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Lack of detailed knowledge on ecological niche, life cycles, spatial distribution, reproductive biology and space use strongly affects the selection of useful tools and measures in the conservation of threatened marine species. Especially for sedentary and slow species, behaviour and movement capacities are supposed to be the most important functional traits. Indeed, behavioural variability concerning available space and the close presence of individuals is considered a crucial trait for the population dynamics assessments, especially when disturbances of various causes are present in the environment. The present study aimed to investigate the site fidelity and degree of movement of Hippocampus guttulatus, an emblematic and threatened Mediterranean seahorse species. With this aim, a number of seahorses were tagged and monitored throughout two years within a limited area of the lagoon of Mar Piccolo of Taranto (Southern Italy). The studied individuals were initially morphometrically measured for size, sex and life-cycle stage and subsequently monitored through repeated four-month surveys each year. Obtained results indicated high site fidelity regardless of habitat type. Movement pattern was in line with the data on congeneric species, although values were slightly higher. The analyses showed differences in movement degree among different sexes and life-cycle stages and indicated greater mobility of adult females compared to males and juveniles. The investigated parameters showed a great variability suggesting that even small-scale environmental factors can influence the species mobility. Finally, a change in the population structure has been observed, with the loss of large individuals in 2016 and reduced recruitment in 2017. These findings indicated the possible presence of stressors that could lead to the alteration of the seahorse population at Mar Piccolo of Taranto.

This is the first description of a Mediterranean mesophotic coral reef. The bioconstruction extended for 2.5 km along the Italian Adriatic coast in the bathymetric range −30/−55 m. It appeared as a framework of coral blocks mostly built by two scleractinians, Phyllangia americana mouchezii (Lacaze-Duthiers, 1897) and Polycyathus muellerae (Abel, 1959), which were able to edify a secondary substrate with high structural complexity. Scleractinian corallites were cemented by calcified polychaete tubes and organized into an interlocking meshwork that provided the reef stiffness. Aggregates of several individuals of the bivalve Neopycnodonte cochlear (Poli, 1795) contributed to the compactness of the structure. The species composition of the benthic community showed a marked similarity with those described for Mediterranean coralligenous communities and it appeared to be dominated by invertebrates, while calcareous algae, which are usually considered the main coralligenous reef-builders, were poorly represented. Overall, the studied reef can be considered a unique environment, to be included in the wide and diversified category of Mediterranean bioconstructions. The main reef-building scleractinians lacked algal symbionts, suggesting that heterotrophy had a major role in the metabolic processes that supported the production of calcium carbonate. The large amount of available suspended organic matter in the area could be the main nutritional source for these species, as already suggested in the literature referred to Mediterranean cold-water corals.

The present paper provides a multidisciplinary fine-scale description of a Mediterranean mesophotic new habitat dominated by the bivalve Neopycnodonte cochlear (Poli, 1795), building large and thick pinnacles on vertical cliffs at two study areas along the southern Italian coast. The pinnacles, constituted by a multilayered aggregation of living and dead specimens of N. cochlear, were interconnected with each other to form a framework of high structural complexity, never observed before for this species. The bioconstruction, considerably extended, resulted very complex and diversified in the associated community of structuring organisms. This latter included 165 taxa attributable to different ecological groups occurring in different microhabitats of the bioconstruction. Among the secondary structuring taxa there were scleractinians, serpulids and bryozoans, all contributing to the deposition of calcium carbonate, and poriferans, helping to bind shells together or eroding carbonate by boring species. In comparison with coralligenous sensu stricto and the recently described Mediterranean mesophotic coral reef, the Neopycnodonte bioconstruction showed peculiar features, since it lacked the major contribution of encrusting coralline algae and scleractinians as reef builders, respectively.