Asian Crab Discovery Is Called Worrisome

An invasive species of Asian crab may be reproducing in the Chesapeake Bay, a Smithsonian Institution researcher said this week, after the discovery of a female that showed signs of having mated.

The Chinese mitten crab was caught by a waterman June 23 off Kent Island, near where the Chesapeake Bay Bridge touches down on Maryland's Eastern Shore. It was the fourth of the species, native to China and Southeast Asia, discovered in the bay since 2005.

The crab was the first female found in the bay, a troubling discovery that, along with the indications of recent mating, could mean that the species has established a reproducing population.

"This is significant, and a point of concern . . . that there are both sexes, and mating is occurring," said Gregory Ruiz, a senior scientist at the Smithsonian's Environmental Research Center.

Ruiz said that the crab was carrying no eggs but that it is possible eggs had been released. He said it is unclear whether the eggs, which require salty water to thrive, could survive in the lower-salinity waters of the northern Chesapeake.

Mitten crabs have become established in Northern Europe and in California. In some places, they are believed to have burrowed into dams and riverbanks, causing erosion, and to have reproduced so fast that they clog water pipes.

Ruiz said it was unclear how the crabs might affect the Chesapeake ecosystem -- whether they might crowd out the bay's famous blue crabs, for example, or simply become food for them.

Ruiz said the crabs may have arrived in the bay in the ballast tanks of cargo ships or been shipped over live for food, then released.