A Three Years' Study of Life Cycle, Population Dynamics and Production of Asellus aquaticus L. in a Macrophyte Rich Stream

Populations of A. aquaticus were sampled quantitatively in 1979–82 at two localities in the river Suså which has a slope of <1 m km−1 and large variations in macrophyte biomass, discharge and stream velocity. The latter two differed significantly between years. A. aquaticus had (1)−2 life cycles per year and summer and winter cohort production intervals of 85 and 290 days. Populations of A. aquaticus varied between 0 and 28,000 ind. m−2 with an exponential increase in the spring and an exponential decrease in the autumn‐winter. The A. aquaticus rate of decrease varied between 0.62 and 5.61 % d−1 and increased with increasing rate of elimination of the macrophyte biomass Differences between the two localities were due to differences in physical heterogeneity. Production varied between 2.8 and 9.1 g DW m−2 yr−1 and between 12.9 and 55 g DW m−2 yr−1 at the two localities and P/B ratios were 7.4–9.9 yr−1. Physical limitations are thought to be most important for the populations of A. aquaticus in the Suså, and the macrophyte biomass played an important role in modifying the physical environment. Differences between streams and lake populations are discussed.