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Virginia Institute of Marine Science

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Fall Survey sampling revealed P. marinus levels to be generally normal to high in Virginia tributaries. By 2007 P. marinus was present on every oyster reef sampled, and by the end of the 2006-2008 period the parasite was probably causing some mortality throughout Virginia waters. Data for H. nelsoni are still incomplete for 2006/7 because of funding limitations, but in 2008 H. nelsoni was observed at 17 of 31 sampled reefs, a marked expansion in distribution since 2003/4. A significant MSX disease outbreak occurred in the Great Wicomico River in 2008, as a mild winter and a long period of elevated salinities supported increased H. nelsoni activity among a population of relatively susceptible oysters.

Analyses of Spring Imports deployments of susceptible upper Rappahannock River oysters to the York River revealed typically high annual levels of disease-related oyster mortality, each year exceeding 88%. Perkinsus marinus began to affect the deployment relatively early in 2006 and 2008, with prevalences around 50% and moderate infections emerging by early July. Infections developed more slowly in 2007, but by August of each year P. marinus levels were similar: 96% prevalence, with abundant moderate and some heavy infections. Late summer and fall P. marinus levels were above the long-term average for Spring Imports deployments. Peak H. nelsoni impacts on the Spring Imports deployments during 2006-2008 were typical, but the onset of serious MSX disease occurred earlier than normal in 2006, with prevalence reaching 88% and intense infections abundant by early July. Early July H. nelsoni levels were lower than normal in 2007 and 2008.



American Oyster Diseases, Virginia, Chesapeake Bay