Background: Baixo de São Mateus is known for its historical importance as a fishing ground south of Pico Island. Fisheries bycatch information suggests that this seamount may host important deep-sea benthic communities. However, Baixo São Mateus has never been explored with video surveying techniques. By taking advantage of the collaboration with the Fundação Rebikoff-Niggeler (FRN) and the use of their submersible LULA1000, based in the harbour of Horta (Faial), we aimed to explore the never surveyed seamount ridge Baixo de São Mateus. The main objective of this survey was to evaluate if this area may fit the FAO criteria that define what constitutes a Vulnerable Marine Ecosystem. Namely, we aimed to: characterize the diversity and spatial distribution patterns of benthic communities and commercial fishes in this important fishing ground; document potential fishing impacts on the main structuring species that conform to the different benthic communities. Deep-sea benthic communities in Baixo de São Mateus: Overall, approximately 3.7 linear kilometers of seafloor were covered during the two exploratory dives carried out on the southern flank of Baixo de São Mateus. A total of seven benthic communities were identified, showing a clear bathymetric zonation. Remnants of longline fishing gears (e.g. ropes and monofilament lines) were recorded during the two dives, with several broken or damaged colonies of corals and sponges observed. Management recommendations: Based on the assessment described in the report, the seamount ridge Baixo de São Mateus does not fit the FAO criteria to be considered a VME and thus there is no sufficient scientific information to support this area as high priority for conservation in the Azores. Despite the presence of some long-lived species, there was an overall low number of species and communities and in low densities, when compared to other geomorphological features of the Azores region. Baixo São Mateus is an important fishing ground in the Azores. The low natural diversity of the benthic communities observed may suggest that existing fishing pressures in Baixo São Mateus will likely not have produced significant adverse impacts in the existing benthic living communities. However, it should be noticed that the present assessment is based only on two video transects, which covered a limited area of the seamount ridge. It is thus possible that we may have missed some important communities or areas with higher species diversity or other large structuring species. Therefore, continued scientific research is necessary to better understand the distribution of species, as well as the structural and functional role of such deep-sea benthic communities to better define adaptive management and conservation strategies.

Main objective: MapGES 2023 is the continuation of our long-term strategy to map deep-sea biodiversity and identify Vulnerable Marine Ecosystems (VMEs) in the Azores using the Azor drift-cam imagery system. As in other MapGES cruises, the objectives were to (i) map benthic communities inhabiting unexplored seamounts, ridges, and island slopes, (ii) identify new areas that fit the FAO Vulnerable Marine Ecosystem definition; and (iii) determine distribution patterns of deep-sea benthic biodiversity in the Azores. The results of this cruise added to the previous contributions to identify the environmental drivers that determine the spatial distribution of deep-sea benthic biodiversity in the Azores. It also provides valuable information in the context of Good Environmental Status (GES), Marine Spatial Planning (MSP) and new insights on how to sustainably manage deep-sea ecosystems. Methodology: We performed several underwater video transects along the seafloor with the Azor drift-cam, a low-cost drifting camera system designed and developed at IMAR & Okeanos (University of the Azores), which allows the recording of high-quality underwater video images of the seabed down to 1000 m depth. The system was deployed from the research vessel RV Arquipélago, owned by the Government of the Azores. Cruise summary: The MapGES 2023 MT Physeter cruise was composed of two parts divided into 5 Legs. In the first part, we visited some unexplored areas such as the geomorphological structures Boureé NE (previously named Açor NW), Açor bank, de Guerne N (previously named Açor SE), São Mateus de Fora, Agulhas das 18 Milhas, Álvaro Martins seamount, Terceira N, Terceira S, Terceira E, Maçarico, Beirada de fora (previously part of Maçarico) and Gastromar. In the second, we also visited some unexplored areas such as the geomorphological structures around the islands of São Jorge (São Jorge E Topo e São Jorge NE) and of São Miguel (São Miguel N, NE, E, SE, S, SW, O, NO, e Mar da Prata Norte), and we revisited other geomorphological structures that needed complementary sampling efforts as, for example, São Jorge SE, e São Jorge S Urzelina. During the MapGES 2023 MT Physter cruise, we performed 204 dives in 212 stations down to 1 000 m depth, and covered about 124 km of seafloor, resulting in more than 211 hours of video imagens. These dives were conducted in 32 different sampling areas, including 11 seamounts and 21 island slopes around the islands of Terceira, São Miguel, and São Jorge. During this cruise, we explored, for the first time, the deep-sea benthic communities inhabiting banks, ridges, seamounts, and slopes located around the Island of São Miguel. Main achievements: 1. We visited thirty-two unexplored geomorphological structures in the Azores EEZ listed in the evaluation of areas with substantial knowledge gaps a. Part 1 (Legs 1, 2, and 3) –geomorphological structures south of Faial and around Pico Islands Boureé NE (Açor NW), Açor, de Guerne N (Açor SE), São Mateus de Fora, Agulhas 18 Milhas; and 6 new areas around Terceira - Álvaro Martins, Terceira N, Terceira S, Terceira E, Maçarico, Gastromar, Beirada de fora. We also visited some areas that have already been explored but needed extra video data, namely Terceira NE and Pico N. We also explored a completely new area named 12 Milhas. b. Part 2 (Legs 4 and 5) – São Jorge E Topo, São Miguel N, NE, E, SE, S, SW, O, NO, e Mar da Prata Norte. We managed to fill some knowledge gaps about the benthic communities located in the southeast and eastern portions of São Jorge Island (São Jorge SE and S Urzelina), an area that was difficult to access and explore from small vessels like the MT Physeter, which we did not have the opportunity to visit in previous campaigns. 2. During Leg 1 MapGES 2023 MT Physeter cruise we explored particularly sensitive areas due to fishing activities, namely south of Faial and Pico islands. As in previous years, the presence of some fishing lines made our deep-sea exploration challenging. After having the Azor drift-cam caught on several lines, we managed to get free with only minor damages. This collateral fishing impact is preventing the acquisition of deep-sea biodiversity data to inform management and deserve to be better quantified. Problems with the Outland laser systems resulted in the lack of laser points in some of the images recorded. 3. In both Leg1 and Leg 2 of MapGES 2023 Physeter cruise, most of the dives performed covered sections of sedimentary bottoms, usually characterized by low levels of biodiversity. Nevertheless, some extensive aggregations of the primnoid corals Narella versluysi and Narella bellissima were occasionally observed colonizing rocky outcrops. The bird’s nest sponge Pheronema carpenteri, together with Asconema fristedti composed most of the sponge assemblage, covering areas of mixed substrate. In MapGES 2023 Physeter cruise Leg2, a particularly surprising highlight, since we were completely unaware of this throughout the dive itself, was the impressive aggregation of the echinoderm Cidaris cidaris. It covered a vast section of flat sedimentary seafloor, being the largest and densest aggregation we have recorded so far in the Azores region. 4. The abundance, diversity, and condition in which the several benthic communities observed were found thriving on the Terceira island’s slopes was particularly special and definitely a highlight of Leg3. Despite these previously unexplored areas being subjected to considerable degrees of fishing effort, most of the benthic fauna observed was visually healthy and harboured many associated fish species as well. The main highlights of Leg 3 were: (1) the sighting of uncommonly large specimens of the coral Dentomuricea aff. Meteor in Terceira N, quite possibly the largest specimens we have recorded so far in the Azores region; (2) The detection of areas with the display of black coral aggregations such as Leiopathes glaberrima and L. expansa; (3) Observation of what we believe are small primnoid corals yet to be identified in at least two different seamounts in Terceira E area. 5. During Leg 4, it was the first time an extensive scientific survey was specifically designed to map and describe deep-sea benthic communities inhabiting banks, ridges, seamounts, and slopes located around the Island of São Miguel. 6. In both Legs 4 and 5 of MapGES 2023, most of the dives performed covered sections of sedimentary bottoms, usually characterized by low levels of biodiversity. Nevertheless, there were locations showing extensive coral aggregations that potentially are indicative of Vulnerable Marine Ecosystems. These aggregations were mostly encountered at depths shallower than 400-500 m depth and were dominated by extraordinarily large colonies of Callogorgia verticillata and, less frequently, by colonies of Dentomuricea aff. meteor often mixed with other coral species commonly found around the Azores, such as Viminella flagellum and Acanthogorgia spp. On a few occasions, extensive aggregations of the primnoid corals Narella versluysi and Narella bellissima were observed at depths greater than 500 m. 7. Noteworthy is the observation, during Leg 5, of some coral aggregations that appear to be particularly rare in the archipelago of the Azores. These include (i) a vast area completely covered by a reef of the stony coral Eguchipsammia cornucopia; (ii) an extraordinarily dense coral garden featuring, among other species, the bubble gum coral Paragorgia johnsoni (a species that do not appear to be very common on island slopes), and particularly high densities of the primnoid species Narella bellissima and N. versluysi; (iii) a large area dominated by an unidentified species of the family Stylasteridae (i.e. lace corals); (iv) an area dominated by a rare purple coral most likely of the genus Paramuricea; (v) an aggregation of black corals (order Antipatharia) on the northern part of Mar da Prata Bank. 8. Regarding sponge aggregations, the highlights of these two legs are (i) the observation of extensive areas with the presence of the species Pseudotrachya hystrix, mainly encountered at the common sandy floors where we usually drifted over, (ii) some frequent sightings of even bigger specimens of the often-robust Characella pachastrelloides complex and, (iii) the frequent notice of big and widespread aggregations of the “bird nest” sponge, Pheronema carpenteri. 9. A potential new species of deep-sea fish may have been observed for the first time in the Azores archipelago, named Gaidropsaurus spp., spotted on two different days. 10. The invasive alga Rugulopteryx okamurae, which in recent years appeared on most Azorean shores, was very frequently observed in large patches down to depths of about 900 m, suggesting that the impact of this species on resident communities may not only be limited to coastal areas but also extend into the deep sea of the Azores. Therefore, to fully understand how Rugulopteryx okamurae alters the distributional and niche dynamics of native species and the extent of its impacts, there is a need to investigate how it affects both shallow and deep-sea communities. 11. In general, it was found that the benthic communities around São Miguel Island present an apparent good environmental status. This observation is particularly relevant if we consider that this area concentrates a significant part of the bottom fishing effort in the Azores Region. 12. During Leg2 of this cruise, we achieved a long waiting milestone: teaching our South Atlantic partners how to operate the Azor drift-cam. The iAtlantic capacity building workshop aimed to share the technological and methodological details for the use of the Azor drift-cam. It ran from 5-8th June 2023 in the facilities of Escola do Mar (EMA) in the city of Horta (Faial Island, Portugal). A total of 12 researchers from the iAtlantic consortium

