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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Ref ID : 6940

Walter Traunspurger; Distribution of benthic nematodes in the littoral of an oligotrophic lake (Konigssee, National Park Berchtesgarden, FRG). Arch.Hydrobiol. 135(3):393-412, 1996

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Although nematodes are the most abundant and species richest organisms in the benthos of aquatic ecosystems, little is known about their seasonal, bathymetrical and vertical distribution in lakes. In this study, the spatial and temporal distribution of the nematode fauna of an alpine, oligotrophic lake was studied over a one-year period. In the littoral of Konigssee, nematodes comprise 78% of the meiobenthic organisms, with a mean abundance of 2960 individuals/100 cm2. Seasonal variation and differences between the depths examined (1 m, 2 m, 5 m and 10 m) however, were considerable. Minimum nematode abundances were recorded in winter and maximum values in the warmer months. The highest abundance with regard to water depth was recorded at 5 m and the lowest at 10 m. The fresh weight biomass ranged from 0.2 to 1.7 mg/100 cm2 depending of the season and water depth. Rhabdolaimus terrestris was by far the most abundant of the 90 species found in the littoral. It was found predominantly in 2 m and 5 m depth, whereas the next most abundant species. Monhystera paludicola, prevailed at 10 m. About 3/5 of the nematodes were found in the upper 2 cm of the sediment and overall 90% of all individuals in the first 5 cm. The remainder was found between 5 cm and 20 cm sediment depth. The proportion of nematodes in the top sediment layer was highest in spring and summer. Deposit-feeders were the most common feeding-type, followed by epistrate-feeders. The study shows that the structure of freeliving nematodes of an oligotrophic lake is very dependent on seasonal, bathymetric and vertical distribution. Hence, general conclusions and comparisons with other aquatic ecosystems should be done with caution.