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The by-the-wind sailor Velella velella is a cosmopolitan, pleustonic colonial hydrozoan, common in the Mediterranean Sea. It forms offshore aggregations that occasionally strand on the coasts, following strong wind conditions. Colonies are frequently discovered around Janthina pallida Janthina pallida, a pleustonic gastropod that feeds on them and floats on the secretion of a bubble raft. Because of the massive occurrence of these species along the Italian coasts, and their often neglected ecological roles, it is pivotal to increase the knowledge of their genetic structure. Analyses of the genetic variability of V. velella and J. pallida, stranded on the beach in springs 2016 and 2017 at ten locations along the Ligurian and Tyrrhenian seas, show the existence of panmictic Mediterranean populations. Nevertheless, V. velella showed high genetic variability with a high number of singleton haplotypes, while J. pallida showed a recent population expansion. Considering the ecological and socio-economic importance of gelatinous zooplankton in today's changing marine ecosystems, these results lay the basis for a better understanding of the ecological role and population dynamics of Mediterranean pleustonic species.

The precious coral Corallium rubrum (Linnaeus, 1758) is a charismatic Mediterranean species. A recent large-scale investigation along the Italian coast highlighted its widespread occurrence at mesophotic and upper bathyal depths, especially on coralligenous and bathyal vertical hardgrounds. The lack of morphometric data limited the considerations on the structure and health status of the populations, fundamental to identify the most vulnerable sites and the correct management actions. For this reason, a ROV dataset, consisting of 624 dives carried out between 40 m and 1825 m in the Ligurian Sea, Tyrrhenian Sea, and Sicily Channel, was analysed to extrapolate quantitative data to describe the populations. Ten random frames were obtained from each of the 170 sites hosting red coral. Density, height, and entanglement were evaluated for about 15700 colonies counted in the frames. The densest populations were mainly found between 40 m and 80 m, with a clear latitudinal density decrease. The mesophotic populations were characterized by both scattered and densely aggregated colonies, while the bathyal ones were dominated by sparse colonies. This study identified 17 major coral areas based on the geographic proximity of the sites hosting red coral and their topographic and oceanographic affinity. The size-frequency distribution of the heights was skewed towards the smaller classes in almost all populations, with a modal class between 2 cm and 4 cm. This study depicted a stress situation of the populations throughout the entire study area, which could be correlated also to the long-term harvesting pressure carried out in the basins. Two additional sources of direct mortality were pointed out in this study. Entanglement to artisanal and recreational fishing gear interested about 18% of the recorded colonies, mainly at mesophotic depths. Almost all populations suffered from mechanical entanglement, with the highest percentages in the Ligurian Sea and Sicilian areas. This study also highlighted a massive occurrence of recent deep mortality events, mainly along the eastern and southern coast of Sardinia and in the Campanian Archipelago. Thirty sites with extensive patches of dead colonies still in place were reported from 70 m to around 200 m, but their formation remains unclear.

Detailed knowledge about the distribution of species in need of protection is required for the management of Marine Protected Areas, a major tool to reduce marine biodiversity loss. Such knowledge is deficient for most marine invertebrates. Axinella polypoides is a marine sponge included on the list of protected species by the Barcelona Convention (1976) and the Bern Convention (1987). This large and erect species has an important ecological role in habitat forming and benthic–pelagic coupling. Bathymetrical, geographical and ecological data over the last 60 years were collated from publications and reports, together with new surveys to assess the distribution and protection status in Liguria of A. polypoides. It identified a more widespread distribution than previously thought, which points at a general need for dedicated investigations on the occurrence of species that require protection. Bathymetrical distribution was trimodal, with peaks corresponding to different geomorphological settings: coastal cliff bases (around 38 m depth), inner shelf shoals (52 m) and rocks amidst coarse sediment on the outer shelf (79 m). Density was significantly greater at the shallowest depths. The species was mostly found in the coralligenous biocoenosis, in association with other characteristic species or forming a monospecific facies. On (sub)vertical cliffs, A. polypoides often exhibited an unusual cane shape, rather than the typical bushy morphology, thus causing confusion with the congeneric A. cannabina, a more southern species. Records of the latter in the Ligurian Sea therefore need confirmation. Only a minority (22.6%) of A. polypoides records were in Marine Protected Areas, the remainder being located in areas with no current environmental protection plans in place. While the occurrence of this species in MPAs remained stable over the decades, the only quantitative historical data available indicated that populations in non‐protected areas were declining owing to anthropogenic impacts (fishing and anchoring).

The analysis of 879 ROV dives carried out along the Italian coasts on hard substrata at mesophotic and upper bathyal depths (40-775 m) allowed us to evaluate the current basin-scale presence, relative abundance, bathymetric limits, and habitat preferences of one of the most charismatic Mediterranean habitat-former anthozoan species, Corallium rubrum (Linnaeus, 1758). The species is widespread, and its occurrence ranged from 13% of the explored sites in Ionian Calabria to a hotspot of approximately 80% in Sardinia. Population relative densities were generally low (< 10 colonies m-2), except along the Sardinian coasts and in some areas along the Apulian coast. Almost no red coral colonies were observed between 60 m and 590 m in the nine explored offshore seamounts in the Ligurian and Tyrrhenian Seas. A distinctive coastal distribution discontinuity was found in the Ionian Sea. The optimum bathymetric distribution was between 75 m and 125 m, and no colonies were found below 247 m. Red coral colonies showed a preference for biogenic habitats dominated by crustose coralline algae (CCA) and vertical substrata. The species was absent on iron wrecks. Corallium rubrum disappeared from 14% of the historical fishing banks, while it was confirmed in 86% of them, some of which have been deeply harvested in the past. In particular, the still flourishing Sardinian populations could be supported by the high reproductive potential and favourable hydrodynamic conditions in the area.

Spiculosiphon oceana Maldonado, López-Acosta, Sitjà, Aguilar, García & Vacelet, 2013 is a Mediterranean endemic giant stalked foraminifer described as a potential bio-indicator of acidic environments, thanks to its ability to cope with stressful chemical conditions. Here, we present the first record and the first video images of living specimens of this giant foraminifera in the Panarea Volcanic Complex (PVC; southern Tyrrhenian Sea), representing the third discovery worldwide. Specimens of S. oceana were identified through microscopic and remotely operated vehicle (ROV) image analyses, in two different areas characterised by water column physico-chemical parameters typical of the non-vented areas, but with some evidence of hydrothermal alteration. This new finding enhances knowledge on the ecology of S. oceana, enlarges its known spatial distribution, and corroborates its affinity to intermediate stress conditions related to hydrothermal activity.

