Developing expert scientific consensus on the environmental and societal effects of marine artificial structures prior to decommissioning.

Thousands of artificial ('human-made') structures are present in the marine environment, many at or approaching end-of-life and requiring urgent decisions regarding their decommissioning. No consensus has been reached on which decommissioning option(s) result in optimal environmental and societal outcomes, in part, owing to a paucity of evidence from real-world decommissioning case studies. To address this significant challenge, we asked a worldwide panel of scientists to provide their expert opinion. They were asked to identify and characterise the ecosystem effects of artificial structures in the sea, their causes and consequences, and to identify which, if any, should be retained following decommissioning. Experts considered that most of the pressures driving ecological and societal effects from marine artificial structures (MAS) were of medium severity, occur frequently, and are dependent on spatial scale with local-scale effects of greater magnitude than regional effects. The duration of many effects following decommissioning were considered to be relatively short, in the order of days. Overall, environmental effects of structures were considered marginally undesirable, while societal effects marginally desirable. Experts therefore indicated that any decision to leave MAS in place at end-of-life to be more beneficial to society than the natural environment. However, some individual environmental effects were considered desirable and worthy of retention, especially in certain geographic locations, where structures can support improved trophic linkages, increases in tourism, habitat provision, and population size, and provide stability in population dynamics. The expert analysis consensus that the effects of MAS are both negative and positive for the environment and society, gives no strong support for policy change whether removal or retention is favoured until further empirical evidence is available to justify change to the status quo. The combination of desirable and undesirable effects associated with MAS present a significant challenge for policy- and decision-makers in their justification to implement decommissioning options. Decisions may need to be decided on a case-by-case basis accounting for the trade-off in costs and benefits at a local level.

Carbonate compensation depth drives abyssal biogeography in the northeast Pacific.

Abyssal seafloor communities cover more than 60% of Earth's surface. Despite their great size, abyssal plains extend across modest environmental gradients compared to other marine ecosystems. However, little is known about the patterns and processes regulating biodiversity or potentially delimiting biogeographical boundaries at regional scales in the abyss. Improved macroecological understanding of remote abyssal environments is urgent as threats of widespread anthropogenic disturbance grow in the deep ocean. Here, we use a new, basin-scale dataset to show the existence of clear regional zonation in abyssal communities across the 5,000 km span of the Clarion-Clipperton Zone (northeast Pacific), an area targeted for deep-sea mining. We found two pronounced biogeographic provinces, deep and shallow-abyssal, separated by a transition zone between 4,300 and 4,800 m depth. Surprisingly, species richness was maintained across this boundary by phylum-level taxonomic replacements. These regional transitions are probably related to calcium carbonate saturation boundaries as taxa dependent on calcium carbonate structures, such as shelled molluscs, appear restricted to the shallower province. Our results suggest geochemical and climatic forcing on distributions of abyssal populations over large spatial scales and provide a potential paradigm for deep-sea macroecology, opening a new basis for regional-scale biodiversity research and conservation strategies in Earth's largest biome.

How many metazoan species live in the world's largest mineral exploration region?

The global surge in demand for metals such as cobalt and nickel has created unprecedented interest in deep-sea habitats with mineral resources. The largest area of activity is a 6 million km2 region known as the Clarion-Clipperton Zone (CCZ) in the central and eastern Pacific, regulated by the International Seabed Authority (ISA). Baseline biodiversity knowledge of the region is crucial to effective management of environmental impact from potential deep-sea mining activities, but until recently this has been almost completely lacking. The rapid growth in taxonomic outputs and data availability for the region over the last decade has allowed us to conduct the first comprehensive synthesis of CCZ benthic metazoan biodiversity for all faunal size classes. Here we present the CCZ Checklist, a biodiversity inventory of benthic metazoa vital to future assessments of environmental impacts. An estimated 92% of species identified from the CCZ are new to science (436 named species from a total of 5,578 recorded). This is likely to be an overestimate owing to synonyms in the data but is supported by analysis of recent taxonomic studies suggesting that 88% of species sampled in the region are undescribed. Species richness estimators place total CCZ metazoan benthic diversity at 6,233 (+/-82 SE) species for Chao1, and 7,620 (+/-132 SE) species for Chao2, most likely representing lower bounds of diversity in the region. Although uncertainty in estimates is high, regional syntheses become increasingly possible as comparable datasets accumulate. These will be vital to understanding ecological processes and risks of biodiversity loss.

