Changes in the biodiversity of aquatic environments over time and space due to human activities are a topic of theoretical and conservational interest in ecology. Thus, variation in taxonomic beta diversity of the planktonic ciliates community was investigated along a temporal and spatial gradient in two subsystems of a Neotropical floodplain, one impacted by dams (Paraná) and the other free of them along its course (Ivinhema). For the spatial analysis, the Paraná subsystem did not show a significant decrease in beta diversity, presenting a pattern like that observed for the Ivinhema subsystem. Therefore, biotic homogenization was not observed for the ciliate's community downstream of the dams. It was noted that there was a fluctuation in the relevance of the components of beta diversity, regardless of the subsystem analyzed. For the temporal analysis there was a significant change in species composition from the first to the last year investigated, essentially for the subsystem impacted by dams, and that this was determined mainly by species loss. Although spatial beta diversity remained high without a clear process of biotic homogenization, dams promoted remarkable changes in ciliate species composition over the years mainly by continuous loss of species.

Aim In this study, we focused on patterns of ciliate protist community composition in urban and rural streams.

Planktonic freshwater organisms, such as ciliates, play an important role in the transfer of matter and energy and, therefore, in the functioning of aquatic ecosystems. Due to their small size, the analysis of these communities is usually carried out using optical microscopy and various techniques. However, there are many challenges regarding this group, such as the difficulty in identifying them and the lack of experienced personnel for counting these organisms. Therefore, the aim of this study was to compare possible discrepancies in the results of organism counts, taking into account that these results may be influenced by the individual carrying out the sampling. To this end, the differences in the analyses of richness and abundance performed by four (4) analyzers and their respective ratings of the fixed samples were compared. The hypothesis was that more experienced analyzers would record higher values of species richness and density scores than those with less experience. The results obtained were consistent with the initial hypotheses and showed that two of the more experienced analyzers were associated with higher values for the attributes analyzed.