Assessment of environmental variables determining the spatial distribution and species structure of testate amoebae in a stratified freshwater lake

1. Testate amoebae are unicellular organisms that occur worldwide in lacustrine habitats and have been widely used as proxies for palaeoreconstruction and bioindicators of contemporary ecosystems. Our knowledge of the environmental factors determining the spatial distribution of testate amoebae in stratified freshwater lakes is still limited.2. The aim of this study was to assess the influence of environmental variables on testate amoebae assemblages living within one lake basin and to determine the factors influencing the species structure and spatial distribution of testate amoebae communities along a depth gradient and within one limnological zone.3. In our study, we used a multystation approach within one waterbody. We collected samples at five transects at five depths in four limnological zones, for a total of 69 samples from 24 sites. Redundancy and k-means analysis distinguished four groups of samples associated with different environmental conditions.4. Our results indicate that the distribution of testate amoebae species was determined by a variety of factors. The distribution of communities along the depth gradient was determined by temperature, electrical conductivity, and blue-green algal phycoerythrin. Within the littoral zone, the distribution of species was determined either by differences in sand content in sediments or by the stochastic beginning of community assembly. In deepwater habitats, the distribution of species was determined by dissolved oxygen concentration, pH and blue‒green algal phycoerythrin.5. We suggest that assessing habitat and community differences in stratified lakes requires a multystation sampling approach.