Japanese Shore Crabs Invade Penobscot Bay, Maine

Japanese shore crabs, a square-shaped crustacean that poses a direct threat to soft-shell (steamer) clams, mussels and lobsters, were discovered July 13 by Cornell University marine biologists in Owl's Head, Maine, on the shores of Penobscot Bay. The detection of this crab, which has the potential to hurt Maine's seafood industry, means that Penobscot Bay becomes the most-northern point along the Atlantic seaboard where these crabs have been found.

The Japanese shore crabs (Hemigrapsus sanguineus ), which feast voraciously on mussels, clams and other shellfish, were found at Crescent Beach in Owl's Head by Robin Hadlock Seeley, a marine biologist and an associate curator of Cornell's Malacology Collection, and Erin McDonald, a Cornell junior from New Hartford, N.Y.

Last summer Seeley was conducting her annual survey of the green crab, another invasive species, when she found the smaller purple crab in Casco Bay, Maine. The Japanese shore crabs, which already have invaded the waters of Chesapeake Bay, Long Island Sound, the Jersey shore and the coast of Massachusetts, were not expected to be found this far north so soon.

"The shock is that they've been in almost every place we've looked in Maine," Seeley said. "Anytime you have a new species which is a predator, you have cause for concern."

To find these crabs, the researchers had combed the southern shores of Penobscot Bay. The low tide on July 13 was at 7:45 a.m., which is when the researchers began inspecting Birch Point Beach in Owl's Head. After three hours they had found no Japanese shore crabs there.

However, the researchers continued their morning hunt. "We really didn't have much time left before high tide, but we wanted to make sure the crabs weren't this far north," said Seeley. With two hours until high tide, at about 11 a.m., they visited nearby Crescent Beach.

The Japanese shore crabs enjoy living in craggy shore conditions and have an affinity toward hiding under rocks. "Barnacles are really sharp, and we were cutting up our fingers turning over the rocks looking for them. In the meantime, the tide was creeping in, and we knew that our time on Crescent Beach was limited," said Seeley. "The waves were lapping at our feet."

Within 10 minutes at Crescent Beach, McDonald saw a purple flash. The creature evaded McDonald's capture by ducking under a boulder. She called out to Seeley, who ran over and helped turn over the boulder. Indeed, the purple flash was a Japanese shore crab.

Meet Hemigrapsus sanguineus (pronounced hemmy-grap-sis san-gwinn-ee-us), also called the Asian shore crab, or the Pacific shore crab. It was first found along the Atlantic Coast in 1988, when a Franklin and Marshall College undergraduate student saw the unusual-looking crab under a bridge at Townsends Inlet in Cape May, N.J. The crab likely arrived on the Atlantic shores by way of dumped ballast water from an Asian merchant ship.

Since then millions of these crabs have migrated north and south. Until now the crab has been found as far north as Long Island Sound, Massachusetts and Harpswell, Maine. It has been seen as far south as North Carolina.

It's quite a crabby crab. "The shore crabs are more aggressive than the European green crabs, and the green crabs are bad enough," says Seeley. It feeds on clams, mussels, other crabs and possibly lobsters. Where it lives, in the rocky intertidal (the areas of shore that are above low tide) zones, the Japanese crabs are smaller than the adult green crabs but reportedly stronger and quite able to tear the claws off larger species of crabs.

John J. McDermott, the B.F. Fackenthal professor emeritus of marine zoology at Franklin and Marshall College, Lancaster, Pa., has been studying the crab since its 1988 discovery. Japanese scientists determined that the adult female can live as many as three years and can carry as many as 52,000 eggs, but McDermott believes that the females may have many more eggs than that.

Seeley and McDonald's summer research is supported by a grant from Cornell's New York Science Education Program.

Understanding the impact this discovery might have on Maine's seafood industry, including Maine's emerging aquaculture industry, Seeley indicated that the Japanese shore crabs could take years to become strongly established in the Penobscot Bay tidal areas. Said Seeley: "By sounding this early warning, maybe we'll have a few years to put a combat plan together. Having found it in Penobscot Bay, we're continuing our search for it, and we will be working our way up the coast."