Habitat Preferences of Aquatic Oligochaeta (Annelida) in the Rokytná River, Czech Republic – a Small Highland Stream

Research was carried out to determine aquatic oligochaete habitat preferences in the Rokytná River (Thaya River basin), a sixth order highland stream in the Czech Republic during the period of April 1999–April 2001. Quantitative samples were collected and current velocity and basic physico-chemical variables were measured monthly in four typical habitats in the Rokytná River. During this study, 28, 842 individuals representing 44 oligochaete species or higher taxa were collected. Temporal variability of proportional occurrence of trophic groups found on selected habitats (gathering collectors and grazers) was analysed. Habitat preferences of oligochaete species were evaluated by Canonical Correspondence Analysis (CANOCO). Biochemical oxygen demand (BOD) and nitrate (NO3−) ion concentration were the most important variables explaining the distribution of Oligochaeta along the first axis. Current velocity (at 40% of the depth) and presence of oligochaetes associated with the habitat where gravel bars never formed were the most important variables along the second axis. Both axes were correlated with the temperature, reflecting the sampling in summer along the first axis and sampling in late spring along the second axis. The amount of organic matter (BOD) and concentrations of NO3− ions represented both oligochaete food source and decomposition products contributing to the growth of algae. Current velocity and preferred habitat explained the spatial pattern of oligochaete distributions.