Spatial community concordance of summer phytoplankton and profundal macroinvertebrates in boreal lakes

Abstract

Reliance of profundal benthic macroinvertebrate assemblages on epilimnetic algal production — a key element of pelagic–benthic coupling — is a well-recognized phenomenon in the literature but the details are still poorly understood. In particular, the importance of taxonomic composition of algal communities and associated qualitative aspects of the settling material to benthic invertebrates is poorly known. We addressed this issue by investigating concordance of summer phytoplankton and profundal macroinvertebrate community composition using data from 47 boreal lakes. We examined community variation and environmental correlates of phytoplankton and macroinvertebrates with nonmetric multidimensional scaling ordinations. We also used cluster analysis to group sites according to their macroinvertebrate assemblages and evaluated the differences in phytoplankton composition and class-specific relative abundance among the clusters. Community concordance was evaluated with Procrustes rotation and partial Mantel tests, using oxygen concentration and phytoplankton biomass — the main drivers of macroinvertebrate community structure — as controlling factors. Procrustes and Mantel tests suggested congruence between macroinvertebrate and summer phytoplankton community composition. The concordance remained significant even after controlling for oxygen and biomass, by partial Mantel tests, suggesting a unique effect of phytoplankton species composition on macroinvertebrate assemblages. The four groups of lakes clustered by their macroinvertebrate assemblages also differed significantly in their phytoplankton taxa composition, and there were among-cluster differences in relative abundance of the seven most abundant phytoplankton classes. Our findings of community concordance of phytoplankton and profundal macroinvertebrates suggest a functional dependency of these two components, but further studies are needed to verify the actual causal mechanisms.