Feature Story                                                January 2011

Searching for an Invasive Shrimp in Chesapeake Bay

Twenty years ago the Marine Invasions Lab began studying the interactions between native grass shrimps (Palaemonetes pugio, P. intermedius, and P. vulgaris) and their common predators along the shores of the Rhode River. This nearshore survey was designed to look at long-term population trends and the community dynamics of the shrimp and their predators. Several of these animals, including Rockfish (Morone saxatilis), White Perch (Morone americana) and Blue Crab (Callinectes sapidus), are economically and

Pulling in a seine net on the Rhode River for the nearshore survey

ecologically important species in the Bay, and grass shrimps serve as a key food source. Research is carried out every June, July and August at two sites on the Rhode River in the shallow waters of the nearshore zone where shrimp seek refuge from these predators. Three types of surveys are conducted each month: seines, dipnet sweeps and tethering. Seine net surveys track the presence and abundance of fish and crab predators in the near shore zone. Dipnet sweeps measure the relative abundance of shrimp at different depths. Tethering involves placing shrimp tied to lines in 1 foot (30 cm) of water for several timed intervals and measuring relative predation to determine how effective this zone is as a refuge habitat.

During summer field work in 2007, researcher Eric Bah found a shrimp off of SERC’s dock that had orange bands on its walking legs. This was not a characteristic we had seen before. After careful examination, we determined that this shrimp was not one of the grass shrimp native to our region; it was the non-native Oriental Shrimp, Palaemon macrodactylus. This species is native to the waters of Japan and China and is already established in parts of Western Europe, Argentina, and San Francisco Bay. Scientists at Williams College’s Mystic Seaport research facility recently discovered established populations of P. macrodactylus in estuaries near New York City and in the Mystic River in Connecticut. The specimen found here at SERC is one of three found to date in Chesapeake Bay; the other two were discovered in the James River. Ballast water is believed to be the leading vector by which these shrimp have been introduced to other regions. Based on successful invasion and establishment in other bays and estuaries near major ports, and given that the Baltimore Harbor in Chesapeake Bay is a major port and shipping lane, establishment of this species in the Chesapeake is considered likely.

Palaemon macrodactylus. This species is characterized by the forked apical point (A.) of the rostrum, the double row of setae (fine hairs) between the ventral teeth of the rostrum (B.), and three dorsal teeth located behind the eye orbital (C.). The adults are larger than the native grass shrimp and frequently have orange bands of color at the joints of their walking legs and a whitish longitudinal stripe down the back of their carapace.

We decided to initiate a wide sampling effort to assess how many of these shrimp are really present in the Chesapeake. Stacey Havard, Eric Bah, and intern Cari Zourdos (a recent Coastal Carolina University graduate) worked with scientists at Old Dominion University (ODU) and Virginia Institute for Marine Science (VIMS) to design sampling protocols and develop a strategy for site selection. This past summer, they collected shrimp along the western shore of the Middle Bay at 22 sites. When combined with efforts by VIMS and ODU in the Lower Bay, a total of 31 sites were sampled. All shrimp collected were examined microscopically and no P. macrodactylus were found. This is good news for Chesapeake Bay, since the ecological impact of this shrimp on native species of plants and animals is not yet known. But the search for non-native shrimp is not over. We will continue to watch for this species as we conduct future research, and we hope that others curious enough to collect and observe grass shrimp will look for this species and notify us about any discoveries. Please contact Stacey Havard at 443-482-2486 or havards@si.edufor more information or to report this species. The Marine Invasions Lab does take summer interns to work on several projects, including the nearshore survey.