Species Structure of Communities of Oligochaetes (Oligochaeta, Annelida) in the Upstream Water of the Pechora and Vychegda Rivers: a Comparative Faunal Analysis

A comparison of oligochaete communities of different landscapes in the upstream water of two large rivers, which flowing through the European Northeast of Russia – Pechora and Vychegda. A high diversity of oligochaetes (42 taxa) was found, with species common to both rivers comprising only 26% of the fauna. The family Naididae prevailed in species richness in both rivers. Dominant species included Lumbriculus variegatus, Nais communis, and Propappus volki in the Pechora River and in the Vychegda River – Nais bretscheri, Stylodrilus heringianus, Spirosperma ferox, Limnodrilus hoffmeisteri, and Potamothrix hammoniensis. It was shown that the diversity in the studied parts of the rivers is primarily based on a large number of rarely encountered species. Calculations of diversity indices revealed opposite trends for the oligochaete communities in the upper reaches of the Pechora and Vychegda rivers. For the Pechora River, an increase in alpha diversity, expressed by the Shannon (Hλ) and Simpson (1-Dδ) indices and species richness, was observed from the upper (mountainous) to the lower (plains) section. Conversely, for the Vychegda River, a decrease in diversity downstream was noted. The comparison of faunas between the rivers (beta diversity), expressed by the Whittaker index, showed higher diversity of oligochaete communities in the upper reaches of the Pechora River.