Oligochaete assemblages of Swiss Alpine lakes

Colombo, Luca and Steingruber, Sandra and Boggero, Angela and Dumnicka, Elzbieta and Zaupa, Silvia (2014) Oligochaete assemblages of Swiss Alpine lakes. Italian Journal of Zoology. pp. 112-123. ISSN 1125-0003

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The present paper describes the oligochaetes’ assemblage composition in 12 Swiss Alpine lakes (1700 - 2500 m a.s.l.) of Canton Ticino. The geology of the studied lake catchments is dominated by gneiss, while carbonate rocks are rare. As a consequence, the buffering capacity of most lake waters is low so that they are sensitive to acidification. Because of their very low phosphorus concentrations they are defined as ultraoligotrophic. Oligochaetes were identified in littoral and outlet samples taken through kick-sampling technique from 1 to 3 times per year at the beginning of the 1990’s and in 2003 and 2007. At the same time lake water chemistry has also been characterized. Oligochaete assemblages consisted of nineteen species in total, eighteen of which were found along lake littorals and ten in the outlets. Among them, Cernosvitoviella goodhui Healy 1975 was recorded in Switzerland for the first time. A PCA, performed excluding the alkaline Lake Bianco (pH = 7.8 and alkalinity = 566 µeq L-1) due to its highly different chemical composition, divided the remaining lakes into two groups with different sensitivity to acidity: the first group of 4 lakes is characterized by higher average pH (6.4) and alkalinity (32 µeq L-1) values, while the second group formed by 7 lakes is characterized by lower average values of pH (5.7) and alkalinity (5 µeq L-1). Multivariate analysis performed on lake littorals highlighted geo-lithology as a key driver in determining species distribution among lakes, while the same statistical approach carried out on lake-outlets showed again a split-up between acidic and calcareous waters. Precipitations influenced oligochaete assemblage composition in lake littorals. During years with higher annual rainfall the relative abundance of Enchytraeidae increased, probably because of their semi-aquatic nature which allows them to colonize the littoral zones that dry out periodically.

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