Marine polychaetes in the genus Polydora (and other related genera) can burrow into the shells of commercially important bivalves, creating unsightly blisters and burrows. Because they are unappealing to consumers and can burst, these blisters are an economic burden on producers whose stock goes to the half-shell market. The west coast of the US is the leading producer of aquaculture oysters in the country, making it important to understand the prevalence of these pests in Pacific oysters. We obtained over 3,000 oysters from 35 farms in four states (CA, OR, WA and AK) and determined infestation prevalence across four sampling seasons. Prevalence per state ranged from 13 to 37%. Polychaetes were extracted from infested shells for molecular analyses. We used mitochondrial (CO1) and nuclear (18S) genes for species-level identification. Genetic markers confirmed the presence of P. websteri and P. hoplura at more than one site in the west coast, as well as multiple other polychaete species.
Given the difficulties faced by growers in controlling this pest, we consulted shellfish farmers from Washington State to create treatments that are both effective and easy to apply on farms.
We tested three treatments in experiments carried out with diploid Pacific oysters infested with shell-boring polychaetes and collected from Washington State. Our experimental design consisted of three stages: (1) the main experiment to test treatments, (2) a growth assessment, (3) and respirometry trials. We subjected 675 oysters to three treatments: ‘Dry’, ‘Fresh-Dry’, ‘Refrigeration’ and a Control. The ‘Dry’ treatment was 100% effective at killing worms and the other two treatments were nearly as effective (Fig. 1). The growth assessment indicated that none of the treatments negatively affected oyster growth, and the respirometry trials showed no significant differences in oxygen between treatments.
Findings from this study will allow us to advise the US west coast shellfish industry on the progress of the spread of shell-boring polychaetes and strategies for reducing the economic impacts of these globally-distributed pests.