Lenaick Menot

Cold-water coral reefs, classified as vulnerable marine ecosystems, and as such, their good conservation status is a target for an increasing number of regional and international regulations. Beyond present-day anthropogenic disturbances, deep-sea corals are under long-term threat from ocean warming and acidification. These ecosystem changes call for the implementation of long-term and high frequency ocean monitoring systems.,Here we present the design, implementation, and operational performance of the MARLEY observatory (Monitoring deep-seA coRaL EcosYstems), an autonomous, multi-parameter platform deployed in the Lampaul Canyon (Bay of Biscay) at 776 metres depth to monitor cold-water coral health with minimal environmental footprint. A primary design objective was to eliminate the deposition of dead weight on the seafloor, which represents a significant source of cumulative waste. To achieve this, MARLEY incorporates reversible ballasts enabling dynamic buoyancy adjustment during deployment and recovery. The platform features a decoupled camera module that allows flexible positioning of sensors relative to coral colonies while maintaining the main lander on sedimented peripheries.,For its first deployment in the Lampaul Canyon (Bay of Biscay), MARLEY successfully monitored Madrepora oculata polyp behaviour, associated fauna, and environmental parameters over a five-month operational period. Video data processing employed convolutional neural networks to classify polyp behaviour. Associated fauna was annotated via the Ocean Spy citizen science platform, demonstrating effective public engagement. Despite current limitations in real-time automated analysis, MARLEY demonstrates the feasibility of long-term, waste-free deep-sea observatories capable of generating essential variables for coral ecosystem health assessment and conservation management.

Reef-building cold-water corals act as ecosystem engineers in the deep-sea, supporting a rich biodiversity and various ecosystem services, including fisheries resources, carbon sink, paleoclimate archives and biomedical compounds. The study and the protection of these ecosystems is an important pillar of strategies for assessing the ecological status and conservation of the biodiversity associated to deep reef habitats, as promoted by various national and international conventions (IUCN, Habitat Directive, Marine Framework Directive…).In submarine canyons, coral reefs face major threats: climate change, pollution (particularly plastics and other waste discharges) and fishing activities (trawling and longlining). The corals of the Mediterranean Sea are particularly at risk as they are already living close to their known upper thermal maximum (i.e., 13°C), the Mediterranean canyons are among the most polluted in the world (with an average of 51,000 items.km-2), and are subject to direct or indirect damage by trawling in the canyons and on the outer shelf.To characterize the response of the main reef building species and their resilience to global change, in situ and controlled aquaria experiments have been conducted over the last 15 years on corals from the Gulf of Lion and the Bay of Biscay. In particular, the impact of temperature, exposure to plastics and sediment flux were investigated, showing the urgent need for collective awareness and the implementation of drastic management measures. Cross-border areas such as the French-Spanish zone are particularly sensitive because of the difficulties in regulating human activities and applying conservation measures. Supra-national regulatory processes must be engaged to act coercively on limiting the impacts of global change.

