Alpha and beta diversity in Mediterranean macroalgal assemblages: relevancy and type of effect of anthropogenic stressors vs natural variability

This work aimed at evaluating changes in alpha and beta diversity of major Mediterranean macroalgal assemblages across gradients of human pressure. To achieve these goals, data from four different experiments, both correlative and manipulative, were used. In particular, patterns of alpha and beta diversity were evaluated across depths and macroalgal habitats, in relation to different levels of urbanization, nutrient concentration, sedimentation and biological invasions. Results of the study showed that patterns of alpha and beta diversity of macroalgal assemblages can change depending on the nature of the source of variation. Regarding natural variability, alpha and beta diversity can vary according to the specific depth and to the presence of canopy-forming species. Both alpha and beta diversity were eroded by human-induced pressures, although different trends have been highlighted between alpha and beta diversity suggesting different sensitivity depending on the type of pressure and the assemblage considered.