Seasonal distribution of free-living nematodes in the Krahenbach, a fine-grained submountain carbonate stream in southwest Germany

摘要

The temporal distribution of the nematode fauna in the upper 5 cm sediment of the streambed of a small submountain carbonate stream (Krahenbach, Germany) was investigated over a 1-year period. The total nematode density was low during autumn and winter and reached a maximum value of 84 individuals/10 cm(2) in summer. The fresh biomass of nematodes ranged from 3.6 to 44.2 mug/10 cm(2). Deposit-feeders (65% of total fauna) and chewers (21%) were the two dominant feeding types. Of the 1027 nematodes examined, 9% were gravid females, 35% females, 2% males and 54% juveniles. At least 71 nematode species were identified. The relative low value of the Shannon Wiener index of diversity (2.61) is not the consequence of a low number of species, but of the presence of three species with a much higher frequency (57% of total fauna) than the others. The dominant species are Eumonhystera filiformis (Bastian, 1865)/vulgaris (de Man, 1880), Tobrilus cf. pellucidus (Bastian, 1865) and E. simplex (de Man, 1880). The seasonal pattern of E. filiformis/vulgaris showed a minimum density in summer and a maximum density in spring and is similar to the abundance variation of all deposit-feeders. The seasonal pattern of T. cf. pellucidus showed a minimum density in winter and a maximum density in summer and is similar to the abundance variation of all chewers. Throughout the year, nematodes were found in both layers (analysed depths: 0-2 cm, 2-5 cm), but higher mean annual densities occurred in the upper layer (68% of all nematodes). The preference for the upper cm of sediment was independent of feeding-type, age structure or species. The calculation of the Maturity Index and of the ratio of Secernentea/Adenophorea indicate a 'high status' of water quality at the analysed sampling site.