The impact of environmental factors on zooplankton communities in the Vistula Lagoon

The Vistula Lagoon, an estuarine system exposed to both continental and marine impacts, is marked by rapid changes in local environmental conditions, including salinity levels, water transparency, temperature, pH, dissolved oxygen concentrations, trophic state and wind speed. Here, the effect of environmental factors on the abundance and horizontal distribution of zooplankton was analysed. A higher number of taxa were noted in the saltwater intrusion section of the Vistula Lagoon (Central Basin) compared to the area of freshwater inflow (Western Basin). The average density of the analysed zooplankton in the western section of the Vistula Lagoon reached 654 indiv. dm−3, three-fold higher than in the central section (224 indiv. dm−3). Differences in zooplankton biomass were even more pronounced (13.43 mg dm−3 vs. 2.33 mg dm−3). The Central Basin of the Vistula Lagoon was dominated by Copepoda (approx. 50% total abundance), mostly Calanoida (genus Acartia) typically found in brackish waters. Marine species, including Acartia bifilosa and Acartia tonsa, were also reported. Species of freshwater Cladocera predominated in the Western Basin (over 50% total abundance, mostly the eutrophic species Chydorus sphaericus) where Copepoda were represented by a single cyclopoid species, Cyclops vicinus. The saline and freshwater environments of the Vistula Lagoon differed significantly (p<0.001) with respect to the abundance and biomass of zooplankton. The above differences resulted not only from salinity and temperature conditions, but also from dissolved oxygen concentrations, the trophic state of the investigated water body, and the existing biocenotic relationships.