals Face Extinction Due to Global Warming, Over-Fishing

By Alex Morales

July 10 (Bloomberg) -- A third of reef-building corals face extinction as global warming adds to other man-made threats including over-fishing and coastal development.

A team of 39 researchers assessed the state of 704 coral species and found 32.8 percent are threatened with extinction. The study results, published today in the journal Science, are ``worse than expected,'' said co-author Suzanne Livingstone, a marine biologist at Old Dominion University in Norfolk, Virginia.

``When we began this process, we didn't think it would be anywhere near as high as that,'' Livingstone, also a marine species assessor for the International Union for Conservation of Nature, said yesterday in a telephone interview. ``Climate change is the overarching threat which comes in on a much larger, global scale,'' adding to localized disturbances, she said.

The fate of corals is crucial to the livelihoods of millions of coastal dwellers around the world. Reefs are worth about $30 billion a year to the global economy, through tourism, fisheries and coastal protection, according to the Millennium Ecosystem Assessment, a United-Nations supervised study published in 2005.

Corals build reefs by secreting exoskeletons of calcium carbonate that accumulate over hundreds of years. The corals have a symbiotic relationship with zooxanthellae, single-celled algae that shelter in their tissues and provide the reef-building organisms with nutrition and energy, enabling faster growth.

`Irreversible Declines'

Warmer temperatures, disease and pollution cause corals to expel the zooxanthellae. Because the algae are the source of the corals' bright colors, when they are rejected, it is known as bleaching, and it makes corals more likely to die.

``If bleaching events become very frequent, many species may be unable to re-establish breeding populations before subsequent bleaching causes potentially irreversible declines,'' the scientists wrote. ``If corals cannot adapt, the cascading effects of the functional loss of reef ecosystems will threaten the geologic structure of reefs and their coastal protection function, and have huge economic effects on food security for hundreds of millions of people dependent on reef fish.''

The Caribbean and western Pacific were identified by the researchers as the areas where most corals are threatened.

Corals are undermined by the buildup of silt, and run-off of nutrients from fertilizers into the sea, which creates surface algal blooms. Both processes block light from reaching the zooxanthellae. Over-fishing can change the balance of the food chain by removing large herbivores, and some reefs are destroyed to make way for coastal development.

Stresses

While the best way to help preserve corals is to cut the emissions of greenhouse gases blamed for rising temperatures, tackling local threats by tightening regulations on fishing, coastal building and marine protection will reduce stress to corals, Livingstone said.

``One of the big problems is these localized disturbances from human activities in conjunction with climate change,'' Livingstone said. ``They are much more resistant and able to adapt if there are no other stresses acting on them.''

Results of the Gland, Switzerland-based IUCN's assessment will be included in the group's Red List of endangered species in October. In addition to the 704 species rated by the scientists, insufficient data existed on a further 141 reef-building corals.

To contact the reporter on this story: Alex Morales in London at amorales2@bloomberg.net.
Last Updated: July 10, 2008 14:00 EDT