Intra-annual variation in planktonic ciliate species composition (Protista: Ciliophora) in different strata in a shallow floodplain lake

Abstract Aim: We aimed to evaluate the variation in planktonic ciliate species composition in different strata of the Guaraná Lake, encompassing high and low water periods, at the Upper Paraná River floodplain. Methods Samplings were collected monthly between March 2007 and February 2008, from the epilimnion, metalimnion and hypolimnion. Ciliates samples were filtered using a plankton net of 10µm mesh size and identified in vivo under an optical microscope. Results Among 112 species identified, 13 were found exclusively during the high water periods and 39 during the low water period. Results of nonparametric extrapolation indices evidenced that the observed richness represented between 70% and 90% of the estimated richness. Regarding the variation in species composition, Beta1 index showed that the alteration in composition between strata during the low water period was slightly greater than that registered during high waters. Cluster analysis evidenced a higher dissimilarity in ciliate species composition between periods than among the different strata. The greatest variation in species composition was verified during the distinct hydrological periods, whereas no significant differences were observed for the different strata analysed. Conclusions We found that in the pelagic compartment, ciliate species composition changed significantly between hydrological periods, and a higher similarity in species composition among strata was observed during the high water period. Therefore, alterations in the vertical distribution seem to be related to the homogenizing effect of the floods in the water column stability.

摘要 研究目的：本研究旨在评估巴拉那河上游泛滥平原瓜拉尼湖不同水层（涵盖丰水期与枯水期）的浮游纤毛虫物种组成变化。
研究方法：于2007年3月至2008年2月期间每月开展采样，采样覆盖湖上层（epilimnion）、温跃层（metalimnion）与湖下层（hypolimnion）。采用孔径10μm的浮游生物网过滤纤毛虫样本，并通过光学显微镜进行活体鉴定。
研究结果：本次共鉴定出112个纤毛虫物种，其中13个仅在丰水期检出，39个仅在枯水期检出。非参数外推指数结果显示，本次观测到的物种丰富度占估计总丰富度的70%~90%。针对物种组成变化的分析表明，Beta1指数显示枯水期各水层间的物种组成差异略高于丰水期。聚类分析结果显示，不同水文时期间的纤毛虫物种组成差异显著高于不同水层间的差异。物种组成的最大变异出现在不同水文时期之间，而所分析的各水层间未观测到显著差异。
研究结论：本研究发现，在浮游水层（pelagic compartment）中，纤毛虫物种组成在不同水文时期间存在显著变化，且丰水期各水层间的物种组成相似性更高。由此可见，垂直分布的变化似乎与洪水对水柱稳定性产生的均质化效应密切相关。