The community structure of Testate amoebae (Amoebozoa, Rhizaria) and their relation to water pH in reservoirs in Northeastern Bulgaria

The identification of variability in testate amoebae communities and their environmental dependencies makes it possible to clarify many issues related to the changes in natural and artificial ecosystems. The present study covers the benthic testate amoebae fauna of seven reservoirs: Brestovene, Beli Lom, Loznitsa, Kara Michal, Bogdantsi, Isperih, and Lipnik. Regression analysis and canonical correspondence analysis were performed to determine differences in testate amoebae communities between reservoirs. The obtained results show that in the Bogdantsi Reservoir, only two genera, Centropyxis and Difflugia, dominate, which, together with the established extremely low taxonomic diversity and abundance of testate amoebae, is an indication of the presence of strong eutrophication and unsuitable conditions in it. In the Loznitsa and Beli Lom reservoirs, dominance is distributed among a large number of genera, and a significantly larger number of species and individuals are found, which indicates the presence of a sustainable and suitable environment for development of testate amoebae. Our CCA results suggest that species distribution differs along the pH gradient. The species Centropyxis aerophila, C. aerophila v. sphagnicola, Difflugia pristis, and Schonbornia viscicula have a very positive correlation with pH, while Cyclopyxis ambigua, Difflugia minuta, and D. elegans have a negative correlation with pH.