Michela Angiolillo

Scleractinians are key components of Mediterranean mesophotic and bathyal benthic ecosystems, comprising 30 species known to occur below 40 m. A large ROV dataset, including 625 dives, each corresponding to a distinct geographical site, conducted between 40 and 1825 m across the Italian seas, was used to assess the diversity of this taxon, focusing on the distribution, habitat preferences, and population density of four Data Deficient, yet well-represented species: solitary Caryophyllia cyathus , Paracyathus pulchellus , and Javania cailleti , and colonial Thalamophyllia gasti . The study recorded 18 scleractinian species (representing 60% of the known deep ones) and analysed almost 2600 records of the four target species. Caryophyllia cyathus , Paracyathus pulchellus, and Thalamophyllia gasti were the most common, occurring between 80 and 150 m on inclined outcropping rocks encrusted with coralline algae along the continental platform, with major hotspots in the Tyrrhenian Sea and average densities ranging between 2.4 and 36 individuals or colonies m ⁻² . Thalamophyllia gasti was observed for the first time in a cave habitat in Southwest Sardinia, forming large colonies. Javania cailleti was recorded at only 4% of the investigated sites, mainly along the Northeast Sardinian canyons, Corse Channel, Dohrn Canyon, and on seamounts between 400 and 550 m. This species, thriving on Fe–Mn-rich rocks, thanatocoenoses, and coral frameworks, tolerated high levels of silting and occasionally formed dense populations, averaging 12 individuals m ⁻² . This study expands biogeographic and ecological knowledge of these four species, highlighting their environmental preferences and distribution hotspots and confirming their significant yet underappreciated role in benthic communities in the Mediterranean mesophotic and bathyal zones.

Rosalinda incrustans (Kramp, 1947) is a poorly known, deep-sea capitate hydrozoan whose biology, morphology, and ecological traits have remained largely obscure due to the rarity of collected material and its small, inconspicuous epibiontic habitus. Since its original description, the species has been collected only twice and recorded two additional times with Remotely Operated Vehicles (ROVs), invariably observed as an epibiont of the crab Anamathia rissoana (Roux, 1828). Here, we report a detailed morphological description of the species based on newly collected material, adding information from in situ pictures, as well as from ecological, structural, and histological perspectives. For the first time, the species is documented growing on substrates other than the crab, including polychaete tubes and scleractinian skeletons, revealing a broader host range and a non-obligate association with A. rissoana . These findings, supported by the analysis of an extensive ROV archive, allow a reevaluation of the species’ life habit, its symbiotic relationships, and its role as an early coloniser of deep-sea hard substrates. The combination of new host records, morphological plasticity of the hydrorhiza, and overlapping diagnostic traits also suggests a possible synonymy with the Atlantic species Rosalinda williami (Totton, 1949).

Synagoga mira Norman, 1888 is a poorly known ascothoracidan that has never been reported since its original description in 1888, which was based on a few specimens recovered from colonies of the black coral Parantipathes larix (Esper, 1788) collected in the Gulf of Naples (Mediterranean Sea). A series of Remotely Operated Vehicle (ROV) campaigns conducted between 2006 and 2022 along the Italian coast (western Mediterranean Sea) identified numerous P. larix forests, allowing the investigation of the presence of S. mira on a broad geographical and bathymetric scale and the collection of twelve specimens. The first pictures of both in situ and collected specimens are reported here. The sexes seem separated and slightly skewed towards females. Synagoga mira, specialised in grazing the living tissue of P. larix, is confirmed overall as a rare species (19.2% of the sites with black coral forests between 109 and 251 m). The highest frequency of records (12 sites) and abundance of individuals (588) were confined to the Pontine Archipelago, a hot spot of occurrence of this black coral. Infestation occurred in up to 68.8% of the host colonies, with up to 46 individuals per infested colony. The health status of the coral colonies seems not to influence the infestation from S. mira. This study provides the first ecological data on an enigmatic and poorly known crustacean, also representing the first information for mesophotic ascothoracidans.

The bluntnose sixgill shark ( Hexanchus griseus ), an apex predator, prefers deep waters, making it extremely difficult to obtain reliable estimates of its population due to the challenges posed by such remote environments. This study presents 17 years (2007–2024) of Remotely Operated Vehicle (ROV) expeditions in the Western and Central Mediterranean Sea, opportunistically documenting H. griseus at depths of 50–500 m, near the islands of Capraia, Sardinia, Sicily and in the Bari canyon. Nine sharks were observed in eight encounters, with lengths ranging from 243 to 288 cm. The sharks displayed cautious, curious behaviour approaching the ROV and fleeing when they got too close. The study suggests that ROV emissions influenced the sharks' behaviour. Despite the opportunistic data collected, the small number of encounters could suggest a low‐density population for this species in the region. Our findings provide important in vivo data that will aid in estimating the abundance of H. griseus in its preferred environment and increase our knowledge of this charismatic species.

