Rocky reef fish assemblages at six Mediterranean marine protected areas: broad scale patterns in assemblages structure, species richness and composition

Fish assemblages inhabiting shallow rocky reefs at six Italian marine protected areas (MPAs) were investigated to assess broad-scale patterns in assemblage structure, species richness and composition, and to evaluate the presence of a latitudinal gradient in the distribution pattern of a thermophilic fish, the ornate wrasse Thalassoma pavo. Fish abundance was estimated by visual censuses carried out within the integral reserve zones, within the 1--7 m depth range and during four sampling periods. Multivariate analyses revealed significant differences in the assemblage structure among MPAs, although patterns of variation changed considerably from time to time and they were not consistent with latitudinal or longitudinal gradient. Fish assemblages of Miramare (northern Adriatic) and those of the other MPAs clearly separated into two groups. Multivariate differences among MPAs mainly relied upon some relatively common species (e.g. Diplodus puntazzo and Muraena helena). Substantial contribution to these differences was also accounted for by T. pavo. Significant differences among MPAs were detected also in species richness and total density of fish, although the effect of MPA on species richness varied significantly from time to time. Both species richness and total density of fish at Miramare were always higher compared to the other MPAs, likely in relation to peculiar habitat characteristics. Density of T. pavo declined significantly from south to north, thus confirming the thermophily of this species. Present data point out the importance of monitoring marine fish diversity through long-term surveys across a wide spatial scale, in order to detect the early effects of water warming and to develop future plans of management and conservation.