Structure and dynamic of planktonic ciliate community in a large Neotropical river: the relevance of the pluviosity and tributaries in the biodiversity maintenance

Abstract Aim: We investigated the spatial and temporal patterns of abundance and diversity of planktonic ciliate community, in the last undammed stretch of the Upper Paraná River, Brazil. Methods In order to reach this result, seven field campaigns were performed over two years. Plankton samples were collected from 10 transects through this stretch of the river (230 Km), near the banks and on the center, as well on seven of its tributaries. Results 118 ciliate species were identified, among which the peritrichs were the most abundant while the order Hymenostomatida was the most specious group. We recorded a remarkable increase in abundance and species richness along the river, especially in the rainy period. Moreover, in this period we found an increase in the beta-diversity along the river, which consists in a remarkable distinction among the low, middle and high stretch of the river. In this way, continuous changes in the community structure of planktonic ciliates were evidenced, highlighting the importance of the precipitation and tributaries in the maintenance of the highest regional diversity in the studied area. Conclusion Our results strongly suggest the requirement for conservation actions with the purpose to maintain those tributaries undammed, in order to avoid biotic homogenization processes and the consequent reduction of aquatic biodiversity in this important neotropical ecosystem.研究目的：针对巴西巴拉那河上游（Upper Paraná River）最后一处未筑坝河段，本研究探究了浮游纤毛虫（planktonic ciliate）群落丰度与多样性的时空分布格局。 研究方法：为达成该研究目标，本研究在两年内开展了7次野外采样工作。研究人员于该230公里的河段内设置10条采样断面，分别在近岸及河道中心区域采集浮游生物样本，同时对该河段的7条支流进行同步采样。 研究结果：本研究共鉴定出118种纤毛虫，其中缘毛目（Peritrichs）类群丰度最高，而膜口目（Hymenostomatida）为物种丰富度最高的类群。研究发现，沿河道方向的纤毛虫丰度与物种丰富度均呈现显著上升趋势，且该趋势在雨季尤为明显。此外，雨季期间沿河道的β多样性（beta-diversity）亦有所提升，具体表现为该河段的上游、中游、下游区段群落结构存在显著差异。综上，本研究证实浮游纤毛虫群落结构存在连续的空间变化，明确了降水过程与支流输入对维持研究区域内最高区域生物多样性的重要作用。 研究结论：本研究结果强烈表明，需开展针对性保护行动以维持该区域支流的未筑坝状态，从而避免生物均质化过程的发生，进而防止这一重要新热带（neotropical）水生生态系统的生物多样性出现衰退。