Eelgrass study seen as key to protecting Maine clam flats from green crab devastation

Posted Aug. 23, 2013, at 2:09 p.m.
Last modified Aug. 23, 2013, at 3:16 p.m.

FREEPORT, Maine — As Maine’s softshell clam industry reels from the devastating invasion of European green crabs, local harvesters hope a new study of eelgrass habitat might also provide clues to protecting the state’s lucrative clam resource from the voracious creatures.

Early Friday morning, U.S. Geological Survey scientist Hilary Neckles led a team of volunteers into the thick, gray mud off Little Flying Point in Maquoit Bay. There, the team began assembling “exclosures” designed to protect several 100-square-foot pens from the crabs and allow transplanted eelgrass to grow undisturbed within.

Until 2007, eelgrass flourished in shallow Maquoit Bay, according to Neckles, but it then began to decline. By July 2013, nearly all the eelgrass was gone from the intertidal portion of the bay.

At the same time, the green crab population “exploded,” Neckles wrote in her project description, and eelgrass shoots were found “clipped and shredded” at the base — a sure sign that they had been destroyed by green crabs.

Neckles hypothesizes that the crabs are at least in part responsible for the decline in eelgrass. Local clammers are sure of it, and say the crabs are also destroying just about everything else in the bay.

Pounding the structure’s wooden posts deep in the mud on Friday, Brunswick clammer Chris Green said green crabs eat other crabs and lobsters, posing a major threat to the population of species that local fishermen rely on for their livelihoods.

“This is potentially catastrophic for the shorelines — for the ecosystem in the area,” he said.

Green crabs have crawled through the Brunswick mudflats for years, but in the last 18 months “the population has increased significantly to the point where [controlling them] now becomes a priority,” Brunswick Marine Resources Officer Dan Devereaux said.

Harvesters in Freeport identified green crabs as a problem and with town funding, they enlisted the services of environmental consultant Darcie Couture to assess the impact on the shellfish resource.

Couture, of Resource Access International, and formerly with the Maine Department of Marine Resources, said the crabs “are probably the biggest issue out there facing shellfish harvesters in the area … it’s really a problem every [coastal] town has. Just not all of them realize it yet.”

In Freeport, harvesters have set traps for the crabs and installed fencing to keep them from the shellfish beds. According to Devereaux, Freeport harvesters have removed tens of thousands of pounds of the crabs and given them away as compost. Brunswick harvesters now trap the crabs as well, and some are given to local lobstermen as bait.

European green crabs have lived off American waters since stowing away on ships during the late 1800s, according to Couture. They then “crept their way up the Eastern Seaboard,” and were first reported in Maine in the early 20th century.

When their numbers increased in the 1950s, the infestation was quelled by a series of particularly harsh winters.

But a trend toward warmer-than-average winters doesn’t suggest that solution is likely this time.

Neckles said it remains to be seen whether green crabs can be pinpointed as a cause of eelgrass decline, although studies in Nova Scotia have shown that to be the case.

“In one bay, they had a very intensive removal program where in 2010 or 2011 they removed over 1 million crabs and were now restoring eelgrass successfully,” she said.

Couture is more definite about the impact the crabs are having. Only a month into the Freeport study, she said “early results are showing significant differences” using fencing to keep the crabs away from clam beds.

And Devereaux said he hopes Brunswick will undertake an effort next year to install similar fencing to protect their beds from the green crabs.

Couture said the work being done in Freeport, Harpswell and now in Brunswick is evolving into a regional effort to eradicate the crabs.

She said she’s concerned that after consuming local clams, the crabs would likely move on to Brunswick’s quahog resource.

“We’re trying to take a full approach to how we can save the softshell clam industry,” she said.