Main objective: MapGES 2023 is the continuation of our long-term strategy to map deep-sea biodiversity and identify Vulnerable Marine Ecosystems (VMEs) in the Azores using the Azor drift-cam imagery system. As in other MapGES cruises, the objectives were to (i) map benthic communities inhabiting unexplored seamounts, ridges, and island slopes, (ii) identify new areas that fit the FAO Vulnerable Marine Ecosystem definition; and (iii) determine distribution patterns of deep-sea benthic biodiversity in the Azores. The results of this cruise added to the previous contributions to identify the environmental drivers that determine the spatial distribution of deep-sea benthic biodiversity in the Azores. It also provides valuable information in the context of Good Environmental Status (GES), Marine Spatial Planning (MSP) and new insights on how to sustainably manage deep-sea ecosystems. Methodology: We performed several underwater video transects along the seafloor with the Azor drift-cam, a low-cost drifting camera system designed and developed at IMAR & Okeanos (University of the Azores), which allows the recording of high-quality underwater video images of the seabed down to 1000 m depth. The system was deployed from the research vessel RV Arquipélago, owned by the Government of the Azores. Cruise summary: The MapGES 2023 RV Arquipélago cruise was composed of two Legs. In the first, we visited some unexplored areas such as the geomorphological structures around the Princesa Alice bank and the seamounts north of Graciosa (Sedlo, Borda, João Leonardes, and Gaillard) (central Azores). In the second, we also visited some unexplored areas such as the geomorphological structures of Hard Rock Café (northern of Corvo Island), Kurchatov SE (in the north mid Atlantic-ridge), Albatroz N, Ferraria N, Ferraria Mar, Sauerwein, Mar da Prata, Grande Norte (south of Faial Island), and the seamounts around Princesa Alice (Princesa Alice S, Princesa Alice SE, and De Guerne) and we revisited other geomorphological structures that needed complementary sampling efforts as, for example, Isolado, Kurchatov N, Kurchatov SW, and Mar da Prata South. During the MapGES 2023 RV Arquipélago cruise, we performed 145 dives in 148 stations down to 1 125 m depth, and covered about 85 km of seafloor, resulting in more than 141 hours of video images. These dives were conducted in 28 different sampling areas, including 26 seamounts and 2 island slopes around the island of São Jorge. During this cruise, we explored, for the first time, some areas such as the famous Hard Rock-Café and Sedlo seamounts. Data on the benthic communities inhabiting these seamounts was lacking to complement existing information that supported the designation of these areas as Marine Protected Areas (MPA) of the Azores Marine Park (PMA). Main achievements: 1. Eighteen unexplored geomorphological structures in the Azores EEZ were visited, being listed in the evaluation of areas with substantial knowledge gaps. a. Leg1 – Sedlo W, Sedlo, Borda, São Jorge NE, Princesa Alice W (formerly part of Princesa Alice), Princesa Alice SW (formerly Alberto do Mónaco), Picos S do Princesa Alice-, plus two areas that were not listed - the Gaillard seamount and the an area West of Picos S do Princesa Alice. We also visited some areas that have already been explored but were in need of extra video data namely João Leonardes, Serreta Mar, Mar da Fortuna, and São Jorge NW. b. Leg 2 – Hard Rock Café, Kurchatov SE, Albatroz N, Ferraria N, Ferraria Mar, Sauerwein, Mar da Prata, Mar da Prata N, Grande Norte and one seamount around Princesa Alice (De Guerne). We also visited four areas that have already been explored but needed extra video data namely the Isolado, Kurchatov N, Kurchatov SW, and Mar da Prata S. We also visited the Perestrelo Bartolomeu area, for which some information already existed, and the Petrov area, which turned out to be deeper than what the maps indicated. 2. During the MapGES 2023 cruise we accomplished 143 underwater video transects and the deepest dive to date performed with the Azor drift-cam, at 1 125 m depth. In total, we collected 141 hours of new underwater video footage of seabed habitats. As in previous years, the presence of some fishing lines made our deep-sea exploration challenging. After having the Azor drift-cam caught on several lines, mainly around São Miguel Island (Mar da Prata and Grande Norte seamount) and Kurchatov SE, we managed to get it free only with minor damages. This collateral fishing impact is hampering the acquisition of deep-sea biodiversity data to inform management deserve to be better quantified. Problems with the Outland lasers systems resulted in the lack of laser points the some of the images recorded. 3. We finally explored the Sedlo seamount with the Azor drift-cam. From 2002–2005, Sedlo was the focus of a multidisciplinary EU project, OASIS (Oceanic Seamounts: An Integrated Study), which showed highly complex hydrographical patterns with anticyclonic circulation around its three summits, driven principally by Taylor column formation. This seamount was speculated to accommodate one the Azores’ most important spawning ground for orange roughies and alfonsinos. 4. Deep-sea explorations with the Azor drift-cam contributed with supporting evidence to consider Sedlo seamount as an Essential Fish Habitat. We found areas that are home to the highly endangered deep-sea fish orange roughy Hoplostethus atlanticus and discovered that Sedlo and other neighbouring seamounts host a high number of deep-sea shark species, some of which rarely observed in the Azores. We also discovered large aggregations of the black coral Leiopathes expansa on the summit of the Sedlo W, with most specimens of relatively small sizes. This area seemed to be a good candidate for being considered a Vulnerable Marine Ecosystem and should be kept in the list of priority areas for conservation in the Azores. 5. We also explored Borda, João Leonardes, Gaillard seamount, north of Graciosa Island. Along with Sedlo, these seamounts seem to host slightly unique deep-sea benthic communities when compared to other areas in the Azores EEZ explored so far with black corals Leiopathes expansa and Parantipathes hirondelle, the bamboo coral Acanella arbuscula, stylasterids of the genus Errina, the sea urchin Cidaris cidaris, and lamellate sponges of the genus Phakellia among others 6. We started exploring the morphological features south of Princesa Alice peak. Most dives covered soft and mix sediments with relatively low biodiversity and abundance, although some areas hosted high densities of Narella bellissima and Narella versluysi, while others were dominated by patches of Pheronema carpenteri and other sponges (e.g., Asconema sp.). We also observed some sparse colonies of cold-water such as corals Narella versluysi, Hemicorallium niobe, H. tricolor, Acanella arbuscula, Chrysogorgya sp., cf. Leptopsammia, cf. Candidella imbricata, and Flabellum sp., and some deep-sea sponges such as cf. Regadrella, and specimens from the genus Geodia, along with some shrimps Aristaeopsis edwardsiana, sea-urchins Cidaris cidaris and deep-sea fishes such as Mora moro, Synaphobranchus kaupii, Helicolenus dactylopterus, Hoplostethus mediterraneus, Gephyroberix darwinii, Dalatias licha, and one Trachyscorpia cristulata. 7. The Hard Rock Café seamount was finally explored with the Azor drift-cam. The hydrographic Institute had mapped this seamount in 2020 but given its location at 210 nautical miles from the natural starting point of the MapGES cruises (Horta) and its position to the north of the Azores archipelago (usually more affected by adverse weather conditions), the visit to this seamount had been postponed for a few years. After all conditions were met, the Hard Rock Café was visited. It is a geomorphological structure that, due to its characteristics, was from the first moment on the list of the first options for the expansion of the Azores Marine Park, hence the increased importance of this visit. 8. We also visited a seamount named Petrov. This area does not yet have high-resolution bathymetry data, so we tried to prospect the area looking for a peak between 300 m and 1,000 m depth. However, after launching the Azor drift-cam in search of a shallower peak we were unable to reach the bottom. All sonars on board showed depths between 1,900 m and 2,500 m deep, indicating that this area is much deeper than current nautical charts demonstrate and highlighting, once again, the importance of carrying out multibeam bathymetry surveys in the Azores. 9. Deep-sea explorations with the Azor drift-cam contributed with supporting evidence to consider Hard Rock Café and Isolado, Essential Fish Habitats. We found that these areas were both home to the highly endangered deep-sea fish orange roughy (Hoplostethus atlanticus) and large schools of the wreckfish (Polyprion americanus). These areas also showed a high number of deep-sea shark species, some of which rarely observed in the Azores. Although these areas showed low abundances in terms of benthic megafauna, we detected some frequent colonies of the slow-growing black corals Antipathes dichotoma and Leiopathes expansa. 10. Most seamounts on the way to and around São Miguel Island, such as Albatroz N, Ferraria N, Ferraria Mar, Mar da Prata and Grande Norte host interesting deep-sea benthic communities with the deeper areas demonstrating abundant coral gardens of both Narella versluysi and Narella bellissima, sometimes, in aggregation with Callogorgia verticillata, Acanthogorgia sp. or Leiopathes expansa. Shallower areas were mainly characterized by large gardens of Viminella flagellum, sometimes associated with Callogorgia verticillata and other times with frequent and large colonies of Dentomuricea aff. meteor. 11. The Sauerwein ridge, between the islands of São Miguel and Sa

