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Dionne DaCosta - Marine Invasions

Howard University, Washington DC

Prevalance of a trematode parasite among Grass Shrimp (Palaemonetes pugio)
and habitat preference

Palaemonetes pugio, commonly known as ‘grass shrimp’ are small translucent crustaceans found in the swallow areas of the Chesapeake Bay. They tend to live nearshore usually in estuaries where they find refuge in the shallow waters and structures such as woody debris and marsh vegetation. There exists parasites within these estuaries that contribute to the dynamic of these ecosystems. For the purpose of this experiment the prevalence and habitat preference of a trematode parasite that utilizes the grass shrimp as an intermediate host was studied. The trematode, strongly assumed to be Microphallus turgidus based on previous research, is passed onto P.pugio through contact with hydrobiid snails (first intermediate host) which are mainly found among marsh vegetation. To determine the prevalence of the trematode in the grass shrimp, daily sweeps were conducted at Fox point, along the Rhonde River, at a 15cm depth using a dip net. Three different types of habitats were sampled: Heavy vegetation (3 transects), Woody Debris/Medium vegetation (3 transects) and Bare sediment (2 transects). Shrimp were collected and measured to the nearest mm and checked for the presence of the trematode cysts (metacercaria) which encyst in the abdomen of the grass shrimp. Intensity was also determined by counting the number of cysts observed and were classed in three groups; low (1-5cysts), medium (5-10 cysts) and high (> 10 cysts). Based on data collected and analyzed it was determined that there was a significant difference in the proportion of shrimp infected between bare sediment and woody debris/medium vegetation as well as bare sediment and heavy vegetation. However there was no significant difference between the proportion of shrimp infected in heavy vegetation versus woody debris/ medium vegetation. However, though not statistically proven, a trend was observed that infection intensity does increase in areas of heavy vegetation Data analyses also showed no correlation between shrimp size and infection intensity.
Knowledge of the prevalence of Microphallus turgidus is of great importance as it has already been proven by Pung et. al (2002) to have a negative behavioral effect on Palaemonetes pugio and thus should be further studied.

Funding provided by the Smithsonian Institution Women’s Committee