Abstract
Dispersal of crustacean zooplankton from a reservoir in a lowland river was observed over a relatively long distance. Zooplankton samples were collected by a unique technique from “the same water”. Large Cladocera (Daphnia cucullata and Diaphanosoma brachyurum) showed the greatest reduction in a river, but they were common over a distance of up to 130 km below a dam. These two planktonic species revealed a low potential for colonizing oxbow lakes. Eurytopic Chydorus sphaericus and Mesocyclops leuckarti transferred from the Siemianówka Reservoir had a great dispersal capacity in the Narew River and could effectively support local populations in oxbow lakes over a distance of 180 km.
Similarity between the crustacean communities in the river and the reservoir significantly decreased with the increasing distance from the dam. At the same time, crustacean communities in oxbow lakes were not affected by the distance from the source. Dispersal from the large source of zooplankton to local communities is a very important process but the local environmental factors such as habitat heterogeneity, aquatic vegetation and the hydrological connectivity can be strong enough to affect the structure of local crustacean communities in oxbow lakes.