Deep Mediterranean Sea Research Articles

The Historical Realities of Illustrative Images of African Youths with Deadly Dangerous Voluntary Crossing of the Saharan Desert Through the Mediterranean Deep Sea to European Clandestine Destinations 2000-2021

The Historical Realities of Illustrative Images of African Youths with Deadly Dangerous Voluntary Crossing of the Saharan Desert Through the Mediterranean Deep Sea to European Clandestine Destinations 2000-2021

Mapping the habitat refugia of Isidella elongata under climate change and trawling impacts to preserve Vulnerable Marine Ecosystems in the Mediterranean

The bamboo-coral Isidella elongata is a key habitat-forming species in the deep Mediterranean Sea. This alcyonacean is listed as an indicator of Vulnerable Marine Ecosystems (VMEs) and as Critically Endangered due to bottom trawling impacts. In this work, a modeling approach was used to predict and map the habitat suitability of I. elongata in the Mediterranean Sea under current environmental conditions. Occurrence data were modeled as a function of environmental parameters. Using climate change scenarios and fishing effort data, the risk of climate change and fisheries impacts on habitat suitability were estimated, and climate refugia were identified. A drastic loss of habitat is predicted, and climate change scenarios suggest a loss of 60% of suitable habitats by 2100. In the central Mediterranean, climate refugia overlapped with active fishing grounds. This study represents the first attempt to identify hot spots for the protection of soft bottom Vulnerable Marine Ecosystems for the entire Mediterranean Sea, and highlights areas most at risk from trawling. This work is relevant to the objectives of the EU Marine Strategy Framework and Maritime Spatial Planning Directives, the Biodiversity Strategy for 2030 regarding priority areas for conservation.

Humid climate phases on the Island of Rhodes (Greece) during the late Pliocene at times of sapropel formation

The Island of Rhodes, located in the Eastern Mediterranean Sea, is affected by an active convergent plate boundary. In this context, marine sediments of Plio-Pleistocene age have been uplifted and are outcropping along the eastern coast of Rhodes. These archives provide an excellent opportunity to unravel the hydrological and climatic changes of the region during the late Pliocene. Our results provide new evidence for a more humid climate and an increased precipitation on the island during times of Northern Hemisphere summer insolation maxima and related sapropel formation in the Mediterranean deep sea. The periodic occurrence of eutrophic conditions at the shelf and upper slope off Rhodes is indicated by the recurrent dominance of eutrophic indicator species (of the genera Bolivina, Eubuliminella and Rectuvigerina), simultaneously with a decline in diversity and oligotrophic indicator species. These conditions resulted from higher primary productivity, triggered by local effects, such as enhanced precipitation and river run-off, which consequently favors the appearance of eutrophic taxa. The ∆δ13C records of the epibenthic foraminifera Cibicidoides pseudoungerianus and the shallow infaunal species Uvigerina peregrina indicate a slight productivity decrease towards younger times.

Estimating preferences for Mediterranean deep-sea ecosystem services: A discrete choice experiment

The deep sea represents Earth’s largest (but least explored) biome. It is increasingly affected by anthropogenic stressors and climate change, which threaten the provision of essential ecosystem services. The monetary value of these benefits has rarely been assessed. High biodiversity is hosted in the deep sea and, more generally, in the oceans. This paper uses a hypothetical choice experiment to investigate Italian households’ preferences for deep-sea ecosystem services. The data show wide heterogeneity of the preferences for preserving the Mediterranean deep sea. Many respondents indicate that they would refuse to pay to support the protection of biodiversity and scientific research in this remote and unfamiliar environment. Overall, global warming was of little concern for most respondents, who would not be willing to pay to limit the increase in global temperatures. High income and formal education positively influenced the willingness of the respondents to donate to Non-Governmental Organization’s initiatives to support the Mediterranean deep sea. Deep-water corals appear more ‘charismatic’ to respondents than submarine canyons among deep-sea habitats.

