Selective grazing of the isopod Idotea baltica between Fucus evanescens and F. vesiculosus from Kiel Fjord (western Baltic)

Grazing rates of the isopod Idotea baltica on Fucus evanescens and F. vesiculosus (Phaeophyta) were quantified in laboratory feeding preference experiments. Fucus species were offered alone (no-choice) or simultaneously (choice). In three of four no-choice experiments and in all four choice experiments, I. baltica significantly preferred F. vesiculosus to F. evanescens. F. evanescens recently immigrated into Kiel Fjord and has increased in abundance since 1990. One possible reason for the competitive success of this species may be that, compared to F. vesiculosus, it is less preferred by I. baltica, the most abundant mesograzer at the study site.