We present the results of a collaborative effort to compile data on kelp species distribution (orders Laminariales and Tilopteridales) in Spanish and Portuguese waters encompassing both the mainland coasts as well as the Balearic and Macaronesian archipelagos. This initiative involved a regional call for experts’ knowledge input and data collection, followed by a workshop where findings were discussed. Discussions focused on the current status of kelp populations, trends and causes of observed changes as well as priority areas for future research.Contrasting trends across species and geographic areas and the temporal dynamics of certain deep-water populations were detected. The need for monitoring studies assessing environmental change and populational trends in these refugial populations is highlighted.These findings provide valuable insights to inform both management and protection strategies, as well as designing future restoration programmes, which are crucial for the preservation of kelp forests in the region.

Effective marine protected area (MPA) networks require accurate knowledge of habitat distribution, yet in remote oceanic archipelagos, the logistical and financial costs of comprehensive surveys render this difficult to obtain. Species distribution models (SDMs) offer a practical alternative, however their application to MPA placement evaluation in data-deficient oceanic archipelagos remains limited. The Azores archipelago has an MPA network currently under consideration for expansion, yet site suitability remains unknown and knowledge of coastal reef-fish habitat distribution is incomplete, with extensive surveys being impractical. To address this, we used underwater visual census data collected between 2010 and 2023 across the archipelago, along with seabed and oceanographic variables, to construct SDMs predicting the distributions of six coastal reef-fish species using a random forest approach. These predictions identified areas of high biomass or probability of presence as proxies for high-suitability habitat, and the proportion covered by the present MPA network was assessed. Results suggest Azorean MPAs are generally placed in areas of predicted high-suitability habitat, although due to their small size, no-take reserves protect a minute proportion of this. MPAs with more lenient regulations cover a larger area of predicted high-suitability habitat, although as these permit certain extractive activities, the protection provided is questionable. Given the large proportion of shelf areas assigned legal protection that we suggest to be appropriately placed, we argue MPA policy should prioritise tighter restrictions and stronger enforcement over spatial expansion. We conclude that SDMs are a valuable tool for evaluating reef-fish habitat protection in remote, data-deficient oceanic archipelagos.

Crypthelia Milne-Edwards Haime, 1849 is the most diverse genus of lace corals inhabiting the Azores. During the 2012 DEEPFUN cruise, the first coral garden structured by this genus was recorded in the Menez Gwen Marine Protected Area (MPA). Identification of the species was based on morphology of specimens collected in situ and characterized using scanning electron microscopy (SEM). Imagery acquired by the remotely operated vehicle (ROV) Victor 6000 was used to document the species density as well as seabed geomorphology. The stylasterid Crypthelia vascomarquesi Zibrowius Cairns, 1992 is described for the first time based on entire specimens, including female representatives. To date, this is the only Crypthelia species with female efferent pores located on dactylostomes, adding a new category to the feminine ampullar formula developed for the genus. The dense coral garden formed by C. vascomarquesi was recorded between 832 and 856 m depth at 37°48.896′N; 31°33.774′W. This vulnerable marine ecosystem (VME) represents a rare record of fragile and highly endemic corals that reinforces the value of natural heritage protected within a mid-Atlantic ridge MPA. We suggest that the C. vascomarquesi coral garden is included at level 5 of the deep-sea section of the European habitat classification system (EUNIS), as a means to emphasize its conservation value and the monitoring of MPAs.

Knowledge of the strength of submarine volcaniclastic deposits is important for assessing the stability of slopes of such materials and their geohazards but is difficult to measure. An opportunity for an alternative evaluation has been presented by an earthquake swarm under a volcanic seamount in the Azores. Attenuation relationships applied to earthquake data suggest that a cone field and flanks of the seamount experienced horizontal accelerations of >0.3 g during the swarm. However, multibeam sonar data collected before and after the swarm suggest that no slope failures occurred. Furthermore, in backscatter data collected after the swarm, low intensities below slopes suggest that muddy aprons were undisturbed by landslide debris. The swarm overlies cones with slopes near typical repose angles of non-cohesive particles. During earthquake shaking, the direction of maximum acceleration deviates from that due to gravity alone. We show that cone slopes effectively experienced much steeper gradients than their repose angles during the swarm. As they survived the shaking without failing, they were effectively stronger than non-cohesive sediment. We use a pseudo-static analysis to investigate the implied sediment strength, finding a ratio of undrained shear strength to vertical stress of >0.4-0.5. This implies shear strength of >24-30 kPa at 10 m depth below seabed. We speculate that carbonate cements and/or compaction may be responsible. If shallow areas are more widely strengthened, slope failure may then be less likely during moderate (M-L - 4.0 or less) seismic shaking and hence be less hazardous than if the slopes comprised wholly non-cohesive materials.

