Discharge regime and the effect of drying on macroinvertebrate communities in a temporary karst stream in East Westphalia (Germany)

The special hydrological situation of temporary streams has a great influence on the abiotic processes and other habitat conditions for organisms. To monitor possible impacts of stream drying on the composition of lotic communities, streamflow measurements and collections of the macrozoobenthos were conducted in a temporary and an adjacent upstream permanent section of the karat stream Sauer (East Westphalia, Germany) in 1996. The Sauer has a summer-dry temporary now regime. The seasonal dry phase: can last from spring to early autumn, so the duration of the dry phase varies from one to several months, increasing with distance downstream from the upstream permanent section. The number of invertebrate taxa and individuals decreases with increasing duration of the dry phase. The permanent section is characterized by taxa typical of montane and submontane streams, whereas the fauna of the temporary section is quite different, composed of representatives of various zonal areas. Limnephilid caddisflies are particularly characteristic of this section. Life cycle strategies and specific adaptations with respect to habitat drying are discussed for several species. It can be concluded that the temporary discharge regime of the karst stream Sauer has a clear effect on the invertebrate communities. They mainly consist of species which can be seen as characteristic faunal elements of temporary streams.