The spatial structure of zooplankton communities and trophic state of mid-city Strzeszyńskie Lake

Abstract

Studies on Strzeszyńskie Lake were conducted in May and June 2007. The main aim of this study was to compare the composition and dynamics of the zooplankton communities between two different zones: the open water area and the littoral zone (including Chara tomentosa and Typha angustifolia stands). The stand located within Chara tomentosa possessed the highest number of identified species and most abundant zooplankton communities, while the station loc- ated within the pelagic zone was characterised by the poorest taxonomic structure and the lowest mean zooplankton densities for both rotifers and crustaceans. Zooplanktonic organisms moved in a horizontal direction in order to avoid predators. In the littoral zone, markedly high densities of pelagic species were also recorded. Furthermore, in the zone of stoneworts six Chara-associated species were found. The open water zone of Strzeszyńskie Lake was dominated by limnetic spe- cies, while within macrophyte-dominated stands a more diverse dominating structure occurred, representing both limnetic and littoral species. Among dominating species the presence of species indicating low trophic conditions was recorded. The low state of the trophic conditions of the wa- ter of Lake Strzeszyńskie was also confirmed by the participation of mesotrophic species in the total zooplankton abundance which reached between 14 and 72%.