Molecular diversity of black corals from the Saudi Arabian Red Sea: a first assessment.

Black corals occur as part of benthic assemblages from shallow to deep waters in all oceans. Despite the importance in many benthic ecosystems, where these act as biodiversity aggregators, antipatharians remain poorly studied, with 75% of the known species occurring below recreational SCUBA diving depth limits. Currently, information regarding the diversity and evolutionary history is limited, with most studies focusing on Hawaii and the South Pacific Ocean. Other regions of the world have received less attention, such as the Red Sea, where only two black coral families and four genera have been recorded. We provide the first analysis of the molecular diversity of black corals in the eastern Gulf of Aqaba and the northern and central Saudi Arabian Red Sea, based on a dataset of 161 antipatharian colonies collected down to 627 m deep. Based on specimen morphology, we ascribed our material to 11 genera belonging to 4 of the 7 known Antipatharia families, i.e. Antipathidae, Aphanipathidae, Myriopathidae and Schizopathidae. The genus level phylogeny of three intergenic mitochondrial regions, the trnW-IGR-nad2 (IgrW ), nad5-IGR-nad1 (IgrN ) and cox3-IGR-cox1 was reconstructed including previously published material. Overall, we recovered six molecular clades that included exclusively Red Sea sequences, with the highest diversity occurring at mesophotic depths. This study highlights that diversity of black corals in the Red Sea is much higher than previously known, with seven new generic records, suggesting that this basin may be a hotspot for antipatharian diversity as is known for other taxa. Our results recovered unresolved relationships within the order at the familial and generic levels. This emphasises the urgent need for an integration of genomic-wide data with a re-examination of informative morphological features necessary to revise the systematics of the order at all taxonomic levels.

Assessing the economic value of Posidonia oceanica (L.) at Tremiti Islands (Mediterranean Sea): An ecosystem condition-based approach.

In the context of limiting global warming, the seagrass Posidonia oceanica (L.) gained the centrality of several international climate change mitigation projects being the most effective carbon storage sink among Mediterranean seagrasses. To assess and monitor the change of environmental conditions and economic values of natural resources, the present study moves from the insights of the System of Environmental-Economic Accounting - Ecosystem Accounting to assess the economic value of the carbon sequestration and storage capacity of the Mediterranean-endemic seagrass P. oceanica at the Tremiti Islands Marine Protected Area. The economic value is compared across: i. the reference study by Pergent-Martini et al.; ii. the ecological condition-based approach; and iii. the unit value transfer. Based on the obtained outcomes, an ecosystem-based approach would prevent biases in the accounting of the ecosystem-service provision capacity of P. oceanica and help the policy maker to implement adequate public investment policies to mitigate its overall degradation.

Conservation status of upper-mesophotic octocoral habitats at Sporades Archipelago (Aegean Sea).

Octocoral forests created by the yellow sea fan Eunicella cavolini and the red sea fan Paramuricea clavata were studied at the National Marine Park of Alonissos Northern Sporades (Aegean Sea, Greece), between 30 and 45 m depth, in order to assess their conservation status and the occurrence of both natural and anthropogenic stressors. The area was characterized by rich and dense coral forests, with densities up to 55.2 colonies m-2 for E. cavolini and 28.0 colonies m-2 for P. clavata. The coral population showed signs of stress, although mortality was low. A combination of stressors linked to global warming and fishing impacts, including macroalgal epibiosis, tip necrosis, increasing coral feeders, and abandoned fishing gears, could impair the status of these habitats in the near future. Although the effects of climate change are global, local conservation actions may reduce direct anthropogenic impacts and enhance habitats' resilience.

First record of Boulenger's anthias Sacura boulengeri (Heemstra 1973) in the Red Sea.

In November 2020, we observed several individuals and collected one juvenile of an unidentified anthiadine fish (Serranidae) between depths of 250 and 307 m near vertical walls of rocky reefs in the northern Red Sea. Further morphological and molecular analyses revealed that the collected specimen matches Sacura boulengeri, a species previously reported only from the Gulf of Oman to India.

The Status of Posidonia oceanica at Tremiti Islands Marine Protected Area (Adriatic Sea).

