Structure and dynamics of the protoplankton community in an environmentally protected urban stream.

We aimed to investigate spatial and temporal scales, abundance, and factors that structure the communities of protozoans in a tropical urban stream. METHODS: Samples of water for analysis of biological communities (testate amoebae, ciliates and bacteria) and limnological variables were taken in the Mandacaru stream located in the Conservation Unit of Parque do Cinquentenário, in the city of Maringá, Paraná State, Brazil, in two hydrological periods (dry and rainy). We calculated the Water Quality Index (WQI) composed by nine parameters of water quality (dissolved oxygen, thermotolerant coliforms, pH, BOD, water temperature, total nitrogen, total phosphorous, turbidity, and total solids), Trophic State Index (TSI) for phosphorous and we used a Redundancy Analysis (RDA) to verify the influence of environmental variables in the protozoan community. RESULTS: The WQI showed that water quality was considered good in some points and considered bad in other points. The TSI for phosphorus classified the stream as mesotrophic in the majority of sampled sites points (mean between 53.09 and 58.35). We identified 19 taxa of testate amoebae, belonging to six families, being Difflugiidae, Centropyxidae, and Arcellidae those with more species and 71 infrageneric taxa of ciliates, distributed in 12 orders being Peniculida the most representative order, followed by Euplotida. According to RDA analysis, samples of the dry period were characterized by higher values of bacteria density and concentrations of chlorophyll-a, total phosphorous, and total nitrogen. Ciliates and testate amoebae presented higher abundance values in some of the months characterized by higher precipitation and in conditions of higher system productivity. CONCLUSION: we may conclude that the Mandacaru stream, although strongly influenced by anthropic action, still presents an acceptable water quality. Lastly, we emphasize that protists abundance was strongly influenced by system productivity. This was evidenced by elevated protozoan densities where there was higher primary and bacterial productivity. Thus, these organisms must be considered in studies that aim at the identification of organisms that may indicate anthropic impacts and environmental quality.