Water mass age and dissolved organic matter properties drive the diversity of pelagic prokaryotes in the Western Mediterranean Sea

The deep sea is among the largest, yet still poorly known, ecosystems on Earth. This knowledge gap is particularly evident for the bathypelagic layer (between 1000 and 4000 m) of the deep Mediterranean Sea (MS), characterized by peculiar environmental conditions at meso- and bathypelagic depths, such as the thermal signature of the deep waters, showing temperatures approximately 10 °C higher than any oceanic system at comparable depths. This sustains high rates of prokaryotic activities and fast dissolved organic matter (DOM) mineralization rates, and likely selects for unique microbial assemblages. We collected seawater samples in stations representative of different areas of the Western Mediterranean Sea (Algero-Provençal Basin, Alboran Sea and Gulf of Lion), from the surface to the bathypelagic layer (down to 2680 m) and in different water masses, and described the composition of pelagic prokaryotic communities, along with measurements of the main physical-chemical variables, concentration and optical properties (absorption and fluorescence) of DOM. Remarkable differences in DOM optical properties were observed among water masses, with highest dissolved organic carbon (DOC) values in surface waters and lowest in the oldest water masses represented by the Western Mediterranean Deep Water (WMDW) and the Levantine Intermediate Water (LIW), which were characterized by the highest concentration of recalcitrant DOM. The water mass had a significant partitioning effect on microbial community composition, which showed the highest richness in LIW. DOC, the marine humic-like component of DOM (C1mh) and oxygen were the main drivers of prokaryotic community structure. Changes in quality of DOM were reflected in shifts in community composition, supporting the existence of strong relationships between DOM quality and microbial community composition in the deep MS. Our data shed light on the community composition and diversity patterns of prokaryotic plankton in the deep western MS, helping to elucidate the major microbial players in the DOM cycling, and to progress towards a better comprehension of its future trends in light of changing conditions that are modifying the oceanography of the entire MS basin.

Brachiopod Fauna from the Deep Mediterranean Sea: Distribution Patterns and Ecological Preferences

Compared to their fossil counterparts, living brachiopods are investigated far less often, due to their occurrence in remote environments such as dark caves or deep environments. Due to the scarcity of studies targeting in situ brachiopods’ populations, large-scale information on their distribution and ecological preferences is still lacking, especially on hardgrounds. The extensive employment of remotely operated vehicles (ROVs), however, has opened up the chance to better explore this taxon’s diversity and ecology in the mesophotic and bathyal zones. The analysis of over 600 h of video footage collected from 624 sites, from 40 m to 1825 m, located along the Ligurian and Tyrrhenian coasts of Italy and the Sicily Channel, allowed for a large-scale investigation. The four identified species, Novocrania anomala, Gryphus vitreus, Megerlia truncata and Terebratulina retusa, emerged as common macrofaunal components of the explored habitats, especially between 150 m and 250 m, with high occurrences in the northern areas, especially on offshore seamounts. All species can form dense aggregations of individuals, with M. truncata showing the densest populations on steep rocky terraces (up to 773 individuals m−2). Except for G. vitreus, the only species also recorded on soft bottoms, the others were found exclusively on hardgrounds, with N. anomala showing a peculiar ability to exploit anthropogenic substrates such as terracotta amphorae. No stable species-specific associations were noted, even if numerous species were frequently observed together. Although brachiopods do not show the conspicuous tridimensionality of large filter-feeders, their substrate occupancy and their role in pelagic–benthic processes support their importance in deep-sea Mediterranean ecosystems.

Into the Dark: Exploring the Deep Ocean with Single-Virus Genomics.

Single-virus genomics (SVGs) has been successfully applied to ocean surface samples allowing the discovery of widespread dominant viruses overlooked for years by metagenomics, such as the uncultured virus vSAG 37-F6 infecting the ubiquitous Pelagibacter spp. In SVGs, one uncultured virus at a time is sorted from the environmental sample, whole-genome amplified, and sequenced. Here, we have applied SVGs to deep-ocean samples (200–4000 m depth) from global Malaspina and MEDIMAX expeditions, demonstrating the feasibility of this method in deep-ocean samples. A total of 1328 virus-like particles were sorted from the North Atlantic Ocean, the deep Mediterranean Sea, and the Pacific Ocean oxygen minimum zone (OMZ). For this proof of concept, sixty single viruses were selected at random for sequencing. Genome annotation identified 27 of these genomes as bona fide viruses, and detected three auxiliary metabolic genes involved in nucleotide biosynthesis and sugar metabolism. Massive protein profile analysis confirmed that these viruses represented novel viral groups not present in databases. Although they were not previously assembled by viromics, global fragment recruitment analysis showed a conserved profile of relative abundance of these viruses in all analyzed samples spanning different oceans. Altogether, these results reveal the feasibility in using SVGs in this vast environment to unveil the genomes of relevant viruses.

