Diversity of chironomid assemblages in contrasting subarctic lakes - impact of fish predation and lake size

Abstract

Potential effects of fish presence and lake size on chironomid community structure were investigated in subarctic alpine lakes of the Senja Island (69 °N), North Norway. Four small lakes and three relatively large lakes with similar physical and chemical characteristics but different impacts of fish predation were compared. The results indicated that the differences in lake size had little or no impact on either species richness, diversity, density or composition of the chironomid larvae assemblages. In contrast, several likely effects of fish predation were revealed. Higher species richness and diversity were observed in fishless than in fish-inhabited lakes, especially in the profundal zone, but a similar tendency also existed in the littoral zone. Further, higher densities of both subfamily Tanypodinae and Orthocladiinae were consistently found in fishless compared to fish-inhabited lakes. The species composition in the littoral zone was apparently little affected by fish predation as indicated by both DCA, PCA and similarity indices. Large differences in the composition of chironomid taxa were, however, found in the profundal, with a total dominance of Heterotrissocladius subpilosus (KIEFFER) in fish-inhabited lakes compared to a co-occurrence of several evenly important taxa in the fishless. Large-sized and free-swimming chironomid species like most Tanypodinae and several Orthocladiinae were seemingly most vulnerable to fish predation, whereas burrowers and tube builders like many Chironominae and some Orthocladiinae appeared to be less susceptible. Indirect predator-prey interactions also seemed to play a role for the chironomid assemblage structure, particularly with respect to the relationship between Procladius sp. and Heterotrissocladius subpilosus.