Balık Gölü'nün (Bafra Balık Gölleri, Kızılırmak Deltası) Zooplanktonik Organizmalarının Mevsimsel Değişimi Üzerine Ekolojik Araştırmalar

Abstract

This study, conducted on Lake Balık between September 2015 and August 2016, aimed to determine the seasonal dynamics of zooplanktonic organisms in the lake. In this study, some physical and chemical characteristics of the lake water were revealed, species composing the zooplankton community were determined, and the zooplankton community was examined based on community parameters such as relative abundance, frequency, similarity, species diversity, and species evenness. Furthermore, the relations between environmental variables were examined by means of Pearson correlation analysis, and the relation between zooplanktonic organisms and environmental variables was examined by means of RDA analysis. The salinity values measured in the lake confirmed the typical mixooligohaline brackish lagoon. It was found that the turbity of the lake water was mostly found to be over 10 ntu and the lake had high turbidity. With the use of Carlson TSI (TP) and Carlson TSI (Chl-a) indexes, it was found that Lake Balık was generally eutrophic as well as reaching hyperthropic level in several months, in terms of its trophic state. In addition, TA:TP means of the lake were found to be over 20, which showed that phosphorus was limiting factor. In the zooplankton community of Lake Balık, 4 of Cladocera, 2 of Copepoda and 32 of Rotifera –a total of 38 taxa– were determined. Based on the months, the species richness in the lake varied significanly (p<0,05). Moreover, it was revealed that there was a positive relation between temperature and species richness according to Pearson correlation analysis, and it was unveiled that rotifer species contributed more to this situation. In addition to this, it was found that species richness was also associated with the presence of submersed macrophyte and the predation of planktivorous fish. In Lake Balık, 99.4% of the zooplankton consisted of organisms in the Rotifera group, 0.13% of the zooplankton was made up of organisms in the Copepoda group, and 0.45% of the zooplankton was composed of organisms in the Cladocera group. The results of the RDA analysis showed that Brachionus calyciflorus, Filinia longiseta, Polyarthra dolicoptera, Keratella cochlearis, Keratella quadrata, Synchaeta pectinata were species that had a negative relation with temperature. Hexathra mira, Keratella tropica and Trichocerca marina had a positive relation with turbidity, pH and Chl-a, but had a negative relation with dissolved oxygen. In Lake Balık, Brachionus angularis, Brachionus diversicornis, Filinia terminalis, Keratella cochlearis, Keratella tropica and Polyarthra vulgaris were found to be eudominant species, while Filinia longiseta, Keratella quadrata and Trichocerca stylata were found to be dominant species. Species frequently found in the lake were typical in freshwater and most of them were those regarded as an indicator of eutrophication and associated with high trophic status. Brachionus/Trichocerca (QB/T) index value of the lake was calculated to be 3. Species diversity of the zooplankton in Lake Balık was evaluated to be between 0.77 and 2.05 on average. All of the mean values within the year were below 2.5, which showed that some species in the community were dominant. Mean Pielou evenness index value was calculated to be between 0.35 and 0.83. The results confirmed that species did not distribute homogenously in the community. According to the results of Pearson correlation analysis, there was a positive relation between the indexes of species evenness and species diversity and turbidity and chlorophyll-a, and there is negative relation between indexes of species evenness and species diversity and light availability.