Mortality and hematology of blue crabs, Callinectes sapidus, experimentally infected with the parasitic dinoflagellate Hematodinium perezi

On the eastern seaboard of the United States, populations of the blue crab, Callinectes sapidus, experience recurring outbreaks of a parasitic dinofla gellate, Hematodinium perezi. Epizootics fulminate in summer and autumn cau sing mortalities in high-salinity embayments and estuaries. In laboratory s tudies, we experimentally investigated host mortality due to the disease, a ssessed differential hematological changes in infected crabs, and examined proliferation of the parasite. Mature, overwintering, nonovigerous female c rabs were injected with 10(3) or 10(5) cells of H. perezi. Mortalities bega n 14 d after infection, with a median time to death of 30.3 +/-1.5 d (SE). Subsequent mortality rates were greater than 86% in infected crabs. A relat ive risk model indicated that infected crabs were seven to eight times more likely to die than controls and that decreases in total hemocyte densities covaried significantly with mortality. Hemocyte densities declined precipi tously (mean=48%) within 3 d of infection and exhibited differential change s in subpopulations of granulocytes and hyalinocytes that lasted throughout the course of the infection. Crabs that did not present infections after i njection (i.e. "immune" hosts) did not show hemocytopenia and exhibited sig nificant long-term (21-27 d;) granulocytemia. Detection of the parasite in the hemolymph of infected crabs increased from approximately 30% after 14 d to 60% after 21 d to 100% after 35 d. Plasmodial stages were, however, det ectable in histological preparations of the heart within 3 days of infectio n and increased in number over 5 and 7 days. Sporulation of the parasite oc curred over a short time (at least 4 d, after 43 d of infection) and did no t culminate in the immediate death of the host. Hematodinium perezi represe nts a significant threat to the blue crab fisheries in high-salinity estuar ies. Although the parasite infects male and female crabs, it may have a gre ater impact on mature females as they move to higher salinities to breed.