Main objective: The OceanX 2023 (OCX 2023) is the continuation of our long-term strategy to map deep-sea biodiversity and identify Vulnerable Marine Ecosystems (VMEs) in the Azores. In this cruise, we operated from the RV OceanExplorer and planned to visit some unexplored areas such as the geomorphological structures around the Princesa Alice bank and Dom João de Castro seamount, as well as other areas near the slopes of Pico and Faial islands. As in the MapGES cruises, the objectives were to (i) map benthic communities inhabiting unexplored seamounts, ridges and island slopes, (ii) identify new areas that fit the FAO Vulnerable Marine Ecosystem definition, (iii) determine distribution patterns of deep-sea benthic biodiversity in the Azores, and (iv) determine the condition of benthic communities by looking at evidence of fishing damage to fauna, presence of lost fishing gear and marine litter. Moreover, this cruise aimed to collect biological samples of poorly known or unidentified species observed on video footage. The results of these explorations will directly contribute to the Regional Government of the Azores efforts to declare 30% of the Azores EEZ as marine protected areas of which 10% should be strictly protected. The results of this cruise added to the previous contributions to identify the environmental drivers that determine the spatial distribution of deep-sea benthic biodiversity in the Azores. It also provides valuable information in the context of Good Environmental Status (GES), Marine Spatial Planning (MSP) and new insights on how to sustainably manage deep-sea ecosystems. Methodology: We performed several underwater video transects using the vehicles available in the RV OceanXplorer. These assets included the Argus ROV Chimaera, rated to 6000 meters depth, and the Triton submersibles Nadir and Neptuno rated to 1000 meters and with similar sampling capabilities as the ROV Chimaera. In each of the areas or geomorphological structures to be explored, we carried out video transects from a depth of about 1 000 m to the shallowest depth of each structure. The objective was to obtain underwater images to characterize the biodiversity along the entire bathymetric gradient and substrate types of each structure and to collect as many samples of unknown species as possible. Since in-situ data of water-mass characteristics is very scarce, one of the goals of the cruise is to collect information that can contribute to the understanding of the water masses distribution in the Azores. Vertical CTD/Rosette profiles could be conducted at each of the video stations at a seabed depth of about 1,000 m in order to measure physical and chemical seawater properties that characterize the dominant water masses described for the Azores: 0-150m, Mixed layer and seasonal thermocline; 150-550 m, North Atlantic Central Water (NACW); 500-1500 m, Mediterranean Outflow Water (MOW) / Subarctic Intermediate Water (SAIW, west of MAR). The North Atlantic Deep Water (NADW; >1500 m) will not be targeted during this cruise. One open-ocean control station should also be considered. Accurate knowledge of seabed characteristics is crucial in order to effectively plan the biological surveys and to better understand the ecological processes that are observed in the video images. Considerable effort has been placed in the last few years in collecting accurate bathymetric data in the Azores region and, therefore, most areas to be visited have already been surveyed with MB. Nevertheless, we suggested conducting surveys in all 3 main areas to improve coverage or complement existing data (Princess Alice bank, D. João de Castro bank and SE Pico area). Additionally, opportunistic MB surveys were conducted during the transits. In order to achieve our communication goals, our media team onboard Ocean Explorer was in permanent contact with the OKEANOS institute media team on land to organize social media posts about the mission. Several science communication activities were organized during the cruise, including full photo and video coverage of the scientific activities. Cruise summary: During the OXR 2023 survey we visited several areas in the central group of the Azores, namely D. João de Castro seamount and Princesa Alice bank and the slopes of Faial Capelinhos, Pico S Lajes, and Pico Ponta da Ilha (Table 1). Taking advantage of the technological assets onboard RV OceanXplorer, namely the ROV Chimaera and the Submersibles Neptune and Nadir, we were able to conduct 8 manned submarine dives and 12 remotely operated vehicle dives, one ROV D. João de Castro seamount, 3 SUB and 3 ROV dives in Capelinhos, 5 SUB and 6 ROV dives in Princesa Alice (Princesa Alice, Princesa Alice W, Bourée E), and one ROV dive in Pico S Lajes and another one in Ponta da Ilha N. From the 20 ROV and SUB dives, 19 were successful. In general both the ROV and the submersible dives covered a much smaller linear distance (average 952 m) per hour of survey (206 m·h-1) when compared to the Azores drift-cam. One of the reasons for the shorter distances was the need to collect biological samples to clarify the taxonomic identification of several organisms. During these dives, we were able to collect 268 biological samples belonging to approximately 197 different morphotypes. It is likely that this sampling effort will help solving about 100 taxonomic questions. After each ROV or submersible dive we performed a CTD cast to measure water masses properties and collect water samples for more detailed analyses. Form the 27 CTD stations, 15 were specifically conducted to address deep-sea related questions, while the other stations were performed to address the Pelagic team objectives. From these 15 dedicated CTD casts, we obtained 157 water samples for different types of analyses. Main achievements: The deep-sea component of the OceanX 2023 expedition revealed that banks and seamounts heavily exploited by bottom longline fishing are still home deep-sea benthic communities with a high natural and ecological value. 1. During the OXR 2023 we visited 7 different areas, and mapped 3,840 km2 of seabed, of which 630 km2 is new information to be included in official Portuguese databases. We were able to participate in 8 manned submarine dives and 12 remotely operated vehicle dives, which produced 84:30 hours of deep sea video, over 19 km of bottom, and 268 biological samples. We also performed 27 stations for analysis of water masses, in which 157 samples were collected for analysis of environmental DNA and other parameters. 2. We observed many benthic communities, some of them quite special. One of the highlights of this campaign was the big basalt outcrops found at around 800 m depth that were densely colonized by many colonies of the black coral Leipathes expansa. Most of the colonies observed were visually healthy, particularly large, probably older than 1.000 years, and with a lot of associated biodiversity. It is possible that before demersal fishing exploited this bank, these arborescent black corals, vulnerable to fishing, were even much more abundant, larger and older. These corals are very slow growing and can live for thousands of years. 3. We also discovered one of the few hard coral reefs known in the Azores composed by the lace corals Lophelia pertusa and Madrepora occulata. This small reef was observed at around 850 m depth on the Capelinhos area, west of Faial. Hard coral reefs play an important role in the biogeochemical cycles of the deep sea, but are very vulnerable to ocean acidification. Some portions of this reef were not alive, forming a compact coral framework to which many other associated species were attached. A better understanding of their distribution and their susceptibility to climate change are priority lines of research for the future. 4. We also discovered one of the largest and densest coral garden dominated by the primnoid Callogoria verticillata found in the Azores. This gorgonian forest, found on the Dom João de Castro seamount, is characterized by fan-shaped colonies whose feathery branches resemble palm leaves. Most of the colonies observed were smaller than usual, but possibly the densest aggregation of this species observed so far. 5. We observed dense aggregations of the largest species of sponges that inhabit the deep sea of the Azores (e.g., Characella pachastrelloides, Haliclona magna), on the Princesa Alice bank. Sponges play a structuring role in the deep sea, increasing ecosystem productivity and creating habitat for other species. 6. In one of the areas explored with multibeam probes, an unknown canyon (or gorge) of about 15 km long, 340 m wide and with cliffs about 100 m high was found. The canyons and gorges of the Azores are fairly unknown habitats where unique ecosystems can be found. 7. The OceanX 2023 expedition made it possible to identify that a large part of the benthic communities, including corals and sponges, observed in one of the Azores' main demersal fishing grounds are still in good environmental condition and have a high natural and ecological value. However, some long-lived coral colonies with visible fishing impacts were observed. These in situ observations corroborate the conclusions of previous studies which suggest that well-regulated deep-sea fishing based on hook-and-line gear (preferably handlines) could contribute to a sustainable exploitation of the deep sea. 8. The manned submarines and the ROV available on the RV OceanXplorer, allowed collecting 268 biological samples belonging to approximately 197 different morphotypes. It is likely that this sampling effort will help solving about 100 taxonomic questions, and some samples could even reveal new species to science. In summary, we found areas that fit the definition of Vulnerable Marine Ecosystems, and compiled valuable scientific information to inform policies that promote the preservation of the natural

