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Photograph of an Asian Crab (Hemigrapsus sanguineus). Photo courtesy of MIT Sea Grant, P. Erickson

A Canadian researcher made an alarming discovery on the Schoodic Peninsula this summer. A volunteer with his monitoring network found a pregnant female crab, Hemigrapsus sanguineus, commonly known as the Asian shore crab.

It doesn’t have a good reputation.

“To my knowledge this is the furthest north that the invasive crab has been confirmed,” said David Delaney of Montreal’s McGill University.

Acadia National Park staff Jim McKenna and David Manski are working with Delaney, a graduate student, to monitor the spread of these crabs, which multiply and threaten the lives of native crustaceans in the intertidal zone.

McKenna, coordinator of Schoodic Education and Research Center in Acadia, has studied Asian crabs for years, watching them take over the rocky intertidal zone in Long Island Sound. They even overpowered green crabs, an invasive species that arrived many years ago.

McKenna thinks it’s likely the Asian crabs were brought to the Atlantic coast via water ballast, which could have been pumped aboard a container ship in southeast Asia, then pumped out as the ship arrived at a busy international terminal such as Port Elizabeth, New Jersey. A former professor at Williams College working at the school’s marine studies program in Mystic, Conn., McKenna said Asian crabs totally took over.

“They are small but they are very aggressive, both in terms of going after their food source and defending their turf.” Most crabs are two inches and under, but they can gobble up periwinkles, small mussels and even survive long periods with no food at all.

If you lift a football-sized rock in the intertidal zone on Long Island Sound, you will find at least a dozen Asian crabs under it, he said.

The invasive crabs “turned the corner” of Cape Cod about five years ago, and last year showed up in Penobscot Bay. “This thing is moving north, no doubt about it. The implications are quite significant for the rocky intertidal community,” he said, pointing out there is the potential to directly affect Maine’s mussel harvesting industry. There could be complex indirect effects, too, and these are being studied.

Can you head off the invasion of Asian crabs? “I don’t think it’s at all practical to stop the invasion,” McKenna said. “You’re not going to stop it.”

Meanwhile over in Cobscook Bay, a joint study by The Nature Conservancy and Cornell University has found another invasive, Didemnum, commonly known as sea squirt. This rapidly-spreading species was first discovered on the Damariscotta River. Experts believe it was carried there by Japanese oysters imported by aquaculture businesses along the river. Since then, it has spread along the bottom of Georges Bank, where it now covers 40 square miles. The invasion threatens fisheries, including aquaculture.

A fisherman was the first to detect the strange invasive in Cobscook Bay, when his drag brought up a “pancake batter” substance — sometimes a rubbery mat, or “sea grape” — which turned out to be sea squirt. A spokeswoman for the Nature Conservancy said fishermen are a valuable source of information since they know the local waters and can relay information to scientists.

Larry Harris, a University of New Hampshire professor who joined the Cobscook Bay survey, said sea squirts can kill off mussels and scallops by smothering them. Harris was among 20 biologists in the study, which had help from Cobscook Bay Resource Center, the State Planning Office and Department of Marine Resources. Harris believes the bay’s cold temperature may slow the spread of the sea squirt.

Researchers identified about a half dozen non-native species in Cobscook Bay, while in Casco Bay to the south, there were 28 non-native species found in 2003.