This story first appeared in the SERC quarterly Newsletter Summer 2007

Crab Invasion: Predicatable Pattern

SERC researchers have been on the leading edge of an invasion that is playing itself out as if by script. In June 2005, a local waterman delivered a Chinese Mitten crab to SERC for identification. It was the first specimen of this non-native species ever captured in the Chesapeake Bay.

According to ecologist Greg Ruiz, the conditions were ripe for the arrival of the Chinese Mitten Crab in Chesapeake Bay waters just as they had been in San Francisco Bay when they first appeared there in 1992. Not only was the habitat suitable, but the presence of a delivery mechanism for juvenile crabs and larvae seemed irrefutable. Ships entering Baltimore Harbor are not required to treat their ballast water to remove or destroy organisms that may have hitched a ride from the last port of call. Untreated ballast water provides a veritable transoceanic shuttle service for larvae and small organisms.

Since the first report, the development of the Mitten Crab story has followed the pattern scientists have observed time and again. When the public was put on the lookout, Mitten Crab specimens began steadily creeping in. One crab was delivered to us by a watermen who had captured it in 2005 and kept it in his freezer. Between May and early June of this year six additional male crabs were confirmed. True to the pattern, the findings expanded the region of original capture to include Delaware Bay and New York's Hudson River.

The crabs are a concern because they can cause considerable damage, eroding embankments with their burrows, fowling fishing gear and clogging water intake equipment for power plants. In California, as in Europe, economic loses have been significant.

The subsequent capture of two female crabs in June and July, both of which had mated and carried eggs, may herald the next phase in the progression of species invasions. "We have not yet found larvae or juvenile crabs, the latter occurring in freshwater tributaries," Ruiz says, indicating that "we do not know whether the Mitten Crabs have established a self-sustaining population in the Mid-Atlantic region."

Ruiz's caution is warranted, as mitten crabs found in the Detroit River and Lake Erie 30 and 40 years ago seem not to have become established. However, the pattern looks suspiciously familiar. The conditions are more appropriate along the Mid-Atlantic coast, and according to Ruiz, "the door remains wide open."

For more information, or to reach Dr. Ruiz, please contact SERC science writer Kristen Minogue.