CHANGES IN THE ZOOPLANKTON COMMUNITY OF THE ECOTONE ZONE BETWEEN ISKAR RIVER AND ISKAR RESERVOIR AND THE PELAGIAL OF THE RESERVOIR
MILENA STEFANOVA*, DIMITAR KOZUHAROV, GALERIDA RAJKOVA
Department of General and Applied Hydrobiology, Faculty of Biology, Sofia University “St. Kliment Ohridski”, Sofia, Bulgaria
*Corresponding author: miki_milena.s@abv.bg
Keywords: zooplankton, quantitative parameters, ecotone zone, Iskar reservoir, Iskar River
Abstract: Iskar Reservoir is the largest reservoir in Bulgaria and provides more than 2/3 of the water for the capital Sofia. There are no data about the zooplankton of the reservoir for the last 30 years. The qualitative and quantitative zooplankton parameters in the ecotone zone Iskar river – Iskar reservoir were studied from July 2009 to March 2014. The zooplankton community was composed of 29 species of Rotifera, 17 species of Cladocera, 4 species of Copepoda and 3 species of Protozoa. Some not typical plankton elements were also found. The broad characteristics of the zooplankton in Iskar reservoir were compared with the available previous data and publications. There is a significant difference in the species composition. Daphnia hyalina and Syda crystalina are among the dominants in earlier periods. Recently these two species weren’t found in the zooplankton composition of Iskar reservoir. Among the copepods Thermocyclops crassus is a species, that a few years ago occurs sporadically in Bulgarian waters. At present, it is common for Iskar reservoir. The cladocera Leptodora kindti was registered for the first time in the reservoir. Some relations were found between the trophic state of the reservoir and the zooplankton community. The obtained preliminary results from this study indicate an advanced process of eutrophication.