Temporal dynamics of meiofauna communities in two small submountain carbonate streams with different grain size

The meiofauna community (especially nematodes, oligochaetes and chironomids) in the streambed surface of two small submountain carbonate streams (Krahenbach and Korsch, Germany) was investigated from April 1998 to March 1999. The Krahenbach stream is relatively sorted and fine-grained, while the Korsch stream is more heterogeneous and coarse-grained. The streams also differ in velocity, water level, conductivity, chloride concentration and organic content of sediment. Total meiofauna density reached a maximum value of 906 individuals per 10(2) cm in the Krahenbach and 3166 individuals per 10(2) cm in the Korsch. Rotifers were the most abundant group in the Krahenbach (52% of total fauna), whereas nematodes were dominant in the Korsch (63%). Meiofauna showed one abundance peak in the Korsch and two abundance peaks in the Krahenbach. In the Krahenbach, distinct seasonal patterns at family and species level occurred, whereas in the Korsch even at high taxonomic level only one abundance peak was observed. The most abundant nematode family in both streams were Monhysteridae, followed by Tobrilidae in the Krahenbach and by Tylenchidae in the Korsch. The dominant oligochaete family in both streams were Naididae (especially Chaetogaster langi (Bretscher, 1896) and Nais elinguis (O. F. Muller, 1773)), followed by Tubificidae. The most abundant chironomid genera in the Krahenbach were Stichtochironomus and Corynoneura. Prodiamesa olivacea (Meigen, 1818) was the dominant chironomid species in the Korsch. Deposit-feeding and detritus-feeding animals were numerically dominant in both streams. The increased mean abundance of Diplogasteridae, Rhabditidae, Tubificidae and N. elinguis in the Korsch compared to that in the Krahenbach indicates an organically enriched situation.