Mark Green, associate professor of marine science at Saint Joseph's College and a resident of Peaks Island, has received a $419,898 National Science Foundation grant to continue research on two commercially valuable clam species in Casco Bay. The three-year grant, the second Green has received from the National Science Foundation, will include field work along the shorelines in Freeport and South Portland.
The study will definitively answer the question about why so many juvenile hardshell and softshell clams die. Green's earlier study, which suggested tiny clams die because their shells dissolve under naturally occurring acidic conditions, countered a nearly 100-year-old theory suggesting predation as the dominant cause. Roughly 98 percent of clams die off within the first two weeks of life in the sediment, leading to a much-lowered abundance of harvestable adults.
According to Green, the research has an applied aspect. "If we conclude most juvenile clams die because their shells dissolve, we might greatly increase clam yields by 'treating' the marine sediment where clams live," Green states. One way to do this, he adds, is to grind up clams shells discarded from commercial and retail operations and spread the mixture on clam beds. "This would effectively buffer some regions of the sediment and allow small zones of less acidic sediment where the smaller clams could flourish and grow to a viable size class," Green notes.
The shellfish industry in Maine generates roughly $16 million per year, and the research is applicable to clam habitat throughout the world.
In the laboratory phase of the research, Green's experiments will manipulate the chemistry of the marine sediment in which clams live, and look at the effect of changing pH on the clam death rate, using different size classes and species of clams. Field studies at the two sites will sample clams every other day immediately following their transition from the water column to the sediment - usually mid-summer - to see if their shells are dissolving. Sampling locations will take into account tidal variations and the type of sediment where the clams live.
The results from the field and laboratory will be used to model scenarios of clam mortality due to man-made and natural changes in the sediment's acidic levels. Green says that as greenhouse gases dump carbon dioxide into the atmosphere and, ultimately, into the oceans, it mixes with ocean water to create carbonic acid.
"It's unknown whether this chain reaction from greenhouse gases could play a future role in dissolving the juvenile clam shells," Green says. "The addition of carbon dioxide from human activities such as fossil fuel combustion could exacerbate dissolution of juvenile clams by further increasing the acid content of the ocean water that lies above the sediments in which they reside," he adds. According to Green, ocean acidification is a recently acknowledged man-made process that has far-reaching implications for the overall health of the ocean.
Experiments with simulated seawater and sediment conditions will determine whether juvenile clams can themselves select less acidic conditions as they search for suitable habitat when transitioning from the water to the sediment. These experiments will be performed at Chesapeake Biological Laboratory in Maryland, where Dr. George Waldbusser will aid in running the experiments.
Green has hired Shannon Reilly of Windham as a full-time lab technician and will employ undergraduate marine science students at Saint Joseph's College as research assistants.
October 19, 2006 Contact: Charmaine Daniels at (207) 893-7723 or e-mail email@example.com