The distribution of floating litter in marine waters, influenced by currents and wind drag, often determines the dispersal of its encrusting fauna. In the present paper, we observed for the first time the colonization of rafting floats from abandoned, lost or derelict fishing gears (ALDFG) by the four protected deep-sea species: Errina aspera, Desmophyllum pertusum, Madrepora oculata Pachylasma giganteum. Overall, 41 floats, colonized by deep benthic species, were found stranded on the shore of the Sicilian coast of the Strait of Messina, between 2016 and 2019. Species composition, number and occurrence of colonizing organisms were analyzed. On the basis of the species composition (the association between E. aspera, P. giganteum and Megabalanus tulipiformis), the knowledge on their ecology, biogeography, path of local currents, it was possible to define that the area of origin of the most part of these fishing net floats was the Strait of Messina.

The close relationship between a polyclad (Platyhelminthes, Rhabditophora, Polycladida) and the mesophotic Atlantic–Mediterranean black coral Antipathella subpinnata (Ellis & Solander, 1786) (Cnidaria, Hexacorallia, Antipatharia) is herein described for the first time. Worms, up to 50 mm long, are elongated with sparse dorsal papillae, an anterior, ruffled pharynx and caudal, well-separated gonopores. The bulbous vagina is connected to a very elongated Lang’s vesicle, while the male apparatus, hosting a cuticular penis papilla, consists in a muscular interpolated prostatic vesicle, formed by few chambers surrounding the ejaculatory duct, a major seminal vesicle and numerous spermiducal bulbs. These features, as well as the uniqueness of the symbiotic relationship and relative reproductive adaptations, support the description of a new taxon, Anthoplana antipathellae gen. et sp. nov. (Acotylea, Notoplanidae). The observed symbiosis is ascribable to exclusive inquilinism with some parasitic traits. The individuals, living in large numbers on the colonies, are highly cryptic thanks to a characteristic pigmentation and a wrapped habitus. They lay numerous annular yellow cocoons (rigid, nest-like structures containing the fertilised eggs), in single or multiple rows on the distal branches of the coral, temporarily denudated of coenenchyme. The occurrence of the polyclad is consistent with the Atlantic–Mediterranean geographical and bathymetrical distribution of the A. subpinnata forests as demonstrated by the analysed photo archive, and a summer reproductive peak can be hypothesised based on the temporal observations carried out in the study areas.

Vulnerable Marine Ecosystems (VMEs) are characterized by prominent biological features susceptible to anthropogenic disturbances. Following international guidelines, the identification and protection of VMEs require a detailed documentation regarding both the community structure and the fishing footprint in the area. This combined information is lacking for the majority of the Mediterranean mesophotic rocky reefs that, similarly to deep-seabottoms, are known to host valuable animal forests. A deep coralligenous site exploited by artisanal fishermen in the NW Mediterranean Sea is here used as a model to assess the vulnerability of animal forests at mesophotic depths and evaluate the sustainability of artisanal fishing practices, particularly lobster trammel net. The Remotely Operated Vehicle (ROV) footage is used to document the biodiversity and health status of the megabenthic communities, while discard data are employed to quantify the entanglement risk, discard rates of fragile species and threats to sea floor integrity. A multidisciplinary approach is proposed for the assessment of the vulnerability criteria of an EU Special Area of Conservation, leading to specific management measures, including the delineation of fishing restrictions.

In 2015, the Strait of Sicily, which includes several banks, was candidate as a future Specially Protected Area of Mediterranean Importance (SPAMI) by the Contracting Parties of the Barcelona Convention. In this context, the present study aims to provide the first biological and ecological characterisation of this poorly known area, focusing on habitats and species of conservation concern. Surveys were carried through a remotely operated vehicle (ROV) and allowed the identification of 19 habitat types, mostly considered of priority interest by the SPA/BD Protocol of the Barcelona Convention. A total of 269 taxa were also identified, mostly Porifera, Cnidaria and Pisces, among which 115 species are of conservation concern according to the International Union for Conservation of Nature (IUCN) Red Lists, the Habitats Directive, the Bern Convention, the SPA/BD Protocol and CITES. ROV surveys allowed some interesting observations on poorly known species and habitats. Results underlined that remarkable discrepancies in species conservation status assessment that exist between the several lists of protected species considered. The IUCN Red Lists, although not legally binding for European States, are the most complete, but, in spite of this, the conservation policies in the EU are largely focused on the Habitats Directive, which is really not exhaustive. An exhaustive and legally binding instrument to protect species of conservation concern at European scale is highly recommended. Acquired results could be useful for the delimitation of a future SPAMI or a network of Marine Protected Areas (including the investigated banks) and the identification of zones within them suitable for different area-based management measures.

Antipathella subpinnata (Ellis and Solander 1786) is one of the most frequently observed black corals at mesophotic depths (60–200 m) of the Mediterranean Sea, particularly in the northwestern part of the basin, where its populations can reach high densities and create forest-like aggregations, both along the coast and in offshore locations such as seamounts. Similar to other marine underwater forests, black coral gardens host a rich associated fauna and attract numerous species of commercial interest. As such, these corals are targeted by recreational and artisanal fisheries and are vulnerable to human impact due to their arborescent morphology and low growth rates. Genetic connectivity can provide valuable insight into the processes of population maintenance and replenishment following environmental disturbance and is often used as a proxy for population resilience. In our study, a restriction-site associated DNA analysis (2bRAD) was used to evaluate fine-scale population structure of the Mediterranean black coral A. subpinnata, and to understand which populations could serve as a potential source of genetic diversity for adjacent populations. Colonies from two offshore localities (a Ligurian seamount and a Tyrrhenian canyon) and four coastal populations from Liguria and Sicily were sampled and genotyped. Significant genetic differentiation was recorded between coastal and offshore localities. Moreover, offshore localities were genetically distinct from one another, while all coastal populations were characterized by panmixia. This indicates that offshore A. subpinnata gardens are potentially less resilient to human impact (i.e., demersal fishing activities) due to a limited influx of larvae from adjacent habitats. In addition, they are unlikely to supply coral propagules to coastal populations. Overall, this study highlights the vulnerability of Mediterranean A. subpinnata forests, and the importance of enforcing conservation and management measures to achieve Good Environmental Status (GES, EU Marine Strategy Framework Directive) of these valuable marine ecosystems.

