Innovative approaches are needed to help understanding the latitudinal gradient in species diversity. Here we have applied a novel approach, by combining morphological and biological traits, to assess the relative importance of the large-scale latitudinal gradient and regional morphodynamic drivers in shaping the functional diversity of polychaete assemblages in shallow water habitats, from exposed sandy beaches to estuarine ones. Literature data on the occurence of polychaetes in shallow habitats along the south and southeastern Brazilian coast was collected together with environmental variables such as slope, grain size, temperature, salinity, chlorophyll A concentration and shallow habitat type. Generalized linear models on the functional dispersion index calculated for each site and a combined RLQ and fourth-corner analysis were used to investigate relationships between functional traits and environmental variables. No latitudinal functional diversity gradient was found but significant negative correlations with grain size and beach slope. Functional diversity was highest in flat habitats with small grain size, little wave exposure and enhanced primary production, indicating that that small-scale morphodynamic conditions are the primary drivers of polychaete functional diversity along the eastern, southeastern and southern Brazilian coast.
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