Global variability in seawater Mg:Ca and Sr:Ca ratios in the modern ocean.

Seawater Mg:Ca and Sr:Ca ratios are biogeochemical parameters reflecting the Earth-ocean-atmosphere dynamic exchange of elements. The ratios' dependence on the environment and organisms' biology facilitates their application in marine sciences. Here, we present a measured single-laboratory dataset, combined with previous data, to test the assumption of limited seawater Mg:Ca and Sr:Ca variability across marine environments globally. High variability was found in open-ocean upwelling and polar regions, shelves/neritic and river-influenced areas, where seawater Mg:Ca and Sr:Ca ratios range from ∼4.40 to 6.40 mmol:mol and ∼6.95 to 9.80 mmol:mol, respectively. Open-ocean seawater Mg:Ca is semiconservative (∼4.90 to 5.30 mol:mol), while Sr:Ca is more variable and nonconservative (∼7.70 to 8.80 mmol:mol); both ratios are nonconservative in coastal seas. Further, the Ca, Mg, and Sr elemental fluxes are connected to large total alkalinity deviations from International Association for the Physical Sciences of the Oceans (IAPSO) standard values. Because there is significant modern seawater Mg:Ca and Sr:Ca ratios variability across marine environments we cannot absolutely assume that fossil archives using taxa-specific proxies reflect true global seawater chemistry but rather taxa- and process-specific ecosystem variations, reflecting regional conditions. This variability could reconcile secular seawater Mg:Ca and Sr:Ca ratio reconstructions using different taxa and techniques by assuming an error of 1 to 1.50 mol:mol, and 1 to 1.90 mmol:mol, respectively. The modern ratios' variability is similar to the reconstructed rise over 20 Ma (Neogene Period), nurturing the question of seminonconservative behavior of Ca, Mg, and Sr over modern Earth geological history with an overlooked environmental effect.

Climate change considerations are fundamental to management of deep-sea resource extraction.

Climate change manifestation in the ocean, through warming, oxygen loss, increasing acidification, and changing particulate organic carbon flux (one metric of altered food supply), is projected to affect most deep-ocean ecosystems concomitantly with increasing direct human disturbance. Climate drivers will alter deep-sea biodiversity and associated ecosystem services, and may interact with disturbance from resource extraction activities or even climate geoengineering. We suggest that to ensure the effective management of increasing use of the deep ocean (e.g., for bottom fishing, oil and gas extraction, and deep-seabed mining), environmental management and developing regulations must consider climate change. Strategic planning, impact assessment and monitoring, spatial management, application of the precautionary approach, and full-cost accounting of extraction activities should embrace climate consciousness. Coupled climate and biological modeling approaches applied in the water and on the seafloor can help accomplish this goal. For example, Earth-System Model projections of climate-change parameters at the seafloor reveal heterogeneity in projected climate hazard and time of emergence (beyond natural variability) in regions targeted for deep-seabed mining. Models that combine climate-induced changes in ocean circulation with particle tracking predict altered transport of early life stages (larvae) under climate change. Habitat suitability models can help assess the consequences of altered larval dispersal, predict climate refugia, and identify vulnerable regions for multiple species under climate change. Engaging the deep observing community can support the necessary data provisioning to mainstream climate into the development of environmental management plans. To illustrate this approach, we focus on deep-seabed mining and the International Seabed Authority, whose mandates include regulation of all mineral-related activities in international waters and protecting the marine environment from the harmful effects of mining. However, achieving deep-ocean sustainability under the UN Sustainable Development Goals will require integration of climate consideration across all policy sectors.