Chilean Patagonia hosts one of the extensive fjord systems in the world, spanning more than 1,600 km between 41 and 55°S, and with a complex geomorphology and hydrography that supports rich and unique assemblages of marine fauna. The biodiversity of benthic organisms is possibly further enhanced by the geographic position of the region that extends far south into subantarctic waters. However, we currently lack an exhaustive picture of the zonation and ecological functioning of the benthic communities within Chilean fjords. The present study provides a detailed examination of the hard substrata megabenthic communities inhabiting the Puyuhuapi and Jacaf fjord system, in the Aysén Region of Chile. Fifty-nine stations scattered along these fjords were explored through SCUBA diving surveys, at depths between 5 and 30 m, and 16 stations were characterized in terms of benthic cover and diversity using replicated underwater photography. Ten hard bottom megabenthic communities were identified within the fjords, with some communities newly described for this region. Community composition varied both along-fjord, and with depth, and was apparently driven by variation in environmental properties. Our characterization of these fjord communities improves overall knowledge of the functioning of the fjords, and provides a useful baseline against which future anthropogenic pressures can be assessed. Future shifts in bathymetric and geographical distributions might indicate detrimental effects of climate changes, and we therefore propose that characteristic communities could be adopted as “sentinels” for overall environmental status of these unique fjord ecosystems. In this regard, detailed mapping of the distribution of megabenthic communities can provide a fundamental tool that assists in best management practices for these ecosystems.

23 pages, 21 figures, 3 tables, This Collective Article presents information about 21 taxa belonging to seven Phyla (one Ochrophyta, one Porifera, three Cnidaria, two Arthropoda, three Mollusca, one Echinodermata, and ten Chordata) and extending from the western Mediterranean Sea to the Levantine Sea. The new records were reported from nine countries as follows: Spain: first records of three deep-sea species from the Blanes Canyon along the Catalan margin, namely the gorgonian Placogorgia coronata, the bivalve Acesta excavata, and the Azores rockling Gaidropsarus granti; Italy: first record of the mesopsammic nudibranch Embletonia pulchra from Ligurian shallow-waters; first record of the deep-sea carnivorous sponge Lycopodina hypogea from the north-central Tyrrhenian Sea, living in dense clusters over dead black corals; new records of the Portuguese man o’ war Physalia physalis from Sardinian and Sicilian waters; first Italian record of the large asteroid Coronaster briareus from the Ionian Sea; first record of the white grouper Epinephelus aeneus in the northernmost point of the Adriatic Sea; Croatia: first record of the gastropod Haliotis mykonosensis for the Adriatic Sea; Malta: new sightings of Physalia physalis from Maltese waters; Libya: first record of the sand crab Albunea carabus from two localities along the Libyan coast; Greece: first records of the deep-sea black coral Parantipathes larix from the eastern Mediterranean Sea; first verified record of the agujon needlefish Tylosurus imperialis in the Hellenic Ionian Sea; first confirmed record of the brown algae Treptacantha squarrosa in the eastern Mediterranean Sea; new records of three deep-sea fish species from the Aegean Sea, namely the bluntnose sixgill shark Hexanchus griseus, the Atlantic pomfret Brama brama, and the rudderfish Centrolophus niger; new record of the tripletail Lobotes surinamensis from Lesvos Island; new record of the shrimp Brachycarpus biunguiculatus from the gut content of the non-indigenous lionfish Pterois miles; Turkey: new record of the imperial blackfish Schedophilus ovalis from Turkish waters; Lebanon: first record of the slender sunfish Ranzania laevis, stranded along the Lebanese coast; Israel: new record, after about 60 years from the last catch, of the spotted dragonet Callionymus maculatus, Their studies presented in this Collective Article received funding from the Spanish Ministry of Science and Innovation (ABRIC Project, Ref. RTI2018-096434-B-I00). The study by Bo et al. was funded by EU-ENPI CBC MED 2007–2013, “Ecosystem conservation and References sustainable artisanal fisheries in the Mediterranean basin” (ECOSAFIMED) (grant number ECOSAFIMED - Abushaala, N.M., Shaibi, T., Howaege, H.M., 2014. The abun-II-B/2.1/1073), With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)

The Tavolara-Punta Coda Cavallo Marine Protected Area (North-eastern Sardinia, western Mediterranean Sea) includes, in a restricted area, substrates of different lithology. In fact, the Tavolara Island is characterized by limestone (high carbonate content), while the nearby Molara Island and the Molarotto islet are granitic (high quartz content). These peculiar features create a suitable condition to test the hypothesis that the taxonomic richness of the Mediterranean coralligenous communities could be also driven by the lithological characteristics of the substrate. Differences, in terms of recurrences of the macrobenthic sessile species, mainly macroalgae, sponges, anthozoans and bryozoans, of the coralligenous communities settled on limestone and granite, were investigated by image analysis. 240 photos on standard surfaces and four video transects were taken in 12 sites at comparable depth (40–50 m) but characterized by a different lithology. Multivariate analyses highlighted significant differences among sites, characterized by carbonate and granitic substrates. In general, limestone proved to be more suitable for the development of a thick differentiated coralligenous basal layer and showed a marked heterogeneity. Among structuring species, the gorgonian Eunicella cavolini was more recurrent on limestone than on granite, while the sponges Sarcotragus foetidus, Axinella polypoides and Axinella spp. were significantly more abundant on granite. Results suggest that a number of mechanisms could be involved to explain the observed patterns, such as a selective capacity of several sessile organisms, towards substrate, with ultimate repercussions on the structure of the whole coralligenous assemblage.

Exceptional meteo-marine events, such as storms, may have profound effects on the structure of benthic communities, yet their consequences on these ecosystems in the Mediterranean basin are still poorly known, mainly due to the unpredictability of such phenomena as well as the general lack of comparative datasets. The highly destructive storm of fall 2018, sustained by SE winds exceeding 130 kmh−1 and generating 10-m high waves, hit the coasts of the Ligurian Sea with devastating strength, producing vast damages and profound changes to the coastal morphology. Quantitative surveys performed soon after the catastrophic event were used to study the effects of the storm on the population structure of the habitat-forming gorgonian Paramuricea clavata (Risso, 1826) along the cliffs of the Portofino Promontory, a site particularly stricken by the storm. The same population was studied in 1997, 2002 and 2016, therefore it was possible to compare its health status before and after the impact of the storm. The P. clavata forest lost about one-third of the colonies between 2016 and 2018; colonies up to 25 m depth utterly disappeared, while below 30 m the storm effects were reduced, although the remaining population showed increased levels of epibiosis and necrosis. Over 21-years of observation, the effects of the storm have significantly slowed-down the recovery of the Portofino Promontory population after the massive mortality events of the last decades. Natural stress factors, although unpredictable, are fundamental to put into perspective changes in the benthic communities over time.

