Abstract

The introduced signal crayfish, Pacifastacus leniusculus (Dana), is now a permanent resident in many lakes in Finland and other European countries, but the effects of this large omnivore on lake ecosystems of the region are not well known. Previous studies, mainly experimental, suggest that, among other impacts, crayfish can directly change the composition of benthic invertebrate communities towards domination by species less vulnerable to crayfish predation. We conducted a preliminary study on the impacts of the introduced signal crayfish on the littoral macroinvertebrate communities of large boreal lakes by comparing the invertebrate assemblages of stony shores between an impact area with well established crayfish populations and control areas without crayfish in the second largest Finnish lake, Lake Päijänne. The composition of the invertebrate community consistently differed between the impact and control areas, and total abundance, species richness and snail abundance were significantly lower in the presence of signal crayfish. The sites inhabited by crayfish were strongly dominated by Chironomidae, whilst the control sites were represented by more balanced assemblages of taxa. The results of this pilot study suggest that the introduced signal crayfish can significantly alter littoral communities and food webs in large boreal lakes.

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