Urban vs. extra-urban environments: scales of variation of intertidal benthic assemblages in north Portugal

Littoral areas are subject to severe and increasing pressures resulting from human activities occurring along or next to the coast. In this study, patterns of variability in the structure of rocky intertidal benthic assemblages and in the abundance of individual taxa were compared between locations close to the coastal cities of Porto and Vila Nova de Gaia (north Portugal) and reference locations far from it in much less urbanized conditions over a temporal scale of fourteen months and multiple spatial scales. Present findings indicated that assemblages were more heterogeneously distributed in the urban than in the extra-urban condition. The total number of taxa and several individual taxa displayed, in general, this same pattern of variability. This could be interpreted as the beginning of a habitat deterioration process with largely unpredictable consequences. The adopted sampling design supports the need for simultaneously including a range of temporal and spatial scales when evaluating responses of coastal marine biodiversity to anthropogenic disturbances.