Zooplankton Community Structure in Small Ponds in Relation to Fish Community and Environmental Factors

The studies were conducted in two small temperate mid-field ponds. The purpose of the research was to determine changes in the zooplankton communities in ponds with diverse ichthyofauna compositions and diverse values of environmental factors. Two research hypotheses were assumed. One pertained to the growth of the number and biomass of Daphnia and the loss of illoricate rotifers due to the top predator influence. The other one assumed that the top predators and the value of conductivity indirectly affect the diversity of zooplankton. We assumed that significant differences in the number of Daphnia between the ponds result from the regulation of the trophic web from the top down and bottom up, that affect the total zooplankton composition. In the small water bodies where Daphnia dominated among cladocerans, the highest numbers belong to loricate rotifers, e.g. Brachionus sp. and Keratella sp., whereas in the ponds where the dominance among Cladocera was Chydorus sphaericus, illoricate rotifers were abundant, e.g. Bdelloidea and Synchaeta sp. We concluded that the presence of the top predator caused a significant increase in the species richness and in the biodiversity index for Cladocera. However, the biodiversity index for the whole zooplankton (determined mainly by small rotifers) decreased with the presence of top predator and increased with high conductivity.