Subtidal macrozoobenthic assemblages along the River Minho estuarine gradient (north-west Iberian Peninsula)

1. The community composition and spatial distribution of the macrobenthic fauna in relation to abiotic factors was investigated at 20 sites along the River Minho estuarine gradient, in the north-west Iberian Peninsula. 2. A total of 68 taxa were identified and the non-indigenous invasive species Corbicula fluminea dominated both numerically (43.1%) and by biomass (97.7%). 3. Multivariate analysis identified spatial differences in structure and composition of assemblages and suggests a continuum between five distinct assemblages along the length of the estuary. This situation fits the two-ecocline model in which an ecocline from the sea to mid-estuary overlaps with,in ecocline from freshwater to mid-estuary. 4. Each assemblage was found in a particular physico-chemical environment and had a specific composition. The distribution and diversity patterns were linked to salinity. However, inside each assemblage the sediment characteristics (granulometry and organic matter content) played all important role. 5. The highest abundances, biomasses and total species numbers were recorded from upstream freshwater tidal areas, indicating the importance of these habitats within estuarine ecosystems. Copyright (c) 2007 John Wiley & Sons, Ltd.