The Heat Is Online

EnhancedCO2 Starves Coral Reefs

Carbon dioxide has choke-hold on coral reefs

By John Roach, Lycos ENN News, May 22, 2000

Scientists with a license to "play God" in a three-acre, glass-enclosed biosphere in the Arizona desert have learned a sobering truth: If humans stay addicted to carbon dioxide-spewing fossil fuels, the world's complex coral reef ecosystems will be reduced by as much as 40 percent by the middle of this century.

"Often times organisms have an incredible ability to adjust to environmental change," said Christopher Langdon, a researcher at Columbia University's Lamont Doherty Earth Observatory in Palisades, New York. But Langdon found that corals are unable to acclimate to reduced carbonate levels over prolonged periods.

Corals are tiny, soft-bodied organisms that thrive in large colonies in warm, shallow ocean waters. They secrete a substance called calcium carbonate to build skeletons that form reefs. Reefs in turn host ecosystems that are as diverse as rain forests and serve as natural breakwaters that prevent beach erosion.

Carbon dioxide reacts with carbonate to produce bicarbonate. The result is less carbonate available for corals to combine with calcium to form calcium carbonate. Less calcium carbonate translates to weaker coral reefs, less biodiversity and greater beach erosion.

"Coral growth is proportional to carbonate concentration," said Langdon, whose research appears in the June issue of Global Biogeochemical Cycles, a journal of the American Geophysical Union. "If carbon dioxide increases by 30 percent, you get a 30 percent reduction in growth."

By 2065, carbon dioxide levels are expected to be twice what they were before the Industrial Revolution. The increase is a portent of changes in the Earth's atmosphere, biosphere and hydrosphere, Langdon and colleagues note.

To determine the impact of changing seawater chemistry on coral reef calcification, the researchers reduced the carbonate concentration to projected levels for the year 2065 in a 28,525 square foot aquarium inside the Biosphere 2 complex near Tucson, Arizona.

They observed a significant reduction in calcification rates for the corals and coralline algae. When the researchers returned carbonate concentration to the current level, they observed a large increase in coral growth, proving that carbonate concentration and not some other factor limited the growth, said Langdon.

"There have been times in the geologic past when carbon dioxide has been high and reefs disappeared from the geologic record," he said. "When carbon dioxide levels fall, they (corals) grow back and become important (in the ecosystem) again."

To prevent the reduction of coral reefs, aggressive efforts to reduce the amount of carbon dioxide in the air are imperative, Langdon said. Fuel-efficient vehicles and carbon sequestration technology are two good places to start, he added.