Litter has become a common component of marine ecosystems, and its assessment and monitoring are now of primary interest. Here, we characterized seafloor litter in the mesophotic depth range of the Ligurian Sea, one of the most urbanized basins of the Mediterranean Sea. Eighty sites (30–220 m depth) were investigated by by means of ROV video transects. Data regarding environmental parameters and anthropic pressures were used to explain the distribution of human-derived objects. Litter resulted widely distributed in all the investigated areas, with maximum densities of 7900 items ha−1. It was mainly represented by abandoned fishing gears, with highest abundances found on the deep coastal rocky shoals exploited by artisanal and recreational fishermen. Urban litter, primarily represented by plastics, was generally higher close to shore, especially near river mouths and large harbors. Litter densities reported here are among the highest ever recorded in Europe, denoting the urgency for specific actions to prevent further spreading.

Cnidarians are known to undergo reverse development as a survival mechanism against adverse environmental conditions. Polyp bail-out consists in the polyps’ detachment from the mother colony due to stressful conditions, followed by a complete tissue and cells rearrangement and in some cases in a regression into a simple, ciliated form. Here we describe a massive polyp bail-out event occurred in the mesophotic black coral Antipathella subpinnata in reared conditions. This is the first report of a bail-out event in this species providing new insights into the life cycle and ecology of black corals.

Seamounts represent ecologically important marine environments and undeniably play a crucial role in the functioning of the deep-sea ecosystems, thanks primarily to their contribution in supporting offshore benthic and pelagic biodiversity. In the last decades, these features have received attention in all oceans of the world, but they were relatively overlooked in the Mediterranean Sea. In particular, the Ligurian Sea hosts six major structures, whose summits, ranging from 150 to nearly 2000 m depth, are virtually unknown from the biological point of view. The summit region of the Janua Seamount, located approximately at 40 nautical miles off the harbour of Genoa at 810 m depth, was explored for the first time using Remotely Operated Vehicles. The sea bed topography is characterized by a heterogeneous hard bottom, dominated by sub-fossil thanatocoenoses of Lophelia pertusa (Linnaeus, 1758) covered in a thick Ferrous-Manganese crust, and colonized by a scattered bathyal assemblage dominated by hexactinellids and benthic cnidarians showing a distinct regionalization around the summit. Cnidarians observed in this site include a rare Atlantic bamboo coral (Isididae, Chelidonisis aurantiaca Studer, 1890), described herein for the first time for the Mediterranean Basin. These findings provide new information on the biogeographic patterns of colonization of the bathyal Mediterranean fauna but also highlight the large knowledge gap that still exists for deep-sea biodiversity of this basin.

This study presents a description of Bispira riccardi sp. nov., a new habitat-forming sabellid polychaete from the mesophotic NW Mediterranean Sea. Individuals, up to 20 cm long, show a peculiar morphology of radioles, thoracic uncini, companion chaetae and ventral shield of the collar. The phylogenetic position of this new taxon in the genus Bispira has been validated using nuclear (18S rRNA) and mitochondrial (COI) markers. Aggregations of B. riccardi sp. nov. were found by ROV on horizontal muddy bottoms between 56 and 85 m, in areas subjected to high trophic inputs. Patches are fragmented and dense (up to 943 individuals m 2) probably accounting for various hectares. A 5-days continuous monitoring, carried out using an autonomous lander, revealed that the contraction of the branchial crown was positively affected by temperature and current, rapidly responding to meteorological events. The filtering activity and high density of these fields suggest a considerable impact on the pelagic-benthic coupling and the amount of organic matter in the sediments. Indeed, meiofaunal abundance and diversity within the aggregations resulted significantly higher than in outer stations. These findings highlight the undisclosed potential of the deep Mediterranean Sea for sabellid diversity and their importance as habitat-forming species on mesophotic soft bottoms.

The predatory activity of the asteroid Peltaster placenta (Muller and Troschel, 1842) on the black coral Parantipathes larix (Esper, 1790) is here described for the first time based on video footage obtained during a Remotely Operated Underwater Vehicle (ROV) survey conducted in the Pontine Archipelago (Southern Tyrrhenian Sea, Mediterranean Sea). Feeding is carried out on the living coenenchyme of the basal axis and pinnules of the antipatharian and is confirmed by the occurrence of its cnidocysts in the sea star gut content. The chitinous skeletal parts of the black coral are left intact as bare tissue, which helps to relate colonies to the predation event. Among all black coral species present in the research area, P. placenta was observed grazing exclusively on P. larix, similarly to other goniasterids known to be deep-sea corallivores with a marked selectivity for their prey. The predatory behaviour of P. placenta was previously unknown. The extent of its feeding traces suggests a significant influence on benthic trophic relationships and, ultimately, on the functioning, structure and health status of deep Mediterranean black coral forests.

On marine rocky shores, several physical, chemical and biological processes operate to maintain the benthic assemblages’ heterogeneity, but among the abiotic factors, the composition and texture of the rocky substrata have been only sporadically considered. However, biomineralogical studies have demonstrated an unsuspected ability of the benthic organisms to interact at different levels with rocky substrata. Therefore, the mineralogy of the substratum can affect the structure of benthic communities. To evaluate this hypothesis, the macrobenthic assemblages developed on two different ophiolitic rocks (serpentinites and metagabbros) in contact at a restricted stretch of the western Ligurian Riviera (western Mediterranean Sea), with identical environmental and climatic conditions, were analysed. Samplings were carried out at four bathymetric levels (+1m, 0m, -1m, and -3m respect to the mean sea level) and the analysis of the data evidenced differences in terms of species distribution and percent coverage. Algal communities growing on metagabbros were poorer in species richness and showed a much simpler structure when compared to the assemblages occurring on the serpentinites. The most widely distributed animal organism, the barnacle Chthamalus stellatus, was dominant on serpentinites, and virtually absent on metagabbros. Our results suggest a complex pattern of interactions between lithology and benthic organisms operating through processes of inhibition/facilitation related to the mineral properties of the substratum.

