Hematodinium perezi is a parasitic dinoflagellate that infects blue crabs along the eastern seaboard. The prevalence of this parasite can approach 100% in focal outbreaks that occur in the summer and fall. These coincide with molting periods of the host. We have been studying the infection dynamics of Hematodinium in blue crabs from small embayments in Virginia. The bays have long residence times that may contribute to the outbreaks. We developed a quantitative PCR assay to detect dinospores of Hematodinium in environmental samples. The dinospore abundance in water samples was significantly correlated with prevalence of infection in crab hosts from high salinity embayments. In several bays, crab abundance is negatively correlated with prevalence of infection. We are developing a model for the blue crab - Hematodinium system that is intended to gage how physiographic features, fish pressure and host factors contribute to outbreaks of disease. There is circumstantial evidence that overexploitation has contributed to the emergence of disease in several marine fisheries, but the effect of fishing pressure on disease has received little attention. We want to understand how fishing pressure and declining water quality combine withthe physiography of small coastal estuaries to promote outbreaks of disease in blue crabs.

Dr. Shields began his "surfing" career with a B.A. in 1980 from the University of California, Santa Barbara. He left the water for a M.S. in 1983 from UC, Berkeley, but the waves beckoned and he returned to UC Santa Barbara for a Ph.D. in 1987. After a postdoc at the University of Queensland, he would up at the Virginia Institute of Marine Science (VIMS). Dr. Shields studies the etiology and epizootiology of parasitic and microbial diseases of commercially important invertebrates and fishes. He has recently worked in three distinct areas: the epidemiology of parasitic diseases in blue crabs in Virginia, the etiology of epizootic shell disease in the American lobster in southern New England, and the genetic diversity of an emerging viral pathogen in spiny lobsters from the Caribbean Sea. At least he eats well!

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