Main objectives: MapGES 2025 continues our longstanding commitment to map deep-sea biodiversity and identifying Vulnerable Marine Ecosystems (VMEs) in the Azores with the Azor drift-cam imagery system. Our 2025 expedition aimed to enhance the data collected in previous surveys by conducting new video transects along seamounts over a widespread area in the Azores archipelago, namely the new area on the southern limit of the EEZ, Pico Sul, seamounts and ridges eastern of Terceira Island and a diversity of sites along the Mid-Atlantic ridge and adjacent areas. This fieldwork focused mostly on under-sampled areas and deeper strata. Our ultimate goal is to achieve a comprehensive understanding of the deep-sea fauna dwelling on the slopes, banks, and seamounts in these areas. Like previous MapGES cruises, our objectives included: (i) mapping benthic communities in previously unexplored seamounts, ridges, and island slopes; (ii) identifying new areas that meet the FAO definition of Vulnerable Marine Ecosystems; and (iii) determining the distribution patterns of deep-sea benthic biodiversity in the Azores. The results of this cruise added to the previous contributions to identify the environmental drivers that determine the spatial distribution of deep-sea benthic biodiversity in the Azores. It also provides valuable information in the context of Good Environmental Status (GES), Marine Spatial Planning (MSP) and new insights on how to sustainably manage deep-sea ecosystems. Methodologies: We conducted several underwater video transects along the seafloor using the Azor drift-cam, a cost-effective drifting camera system developed by IMAR and Okeanos at the University of the Azores. This system is capable of recording high-quality underwater video images of the seabed down to 1200 meters depth, and it was deployed from the RV Arquipélago. In each sampling area, we performed a representative number of dives using the video system, ranging from approximately 1200 m to the shallowest point of each structure. The objective was to capture underwater images that would effectively characterize the biodiversity across the entire bathymetric gradient and various substrate types. The video transects were strategically planned based on the most accurate bathymetric data available, allowing the camera system to drift from deeper to shallower regions. This methodology was designed to ensure optimal image quality by maximizing light incidence and minimizing attenuation in the water column, a challenge typically encountered during descending transects. Each transect with the Azor drift-cam was planned for approximately 60 to 120 minutes on the seafloor, with the system drifting over benthic habitats at an average speed of 0.5 to 1 knot. Under favourable conditions, each working day facilitated 5 to 6 dives, corresponding to approximately 5 kilometres of seafloor explored daily. Cruise summary: The MapGES 2025 cruise aboard RV Arquipélago consisted of 2 legs and aimed at exploring and revisiting banks, ridges, and seamounts on the south limit of the EEZ of the Azores, south of São Miguel in Mar da Prata, East of Terceira Island and in the Mid-Atlantic ridge. A total of 55 successful dives were conducted out of 56 planned, covering 16 sampling areas. During Leg 1, from the 16th to 24th of August, we performed 23 successful dives with the Azor drift-cam. These first deployments surveyed the deep-sea benthic communities dwelling on the slopes of the geomorphological structures on the south limit of the EEZ of the Azores, named Pico Sul, in the southern area of Mar da Prata and in structures located on the east side of Terceira Island (Heitor Álvares, Alcatraz and Dom João de Castro). This first leg had the purpose to complete some areas we wanted to visit for some time now and to visit two new unexplored areas, Pico Sul, around 230 nm away from Faial Island and Heitor Álvares. During Leg 2, from 27th August to 5th September, a total of 32 successful dives were performed with the Azor drift-cam. This Leg aimed at exploring the seamounts along the Mid-Atlantic Ridge and adjacent areas, some for the first time, and others re-visited in order to complement the previous survey work done there. During this year’s survey, we decided to check what differences could exist in terms of fauna in an isolated and deep seamount (Pico Sul) when compared with the fauna already recorded elsewhere. Fauna encountered in this deep structure was mainly sparse and in low densities. Very interesting deep fauna was observed in the east peaks of Alcatraz geomorphological structure, with sightings of several individuals of the black coral Leiopathes expansa, the rarely recorded glass sponge Asconema cf. setubalense and multiple individuals of the sponge Hertwigia falcifera. Just like it was observed in recent dives performed in the north sectors of Mar da Prata structure, assemblages of a seemingly shallow morphotype of Candidella imbricata were recorded, possibly showing evidence of the wide distribution of this species along all this geomorphological complex. The shallow dives conducted in Dom João de Castro showed extensive and dense coral gardens essentially composed by Viminella flagellum, Dentomuricea aff. meteor and Callogorgia verticillata. We also explored and revisited several Azorean seamounts along the Mid-Atlantic Ridge, documenting unexpected biodiversity and novel records for us. At Ferradura E, we recorded one of the densest aggregations of Hertwigia falcifera recorded in the region and vast ridges dominated by Narella spp. with frequent colonies of black corals Leiopathes expansa. At the newly named Fantas seamount, we observed a possible first Azorean record of a Mid-Atlantic skate Rajella cf. kukujevi. At Menez Gwen, long drift-cam transects revealed recent pillow lavas colonized by large Leiopathes expansa and Placogorgia sp. Picoto seamount hosted one of the largest aggregations of Acanella arbuscula and Chrysogorgia sp. recorded in the region, while Alfa seamount hosted impressive Paragorgia johnsoni “forests” and diverse associated fauna. Main achievements: During the MapGES 2025 survey conducted aboard the RV Arquipélago, 55 stations were completed using the Azor drift-cam. The performed stations spanned depths ranging from 230 to 1234 m, encompassing a broad spectrum of marine strata. The survey covered approximately 45 km of the seafloor and generated more than 74 hours of video footage for analysis. These numbers represent a big achievement considering that we successfully operated, once again, the Azor drift-cam with several improvements, including an umbilical cable of 1500m, the underwater positioning system (USBL), the external power feeding of the GoPro camera and the addition of a second spotlight. We visited one of the most isolated and offshore seamounts of the Azores EEZ, Pico Sul. This geomorphological structure is at a total distance of around 230 nm from Faial Island. The transit took more than 27h to reach this area and is among the furthest areas ever explored with the Azor drift-cam. The deepest and longest dives with the Azor drift-cam were carried out during this year’s survey: the deepest at Pico Sul, largely exceeding 1200 m, the longest in distance at Menez Gwen (~2.6 km), and the longest in terms of duration at Beta, lasting more than 3 hours. At the newly explored A10 area, our cameras captured a very pale, ghost-like ray that lingered calmly in front of the system. This sighting may represent the first record of the Mid-Atlantic skate (Rajella cf. kukujevi) in the Azores. Inspired by this unusual encounter, the site was renamed “Fantas” seamount, short for Fantasma (“ghost” in Portuguese). The A13 seamount is yet to be renamed. The deeper strata, including the intermediate and lower slopes of the visited seamounts, harboured lush benthic communities, visibly thriving on the seafloor. The richness, abundance, and environmental conditions of many of these assemblages were unexpected, especially as some areas surveyed in the past revealed substantially poorer megabenthic communities. These observations demonstrate how quickly one’s perception of a seamount’s ecological value can change with a few complementary dives and additional seafloor coverage. They also highlight the importance of systematic and repeated exploration to capture the full extent of habitat diversity, ensuring that future spatial planning and conservation measures are grounded in comprehensive and representative knowledge. This year’s survey revealed contrasting patterns of benthic diversity, from sparse communities at Pico Sul to notably rich assemblages in other areas. At this isolated seamount, benthic megafaunal assemblages appear limited, with most species occurring solitarily. Such patterns may offer preliminary clues to the structure of communities on deep, isolated seamounts. The black coral Leiopathes expansa and the glass sponge Hertwigia falcifera were frequently spotted on the multiple outcrops and overhangs found. During the exploration of Ferradura E area, the deeper sectors revealed unique and localized megabenthic communities usually composed of a large variety of species. We recorded what we think could be one of the densest aggregations of the large yellow hexactinellid Hertwigia falcifera. The increment in the observations of these species can also be influenced by the deeper sectors explored this year. Thriving benthic fauna was observed on the deep eastern summits of Alcatraz, including a localized patch of the rarely seen glass sponge Asconema cf. setubalense on a basaltic boulder. This was possibly the first record of this species with the Azor drift-cam. Dense assemblages of a shallow morphotype of Candidella imbricata point to a broad ecological footprint of this primnoid coral within Mar da Prata complex. This interpretation is supported by the remarkable aggregations documented during last year’s survey in M