A comprehensive checklist of the marine flora from Faial Island, mid-north Atlantic, is still unavailable, despite the numerous works that gathered data around its coasts for over 150 years. This study brings together and harmonises all macroalgae collections and taxonomical records from multiple projects and teams over the last thirty years. The result is a list of taxonomic records and georeferenced species occurrence data that substantially increases our knowledge of the coastal Azorean marine biodiversity while providing key information for future ecological studies and to support local, marine management and conservation. A total of 2283 specimens belonging to 118 taxa of macroalgae are registered here, comprising 61 Rhodophyta, 26 Chlorophyta, 30 Ochrophyta (Phaeophyceae) and one Cyanophyta (Cyanobacteria). From these, 26 taxa are identified only at the genus level and 92 to species level (47 Rhodophyta, 21 Chlorophyta and 24 Ochrophyta). The list comprises 75 native species, 12 records of uncertain origin and five introductions ( Caulerpa prolifera (Forsskål) J.V.Lamouroux, Caulerpa webbiana Montagne, Hydroclathrus tilesii (Endlicher) Santiañez & M.J.Wynne, Asparagopsis armata Harvey and Symphyocladia marchantioides (Harvey) Falkenberg). Codium elisabethiae O.C.Schmidt represents the only Macaronesian endemism known on the Island. Twenty-three species are newly recorded to the algal flora of the Island.

Understanding connectivity patterns exhibited by endangered species living in fragmented habitats is fundamental to improving management and conservation actions. Such improvements can be particularly pressing at the trailing edges of these habitats, where populations are facing the greatest challenges from climate change, and appear even more crucial if the species is commercially harvested. Seascape genetics have been increasingly used to meet these needs. In this study, we examined connectivity patterns among 32 populations of the oarweed kelp Laminaria digitata located at the species' southern range limit. The distance (or sampling gap) between neighboring populations ranged from a few km to a few 100s of km. By genotyping 11 microsatellite markers, we aimed to (1) refine analyses of population structure; (2) test whether on-shelf islands are genetically more differentiated than mainland populations; (3) evaluate the relative importance of various abiotic conditions in shaping the genetic structure; and (4) evaluate if the relative importance of each environmental factor varied according to sampling schemes. Our analyses revealed a positive relationship between connectivity links and genetic diversity: populations with high levels of connectivity were genetically enriched while isolated populations showed signs of genetic erosion. The genetically impoverished populations corresponded to the southernmost populations as well as populations along the northern coast of Brittany (Locquirec, Saint-Malo Bay) and the northernmost population in Pas-de-Calais. By performing distance-based redundancy analysis on various sampling schemes, geographic distance appeared as the dominant factor influencing connectivity between populations separated by great distances, while hydrodynamic processes were the main factor when analyzing at a final spatial resolution.

Habitat-forming cold-water corals (CWCs) represent a key component of deep-sea benthic communities and a priority target for conservation.Although research efforts have been mounting to try and identify the drivers of CWC distributions, progress has been limited by the scarcity of ecological data.The present work employs habitat suitability models (HSMs) to estimate spatial distributions, environmental drivers and co-existence patterns of 14 habitat-forming CWCs in the Azores, an area considered a hotspot of coral diversity in the Atlantic.The modelled CWCs showed a strong bathymetric zonation, which seems to be determined by the vertical stratification of water masses in the region.In particular, the modelled CWCs can be clustered in four groups named after the isopycnal (vertical) layers in which Atlantic water masses are organized: species restricted to upper water masses, species extending down from upper water masses, species restricted to intermediate water masses and species extending up from deep water masses.Horizontal patterns further indicate that the Azores Current and different production regimes north and south of the archipelago likely influence the distribution of CWCs in sub-surface waters.Such results have important implications for the regional management of deep-sea benthic communities and, in particular, for the design of representative networks of protected areas.The combined habitat of all modelled species covered only 11%.Given that they all possess the characteristics of benthic foundation organisms and represent indicator taxa of vulnerable marine ecosystems all the modelled species should be viewed as important targets for conservation.The lace coral Errina dabneyi deserves particular attention since this species appears to be endemic to the Azores and has a very limited estimated distribution.

