Pacific coral reefs dying faster than expected

Posted: 14 August 2007

The central and western Pacific Ocean contains 75 per cent of the world's coral reefs and the world's highest coral diversity, but corals in this region are vanishing much more rapidly than previously thought, according to new research. ENS reports:

The reefs are disappearing at a rate of one per cent per year, a decline that began decades earlier than expected, scientists from the University of North Carolina-Chapel Hill have learned. The study provides the first regional-scale and long-term analysis of coral loss in the central and western Pacific, where relatively little was known about patterns of reef loss.

Butterfly fish on a coral reef
Butterfly fish on a coral reef
Butterfly fish on a coral reef, Chuuk Island, Micronesia. Photo © James McVey / NOAA
"We have already lost half of the world's reef-building corals," said John Bruno, lead study author and associate professor of marine ecology and conservation in the Department of Marine Sciences at UNC-Chapel Hill.

Bruno and ecology graduate student Elizabeth Selig, compiled and analysed a database of 6,000 surveys performed between 1968 and 2004 of more than 2,600 Indo-Pacific coral reefs. The surveys tallied coral cover, a measure of the ocean floor area covered by living corals.

Scientists rely on coral cover as a key indicator of reef habitat quality and quantity, the way forest scientists would measure an area covered by a tree canopy as a gauge of tropical forest loss.

Bruno and Selig found that coral cover in the Indo-Pacific region declined from 40 percent in the early 1980s to about 20 percent by 2003. They were surprised to find that coral cover was similar whether reefs were maintained by conservationists or were unprotected.

"This consistent pattern of decline across the entire Indo-Pacific indicates that coral loss is a global phenomenon, likely due in part to large-scale stressors such as climate change," Bruno said.

Historically, coral cover hovered around 50 per cent. But today, only about two per cent of reefs in the Indo-Pacific have coral cover close to the historical baseline. Nearly 600 square miles of reef have disappeared each year since the late 1960s, twice the rate of rainforest loss, the scientists found.

Coral disease, predators, rising ocean temperatures due to climate change, nutrient pollution, destructive fishing practices and sediment run-off from coastal development can all destroy reef communities.

"Indo-Pacific reefs have played an important economic and cultural role in the region for hundreds of years and their continued decline could mean the loss of millions of dollars in fisheries and tourism. It's like when everything in the forest is gone except for little twigs, a few lone trees," Selig said.

Although reefs cover less than one percent of the ocean globally, they play an crucial role for coastal communities, Bruno said. They underpin the fisheries and tourism industries and buffer coastlines from storms. When corals die, these benefits disappear.

Policy makers and resource managers searching for ways to reverse coral loss do have options, Bruno said.

"We can do a far better job of developing technologies and implementing smart policies that will offset climate change," he said. "We can also work on mitigating the effects of other stressors to corals including nutrient pollution and destructive fishing practices."

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