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May 10, 2004 Contact: Charmaine Daniels at (207) 893-7723 or e-mail cdaniels@sjcme.edu

Research leads to important discovery about clam die-off

With the help of a four-year National Science Foundation grant, Dr. Mark Green of Saint Joseph's College has made an important discovery affecting Maine's $12 million soft-shell clam industry. In a major contribution that merges pure and applied science, Green determined that a large percentage of early-juvenile clams die within the first weeks of life in the mud of Casco Bay because their shells dissolve.

For more than 40 years scientists have published work connecting the loss of these juvenile clams to predators, but Green has shown that a large percentage of juvenile clams die when their shells dissolve as a result of natural geochemical reactions producing weak acids in the top layer of sediments where they live.

"The applied part of this research is that if we know what kills the juvenile clams, we may be able to substantially increase the yield of the commercial harvest by modifying sediments so that juveniles are no longer exposed to these natural acids," Green continues. Buffering sediments with calcium carbonate, the material that composes a clam shell, when seeding clam flats or when clams set naturally is one way to do this, he says.

"There may be ways to prevent the significant loss of juvenile clams. Even if we decrease the mortality rates by only several percentage points, it would translate to a potentially huge increase in yield and a significant contribution to the Maine economy," claims Green.

The research could help sea farmers become more efficient and profitable by detailing when and where they should put out their stock for maximum survival, as well as explain changes in the abundance of bivalves.

Scientists first speculated on the loss of clams in the 1960s, but no one knew for certain why they died. Quantifying reasons for the high mortality was difficult, largely because juvenile clams can't be seen without a microscope, Green states. His study, which used undergraduate environmental science majors as research assistants, cleared up the longstanding mystery by hauling up sediment "grabs" at five stations in Casco Bay and examining them back at the campus lab.

"It just so happens that juvenile clams settle to the mud in Casco Bay during early summer when the pH of the top several millimeters of sediment is relatively low, making the very small clams susceptible to dissolving," he says.

Green points to evolutionary implications as well. For example, juveniles which are capable of more rapid growth might be better suited to survive this initial period since they can grow out of the early critical stage faster. "Our research shows that slightly larger juveniles are far less susceptible to dissolving than their smaller counterparts," adds Green, who teaches environmental and marine science at the campus in Standish.

Up until recent years, marine scientists assumed shell material dissolved in the deep sea, not in coastal regions. It was Green's research with world-renowned Dr. Robert Aller at Stony Brook University's Marine Sciences Research Center that showed shell material can dissolve in winter near-shore regions.

Besides a potential impact on the regional economy, Green's research may dramatically influence the work of paleoecologists who interpret the past by looking at fossil records that explain what the climate was like and community structure in ancient ocean communities. Scientists have largely assumed shells in near-shore zones don't dissolve and are, therefore, preserved in the fossil record. "If shells are actively dissolving, then some of their previous interpretations about past environments could be wrong," says Green. "What remains preserved in the fossil record may not be representative of all the species originally present," he adds.

"Dissolution Mortality of Juvenile Bivalves in Coastal Marine Deposits," Green's research results co-authored with students at Saint Joseph's College, is published in the current issue of Limnology & Oceanography.