Seasonal succession and spatial distribution of the zooplankton community in the reservoir of Esch-sur-Sûre (Luxembourg).

During three years (1990, 1999 and 1993), the zooplankton community of the Esch-sur-Sure reservoir was investigated. A total of 75 taxa, dominated by rotifers, was observed. Zooplankton densities increased from the damsite towards the headwaters of the reservoir; they peaked in spring and at the end of summer. Despite quantitative differences, the same species succession was observed during the three years and at all the lake sampling stations. Thus the zooplankton community shifted from rotifers in early spring to small-bodied cladocerans (Bosmina spp.), and, finally, to larger cladocerans (Daphnia spp.) in early summer. Shifts in zooplankton composition have also frequently been observed in midsummer, when the cladoceran assemblage of Daphnia-Bosmina was generally replaced by a combination of Ceriodaphnia-Diaphanosoma. These species successions are discussed in relation to size-selective predation, resource limitation and interspecific competition.