Invasion of the southern bight of the North Sea by Ensis directus: Ecological consequences and fishery perspectives

The American jackknife clam (Ensis directus), first detected in the German Bight of the North Sea in 1978, was observed for the first time in the Belgian sector in 1987. Since then, increasing numbers of specimens wash ashore every year, suggesting that the species forms large nearshore populations likely to significantly alter the local biological communities. A research project was started in 2009 to study this issue, extending the studied area to Dutch waters. On the one hand, the population dynamics will be investigated as well as its impact on the local fauna, making use of pre-1987 macrobenthic datasets; using knowledge acquired since some years on benthos–sediment relationships in this area, optimum habitats for this alien species will tentatively be determined through a modelling exercise (“habitat suitability modelling”) and acoustic seabed mapping. On the other hand, the impact of altered composition of macrobenthic communities on populations of seabirds will be evaluated. These data will further allow us to evaluate the feasibility, sustainability, and ecological impact of a targeted Ensis fishery within Belgian waters, incorporating lessons learned from commercial vessels operating in the nearby Dutch waters. In this contribution, our preliminary results are presented and discussed.