Salem Harbor falling prey to prawn invader

SalemNews.com, Salem, MAAugust 20, 2010Salem Harbor falling prey to prawn invaderBy Will BroaddusStaff Writer¢ This article has been corrected since publication. To read the correction, please click here.SALEM ¢ An invasive species of European shrimp, the rock pool prawn, was recently discovered in American waters for the first time at Hawthorne Cove Marina and Palmer’s Cove Yacht Club in Salem Harbor.A team of 25 scientists from the Massachusetts Office of Coastal Zone Management and MIT’s Sea Grant College Program found the shrimp in a sample they took July 30.James Carlton, director of the Williams College-Mystic Seaport Maritime Studies program, confirmed the shrimp’s identity, Palaemon elegans, one week later. He consulted with an expert at Oxford University, after failing to find the creature in guides to American species.The shrimp is normally found in England and on the Atlantic coast of Africa and was described by Jan Smith, water quality and habitat manager for Mass. CZM and leader of the survey team, as “an omnivore that eats amphipods,” including the crustaceans found in tidal pools.A Mass. CZM release cited “recent studies in Sweden” that have shown the rock pool prawn “can eat so many smaller creatures that green algae is no longer controlled.” The rock pool prawn grows to 21/2 inches and is itself edible.Smith said this year’s survey, which has been conducted every three years since 2000 specifically to look for invasive species, went to 20 sites, mostly floating docks and piers, between Naragansett Bay in Rhode Island and Casco Bay in Maine. Sandwich, Plymouth, Gloucester and Boston’s Rowe’s Wharf were visited, but the rock pool prawn was only found in Salem Harbor.Carlton, who said global warming is a factor in such documented phenomena as “Caribbean creep,” in which warm-water species have steadily migrated to previously cold-water habitats, said it also may have made New England’s waters amenable to species from across the Atlantic.Another culprit is the failure of deep-draft commercial ships to conduct ballast exchange, in which water they have carried from the coastal waters of their home ports is dumped at midocean and replaced with new, mid-ocean water.For a few years now, the U.S. Coast Guard has declared ballast exchange mandatory. Carlton said there are exceptions to the rule, when safety is a concern in rough seas.He also said there instances in which, even when ballast exchange is conducted, it may not succeed in ridding ships of stowaway species.Globalization compounds these failures.”Ninety percent of all world goods travel by ship,” Carlton said, and as trade intensifies, so do opportunities for species to travel in the freighters’ ballast.Carlton, who has been studying invasive species since 1962, cited studies of Salem Harbor by professor Larry Harris of the University of New Hampshire, which reveal that it is the unique home to another visitor to American waters, the European sea anemone.”I am given to understand the Salem power plant keeps the water a little more ambient than usual,” Carlton said, suggesting a local rather than global source for raised water temperature.Whatever makes the water warmer, higher temperature could explain not only why the rock pool prawns like Salem, but may guarantee that they flourish here through the winter, when normally they would go to deeper waters, Carlton said.