Evidence for seasonal cycles in deep-sea fish abundances: A great migration in the deep SE Atlantic?

Animal migrations are of global ecological significance, providing mechanisms for the transport of nutrients and energy between distant locations. In much of the deep sea (>200 m water depth), the export of nutrients from the surface ocean provides a crucial but seasonally variable energy source to seafloor ecosystems. Seasonal faunal migrations have been hypothesized to occur on the deep seafloor as a result, but have not been documented. Here, we analyse a 7.5-year record of photographic data from the Deep-ocean Environmental Long-term Observatory Systems seafloor observatories to determine whether there was evidence of seasonal (intra-annual) migratory behaviours in a deep-sea fish assemblage on the West African margin and, if so, identify potential cues for the behaviour. Our findings demonstrate a correlation between intra-annual changes in demersal fish abundance at 1,400 m depth and satellite-derived estimates of primary production off the coast of Angola. Highest fish abundances were observed in late November with a smaller peak in June, occurring approximately 4 months after corresponding peaks in primary production. Observed changes in fish abundance occurred too rapidly to be explained by recruitment or mortality, and must therefore have a behavioural driver. Given the recurrent patterns observed, and the established importance of bottom-up trophic structuring in deep-sea ecosystems, we hypothesize that a large fraction of the fish assemblage may conduct seasonal migrations in this region, and propose seasonal variability in surface ocean primary production as a plausible cause. Such trophic control could lead to changes in the abundance of fishes across the seafloor by affecting secondary production of prey species and/or carrion availability for example. In summary, we present the first evidence for seasonally recurring patterns in deep-sea demersal fish abundances over a 7-year period, and demonstrate a previously unobserved level of dynamism in the deep sea, potentially mirroring the great migrations so well characterized in terrestrial systems.

As migrações dos animais são importantes para a ecologia global pois fornecem mecanismos para o transporte de nutrientes e energia entre diferentes locais. Em grande parte do oceano profundo (>200 m de profundidade), a exportação de nutrientes da superfície para os ecossistemas do fundo marinho é uma fonte de energia crucial, mas que varia entre estações. Consequentemente, calcula-se que ocorram migrações sazonais de animais no fundo marinho, mas tal nunca foi reportado. Neste estudo, nós analisamos dados fotográficos do observatório do fundo marinho DELOS colhidos ao longo de 7.5 anos, para determinar se existem indícios de comportamentos migratórios sazonais (intra-anuais) na comunidade de peixes de profundidade na costa oeste africana ao largo de Angola e, se se confirmar, tentar identificar o que desencadeia este comportamento. Os resultados obtidos mostram que há uma correlação entre as alterações intra-anuais da densidade de peixes demersais a 1,400 m de profundidade e as estimativas de produção primária obtidas por satélite. A densidade de peixes atinge o seu máximo no final de Novembro, com um pico menos acentuado em Junho, aproximadamente quatro meses após os respectivos picos de produção primária na superfície. As alterações na densidade de peixe ocorreram de uma forma tão rápida que não podem ser explicadas por recrutamento ou mortalidade, e como tal devem só podem ser geradas por uma alteração do comportamento. Dado a recorrência do padrão observado, e importância da estrutura trófica fundo-topo em ecossistemas do oceano profundo, nós colocamos a hipótese de que uma fracção grande da comunidade de peixes faz migrações sazonais nesta região, e propomos que a variação sazonal da produção primária na superfície esteja na sua origem. Este controlo trófico poderá levar a alterações na densidade de peixes no fundo marinho via, por exemplo, a produção secundária de presas e/ou disponibilidade de corpos em processo de decomposição. Resumindo, nós apresentamos aqui a primeira evidência de padrões sazonais recorrentes na densidade de peixes demersais de profundidade ao longo de um período de sete anos, e provamos existir um nível de dinamismo nunca dantes observado no oceano profundo, que poderá espelhar as grandes migrações comummente observadas em sistemas terrestres.

