SELECTIVE GRAZING OF THE ISOPOD IDOTEA-BALTICA BETWEEN FUCUS-EVANESCENS AND FUCUS-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 prefere nce experiments. Fucus species were offered alone (no-choice) or simul taneously (choice). In three of four no-choice experiments and in all four choice experiments, I. baltica significantly preferred F. vesicul osus to F. evanescens. F. evanescens recently immigrated into Kiel Fjo rd and has increased in abundance since 1990. One possible reason for the competitive success of this species map be that, compared to F. ve siculosus, it is less preferred by I. baltica, the most abundant mesog razer at the study site.