Worms on the Cape: an integrative survey of polydorid infestation in wild and cultivated oysters (Crassostrea virginica) from Massachusetts, USA

Polydorid infestations pose a significant challenge to shellfish aquaculture by impacting marketability and profitability of farms. In this study, we investigated the prevalence, intensity, identity and biogeography of shell-boring worms infecting both farmed and wild oysters ( Crassostrea virginica ) from three sites in Wellfleet Harbor, Massachusetts – an economically important shellfishing region in the northeastern United States. DNA barcoding revealed that Polydora websteri was the sole culprit responsible for infecting oysters from all three sites, reaching maximum prevalence (100% infection) and intensity (mean intensity: 38.63) in the Herring River. The oysters in the Herring River are subjected to restricted tidal flow due to the presence of a physical barrier (dike), and this could be responsible for the high infestation levels of P. websteri observed in this population. In addition, a population genetic analysis incorporating COI sequence data from Wellfleet P. websteri in addition to newly published sequences from the Black Sea and the Sea of Azov found very low levels of genetic differentiation across several intercontinental populations (0.000 – 0.399), which is likely being driven by multiple introductory events such as oyster importations. These findings are discussed in relation to the future of shellfish aquaculture in the United States.