Shallow-water sea fans: the exceptional assemblage of Leptogorgia sarmentosa (Anthozoa: Gorgoniidae) in the Genoa harbour (Ligurian Sea)

Cohabiting with litter: Fish and benthic assemblages in coastal habitats of a heavily urbanized area

Anthropogenic litter negatively impacts the marine environment and threatens biodiversity. At the same time, it represents a suitable substrate for the settlement of sessile species, thus potentially altering composition and structure of soft bottom benthic assemblages. By using a Remotely Operated Vehicle (ROV), we hereby investigated patterns of abundance, distribution, and origin of benthic litter in three subtidal habitats of a heavily urbanized area and tested whether litter distribution related to patterns of fish and mega- and macro-benthic diversity. Litter accumulation mostly occurred on soft bottoms, while rocky substrata were the least affected, albeit being particularly threatened by sea-based pollution. As expected, the highest biodiversity was observed on rocky bottoms, hosting notable biogenic formations (Cladocora caespitosa, Leptogorgia sarmentosa) despite the area is historically affected by anthropogenic activities. No correlation was found between biota and marine litter, suggesting that litter does not apparently influence biodiversity and distribution of the investigated assemblages.

Bottom-trawl catch composition in a highly polluted coastal area reveals multifaceted native biodiversity and complex communities of fouling organisms on litter discharge

Areas subjected to anthropogenic impacts are important to test the effect of stressors on local biota. We assessed with trawl net the composition and abundance of megafauna, litter, and litter-fouling communities in the soft bottoms of the National Interest Priority Site (NIPS) of Bagnoli-Coroglio (Gulf of Naples, Tyrrhenian Sea) at different depths. The megafauna accounted for 3444 specimens referred to 133 taxa (91 invertebrates and 42 fishes), for a biomass of ~102 kg and including species of wide ecological and commercial interest. Metrics of community structure yielded high values. The NIPS, hence, is characterized by a high biodiversity. Litter accounted for 3590 items, mostly in plastic and ranging between 10< × ≤20 cm, for a weight of ~260 kg, with values of 299.2 item/km² and 21.67 kg/km². The putative origin of most items was land-based (83.6%), whereas sea-based litter accounted for 16.4%. More than 50% of the litter items found showed colonization by invertebrates and/or molluscan egg masses. Marine benthic litter, thus, locally constitutes a complex issue since litter items hosted complex communities of fouling organisms. Future remediation procedures should take the resident NIPS biota into account and not disrupt the environmental balance of the area.

Megabenthic communities of the Ligurian deep continental shelf and shelf break (NW Mediterranean Sea)

The Ligurian Sea is one of the most studied Mediterranean basins. Since the beginning of the last century, many research expeditions have characterized its benthic and pelagic fauna through scuba diving and trawl surveys. However, a large knowledge gap exists about the composition of benthic communities extending into the so-called mesophotic or twilight depth range, currently under intense pressure from commercial and recreational fishing. A series of visual surveys, carried out by means of remotely operated vehicles between 2012 and 2018, were conducted along the Ligurian deep continental shelf and shelf break, between 30 and 210 m depth, in order to characterize the main benthic biocoenoses dwelling at this depth range and to determine the most relevant environmental factors that explain their spatial distribution. Deep circalittoral communities of the Ligurian Sea were represented by a mixture of species belonging to the deepest extension of shallow-water habitats and deep circalittoral ones. Twelve major biocoenoses were identified, each one characterized by specific preferences in depth range, substrate type and seabed slope. Those biocoenoses included gorgonian and hydrozoan forests, dense keratose sponge grounds, Dendrophyllia cornigera gardens, bryozoan beds and soft-bottom meadows of sabellid polychaetes and soft-corals. Other less common aggregations included six forests of black corals and two populations of Paramuricea macrospina. A georeferenced database has been created in order to provide information to managers and stakeholders about the location of the identified communities and high-diversity areas, aiming to facilitate sustainable long-term conservation of the Ligurian benthic ecosystem.