In the Intertidal Zone
A $13 million soft-shell clam industry in Maine has been severely threatened by a combination of factors. Ocean acidification, linked to the increased carbon dioxide levels in the Earth’s atmosphere, inhibits shell growth in clams, oysters and other organisms. In addition, the free-floating, soft-shell clam larvae avoid burrowing into more acidic mud, which means they spend more time exposed to predators as they seek appropriate habitat. Two such predators are the milky ribbon worm and the invasive European green crab, Carcinus maenas. This crab has been in Maine since 1900, however a recent series of warm winters has allowed its population to explode. Juvenile soft-shell clams, which grow into “steamers,” are a significant food source for the green crabs.
Predation by these invasive crabs has decimated productive clam flats in Georgetown. In 2014, a Georgetown shellfish harvester partnered with a landowner and Manomet, https://www.manomet.org/ a non-profit organization, to establish an experimental clam farm. Baby clams from a hatchery were seeded into intertidal flats at Heal Eddy and then covered with plastic netting to protect the clams from green crabs. The Georgetown Conservation Commission, Shellfish Commission, and Georgetown Central School students all helped seed and monitor this project.
While there is yet some promise that a similar approach now underway on the flats of our neighboring Arrowsic Island may yield a commercially viable harvest in 2019, by 2018 the netting experiment at Heal Eddy had not yielded a sufficiently plentiful supply of growing soft shell clams to warrant continuation.
Manomet continues to use Heal Eddy as testing grounds for understanding the biological and financial components of clam farming.
Heal Eddy is also the site of a long-term green crab monitoring study. For the past five years, local citizens have monitored green crabs at Heal Eddy twice a month, year round. Over 4,000 crabs have been trapped at the site and their size, gender, and other physical characteristics meticulously recorded. Monitoring data from Heal Eddy is one of the longest running green crab monitoring sites in the state providing valuable information on the seasonal population dynamics of green crabs within the intertidal zone. This could contribute either to a commercial use for green crabs (restaurants are experimenting!) or improved methods for their eradication.