Timing of seasonal pathogen exposure relative to oyster lifecycle

Protozoan parasites Perkinsus marinus (dermo) and Haplosporidium nelsoni (MSX) are associated with extensive epizootic mortality in eastern oyster Crassostrea virginica populations along the coastlines of the Atlantic Ocean and Gulf of Mexico. For decades, both diseases have resulted in substantial losses to ecological functioning of natural oyster habitat and have undermined the economic stability of wild oyster fisheries and mariculture industries in the USA. Both pathogens are widespread in coastal Georgia and are established regionally within native oyster populations, yet a clear timeline of transmission is not defined. Here, high frequency sampling was used to investigate when disease transmission is most probable relative to oyster lifecycle stage based in a localized region of the South Atlantic Bight (SAB). Dermo was present in the water column throughout the year with peaks in abundance concurrent with spawning activity, resulting in significant positive correlations among P. marinus concentration and the number of spawning females, egg yield, and shell height per spawning female. Detection of MSX in water samples appeared during 3 punctuated periods throughout the year but was not significantly associated with any environmental or life cycle metric. Overall, this research indicates that spawning events may be a mechanism for P. marinus transmission in oyster populations of the SAB.