Asian shore crabs terrorizing N.H. Experts suspect aggressive invader has crossed into Maine waters

DOVER, N.H. – Scientists are growing more concerned about a small but scrappy invader that’s showing up along New Hampshire’s shores.

The Asian shore crab is just 3 inches wide, but it eats just about anything in its path, including shellfish seedlings, and is capable of ripping the claws off other crabs.

The crab first appeared in the United States in New Jersey in 1988, and has been spotted in New Hampshire since 1997. The state’s first Asian shore crab was found at Hampton Beach, and about 30 others have appeared since then at Hilton Park in Dover.

“There’s no way we’re going to stop the invasion,” said Megan Tyrrell, a marine biologist at the University of New Hampshire. “It’s not a disaster, but a lot of scientists are interested.”

The crab’s mottled shell can range from green to purple to orange-brown. It has three spines on each side and is somewhat triangular in shape. The legs have distinct alternating light and dark bands.

The crabs haven’t been identified in Maine, though researchers say it’s likely they’ve moved that far north by now.

“I’m almost sure that they’re in Maine somewhere,” Tyrrell said. “I mean, they’ve been here for three years and haven’t crossed the river? I doubt it.”

The concern in Maine is whether the crabs pose a threat to the lobster industry.

“What happens when you put one face to face with a juvenile lobster?” said Ron Huber, director of Penobscot Bay Watch. “Are we going to end up with a bunch of clawless lobsters?”

The group had been offering a $5 bounty for every Asian shore crab found in Maine, but recently canceled the program because members feared people might seed crabs in Maine waters to have a ready supply.

Elsewhere, the crabs haven’t been blamed for the demise of any commercial stocks so far.

After three years of research, Tyrrell has a good picture of what New Hampshire’s rocky intertidal communities look like without many Asian shore crabs. As their numbers increase, she’ll be watching for changes in the ecological landscape.

“It will be a shift in who some of the major predators are out there,” she said.

The crabs eat eelgrass, seaweed, barnacles, soft-shelled clams, mussels, scallops and snails. One likely loser in the invasion is the green crab, which has a similar diet but is less aggressive than the Asian crab.

But because the Asian shore crab prefers an area between the high and low water marks on rocky shores, it’s unlikely it will pose a serious threat to clams and mussels, which bury themselves in sand.

Other commercial species, such as scallops, live in deeper water, though the crabs could become a problem if they infest the cages where scallops are raised.