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Discovery of Second Invasive Mitten Crab Raises Worries

By Elizabeth Williamson and David A. Fahrenthold
Washington Post Staff Writers
Tuesday, August 8, 2006

Fisheries experts across the Chesapeake Bay went on alert yesterday after scientists identified a second Chinese mitten crab, raising questions that the species could threaten the bay's already struggling native crabs and shellfish and further harm its ecosystem.

Like the bay's beloved blue crab, the mitten crab -- a native of China and the Korean Peninsula named for the furry growths on its pincers -- eats small worms and juvenile shellfish. It prefers habitat similar to native crabs', and under the right conditions can breed furiously.

That all raises fears that if it manages to establish itself, the mitten crab would eat already scarce oyster populations and compete for food with the blue crab, the region's marquee species and its most lucrative aquatic commodity.

Finding another crab "suggests there might be more," said Gregory Ruiz, a marine ecologist at the Smithsonian Institution's Environmental Research Center in Edgewater, who identified the second mitten crab yesterday afternoon. "They could compete for food and habitat in some way. How that plays out, in my view, is pretty uncertain at this point."

Key to containing any damage, scientists say, is learning -- quickly -- how the mitten crabs arrived here.

"What we don't know is whether the two crabs are related to each other," said Lynn Fegley, a fisheries biologist with the Maryland Department of Natural Resources.

If the two were adults discarded at random, chances that the species has established itself remain low. But if the two adult crabs were among many that arrived as young, perhaps in a ship's ballast water, there may be more out there.

"The last thing we need is one more introduction in the bay, which may be the final nail in the coffin for some native species on the verge of collapse or decline," said Rom Lipcius, a researcher at the Virginia Institute for Marine Science. "To me, it's unlikely that there's already a population . . . [but] the urgency is to find out how these crabs got there and stop it."

The mystery of the crabs' appearance began when a waterman caught a funny-looking crab near the mouth of the Patapsco River and handed it over to Steve Takos, a volunteer ranger at North Point State Park near Baltimore. Takos recalls the incident as taking place in 2003, but Ruiz said the waterman told him he caught it last summer.

Takos said he believed the specimen was a spider crab from South America, but he noticed its odd pincers. "It does look like it has mittens, like boxing gloves, on the end of his claws," he said.

The crab lived for a few months, then Takos noticed a mass on its underbelly, in the same place where female blue crabs carry eggs. The mass attracted the attention of a catfish living in the same tank.

"I found [the crab] the next day upside down," the ranger said.

Takos was shocked over the weekend to see a photo of a similar crab in the newspaper, after a mitten crab was caught in the same area this June. On Sunday, he called authorities.

"It's a good thing I had the forethought to freeze it," he said yesterday. Despite Takos's suspicions, Ruiz said the crab was male. The crab found in June was also male.

Lipcius said clues to the crabs' appearance could come from shipping operators who may recall ballast accidents or residents who may know of someone who possesses or breeds the creatures.

The mitten crab is fully established in San Francisco Bay, where it was first found in the early 1990s and is believed to have arrived in ship ballast water.

"They are quite problematic. They are very aggressive crabs and compete with our native crabs," said Andrea Swensrud, program manager at the Marine Science Institute in Redwood City, Calif.

The crabs also burrow into levees and banks to make their homes, contributing to erosion and potential flooding problems, she said. In Europe, they weaken dams and clog water intake pipes.

Lipcius believes the chances that the mitten crab has established itself remains small. "There are a lot of hurdles a species like this would have to overcome to become resident," including temperature, migration and adaptation problems, he said, as well as the effect of the bay's infamous pollution.

"We've done many, many surveys throughout the bay, and you'd think we'd have caught them" before, he said. "It's not likely that we have an actual resident viable population, but of course we're on the lookout."

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