National Science Foundation study

Oceanographer seeks far-reaching solution to clam deaths

Mark Green and research assistant Shannon Reilly ’06

Lab technician Shannon Reilly ’06 and Dr. Mark Green will work with undergraduate marine science students on the clam research project funded by the National Science Foundation.

Associate professor of marine science Mark Green has received a $419,000 National Science Foundation grant to continue his research on two commercially valuable clam species in nearby Casco Bay. The three-year grant, which is the second Dr. Green has received from the National Science Foundation, will include field work along the shoreline in Freeport and South Portland.

The new study will definitively answer the question of why so many juvenile hardshell and softshell clams die, says Green. His 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 ocean sediment, leading to far fewer harvestable adults.

According to Green, the research can lead to real-world solutions. "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 is to grind up clams shells discarded from commercial and retail operations and spread the mixture on clam beds, he adds. "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 clam industry in the United States generates roughly $57 million per year, and Green's 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. With the grant funding, Green has hired Shannon Reilly '06 as a full-time lab technician and will employ undergraduate marine science students at Saint Joseph's College as research assistants, both in the lab and in the field.

Field studies at the two intertidal sites will provide more detailed sampling of juvenile clams than has ever been attempted before. The researchers 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 procedure involves manually extracting a 12-to 14-inch layer of the tidal flat - which can capture a sediment history of more than 12,000 years - using a small cylinder. Once back in the lab, precise measurements and controlled manipulation of the carbon dioxide levels of the clams' environment will allow Green to measure the rate of the clam shell dissolution. Field and laboratory results 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.

clam digger

"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 simulation experiments will be performed at Chesapeake Biological Laboratory in Maryland, where Dr. George Waldbusser will aid in running the experiments in cooperation with Dr. Green. Lab technician Shannon Reilly '06 and Dr. Mark Green will work with undergraduate marine science students on the clam research project funded by the National Science Foundation.

Professor will test use of laser light to deter predation of mussels

The Maine Aquaculture Innovation Center awarded Dr. Mark Green nearly $9,000 for a study on the use of submerged green-laser light to deter sea ducks from feeding on cultivated mussels. Maine's 13 mussel farms face losing up to hundreds of tons of mussels each year because of predation by sea ducks, primarily eider ducks. Worldwide, millions of pounds of cultured product are eaten annually by eider ducks.

Mussel growers often use a raft system to culture mussels, but even with huge nets draped from the raft to prevent predation, the growers can still suffer significant losses. If the green-laser light system works on the rafts, it is potentially less expensive, far easier to use and a much better deterrent to predation than the nets.

Green will construct and test a low-cost, submersible, green-laser light system in the Casco Bay Estuary, Gulf of Maine. Field studies will run periodically for a year beginning this winter. The use of above-water, hand-held lasers - though shown to be a non-lethal and environmentally benign way of scaring away certain bird species - is labor intensive. The submerged laser light system uses solar power and interfaces with timing devices, so it can be left for weeks at a time with light maintenance every 4 to 7 days.

The laser light system could prevent hundreds of thousands of dollars from being lost because of mussel predation and translate into more money for industry growth and profitability, according to Green.