David Andrew A.
Shellfish farming is quickly becoming the most expansive and profitable sectors of commercial aquaculture but is expected to face several challenges, including diseases. Shell-boring polychaete worms exert considerable stress on both wild and farmed molluscs by boring into the shells of scallops, oysters and abalone, where they weaken the structural integrity of the shell, reduce growth rates, and in cases of heavy infestation, compromises tissue quality. Here, we investigate the identity and infestation levels of shell-boring polychaetes in the last commercially viable wild bay scallop fishery in the world: Nantucket Island, located off the eastern coast of the US. While shell-borers were studied on the mainland US for decades, recent anecdotes by scallop farmers on Nantucket reported unusually high infestation levels of worms over the last few growing seasons, indicating that a potentially new worm may have arrived in the region. To determine the identity of these polychaetes, 30 scallops were obtained from submerged cages at the hatchery and worms were extracted, identified morphologically and DNA barcoded using the COX1 marker. Prevalence and intensity were measured to determine infestation levels. Our results showed that the main culprit responsible for infestation was Polydora neocaeca (>90% of infections), a species often associated with gastropod shells. Phylogenetic analyses showed that the Nantucket population formed a distinct North American clade with specimens from New York and Rhode Island (type locality), and were genetically isolated from other global P. neocaeca. Prevalence was low (40%) while intensity ranged from 2 – 14. This is the first report P. neocaeca infecting commercially reared bivalves from North America and its first detection in Nantucket scallops. The status of the species as an introduced pest will be discussed.
Acknowledgements: Funding for this study was provided by the Nantucket Biodiversity Initiative and the Nantucket Shellfish Association.