Eficiência de diferentes abordagens metodológicas e caracterização das associações macrobentônicas estuarinas da zona costeira amazônica

Abstract

The estuarine macrobenthic communities from Amazonian coastal regions were characterized using different mesh sizes and sampling depths. The samplings were performed in Algodoal island and peninsula of Ajuruteua (PA), during rainy and dry seasons (June and December 2007, respectively) at the following habitats: mangrove edge, mangrove, sandy and muddy-sandy paths. At each habitat eight biological samples were collected using a cylindrical corer with 0.0079 m², as well as samples for sediment analysis (texture, moisture and organic matter concentrations) and chlorophyll a and pheopigments concentrations. Each biological sample was devided into three strata (0-5, 5-10 and 10-20 cm) and they were sieved on mesh screen sizes of 1.0, 0.5, 0.3 and 0.25 mm. Univariate (ANOVA) and multivariate (MDS, ANOSIM, SIMPER and BIOENV) techniques were used for data analysis. Macrofaunal composition consisted of 68 taxa with dominance of Annelida (Tubificidae and Capitellidae). Meshes of 0.3 and 0.25 mm were the most efficient in terms of retention of organisms and species, while the mesh of 1.0 mm lost significant quantities of organisms, especially Tubificidae. The samples collected at 10 and 20 cm depth did not differ significantly regarding to the number of taxa and organisms. Significant spatial variations were observed on the macrofaunal structure between habitats in both locations and sampling moments, with higher density and richness in muddy paths (mangrove edge and mangrove). The amount of clay, organic matter and moisture concentrations of the sediment were the most correlated environmental variables with the fauna. It could be concluded that: 1. the benthic macrofauna in Algodoal island and peninsula of Ajuruteua was composed by few taxa, and those were typically estuarine and of small dimensions, dominated by Annelida; 2. for characterization of benthic macrofauna is necessary to take samples at 10 cm depth and sieve them on mesh of 0.3 mm size; 3. Muddy-sandy habitats presented normally highest densities and richness; 4. only in Algodoal island was observed temporal variation in the structure of benthic macrofauna; 5. the amount of clay, pheopigments and moisture content in the sediment were the main factors responsible for macrofaunal structure.