Polychaete assemblages of the Gallegos river estuary, Southern Patagonia, Argentina

During the spring of 2013, benthic samplings were conducted in four sites located on both banks of the Gallegos river estuary. Five samples were taken per tidal level at each site following a transect perpendicular to the coast. The relative abundance of the species, the dominance, the species richness, the equitability and the diversity index of Shannon-Wiener were calculated. The abundance data were compared by multivariate analysis, using the Bray-Curtis similarity index, and the nonparametric ordination technique. We identified fourteen polychaete species, being Fabricinuda sp. the most abundant, followed by Notocirrus lorum and Kinbergonuphis dorsalis. Abundance, equitability and diversity showed significant differences between sites. The highest abundance was recorded in the lower intertidal level of S1 site, next to Rio Gallegos city, due to the presence of Fabricinuda sp. that forms biogenic structures of great extension with high density of organisms. In the same place, the highest species richness and the lowest diversity and equitability were observed. The results of the multivariate analysis indicated the presence of three main groups of polychaetes, associated with sediments with different organic matter content and different granulometric composition.