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Marine Protected Areas (MPAs) are at the core of management and conservation plans aimed at counteracting the ongoing widespread degradation of marine ecosystems. Although the outcomes of protection in enhancing marine biodiversity and restoring populations of exploited species are widely recognized, the putative effect of MPAs in increasing the resilience of marine communities and ecosystems is still underexplored. In this study, long-term data from a no-take area of a Mediterranean MPA and unprotected locations were used to investigate the effects of full protection on the temporal stability of sessile assemblages on shallow subtidal rocky reefs. Results highlighted that assemblages within the no-take area exhibited a more consistent structure over 20 years of study, whereas a significantly larger temporal variability characterized assemblages at the unprotected locations. Reduced levels of human pressure and stabilizing processes related to the re-establishment of the integrity of trophic networks within the MPA could underlie the observed patterns. Assessing whether MPAs may improve the ability of marine communities to absorb disturbance, from local to large scale sources, is essential to ascertain their contribution to future adaptive conservation strategies in the face of global change. This study provided evidence that MPAs, if well managed, can represent an effective tool to smooth fluctuations in the structure of marine communities, thus potentially reducing their vulnerability to natural and human-driven environmental changes.

High complexity habitat traits (i.e. high heterogeneity and/or size of discrete habitat units) often promote larger abundances of fauna. Sandy and rhodolith sea bottoms are typically interspersed as mosaics within coastal landscapes. The aim of this study was to experimentally assess the effect of two complexity attributes of rhodolith nodules (i.e. their heterogeneity and size) on the abundance and structure of vagile epibenthic assemblages. An early-colonization experiment was set up (July 2016), where experimental units containing rhodolith nodules of varying heterogeneity and size were deployed at two adjacent recipient habitats: a sandy bottom and a rhodolith seabed. After one month, the abundance of fauna colonizing the experimental units was similar in both habitats, but the assemblage structure (i.e. composition) notably differed. Importantly, the heterogeneity, rather than the size, of experimental rhodolith nodules influenced patterns of vagile macrofauna (>0.5 mm) colonization, despite the habitat type where these experimental units were deployed considerably influenced colonization patterns. This result reinforces the idea of the importance of rhodolith tri-dimensional structure, as key influencer on faunal communities of nearshore habitats.

Connectivity is a fundamental ecological property affecting stability, resilience and recovery of marine populations, in particular in networks of patchy habitats as the Mesophotic Biogenic Habitats of the Northern Adriatic Sea. Specific information on the dispersal behaviour of many species living in these habitats is lacking, thus the connectivity simulations were performed over different pelagic propagules duration and different reproductive seasons of six consecutive years, covering most of the possible dispersal behaviour variability. The connectivity simulations were analysed with graph analysis methods by characterizing each connectivity graph with several structural measures and by identifying sites with greatest individual and group centrality. We tested the hypothesis that geographic proximity of sites cannot be a proxy for the connectivity and that hydrodynamic connectivity is statistically significantly related to the observed beta diversity among the studied sites. Results showed that species with different pelagic propagules duration follow greatly different dispersal dynamics, and that the network of studied outcrops is only partially connected to coastal benthic populations. Our results also made possible a critical appraisal of the current conservation strategies, evidencing gaps in the existing network of protected Mesophotic Biogenic Habitats in the Northern Adriatic Sea. We suggest possible improvements for an efficient preservation strategy of these unique biodiversity hotspots by including a fundamental ecological process, the dispersal connectivity, into the process of decision making for conservation.