Disease Ecology of the Blue Crab and its Parasite Hematodinium perezi in the Maryland and Virginia Coastal Bays

A primary ecological consideration for parasitic systems is the close relationship between host and parasite. Changes in host ecology, such as shifts in habitat usage or seasonality, can lead to extinction for a parasite. In light of this, parasites must quickly respond and adapt to these changes. Such adaptations may be integral to parasites such as Hematodinium, a dinoflagellate known to infect a number of crustacean species worldwide. In conjunction with the National Park Service and the Maryland Department of Natural Resources, we are conducting a long term study monitoring Hematodinium perezi in blue crabs, Callinectes sapidus, within the Maryland and Virginia coastal bays. Through the use of qPCR, we are able to identify and monitor parasite DNA in environmental samples as well as crab hemolymph and tissues. Our data show that parasite DNA is present in the water column in all months sampled (February to November). This suggests that H. perezi may be a year round member of dinoflagellate communities and that alternative hosts may be involved in the life cycle. To this end, we have identified parasite DNA in sand shrimp, Crangon septemspinosa. This species is active throughout the entire year in this system and may serve as a reservoir during winter months when blue crabs are senescent. This senescence does not occur in warmer regions, such as the Gulf of Mexico, which suggests that the jump to this alternative host may be an adaptation of the parasite to changes in host ecology.