Recognizing megatsunamis in Mediterranean deep sea sediments based on the massive deposits of the 365 CE Crete\xa0event

The Mediterranean Sea hosts two subduction systems along the convergent Africa-Eurasia plate boundary that have produced strong ground shaking and generated tsunamis. Based on historical descriptions and sedimentary records, one of these events, in 365 CE, impacted a broad geographical area, including tsunami evidence for distances of 700–800 km from the source event, qualifying it as a ‘megatsunami’. Understanding how megatsunamis are produced, and where they are more likely, requires a better understanding of the different secondary processes linked to these events such as massive slope failures, multiple turbidity current generation, and basin seiching. Our sedimentary records from an extensive collection of cores located in distal and disconnected basins, identify turbidites which are analyzed using granulometry, elemental (XRF), micropaleontological, and geochemical data in order to reconstruct their coastal or marine source. The results show that the 365 CE basin floor sediments are a mixture of inner shelf and slope materials. The tsunami wave produced multiple far-field slope failures that resulted in stacked basal turbidites. It also caused transport of continent-derived organic carbon and deposition over basal turbidites and into isolated basins of the deep ocean. The composition of sediment in isolated basins suggests their deposition by large-scale sheet like flows similar to what has been caused by the Tohoku earthquake associated tsunamis. This is significant for rectifying and resolving where risk is greatest and how cross-basin tsunamis are generated. Based on these results, estimates of the underlying deposits from the same locations were interpreted as possible older megatsunamis.

Ecological role and phylogenetic position of a new habitat-forming species (Canalipalpata, Sabellidae) from the Mediterranean mesophotic soft bottoms

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.

Occurrence of microplastics in the gastrointestinal tract of benthic by–catches from an eastern Mediterranean deep–sea environment

Concern about microplastic pollution little is known about levels in deep-sea species; to fill this knowledge gap, levels of microplastics in the gastrointestinal (GI) tracts of 34 fish from eight different deep–sea by–catches: blackmouth catshark, lesser spotted dogfish, and velvet belly, armless snake eel, hollowsnout grenadier, phaeton dragonet, royal flagfin, and slender snipe eel were measured. All were collected at the same site (east Sardinia, Mediterranean Sea; 40°10′12.49″N, 9°44′12.31″E) using a bottom gillnet at depths between −820/250 and −1148 ft./350 m. Microplastics (MPs) were retrieved in 16 out of 34 fish. At least one microplastic item was found in 48% (33%, E. spinax - 75%, G. melastomus) of the samples. The most frequent was polyethylene (PE), with nine items (filaments, films, fragments) found in five specimens. This preliminary study of by–catches adds new data on MPs ingestion by species inhabiting a deep–sea environment of the Mediterranean.

First record of the rendezvous fish, Polymetme corythaeola (Alcock, 1898), in the Mediterranean Sea

The occurrence of the rendezvous fish, Polymetme corythaeola (Alcock, 1898) in Mediterranean Sea is here reported for the first time. A single individual of this benthopelagic fish was caught in February 2020 during a scientific trawl survey. The specimen was collected at a depth of 369 m (upper slope) in the Gulf of Roses (Catalonia, north-western Mediterranean). This circumglobal species could have naturally expanded its distribution through the Strait of Gibraltar, but we cannot totally exclude that its Mediterranean occurrence has been overlooked thus far. This finding highlights the importance of continuous monitoring of Mediterranean deep-sea habitats for a better understanding of their diversity and ongoing transformation.

New records of scleractinian cold-water coral (CWC) assemblages in the southern Tyrrhenian Sea (western Mediterranean Sea): Human impacts and conservation prospects

Scleractinian cold-water corals (CWCs) are among the main habitat engineers of the deep Mediterranean Sea, hosting a high diversity of species and playing a significant ecological role. In the last two decades, many new living scleractinian CWC sites throughout the Mediterranean Basin have been recorded and their distribution has been updated. In the summer of 2018, new scleractinian CWC assemblages were discovered by means of remotely operated vehicle (ROV) and multibeam echosounder (MBES) surveys on the Aceste–Tiberio seamount and Marettimo bank in the southern Tyrrhenian Sea, at depths ranging from 240 to 310 m. In the explored areas, megabenthic communities were dominated by habitat-forming species, some of which have never been reported before on these submarine structures. Healthy patches of Madrepora oculata and Desmophyllum pertusum, together with the solitary coral D. dianthus, were found on rocky pinnacles between inclined silted bottoms, as well as on a wreck. Deep-water fishing activities, mainly longline fishing, negatively affected these communities, particularly coral species. The discovery of these new sites adds new knowledge about the distribution of scleractinian CWCs in the Mediterranean Sea. Moreover, the documented negative effect of fishing activities on CWC species further stresses the need for urgent and specific conservation measures. In this regard, the co-occurrence of several long-lived, slow-growing, and vulnerable species on these seamounts and banks supports the establishment of specific marine protected areas [i.e., offshore Natura 2000 sites, in accordance with the Habitats Directive (92/43/EEC) - Habitat 1170 - Reefs].

