First record of shell-boring polychaetes in Pacific oyster (Magallana gigas) seed

Shell-boring polychaetes such as Polydora websteri have eroded the value of aquaculture operations worldwide. These pests burrow into the shells of bivalves, creating blisters that are unappealing to consumers and that make oysters less valuable on the half-shell market. Our team has documented the impact of these polychaetes on Pacific oysters (Magallana gigas) of the US West Coast, a region that produces 38 % of the farmed shellfish in the US. In the course of our research, we also noticed the presence of these polychaetes in oyster seed. To assess the prevalence of shell-boring polychaetes in seed, we sampled Floating Upweller Systems (FLUPSYs) from Alaska (n seed = 50), Hawai'i (n seed = 150), and Washington (n seed = 400). Prevalence of infestation varied by state (Alaska = 10 %; Hawai'i = 33 %; Washington = 8.5 %), and ranged from 0 to 100 % across FLUPSYs. We found no evidence for larger seed (∼5 cm) being more infested than smaller seed (∼1 cm). These data confirm that shell-boring polychaete pests are present in oyster seed. We end by proposing ideas for control treatments that could be tested on seed to mitigate infestation by shell-boring polychaetes. •Because oyster seed is broadly exchanged, it could transport aquaculture pests.•We report the presence of shell-boring polychaetes in Pacific oyster seed.•We tested 600 oyster seed across 7 FLUPSYs from 3 US states.•Prevalence of infestation per state ranged between 8.5 % and 33 %.•A sample from bottle culture using water filtered through a 60 μm drum was not infested.