Ifremer is the French research institute entirely dedicated to the ocean. As part of its mission of public policy support, Ifremer, sponsored by France, holds two contracts for the exploration of deep-sea minerals in the Area with the International Seabed Authority (ISA), one for polymetallic nodules in the Pacific Ocean, the other for polymetallic sulphides along the Mid-Atlantic Ridge.As per the ISA regulations for the exploration of deep-sea minerals, an exploration contract involves: assessing the mineral resources; defining the environmental baseline; assessing and monitoring the impact of exploration activities that could impact the environment; developing mining and processing technologies; and providing training opportunities to the personnel of the ISA and developing States. Deep-sea environments, where mineral resources are found, are home to a wealth of life that is still largely unknown, as is their role in the major global cycles. Starting their exploitation at this stage could have irreversible impacts on these ecosystems and on the overall functioning of the oceans. Although this places Ifremer, as a research institute and contractor in a peculiar position, it justifies a focus on further studying the functioning of the ecosystems associated to marine minerals resources and their role in the global functioning of the ocean, prerequisites to inform future decisions and the set-up of adequate regulations.In this context and in line with Ifremer’s scientific strategy, the objectives of Ifremer’s programmes of activities, funded by the French government under the France 2030 “deep-sea” programme, are:Nodules:Improve the confidence in the resource assessment by performing additional sampling and acquiring acoustic and optical high resolution data; Progress our knowledge of biological communities: quantify and model the impact of test-mining activities; characterize habitats and benthic fauna; improve the tools of integrative taxonomy; define an environmental impact assessment and monitoring strategy. Sulphides:Conduct a first unclassified resource assessment of the TAG hydrothermal vent field, identify new sites and conduct local exploration; Increase knowledge on biological diversity, ecosystem dynamics and functioning and habitat characterization of active and inactive vent sites, life cycles, colonization processes and connectivity of species; improve knowledge on microbial communities and fauna of inactive vent sites; study of adaptation and acclimation capacities of communities to assess their resilience. Beyond this research conducted as a contractor, Ifremer is also contributing to: the development of methodologies to facilitate the assessment of the deep-sea biodiversity, the taxonomic identification of deep-sea species and the monitoring of hydrothermal fields; capacity development via initiatives such as Meioscool; the independent assessment of the environmental impact of the test of the “Patania II” prototype, conducted by Global Sea Mineral Resources, as a partner to the Joint Programming Initiatives Oceans projects “Mining Impact” I and II led by Geomar; and to the work of the ISA by participating to ISA led workshops and by providing scientific expertise to the French Ministries for their contribution to the development of the ISA regulations and recommendations. The presentation will highlight some key scientific results and contributions as an ISA contractor as described above.

Cold-water coral reefs and communities can be locally important calcium carbonate factories in continental shelf and slope environments. Cold-water coral mounds dominated by Desmophyllum pertusum (=Lophelia pertusa) occur within Bay of Biscay submarine canyons. Here we present a late Holocene record of coral carbonate accumulation through a colonial scleractinian coral mound in the 750-850 m depth range in Guilvinec Canyon, northern Bay of Biscay. Guilvinec Canyon, like most submarine canyons of the Bay of Biscay, is a dominantly siliciclastic sandy environment, with occasional coral gardens. Maximum live coral cover in the area surveyed in Guilvinec Canyon was about 9%, measured close to the site of the sediment core analyzed.A 2011 sediment core through the mound recovered 1.18 m of sediment, consisting of mostly siliciclastic silty sand and coral gravel, strongly dominated by Lophelia pertusa fragments. In addition to standard geophysical, grain size, and mineralogical analyses, the core was analyzed by CT-scan. The number of coral calices visible per cm3 was counted, and the core was subsampled for coral calice abundance and mass in 5 mm increments, calculating the number of calices and mass of coral carbonate skeletons per cm3 subsample. An age model from previous 14C and U/Th ages of coral fragments in the core yielded a long-term average coral carbonate accretion rate of 78 g CaCO3 m-2 y-1 over the past ~2150 y, divided into two phases: 40.8 g CaCO3 m-2 y-1 (from core-bottom to -59 cm, approximately 685 ybp), and 156.2 g CaCO3 m-2 y-1 in the upper half of the core. Coarse coral-dominated gravel in the core-catcher contained coral fragments approximately 7 ka in age, indicating a long hiatus before the renewal of coral growth at this site. Aragonite % in the fine sediment was not correlated with coral abundance in the core. A second core recovered nearby was composed of siliciclastic silty sand, but contained almost no coral fragments. The large variation between the two cores indicates high levels of local heterogeneity in sediment accumulation patterns, apparently much greater than the variation in live coral cover at the surface.Coral carbonate accumulation rates in Guilvinec Canyon were 1-2 orders of magnitude lower than coral carbonate accumulation estimates from Lophelia pertusa reefs on the Norwegian Margin. Nonetheless, coral carbonate accumulation rates in the core were an order of magnitude higher than Recent coral carbonate production rates based on ROV-video estimates of coral biomass and published growth rates. This difference may be attributable to time-averaging, local heterogeneity, changes in sedimentation or current regime, or to late-20th century decline in coral abundance resulting from a variety of anthropogenic pressures. Recent threats to Bay of Biscay cold-water coral reefs include increased sediment mobilization from bottom trawling near the heads of submarine canyons, rising seawater temperatures, and declining aragonite saturation. New field and lab experiments on coral growth rates and skeletal degradation may help to disentangle anthropogenic pressures and project the fate of Bay of Biscay cold-water coral reefs in the face of climate change and ocean acidification.

