Large-scale spatial patterns of benthic assemblages in the SW Atlantic: the Río de la Plata estuary and adjacent shelf waters

This study deals with the spatial distribution of macrobenthic communities (biomass and abundance) in the Rı´o de la Plata estuary, ArgentinaeUruguay, and the adjacent shelf waters. The benthic invertebrates were caught with an epibenthic dredge (41 samples). Multivariate analysis (cluster, MDS), SIMPER and BIO-ENV analyses were applied to analyze benthic community structure and their relationships with environmental variables. A consistent large-scale diversity pattern was found: a distinctive estuarine zone could be distinguished, with muddy sediments and a wide range of salinity, characterized by higher abundance of fauna and lower diversity, dominated by the deposit-feeding bivalve Mactra isabelleana; and a marine zone, with sandy-shell debris sediments and higher and less variable salinity values, with higher values of diversity. Major presence of deposit feeders was related to higher particulate organic matter in the estuarine area. Bottom type, salinity and the presence of a turbidity front are considered the main physical variables in structuring benthic communities of the Rı´o de la Plata estuary.