Population Genetics of the Invasive European Green Crab, Carcinus maneas and its Role in Eelgrass Loss in the Gulf of Maine

Mary Badger, Smith College


CrabGraph.jpgAbstract: In 2013, there was a devastating loss of eelgrass (Zoestra marina) in upper Frenchman Bay, Mount Desert Island, Maine. This study examined the relationship between the most recent invasion of novel haplotypes of the European Green Crab (Carnicus maneas) and the decline of eelgrass in upper Frenchman Bay. While C. maneas is an invasive species that has been present in the Gulf of Maine for over 100 years, a second invasion of C. maneas in Nova Scotia occurred during the 1980s and 1990s, bringing novel haplotypes of the species that have been cited to be more cold tolerant and voracious as compared to other haplotypes.  The presence of these new haplotypes has been hypothesized to be a contributing factor to habitat destruction along the Maine coast. In 2013, northern haplotypes of green crab were documented in upper Frenchman Bay where the eelgrass had disappeared. In order to assess this relationship, the cytochrome oxidase I (COI) haplotype of the crabs at sites around Mount Desert Island was determined as well as the abundance of the eelgrass at corresponding study sites. The study did not find a significant correlation between the presence of northern green crab haplotypes and eelgrass abundance at the study sites. This indicates that the status of eelgrass health is not dependent on the genetic composition of green crabs that are present.  It is more likely that factors such as green crab abundance or water quality are contributing to the declining health of eelgrass beds along the Maine coast.


Eelgrass (Zostera marina L.) loss in Maine: An investigation into possible causes

Alden Dirks, Swarthmore College

Abstract: Eelgrass (Zostera marina L.) supplies myriad ecosystem services that make it an indispensable cornerstone of coastal environments. The complete disappearance of eelgrass in upper Frenchman Bay, Mt. Desert Island (MDI), Maine, in 2013 matched a precipitous drop in the concentration of dissolved silica (DSi). Eelgrass in outer Frenchman Bay and other locations around MDI appeared to be intact; however there were no DSi data to compare with upper Frenchman Bay locations. To investigate the relationship between eelgrass health and DSi, we determined eelgrass abundance and biomass at six locations around MDI. Furthermore, we measured dissolved nutrient concentrations in the water column as well as tensile strength and nutrient composition of tissue samples. We found a positive relationship between eelgrass abundance and biomass, and a positive relationship between biomass and the concentration of nitrite and nitrate. In addition, tensile strength was significantly different across the six sample sites. However, neither abundance nor tensile strength was significantly correlated with nutrient composition of the plants or water quality.  These results reveal a deeper complexity to the issue of eelgrass abundance and tensile strength that requires further nuanced investigation into other factors such as local geography, oceanographic currents, and sediment type as they relate to eelgrass viability.


Green Crabs in Frenchman Bay: The Continuing Saga

Everyone has been hearing a lot about green crabs and their destructive nature these days.  Frenchman Bay definitely has its share of them.  Green crabs are an invasive species from Europe that were unintentionally introduced to the Eastern shores of America in the 1800s. Their numbers have been increasing ever since.


Maine Sea Grant sponsored a Green Crab Summit at University of Maine in December 2013.  Many Frenchman Bay Partners were in attendance.  The presentations provided a lot of detail about green crabs, their life history, and their impacts on shellfish populations and as well as salt marshes and seagrass beds.  They can be viewed at http://www.seagrant.umaine.edu/green-crab-summit. Several Frenchman Bay Partners, including representatives of the Bar Harbor Shellfish Committee, MDI Bio Lab, and Frenchman Bay Regional Shellfish Committee participated in a  one-day, state-wide survey of green crabs last summer, focusing their sampling efforts in Bar Harbor, Lamoine, Trenton, Sorrento and Sullivan.  The results of the survey can be found on the Maine DMR website .  The report concludes that green crabs are present throughout the state and in numbers that represent a detrimental impact to bivalve shellfish.


Population Genetics of Invasive Green Crab

Click here to access an academic poster by Bates College student Camilla Nivison, and advisors Larissa Williams and William Ambrose detailing the population genetics of invasive green crab, Carcinus maenas, in the Gulf of Maine. One of the most successful marine invaders, Carcinus maenas has established populations on all temperate coasts. The Read more…

Mudflat project updates

At College of the Atlantic, students have been developing protocols for measuring the pH on clamflats, and comparing different meters to see which ones are the most precise, and this fall will measure pH on several flats in Bar Harbor. One student, Katie O’Brien, has also buried clam pre-weighed clam at three different sites in look at rate of weight loss of shells as a measurement of the potential threat to clam growth from low pH on clamflats. Those clams are being collected in October and if the technique shows promise, the study will be expanded next year.