Imagery has become one of the main data sources for investigating seascape spatial patterns. This is particularly true in deep-sea environments, which are only accessible with underwater vehicles. On the one hand, using collaborative web-based tools and machine learning algorithms, biological and geological features can now be massively annotated on 2D images with the support of experts. On the other hand, geomorphometrics such as slope or rugosity derived from 3D models built with structure from motion (sfm) methodology can then be used to answer spatial distribution questions. However, precise georeferencing of 2D annotations on 3D models has proven challenging for deep-sea images, due to a large mismatch between navigation obtained from underwater vehicles and the reprojected navigation computed in the process of building 3D models. In addition, although 3D models can be directly annotated, the process becomes challenging due to the low resolution of textures and the large size of the models. In this article, we propose a streamlined, open-access processing pipeline to reproject 2D image annotations onto 3D models using ray tracing. Using four underwater image datasets, we assessed the accuracy of annotation reprojection on 3D models and achieved successful georeferencing to centimetric accuracy. The combination of photogrammetric 3D models and accurate 2D annotations would allow the construction of a 3D representation of the landscape and could provide new insights into understanding species microdistribution and biotic interactions.

In the abyssal equatorial Pacific Ocean, most of the seafloor of the Clarion-Clipperton Fracture Zone (CCFZ), a 6 million km² polymetallic nodule province, has been preempted for future mining. In light of the large environmental footprint that mining would leave and given the diversity and the vulnerability of the abyssal fauna, the International Seabed Authority has implemented a regional management plan that includes the creation of nine Areas of Particular Environmental Interest (APEIs) located at the periphery of the CCFZ. The scientific principles for the design of the APEIs were based on the best – albeit very limited – knowledge of the area. The fauna and habitats in the APEIs are unknown, as are species' ranges and the extent of biodiversity across the CCFZ. As part of the Joint Programming Initiative Healthy and Productive Seas and Oceans (JPI Oceans) pilot action “Ecological aspects of deep-sea mining”, the SO239 cruise provided data to improve species inventories, determine species ranges, identify the drivers of beta diversity patterns and assess the representativeness of an APEI. Four exploration contract areas and an APEI (APEI no. 3) were sampled along a gradient of sea surface primary productivity that spanned a distance of 1440 km in the eastern CCFZ. Between three and eight quantitative box cores (0.25 m²; 0–10 cm) were sampled in each study area, resulting in a large collection of polychaetes that were morphologically and molecularly (cytochrome c oxidase subunit I and 16S genes) analyzed. A total of 275 polychaete morphospecies were identified. Only one morphospecies was shared among all five study areas and 49 % were singletons. The patterns in community structure and composition were mainly attributed to variations in organic carbon fluxes to the seafloor at the regional scale and nodule density at the local scale, thus supporting the main assumptions underlying the design of the APEIs. However, the APEI no. 3, which is located in an oligotrophic province and separated from the CCFZ by the Clarion Fracture Zone, showed the lowest densities, lowest diversity, and a very low and distant independent similarity in community composition compared to the contract areas, thus questioning the representativeness and the appropriateness of APEI no. 3 to meet its purpose of diversity preservation. Among the four exploration contracts, which belong to a mesotrophic province, the distance decay of similarity provided a species turnover of 0.04 species km⁻¹, an average species range of 25 km and an extrapolated richness of up to 240 000 polychaete species in the CCFZ. By contrast, nonparametric estimators of diversity predict a regional richness of up to 498 species. Both estimates are biased by the high frequency of singletons in the dataset, which likely result from under-sampling and merely reflect our level of uncertainty. The assessment of potential risks and scales of biodiversity loss due to nodule mining thus requires an appropriate inventory of species richness in the CCFZ.

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.