Distribution of aquatic insect communities in the longitudinal gradient of a river basin in southeastern Brazil

Abstract

The distribution und abundance of aquatic insects were studied in the longitudinal gradient of the Rio Macaé basin, a coastal river of the tropical rain forest in the State of Rio de Janeiro. River sections were selected in the 1ª, 2ª, 4ª, 5ª and 6ª orders. In each of these reaches four samples were collected by means of a surber sampler in each of the following substrates: sand, pool litter, riffle litter, and stone. The data were analysed by the multivariate methodologies of Correspondence Analysis (CoA) and Cluster Analysis (UPGMA) using the similarity index of Morisita. These procedures were applied to an abundance matrix of 100 OTUs (Operational Taxonomic Unities), in 19 samples of April 1905. The Mantel test was used to check ecological factors that could explain the distribution patterns found. The quantitative and qualitative CoAs, as well as the Cluster Analysis, showed a significant faunal disrupture in the river: the upper reach, from 1ª to 4ª orders,   and the lower reach, grouping 5ª and 6ª orders. Among the factors analysed in order to understand the community structure, just the biophysiographic conditions and the distance from the river source were significant to explain the longitudinal pattern.