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Abstract The golden coral Savalia savaglia is a long-living ecosystem engineer of Mediterranean circalittoral assemblages, able to induce necrosis of gorgonians’ and black corals’ coenenchyme and grow on their cleaned organic skeleton. Despite its rarity, in Boka Kotorska Bay (Montenegro) a shallow population of more than 1000 colonies was recorded close to underwater freshwater springs, which create very peculiar environmental conditions. In this context, the species was extremely abundant at two sites, while gorgonians were rare. The abundance and size of S. savaglia colonies and the diversity of the entire benthic assemblage were investigated by photographic sampling in a depth range of 0–35 m. Several living fragments of S. savaglia spread on the sea floor and small settled colonies (

The deep shoal of Punta del Faro (Ligurian Sea, Mediterranean Sea) is a mesophotic rocky elevation hosting complex animal forests threatened by fishing activities. To identify appropriate conservation measures and set a reference example for similar cases, we present a detailed characterization of its megabenthic communities and a quantification of the fishing pressure. The results highlight the high natural value of the area, presenting high biodiversity (111 megabenthic and demersal species) and diverse types of animal forest, predominantly dominated by cnidarians. The tridimensional seascape is among the most complex in the eastern Ligurian Sea, but the long-term evaluation of its environmental status suggested consistent affects due to the high abundance of lost fishing gear (0.65 items m−2) directly entangled with structuring cnidarians. The artisanal and recreational fishing pressure are currently moderate. However, the use of bottom-contact fishing gear causes significant modifications to the seafloor's integrity. This study emphasizes the high conservation value and vulnerability of the shoal, highlighting the importance of its protection through its inclusion in the Portofino MPA, whose external perimeter is 200 m from the study area. A critical discussion of the advantages and disadvantages is provided with a map of the possible extension of the MPA boundaries. [ABSTRACT FROM AUTHOR]

Modular colonial benthic organisms exhibit high phenotypic plasticity, which is considered an effective strategy when faced with fluctuations in abiotic and biotic factors. However, when environmental changes occur abruptly, organisms' adaptive capabilities can be limited, leading to the death of some colonies or to mass mortalities. Additionally, a decrease in body size has been proposed as one of the most common responses in both terrestrial and aquatic organisms to face global warming. Here, temperate corals' response to thermal stress was documented using the precious red coral Corallium rubrum as a model species. The increased frequency of marine heat waves recorded in the north-western Mediterranean has led to a decrease in the total number of colonies of the analysed populations and reduced colony size in those that have survived, likely through fragmentation and branch loss. The laboratory analyses carried out on collected fragments showed an unexpected swelling, similar to resorption. Additionally, the occurrence of regular sclerite-like protuberances, typical of a normal skeleton surface, suggested a regeneration process. The documented phenomenon supports the hypothesis that C. rubrum exhibits an adaptive behaviour via the autotomy of branches, providing it with an unexpected resilience against climate anomalies thanks to phenotypic plasticity. [ABSTRACT FROM AUTHOR]

The deep shoal of Punta del Faro (Ligurian Sea, Mediterranean Sea) is a mesophotic rocky elevation hosting complex animal forests threatened by fishing activities. To identify appropriate conservation measures and set a reference example for similar cases, we present a detailed characterization of its megabenthic communities and a quantification of the fishing pressure. The results highlight the high natural value of the area, presenting high biodiversity (111 megabenthic and demersal species) and diverse types of animal forest, predominantly dominated by cnidarians. The tridimensional seascape is among the most complex in the eastern Ligurian Sea, but the long-term evaluation of its environmental status suggested consistent affects due to the high abundance of lost fishing gear (0.65 items m−2) directly entangled with structuring cnidarians. The artisanal and recreational fishing pressure are currently moderate. However, the use of bottom-contact fishing gear causes significant modifications to the seafloor’s integrity. This study emphasizes the high conservation value and vulnerability of the shoal, highlighting the importance of its protection through its inclusion in the Portofino MPA, whose external perimeter is 200 m from the study area. A critical discussion of the advantages and disadvantages is provided with a map of the possible extension of the MPA boundaries.

