Seasonal infection intensity cycle of the parasite Perkinsus marinus (and an absence of Haplosporidium spp.) in oysters from a South Carolina salt marsh

Investigation of the prevalence of the protozoan parasite Perkinsus marinus in populations of intertidal oysters (Crassostrea vircjnica) from a South Carolina salt marsh led to the finding of a distinct, 4 phase cycle of infection intensity.The cycle consisted of characteristic quiescent, pre-virulent, virulent and remission stages of infection.For the first time, P. marinus infection intensity in South Carolina oysters was found to have a statistically significant positive correlation with temperature and salinity, and a negative correlation with oyster condition index.Our data also indicated that P. marinus infection in adult oysters from South Carolina is not size dependent.Based on a limited, qualitative h~stopathological examination of oyster tissue samples, we found no evidence to indicate the presence of Haplosporidium spp. in the North Inlet salt marsh/estuary system.These results strongly suggest that highly localized mass mortalities of oysters in North Inlet have been due to virulent levels of P. marinus mfecbons.