Planktonic ciliates in Neotropical streams: taxonomic and numerical sufficiency and implications for environmental impact assessment

Abstract Bioindicators are widely used to describe environmental impacts through rapid and cost-effective assessments. However, identifying them at the species level with detailed quantitative sampling is time-consuming, expensive, and requires specialized knowledge. This study evaluated, using planktonic ciliates, taxonomic and numerical sufficiency approaches to test whether higher taxonomic levels and different numerical resolutions provide patterns comparable to those obtained at the species level. Sampling was carried out in ten streams during two hydrological periods. Results showed that genus and family levels consistently retained the structure observed at the species level, while the order level implied loss of information. Abundance-based approaches captured hydrological differentiation and environment-community relationships more clearly than presence-absence data. The environmental component stood out as the main driver in structuring the community, at different taxonomic and numerical levels, with weaker relationships at the order level and using presence-absence data, while sharing contributions with the temporal component. This suggests that hydrological seasonality modulates the abiotic “template” that organizes biotic communities, including ciliates. Thus, a monitoring strategy for planktonic ciliates that uses genus and family, preferably abundance-based, is efficient for routine ecological assessments, but not at the expense of reliable species-level biodiversity surveys as references for ecological theories and conservation.