PERKINSUS-MARINUS TISSUE DISTRIBUTION AND SEASONAL-VARIATION IN OYSTERS CRASSOSTREA-VIRGINICA FROM FLORIDA, VIRGINIA AND NEW-YORK

Perkinsus marinus infection intensity was measured in eastern oysters Crassostrea virginica collected in October and December 1993, and Marc h, May, and July 1994 from 3 U.S. sites: Apalachicola Bay (FL), Chesap eake Bay (VA), and Oyster Bay (Mr'). Gill, mantle, digestive gland. ad ductor muscle, hemolymph, and remaining tissue (including gonadal mate rial and rectum) were dissected from 20 oysters from each site at each collection time. Samples were separately diagnosed for P. marin us in fections by incubation in Ray's Fluid Thioglycollate Medium (RFTM) and subsequent microscopic quantification of purified enlarged hypnospore s. At all sampling times and sites, average P. marinus infection inten sity (g wet wt tissue(-1) or ml hemolymph(-1)) was lowest in hemolymph samples, and generally highest in the digestive gland. Perkinsus mari nus prevalence was 100% at both FL and NY sites for each of the 5 coll ection times, and, for the VA site, was less than 100% in only 1 month (May 1994). Seasonal intensity patterns and mean total body burdens d iffered among the sites. Average body burden was highest in VA during October and progressively declined to a minimum in May. This decline w as probably due to mortality of heavily infected oysters and diminutio n of parasite activity associated with colder temperatures and reduced salinities. Intensities varied little during the months of October an d December at both the FL and NY sites. Minimum average intensities we re observed in March in FL oysters and May in NY oysters. Relatively h igh P. marinus infection levels that persisted throughout the winter i n NY oysters compared with VA oysters could reflect constant high sali nity in Long Island Sound which favors parasite activity, and also rap id decline in temperature in the fall that may have prevented epizooti c oyster mortalities.