Recent ROV surveys conducted on the Ragusa bank in the Sicily Channel (Mediterranean Sea) documented illegal and continuous use of the ‘ingegno’ gear for red coral fishing. Three lost gears were recorded showing different levels of epibiosis thus supporting multi-annual exploitation of the bank. The red coral population of the Ragusa bank showed a typical ‘forest-like’ configuration with upright, medium-sized colonies similar to those of other commercially exploited deep Mediterranean banks. The direct negative effect of this trawling gear was evident from numerous rocky boulders completely enveloped by lost nets and occasionally turned over. Red coral fragments as well as fragments of ‘ingegno’ nets were observed in high abundance on the sea floor. This evidence suggests that this gear is highly destructive even on rough sea floors, contrary to the traditional view, which is that it has a more random impact on rough rocky bottoms. The estimated coral uptake of ‘ingegno’ is 45% of the total coral biomass, while the estimated coral loss, in terms of fragments, is 9%, demonstrating the high impact of this gear. The study highlighted the infringement of the red coral fishing ban by trawling gears as well as a lack of effective policing. The strengthening of controls on landings at nearby harbours, and education programmes for the local maritime communities are among the management actions proposed to protect these surviving red coral populations from the ongoing illegal fishing activity.

The three-dimensional coral scaffolds formed by the skeletons of the cold-water corals Madrepora oculata and Lophelia pertusa represent an important deep-sea hard substratum and create an optimal shelter for a rich associated fauna in which the contribution of Porifera has still not been fully considered. The taxonomic analysis of sponges collected from two Sardinian canyons (Nora and Coda Cavallo, 256–408 m) and associated with the dead coral matrix resulted in 28 species, including new records for the Mediterranean Sea, Italian fauna or Central Tyrrhenian Sea. In addition, for many species this is the first finding associated with the coral framework or the first documentation of the in situ morphology. The taxonomic comparison with sponge assemblages associated with coral frameworks from Santa Maria di Leuca, Strait of Sicily and Bari Canyon, gave the opportunity to evaluate the similarities among geographically separated banks. Overall, the percentage of exclusive species (recorded only in one site), is very high (81%) and only one species is shared by all four sites, suggesting a low connectivity among the sponge communities. The percentage of shared species is higher for the Maltese community, supporting the role of the Sicily Channel as a crossroads between the communities of the eastern and western Mediterranean basins. Here, 55% of the sponges associated to the coral framework are also reported in shallow-water coralligenous assemblages, indicating a high bathymetric connectivity as well as an ecological plasticity allowing these species to occupy a wide range of small, dark refuges.

Biodiversity of coral forests and occurrence of Derelict Fishing Gears (DFGs) have been assessed in canyon systems of the western Ligurian Sea (Dramont, Monaco, Bordighera, Arma di Taggia and Bergeggi) exposed to different anthropic pressures. Arborescent cnidarians were elected as representative species due to their role as structuring organisms and their vulnerability to DFGs damage; hence, their occurrence, density and distribution were correlated to the presence of DFGs. The canyon systems were mapped using a Multibeam Echo Sounder and visually surveyed by means of a Remotely Operated Vehicle between 20 and 445 m depth. With the exception of the Bergeggi canyon system, all sites host rich assemblages of structuring anthozoans, accounting for more than 2000 colonies belonging to 11 species, predominantly Eunicella cavolinii, Paramuricea clavata, Corallium rubrum, Dendrophyllia cornigera, and E. verrucosa. We noticed that the large structuring gorgonians were affected most, with a high number of entangled colonies. DFGs represent 85% of the marine litter found, and are the most serious threat to resident sessile communities, most noticeably in the eastern canyons. Ports, size and fishing effort of local fleets, and socio-economical differences in the fishing activities, strongly influence the fishing footprints. Our study further confirms the role of submarine canyons as site of high coral biodiversity and vulnerability to the mechanical damages by fishing-related littering, calling for adequate management measures to reduce fishery pressure and concomitant DFGs discharge.

Cnidarians are known for their simple body plan and their complex life cycles, involving high regenerative and asexual-reproduction potential. In particular, several asexual reproductive strategies are known for anthozoans, including fragmentation, carried out by tentacles, by groups of polyps or by portions of colonies. Here, we report the first observation of an extensive event of fragmentation in the Mediterranean black coral species Antipathella subpinnata (Antipatharia: Myriopathidae) in rearing conditions. Once detached, fragments lose their polarity and new anchorages are rapidly created with polyps and cnidocysts participating in the adhesion phases. Multiple attachments are frequently observed, with new skeletal plates produced through the expansion of spines. Dendritic spines gradually arise on these new plates. Fragments start to generate numerous new branchlets orientating upward and with a fixed arrangement. In 7 months of monitoring, fragments revealed fast growth rates, up to 1.85 and 1.58 cm month−1, for the whole fragments and new branchlets, respectively. Attachment of black coral fragments has never been recorded in the field; nevertheless, frequent adhesions observed in aquaria suggest that fragmentation could be a successful reproductive strategy in these anthozoans.

The main aims of Marine Protected Areas (MPAs) are the conservation of natural habitats and their biological resources, together with the promotion of an eco-compatible economic fruition. In Mediterranean MPAs, the main threats for hard bottom benthic communities come from fishing and mass tourism, in terms of boating and SCUBA diving. The Portofino MPA (Ligurian Sea, North-western Mediterranean Sea) is one of the top diving destinations in Europe and currently hosts an average of 40,000 dives per year, which are mainly carried out along coralligenous cliffs, a habitat of European Community interest, particularly vulnerable to mechanical damages due to the fragility of its numerous calcified species. The aim of this paper is to evaluate the effects of recreational SCUBA diving on benthic ecosystems characterised by the presence of red coral and other associated fragile species. The impact was assessed through the analysis of the biomasses of target organisms (Corallium rubrum, Leptopsammia pruvoti, Madracis pharensis, and six species of bryozoans) whose fragments were found in the sediments at the base of the cliff. The amounts of these fragments inside the detritus in highly frequented sites were significantly higher than those measured in undisturbed sites, of up to 10 times. Our data suggested a recurrent mechanical action, with also very recent breakages, as demonstrated by the occurrence of living, freshly detached organisms. Red coral and other calcified species may be sensitive also to natural (heavy storms) and human (fishing) mechanical pressures other than diving: the characterization of these impacts in the study sites, however, indicates divers frequentation as the major contributor to the damages inflicted and suggests the need for specific management measures.