Sediment waves are common on the submarine flanks of volcanic islands, but the processes that form them are difficult to decipher from geophysical data alone. Here, we identify downslope-trending trains of sediment waves in multibeam sonar data from five islands of the Azores. Train abundances are derived by counting the train intersections with depth contours around each island, revealing that they are typically twice as common on the north slopes of the islands compared with their south slopes. To provide context, we also characterise the Holocene mobility of sediments on the shelves, ocean density structure (for evaluating internal wave critical gradients) and sediment lithologies in four cores from beneath the slopes, which contain shelf carbonates in some volcaniclastic turbidites. Holocene mobility is assessed using sidescan sonar data, which reveal shelf-crossing sand streams. Using results of a high-resolution wave model, wave-imposed shear stresses are found to have exceeded the stresses at threshold of motion for most of the modern shelf sediments during recent extreme wave conditions.Sediment waves could potentially arise from sedimentary flows, gravity mass movements (shallow slumping) or ocean internal waves. Sedimentary flow origins are favoured by streamwise changes of wavelengths and upslope bedform migrations suggested by seismic reflections. The asymmetry of abundances north and south of each island is also an important clue. For example, it is unlikely that systematically different sediment geotechnical properties occur on the two sides of the islands, hence no reason to expect greater mass movements on northern slopes. Internal waves originate mainly from the south and hence also do not explain the asymmetry. Primary volcaniclastic flows are likely to be equally important on both sides. Sedimentary flows originating from shelf sediment agitated during storms or from failed slope sediment appear to explain best the asymmetry. In that case, prevailing wind and waves approaching the islands from the northwest lead to more frequent sediment gravity flows because they lead to greater flux of sediment from coastal erosion towards northerly outer shelves and upper slopes, where it is prone to slope failure. Offshore-directed near-bed currents originating from northwesterly wind-driven surface currents also transport shelf sediment efficiently to the north, further aided by greater wave agitation on that side. The high abundances of wave trains on the north sides of the islands therefore favours origins involving sedimentary gravity flows associated with wind and wave effects.

Erosion of volcanic islands ultimately creates shallow banks and guyots, but the ways in which erosion proceeds to create them over time and how the coastline retreat rate relates to wave conditions, rock mass strength and other factors are unclear. The Capelinhos volcano was formed in 1957/58 during a Surtseyan and partly effusive eruption that added an 2.5 km(2) tephra and lava promontory to the western end of Faial Island (Azores, central North Atlantic). Subsequent coastal and submarine erosion has reduced the subaerial area of the promontory and created a submarine platform. This study uses historical information, photos and marine geophysical data collected around the promontory to characterize how the submarine platform developed following the eruption. Historical coastline positions are supplemented with coastlines interpreted from 2004 and 2014 Google Earth images in order to work out the progression of coastline retreat rate and retreat distance for lava- and tephra-dominated cliffs. Data from swath mapping sonars are used to characterize the submarine geometry of the resulting platform (position of the platform edge, gradient and morphology of the platform surface). Photographs collected during SCUBA and ROV dives on the submarine platform reveal a rugged surface now covered with boulders. The results show that coastal retreat rates decreased rapidly with time after the eruption and approximately follow an inverse power-law relationship with coastal retreat distance. We develop a finite-difference model for wave attenuation over dipping surfaces to predict how increasing wave attenuation contributed to this trend. The model is verified by reproducing the wave height variation over dipping rock platforms in the UK (platform gradient 1.2 degrees to 1.8 degrees) and Ireland (1.8 degrees). Applying the model to the dipping platform around Capelinhos, using a diversity of cliff resistance predicted from known lithologies, we are able to predict erosion rate trends for some sectors of the edifice. We also explore wider implications of these results, such as how erosion creates shallow banks and guyots in reef-less mid-oceanic archipelagos like the Azores. (c) 2019 John Wiley & Sons, Ltd.

