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Coralligenous bioconstructions are among the most important Mediterranean habitats for biodiversity maintenance. However some characteristic and sensitive organisms, such as the fan corals, are considered endangered in the international community; indeed, they may be severely damaged by fishing activities causing mechanical damage and increasing sedimentation rate. ROV (Remotely Operated Vehicle) investigations were carried out in order to characterize different morphological types of coralligenous habitat (rim, bank and shoal) located in the southern Bay of Naples (Italy), and to assess the presence of lost fishing gears and their impact on these benthic communities. A rapid classification of different fishing pressures and impacts was obtained through the development of new, representative and synthetic categories. Image analysis revealed the presence of rich and diversified communities, characterized by several fan coral colonies. However, fishing activity dramatically affects these coralligenous habitats, entangling and covering benthic assemblages and leading to necrosis and to parasitic epibionts growth especially on branched organisms. Monitoring programmes may provide a detailed assessment of coralligenous habitats characterization, distribution and health status. An accurate evaluation of fishing pressure and impact may be considered a useful tool to improve sustainable management of these valuable habitats.

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.

Aim Coralligenous reefs are the main marine bioconstructions in terms of spatial distribution within the Mediterranean basin. Two distinct reef morphologies can be distinguished based on the surface and topographical features of the seafloor: cliffs developing vertical slopes and banks found on gently steep or horizontal bottoms. Despite their importance for monitoring and conservation efforts, observations regarding the variability of biogeographical patterns are scarce. Here, we aimed to assess the differences in the composition and structure of these cliffs across ecoregions and estimate the relative role of abiotic environmental features, geographic location, and connectivity in shaping diversity patterns. Location The study was carried out in the Central‐Western Mediterranean Sea. Samples were collected at 65 sites across the Algero‐Provençal Basin, the Ionian Sea and the Tyrrhenian Sea. Methods We assessed the composition and structure of coralligenous cliffs through photographic samplings collected by scuba divers. Patterns in α‐ and β‐diversity were associated with 9 abiotic environmental variables, latitudinal and longitudinal gradients, and connectivity measures using Generalized Additive (GAM) and Conditional Autoregressive (CAR) models. Results Coralligenous cliffs were primarily composed of algae and displayed a high degree of variability. The Partition Around Medoids (PAM) clustering method successfully delineated seven distinct clusters with a non‐uniform distribution within the studied ecoregions. The α‐diversity increased in eastern and northern sites and with phosphate concentration, while decreased with temperature, chlorophyll and nitrates concentration. β‐diversity at the site level increased with temperature, while it was negatively affected by northward current speed and chlorophyll concentration. Moveover, β‐diversity increased within connected sites. Main Conclusions Coralligenous cliff diversity responds both to the physico‐chemical features of the habitat and between‐habitats connectivity. However, our findings suggest that small‐scale abiotic and biotic processes could contribute to explaining the variability observed. These findings can significantly enhance the monitoring and conservation efforts of this Mediterranean endemic ecosystem.

Mesophotic habitats in the Mediterranean Sea host rich and diverse benthic assemblages, dominated by invertebrates alongside sciaphilous algae. Recent findings suggest that certain mesophotic bioconstructions built by invertebrates, while classified under the coralligenous definition, differ significantly in their taxonomic composition. This study investigates diversity patterns in megabenthic assemblages associated with algal and invertebrate bioconstructions along the Apulian coast, using α- and β-diversity metrics derived from an image analysis approach. Across 360 analyzed frames, 81 taxa were identified, revealing distinct coverage patterns that separate mesophotic algal assemblages from both coral and oyster bioconstructions. Morphological seabed features and primary bioconstructors played a key role in shaping the associated communities. These findings highlight the substantial differences between upper and deeper megabenthic assemblages and emphasize the ecological importance of mesophotic bioconstructions as biodiversity hotspots, underscoring their role in supporting Mediterranean marine ecosystems and the need for targeted conservation strategies.

Coralline algae are foundation species in many ecosystems they inhabit, acting as a settlement substrate, and binding together and even creating reefs in some locations. Ocean acidification is known to be a major threat to coralline algae. However, the effects of ocean warming are less certain. Here we bring multiple lines of evidence together to discuss the potential impacts of ocean warming on these ecologically crucial taxa. We use a meta-analysis on across 40 responses within the 14 different studies available that have assessed the effects of increasing temperature on coralline algal calcification in laboratory experiments. We do find a net negative impact of increasing temperature on coralline algal calcification at 5.2° C above ambient conditions under the singular effects of warming. Conversely, similar effects are seen when temperature drops below 2.0° C from ambient conditions. We propose that some coralline algae will be more capable of both acclimating and locally adapting to increasing ocean temperatures over the coming decades. This is due to the fact that many species possess short generation times, the ability to opportunistically rapidly utilise open space, and relatively high phenotypic plasticity compared to other important benthic species (e.g. corals). However, long-lived species, those with long generation times, or with narrow thermal tolerances could be at particular risk from ocean warming. Additionally, ocean warming will occur simultaneously with ocean acidification, a potentially greater threat to coralline algae, which could also reduce this tolerance to ocean warming in many species. We give key recommendations that will maximise the potential for future research to accurately determine how coralline algae will respond to future ocean warming.

