June 3, 2009
In a paper published last month in PLoS One, a team led by ecologist Whitman Miller, showed that the shells of Eastern oysters, Crassostrea virginica, the jewels of the Chesapeake Bay, will be slightly smaller (16 percent decrease in shell area) and weaker (42 percent reduction in calcium content) in the waters of 2100. The other species tested, the Suminoe oysters from Asia, showed no change in an acidic ocean.
“We are bound to our bodies like an oyster is to its shell,” said Plato, the ancient Greek philosopher.
But that was over 2,000 years ago, long before rising levels of carbon dioxide began to trap heat in our atmosphere and seep into our oceans. As CO2 dissolves into seawater, it is broken down into carbonic acid and hydrogen ions. Hydrogen determines whether a liquid is acidic or basic. The more hydrogen ions that leach into the ocean, the more acidic it becomes.
As more of the green house gas, carbon dioxide, is released, the world’s oceans are slowly becoming more acidic, and shellfish, like oysters are especially vulnerable to this kind of change. An acidic ocean hinders the ability of some species of oyster young to build their shells, scientists with the Smithsonian’s Environmental Research Center found.
According to the scientists, the results suggest that acidification may be tied to a species’ unique evolutionary history, 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,” Miller says. “Whether acidification will push Eastern oysters, and the many species that depend on them, beyond a critical tipping point remains to be seen.”
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