Kelp was first recorded for the remote warm‐temperate Azores archipelago (central North Atlantic) in 1971, when a few Laminaria specimens were collected on the Formigas Bank at depths beyond conventional SCUBA diving reach. A shortage of technical means and projects targeting mesophotic environments has since kept this offshore marine protected area as the single known kelp occurrence site. Here, we present new kelp records collected on previously unexplored mesophotic reefs using remote imaging systems, open‐ and closed‐circuit SCUBA diving, and fisheries bycatch information. The new data extend the known distribution range of kelp in the Azores 350 km to the west and 25 km to the southwest, henceforth including several island shelves in the eastern and central Azores. In addition to the previously recorded Laminaria ochroleuca , kelp specimens with a morphology akin to Phyllariopsis brevipes subsp. brevipes are also reported. For the first time, seabed imagery is used to document the depth‐wise diversity of the Azores kelp beds and their associated biota. Our findings emphasize the poor knowledge that persists in regard to Macaronesia’s mesophotic environments located beyond conventional SCUBA diving limits. The new on‐shelf kelp occurrences add conservation value to coastal areas and should facilitate island‐based research. However, their greater proximity to land‐based impacts and exposure to climate change also raise management needs.

Marine ecosystem-based management requires good spatial information on the distribution of marine species and habitats. Often, such information is limited to a few sampled locations, but modelling techniques can be applied to produce predictive distribution maps. A harmonized broad-scale seabed habitat map was recently produced for the archipelagos of Macaronesia under the EMODnet Seabed Habitats Programme. We use this new information to produce an extent-based evaluation of the representativeness and level of protection conferred by the current set of marine protected areas (MPAs) in the Azores to the variety of benthic marine habitats found in this oceanic region. A more objective assessment of the protection effectively provided to the habitats is obtained by applying a scoring system to the MPAs based on the number of allowed extractive and non-extractive human activities and their potential impact on marine biodiversity and habitats. Results show that Azorean habitats within the MPAs are nearly entirely classified as highly protected. In total, 26 habitats (7 of which are endangered and 2 are rare) have at least 10% of their extent in the Azores EEZ protected by MPAs, but another 29 fail to meet this target (4 on-shelf habitats and 25 deep-sea habitats), highlighting the need to extend current protection of bathyal and abyssal habitats and applying adequate ecological coherence criteria. This approach sets a standard that can be used wherever similar information is available, be it in other European regions or beyond.

Bryozoan records from the shores and upper shelf (≤50 m depth) of the remote Azores Archipelago (central North Atlantic) have been analyzed, along with unpublished data and data from recent surveys. A checklist of 67 shallow-water species is hereby compiled for the region, of which more than one third represent records from campaigns conducted during the last 20 years. A classification on the origin of the species indicates that the majority (62%) are cryptogenic while 27% (n = 18) are considered native. Given the natural limitations for genetic exchange between the archipelago’s bryozoan populations and those from neighboring shores, the taxa presently considered as cryptogenic may yield a considerable amount of endemic species after taxonomic revision. The remaining 11% are confirmed as non-indigenous species, highlighting the importance of human-mediated transport in considerably enhancing the diversity of bryozoans in remote oceanic archipelagos, which would otherwise be off-limits to their natural dispersal capacity. In view of the need to quantitatively evaluate the certainty of species-level identification when assembling such biodiversity inventories, we have developed a method to attribute a degree of certainty to species records. The application of this method to the current checklist highlights the importance of further studies to ascertain the identification of many species recorded for the Azores, and to be able to categorize them confidently as either native, cryptogenic or non-indigenous.

Marine reserves across different eco-regions and habitats have proven to benefit exploited fish populations within their borders. There is also mounting evidence, mostly from continental shelf regions, that such positive effects will depend on the species ecological traits (e.g. mobility) and on the characteristics of the reserves (e.g. design, age and enforcement). This study examines the effects of protection on commercial coastal fishes with different ecological traits from three marine reserves with distinct habitats (coastal vs. offshore reefs), protection regime (legal vs. voluntary, partial vs. total protection) and age (8, 15 and 26 years old) across the oceanic archipelago of the Azores, mid North Atlantic. Overall, positive effects of protection on fish abundance or individual size were limited to species of larger maximum size and lower mobility in reserves with higher compliance levels. This result agrees with many studies elsewhere showing that reserves of small size and/or insufficient compliance do not provide adequate protection to the entire fish community, limiting their contribution to manage fisheries and conserve biodiversity. That might very well be the case of Azorean marine reserves but a more conclusive result will require testing the effects of protection on larger, well enforced reserves, which still do not exist in the region. There was also a clear influence of depth in commercial fish distribution and a common preference for substrates of higher complexity across ecological traits. Combined, these results highlight the need to include complex reef structures, diverse coastal habitats and larger areas when designing multispecies marine reserves and stress that an appropriate management regime is crucial for the success of the reserve, in particular to promote compliance.