Main objectives: MapGES 2025 continues our longstanding commitment to map deep-sea biodiversity and identifying Vulnerable Marine Ecosystems (VMEs) in the Azores with the Azor drift-cam imagery system. Our 2025 expedition aimed to enhance the data collected in previous surveys by conducting new video transects along the slopes of several islands in the archipelago, including Faial, Pico, Graciosa and Terceira. This fieldwork focused mostly on under-sampled areas and deeper strata. Additionally, we planned to explore one new area, specifically Vasco Gil seamount. Our ultimate goal is to achieve a comprehensive understanding of the deep-sea fauna dwelling on the slopes, banks, and seamounts in these areas. Like previous MapGES cruises, our objectives included: (i) mapping benthic communities in previously unexplored seamounts, ridges, and island slopes; (ii) identifying new areas that meet the FAO definition of Vulnerable Marine Ecosystems; and (iii) determining the distribution patterns of deep-sea benthic biodiversity in the Azores. The results of this cruise added to the previous contributions to identify the environmental drivers that determine the spatial distribution of deep-sea benthic biodiversity in the Azores. It also provides valuable information in the context of Good Environmental Status (GES), Marine Spatial Planning (MSP) and new insights on how to sustainably manage deep-sea ecosystems. Methodology: We conducted several underwater video transects along the seafloor using the Azor drift-cam, a cost-effective drifting camera system developed by IMAR and Okeanos at the University of the Azores. This system is capable of recording high-quality underwater video images of the seabed, and it was deployed from the MT Physeter. This year, the operation capabilities of the Azor drift-cam was expanded to ~1500 m depth. In each sampling area, we performed a representative number of dives using the video system, ranging from approximately 1200 m to the shallowest point of each structure. The objective was to capture underwater images that would effectively characterize the biodiversity across the entire bathymetric gradient and various substrate types. The video transects were strategically planned based on the most accurate bathymetric data available, allowing the camera system to drift from deeper to shallower regions. This methodology was designed to ensure optimal image quality by maximizing light incidence and minimizing attenuation in the water column, a challenge typically encountered during descending transects. Each transect with the Azor drift-cam was planned for approximately 60 to 120 minutes on the seafloor, with the system drifting over benthic habitats at an average speed of 0.5 to 1 knot. Under favourable conditions, each working day facilitated 3 to 5 dives, corresponding to approximately 5 kilometres of seafloor explored daily. Cruise summary: The MapGES 2025 cruise aboard MT Physeter consisted of 1 leg, divided in 3 parts, aimed at exploring and revisiting slopes, banks, ridges, and seamounts surrounding Faial, Pico, Graciosa and Terceira Islands. A total of 40 successful dives were conducted out of 41 planned, covering 11 sampling areas. During Leg 1a, on the 4th of June, we performed 2 successful dives with the Azor drift-cam. These first deployments surveyed the deep-sea benthic communities dwelling on the slopes of the geomorphological structures on the north flank of Faial Island. These first dives were also a practical test to experience some add-ons on our structure, such as the external feeding of the GoPro camera, the implementation of a second spotlight, the use of a 1500m umbilical cable and the USBL system. During the Leg 1b, from 21st June to 1st of July, we performed 35 successful dives with the Azor drift-cam around Graciosa and Terceira Island slopes and some adjacent geomorphological structures such as Vasco Gil, Ilha Azul E and João de Melo. Several deep dives (>1000 m) were performed during this leg with no major problems across the components of the drift-cam. During the Leg1c, on the 25th of July, we performed 3 successful dives with the Azor drift-cam on the deeper sectors of the NW slopes in Pico Island. During this year’s survey we observed diverse benthic and fish communities, from which we may highlight impressive and extensive aggregations of the primnoid corals Narella versluysi and N. bellissima, in Ilha Azul E, the notably large specimens of the octocoral Callogorgia verticillata, in Maçarico, the black corals Leiopathes expansa, in Beirada de Fora, and Antipathes dichotoma, in Vasco Gil. Also, an incredible and most likely record-breaking aggregation of anguilliform fishes Halosauridae was recorded at approximately 900 m depth in Graciosa S area. Main achievements: During the MapGES 2025 survey conducted aboard the MT Physeter, 41 stations were completed using the Azor drift-cam. The stations spanned depths ranging from 205 to 1130 m, encompassing a broad spectrum of marine strata. The survey covered approximately 31 km of the seafloor and generated more than 49 hours of video footage for analysis. These numbers represent a big achievement considering that we successfully operated, once again, the Azor drift-cam for deep-sea exploration on board a small vessel and this year with several improvements on our system including an umbilical cable of 1500m, the underwater positioning system (USBL), the external power feeding of the GoPro camera and the addition of a second spotlight. This year’s survey aimed to complete the coverage of selected Island slopes around Faial, Graciosa, Terceira and Pico Islands. We successfully accomplished nearly all our objectives in each one of the areas re-visited and were also able to explore the Vasco Gil seamount for the first time. For the third consecutive year of the MapGES survey onboard the MT Physeter, no Azor drift-cam structures were lost, despite that we were challenged by an entanglement on a lost fishing line, the unexpected encounter of the largest basaltic wall recorded with the Azor drift-cam dive (around 300m high) and an incident where the umbilical cable became entangled in the vessel’s propeller. As one of our key objectives this year was to explore deeper strata previously unsampled in certain areas, the drift-cam was repeatedly deployed at depths exceeding 900 m and performed outstandingly with minimal issues across all components. Ilha Azul E exhibited impressive and extensive aggregations of the primnoid corals Narella versluysi and N. bellissima. Exploration of several areas East of Terceira Island continue to reveal interesting communities. Notably, large specimens of the octocoral Callogorgia verticillata and large black corals Leiopathes expansa were observed in the Maçarico area and Beirada de Fora areas, respectively. The first exploration of Vasco Gil seamount revealed large black corals Antipathes dichotoma. Remarkable geological features were observed across the surveyed areas: around the Vasco Gil seamount a heterogenous seafloor composed of contrasting black and white rock types suggests a complex geological origin in this geomorphological structure. Interesting geological patterns of the seafloor was sighted in Ilha Azul E and Beirada de Fora areas, where evidence of ancient stratification was recorded. A deceased undetermined shark was observed on a sandy bottom in Graciosa S area, probably resulting from fisheries discards. This marks the first recorded shark carcass during an Azor drift-cam deployment. The rarity of such observations rise questions about the visibility and persistence of large organic falls in deep-sea environments. An incredible and most likely record-breaking aggregation of anguilliform fishes Halosauridae was recorded at approximately 900 m depth in the southern area of Graciosa Island. An unusually high number of angler fish (Lophius piscatorius) was repeatedly observed along the slopes of Graciosa Island. The decapod Cancer bellianus was observed on top of the vase-shaped Characella pachastrelloides while holding another sponge. This behaviour is likely uncommon for this species of crustacean.

The MEDWAVES (MEDiterranean out flow WAter and Vulnerable EcosystemS) cruise targeted areas under the potential influence of the MOW within the Mediterranean and Atlantic realms. These include seamounts where Cold-water corals (CWCs) have been reported but that are still poorly known, and which may act as essential “stepping stones” connecting fauna of seamounts in the Mediterranean with those of the continental shelf of Portugal, the Azores and the Mid-Atlantic Ridge. During MEDWAVES sampling has been conducted in two of the case studies of ATLAS: Case study 7 (Gulf of Cádiz-Strait of Gibraltar-Alboran Sea) and Case
study 8 (Azores). The initially targeted areas in the Atlantic were: the Gazul Mud volcano, in the Gulf of Cádiz (GoC) area, included in the case study 7, and the Atlantic seamounts Ormonde (Portuguese shelf) and Formigas (by Azores), both part of the case study 8. In the Mediterranean the targeted areas were The Guadiaro submarine canyon and the Seco de los Olivos (also known as Chella Bank) seamount. Unfortunately it was not possible to sample in Guadiaro due to time constraints originated by adverse meteorological conditions which obligate us to reduce the time at sea focusing only in 4 of the 5 initially planned areas. MEDWAVES was structured in two legs; the first leg took place from the 21st September (departure from Cádiz harbour in Spain) to the 13th October 2016 (arrival in Ponta Delgada, São Miguel, Azores, Portugal took place the 8th of October due to the meteorological conditions that obligated to conclude the first leg earlier as planned). during the Leg 1 sampling was carried out in Gazul, Ormonde and Formigas. The second leg started the 14th October (departure from Ponta Delgada) and finished the 26th October (arrival in Málaga harbour, Spain). MEDWAVES had a total of 30 effective sampling days, being 6 days not operative due to the adverse meteorological conditions experienced during the first leg which forced us to stay in Ponta Delgada from the 08th to the 13th October. During MEDWAVES the daily routine followed a similar scheme, depending of course on the weather and sea conditions. The main activity during the day, starting early in the morning (around 08:00 AM, once the night activities were finished), was the ROV deployment. Generally a single ROV dive of around 8 hours was performed, however in several occasions two dives were carried out in the same day (see General station list, Appendix II). After the ROV (and sometimes between two dives) the Box Corer and/or Van Veen Grab and/or Multicore was deployed. After these activities, during the night CTD-Rosette deployments and MB was conducted. Accordingly to this schema the scientific personnel worked in the day or in the night watch. A total of 215 sampling stations have been covered in MEDWAVES, using the following sampling gears: Multibeam echosounder, CTD-Rosette, LADCP, Box Corer, Van Veen Grab, Multicorer and a Remotely Operated Vehicle (ROV). Table 1 sumamrised the number of sampling stations conducted with each gear in each sampling zone. Additionally MB surveys have been conducted during the transits between areas.

This dataset includes 11 regional EUNIS-classified habitat maps (100-1000 km) and associated confidence maps that were created as a project milestone (Nr. 12) of the EU H2020 project 'iAtlantic'. The 12 iAtlantic regions encompass 1. Subpolar Mid-Atlantic Ridge, off Iceland MFRI, 2. Rockall Trough to PAP, 3. Central mid-Atlantic Ridge, 4. NW Atlantic, Gully Canyon, 5. Sargasso Sea, 6. Eastern Tropical North Atlantic, Cape Verde, 7. Equatorial Atlantic, Romanche Fracture Zone, 8. Slope & margin off Angola & Congo Lobe, 9. Benguela Current, Walvis Ridge to South Africa, 10. Brazil margin & Santos and Campos Basin, 11. Vitória-Trindade Seamount Chain and 12. Malvinas Current. For each of the regions 2-12, a shapefile of polygons classified according to the 2022 EUNIS classification level 3 and a second shapefile of the same polygons attributed with their confidence level according to the MESH Accuracy & Confidence Working approach was created. EUNIS classifications combined biozone and substrate data. Biozones were assigned from bathymetry. Where MBES was not available, GEBCO bathymetry was used. Substrate data were extracted from pre-existing geological/substrate mapping efforts and converted to EUNIS classifications via cross walks or, where substrate data were limited, substrate layers were modelled using Random Forest. The EUNIS habitat map for Region 4 was based on the pre-existing surficial geology compilation of the Scotian Shelf bioregion compiled by the Geological Survey of Canada. The EUNIS habitat map for Region 9 was based on the pre-existing South African habitat map that uses a modified IUCN hierarchical classification system. No additional information to that used in the EUSeaMap was available for Region 1. Therefore, shapefiles were not created for Region 1.

