Shellfish threatened by rising levels of CO2

Washington, May 27 (ANI): In a new research, scientists have discovered that shellfish are threatened from rising levels of atmospheric carbon dioxide (CO2) that contribute to the acidification of open ocean.

The research was done by Smithsonian scientists, led by Whitman Miller, ecologist at the Smithsonian Environmental Research Center in Edgewater, Maryland.

For shellfish and other organisms that have 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.

Increased acidity tips the balance toward bicarbonate formation and away from carbonate.

Less carbonate in the water means that shellfish have fewer building blocks to generate their shells. 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," said Miller.

For many calcifying organisms, CO2-induced acidification poses a serious challenge because these organisms may experience reduced rates of growth and calcification that "when combined with other environmental stresses, could spell disaster," he added.

In Miller's study, the larvae of Eastern oysters and Suminoe oysters were cultured in estuarine water that was held at four separate CO2 concentrations, reflecting atmospheric conditions from the pre-industrial era, the present, and those predicted in the coming 50 and 100 years.

To test the effects of acidification, Miller monitored their growth and measured the amounts of calcium carbonate deposited in larval shells over the course of one month.

Miller and his team found that Eastern oysters experienced a 16 percent decrease in shell area and a 42 percent reduction in calcium content when specimens in the pre-industrial CO2 treatment were compared with those exposed to the levels predicted for the year 2100.

The results reported suggest that the impacts of acidification may be tied to a species' unique evolutionary history and environmental setting, implying that predictions may be more complex than previously thought.

"In the Chesapeake Bay, oysters are barely holding on, where disease and overfishing have nearly wiped them out," said Miller. Whether acidification will push Eastern oysters, and the many species that depend on them, beyond a critical tipping point remains to be seen," he added. (ANI)