Posidonia oceanica meadows are Mediterranean coastal habitats of great conservation importance. This study is focused on a meadow located at Tremiti Islands Marine Protected Area (Adriatic Sea, Italy), which was monitored in 2003, 2015, and 2020 to evaluate its health state over time in relation to coastal human activities, which have been highly affecting this MPA for the last 20 years. To assess any change in the physiognomy of the meadow, rhizome density, percentage coverage, and lower limit progressions and/or regression over time were evaluated by scuba diving, while the distribution and extension of the meadow were assessed through habitat mapping using a side-scan sonar. Moreover, phenological and lepidochronological analyses were performed on the collected rhizomes to assess the leaf area index (LAI, m2m-2) and the rhizome age (lepidochronological years). Our study showed a general deterioration of P. oceanica meadow from 2003 to 2020, with a significant reduction of its absolute and relative rhizome density and LAI at almost all sampling stations, absence of renovation of the meadow, and lower limit regression and overall worsening of the main conservation status indicators. However, appropriate management actions, such as the establishment of mooring buoy fields, supported the improvement of the P. oceanica status at the local scale with a significant increase in density and LAI and the presence of active stolonization processes, suggesting that mitigation actions can play a crucial role in the conservation of this habitat. On the contrary, local anthropogenic impacts, especially anchoring and coastal development, markedly affect the resilience of P. oceanica meadows to global stressors, such as climate change.

The complete mitochondrial genome of Dendrophyllia minuscula (Cnidaria: Scleractinia) from the NEOM region of the Northern Red Sea.

The scleractinian coral family Dendrophylliidae is a major component of shallow and deep-water coral ecosystems worldwide, but our knowledge on the evolutionary history of the family remains scarce. Here, we used ezRAD coupled with Illumina sequencing technology and reconstructed the complete mitochondrial genome of Dendrophyllia minuscula (GenBank accession number OL634845), from mesophotic depths in the Red Sea NEOM area. The mitochondrial genome of D. minuscula consisted of 19,054 bp, organized in 13 protein-coding genes, 2 rRNA genes, and 2 tRNA genes, in agreement with the Scleractinia typical mitogenome organization. This complete mitochondrial genome contributes toward a better knowledge of mesophotic and deep-water coral diversity and evolutionary history.

A new species of Bathypathes (Cnidaria, Anthozoa, Antipatharia, Schizopathidae) from the Red Sea and its phylogenetic position.

A black coral, Bathypathesthermophila Chimienti, sp. nov. is described from the Saudi Arabian coasts of the Gulf of Aqaba and north Red Sea (Neom area) using an integrated taxonomic approach. The morphological distinctiveness of the new species is confirmed by molecular analyses. The species thrives in warm and high salinity waters typical of the Red Sea at bathyal depths. It can form colony aggregations on muddy bottoms with scattered, small hard substrates. Colonies are monopodial, feather-like, and attached to a hard substrate through a thorny basal plate. Pinnules are simple, arranged biserially and alternately, and all the same length (up to approximately 20 cm) except for few, proximal ones. Spines are triangular, laterally compressed, subequal, smooth, and simple or rarely bifurcated. Polyps are elongated transversely, 1.5-2.0 mm in transverse diameter. Large colonies can have one or few branches, whose origin is discussed. The phylogenetic position of B.thermophila sp. nov. within the order Antipatharia, recovered using three mitochondrial markers, shows that it is nested within the family Schizopathidae. It is close to species in the genera Parantipathes, Lillipathes, Alternatipathes, and Umbellapathes rather than to the other available representatives of the genus Bathypathes, as currently defined based on morphology. In agreement with previous findings, our results question the evolutionary significance of morphological characters traditionally used to discriminate Antipatharia at higher taxonomic level.

Effects of global warming on Mediterranean coral forests.

The effects of global warming have been addressed on coral reefs in tropical areas, while it is still unclear how coral forests are reacting, particularly at temperate latitudes. Here we show how mesophotic coral forests are affected by global warming in the Mediterranean Sea. We highlight how the current warming trend is causing the lowering of the thermocline and it is enhancing mucilaginous blooms. These stressors are facilitating a massive macroalgal epibiosis on living corals, here reported for the first time from different areas in the Western and Central Mediterranean Sea. We provide a focus of this phenomenon at Tremiti Islands Marine Protected Area (Adriatic Sea), were the density of the endemic red gorgonian Paramuricea clavata decreased of up to 47% in 5 years, while up to the 96% of the living corals showed signs of stress and macroalgal epibiosis. Only populations deeper than 60 m depth were not touched by this emerging phenomenon. Spot observations performed at Tuscan Archipelago and Tavolara Marine Protected Area (Tyrrhenian Sea) suggest that this this combination of stressors is likely widespread at basin scale.