Identifying Priorities for the Protection of Deep Mediterranean Sea Ecosystems Through an Integrated Approach

Benthic habitats of the deep Mediterranean Sea and the biodiversity they host are increasingly jeopardized by increasing human pressures, both direct and indirect, which encompass fisheries, chemical and acoustic pollution, littering, oil and gas exploration and production and marine infrastructures (i.e., cable and pipeline laying), and bioprospecting. To this, is added the pervasive and growing effects of human-induced perturbations of the climate system. International frameworks provide foundations for the protection of deep-sea ecosystems, but the lack of standardized criteria for the identification of areas deserving protection, insufficient legislative instruments and poor implementation hinder an efficient set up in practical terms. Here, we discuss the international legal frameworks and management measures in relation to the status of habitats and key species in the deep Mediterranean Basin. By comparing the results of a multi-criteria decision analysis (MCDA) and of expert evaluation (EE), we identify priority deep-sea areas for conservation and select five criteria for the designation of future protected areas in the deep Mediterranean Sea. Our results indicate that areas (1) with high ecological relevance (e.g., hosting endemic and locally endangered species and rare habitats),(2) ensuring shelf-slope connectivity (e.g., submarine canyons), and (3) subject to current and foreseeable intense anthropogenic impacts, should be prioritized for conservation. The results presented here provide an ecosystem-based conservation strategy for designating priority areas for protection in the deep Mediterranean Sea.

Potential factors influencing the condition of demersal sharks in the Mediterranean deep sea ecosystems

The Alboran Sea and the Balearic Islands are two contrasting areas in terms of primary productivity. The former is among the most productive areas of the whole Mediterranean Sea, whereas the Balearic Islands is among the less productive ones in the western Mediterranean. The two areas also show different patterns in the bottom trawl fishing footprint. In the Alboran Sea, the fishing effort on the upper slope is much higher than in Balearic Islands. However, the opposite applies to the middle slope, the vast majority of it remaining unexploited in Alboran Sea, whereas a widespread fishery targeting blue and red shrimp Aristeus antennatus develops in Balearic Islands.Galeus melastomus is a small demersal shark species inhabiting slope bottoms, where adults and juveniles are segregated and concentrate in the middle and upper slope, respectively. It feeds intensively on mesopelagic preys which, in turn, feed on low trophic level organisms close to primary producers. In this work we aimed to study the effect of surface primary production on the condition of deep sea demersal communities. We compared the condition, diet and potential intra- and inter-species competition for feeding resources in the juveniles of G. melastomus between Alboran Sea and Balearic Islands. The comparisons of Le Cren’s relative condition factor, and hepatosomatic and digestivosomatic indices evidenced an opposite pattern to that a priori expectable: better condition in the less productive area. The analysis of stomach contents showed similar diets in both areas, but lower food ingestion in Alboran Sea than in Balearic Islands. Different abundances of potential intra- and inter-specific competitors for feeding resources in the two areas, apparently linked to the different fishing footprints, seems the most likely explanation for the better nourished individuals in Balearic Islands. Whereas juveniles of G. melastomus dominate the shark community in the Balearic Islands upper slope, where the presence of adults of this species is almost negligible, in Alboran Sea this stratum is dominated by adults and potential competitors of other small demersal shark species. All shark species together, including G. melastomus, showed abundances 38% higher in Alboran than in Balearic Islands. Our results show that condition of deep sea demersal fish is ruled by complex inter-relationships among different factors, needing the combination of biological, ecological and fisheries knowledge to understand its variability.

