Fisherman Bill Fetzer, of Bayville, prepares to empty a basket...

Fisherman Bill Fetzer, of Bayville, prepares to empty a basket of clams onto a cull rack for sorting and counting aboard his boat, The Rolic. He fishes Long Island Sound full time. (July 13, 2010) Credit: Jesse Newman

Rising greenhouse gases are lowering the pH level of the world's oceans, diminishing the population of shellfish, including many common around Long Island, according to new Stony Brook University research.

In a paper published Monday, two researchers studied the impact of higher carbon-dioxide levels on oceans since industrial times. They tracked the development of hard clam and bay scallop larvae in labs that mimicked carbon dioxide levels of 200 years ago. Then they compared them to shellfish grown in waters at today's CO2 levels, and then in estimated future levels. The lowering of ocean pH levels, known as ocean acidification, is the result of centuries of burning fossil fuels.

The findings: Clams and scallops grown under preindustrial CO2 levels showed "significantly faster growth and metamorphosis as well as higher survival" rates and thicker, healthier shells.

The study, conducted by professor Christopher Gobler and PhD candidate Stephanie Talmage of the university's Marine and Atmospheric Science Department, appeared in the journal Proceedings of the National Academy of Sciences.

"Our results suggest that ocean acidification is another process that may have contributed to the declines of these [shellfish] populations in the recent past and could further impact bivalve population densities and diversity in the future," the study says.

Gobler said Monday that because it's so difficult to alter the large-scale impacts of ocean acidification, the primary beneficiaries of the study may be local shellfish hatcheries.

"Aquaculture facilities can buffer their seawater and increase the levels of pH to benefit survival of shellfish," he said, noting shellfish for the study came from the East Hampton Town hatchery.

Roger Tollefsen, president of the New York Seafood Council and a chemical engineer, said the study provides clear evidence of harmful impacts of greenhouse gases beyond warming.

"There's no question this is another reason to look at what we're doing to our environment," Tollefsen said, "pH is as important to the sea as pH in your blood is to you."

But he said acidification alone can't explain the 95 percent drop in shellfish populations in the waters around Long Island since 1975. Tollefsen said he believes efforts to curb nitrogen runoff in waterways such as the Peconic Bay have depleted natural algae and reduced a crucial food for shellfish. He has been urging scientists and state environmental officials to continue to fund the water studies to examine the theory. As for CO2, Gobler said reversing its impact in oceans "could be more difficult than anticipated," because "when you're dealing with a global phenomenon it's harder to counteract."

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