Ecology of a polymetallic nodule occurrence gradient: Implications for deep-sea mining.

Abyssal polymetallic nodule fields constitute an unusual deep-sea habitat. The mix of soft sediment and the hard substratum provided by nodules increases the complexity of these environments. Hard substrata typically support a very distinct fauna to that of seabed sediments, and its presence can play a major role in the structuring of benthic assemblages. We assessed the influence of seafloor nodule cover on the megabenthos of a marine conservation area (area of particular environmental interest 6) in the Clarion Clipperton Zone (3950-4250 m water depth) using extensive photographic surveys from an autonomous underwater vehicle. Variations in nodule cover (1-20%) appeared to exert statistically significant differences in faunal standing stocks, some biological diversity attributes, faunal composition, functional group composition, and the distribution of individual species. The standing stock of both the metazoan fauna and the giant protists (xenophyophores) doubled with a very modest initial increase in nodule cover (from 1% to 3%). Perhaps contrary to expectation, we detected little if any substantive variation in biological diversity along the nodule cover gradient. Faunal composition varied continuously along the nodule cover gradient. We discuss these results in the context of potential seabed-mining operations and the associated sustainable management and conservation plans. We note in particular that successful conservation actions will likely require the preservation of areas comprising the full range of nodule cover and not just the low cover areas that are least attractive to mining.

On the impact of Citizen Science-derived data quality on deep learning based classification in marine images.

The evaluation of large amounts of digital image data is of growing importance for biology, including for the exploration and monitoring of marine habitats. However, only a tiny percentage of the image data collected is evaluated by marine biologists who manually interpret and annotate the image contents, which can be slow and laborious. In order to overcome the bottleneck in image annotation, two strategies are increasingly proposed: "citizen science" and "machine learning". In this study, we investigated how the combination of citizen science, to detect objects, and machine learning, to classify megafauna, could be used to automate annotation of underwater images. For this purpose, multiple large data sets of citizen science annotations with different degrees of common errors and inaccuracies observed in citizen science data were simulated by modifying "gold standard" annotations done by an experienced marine biologist. The parameters of the simulation were determined on the basis of two citizen science experiments. It allowed us to analyze the relationship between the outcome of a citizen science study and the quality of the classifications of a deep learning megafauna classifier. The results show great potential for combining citizen science with machine learning, provided that the participants are informed precisely about the annotation protocol. Inaccuracies in the position of the annotation had the most substantial influence on the classification accuracy, whereas the size of the marking and false positive detections had a smaller influence.

Biological effects 26 years after simulated deep-sea mining.

The potential for imminent abyssal polymetallic nodule exploitation has raised considerable scientific attention. The interface between the targeted nodule resource and sediment in this unusual mosaic habitat promotes the development of some of the most biologically diverse communities in the abyss. However, the ecology of these remote ecosystems is still poorly understood, so it is unclear to what extent and timescale these ecosystems will be affected by, and could recover from, mining disturbance. Using data inferred from seafloor photo-mosaics, we show that the effects of simulated mining impacts, induced during the "DISturbance and reCOLonization experiment" (DISCOL) conducted in 1989, were still evident in the megabenthos of the Peru Basin after 26 years. Suspension-feeder presence remained significantly reduced in disturbed areas, while deposit-feeders showed no diminished presence in disturbed areas, for the first time since the experiment began. Nevertheless, we found significantly lower heterogeneity diversity in disturbed areas and markedly distinct faunal compositions along different disturbance levels. If the results of this experiment at DISCOL can be extrapolated to the Clarion-Clipperton Zone, the impacts of polymetallic nodule mining there may be greater than expected, and could potentially lead to an irreversible loss of some ecosystem functions, especially in directly disturbed areas.