A Newly Discovered Forest of the Whip Coral Viminella flagellum (Anthozoa, Alcyonacea) in the Mediterranean Sea: A Non-Invasive Method to Assess Its Population Structure.

Coral forests are vulnerable marine ecosystems formed by arborescent corals (e.g., Anthozoa of the orders Alcyonacea and Antipatharia). The population structure of the habitat-forming corals can inform on the status of the habitat, representing an essential aspect to monitor. Most Mediterranean corals live in the mesophotic and aphotic zones, and their population structures can be assessed by analyzing images collected by underwater vehicles. This is still not possible in whip-like corals, whose colony lengths and flexibilities impede the taking of direct length measurements from images. This study reports on the occurrence of a monospecific forest, of the whip coral Viminella flagellum in the Aeolian Archipelago (Southern Tyrrhenian Sea; 149 m depth), and the assessment of its population structure through an ad-hoc, non-invasive method to estimate a colony height based on its width. The forest of V. flagellum showed a mean density of 19.4 ± 0.2 colonies m-2 (up to 44.8 colonies m-2) and no signs of anthropogenic impacts. The population was dominated by young colonies, with the presence of large adults and active recruitment. The new model proved to be effective for non-invasive monitoring of this near threatened species, representing a needed step towards appropriate conservation actions.

A Minimal Metric for the Characterization of Acoustic Noise Emitted by Underwater Vehicles.

Underwater robots emit sound during operations which can deteriorate the quality of acoustic data recorded by on-board sensors or disturb marine fauna during in vivo observations. Notwithstanding this, there have only been a few attempts at characterizing the acoustic emissions of underwater robots in the literature, and the datasheets of commercially available devices do not report information on this topic. This work has a twofold goal. First, we identified a setup consisting of a camera directly mounted on the robot structure to acquire the acoustic data and two indicators (i.e., spectral roll-off point and noise introduced to the environment) to provide a simple and intuitive characterization of the acoustic emissions of underwater robots carrying out specific maneuvers in specific environments. Second, we performed the proposed analysis on three underwater robots belonging to the classes of remotely operated vehicles and underwater legged robots. Our results showed how the legged device produced a clearly different signature compared to remotely operated vehicles which can be an advantage in operations that require low acoustic disturbance. Finally, we argue that the proposed indicators, obtained through a standardized procedure, may be a useful addition to datasheets of existing underwater robots.

A mesophotic black coral forest in the Adriatic Sea.

A forest of the black coral Antipathella subpinnata was found from 52 to 80 m depth in three different sites at Tremiti Islands Marine Protected Area (MPA; Mediterranean Sea), with two of them hosting a monospecific forest on horizontal and vertical substrates. Colonies of A. subpinnata showed a mean density between 0.22 ± 0.03 and 2.40 ± 0.26 colonies m-2 (maximum local values of 2.4-7.2 colonies m-2). The link between the local distribution of A. subpinnata and the main oceanographic features confirmed the fundamental role of the currents in shaping the distribution of the species in presence of hard substrata. This black coral forest represents the only one known thus far in the Adriatic Sea, but it could be linked with other unseen forests all over the Mediterranean Sea. The associated megafauna highlights the importance of these forests as habitat for species of both conservation and commercial importance but, at the same time, makes such habitat a target for fishing practices, as many lost fishing gears were found within the coral forest. The enlargement of the MPA borders and the enforcement of controls in the area of the A. subpinnata forest is urgently needed for the proper conservation of this protected species.

Climate-induced changes in the suitable habitat of cold-water corals and commercially important deep-sea fishes in the North Atlantic.