Bazairi, Hocein/0000-0002-1788-0580; Gattuso, Jean-Pierre/0000-0002-4533-4114; Gerovasileiou, Vasilis/0000-0002-9143-7480; Cerrano, Carlo/0000-0001-9580-5546; Turicchia, Eva/0000-0002-8952-9028; Topcu, Nur Eda/0000-0003-2734-2695; Ponti, Massimo/0000-0002-6521-1330; deudero, salud/0000-0001-5584-2801; Ledoux, Jean-Baptiste/0000-0001-8796-6163; Fraschetti, Simonetta/0000-0002-1780-1651; BERTOLINO, Marco/0000-0003-3233-303X; Duarte, Carlos M./0000-0002-1213-1361, WOS: 000499719400001, [No abstract available], postdoctoral contract Juan de la Cierva-Incorporacion [IJCI-2016-29329]; Ministerio de Ciencia, Innovacion y Universidades [PTA2015-10829-I]; Interreg Med Programme [MPA-Adapt 1MED15_3.2_M2_337]; European Regional Development Fund - Foundation Prince Albert II Monaco; European UnionEuropean Union (EU) [689518, FPU15/05457]; Spanish Ministry of EducationSpanish Government [UID/Multi/04423/2013]; FCT - Foundation for Science and TechnologyPortuguese Foundation for Science and Technology; European Regional Development Fund (ERDF)European Union (EU), MV-L was supported by a postdoctoral contract Juan de la Cierva-Incorporacion (IJCI-2016-29329) of Ministerio de Ciencia, Innovacion y Universidades. AI was supported by a Technical staff contract (PTA2015-10829-I) Ayudas Personal Tecnico de Apoyo of Ministerio de Economia y Competitividad (2015). Interreg Med Programme (grant number Project MPA-Adapt 1MED15_3.2_M2_337) 85% cofunded by the European Regional Development Fund, the MIMOSA project funded by the Foundation Prince Albert II Monaco and the European Union's Horizon 2020 research and innovation programme under grant agreement no 689518 (MERCES). DG-G was supported by an FPU grant (FPU15/05457) from the Spanish Ministry of Education. J-BL was partially supported by the Strategic Funding UID/Multi/04423/2013 through national funds provided by FCT - Foundation for Science and Technology and European Regional Development Fund (ERDF), in the framework of the programme PT2020.

Association between habitat structuring organisms and other species has great relevance for ecosystem-based conservation measures. Those occurring in temperate areas, particularly in the upper portion of the continental margin, are mostly unknown or not properly understood because of the difficulty to discriminate co-occurrence and real functional linkages among species. Deep water coral assemblages over the Carloforte Shoal (south-west Sardinia; 180–210 m depth) were investigated using ROV surveys. During the surveys, more than 740 egg-capsules of the spotted catshark Scyliorhinus canicula, identified after hatching experiments in captivity, were found attached exclusively to colonies of the long-living black coral Leiopathes glaberrima. Although based on a spot finding, the results show that coral forests are not only hotspots of biodiversity, but can also serve as nursery grounds for S. canicula. The protection of these millennial coral forests is therefore to be considered a priority.

A new index of ecological status, named Mesophotic Assemblages Ecological Status (MAES) index, was elaborated on the basis of ROV (Remotely Operated Vehicle) photography and video footage in order to assess the status of mesophotic megabenthic assemblages from hard bottom. The index was tested on seven sites located between 50 and 150 m depth in the Ligurian and Tyrrhenian seas (western Mediterranean Sea). The MAES index considers three main parameters: (i) the community structure (number of megabenthic taxa, percent biotic cover in the basal layer, density of erect species); (ii) the condition of the dominant erect species (average height, percent of colonies with epibiosis/necrosis); (iii) the visible human impact (density of marine litter, including lost fishing gears). Two versions of the index have been elaborated, the complete version (MAES) and the quick version ( q -MAES), which showed comparable results, therefore suggesting the possibility of fastening assessment times. The sensitivity of the MAES index was correlated with the putative human pressure acting upon the site (semi-quantitatively assessed considering fishing effort and coastal urbanization). A standard working protocol related to the evaluation of the MAES index is here proposed with the intent to create an effective monitoring tool for the assessment of the ecological status of mesophotic assemblages on a large scale, as required by the EU Marine Strategy Framework Directive. MAES index will enhance the comprehension of the dynamics of mesophotic Mediterranean megabenthic assemblages with respect to human pressures and will also provide marine scientists and managers with a valuable tool specifically designed for the conservation of such vulnerable marine ecosystems.

The gorgonians Paramuricea clavata (Risso, 1826) and Eunicella cavolini (Koch, 1887) are important habitat-forming species within the Mediterranean coralligenous habitats, creating complex, three-dimensional forests that greatly contribute to the underwater landscape of the coastal hard grounds. Dense forests of both species are present within the Portofino Marine Protected Area (Ligurian Sea, NW Mediterranean Sea), showing a distinct bathymetric separation and site-specific differences. Quantitative evidences obtained with a monitoring census conducted in 2016 in 16 sites within the MPA support the existence of a widespread damage on these populations partially due to the mechanical injuries inflicted by recreational and professional demersal fishing gears. Considering all the studied populations, it resulted that 53% of the colonies of P. clavata and 36% of the colonies of E. cavolini were showing traces of impact, of which 10% in P. clavata and 7% in E. cavolini were due to direct entanglements with lost longlines. In the last decades, recurrent massive mortalities related to temperature anomalies and storms, have greatly reduced the gorgonian populations in this area and fishing impact severely affects survived or recovering colonies. Considering the vulnerable status of these species, and the increasing stress due to climate change, a correct management of the anthropic pressures is strongly needed to help preserving these relevant ecosystems.

Trophic relationships significantly influence ecosystem functioning, ultimately affecting populations’ abundance, size structure and distribution. There is still a substantial knowledge gap on the trophic ecology of deep-sea organisms, particularly those living in the mesophotic depths (30–150 m), despite their crucial importance as ecosystem engineers. The trophic ecology of the most common mesophotic black coral species of the Mediterranean Sea, Antipathella subpinnata (Ellis & Solander, 1786), was studied by means of stable isotopes analysis in two seasons. The δ13C and δ15N analysis of the tissue of A. subpinnata, of the sediment, as well as the main planktonic fractions (pico-nanoplankton, microplankton, and mesozooplankton) indicate a diet based on pico-nanoplankton in autumn and mesozooplankton in spring. We calculated a trophic enrichment of 1‰ in δ13C and of 2.5‰ δ15N between prey and predator. Such information contributes towards drawing a complete picture of the pelagic-benthic coupling in the Mediterranean mesophotic coral forests.