Aim Drivers of intraspecific biodiversity include past climate-driven range shifts and contemporary ecological conditions mediating connectivity, but these are rarely integrated in a common comprehensive approach. This is particularly relevant for marine organisms, as ocean currents strongly influence population isolation or connectivity, keeping or diluting the signatures left by past climates. Here we ask whether the coupling between past range shifts and contemporary connectivity explain the extant gene pools of Laminaria ochroleuca, a large brown alga structuring important marine forests from shallow to deep infralittoral grounds. Location Northeastern Atlantic Ocean. Taxon Laminaria ochroleuca. Methods We estimated population genetic diversity and structure of L. ochroleuca across its entire distribution range using 15 polymorphic microsatellite markers. This was compared with the outcomes of a palaeoclimatic model predicting latitudinal and depth range shifts from the Last Glacial Maximum (LGM) to the present. Genetic differentiation was further compared with potential connectivity inferred with a biophysical model developed with high-resolution data from HYCOM (Hybrid Coordinate Ocean Model). Results The biogeographical distribution of genetic variability showed overall agreement with the predictions from independently inferred past range shifts. Multiple regions of persistence were identified in deep and upwelling settings at the lowest latitudes of the current species distribution, where higher and unique genetic diversity was retained. The biophysical model revealed that despite the possibility of long-distance migration, contemporary oceanographic barriers strongly restrict connectivity of isolated genetic lineages. Main conclusions Integrating different processes at biogeographical scales explained the extant gene pools of marine forests of L. ochroleuca. Low-latitude genetic relics harbour a disproportional evolutionary significance, persisting as ancient populations in isolated deep and upwelling climate refugia. Their inferred rates of dispersal may be insufficient to accommodate anticipated climate warming.

A seabed sediment-sampling survey conducted on the Pico insular shelf found abundant rhodoliths between - 64 and - 73 m off the south coast of the island. These were small and mainly ellipsoidal in shape with a maximum diameter of 3.75 cm. Granules and small pebbles of eroded basalt were also a typical component of these samples. Thin algal crusts were secreted on basalt pebbles by the coralline red algae Phymatolithon calcareum which, in turn, were covered by Lithophyllum incrustans. Additional samples were collected by snorkelling at Mare (Lajes do Pico), a shallow lagoon (2-4 m in depth) on the south coast. Here, rhodoliths are mostly spheroidal and bigger (maximum diameter of 4.75 cm), formed by thin thalli of P. calcareum. Based on these results (distribution of shapes and species) and previous work on the characteristics of fossil specimens from Neogene deposits on Santa Maria Island (Azores) and other North Atlantic Archipelagos, an empirical depositional model is proposed for the development of rhodoliths on the Pico Island shelf: (1) Nearshore rhodoliths, formed solely by P. calcareum, are subjected to a wide range of currents and waves resulting in their spheroidal shapes. However, those of Mare lagoon are protected from offshore transport and tend to grow larger than deep water rhodoliths; (2) Although not sampled, there must be middle shelf rhodoliths formed solely by P. calcareum that tend to form more ellipsoidal shapes due to seafloor oscillatory movements caused by waves crossing the shelf; (3) During storms, these middle shelf rhodoliths are then transported to the outer shelf, where L. incrustans overgrows the initial cover of P. calcareum. Shallow associations are normally larger, reflecting therefore, a longer life span than the deeper associations. Transport by storms appears to be an important factor in the formation of some deep-water rhodoliths around volcanic oceanic islands subjected to high-wave energy. However, their exposure to an energetic environment and likely frequent offshore transport does not allow them to grow as large as those from shallow-water.

In contrast to oceanic islands produced by mantle melting anomalies or "hotspots" lying in mid-plate settings, the central and eastern Azores islands are distributed on the Nubia-Eurasia tectonic plate boundary and experience frequent tectonic earthquakes. As they lie in an extensional to trans-tensional tectonic environment, volcanism is organised into submarine and subaerial ridges oriented perpendicular or oblique to the direction of plate separation. Much of the marine geophysical work undertaken to study these features and the submarine flanks of the islands has involved seabed mapping with sonars of various kinds, beginning with the GLORIA long-range sidescan sonar deployed in the late 1970s and continuing more recently with the deeply towed sidescan sonar TOBI and multibeam bathymetric sonars in dedicated expeditions and ship transits. These datasets give us a view of the topographic structure of the ridges and of the morphologies of the volcanic and tectonic features comprising them. Sonars also have been used to investigate the incidence of large-and small-scale landsliding around the islands, as well as the morphologies of lava flows originating from land and entering the sea. The overall picture emerging is one of landslides, cones, terraces and ridges analogous to those of Hawaii, Canaries and other oceanic island groups but with notable differences. For example, large-scale landslides appear to be rarer in the Azores and submarine cones tend to be steep-sided and pointed, not flat-topped or cratered as they are in some parts of the Hawaiian Islands. Faults are also more common in the Azores tectonic environment.

