Variation in functional trait composition of benthic invertebrates across depths and seasons in a subarctic lake

Benthic invertebrate communities play a fundamental role in lake ecosystems, and the understanding of how those benthic communities are structured, particularly in terms of the identity and spatiotemporal distribution of their functional traits, is key to our understanding of how lake ecosystems work. In Takvatn, a subarctic lake in northern Norway, we identified the taxonomic and functional identity of the species characterizing benthic communities across three seasons and six different depths. Invertebrates were sampled using vacuum pump and Ekman grab. Despite the relative low species richness, we found large variation across depths and seasons in species functional composition using multivariate analyses. In all seasons and habitats, gathering traits were the most common feeding traits within the benthic community. The upper littoral habitat shifted from a community characterized by particle gathers and algal scrapers in spring and summer, to a community largely characterized by leaf shredders in autumn. There was also high relative occurrence of predator traits towards the deeper areas of the littoral zone, as well as in the sub-littoral and profundal habitats. The deeper habitats showed high variation in their taxonomic composition, but a stable composition of functional traits throughout all seasons. In conclusion, our study demonstrates large spatio-temporal differences in functional trait diversity and composition of the benthic invertebrates in Takvatn.