Utjecaj biotičkih čimbenika na raspodjelu zooplanktona eutrofnog jezera

The research of zooplankton in Oxbow Skrcev kut was carried out from May to October 2013. The goals of this study were to determine: (i) diversity, abundance, a size and trophic structure of zooplankton in the pelagic and littoral; (ii) zooplankton species in the sediment; (iii) structure of tactile and visual predators; (iv) impact of predation and food resources on zooplankton distribution in the eutrophic lake. The results of statistical analysis indicated a statistically significant oscillations of physico-chemical factors during the study period, while their differences as well as the zooplankton structure between the the pelagic and littoral were not statistically significant. The increase of turbidity was primarily driven by suspended solids and phytoplankton, which caused little or no cover of macrophytes. Results indicate that zooplankton migrations were not exhibited because the fish as a visual predators were less efficient due to high turbidity. The absence of macrophytes also reduced the role of the littoral zone, although the total abundance of zooplankton was higher in the littoral area. The small abundance of the group Cladocera in zooplankton indicates that due to larger dimensions and low mobility they were the main source of food for visual predators. Removing of large algivornog zooplankton (Cladocera) by predators causes higher abundance of smaller organisms (Rotifera) that have a lower rate of filtration and didn't affect the reduction of turbidity. The size structure zoplanktona was dominated by small individuals. The greatest abundance and diversity in the pelagic and littoral recorded Rotifera, with the highest share of microfiltrator species, of which the greatest abundance species had Keratella tecta. Tactile predators (Insecta larvae and crustaceans Cyclopidae) in macrozoobenthos with their predation contributed to a reduction of planktivory microfiltrators. Results of this study suggest that increasing of trophic level reduces the diversity of habitats and impacts on changing of biotic interactions in shallow lakes.