Chironomidae (Insecta: Diptera) of different habitats and microhabitats of the Vacacaí-Mirim River microbasin, Southern Brazil

The Chironomidae family is one of the main groups of aquatic insects present in streams. This work aimed to investigate the influences of anthropogenic pressures and substrate types on chironomid community composition and structure. Chironomid larvae were collected during the summer of 2007 at four sites along the Vacacaí-Mirim River microbasin, chosen based on the different available benthic substrates. The organisms were identified in the laboratory at the genus level, and the density, the rarefied taxonomic richness and the Shannon diversity index were calculated. The faunal structure was subjected to an ANOVA to compare the metrics among sites and substrates. The community composition of the sites was subjected to a multivariate statistical analysis. Differences in the composition, richness, density, and diversity were observed among the sites due to differences in the levels of nutrients and solids generated by the presence of crops close to water bodies. Samples collected from sandy substrates exhibited a lower density and taxonomic richness because sand is a poorer substrate than the others that were sampled. In organic or mixed substrates with higher energy availability and better shelter conditions, the observed densities were higher. The physical and chemical conditions and the morphometric characteristics of the sites were more influential than the substrates.

摇蚊科（Chironomidae）是溪流中主要的水生昆虫类群之一。本研究旨在探究人为压力与底栖基质（benthic substrates）类型对摇蚊群落组成与结构的影响。2007年夏季，研究人员在瓦卡卡伊-米林河（Vacacaí-Mirim River）微流域的4个采样点采集摇蚊幼虫，采样点依据现有不同类型的底栖基质选取。所有标本均在实验室鉴定至属级水平，并计算了种群密度、稀疏化分类丰富度以及香农多样性指数（Shannon diversity index）。采用单因素方差分析（ANOVA）比较不同采样点与底质间的群落指标差异，并通过多变量统计分析探究各采样点的群落组成特征。研究发现，由于水体附近农田产生的营养物质与固体污染物水平存在差异，不同采样点的群落组成、丰富度、密度及多样性均存在显著差异。沙质底质的采样样本密度与分类丰富度均较低，这是因为沙质基质相较于其他采样底质更为贫瘠。而在有机基质或混合基质中，由于能量可获得性更高且庇护条件更优，观测到的群落密度更高。相较于底栖基质类型，采样点的理化条件与形态计量特征对群落的影响程度更大。