Mussel beds are biogenic habitats and biodiversity hotspots due to their structural complexity. Yet, despite the high biogeographic interest of the Portuguese coast, studies on macroinvertebrate biodiversity in intertidal mussel beds remain limited, mainly focused on the northern region. This study investigated the spatial variability of macroinvertebrate assemblages associated with Mytilus galloprovincialis along the Portuguese rocky intertidal coast, considering large-scale (shores) and small-scale (transects within shores) patterns. Variation among microhabitats (horizontal platforms, rock-pools and vertical walls) and the role of mussel bed physical characteristics were also assessed. A total of 72 taxa were identified, dominated by the classes Bivalvia, Malacostraca, Gastropoda, Polyplacophora and Polychaeta. The graphical and statistical multivariate analyses revealed that the main source of variation in the structure of macroinvertebrate communities associated with M. galloprovincialis was the difference between the sampled shores along the Portuguese coast, particularly between: the northern group (Montedor and Valadares); Peniche (Ponta do Trovão and Consolação) and Queimado group; and the remaining shores which did not group together (Magoito, Cabo Raso, Foz, Almograve and Alteirinhos). Although the variation between microhabitats and transects was significant, it was not considered as important as the variation between shores. The remaining variables selected as responsible for the biological variation observed were related to the physical characteristics of the mussel beds, such as mussel size and associated degree of heterogeneity, as well as sediment retention capacity. This study highlights the ecological importance of mussel beds and the need for their conservation and sustainable management.
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