We developed habitat suitability models for 14 vulnerable and foundation cold-water coral (CWC) taxa of the Azores (NE Atlantic) using GAM and MAXENT models. The modelled taxa are: Acanthogorgia spp., Callogorgia verticillata, Coralliidae spp., Dentomuricea aff. meteor, Desmophyllum pertusum, Errina dabneyi, Leiopathes cf. expansa, Madrepora oculata, Narella bellissima, Narella versluysi, Paracalyptrophora josephinae, Paragorgia johnsoni, Solenosmilia variabilis and Viminella flagellum. Models were built using a model grid having a cell size of a 1.13 x 1.11 km (i.e. about 0.01° in the UTM zone 26N projection). This resolution was considered a good compromise between the original resolution of occurrence and environmental data and our capacity to resolve suitable and unsuitable areas within the same geomorphological feature using model predictions. Study area and model background were limited to depths shallower than 2000 m where most of the sampling events took place. Predictors variables included bathymetric position indexes (5 km and 20 km radii), slope, particulate organic carbon flux, seawater chemistry (principal component of dissolved near-seafloor nutrient concentration and calcite/aragonite saturation levels) and near seafloor values of current speed, oxygen saturation and temperature. Presence records were obtained from two different sources: species annotations from underwater imagery (76%) and longline and handline bycatch records (24 %).The published data include: 1. Binary GAM and Maxent habitat suitability predictions. A bootstrap process (n = 100) evaluated the local confidence of model predictions. Each bootstrap iteration sampled occurrence data with replacement, fitted HSMs models and produced binary suitability maps based on sensitivity‐specificity sum maximization thresholds. Depending on the number of times individual raster cells were predicted as suitable they were classified as: low [1-30%), medium [30-70%) or high [70-100%] confidence suitable cells. This process was repeated independently for GAM and Maxent models. In raster layers: (3) identifies high-confidence suitable cells, (2) medium-confidence suitable cells, (1) low-confidence suitable cells and NAs unsuitable cells. 2. Local fuzzy matching of GAM and Maxent habitat suitability predictions. The level of similarity between the spatial distribution of GAM and Maxent binary predictions (low, medium and high confidence suitable cells) at a local (i.e. cell) level was measured considering two membership functions: category similarity, which assumed that some categories were more similar than others; distance decay, which defined the fuzzy similarity of two cells as (i) identical if they matched perfectly, (ii) linearly decreasing with distance if the matching category was found within a 2-cell radius (~2 km) or (iii) totally different when no matching category was found within a 2-cell radius. After combining the two membership functions similarity scores ranged from 0 (totally different) to 1 (identical). Values of similarity greater than 0.5 indicate raster cells that are more similar than different.3. Combined habitat suitability maps. Suitable raster cells of combined habitat suitability maps were classified as follows: (i) high confidence suitable cell (3 in raster layers), raster cell predicted as suitable with high-confidence by both GAM and Maxent models; (ii) medium confidence suitable cell (2 in raster layers), raster cell predicted as suitable with medium or high confidence by GAM, Maxent or both and with a local fuzzy similarity greater than 0.5; (iii) low confidence suitable cell (1 in raster layers), any other cell predicted as suitable by GAM and/or Maxent.4. Cold water coral richness based on habitat suitability predictions. The .tif file shows the number of taxa predicted as suitable for each raster cell. Note that only high confidence suitable cells of combined habitat suitability maps are considered.

It is increasingly recognised that deep-sea mining of seafloor massive sulphides (SMS) could become an important source of mineral resources. These operations will remove the targeted substrate and produce potentially sediment toxic plumes from in situ seabed excavation and from the return water pumped back down to the seafloor. However, the spatial extent of the impacts of deep-sea mining plumes is still uncertain because few field experiments and models of plumes dispersion have been conducted. Morato et al. (2022) used three-dimensional hydrodynamic models of the Azores region together with a theoretical commercial mining operation of polymetallic SMS to simulate the potential dispersal of sediment plumes originating from different phases of mining operations and to assess the magnitude of potential impacts. The areas used in the modelling work were (from North to South): Cavala seamount (38.265, -30.710), Lucky Strike Hole (37.503, -31.955), Menez Hom (37.109, -32.618), Famous (37.001, -33.039), Saldanha (36.658, -33.420), and Rainbow (36.262 -33.824). The datasets published here contain all the model outputs, namely for 1) the in situ excavation sediment plume, 2) the return water discharge plume, and 3) the return sediments discharge plume:1) The concentration of solids and of the discharge water in each horizontal 2-dimensional space cell is calculated as the maximum concentration in the 50 vertical layers of each 2-dimensional cell, for each output time step (3 hours), averaged over all time steps during each trimester and during a 12-months simulation.1.1) Concentration of sediments produced during the in situ excavation sediment plume calculated as the maximum concentration in the 50 vertical layers of each 2-dimensional cell, for each output time step (3 hours), averaged over all time steps during a 12-months simulation. Sediments were composed of six classes of different particle diameter (0-10 μm, 10-50 μm, 50-100 μm, 100-200 μm, 200-2,000 μm, and >2,000 μm), an average particle density of 3,780 kg·m-3, and resultant settling velocities ranging from 75.1 cm·s-1 to 0.002 cm·s-1.1.2) Concentration of return water discharge plume (shown in dilution folds) in six study areas calculated as the maximum concentration in the 50 vertical layers of each 2-dimensional cell, for each output time step (3 hours), averaged over all time steps during a 12-months simulation and assuming a control temperature as the annual minimum temperature of each location (T1). The salinity of discharge was calculated assuming the MOHID salinity of 83.3% surface water and 16.7% of seafloor water.1.3) Concentration of sediments in the return sediment discharge plume, calculated as the maximum concentration in the 50 vertical layers of each 2-dimensional cell, for each output time step (3 hours), averaged over all time steps during a 12-months simulation. The average particle diameter was assumed to be 4 µm with an average particle density of 3,780 kg·m-3 and a resultant settling velocity of 0.002 cm·s-1.2) The proportion of simulated time (temporal frequency) that a specific 2-dimensional space contained plume concentrations higher than the adopted thresholds; 1.2 mg·L-1 for sediment solids and 5,000 fold dilution for discharge water. Those cells whose temporal frequency above the thresholds was greater than 50%, i.e. 6 months out of 12 months, were considered as cells with persistent plumes.2.1) Proportion of simulated time (temporal frequency) that a specific a 2-dimensional space cell, in six study areas, contained in situ excavation sediment plume above a 1.2 mg·L-1 concentration threshold, during a 12-months simulation, assuming six classes of particle diameter (0-10 μm, 10-50 μm, 50-100 μm, 100-200 μm, 200-2,000 μm, and >2,000 μm), an average particle density of 3,780 kg·m-3, and resultant settling velocities ranging from 75.1 cm·s-1 to 0.002 cm·s-1.2.2) Proportion of simulated time (temporal frequency) that a specific 2-dimensional space, in six study areas, contained return water discharge plume concentrations higher than the adopted thresholds (i.e., 5,000 fold dilution), during a 12-months simulation and assuming a control temperature as the annual minimum temperature of each location (T1). The salinity of discharge was calculated assuming the MOHID salinity of 83.3% surface water and 16.7% of seafloor water.2.3) Proportion of simulated time (temporal frequency) that a specific 2-dimensional space cell, in six study areas, contained return sediments discharge plume above a 1.2 mg·L-1 concentration threshold, during a 12-months simulation, assuming an average particle diameter of 4 µm, an average particle density of 3,780 kg·m-3, and a resultant settling velocity of 0.002 cm·s-1.3) In addition to the thresholds and targets described above, the datasets also present the model results for Cavala seamount and Lucky Strike Hole against other thresholds: 5 mg·L-1, 10 mg·L-1 and 25 mg·L-1 for sediments and 1,000, 600, 300 and 200 fold dilution for discharge water.4) Seasonal variations in the model outputs for plumes dispersal are also presented for Cavala seamount and Lucky Strike Hole by computing the probability of concentration above thresholds for four periods of three months (January-March, April-June, July-September, and October-December). In these scenarios, the model run duration was approximately 90 days.5) The sediment thickness of the settled sediments from the discharge sediment and excavation.5.1) Bottom thickness of settled sediments produced during the in situ excavation sediment plume assuming six classes of particle diameter (0-10 μm, 10-50 μm, 50-100 μm, 100-200 μm, 200-2,000 μm, and >2,000 μm), an average particle density of 3,780 kg·m-3, and resultant settling velocities ranging from 75.1 cm·s-1 to 0.002 cm·s-1. The duration of the simulation is one year.5.2) Bottom thickness of settled sediments from the return sediment discharge plume modelled assuming an average particle diameter of 4 µm, an average particle density of 3,780 kg·m-3, and a resultant settling velocity of 0.002 cm·s-1. The duration of the simulation is one year.

Annotation of Paragorgia johnsoni Gray, 1862 colonies from underwater video footage recorded during the Blue Azores 2018 Expedition with the ROV Luso onboard the NRP Almirante Gago Coutinho, Station 57, Dive 15 (June 23^rd, 2018). The images correspond to the octocoral garden discovered between 545 and 595 m depth on the slopes of a small ridge-like structure located on the Mid-Atlantic Ridge, in the Azores region.