Marine bioconstructions are biodiversity-rich, three-dimensional biogenic structures, regulating key ecological functions of benthic ecosystems worldwide. Tropical coral reefs are outstanding for their beauty, diversity and complexity, but analogous types of bioconstructions are also present in temperate seas. The main bioconstructions in the Mediterranean Sea are represented by coralligenous formations, vermetid reefs, deep-sea cold-water corals, Lithophyllum byssoides trottoirs, coral banks formed by the shallow-water corals Cladocora caespitosa or Astroides calycularis, and sabellariid or serpulid worm reefs. Bioconstructions change the morphological and chemicophysical features of primary substrates and create new habitats for a large variety of organisms, playing pivotal roles in ecosystem functioning. In spite of their importance, Mediterranean bioconstructions have not received the same attention that tropical coral reefs have, and the knowledge of their biology, ecology and distribution is still fragmentary. All existing data about the spatial distribution of Italian bioconstructions have been collected, together with information about their growth patterns, dynamics and connectivity. The degradation of these habitats as a consequence of anthropogenic pressures (pollution, organic enrichment, fishery, coastal development, direct physical disturbance), climate change and the spread of invasive species was also investigated. The study of bioconstructions requires a holistic approach leading to a better understanding of their ecology and the application of more insightful management and conservation measures at basin scale, within ecologically coherent units based on connectivity: the cells of ecosystem functioning.

During the last decades, the Mediterranean shallow-water benthic communities have experienced significant changes in taxa composition and distribution. These variations were related to a complex set of anthropogenic stressors as well as to mass mortality events starting from 1999 and related to the current climatic changes. To evaluate the effect of these changes on long-living species with a limited larval dispersal capacity, a quantitative and qualitative monitoring of the shallow-water hard bottom community structure was performed over a pluri-decennial interval of time. The aim of this work was the comparison of the quali-quantitative occurrence and seasonal cycles of several benthic taxa living on a rocky cliff of the Portofino Promontory (eastern Liguria, Mediterranean Sea), from 15 to 20 m depth. The studied community, within a Lithophyllo–Halimedetum tunae association, was analysed by sets of photographs repeated, exactly in the same site, at 25 years of distance (1987/88 and 2012/13). The results suggest that the macroalgal coverage of the surveyed cliff suffered, during the monitored span of time, a significant depletion in quali-quantitative terms, while the overall sponge coverage remained almost unvaried. Nevertheless, a discrete analysis of the most common sponge species present in the study area showed significant variations, with some taxa now more abundant (Axinella spp. and Agelas oroides), some virtually stable (Cliona viridis and the complex of red encrusting sponges), and others drastically depleted (Chondrosia reniformis, Phorbas tenacior, Acanthella acuta, Ircinia spp., Dysidea avara and Petrosia ficiformis). Finally, some sponge species showed clear seasonal cycles indicating recruitment periods and post-recruit mortalities.

Commercially harvested since ancient times, the highly valuable red coral Corallium rubrum (Linnaeus, 1758) is an octocoral endemic to the Mediterranean Sea and adjacent Eastern Atlantic Ocean, where it occurs on rocky bottoms over a wide bathymetric range. Current knowledge is restricted to its shallow populations (15–50 m depth), with comparably little attention given to the deeper populations (50–200 m) that are nowadays the main target of exploitation. In this study, red coral distribution and population structure were assessed in three historically exploited areas (Amalfi, Ischia Island and Elba Island) in the Tyrrhenian Sea (Western Mediterranean Sea) between 50 and 130 m depth by means of ROV during a cruise carried out in the summer of 2010. Red coral populations showed a maximum patch frequency of 0.20 ± 0.04 SD patches·m−1 and a density ranging between 28 and 204 colonies·m−2, with a fairly continuous bathymetric distribution. The highest red coral densities in the investigated areas were found on cliffs and boulders mainly exposed to the east, at the greatest depth, and characterized by medium percentage sediment cover. The study populations contained a high percentage (46% on average) of harvestable colonies (>7 mm basal diameter). Moreover, some colonies with fifth-order branches were also observed, highlighting the probable older age of some components of these populations. The Ischia population showed the highest colony occupancy, density and size, suggesting a better conservation status than the populations at the other study locations. These results indicate that deep dwelling red coral populations in non-stressed or less-harvested areas may diverge from the inverse size-density relationship previously observed in red coral populations with increasing depth.

During the last several decades, the Mediterranean littoral shallow water benthic communities have suffered significant changes in their structure and taxa composition. Despite numerous studies conducted to characterize these changes at various levels, it has always been very difficult to disentangle the effects of natural factors from anthropic ones. The main purpose of this work was to evaluate possible changes, over a 10-year scale, in diversity and abundance of the most representative species of the benthic communities considered to be primarily and potentially affected by natural stressors in a highly protected area. Sets of macro-photographs were taken in 2002–2003 of three sites inside a small bay called Ca’ dell'Oro, which is the “no entry—no take” zone of the Marine Protected Area of Portofino, in order to analyse the structure of the benthic communities at different depths over a short time scale. The same sampling was repeated 10 years later in 2013. In the 10-year span, a significant change in the macroalgal coverage and composition was observed, while the overall richness and coverage of species remained almost unchanged. This process resulted in a significant reduction of the habitat complexity of the three-dimensional algal components. Likewise, a remarkable change in terms of presence and abundance occurred among all zoobenthic components. The benthic communities seem to have suffered from detrimental effects probably caused by climatic events that have been occurring in recent years in the Ligurian Sea.

Ecological theory predicts that heterogeneous habitats allow more species to co-exist in a given area, but to date, knowledge on relationships between habitat heterogeneity and biodiversity of coral forests in the outer shelf and upper slope along continental margins is rather limited. We investigated biodiversity of coral forests from 8 sites spread over two different geomorphological settings (namely, pinnacles vs . canyons) in the outer shelf along Sardinian continental margin. Using a combination of multivariate statistical analyses, we show here that differences in the composition of coral assemblages among contrasting geomorphological settings were not statistically significant, whereas significant differences emerged among sites within similar geomorphologies (i.e. among pinnacles and among canyons). Our results reveal that environmental and bathymetric factors such as sediment coverage, slope of the substrate, terrain ruggedness, bathymetric positioning index and aspect were important drivers of the observed patterns of coral biodiversity, in both settings. Spatial variability of coral forests' biodiversity is affected by environmental factors that act at the scale of each geomorphological setting (i.e. within each pinnacle and canyon) rather than by the contrasting geomorphological settings themselves. This result allows us to suggest that simple categorization of benthic communities according topographically defined habitat is unlikely to be sufficient for addressing conservation purposes.

The whip-like gorgonian Viminella flagellum (Alcyonacea, Ellisellidae) has an Atlantic-Mediterranean distribution. In Italian seas, the species is a common component of deep-sea rocky environments from the north-western Mediterranean area to the Strait of Sicily. V. flagellum grows in deep habitats, sometimes outlining the environment with dense forests. This work describes its habitat in an area in the southeastern Sardinian waters (central-western Mediterranean Sea), where a dense forest of the species was found. The specimens were filmed and photographed between 120 and 260 m depth with a Remotely Operated Vehicle (ROV). High-resolution multibeam echosounder (MBES) bathymetry data of the area were acquired and morphometric parameters were derived. These parameters were assumed to be relevant for the distribution of the whip-like gorgonians and were used in an Ecological Niche Factor Analysis (ENFA) to explore the niche and habitat preference of the target species. In order to identify which Eco-geographical variables are useful to predict coral distribution, we used the Maximum Entropy model (MaxEnt). Our results gave a first description of the habitat preference of V. flagellum. Specimens were found in a distinctive habitat, with respect to the overall features of the entire studied area which was characterised by a marked slope in a simple rocky seabed system, within a water depth range of 125–150 m.

