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Recent studies suggest that the lithological properties of hard substrates play an important role in influencing the diversity and structure of marine assemblages involving macroalgae, sessile organisms and vagile animals like heterobranchs gastropods and fishes. The present study aims at exploring whether the influence of different substrates (limestone vs granite) could drive the occurrence of different vagile groups (crustacean decapods, echinoderms and fishes). The study was carried out at the "Tavolara-Punta Coda Cavallo" Marine Protected Area (NE Sardinia, Mediterranean Sea) where substrates of different lithology, namely granites and limestones, occur on a local spatial scale. The diversity and the abundance of 16 vagile species (four crustaceans, seven echinoderms and five fishes) were investigated by the analysis of photographs (2352 images) collected in 20 sites (10 limestones and 10 granites), between 30 and 50 m depth. Statistical analyses showed a clear-cut separation between the assemblages assessed on the two lithological substrate types, with assemblages on granites that were tightly grouped and those on limestones more dispersed. The total species richness did not significantly vary between limestones and granites. Galathea strigosa and Marthasterias glacialis were exclusively recorded on granites, while Palinurus elephas, Scyllarides latus, Arbacia lixula, Ophidiaster ophidianus and Serranus scriba were exclusively found on limestones. The observed patterns could be partially explained by multiple factors related to lithology: i) the different availability of preferred food sources, potentially influenced by substrate type; ii) the site geomorphology, that could provide different dens and refuges (in terms of quantity and types of shelters) suitable for different species; iii) the colour of different substrates enhancing the mimicry of different species according to their livery and camouflage ability. Our and literature data suggest that the substrate type in rocky reefs could interact with other environmental factors (i.e., light intensity related to depth) in shaping the structure of rocky-reef assemblages. [ABSTRACT FROM AUTHOR]

Structure and diversity of sessile zoobenthic assemblages seem to be driven not only by chemical-physical constraints and biological interactions but also by substrate lithology and its surface features. Nevertheless, broadly distributed crustose epilithic corallines could mask the role of substrate on animal settling. To evaluate the direct influence of different rocky substrates, occurrence and coverage of several sessile species, growing on the dark (i.e. coralline-free) face of sublittoral limestone and granite boulders were compared in the Tavolara MPA (Mediterranean Sea). The analysis of photographic samples demonstrated significant differences in terms of species composition and coverage, according to lithology. Moreover, limestone boulders were widely bare, while the cover per cent was almost total on granite. The leading cause of observed patterns could be the different level of dissolution of the two types of rocks, due to their different mineral composition and textural characteristics. Limestone has previously been shown to have higher dissolution compared with granite, and consequently, a more unstable surface. Our results suggest that, in dark habitats, the absence of the crustose coralline layer allows more rock dissolution and consequent lower stability of the limestone compared with granite, which, in turn, reduces the zoobenthos colonization. [ABSTRACT FROM AUTHOR]

The genus Paramuricea is present in the Mediterranean Sea with two species, P. clavata and P. macrospina. These species have similar bathymetric distributions and can live in sympatry. P. macrospina shows morphological plasticity leading sometimes to an erroneous classification as P. clavata. Studying four ambiguous morphotypes of P. macrospina collected in different localities of the Mediterranean Sea, we provide new insights on both the taxonomy and the distribution of this species. Our analyses reveal high morphological plasticity within the sampled colonies, which in two cases were characterised by a peculiar pigmentation and a morphological pattern resembling that of P. clavata. After having confirmed the genetic identity of the samples, we tested the validity of traditional taxonomic characters, and found that the most reliable character to discriminate between P. macrospina and P. clavata is the number of rows of spindles in the collaret of the polyps. All other features are highly variable and therefore do not allow a correct identification. The bathymetric and geographic distribution of P. macrospina is here updated, showing, with the exception of the south-eastern side, broad preference in the whole basin. Moreover, further studies are needed to investigate the gene flow among and within the Mediterranean populations of P. macrospina and to assess whether the morphological plasticity is driven by adaptive genetic processes of populations exposed to different environmental, climatic and bathymetric conditions. [ABSTRACT FROM AUTHOR]

During the last twenty years, several studies have demonstrated the primary role of the lithological properties of hard substrates in conditioning the diversity and structure of marine sessile communities (aka bio-mineralogy). This research was dedicated to testing whether different substrates (limestones and granites) influence higher levels of the trophic net. For this purpose, the diversity and abundance of heterobranch molluscs were used to test the hypothesis that their distribution could mirror their prey. The study was conducted in the 'Tavolara-Punta Coda Cavallo' Marine Protected Area (NE Sardinia, Mediterranean Sea), where substrates of different lithology co-occur in a restricted area. Diversity and abundance of heterobranchs were investigated by photographic sampling (3300 studied images) in twelve sites (six limestones and six granites), between 35 and 50 m depth, demonstrating clear preferences of several species for a specific substrate, while others are ubiquitarian. In general, diversity and abundance were higher on limestones due to the exclusive presence of Sacoglossa coupled with a more significant number of Cladobranchia and Doridina; on the other hand, Umbraculida were strongly granite-selected. In some cases, the different affinity of each species was clarified by the distribution of their food sources, but, in others, it is possible to hypothesise that the structure of the whole benthic community, affected by the substrate characteristics, may drive the heterobranchs' distribution. • Lithology (limestone vs granite) drives the marine benthic communities' structure. • The influence of the substrate may reach higher levels of the trophic nets. • Diversity and abundance of heterobranchs were higher on limestone than on granite. • The distribution of some heterobranchs directly mirrors that of their prey. • The occurrence of some species results by the general community complexity. [ABSTRACT FROM AUTHOR]