Macrobenthic functional trait diversity at multiple scales along a subtropical estuarine gradient

The capacity of an infaunal organism to exploit resources in a given sedimentary habitat is reflected by its bioturbation-related traits. Functional traits such as body size, mobility, and type of burrowing behavior reflect the species' bioturbation potential and, therefore, their role in affecting sediment characteristics. In this study, we applied a trait-based approach to assess the variation in the functional diversity of intertidal macrobenthic assemblages from Guaratuba Bay, a subtropical estuarine system in Southern Brazil. We expected that changes in sediment characteristics across and within estuarine zones would be followed by detectable changes in the trait diversity of infaunal assemblages. The estuarine gradient strongly affected overall functional diversity, especially on the largest spatial scale, which corresponded to 3 distinct salinity sectors. This was also the case for the variables grain size and depth of the redox discontinuity layer. We identified 3 assemblages with distinct functional trait composition among the sectors. Although the number of species remained relatively constant across sectors, the functional diversity increased from the inner, less saline to the outer, more saline sectors. Our findings emphasize that drivers at the largest spatial scales (i.e. gradients in salinity and sediment texture) play a major role in maximizing functional diversity and shifts in trait composition along an estuarine gradient.