A multimetric approach was used to detect compositional and functional shifts in the underlying macrobenthic communities of an offshore mussel (Mytilus galloprovincialis) farm in an Aquaculture Production Area (APA) near Armona Island, Portugal. Sampling stations distributed inside and outside the APA were used to evaluate sediment descriptors and macrobenthic samples collected before (April & September 2010) and after (June & September 2014) the initiation of mussel settlement. The sediment fine fraction, organic matter content, and metal concentrations were found to increase with depth, independently from the mussel farm. Both the composition and functionality of the macrobenthic communities were likewise structured by depth. The dominant temporal and spatial pattern of beta diversity for stations inside the APA was turnover, while the functional trait diversity for underlying communities was similar to those outside the APA. These results suggested that an offshore profile allowed hydrodynamic conditions to weaken the impact of mussel farming and highlighted the importance of conducting an integrative multimetric analysis when studying aquaculture impacts on benthic communities.
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