Invasive Shore Crab Migrates Further East

by Laurie Schreiber

MACHIAS – A routine sampling trip by a marine ecology class, on Great Wass Island, revealed the presence of an invasive species called the Asian shore crab.

“I kind of knew it was coming, but I was keeping my fingers crossed it would be much longer in time than it was,” said Brian Beal, professor of marine ecology at the University of Maine in Machias.

The class was on the western side of the island, looking at tidal heights, with a focus on green crabs, blue mussels, two species of periwinkles and dog whelk.

“We were putting quadrats down and searching through them at various tidal heights,” Beal said. “We had done low and mid, and moved to the upper shore.”

A student found the invasive crab in nearly the last quadrat the class sampled for that morning. They found only a single individual. The class has not been back yet to continue sampling.

It was the first time the crab has been seen this far east along the Maine coast since 2005, when the crab was discovered at Schoodic Point.

The arrival of Asian shore crabs in other areas has had impacts on the ecosystem. “In other places where they’ve invaded, they’ve changed the system, especially near the upper intertidal where they don’t have many competitors or predators,” Beal said. “I’m not sure they’ll have a major impact on the lower shore or mid-tide shore, but in places where they have been found in the past, they’ve had some severe consequences on species diversity and the numbers of extant fauna.”

The habitat where this particular individual was found was rocky, but they’re also found in soft bottom areas.

“So their habitat is kind of cosmopolitan,” said Beal. “That’s also a concern.”

According to the Department of Marine Resources (DMR), the Asian shore crab, Hemigrapsus sanguineus, was first identified on U.S. shores in New Jersey in 1988.  It’s since made its way as far north as Schoodic Point, and as far south as North Carolina. Great Wass Island is about halfway between Schoodic and the Canadian border.

“It is expected to continue moving northward along the Maine coast,” the DMR said.

The crab is indigenous to waters from southern Russia to Hong Kong. Growing to about the size of a silver dollar, the crabs are omnivorous, eating macroalgae, salt marsh grass, and small invertebrates such as amphipods, gastropods, bivalves, barnacles and polychaetes, the DMR said. To the south, the crabs’ diet consists of mussels, clams, periwinkles and the European green crab (the latter two are also non-native species).

“Whether the crab will have similar dietary preferences or be able to reproduce as frequently in Maine’s colder climate remains to be seen,” the DMR said.

Maine is also facing an invasion of green crabs, which feed on shellfish resources such as blue mussels and soft-shell clams, “threatening the state’s third-largest wild fishery,” the DMR said. The increase in the green crab population coincides with an increase in ocean temperatures, the DMR said.

However, because of the broad scale of the parameters, it’s difficult to test any potential correlation between warming water temperatures along with the green crab’s population explosion in recent years and the shore crab’s migration north, said Beal.

A quick internet search reveals that both the green crab and the shore crab have some potential for creating new markets as food items. One website, called “eat the invaders,” has recipes by Bun Lai, owner of Miya’s Sushi in New Haven, Conn., “one of the few chefs who proudly serves invasive species. His recipes include Asian Shore Crabs in Coconut Milk and Asian Crab Popcorn.

DMR biologist Peter Thayer invites folks to contact him (pete.thayer@maine.gov) if they have sighted the Asian shore crab, along with the date, location, and number of crabs seen.   

Visit the DMR website to view photographs that assist in distinguishing the Asian shore crab from native species such as the rock crab, as well as the invasive green crab.