Influence of some environmental factors on the distribution of zooplankton complexes in Mandra Reservoir, in Southeastern Bulgaria

The aim of the present study was to trace the influence of some environmental factors (w.temperature, wind, transparency, depth) on the distribution of zooplankton communities in the system Reservoir Mandra and the ecotone zones formed at the confluence of rivers Fakiyska, Sredetska, Izvorska and Rusokastrenska. Four samplings were performed at seven sites between February 2020 and January 2021. After determining the species composition and abundance, the results were subjected to structural analysis and Canonical Correspondence Analysis (CCA). A total of 67 taxa were identified, constituting about 48% of the Rotifera group, 27% of Cladocera and 19% of the Copepoda and only 6% from Protozoa. The Shannon-Weaver index for individual species diversity was between 2.37 and 0.62. The positive and negative correlation of zooplankton distribution in CCA shows that the relative abundance of any species depends on specific environmental variables. Analysis showed that temperature and wind had the strongest impact on the distribution of zooplankton.