Spread of the invasive shell-boring annelid Polydora websteri (Polychaeta, Spionidae) into naturalised oyster reefs in the European Wadden Sea

Andreas M Waser,Dagmar Lackschewitz,Jeffrey Knol,David W Thieltges,Karsten Reise,K Mathias Wegner

doi:10.1007/s12526-020-01092-6

Abstract

With globally growing aquaculture activities, the co-introduction of parasites alongside large-scale movements of commercial species poses an increasing risk for marine ecosystems. Here, we present the first record of the shell-boring polychaete Polydora websteri Hartman in Loosanoff and Engle, 1943 in invasive Pacific oysters Crassostrea (Magallana) gigas (Thunberg, 1793) in the European Atlantic Ocean. In October 2014, mud blisters in the shells of wild Pacific oysters and specimens of a spionid polychaete were observed in close proximity to a commercial oyster farm at the island of Sylt (Germany) in the European Wadden Sea. Subsequent investigations indicated that these blisters only occurred near the farm and that no other mollusc species were affected. Morphological and molecular analysis identified the polychaete as Polydora websteri, a species that nowadays widely occurs around the globe, but likely is native to the Asian Pacific. Later sampling activities detected P. websteri also at other locations around Sylt as well as in the Dutch part of the Wadden Sea at the island of Texel. The number of polychaetes in the oysters was, however, relatively low and mostly below 10 individuals per oyster. Together, this evidence suggests that P. websteri is currently extending its range. As the introduction of P. websteri may have severe ecological and economic implications, this study aims to alert others to look for P. websteri at Western European coasts within farmed or wild Pacific oysters to further document its spread.

Highlights

Our findings constitute the first evidence that the shell-boring polychaete Polydora websteri is present in the Wadden Sea and document its expansion to the European Atlantic coast
Previous records of P. websteri often stem from farmed oysters
We first detected the polychaete at a site in close proximity to a commercial oyster farm where juvenile Pacific oysters are imported primarily from a nursery in southern Ireland, supplied by British hatcheries

Summary

Introduction

Global trade has increased enormously during the last decades resulting in an unparalleled introduction of species across the planet (Vitousek et al 1996; Mack et al 2000). Besides transport in vessel ballast water or as hull fouling on ships, direct and indirect introductions via aquaculture activities are the Communicated by P. These worms are known to penetrate mollusc shells and form burrows therein (Simon and SatoOkoshi 2015). In cases of heavy infestations, shells are severely damaged by the boring activity of the worms which may negatively affect host condition as the hosts divert energy from growth to shell repair (Kent 1979; Lleonart et al 2003). Shell damage reduces shell strength which in turn can lead to increased predation by crabs and other predators (Ambariyanto and Seed 1991; Buschbaum et al 2007)

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