Life strategies and habitat preferences of Bythitidae and Zoarcidae, specialized fishes with particular life histories, in the Mediterranean deep sea

Deep-sea habitats are home for a variety of yet poorly known fish species, some of which display specialized life strategies, as is the case of Bythitidae and Zoarcidae. With the purpose of elucidating biological and ecological aspects of representatives of these families in NW Mediterranean waters, a large dataset based on 599 specimens of Cataetyx alleni, 30 C. laticeps and 284 Melanostigma atlanticum captured during the last 30 years within the framework of different research projects was used to address their geographical and bathymetric distribution, population structure, reproduction, trophic ecology, parasitism and enzymatic markers in the Balearic basin. Present outcomes revealed a patchy distribution mostly for M. atlanticum, possibly related to aggregation during reproduction and to the association with specific sediments. For the three species, higher densities occurred in the mainland vs. the insular margin, and a diminishing trend in estimated densities over the last decades was observed for C. alleni and M. atlanticum likely linked to climatic oscillations. Trophic data indicated that the two Cataetyx species inhabit the water-sediment interface and mainly feed on suprabenthic prey, while M. atlanticum inhabits the water column near the bottom preying on pelagic organisms and moving towards the seabed during reproduction. These results were supported by the parasitological assessment, which revealed that parasite communities were moderately diverse and abundant for Cataetyx spp. while being highly depauperate for M. atlanticum. Present outcomes from the Mediterranean Sea confirmed reproduction of C. alleni during autumn-winter and of M. atlanticum during autumn. Spawning of the former species may occur in winter-spring, as suggested by the finding, by the first time, of two females captured in March with fully-developed embryos inside. Levels of enzymatic markers quantified in muscle were provided for C. alleni and M. atlanticum for the first time. The special interactions found between the distribution and biology of Bythitidae and Zoarcidae and the sedimentary bottoms that they inhabit indicates that such conventional habitats are more heterogeneous than it is generally assumed and deserve higher attention for future protection.

A Perspective for Best Governance of the Bari Canyon Deep-Sea Ecosystems

There is growing awareness of the impact of fishery activities on fragile and vulnerable deep-sea ecosystems, stimulating actions devoted to their protection and best management by national and international organizations. The Bari Canyon in the Adriatic Sea represents a good case study of this, since it hosts vulnerable ecosystems, threatened species, as well as valuable commercial species, but virtually lacks substantial management plans for the sustainable use of resources. This study documents the high level of biodiversity of the Bari Canyon and the impact of human activities by analyzing remotely operated vehicle surveys and benthic lander deployments. An integrated socio-economic study provides information on fishing pressure in the Bari Canyon and in the surrounding areas. Finally, measures of conservation, protection, and management are discussed and suggested for this remarkable site in the context of the deep Mediterranean Sea.

Evaluating the distribution of priority benthic habitats through a remotely operated vehicle to support conservation measures off Linosa Island (Sicily Channel, Mediterranean Sea)

Abstract Explorations of the Mediterranean deep sea using remotely operated vehicles have shown that the sea bed hosts rich habitats, supporting high biodiversity. However, there have been only a few studies dealing with the southern part of the basin, leading to limited protection and conservation efforts in this area. This study aimed to explore the sea bed off Linosa Island (Sicily Channel, southern Mediterranean Sea), which is considered a ‘sentinel area’ for alien species and global environmental changes owing to its geographic position, thus deserving special attention. Remotely operated vehicle surveys, carried out in 2016 and 2017, were analysed to provide the first ecological characterization of benthic assemblages at depths −19 – −384 m around Linosa Island. Communities were dominated by three priority habitats, amounting to 39% of the almost 5 km of the sea floor that was surveyed. These are represented in the euphotic zone by Posidonia oceanica meadows and, at greater depth, by newly discovered dense coral forests and extended rhodolith/maërl beds. Sixteen habitat‐forming species included in the Red List of the International Union for Conservation of Nature (e.g. gorgonians Eunicella cavolini and Paramuricea clavata, and black corals Antipathella subpinnata and Leiopathes glaberrima) were recorded, as well as individuals of Sargassum sp. at −100 m depth. The volcanic island of Linosa represents a small, naturally preserved area, with very limited human pressure, hosting rich marine benthic biodiversity. Given the high species and habitat richness, we recommend its inclusion in the Special Protected Areas of Mediterranean Importance project (United Nations Environment Programme) and suggest a redefinition of the existing marine protected area extension.

