Factors affecting assemblage attributes of freshwater Oligochaeta in Neotropical shallow floodplain lakes

Abstract Aim: Identify the effects of sediment composition and water conditions on diversity, richness, evenness, density and composition of freshwater Oligochaeta in shallow floodplain lakes. Methods We sampled 13 shallow floodplain lakes quarterly during the year 2010 in the Upper Paraná River floodplain. In each lake, four sediment samples were taken from the shore and central regions, three of them were used for biological analysis, and one for granulometric analysis. Concomitantly, temperature, dissolved oxygen, pH, conductivity, alkalinity, turbidity and chlorophyll-a were also measured. Initially, the biological samples were analyzed by a stereoscopic microscope. Oligochaeta individuals were identified under optical microscope at the lowest possible taxonomic level. For data analysis, we quantified density, richness, evenness and diversity index of freshwater Oligochaeta. In order to show differences between the months and the analyzed lakes, in relation to the percentages of coarse and fine organic material, the nonparametric Kruskal Wallis test was used. We also calculated the sediment granulometric diversity using the Shannon-Wienner index, using a simple regression analysis. We correlated assemblage attributes of Oligochaeta with sediment diversity and the assemblage species with the limnological variables using the Spearman correlation. Results A total of 2,090 individuals were found distributed among 27 species. From the total individuals number, 57% were Pristina americana, followed by Dero (Dero) righii with 13%. Assemblage attributes were not significantly correlated with sediment diversity, and 7 of the 27 species recorded showed significant correlations with at least some of the abiotic variables. Conclusions We verified that the abiotic variables of the water present greater influence on the attributes of the assemblage of freshwater Oligochaeta, when compared with sediment influences. Although we found low local diversity of this group, the wide range of water conditions offered by lakes culminates with a great species richness considering the whole landscape.

摘要
研究目的：探明沉积物组成与水体环境条件对浅滩洪泛平原湖泊中淡水寡毛类（Oligochaeta）的多样性、丰富度、均匀度、密度及群落组成的影响。

研究方法：2010年全年按季度对巴拉那河上游洪泛平原的13处浅滩洪泛平原湖泊开展采样工作。在每处湖泊的沿岸与中心区域采集4份沉积物样品，其中3份用于生物学分析，剩余1份用于粒度分析。同步测定水体温度、溶解氧、pH值、电导率、碱度、浊度及叶绿素-a含量。
初步通过体视显微镜对生物样品进行镜检分析，随后在光学显微镜下将寡毛类个体鉴定至尽可能低的分类阶元。数据分析阶段，我们量化了淡水寡毛类的密度、丰富度、均匀度及多样性指数。为比较不同采样月份与研究湖泊间粗、细有机物质占比的差异，采用非参数克鲁斯卡尔-沃利斯（Kruskal Wallis）检验。同时利用香农-威纳（Shannon-Wiener）指数计算沉积物粒度多样性，并开展简单回归分析。采用斯皮尔曼（Spearman）相关性分析，将寡毛类群落特征与沉积物多样性进行关联，并将寡毛类物种组成与湖沼学变量进行关联。

研究结果：共采集到2090个个体，隶属于27个物种。总个体数中57%为美洲普利斯蚓（Pristina americana），其次为德里蚓（Dero (Dero) righii），占比达13%。寡毛类群落特征与沉积物多样性未呈现显著相关性；在所记录的27个物种中，有7个物种与至少一项非生物环境变量存在显著相关性。

研究结论：相较于沉积物的影响，水体非生物变量对淡水寡毛类群落特征的影响更为显著。尽管该类群在局部区域的多样性水平较低，但湖泊所提供的宽泛水体环境梯度使得整个研究区域的物种丰富度处于较高水平。