Rotifer species have positive responses in abundance caused by the increase in nitrogen, phosphorus and chlorophyll-a in reservoirs using Threshold Indicator Rate Analysis

Certain zooplanktonic species show fluctuations in abundance corresponding to increased primary productivity in freshwater lentic ecosystems. The objectives of this study were i) to evaluate the concentration thresholds of eutrophication-related variables (nitrogen, phosphorus, and chlorophyll-a) that influence the frequency and relative abundance of rotifer species, and ii) to identify rotifer species that are positively or negatively associated with these variables. The rotifer structure was investigated in fifteen La Plata River Basin reservoirs, the second-largest in South America. Abundance was correlated with nitrogen, phosphorus, and chlorophyll-a using Threshold Indicator Rate Analysis (TITAN). A total of seventy-one rotifer species were found, with six identified as indicators for alterations in occurrence and relative abundance, exhibiting threshold values of 1.118 µg.L-1, 22.44 µg.L-1 and 3.89 µg.L-1 for nitrogen, phosphorus, and chlorophyll-a concentrations, respectively. Keratella tropica, Plationus patulus, Filinia terminalis, and Synchaeta oblonga demonstrated positive responses to nutrient increase, whereas Conochilus unicornis and Synchaeta stylata exhibited negative responses, indicative of oligotrophic reservoirs. Keratella tropica consistently responded similarly across all variable concentrations, highlighting its ubiquity in South America. These results reinforce the utility of rotifer species as reliable indicators for trophic level-related variables in reservoirs.

This study was supported by: FAPESP #2008/02015-7 and #2009/00014-6; CAPES #88882.180513/2018-01; and CNPq #141323/2018-3.