May 28, 2009

Rising CO2 levels threaten shellfish

U.S. marine scientists say they have discovered that rising levels of atmospheric carbon dioxide are threatening shellfish populations in many ecosystems.

The researchers, led by ecologist Whitman Miller of the Smithsonian Environmental Research Center, said the increasing CO2 levels are contributing to the acidification of open ocean, coastal and estuarine waters.

For shellfish and other organisms having calcium carbonate shells and structures, the problem begins when atmospheric CO2 dissolves in seawater and creates carbonic acid that is then rapidly transformed into carbonate and bicarbonate ions in the water, the researchers said. Increased acidity tips the balance toward bicarbonate formation and away from carbonate -- and less carbonate in the water means shellfish have fewer building blocks to generate their shells. The researchers said if the water is acidic enough, shells can even begin to dissolve.

Estuarine and coastal ecosystems may be especially vulnerable to changes in water chemistry caused by elevated CO2 because their relative shallowness, reduced salinity and lower alkalinity makes them inherently less buffered to changes in pH than in the open ocean, Miller said.

The study appears in the online journal PLoS One.