Echinoderms are among the most charismatic megabenthic taxa in mesophotic and deep waters. However, they generally have a scattered distribution and are difficult to collect, especially on hardgrounds, so defining their abundance, distribution and ecological preferences is challenging. The largest available Italian remotely operated vehicle dataset, including 624 dives carried out between 2006 and 2022 in coastal and offshore areas in the depth range of 40–1825 m, was used to assess echinoderm diversity and large-scale geographic and bathymetric distributions. Thirty-nine taxa were identified, including three rarely reported from the Mediterranean basin. The maximum diversity and occurrence of the deep-sea echinoderm fauna were reported from the northern areas, and generally, they decreased with depth and distance from the coast. Species, mostly of Atlantic origin, were mainly distributed according to their thermic preferences. The recorded species occurred in a large variety of habitats, including some in which, differently from what was reported in the literature, they formed dense aggregations. The high densities of individuals were hypothesised to be related, in some cases, to reproductive, feeding or stress situations. Environmental predictors were considered in order to both investigate patterns in community composition and the response of the studied community to them. This work enhances the knowledge of deep-sea Mediterranean echinoderms, fundamental to implementing more effective monitoring and conservation strategies for the habitats in which they thrive.

An analysis of 483 remotely operated vehicle (ROV) dives carried out along the Italian coast on hard substrata at mesophotic depths (40–200 m) allowed an overview of the rich sponge diversity (53 taxa) of the deep continental platform to be obtained for the first time. About 40% of the potential actual species diversity was recognisable using ROV, suggesting that this group is among the richest yet underestimated using this technology in contrast to other megabenthic taxa. Additionally, the study allowed us to gather data on the current basin-scale distribution and bathymetric limits of five common and easily identifiable demosponges with up to 55% occurrence in the explored sites: Aplysina cavernicola, the group Axinella damicornis/verrucosa, Chondrosia reniformis, Foraminospongia spp., and Hexadella racovitzai. Four of these latitudinal distributions were characterised by high occurrence in the Ligurian Sea and a progressive decrease towards the south Tyrrhenian Sea, with an occasional second minor peak of occurrence in the Sicily Channel. In contrast, Foraminospongia spp. showed a maximum occurrence on the offshore reliefs and a second one in the North–central Tyrrhenian Sea, while it was almost absent in the Ligurian Sea. Trophic and biogeographic reasons were discussed as possible causes of the double-peak distributions. The vertical distributions support a more consistent occurrence of all considered taxa in deeper waters than previously known. This suggests that they may more typically belong to the mesophotic realm than the shallow waters, owing to a more extensive sampling effort in the deeper depth range. The five target taxa are typical or associated species of seven reference habitats in the recently revised UNEP/SPA-RAC classification. However, they may create such dense aggregations that they should be listed as new facies in the abovementioned classification.

The genus Munida, inhabits various marine habitats and exhibits versatile feeding behaviour. This study explored the behavioural patterns of Munida intermedia, shedding light on its opportunistic behaviour and competitive interactions within its ecological niche. In 2018, during an investigation using a remotely operated vehicle (ROV), carried out on the Méjean shoal (north-western Mediterranean Sea), at 397 m depth, specimens were observed engaging in opportunistic predatory feeding, targeting juveniles of the bathypelagic silver scabbardfish Lepidopus caudatus. Our findings underscore the dynamic nature of M. intermedia feeding habits and the significant role of competitive interactions within its habitat, highlighting the role of video technology in capturing real-time information.

Deep-sea coral assemblages are marine biodiversity hot spots. Because of their life history traits, deep-sea corals are highly vulnerable to the impacts of human activities such as fishing. The critically endangered “bamboo coral” Isidella elongata is a key structuring species of deep muddy bottoms that is susceptible to habitat destruction, particularly from trawling. A shallow population of this species was recently discovered by a multibeam and ROV survey offshore of the Asinara Island marine protected area (MPA) (northwestern Sardinia, NW Mediterranean Sea). This vulnerable marine assemblage has been found under healthy conditions at depths ranging from 110 to 298 m. Isidella elongata occurs on a muddy seafloor locally characterised by boulders associated with black coral species (Parantipathes larix and Antipathes dichotoma). The lush colonies of I. elongata seem to be related to natural protection from bottom trawling activity; nevertheless, the presence of lost fishing artisanal nets has been observed in the study area. These structuring species are indicators of vulnerable marine ecosystems, and their conservation is essential for preserving marine biodiversity. Therefore, enlarging the perimeter of the Asinara Island MPA into its deeper western waters is suggested to ensure the protection of these valuable and vulnerable marine ecosystems.

Many sessile and tube-dwelling polychaetes can act as ecosystem engineers, influencing the physical–chemical and biological characteristics of their habitats, increasing structural complexity. Thus, they are considered structuring species. In summer of 2021, in southern Sicily (Ionian Sea), benthic assemblages dominated by Ampharetidae Amage adspersa were discovered via an ROV survey at a depth range between 166 and 236 m on muddy horizontal seafloor. Large aggregations of this species (up to 297.2 tubes m⁻²), whose tubes are formed from Posidonia oceanica debris, occurred alternately with tube-free areas. The area was characterized by the sporadic presence of vulnerable sea pens Funiculina quadrangularis (up to 0.08 col. m⁻²) and Virgularia mirabilis (up to 0.16 col. m⁻²), and it was possible to detect signs of trawling as well the presence of marine litter (up to 24.0 items 100 m⁻²). The habitat description, distribution, and density of the tubes of A. adspersa were assessed via imaging analysis. In addition, morphological diagnostic analyses were carried out on some sampled specimens and on their tubes. The acquired data shed new light on how polychaetes can exploit the dead tissues of P. oceanica, contributing to highlight interactions between benthic fauna and seagrass detritus in the marine environment and their ecological role in enhancing the spatial heterogeneity of soft areas of the Mediterranean seafloor.