Invasive Asian shore crab species digs up trouble in South County

By: Jeff Sullivan

Posted: 1/25/08

1/25/08 - The invasive Asian shore crab species has been causing many problems for the Narragansett Bay ecosystem and researchers studying it.

Kristen Morito, a junior at the University of Rhode Island studying to become an environmental lawyer, has been studying and tracking Asian shore crabs for the past six months. She said that this invasive species is causing severe harm to the South County aquatic habitat, especially because there is no environmentally friendly way to eradicate them.

"The crabs are adapting very well to this habitat, and it is proving to be problematic because it changes the food web ever so slightly," she said. "As far as we know, there is only one species of estuarine fish, the mummichog, that will attempt to eat them. Sea gulls won't even eat them because they taste so terrible."

The effect on the native crab population proved to be staggering as well. Morito and her compatriots at the National Estuarine Research Reserve on Prudence Island set up traps at five sites around the island, checking them once a month. To their astonishment, 95 percent of the crabs captured were Asian shore crabs.

"They're omnivorous, so they'll eat almost anything they can get," she said. "And they are very aggressive and competitive, which is part of the reason why they are able to take over so quickly."

Morito says that there is no economically feasible or environmental friendly method for getting rid of this "aquatic nuisance."

"Basically, at this point all we can do is monitor the crabs and hope something comes up," she said. "They have established themselves here and they are just going to keep taking over, and getting rid of them would not only be a tremendous effort but also completely disrupt the environment in the process."

Morito said that the effects of the invasive species have yet to be felt in the fishing industry.

"I've heard some fishermen complain that they would catch them in their traps every now and then," she said. She continued, saying that the effect on the lobster population, though, "has yet to be determined, but they have been known to eat lobster larvae, so a detrimental effect on the population is very possible."

The Asian shore crab is from the coasts of China and Japan, and was first brought to the United States in the ballast water of a cargo ship in New Jersey. The ballast water is pumped in or out of the ship depending on the weight of the cargo to give the ship the low center of gravity it needs to keep from capsizing. Since the 1990s, they have migrated up to the Narragansett Bay area.

Narragansett Bay Area "has one of the highest rates of invasive species in the United States," she said. "This is mainly because of the temperate climate and high traffic the region experiences, and many non-native species find this combination to their liking."

Morito's interest in studying this species and its effect on the local habitat was sparked from childhood experiences on her father's boat.

"I would have to say that introduction to marine and coastal law with Professor Nixon really got me interested in the field of Environmental Law," she said. "I learned that while it is the scientists who provide the research and information, it's the lawyers and the legislators who take that information and turn it into actual regulation and policy."