Mesophotic habitats, hosting benthic assemblages totally unknown and unexpected in the early 2000s, are attracting an increasing interest from scientists. Realizing that many long living and habitat forming species are playing a unique pocket of biodiversity in the frame of climate crisis, it is important to recognize the potential of the mesophotic zone in conservation strategies. The mesophotic zone is characterized by environmental factors generally more stable than the shallow counterpart; therefore, it represents a refuge habitat to preserve species that, in shallow waters, may be involved in bleaching events, massive mortalities or other pathologies generally triggered by thermal anomalies. The definition of the mesophotic zone in the temperate seas is confused, creating possible misunderstandings and problems not only from a scientific point of view but also in communication and outreach strategies. Here, we review the scientific literature to build the best definition possible based on the maximum consensus coming from papers analysis. Moreover, the key roles of mesophotic habitats, including ecosystem engineers as animal forests, have been schematized to enhance the perception of the potential risks we are running in case of damage or loss of these habitats.

Coral reefs throughout the tropics have experienced large declines in the abundance of scleractinian corals over the last few decades, and some reefs are becoming functionally dominated by animal taxa other than scleractinians. This phenomenon is striking on many shallow reefs in the tropical western Atlantic, where arborescent octocorals now are numerically and functionally dominant. Octocorals are one of several taxa that have been overlooked for decades in analyses of coral reef community dynamics, and our understanding of why octocorals are favoured (whereas scleractinians are not) on some modern reefs, and how they will affect the function of future reef communities, is not commensurate with the task of scientifically responding to the coral reef crisis. We summarize the biological and ecological features predisposing octocorals for success under contemporary conditions, and focus on those features that could have generated resistance and resilience of octocoral populations to environmental change on modern reefs. There is a rich set of opportunities for rapid advancement in understanding the factors driving the success of octocorals on modern reefs, but we underscore three lines of inquiry: (1) the functional implications of strongly mixotrophic, polytrophic, and plastic nutrition, (2) the capacity to recruit at high densities and maintain rapid initial rates of vertical growth, and (3) the emergent properties associated with dense animal forests at high colony densities. [ABSTRACT FROM AUTHOR]

Mesophotic Coral Ecosystems (MCEs) develop on a unique environment, where abrupt environmental changes take place. Using a time-calibrated molecular phylogeny (mtDNA: mtMutS), we examined the lineage membership of mesophotic gorgonian corals (Octocorallia: Cnidaria) in comparison to shallow and deep-sea lineages of the wider Caribbean-Gulf of Mexico and the Tropical Eastern Pacific. Our results show mesophotic gorgonians originating multiple times from old deep-sea octocoral lineages, whereas shallow-water species comprise younger lineages. The mesophotic gorgonian fauna in the studied areas is related to their zooxanthellate shallow-water counterparts in only two clades (Gorgoniidae and Plexauridae), where the bathymetrical gradient could serve as a driver of diversification. Interestingly, mesophotic clades have diversified faster than either shallow or deep clades. One of this groups with fast diversification is the family Ellisellidae, a major component of the mesophotic gorgonian coral assemblage worldwide.

Mesophotic habitats, hosting benthic assemblages totally unknown and unexpected in the early 2000s, are attracting an increasing interest from scientists. Realizing that many long living and habitat forming species are playing a unique pocket of biodiversity in the frame of climate crisis, it is important to recognize the potential of the mesophotic zone in conservation strategies. The mesophotic zone is characterized by environmental factors generally more stable than the shallow counterpart; therefore, it represents a refuge habitat to preserve species that, in shallow waters, may be involved in bleaching events, massive mortalities or other pathologies generally triggered by thermal anomalies. The definition of the mesophotic zone in the temperate seas is confused, creating possible misunderstandings and problems not only from a scientific point of view but also in communication and outreach strategies. Here, we review the scientific literature to build the best definition possible based on the maximum consensus coming from papers analysis. Moreover, the key roles of mesophotic habitats, including ecosystem engineers as animal forests, have been schematized to enhance the perception of the potential risks we are running in case of damage or loss of these habitats. [ABSTRACT FROM AUTHOR]

