Development and testing of a molecular based assay to look for environmental reservoirs of a lethal parasite effecting blue crab fisheries

The Maryland Blue Crab (Callinectes sapidus) is an important fishery that extends along the Atlantic coast into the Gulf of Mexico. Populations of the blue crab within the coastal bays suffer mortalities associated with infections by the parasitic dinoflagellate Hematodinium sp. Infections are usually observed in the hemolymph and tissue of crabs inhabiting warm, high salinity waters. These seasonally-recurring outbreaks are geographically localized in “hotspots”, suggesting that there are environmental or biotic reservoirs of the parasite. Previous studies looking at the prevalence and intensity of Hematodinium sp. in blue crab hemolymph have been done using histology techniques. Even though these techniques give insight into the morphology and localization of the organism within the host, they are impractical to use on environmental samples. We have developed a quantitative PCR-based assay targeting a portion of the rRNA gene sequence which gives the specificity and sensitivity needed to look for environmental reservoirs of Hematodinium sp. We have demonstrated that the assay performs well in the context of environmental samples (water, sediment) which often contain potent PCR inhibitors.  The assay is being used in a study of the Hematodinium sp. dynamics in MD and DE Atlantic coastal bays.