Deep-sea deployment of the KM3NeT neutrino telescope detection units by self-unrolling

KM3NeT is a research infrastructure being installed in the deep Mediterranean Sea. It will house a neutrino telescope comprising hundreds of networked moorings—detection units or strings—equipped with optical instrumentation to detect the Cherenkov radiation generated by charged particles from neutrino-induced collisions in its vicinity. In comparison to moorings typically used for oceanography, several key features of the KM3NeT string are different: the instrumentation is contained in transparent and thus unprotected glass spheres; two thin Dyneema\ extsuperscript{\ extregistered} ropes are used as strength members; and a thin delicate backbone tube with fibre-optics and copper wires for data and power transmission, respectively, runs along the full length of the mooring. Also, compared to other neutrino telescopes such as ANTARES in the Mediterranean Sea and GVD in Lake Baikal, the KM3NeT strings are more slender to minimise the amount of material used for support of the optical sensors. Moreover, the rate of deploying a large number of strings in a period of a few years is unprecedented. For all these reasons, for the installation of the KM3NeT strings, a custom-made, fast deployment method was designed. Despite the length of several hundreds of metres, the slim design of the string allows it to be compacted into a small, re-usable spherical launching vehicle instead of deploying the mooring weight down from a surface vessel. After being lowered to the seafloor, the string unfurls to its full length with the buoyant launching vehicle rolling along the two ropes. The design of the vehicle, the loading with a string, and its underwater self-unrolling are detailed in this paper.

Habitat, morphology and trophism of Tritonia callogorgiae sp. nov., a large nudibranch inhabiting Callogorgia verticillata forests in the Mediterranean Sea

The continuing exploration of the Mediterranean deep sea reveals that a complete census of the biodiversity of one of the most studied marine areas in the world is yet to be fully accomplished. A tritoniid nudibranch new to science is described upon material recovered off the Montenegro margin, Adriatic Sea, associated with the alcyonacean Primnoidae Callogorgia verticillata (Pallas, 1766). Here, a coral forest dominated by C. verticillata, together with other alcyonaceans, antipatharians and scleractinians, represents the habitat of the new species. As documented by Remotely Operated Vehicle (ROV) observations, the coral forest covers an area of 600 m2 at 420–426 m depth, with dense growth of C. verticillata colonies (1.34 ± 0.08 colonies m−2). As many as 66 nudibranch specimens have been observed on C. verticillata. Tritonia callogorgiae sp. nov. (Gastropoda, Nudibranchia, Tritoniidae) is up to 12 cm long, yellow to orange/reddish in colour with white papillae all over the body. It has a velum with six appendages (three per side), and 4–5 pairs of dichotomous gills. Internally, the species is distinguished from other tritoniids for the absence of stomach plates and a distinctive radula with formula 50 × 110.1.1.1.108. It represents the first case of Tritonia species living in the deep Mediterranean Sea and the only one associated to C. verticillata. Stomach content documents that Tritonia callogorgiae sp. nov. feeds on C. verticillata. Further visual ROV records from other sectors of the Mediterranean Sea indicate that the distribution of this new described species is almost basin-wide. The discovery of another undescribed member of the benthic megafauna related to deep-sea coral grounds further highlights the need for conservation of such habitats.

Diversity, distribution, and habitat associations of deep-water echinoderms in the Central Mediterranean

Limited research effort in the Central Mediterranean deep sea has reported a lower species diversity in this area than in adjacent regions. With the recent advent of remotely operated underwater vehicles (ROVs), the deep sea has become more accessible to surveys, especially rocky benthic areas such as canyons and escarpments. The aim of the present study was to assess diversity, spatial and bathymetric distribution, density, habitat, and microhabitat associations of echinoderms in deep waters around the Maltese Islands. Video data were acquired through ROV surveys as part of the LIFE BaĦAR for N2K project, at depths of 216 to 1031 m. In total, 25 echinoderm taxa were recorded, including the first Central Mediterranean records of the sea stars Marginaster capreensis (Gasco, 1876) and Sclerasterias neglecta (Perrier, 1891), and the first record of the holothuroid Mesothuria intestinalis (Ascanius, 1805) from Maltese waters. Six species were observed deeper than their currently accepted depth range in the Mediterranean. The most abundant species were the crinoids Antedon mediterranea (Lamarck, 1816) and Leptometra phalangium (Muller, 1841), which formed very dense aggregations of up to 2900 individuals/1000 m2 in a small area to the south of Malta. This area also supports the only known Mediterranean population of the Atlantic sea star Coronaster briareus (Verrill, 1882). Bathymetric distribution varied for each species, and the overall echinoderm diversity seemed stable across the surveyed depths. Since previous deep-sea studies in the area were based on trawling surveys, many deep-sea echinoderm species are reported in the literature as occurring on sedimentary bottoms. However, the present study revealed that several occur more often on rocky substrata, corals, or anthropogenic objects than on sediments. Our study based on video footage also provided insights into the microhabitat of many deep-sea species, yielding information that is not obtainable through remote sampling.