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Abstract The ability of species to recover from disturbance through natural recruitment is an important factor in determining the resilience of assemblages. The identification of patterns of resilience compatible or favoured by human activities has become a compelling need to address environmental management. In marine coastal systems, barrens are characterized by a dominance of encrusting calcareous algae and by high density of sea urchins and are considered an alternative stable state of systems collapsed due to overgrazing by sea urchins that originally were dominated by canopy-forming macroalga. Sea urchins also represent an important commercial resource, as some species are exploited worldwide. The present study aims at evaluating the effect of the harvesting of the sea urchin Paracentrotus lividus on promoting the shift from barren towards macroalgal beds. Three treatments were considered within a manipulative experiment in a Cystoseira -barren mixed habitat: natural sea urchins density, removal of all sea urchins and removal of only commercial P. lividus (natural density of the non-harvested sea urchin Arbacia lixula and juvenile P. lividus are maintained). Results showed that the removal of commercial P. lividus can promote Cystoseira recruitment. In fact, even if both A. lixula and juvenile P. lividus were present, the barren area decreased due to the spread of fleshy algae and the recruitment of the Cystoseira from the edge of vegetated patches. Therefore, removal of commercial P. lividus urchin is inferred as a reliable strategy to return ecosystems dominated by canopy-forming macroalgae. Highlights • The study evaluated sea urchin harvesting on promoting macroalgal beds. • A manipulative experiment was performed in a Cystoseira -barren mixed habitat. • The removal of the commercial Paracentrotus lividus can promote macroalgal beds. • The non-harvested Arbacia lixula did not prevent the recruitment of Cystoseira. • Sea urchins management should be considered to recovery macroalgal canopy. [ABSTRACT FROM AUTHOR]

In the Mediterranean Sea, Cystoseira species are the most important canopy-forming algae in shallow rocky bottoms, hosting high biodiverse sessile and mobile communities. A large-scale study has been carried out to investigate the structure of the Cystoseira -dominated assemblages at different spatial scales and to test the hypotheses that alpha and beta diversity of the assemblages, the abundance and the structure of epiphytic macroalgae, epilithic macroalgae, sessile macroinvertebrates and mobile macroinvertebrates associated to Cystoseira beds changed among scales. A hierarchical sampling design in a total of five sites across the Mediterranean Sea (Croatia, Montenegro, Sardinia, Tuscany and Balearic Islands) was used. A total of 597 taxa associated to Cystoseira beds were identified with a mean number per sample ranging between 141.1 ± 6.6 (Tuscany) and 173.9 ± 8.5(Sardinia). A high variability at small (among samples) and large (among sites) scale was generally highlighted, but the studied assemblages showed different patterns of spatial variability. The relative importance of the different scales of spatial variability should be considered to optimize sampling designs and propose monitoring plans of this habitat. [ABSTRACT FROM AUTHOR]

Biogenic structures edified by crustose coralline algae (CCA) are known to enhance biodiversity, but the mechanisms involved are only partially defined. This study aims at contributing to the knowledge of the interaction between habitat-builder CCA and epibiont assemblages through a manipulative approach. To achieve this objective, transplantations of the CCA Lithophyllum stictiforme were performed to test the following hypotheses: 1) the structure of L. stictiforme epibiont assemblage changes between depth and biogeographic area; 2) L. stictiforme epibiont assemblage is different and more diversified than the assemblage recruited on bare rock; 3) the early L. stictiforme epibiont assemblage differ from the mature L. stictiforme epibiont assemblage. A total of 63 epibiontic taxa were found on the transplanted L. stictiforme thalli, such as 7 Chlorophyta, 10 Ochrophyta, 40 Rhodophyta, 1 Sarcomastigophora, 1 Porifera, 4 Bryozoa. The sessile assemblage recruited on transplanted L. stictiforme thalli depended on sites and depths, and it had a higher taxa richness compared to that colonizing the bare rock. The early recruited assemblage on L. stictiforme transplanted thalli compared to the mature assemblage on untouched thalli was different mostly in the relative abundance of taxa, rather than in species composition. These manipulative experiments highlighted for the first time the role of a common CCA on the development and biodiversity of coralligenous assemblages, contributing to emphasize the importance of CCA conservation efforts. • Lithophyllum stictiforme thalli were transplanted at different depths and sites. • The interaction between crustose coralline algae and epibionts was investigated. • The assemblages had a higher diversity on transplanted thalli than on bare rock. [ABSTRACT FROM AUTHOR]

The knowledge of natural spatial patterns of variability is crucial to discriminate between natural changes and human-induced effects and to plan monitoring programs and impact evaluation studies. The present study aimed at estimating the spatial variability of coralligenous habitat, one of the main important habitats of the Mediterranean Sea, at several spatial scales. Specifically, the following hypotheses were tested: i) the structure of coralligenous assemblage and ii) the abundance of main taxa/groups both changed among different spatial scales differently depending on protection. A hierarchical sampling design was used to study 14 localities (7 Marine Protected Areas and 7 unprotected) at multiple spatial scales through photographic recording. The study suggested that, in protected conditions, the structure of coralligenous assemblages mostly varied at small spatial scale (m apart), while the structure is similar across different localities, sites and areas, even if the abundance of the main taxa/morphological groups changed. In unprotected conditions, variability among localities was higher than among Marine Protected Areas, while an opposite trend was observed at the smaller spatial scales. [ABSTRACT FROM AUTHOR]