Experimental analysis of the effects of extreme events of mechanical disturbance on rocky shore algal and invertebrate assemblages in the Bagnoli-Coroglio post-industrial area and in reference sites in the Gulf of Naples.

Among the various natural and anthropogenic threats to coastal systems, industrial activities and their heritage of local contamination play a key role, especially where new disturbances are superimposed to extant degraded conditions. This may affect the functioning of assemblages, including their ability to recover, in unpredictable ways. Organisms subject to chronic contamination may respond better to a present discrete disturbance compared to organisms from reference areas not affected by the same contamination due to their adaptation to harsh conditions. By contrast, the same organisms may be more sensitive to the new disturbance if chronic contamination kept them close to their tolerance limit. This study tested such alternatives by comparing the patterns of recovery from the experimental removal of all erect organisms of lowshore benthic assemblages between the post-industrial site of Bagnoli-Coroglio (Gulf of Naples) and reference sites located outside it. Recovery was assessed over six months. Response variables included mean values and temporal trajectories of assemblage structure, richness of taxa and abundance of conspicuous taxa. The examined assemblages showed great recovery ability that was comparable between the post-industrial site and reference sites. Discussed potential explanations include: (i) intertidal organisms would quickly recover irrespective of background contamination as an adaptation to the naturally harsh and variable environmental conditions of their living habitat; (ii) reference sites would be subject to environmental stress comparable to that of Bagnoli-Coroglio being located in the highly urbanized Gulf of Naples; (iii) large variability between- and withinsites may have masked any impacts of experimental disturbance and their differences between the post-industrial site and the reference sites; (iv) historical contamination would be limited to subtidal sediments, without propagating to adjacent rocky habitats.