Cold‐water coral (CWC) ecosystems are protected both in national and international waters. They are considered Vulnerable Marine Ecosystems and, in addition, meet the criteria to be defined ecological or biological significant areas.Two new sites of the "Sardinian CWC province" were discovered by means of remotely operated vehicle surveys in two submarine canyons in the north‐eastern portion of the Sardinian continental margin, at depths ranging from 230 to 430 m.Dense and healthy patches of small and medium‐sized Madrepora oculata colonies were found dwelling on rocky walls and inclined silted soft bottoms.A rich and diverse associated megafauna was found within both live and dead portions of the coral framework. In addition, the presence of benthic litter and derelict fishing gears were also documented.These results further extend the "Sardinian CWC province" extension, providing insights of a potential CWC network along the Sardinian continental margin with implications for the Mediterranean mosaic of CWC provinces, further stressing the need for urgent conservation measures for these habitats. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Mediterranean mesophotic hard bottoms are mostly characterized by coralligenous banks. Although investigations on this habitat have increased in the last years, knowledge about its structure and spatial variability is still very limited as most studies are focused on the description of assemblages of peculiar and small locations such as biodiversity hotspots. This study aimed at i) describing coralligenous megafauna on the western Sardinian continental shelf between 80 and 120 m of depth, ii) assessing the distribution of the dominant taxa, and iii) estimating patterns of spatial variability at different scales. The coralligenous banks were studied along five sectors of the western Sardinian continental shelf by means of Remote Operated Vehicles (ROVs) and images were analyzed to identify the main taxa or morphological groups and their abundance. Results highlighted several common patterns among sectors, with assemblages dominated by the gorgonians Eunicella cavolini and Callogorgia verticillata. On the other hand, some taxa (e.g. Callogorgia verticillata , Paramuricea hirsuta, Antipathella subpinnata, Corallium rubrum Paramuricea clavata , Poecillastra compressa and Aplidium spp.) mainly contribute to segregate the coralligenous assemblages within the considered sectors of this study. A high small-scale variability was also observed. The presence of extensive and well diversified mesophotic animal forests stresses the importance to improve the conservation of the western Sardinian continental shelf. • The structure of coralligenous banks on the Sardinian continental shelf was described. • Patterns of spatial variability at different scales were estimated. • Sardinian coralligenous bank assemblages were dominated by erect anthozoans. • Sectors segregated among them due to the local abundance of different taxa. [ABSTRACT FROM AUTHOR]

Mesophotic Coral Ecosystems (MCEs) develop on a unique environment, where abrupt environmental changes take place. Using a time-calibrated molecular phylogeny (mtDNA: mtMutS), we examined the lineage membership of mesophotic gorgonian corals (Octocorallia: Cnidaria) in comparison to shallow and deep-sea lineages of the wider Caribbean-Gulf of Mexico and the Tropical Eastern Pacific. Our results show mesophotic gorgonians originating multiple times from old deep-sea octocoral lineages, whereas shallow-water species comprise younger lineages. The mesophotic gorgonian fauna in the studied areas is related to their zooxanthellate shallow-water counterparts in only two clades (Gorgoniidae and Plexauridae), where the bathymetrical gradient could serve as a driver of diversification. Interestingly, mesophotic clades have diversified faster than either shallow or deep clades. One of this groups with fast diversification is the family Ellisellidae, a major component of the mesophotic gorgonian coral assemblage worldwide. [ABSTRACT FROM AUTHOR]

Coral reefs throughout the tropics have experienced large declines in the abundance of scleractinian corals over the last few decades, and some reefs are becoming functionally dominated by animal taxa other than scleractinians. This phenomenon is striking on many shallow reefs in the tropical western Atlantic, where arborescent octocorals now are numerically and functionally dominant. Octocorals are one of several taxa that have been overlooked for decades in analyses of coral reef community dynamics, and our understanding of why octocorals are favoured (whereas scleractinians are not) on some modern reefs, and how they will affect the function of future reef communities, is not commensurate with the task of scientifically responding to the coral reef crisis. We summarize the biological and ecological features predisposing octocorals for success under contemporary conditions, and focus on those features that could have generated resistance and resilience of octocoral populations to environmental change on modern reefs. There is a rich set of opportunities for rapid advancement in understanding the factors driving the success of octocorals on modern reefs, but we underscore three lines of inquiry: (1) the functional implications of strongly mixotrophic, polytrophic, and plastic nutrition, (2) the capacity to recruit at high densities and maintain rapid initial rates of vertical growth, and (3) the emergent properties associated with dense animal forests at high colony densities., (© 2020 Published by Elsevier Ltd. All rights reserved. Peter Edmunds retains copyrights for images.)