Description: We developed predictive distribution models of deep-sea elasmobranchs for up to 2000 m depth in the Azores EEZ and neighboring seamounts, from approximately 33°N to 43°N and 20°W to 36°W. Georeferenced presence, absence, and abundance data were obtained from scientific surveys and commercial operations reporting at least one deep-sea elasmobranch capture. A 20-year 'survey dataset' (1996-2017) was compiled from annual scientific demersal surveys using two types of bottom longlines (types LLA and LLB), and an 'observer dataset' (2004-2018) from observer programs covering commercial fisheries operations using bottom longline (similar to type LLA) and vertical handline ('gorazeira'). We used the most ecologically relevant candidate environmental predictors for explaining the spatial distribution of deep-sea elasmobranch in the Azores: depth, slope, northness, eastness, Bathymetric Position Index (BPI), nitrates, and near bottom currents. We merged existing multibeam data for the Azores EEZ with bathymetry data extracted from EMODNET (EMODnet Bathymetry Consortium 2018) to calculate depth values (down to 2000m). All variables were projected with the Albers equal-area conical projection centered in the middle of the study area and were rescaled using bilinear interpolation to a final grid cell resolution of 1.12 x1.12 km (i.e., 0.012°). Slope, northness, and eastness were computed from the depth raster using the function terrain in the R package raster. BPI was derived from the rescaled depth with an inner radius of 3 and an outer radius of 25 grid cells using the Benthic Terrain Model 3.0 tool in ArcGIS 10.1. Nitrates were extracted from Amorim et al. (2017). Near-bottom current speed (m·s-1) average values were based on a MOHID hydrodynamic model application (Viegas et al., 2018) with an original resolution of 0.054°. Besides the environmental variables, we also included three operational predictors in the analysis: year, fishing effort (number of hooks) and gear type (longline LLA and LLB, and gorazeira).

Abstract Ecosystem-based marine spatial planning is an approach to managing maritime activities while ensuring human well-being and biodiversity conservation as key pillars for sustainable development. Here, we use a comprehensive literature review and a co-development process with experts to build an assessment framework and tool that integrates the fundamental principles of an ecosystem approach to management and translates them into specific actions to be undertaken during planning processes. We illustrate the potential of this tool through the evaluation of two national marine spatial plans (Spain and France), in consultation with the representatives involved in their development and implementation. To ensure more coherent future planning, socio-ecological system evolution in a climate change scenario and the future marine space needs of maritime sectors should be considered, as well as improving the governance structure and knowledge of ecosystem processes. This framework provides a consistent and transparent assessment method for practitioners and competent authorities.

<p>In international fisheries management, scientific advice on the presence of "vulnerable marine ecosystems" (VMEs) per United Nations resolutions, has generally used qualitative assessments based on expert judgment of the occurrence of indicator taxa such as cold-water corals and sponges. Use of expert judgment alone can be criticized for inconsistency and sometimes a lack of transparency; therefore, development of robust and repeatable numeric methods to detect the presence of VMEs would be advantageous. Here, we present a multi-criteria assessment (MCA) method to evaluate how likely a given area of seafloor represents a VME. The MCA is a taxa-dependent spatial method that accounts for both the quantity and data quality available. This was applied to a database of records of VMEs built, held and compiled by the International Council for the Exploration of the Sea (ICES). A VME index was generated which ranged from 1.51 to 4.52, with 5.0 being reserved for confirmed VME habitats. An index of confidence was also computed that ranged from 0.0 to 0.75, with 1 being reserved for those confirmed VME habitats. Overall the MCA captured the important elements of the ICES VME database and provided a simplified, spatially aggregated, and weighted estimate of how likely a given area is to contain VMEs. The associated estimate of confidence gave an indication of how uncertain that assessment was for the same given area. This methodology provides a more systematic and standardized approach for assessing the likelihood of presence of VMEs in the North-East Atlantic.</p>

Zoological nomenclature revisions are essential for biodiversity studies and indispensable to avoid naming and description of already described species and should be valued in all subsequent studies considering biology, molecular biology, ecology or habitat mapping of deep-sea species. Herein, a thorough revision of the taxonomic literature on Octocorallia since the beginning of deep-sea exploration in the Azores is provided. Since 1870, when the first octocoral, Virgularia mirabilis (Müller, 1776), was recorded in the Azores a cyclic pattern on the taxonomical study of octocorals reveals the deep-sea investigation efforts made on the region at different periods: Prince Albert I of Monaco, Biaçores and recent expeditions. The first decade of this millennium was the peak on taxonomic research of cold-water octocorals in the Azores with 11 publications targeting gorgonians and soft corals (Alcyonacea) and specific sub-orders within it. Ninety-eight names of Octocorallia were found to be given in the economic exclusive zone of the Azores. While 25 names were changed or added to the known Azorean octocoral diversity, 3 species identified in the region and unreported in the reviewed literature, increase the number to 101 species. Twenty-five names were synonymized while three species names were unmasked as errors in need of taxonomical clarification. This is the highest species richness of Octocorallia found in Europe and in any Northern Atlantic archipelago so far, representing ~60% of the most diverse center of endemism of South Africa, with a part in the Eastern Atlantic. Further research on taxonomy may reveal new species to science.

Video and image data are regularly used in the field of benthic ecology to document biodiversity. However, their use is subject to a number of challenges, principally the identification of taxa within the images without associated physical specimens. The challenge of applying traditional taxonomic keys to the identification of fauna from images has led to the development of personal, group, or institution level reference image catalogues of operational taxonomic units (OTUs) or morphospecies. Lack of standardisation among these reference catalogues has led to problems with observer bias and the inability to combine datasets across studies. In addition, lack of a common reference standard is stifling efforts in the application of artificial intelligence to taxon identification. Using the North Atlantic deep sea as a case study, we propose a database structure to facilitate standardisation of morphospecies image catalogues between research groups and support future use in multiple front-end applications. We also propose a framework for coordination of international efforts to develop reference guides for the identification of marine species from images. The proposed structure maps to the Darwin Core standard to allow integration with existing databases. We suggest a management framework where high-level taxonomic groups are curated by a regional team, consisting of both end users and taxonomic experts. We identify a mechanism by which overall quality of data within a common reference guide could be raised over the next decade. Finally, we discuss the role of a common reference standard in advancing marine ecology and supporting sustainable use of this ecosystem.

Seamounts constitute an obstacle to the ocean circulation, modifying it. As a result, a variety of hydrodynamical processes and phenomena may take place over seamounts, among others, flow intensification, current deflection, upwelling, Taylor caps, and internal waves. These oceanographic effects may turn seamounts into very productive ecosystems with high species diversity, and in some cases, are densely populated by benthic organisms, such corals, gorgonians, and sponges. In this study, we describe the oceanographic conditions over seamounts and other underwater features in the path of the Mediterranean Outflow Water (MOW), where populations of benthic suspensions feeders have been observed. Using CTD, LADPC and biochemical measurements carried out in the Ormonde and Formigas seamounts and the Gazul mud volcano (Northeast Atlantic), we show that Taylor caps were not observed in any of the sampled features. However, we point out that the relatively high values of the Brunt–Väisälä frequency in the MOW halocline, in conjunction with the slope of the seamount flanks, set up conditions for the breakout of internal waves and amplification of the currents. This may enhance the vertical mixing, resuspending the organic material deposited on the seafloor and, therefore, increasing the food availability for the communities dominated by benthic suspension feeders. Thus, we hypothesize that internal waves could be improving the conditions for benthic suspension feeders to grow on the slope of seamounts.

The increasing public perception that marine megafauna is under threat is an outstanding incentive to investigate their essential habitats (EMH), their responses to human and climate change pressures, and to better understand their largely unexplained behaviors and physiology. Yet, this poses serious challenges such as the elusiveness and remoteness of marine megafauna, the growing scrutiny and legal impositions on their study, and difficulties in disentangling environmental drivers from human disturbance. We argue that advancing our knowledge and conservation on marine megafauna can and should be capitalized in regions where exceptional access to multiple species (i.e. megafauna ‘hotspots’) combines with the adequate legal framework, sustainable practices, and research capacity. The wider Azores region, hosting EMHs of all key groups of vulnerable or endangered vertebrate marine megafauna, is a singular EMH hotspot on a migratory crossroads, linking eastern and western Atlantic margins and productive boreal waters to tropical seas. It benefits from a sustainable development model based on artisanal fisheries with zero or minor megafauna bycatch, and one of the largest marine protected area networks in the Atlantic covering coastal, oceanic and deepsea habitats. Developing this model can largely ensure the future integrity of this EMH hotspot while fostering cutting-edge science and technological development on megafauna behavior, biologging and increased ocean observation, with potential major impacts on the Blue Growth agenda. An action plan is proposed.

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.

Circulation patterns in the North Atlantic Ocean have changed and re-organized multiple times over millions of years, influencing the biodiversity, distribution and connectivity patterns of deep-sea species and ecosystems. In this study, we review the effects of the water mass properties (temperature, salinity, food supply, carbonate chemistry and oxygen) on deep-sea benthic megafauna (from species to community level) and discussed in future scenarios of climate change. We focus on the key oceanic controls on deep-sea megafauna biodiversity and biogeography patterns. We place particular attention on cold-water corals and sponges, as these are ecosystem-engineering organisms that constitute vulnerable marine ecosystems with high associated biodiversity. Besides documenting the current state of the knowledge on this topic, a future scenario for water mass properties in the deep North Atlantic basin was predicted. The pace and severity of climate change in the deep-sea will vary across regions. However, predicted water mass properties showed that all regions in the North Atlantic will be exposed to multiple stressors by 2100, experiencing at least one critical change in water temperature (+2°C), organic carbon fluxes (reduced up to 50 %), ocean acidification (pH reduced up to 0.3), aragonite saturation horizon (shoaling above 1000 m) and/or reduction in dissolved oxygen (5%). The northernmost regions of the North Atlantic will suffer the greatest impacts. Warmer and more acidic oceans will drastically reduce the suitable habitat for ecosystem-engineers, with severe consequences such as declines in population densities, even compromising their long-term survival, loss of biodiversity and reduced biogeographic distribution that might compromise connectivity at large scales. These effects can be aggravated by reductions in carbon fluxes, particularly in areas where food availability is already limited. Declines in benthic biomass and biodiversity will diminish ecosystem services such as habitat provision, nutrient cycling, etc. This study shows that the deep-sea vulnerable marine ecosystems affected by contemporary anthropogenic impacts and with the the ongoing climate change impacts are unlikely to withstand additional pressures from more intrusive human activities. This study serves also as a warning to protect these ecosystems through regulations and by tempering the ongoing socio-political drivers for increasing exploitation of marine resources.

