An aggressive form of the invasive green crab, typically found in Canadian waters, is threatening the coastal ecosystem of Maine as waters warm and the crabs destroy eelgrass and soft-shell clams. The green crab — originally from Europe — has a rich history of invading North American waters, and this latest threat may be greater than feared according to an expert on the species.
Robin Hadlock Seeley, a retired senior research associate at Cornell University, studied green crabs at Shoals Marine Laboratory on Appledore Island, Maine, and is a Maine native and resident.
Hadlock Seeley says:
“Though green crabs in Canada look like Maine green crabs, it has been known for some time that there are northern and southern types of green crabs with detectable genetic differences reflecting two invasion events. If these preliminary results on crab aggression are borne out by further research, and if the Canadian genetic variant increases in Maine along with increasing ocean temperatures, the green crab threat in the U.S. may be even greater than fisheries managers and conservationists have feared.”
Hadlock Seeley offers this additional background:
“European green crabs are an early North American invasive species and one of the most destructive. This crab appeared in Maine at the end of the 19th century and its appearance is associated with an evolutionary change in its snail prey. Green crabs consume nearly everything in their path, causing the loss of soft shell clam populations — and clam digging jobs — herbivore snails, and eel grass; and degrading salt marshes.
“The crab population increases with ocean temperature. In the 1950’s, Maine coastal waters warmed for a few years and the crab population surged, devastating the soft shell clam industry. The following decades saw cooling ocean waters and the green crab threat abated. Clams returned. But now that the Gulf of Maine is warming faster than other parts of the ocean, the green crab threat has recently returned with a vengeance."