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.部分浮游动物类群的丰度波动与淡水静水生境中初级生产力的提升呈现对应关系。本研究的目标包括：① 解析影响轮虫(rotifer)类群出现频率与相对丰度的富营养化相关变量（氮、磷、叶绿素a）的浓度阈值；② 筛选与上述变量呈正相关或负相关的轮虫类群。研究于南美第二大流域——拉普拉塔河流域的15座水库中开展了轮虫群落结构调查。本研究采用阈值指示速率分析(Threshold Indicator Rate Analysis, TITAN)方法，解析轮虫丰度与氮、磷、叶绿素a的关联关系。本次调查共记录到71种轮虫，其中6种可作为轮虫出现模式与相对丰度变化的指示类群，其对应的氮、磷、叶绿素a浓度阈值分别为1.118 µg·L⁻¹、22.44 µg·L⁻¹与3.89 µg·L⁻¹。热带龟甲轮虫(Keratella tropica)、阔口平甲轮虫(Plationus patulus)、末端针簇轮虫(Filinia terminalis)与长形单趾轮虫(Synchaeta oblonga)对营养盐升高呈现正向响应；而独角聚花轮虫(Conochilus unicornis)和尖形单趾轮虫(Synchaeta stylata)则呈负向响应，指示水库处于贫营养状态。热带龟甲轮虫(Keratella tropica)在所有变量浓度梯度下均表现出一致的响应模式，印证了其在南美地区的广布性。本研究结果证实了轮虫类群可作为水库营养水平相关变量的可靠指示生物。 本研究得到以下项目资助：圣保罗研究基金会(FAPESP) #2008/02015-7、#2009/00014-6；巴西高等教育人员发展协调局(CAPES) #88882.180513/2018-01；以及巴西国家科学技术发展委员会(CNPq) #141323/2018-3。