Spatial distribution and population dynamics of a benthic rotifer, Embata laticeps (Murray) (Rotifera, Bdelloidea) in the bed sediments of a gravel brook

• 1 The spatial and temporal distributions of the most abundant bdelloid rotifer, Embata laticeps (Murray), inhabiting the sediment surface and the hyporheic interstitial of a gravel stream were investigated between October 1991 and October 1992. Three temporal peaks of population density occurred during the year at the sediment surface differing in their riming from the density peaks detected within the bed sediments.
• 2 The depth distributions of E. laticeps in pool and riffle areas differed significantly. Higher abundances were found between 10 and 20 cm depth in the pool and between 20 and 30 cm in the riffle area. In these two sites a significant effect of surface discharge (estimated 1 week before sampling) on rotifer densities was found. Discharge greater than 0.424 m³s^?1 significantly reduced the densities in the riffle, while only at values greater than 1.660m³s^?1 were abundances influenced in the pool area.
• 3 The percentages of egg-bearing females were higher within the bed sediment than in the surface layer, and in the pool area than in the riffle. Thus, overall mean values of population increase were higher in the pool habitat (x?= 0.015 ± SE 0.029 day^?1) than in the riffle and at the sediment surface (x?= 0.004 ± 0.025 and 0.005 ± 0.026 day^?1, respectively). In addition, population growth fluctuated more strongly at the sediment surface than within the hyporheic intersiritial. Comparison of the observed values of population increase with a randomization test, where observed densities were randomly permuted, revealed no significant differences between those observed and values from a random model. Thus, a clear trend in population growth of E. laticeps over time could not be demonstrated in this gravel stream.