PORTLAND — A species of invasive crab with a voracious appetite that first showed up in the United States 25 years ago has spread to far eastern Maine, and marine ecologists are worried about its potential impact on the environment.
A group of four marine ecology students at the University of Maine at Machias found an Asian shore crab last week while on a field trip to Great Wass Island in Beals.
The crabs were first recorded in the United States in 1988 in Cape May, N.J., said Brian Beal, a marine ecology professor at the university. The previous northernmost sighting had been on Maine’s Schoodic Peninsula, about 30 miles southwest of Great Wass Island.
Asian shore crabs aren’t as much of a menace as the invasive green crab, which are larger and have cleaned out some clam flats in parts of southern and midcoast Maine.
But Beal said they could outmuscle other species for food and space, posing a threat to a variety of marine organisms that live in intertidal zones, including periwinkles, clams, worms and seaweed.
“You know in some way it’ll change the ecosystem through its new interactions with both plants and animals,” Beal said. “Before it arrives, the system is what it is. But after it arrives, it is changed by the presence of this invader.”
The body of an Asian crab is just a couple of inches wide with a mottled shell that ranges from green to purple to orange-brown. The crab’s native range runs roughly from North Korea to Hong Kong, said Larry Harris, a marine biologist at the University of New Hampshire.
After the crabs’ arrival in New Jersey, most likely in a ship’s ballast, they rapidly moved north to southern New England waters. They have spread more slowly through the colder waters of the Gulf of Maine, but Harris said they can tolerate the cold and will probably make their way to Labrador, north of Newfoundland in Canada.
“It’s not surprising they’re showing up in eastern Maine, but it’s happening faster than we were expecting,” he said. “It’s because of the mild winters, I think.”
There’s not a lot of evidence that shows the crabs are altering the intertidal ecology in any great way, Harris said, but they could end up posing a threat to oyster farms or possibly reduce the population of barnacles.
“The jury’s still out on that,” he said.