Studying how green crabs predate soft-shell clams… and can we stop them?


Dr. Brian Beal of the Downeast Institute and U. Maine Machias has studied green crabs for a long time. He’s also interested in how to prevent them from gobbling up a critter that Mainers and green crabs both love: soft-shell clams.

Soft shell clams are, or were, a major source of income for Maine’s coastal communities. Recently, softshell clams have been under threat from an invasive green crab population boom. As a result, clam populations have been low, and blue mussels, another Maine staple, are all but gone. In the past these population booms were ended by cold, Maine winters. Dr. Beal is worried that might not be something we can count on in the future. To keep clams a viable fishery in Maine, we’re going to need to learn to deal with green crabs.

Photo by Christine Voyer

Dr. Beal has designed and set up a simple test of whether Maine clammers can protect their catch with meshes or barriers from crabs. He’s got several sites with plastic flower pots full of seed clams (itty, bitty clams from the hatchery). Each site has different types of protective coverings to keep green crabs out. These protective treatments may also help keep back other natural predators of softshell clams like predaceous worms. Team VS, folks from Wells NERR and a few local teachers helped set up two of these sites, one in Wells and the other in Portland. David Vaughan and his students at the Waynflete school will help Dr. Beal dig up the Portland site this fall.

Photo by Sarah Kearsley

When the pots are dug up, we'll see how the seed clams fared, getting to see both survival rate and growth rate. Scientists think that seagulls are keeping crabs in check in the upper intertidal zones which helps wild clams. Dr. Beal can use data from his study to compare survival and growth rate in the lower intertidal and upper intertidal.

Here’s to hoping that Dr. Beal has uncovered some solutions to keeping green crabs off softshell clams!