BAR HARBOR, MAINE – Scientists at the Mount Desert Island Biological Laboratory are trying to find out if an invasive species of green crabs is behind the recent loss of eelgrass in Frenchman Bay. They are also asking for the public’s help in finding out where eelgrass is still growing along the coast of the Gulf of Maine by reporting sightings at anecdata.org.
Since 2007, MDIBL has been leading a collaborative effort to restore eelgrass in upper Frenchman Bay, where bottom dragging by shellfish harvesters was thought to have caused a significant drop in the amount of eelgrass over the past fifteen years. Thanks to the efforts of scores of volunteers and an agreement with harvesters about not dragging in restoration areas, eelgrass had been proliferating off Hadley Point in Bar Harbor and Berry Cove in Lamoine. However, the grass, which dies back in late summer, did not come back this spring.
“Green crabs are known to destroy eelgrass,” says Jane Disney, Ph.D., director of the eelgrass program at MDIBL. “Lobstermen in Frenchman Bay have reported that they are pulling up more green crabs than ever before in their traps, and local clammers report that the flats are blanketed with green crabs when they get started at dawn.”
Dr. Disney also reports that eelgrass shoots that have washed ashore in upper Frenchman Bay, Northeast Harbor, and at Sand Beach in Acadia National Park have the characteristic frayed stems of plants cut by green crabs (Carcinus maenas). Her laboratory will be conducting green crab density studies and exclusion studies in the coming weeks.
MDIBL scientists and interns are looking into other possible factors contributing to the loss. They are gathering data about the conditions in the bay this year, setting up experiments to compare the few sites where eelgrass is growing and those where it is not, and ruling out the possibility of disease or pathogens. They are also considering temperature as a direct or indirect cause: 2012 was the hottest year on record for the water of the Gulf of Maine.
The Department of Marine Resources has maps of where eelgrass was growing in Maine between 2001 and 2010. However, no formal statewide monitoring of eelgrass is being done this year.
“Because of the amount of data we want to collect and the small timeframe left in this growing season for collecting it, we decided to try ‘crowd sourcing’ the project,” Disney said.
Over 30 sites have been reported on the collaborative map so far, including additional large-scale losses in Maquoit Bay near Freeport. Camp Kieve and Wavus campers have been mapping eelgrass beds in their areas, and Chewonki campers in Wiscasset are planning on doing the same. Fishermen and kayak guides have been reporting their findings as well.
Eelgrass is an important native seagrass that grows in shallow coastal areas and river estuaries. It grows in thick beds that look like underwater meadows and offers many benefits to the marine ecosystem. It oxygenates water and mud allowing organisms to settle among its roots, stabilizes sediments, protects against erosion and storm surges by damping wave energy, improves water quality by taking up nitrogen and phosphorus, and provides essential nursery habitat for commercially valuable fish species such as cod, hake, lobster, clams and mussels. It also absorbs carbon and can play a role in mitigating climate change.
To learn more about eelgrass and to report your observations, visit anecdata.org.