EDITORIAL article Front. Mar. Sci., 30 October 2020 | https://doi.org/10.3389/fmars.2020.601798

The deep sea is the largest biome on Earth but the least explored. Our knowledge of it comes from scattered sources spanning different spatial and temporal scales. Implementation of marine policies like the European Union’s Marine Strategy Framework Directive (MSFD) and support for Blue Growth in the deep sea are therefore hindered by lack of data. Integrated assessments of environmental status require tools to work with different and disaggregated datasets (e.g. density of deep-sea habitat-forming species, body-size distribution of commercial fishes, intensity of bottom trawling) across spatial and temporal scales. A feasibility study was conducted as part of the four-year ATLAS project to assess the effectiveness of the open-access Nested Environmental status Assessment Tool (NEAT) to assess deep-sea environmental status. We worked at nine selected study areas in the North Atlantic focusing on five MSFD descriptors (D1-Biodiversity, D3-Commercial fish and shellfish, D4-Food webs, D6-Seafloor integrity, D10-Marine litter). The objectives of the present study were to i) explore and propose indicators that could be used in the assessment of deep-sea environmental status, ii) evaluate the performance of NEAT in the deep sea, and iii) identify challenges and opportunities for the assessment of deep-sea status. Based on data availability, data quality and expert judgement, in total 24 indicators (one for D1, one for D3, seven for D4, 13 for D6, two for D10) were used in the assessment of the nine study areas, their habitats and ecosystem components. NEAT analyses revealed differences among the study areas for their environmental status ranging from “poor” to “high”. Overall, the NEAT results were in moderate to complete agreement with expert judgement, previous assessments, scientific literature on human-pressure gradients and expected management outcomes. We suggest that the assessment of deep-sea environmental status should take place at habitat and ecosystem level (rather than at species level) and at relatively large spatial scales, in comparison to shallow-water areas. Limited knowledge across space (e.g. distribution of habitat-forming species) and the scarcity of long-term data sets limit our knowledge about natural variability and human impacts in the deep sea preventing a more systematic assessment of habitat and ecosystem components in the deep sea. However, stronger cross-sectoral collaborations, the use of novel technologies and open data-sharing platforms will be critical for establishing environmental baseline indicator values in the deep sea that will contribute to the science base supporting the implementation of marine policies and stimulating Blue Growth.

Co-designing a multidisciplinary deep-ocean observing programme at the Mid-Atlantic Ridge in the Azores region

Deep-sea mining activities are expected to impact deep-sea biota through the generation of sediment plumes that disperse across vast areas of the ocean. Benthic sessile suspension-feeding fauna, such as cold-water corals, may be particularly susceptible to increased suspended sediments. Here, we exposed the cold-water octocoral, Dentomuricea aff. meteor to suspended particles generated during potential mining activities in a four weeks experimental study. Corals were exposed to three experimental treatments: (1) control conditions (no added sediments); (2) suspended polymetallic sulphide (PMS) particles; (3) suspended quartz particles. The two particle treatments were designed to distinguish between potential mechanical and toxicological effects of mining particles. PMS particles were obtained by grinding PMS inactive chimney rocks collected at the hydrothermal vent field Lucky Strike. Both particle types were delivered at a concentration of 25 mg L -1 , but achieved suspended concentrations were 2-3 mg L -1 for the PMS and 15-18 mg L -1 for the quartz particles due to the different particle density. Results of the experiment revealed a significant increase in dissolved cobalt, copper and manganese concentrations in the PMS treatment, resulting from the oxidation of sulphides in contact with seawater. Negative effects of PMS exposure included a progressive loss in tissue condition with necrosis and bioaccumulation of copper in coral tissues and skeletons, and death of all coral fragments by the end of the experiment. Physiological changes under PMS exposure, included increased respiration and ammonia excretion rates in corals after 13 days of exposure, indicating physiological stress and potential metabolic exhaustion. Changes in the cellular stress biomarkers and gene expression profiles were more pronounced in corals exposed to quartz particles, suggesting that the mechanical effect of particles although not causing measurable changes in the physiological functions of the coral, can still be detrimental to corals by eliciting cellular stress and immune responses. We hypothesize that the high mortality of corals recorded in the PMS treatment may have resulted from the combined and potentially synergistic mechanical and toxicological effects of the PMS particles. Given the dispersal potential of mining plumes and the highly sensitive nature of octocorals, marine protected areas, buffer areas or non-mining areas may be necessary to protect deep-sea coral communities.

It is increasingly recognised that deep-sea mining of seafloor massive sulphides (SMS) could become an important source of mineral resources. These operations will remove the targeted substrate and produce potentially toxic plumes from in situ seabed excavation and from the return water pumped back down to the seafloor. However, the spatial extent of the impact of deep-sea mining is still uncertain because few field experiments and models of plume dispersion have been conducted. In this study, we used three-dimensional hydrodynamic models of the Azores region together with a theoretical commercial mining operation of polymetallic SMS to simulate the potential dispersal of plumes originating from different phases of mining operations, and to assess the magnitude of potential impacts. Although the model simulations presented here were subject to many caveats, they did reveal some important patterns. The model projected marked differences among sites making generalisations about plume-dispersal patterns in mid-ocean ridges difficult. Nevertheless, the models predicted large horizontal and vertical plume-dispersals above the thresholds adopted. Persistent plumes (temporal frequency &gt;50%, i.e., 6 months out of 12 months) were projected to disperse an average linear distance of 10 to 20 km, cover an area of 17 to 150 km2, and extend more than 800 m in the water column. In fact, the model projected that plumes may disperse beyond the licensed mining areas, reach the flanks and summits of nearby topographic features, and extend into the bathypelagic, mesopelagic, and epipelagic environments. Modelled plume-dispersal overlaps with the predicted distribution of cold-water corals and with existing fishing activities. These potential impacts would be of particular concern in regions such as the Azores, where local populations are highly dependent on the sea for their livelihoods. The findings of this study are an important initial step towards understanding the nature and magnitude of deep-sea mining impacts in space and time.

Abstract Deep‐sea exploration relies on cutting‐edge technology, which generally requires expensive instruments, highly specialized technicians and ship time. The increasing need to gather large‐scale data on the distribution and conservation status of deep‐sea benthic species and habitats could benefit from the availability of low‐cost imaging tools to facilitate the access to the deep sea world‐wide. Here we describe the Azor drift‐cam, a cost‐effective video platform designed to conduct rapid appraisals of deep‐sea benthic habitats. Built with off‐the‐shelf components, the Azor drift‐cam should be regarded as an effective, affordable, simple‐to‐assemble, easy‐to‐operate, resilient, operational and reliable tool to visually explore the deep sea to 1,000 m depth. Its performance was assessed during the MapGES_2019 cruise, where 135 successful dives between 100 and 800 m depth were carried out in 22 working days, providing over 100 hr of images for almost 80 km of seabed, mostly in areas that had never been explored before. The system does not aim to become a substitute for more sophisticated underwater video and photography platforms, such as ROVs, AUVs or manned submersibles. Rather, it aims to provide the means to perform quick assessments of deep‐sea benthic habitats in a simple and affordable manner. This drift‐cam system has the potential to make deep‐sea exploration more accessible, playing an important role in the Deep‐Ocean Observing Strategy and measuring some of the Essential Ocean Variables for deep‐sea monitoring and conservation strategies.

Abandoned, lost, or discarded fishing gear (ALDFG), represents a significant percentage of the global plastic pollution, currently considered one of the major sources from sea-based activities. However, there is still limited understanding of the quantities of ALDFG present on the seafloor and their impacts. In this study, data on the presence of ALDFG was obtained from a large archive of seafloor video footage (351 dives) collected by different imaging platforms in the Azores region over 15 years (2006-2020). Most ALDFG items observed in the images relate to the local bottom longline fishery operating in the region, and include longlines but also anchors, weights, cables and buoys. A generalized additive mixed model (GAMM) was used to predict the distribution and abundance of ALDFG over the seafloor within the limits of the Azores Exclusive Economic Zone (EEZ) using a suite of environmental and anthropogenic variables. We estimated an average of 113 ± 310 items km^-2 (597 ± 756 per km^-2 above 1000 m depth), which could imply that over 20 million ALDFG items are present on the deep seafloor of the Azores EEZ. The resulting model identified potential hotspots of ALDFG along the seabed, some of them located over sensitive benthic habitats, such as specific seamounts. In addition, the interactions between ALDFG and benthic organisms were also analysed. Numerous entanglements were observed with several species of large anthozoans and sponges. The use of predictive distribution modelling for ALDFG should be regarded as a useful tool to support ecosystem-based management, which can provide indirect information about fishing pressure and allow the identification of potential high-risk areas. Additional knowledge about the sources, amounts, fates and impacts of ALDFG will be key to address the global issue of plastic pollution and the effects of fishing on marine ecosystems.