The deep sea plays a critical role in global climate regulation through uptake and storage of heat and carbon dioxide. However, this regulating service causes warming, acidification and deoxygenation of deep waters, leading to decreased food availability at the seafloor. These changes and their projections are likely to affect productivity, biodiversity and distributions of deep-sea fauna, thereby compromising key ecosystem services. Understanding how climate change can lead to shifts in deep-sea species distributions is critically important in developing management measures. We used environmental niche modelling along with the best available species occurrence data and environmental parameters to model habitat suitability for key cold-water coral and commercially important deep-sea fish species under present-day (1951-2000) environmental conditions and to project changes under severe, high emissions future (2081-2100) climate projections (RCP8.5 scenario) for the North Atlantic Ocean. Our models projected a decrease of 28%-100% in suitable habitat for cold-water corals and a shift in suitable habitat for deep-sea fishes of 2.0°-9.9° towards higher latitudes. The largest reductions in suitable habitat were projected for the scleractinian coral Lophelia pertusa and the octocoral Paragorgia arborea, with declines of at least 79% and 99% respectively. We projected the expansion of suitable habitat by 2100 only for the fishes Helicolenus dactylopterus and Sebastes mentella (20%-30%), mostly through northern latitudinal range expansion. Our results projected limited climate refugia locations in the North Atlantic by 2100 for scleractinian corals (30%-42% of present-day suitable habitat), even smaller refugia locations for the octocorals Acanella arbuscula and Acanthogorgia armata (6%-14%), and almost no refugia for P. arborea. Our results emphasize the need to understand how anticipated climate change will affect the distribution of deep-sea species including commercially important fishes and foundation species, and highlight the importance of identifying and preserving climate refugia for a range of area-based planning and management tools.

Application of Hyperspectral Imaging to Underwater Habitat Mapping, Southern Adriatic Sea.

Hyperspectral imagers enable the collection of high-resolution spectral images exploitable for the supervised classification of habitats and objects of interest (OOI). Although this is a well-established technology for the study of subaerial environments, Ecotone AS has developed an underwater hyperspectral imager (UHI) system to explore the properties of the seafloor. The aim of the project is to evaluate the potential of this instrument for mapping and monitoring benthic habitats in shallow and deep-water environments. For the first time, we tested this system at two sites in the Southern Adriatic Sea (Mediterranean Sea): the cold-water coral (CWC) habitat in the Bari Canyon and the Coralligenous habitat off Brindisi. We created a spectral library for each site, considering the different substrates and the main OOI reaching, where possible, the lower taxonomic rank. We applied the spectral angle mapper (SAM) supervised classification to map the areal extent of the Coralligenous and to recognize the major CWC habitat-formers. Despite some technical problems, the first results demonstrate the suitability of the UHI camera for habitat mapping and seabed monitoring, through the achievement of quantifiable and repeatable classifications.

Towards Non-Invasive Methods to Assess Population Structure and Biomass in Vulnerable Sea Pen Fields.

Colonies of the endangered red sea pen Pennatula rubra (Cnidaria: Pennatulacea) sampled by trawling in the northwestern Mediterranean Sea were analyzed. Biometric parameters, such as total length, peduncle length, number of polyp leaves, fresh weight, and dry weight, were measured and related to each other by means of regression analysis. Ad hoc models for future inferencing of colonies size and biomass through visual techniques were individuated in order to allow a non-invasive study of the population structure and dynamics of P. rubra.

Haplosporidium pinnae associated with mass mortality in endangered Pinna nobilis (Linnaeus 1758) fan mussels.

The fan mussel, Pinna nobilis (Linnaeus 1758), is an endemic bivalve of the Mediterranean basin, protected by international legislation as an endangered species. In the early summer of 2018, a mass mortality event (MME) of P. nobilis was recorded in the Gulf of Taranto (Southern Italy, Ionian Sea). Moribund specimens of P. nobilis were collected by scuba divers and processed by bacteriological, parasitological, histopathological and molecular analyses to investigate the causes of this MME. Different developmental stages (i.e., plasmodia, spores and sporocysts) of a presumptive haplosporidian parasite were observed during the histological analysis in the epithelium and in the lumen of the digestive tubules, where mature spores occurred either free or in sporocysts. The spores presented an operculum and an ovoid shape measuring 4.4 µm (±0.232) in length and 3.6 µm (±0.233) in width. BLAST analysis of an 18SrRNA sequence revealed a high nucleotide similarity (99%) with the reference sequence of Haplosporidium pinnae available in GenBank database. Phylogenetic analysis clustered the sequence of the pathogen in a paraphyletic clade with the reference sequence of H. pinnae, excluding other haplosporidians (i.e., Bonamia and Minchinia genera). Based on data reported, H. pinnae was the causative agent of MME in the populations of P. nobilis sampled in the Ionian Sea, where the conservation of this endangered species is heavily threatened by such a protozoan infection. Further investigations should contribute to knowledge about the life cycle of H. pinnae in order to reduce spread of the pathogen and to mitigate the burden of the disease where P. nobilis is facing the risk of extinction.

Mediterranean Bioconstructions Along the Italian Coast.

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.