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Gean Zanetti3; Emanuely Ezidio da Silva1; Eliezer Alves Evangelista Junior1; Felipe Souza Cordeiro1; Gabriel Mauri1; Mônica Pereira de Jesus1; Gisele Oliveira Tonácio1; Karla Gonçalves da Costa1; Priscylla Pavione2; Clayton Perônico3, Tatiana Furley2.

1 - Laboratório de Ecologia Bentônica, Universidade Federal do Espírito Santo, Departamento de Ciências Agrárias e Biológicas - DCAB/UFES/CEUNES, Rodovia BR 101 Norte, Km. 60, Bairro Litorâneo, CEP 29932-540, São Mateus, ES.

2 - INSTITUTO APLYSIA, Rua Júlia Lacourt Penna, 335, Jardim Camburi, Vitória, Espírito Santo, CEP: 29090-210

3 - Instituto Federal do Espírito Santo- IFES, Av. Rio Branco, 50 - Santa Lúcia - Vitória, CEP 29056-255

Introduction. Estuarine environments are very important ecologically for nutrient retention, based on water circulation conditions that create great productivity and help in the development of a diversified fauna and flora. The benthic community structure in these environments is controlled by biotic processes (adult-juvenile interactions, predation, competition, etc.), abiotic processes (salinity, temperature, hydrodynamics, substrate nature, etc.), and anthropogenic effects (contamination by toxic compounds, organic enriching, etc.). Organism composition and abundance in estuarine environments and adjacent areas may vary in the spatial as well as temporal scale. However, this study was intended to describe the spatial distribution of benthic community from the estuary of Benevente river at Anchieta, in the south of the State of Espírito Santo (S 20°48.34 W 40°39.41), as part of a larger study, known as "Peixe-Guia project?, for quality analysis of estuarine water.

Results. A total of 32,747 organisms were found, spread out in 12 taxonomic groups. The tanaidaceaMonokalliapseudesschubartiMañé-Garzón, 1949, was the most abundant taxon, with 98.4% of individuals collected, and the remainder (Amphipoda, Isopoda, Decapoda, Bivalve, Pisces, Chironomidae, Odonata, Spionidae, Capitellidae, Nereididae and Lumbrineridae) jointly contributed with 1.57%. Species richness and Shannon-Winner diversity reflected significant higher values at the Upstream, only differentiated from the River Mouth (p<0.05). The taxa Chironomidae, Spionidae, Capitellidae, Nereididae and Lumbrineridae were solely Upstream taxa. However, the abundance of species showed no significant difference among the locations sampled. Multivariate MDS and ANOSIM analyses returned no significant differences in the fauna structure (composition and abundance) among the locations sampled.

Discussion. The tanaidacea M.schubarti, the most abundant taxon in this study, may occur in great densities in some populations exceeding 145,000 ind./m2. These are typical of Brazilian estuarine sediments and intertidal plains. Tanaidacea are animals that build tubes, mainly on the sediment surface, forming dense groups that may lead to an increased spatial heterogeneity. This large tanaidacea density was also found in a 2006 study at the infralittoral close to the Benevente river mouth. The homogeneous distribution of M.schubartialong the estuary suggests that it is tolerant with the variables analyzed. One of the most common causes of environmental impacts throughout the world is eutrophication of estuarine systems caused by an increase in nitrogen and phosphorus from the continent. Usually, the macrofauna community reacts to increased concentrations of nutrients and a rise in organic matter production; however, after an excessive addition of nutrients to the system, the organic matter sedimentation will exceed the degradation rate, causing a decrease of oxygen in the surface layer of sediment as well as changes in the benthic community composition, which may possibly explain the decline in richness and diversity at the River Mouth, where greater values of organic carbon, nitrogen, phosphorus and surfactants were found. The lower salinity value recorded at the Upstream may have led to the appearance of the Chironomidae taxon, as such organisms have a preference for less saline environments.

Conclusion. The estuary of Benevente river has proved to be an environment that favors large densities of the tanaidacea M.schubarti. Nevertheless, physical and chemical variables such as total organic carbon, total nitrogen, phosphorus and surfactants vary along the estuary, with greater values recorded close to the river mouth and decreasing in the upstream direction, which may possibly be related to the greater richness and diversity found upstream. Therefore, the environmental variables of the estuary of the River Benevente seem to directly influence the local macrofauna structure.