| Summary: | Shallow lakes are ecologically and economically important ecosystems because they are significant for biodiversity and they provide many ecosystem services, but most of them are under the eutrophication and desiccation hazard. The first approach towards the evaluation of ecologic conditions of a lake is to determine the patterns of the biological communities, and zooplankton is one of the best indicators. Zooplankton have an important position in the food web between the upper and lower layers both as prey and consumer. Therefore, the determination of species composition and the diversity of zooplankton in a shallow lake can be used as a biological indicator of ecosystem health. In the present study, monthly (except snow covered months) zooplankton variation of Lake Hafik (Sivas, Turkey), and their interaction with the environmental conditions were studied for the first time. Lake Hafik is a mesotrophic lake based on its limnological variables. A total of 19 zooplankton species were recorded with Crustaceans (86% of the total zooplankton abundance) were being dominant. The main abundant taxa (N% > 5 of the total zooplankton abundance) were copepod nauplii, Arctodiaptomus bacillifer (Koelbel, 1885), Keratella quadrata (Müller, 1786), and Daphnia (Daphnia) cucullata Sars, 1862, respectively. The high density and biomass of the zooplankton were determined in May. In terms of diversity, Lake Hafik was not rich. Statistically, the rotifer density and biomass were mainly affected by physical variables (temperature, DO, and pH), whereas the crustaceans was primarily related to nutrients and EC.
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