Composition of Benthic Invertebrate Communities in Relation to Phytoplankton Populations in Five Subarctic Lakes

The effects of algal food supply, temperature, water depth and lake size on the composition of benthic invertebrate communities were determined during 1978 und 1979 in 5 lakes in the Canadian subarctic. The lakes varied widely in physical conditions and trophic level, with peak algal densities ranging from 40 to 2100 mg/m3 during the summer and 10 to 750 mg/m3 in the winter. The correlation coefficients between the size of the populations of herbivorous chironomids (Chironomus riparius, Ch. plumosus, Ch. decorus, Tanytarsus xanthus) and the density of algae during the winter were highly significant and positive. There were also positive, albeit weak, correlations with the summer growth of algae, temperature, depth and lake size. In addition, the seasonal appearances of fourth instar larvae in the sediments were positively correlated with peaks in the abundance of phytoplankton. In contrast, algal food supplies probably had little impact on the density of oligotrophic indicator species (Heterotrissocladius oliveri, H. changi, Protanypus ramosus, Pontoporeia affinis) and were replaced in importance by temperature and water depth. Variations in the densities of the main oligochaete species (Uncinais uncinata, Arcteonais lomondi, Limnodrilus claparedeianus) and mollusc species (Valvata sincera helicoidea) could not be related to any of the factors that were measured. The diversity of the communities was probably limited by low temperatures, whereas food supply, lake depth and lake size had little impact on the fauna.