Many fish species are well-known obligatory inhabitants of shallow-water tropical coral reefs but such associations are difficult to study in deep-water environments. We address the association between two deep-sea fish with low mobility and large sessile invertebrates using a compilation of 20 years of unpublished in situ observations. Data were collected on Northeast Atlantic (NEA) island slopes and seamounts, from the Azores to the Canary Islands, comprising 127 new records of the circalittoral Labridae Lappanella fasciata and 15 of the upper bathyal Ophiididae Benthocometes robustus. Observations by divers, remote operated vehicles (ROV SP, Luso, Victor, Falcon Seaeye), towed vehicles (Greenpeace) and manned submersibles (LULA, Nautile) validated the species association to cold water corals (CWC) and large hydrozoans. L. fasciata occurred from lower infralittoral (41m) throughout the circalittoral, down to the upper bathyal at 398m depth. Smaller fishes (< 10cm) tend to form larger schools up to five individuals, with larger fishes (10–15cm) occurring alone or in smaller groups at greater depths. The labrids favoured areas with large sessile invertebrates (> 10cm) occurring at < 1 body-length, swimming inside or in close vicinity to the tallest and most complex three-dimensional structure in the field of observation. These included hydrozoans (Polyplumaria flabellata, Nemertesia antennina), CWC (e.g. Antipathella wollastoni, Acanthogorgia armata, Stichopathes sp.), and less frequently sponges (e.g. Pseudotrachya hystrix). B. robustus presented a coral-cryptic behavior, being recorded in the bathyal zone between 350 and 734m depth, always inside CWC (e.g. Acanthogorgia spp., Antipathella spp., Callogorgia verticillata, Dendrophyllia alternata, Leiopathes spp.), and remaining within the coral branching. B. robustus were collected with baited traps providing biological information and dietary information reinforcing the trophic linkage between the CWC habitat and this predator. Gathered evidence renders CWC and hydroid gardens as Essential Fish Habitats for both species, being therefore sensitive to environmental and anthropogenic impacts on these Vulnerable Marine Ecosystems. The Mediterranean distribution of L. fasciata is extended to NEA seamounts and island slopes and the amphi-Atlantic distribution of B. robustus is bridged with molecular data support. Both species are expected to occur throughout the Macaronesia and Mediterranean island slopes and shallow seamounts on habitats with large sessile invertebrates.

Cold-water corals (CWC) can form complex structures which provide refuge, nursery grounds and physical support for a diversity of other living organisms. However, irrespectively from such ecological significance, CWCs are still vulnerable to human pressures such as fishing, pollution, ocean acidification and global warming Providing coherent and representative conservation of vulnerable marine ecosystems including CWCs is one of the aims of the Marine Protected Areas networks being implemented across European seas and oceans under the EC Habitats Directive, the Marine Strategy Framework Directive and the OSPAR Convention. In order to adequately represent ecosystem diversity, these initiatives require a standardised habitat classification that organises the variety of biological assemblages and provides consistent and functional criteria to map them across European Seas. One such classification system, EUNIS, enables a broad level classification of the deep sea based on abiotic and geomorphological features. More detailed lower biotope-related levels are currently underdeveloped, particularly with regards to deep-water habitats ( > 200 m depth). This paper proposes a hierarchical CWC biotope classification scheme that could be incorporated by existing classification schemes such as EUNIS. The scheme was developed within the EU FP7 project CoraIFISH to capture the variability of CWC habitats identified using a wealth of seafloor imagery datasets from across the Northeast Atlantic and Mediterranean. Depending on the resolution of the imagery being interpreted, this hierarchical scheme allows data to be recorded from broad CWC biotope categories down to detailed taxonomy-based levels, thereby providing a flexible yet valuable information level for management. The CWC biotope classification scheme identifies 81 biotopes and highlights the limitations of the classification framework and guidance provided by EUNIS, the EC Habitats Directive, OSPAR and FAO; which largely underrepresent CWC habitats.