Coralligenous reefs are calcareous structures edified mostly by coralline algae that characterize the circalittoral zone of the Mediterranean Sea. However, in some cases coralline algae can constitute peculiar infralittoral biogenic reefs which have been studied less than the circalittoral ones. This study aims to contribute to the knowledge of infralittoral coralligenous reefs by describing their macroalgal assemblages on a large rocky platform off the Tuscany coasts, northwestern Mediterranean Sea. To this end, a multifactorial sampling design was used to describe the structure of the assemblages and to evaluate the variability of the system at multiple spatial scales. A total of 71 macroalgal taxa were found on the coralline algae. Macroalgal assemblages were well structured, with high biodiversity values. The dominant taxa included both photophilous and sciaphilous species, guaranteeing peculiar characteristics in these assemblages, above all if compared with the typical infralittoral and circalittoral macroalgal communities of the same geographic area. The assemblages showed greater variability at a small and intermediate spatial scale than at a large scale. Although infralittoral coralligenous outcrops constitute a peculiar system, they are still poorly understood and should not only be the object of specific studies but also be included in monitoring programmes.

A comprehensive overview of the benthic assemblages associated with bioconstructions in the mesophotic zone of the southern Adriatic Sea is provided through a comparison of algal- and invertebrate-based bioconstructions. To characterize these bioconstructions, sampling was conducted at six sites along the Apulian coast (Italy). Algal-based bioconstructions were found in shallower areas and corresponded to coralligenous sensu stricto, while two distinct invertebrate-based bioconstructions, built by scleractinians and bivalves, were observed at greater depths. A multi-taxa approach, which recorded 511 benthic taxa, revealed significant differences in the taxonomic composition of their associated benthic assemblages, although similar species richness values were observed across all types of bioconstructions. Given the marked difference in terms of primary constructor species between the coralligenous sensu stricto and invertebrate bioconstructions, we propose referring to the latter as Mesophotic Coral Bioconstructions (MCB) and Mesophotic Oyster Bioconstructions (MOB). β-diversity analysis identified a turnover in benthic fauna along the North–South gradient, with higher β-diversity values between distant sites and lower values between nearby sites, likely driven by North–South circulation dynamics in the region. Additionally, the distinctions observed along the depth gradient are consistent with the decrease in irradiance, which causes a shift from photoautotrophic to heterotrophic builder species. These findings underscore the role of mesophotic bioconstructions along the Apulian coast as biodiversity hotspots and confirm their importance in understanding mesophotic ecosystem dynamics in the Mediterranean Sea.

Coralligenous reefs are characterized by large bathymetric and spatial distribution, as well as heterogeneity; in shallow environments, they develop mainly on vertical and sub-vertical rocky walls. Mainly diver-based techniques are carried out to gain detailed information on such habitats. Here, we propose a non-destructive and multi-purpose photo mosaicking method to study and monitor coralligenous reefs developing on vertical walls. High-pixel resolution images using three different commercial cameras were acquired on a 10 m2 reef, to compare the effectiveness of photomosaic method to the traditional photoquadrats technique in quantifying the coralligenous assemblage. Results showed very high spatial resolution and accuracy among the photomosaic acquired with different cameras and no significant differences with photoquadrats in assessing the assemblage composition. Despite the large difference in costs of each recording apparatus, little differences emerged from the assemblage characterization: through the analysis of the three photomosaics twelve taxa/morphological categories covered 97–99% of the sampled surface. Photo mosaicking represents a low-cost method that minimizes the time spent underwater by divers and capable of providing new opportunities for further studies on shallow coralligenous reefs.

Coralligenous bioconstructions are biogenic calcareous structures characterized by low accretion rate and high sensitivity to natural and anthropogenic impacts. Assessing their ecological quality and health status requires non-destructive approaches. In the project “FISR 2019_CRESCIBLUREEF”, a ROV-based coring device has been developed to collect samples while ensuring minimal impact on the ecological and structural integrity of bioconstructions and overcoming scuba diving depth and safety constraints. This study evaluates whether fragments retrieved by the device are representative of whole coralligenous build-ups (“tal-quale”) for geobiological characterization at the microscale. Representativeness is assessed through (i) preservation of microfacies textures and framework integrity in thin sections and (ii) relative abundances of skeletal and non-skeletal carbonate components quantified by point-counting. The results suggested that a coring device represents a powerful tool for obtaining representative bioconstruction samples at least in terms of the relationships and distribution between different carbonate components. This innovative approach opens new frontiers in the study of bioconstructed habitats, allowing the collection of samples suitable for qualitative and quantitative analyses while preserving ecosystem integrity. It therefore represents a step toward in sustainable marine research, with great potential for monitoring, conservation, and management of benthic habitats.

In this work, the consequences of a local gorgonian coral mortality on the whole coralligenous assemblage were studied. A Before/After-Control/Impact sampling design was used: the structure of the coralligenous assemblage was compared before and after the gorgonian mortality event at the mortality site and two control sites. At the mortality site, a relevant decrease in alpha and beta diversity occurred, with a shift from a stratified assemblage characterized by gorgonians and other invertebrates to an assemblage dominated by algal turfs; conversely, neither significant variations of the structure nor decrease in biodiversity were observed at the control sites. The assemblage shift involved the main taxa in different times: in autumn 2018, a large proportion of the plexaurid coral Paramuricea clavata died, but no significant changes were observed in the structure of the remaining assemblage. Then, in autumn 2019, algal turfs increased significantly and, one year later, the abundance of the gorgonian Eunicella cavolini and bryozoans collapsed. Although the mechanisms of the assemblage shift following gorgonian loss will remain uncertain and a cause-effect relationship cannot be derived, results suggest the need for detecting signs of gorgonian forests stress in monitoring programs, which should be considered early indicators of their condition. in the coralligenous monitoring programs for detecting any sign of gorgonian forests stress which should be considered an early indicator of the assemblage condition.