Winter Warriors: Seasonal Persistence of Polydora Infestation in Eastern Oysters from a Tidally Restricted New England Estuary

Abstract

Shell-boring polychaetes of the genus Polydora pose a significant threat to oyster aquaculture worldwide, yet little is known about their seasonal dynamics in tidally restricted estuaries. This study investigates the prevalence, intensity, and environmental drivers of Polydora websteri infestation in wild eastern oysters (Crassostrea virginica) over a 12-month period in the Herring River estuary (Cape Cod, Massachusetts), a system slated for tidal restoration. Oysters were collected monthly, and worms were identified using both morphological and molecular methods. Infestations were observed year-round, with prevalence and intensity peaking in fall and winter. A Poisson generalized linear model revealed temperature as a significant negative predictor of infestation intensity, while salinity and pH had no significant effect. Mud-blister pathology also varied by season, with higher severity during colder months. Gravid females and larvae were only observed from April through August, indicating that infestations persisted even in the absence of active reproduction. These findings suggest a seasonal lag between recruitment and peak infestation and highlight the resilience of P. websteri in cold conditions. These results provide critical data for evaluating post-restoration dynamics and suggest that management strategies such as off-bottom culture and seasonal harvesting could help mitigate parasite impacts in future aquaculture and restoration efforts.

Keywords: aquaculture, polychaete, shellfish, polydora