Freshwater Oligochaeta in two mountain ranges in Europe: the Tatra Mountains (Poland) and the Alps (Italy)

The oligochaete fauna of littoral zones, inflows and outflows of 11 lakes in the Polish Tatra Mountains and 10 lakes in the Italian Alps were compared. The study lakes were located in the alpine zone, they varied in size and depth, and were found prevalently on acidic crystalline bedrock containing a small percentage of calcareous rocks. On average, Oligochaeta represented from 10 to 17% of the total benthic fauna. Enchytraeidae had the highest number of species (7 per group of lakes), while Naididae were next with 3 species. Common Enchytraeidae genera were: Cognettia, represented by the same species in both mountain ranges, and Cernosvitoviella, with 1 species in the Polish lakes (Cernosvitoviella tatrensis) and 3 species in the Italian lakes (Cernosvitoviella ampullax, C. atrata and C. microtheca). In the Naididae, the genus Nais was represented by 3 species in the two lake groups, but only 2 species with high percentages (Nais variabilis in the Tatras and Nais communis in the Alps). Although Naididae are more likely to be found in freshwater with more favourable environmental conditions, no correlation existed between pH or alkalinity and their geographical distribution. The results of a two-year study on Lake Czarny pod Rysami (Tatras) are also presented, highlighting the lower number of species collected in the present campaign than in the previous one, due to different sampling methods.