First confirmation of the shell-boring oyster parasite Polydora websteri (Polychaeta: Spionidae) in Washington State, USA

Invasions by the spionid polychaete Polydora websteri have resulted in the collapse of oyster aquaculture industries in Australia, New Zealand, and Hawaii. These worms burrow into the shells of bivalves, creating unsightly mud blisters that are unappealing to consumers and, when nicked during shucking, release mud and detritus that can foul oyster meats. Recent sightings of mud blisters on the shells of Pacific oysters ( Crassostrea gigas ) in Puget Sound, Washington, suggest a new spionid polychaete invasion. To determine the identity of the polychaete causing these mud blisters, we obtained Pacific oysters from two locations in Puget Sound and examined them for blisters and burrows associated with spionid infection. We then extracted polychaetes and sequenced mitochondrial (cytochrome c oxidase I [COI]) and nuclear (18S rRNA) genes to obtain species-level identifications for a subset of these worms. Our data confirm that P. websteri is present in mud blisters of Puget Sound oysters, constituting the first confirmed record of this species in Washington State. The presence of non-native P. websteri could threaten the sustainability of oyster aquaculture in Washington, which currently produces more shellfish than any other US state.