Vertical micro-distribution of psammonic ciliates and their relationship to physical and chemical parameters in two lakes of different trophic status

The aim of this study was to examine the community structure and vertical micro-distribution of psammonic ciliates in two lakes of different trophic status in eastern Poland. Additionally, the size and trophic structure of these microorganisms, and the influence of physical and chemical water parameters on their abundance, were analysed. Psammon samples were collected during spring, summer, and autumn of 2010. In each of the lakes samples were collected in the euarenal, higroarenal, and hydroarenal zones of the psammolittoral. In order to determine the micro-vertical distribution of ciliates, each sample was divided into two sub-samples: the upper part (0–1cm) and the lower part (1–2cm). The species diversity of ciliates decreased with depth. The tendency was particularly clear in mesotrophic lakes. Irrespective of the lake’s trophic type and arenal zones, significantly higher numbers and biomass of ciliates were recorded in the surface layer of the psammolittoral. The upper layer of sand was dominated by omnivorous taxa, whereas the deeper layer showed increases in the proportions of bacterivore species. The factors limiting the occurrence of ciliates are mainly concentrations of total organic carbon and nutrients.