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The European green crab (Carcinus maenas) is a harmful invasive species linked to the decline of the soft-shell clam industry in New England and the degradation and loss of critical eelgrass and salt marsh habitat. Compounding these issues is the link between increasing green crab abundance and increasing ocean temperature, which has had severe ecological and socio-economic consequences in areas such as the Gulf of Maine, where warming is occurring faster than 99% of the world’s oceans.
In 2018, Manomet began our long-term intertidal crab monitoring project to track green crab population trends. We also collect data on native crabs and other invasive species such as the Asian shore crab. Our monitoring sites span much of mid-Coast Maine, from Damariscotta to Yarmouth. We target the low intertidal area of rocky shorelines. To survey green crab populations, we use a meter square quadrat as a unit of measurement, and we sample 10 of these quadrats at each site every month from approximately April or May through November. For each quadrat, we collect all the crabs that we find and take several measurements, including size, sex, shell condition, and color.