Paracoryne huvei is a rare encrusting hydrozoan living in the intertidal zone of the North-western Mediterranean Sea, from the Catalan coast to the Ligurian Sea. In 2014, a large bloom of P. huvei ...

In this study we characterized the deep assemblages dwelling at 200–250 m depth on a large shoal off Capo St. Vito Promontory (Northwestern coast of Sicily, South Tyrrhenian Sea) by means of ROV-imaging. Two assemblages of suspension feeders, dominated by the gorgonian Callogorgia verticillata and by the black coral Leiopathes glaberrima, together with a tanatocoenosis of the colonial yellow scleractinian coral Dendrophyllia cornigera, were examined. The three main species were significatively distributed into two areas corresponding to different habitat preferences: a more elevated hardground hosting black corals and a gently sloping, silted rocky bottom hosting the other coral species. The study area is subjected to a heavy pressure from the professional fishery, resulting in the mechanical damage of numerous colonies, some of which are then overgrown by various epibionts including a parasitic bioluminescent zoanthid, new for the Mediterranean fauna, and tentatively identified as Isozoanthus primoidus. In the Mediterranean Sea, these deep off-shore rocky banks are widely known among recreational and professional fishermen due to their rich fish fauna. However, there has been still little effort into quantifying and characterizing the extent of the impact and its consequences on the benthic communities, which may represent, as in this case, only a partial picture of their original structure and extent.

Microboring or euendolithic microorganisms, which colonize and penetrate various carbonate substrates, are abundant in coral reef ecosystems and play a major role in reef carbonate dissolution. A few studies reported the presence of euendoliths in stylasterid coral skeletons but the biological identity, distribution and abundance of these microorganisms remain largely unknown. Observations of over 100 stylasterid colonies, collected in the Indo-Pacific area, revealed for the first time that the association between these corals and euendolith organisms appears to be quite common in shallow tropical waters. The most abundant euendolith was identified as a cryptic stage in the development of the rhodophyte Porphyra (Conchocelis stage). The euendoliths were observed in the skeletons of seven species of three genera (four Stylaster, two Distichopora and one Lepidotheca). The presence of euendoliths inside skeletons conferred a particular colour to the studied stylasterid corals. Distribution and abundance of microborings varied significantly among stylasterid species and among branches of a single colony and so did the colour of their skeletons. Colonization of skeletons and the associated colour distribution were almost uniform in some stylasterids, forming an upward gradually diminishing or sharply limited gradient. This study shows that patterns of euendolith colonization and growth in stylasterid skeletons may depend on the stage of the euendolith development as well as on their environmental requirements such as light exposure.

The class Anthozoa is the largest meta- zoan group forming mutualistic symbioses with mi- croalgae. These algal symbionts (most commonly dino - flagellates of the genus Symbiodinium) are distributed across most anthozoan orders. Records of algal cells in antipatharian (black coral) tissues have been reported, but no detailed descriptions of a mutualistic endosym- biosis exist. Here we report on zooxanthellate speci- mens of an unidentified black coral species within the genus Cirrhipathes that were collected from reef slopes at depths of 15 to 38 m in the Indonesian Archi- pelago. Symbionts were abundant (~10 7 symbionts cm -2 ) and ultrastructural analysis revealed the presence of a distinct symbiosome surrounding the algae, as well as algal reproduction inside the gastrodermal layer. Mol- ecular analysis revealed the algae to be closely related to the symbionts (Symbiodinium clade G) of clionid sponges. There was also evidence for additional sym- bionts in clade C at low abundance. Taken together, these findings (high abundance, taxonomic identity, presence of symbiosome, in situ reproduction, and depth distribution) strongly suggest that these algae are functioning as mutualists. This study confirms and describes the symbiosis between Symbiodinium and a black coral species of the genus Cirrhipathes, supports the pervasiveness of mutualisms among anthozoan taxa, and highlights the diversity and flexibility of these symbiotic associations in a poorly studied group.

The life cycle of the stoloniferan Cornularia cornucopiae (Pallas, 1766) (Anthozoa: Octocorallia) was studied from March 2009 to October 2010 on the rocky cliff of the Conero Promontory (North Adriatic Sea, 43°34.865′ N, 13°34.320′ E). In this area the species showed unusual high densities never recorded in other sites of the Mediterranean Sea. The density trend of the species showed a marked seasonal cycle, with a winter minimum of about 1000 polyps m−2 and a summer maximum of about 30,000 polyps m−2. In accordance with other Mediterranean literature data, polyps were fertile during spring–summer, from March to August, but the number of eggs per polyp continuously decreased during this span of time. Variations of polyp density were strongly correlated to water temperature, which can be considered the main environmental factor triggering this seasonal behaviour. The possibility, for C. cornucopiae, to face adverse winter conditions is probably related to the presence of a characteristic perisarcal envelope covering the stolon and the calyx of each polyp, which isolates the living tissues from the exterior. During winter, polyps degenerate but the stolons remain dormant inside their envelopes. The perisarc covering represents a morphological convergence of C. cornucopiae with benthic hydrozoans. As the latter, the studied stoloniferans are able to live in habitats characterized by periodic favourable conditions thanks to a seasonal life strategy. A similar trend is shared also by other important components (cnidarians and some sponges) of the filter-feeding community of the North Adriatic Sea. Differently to the Western Mediterranean basin, this area is characterized by high food availability all year around, so benthic organisms are strongly constrained by the very low winter temperatures.

Natural populations of Aurelia aurita scyphopolyps, settled on a wreck in the northern Adriatic Sea, were monitored for 22 months in order to study their seasonal cycle. The trend of Aurelia polyps is strongly dependent on water temperature with a peak of abundance in summer and low densities in winter. The strobilation process occurs only once a year, during the cold season, and the estimated number of released ephyrae is 780,000–2,600,000/m2. The species has been recorded only on the iron wreck while it is completely lacking from the close rocky cliff of Conero Promontory, suggesting that the increase of underwater structures of anthropogenic origin could be related to the increases of jellyfish biomass.