Autonomous marine environmental monitoring: Application in decommissioned oil fields.

Hundreds of Oil & Gas Industry structures in the marine environment are approaching decommissioning. In most areas decommissioning operations will need to be supported by environmental assessment and monitoring, potentially over the life of any structures left in place. This requirement will have a considerable cost for industry and the public. Here we review approaches for the assessment of the primary operating environments associated with decommissioning - namely structures, pipelines, cuttings piles, the general seabed environment and the water column - and show that already available marine autonomous systems (MAS) offer a wide range of solutions for this major monitoring challenge. Data of direct relevance to decommissioning can be collected using acoustic, visual, and oceanographic sensors deployed on MAS. We suggest that there is considerable potential for both cost savings and a substantial improvement in the temporal and spatial resolution of environmental monitoring. We summarise the trade-offs between MAS and current conventional approaches to marine environmental monitoring. MAS have the potential to successfully carry out much of the monitoring associated with decommissioning and to offer viable alternatives where a direct match for the conventional approach is not possible.

Megafaunal variation in the abyssal landscape of the Clarion Clipperton Zone.

The potential for imminent polymetallic nodule mining in the Clarion Clipperton Fracture Zone (CCZ) has attracted considerable scientific and public attention. This concern stems from both the extremely large seafloor areas that may be impacted by mining, and the very limited knowledge of the fauna and ecology of this region. The environmental factors regulating seafloor ecology are still very poorly understood. In this study, we focus on megafaunal ecology in the proposed conservation zone 'Area of Particular Environmental Interest 6' (study area centred 17°16'N, 122°55'W). We employ bathymetric data to objectively define three landscape types in the area (a level bottom Flat, an elevated Ridge, a depressed Trough; water depth 3950-4250 m) that are characteristic of the wider CCZ. We use direct seabed sampling to characterise the sedimentary environment in each landscape, detecting no statistically significant differences in particle size distributions or organic matter content. Additional seafloor characteristics and data on both the metazoan and xenophyophore components of the megafauna were derived by extensive photographic survey from an autonomous underwater vehicle. Image data revealed that there were statistically significant differences in seafloor cover by nodules and in the occurrence of other hard substrata habitat between landscapes. Statistically significant differences in megafauna standing stock, functional structuring, diversity, and faunal composition were detected between landscapes. The Flat and Ridge areas exhibited a significantly higher standing stock and a distinct assemblage composition compared to the Trough. Geomorphological variations, presumably regulating local bottom water flows and the occurrence of nodule and xenophyophore test substrata, between study areas may be the mechanism driving these assemblage differences. We also used these data to assess the influence of sampling unit size on the estimation of ecological parameters. We discuss these results in the contexts of regional benthic ecology and the appropriate management of potential mining activities in the CCZ and elsewhere in the deep ocean.

A framework for the development of a global standardised marine taxon reference image database (SMarTaR-ID) to support image-based analyses.

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.

Implications of population connectivity studies for the design of marine protected areas in the deep sea: An example of a demosponge from the Clarion-Clipperton Zone.

The abyssal demosponge Plenaster craigi inhabits the Clarion-Clipperton Zone (CCZ) in the northeast Pacific, a region with abundant seafloor polymetallic nodules with potential mining interest. Since P. craigi is a very abundant encrusting sponge on nodules, understanding its genetic diversity and connectivity could provide important insights into extinction risks and design of marine protected areas. Our main aim was to assess the effectiveness of the Area of Particular Environmental Interest 6 (APEI-6) as a potential genetic reservoir for three adjacent mining exploration contract areas (UK-1A, UK-1B and OMS-1A). As in many other sponges, COI showed extremely low variability even for samples ~900 km apart. Conversely, the 168 individuals of P. craigi, genotyped for 11 microsatellite markers, provided strong genetic structure at large geographical scales not explained by isolation by distance (IBD). Interestingly, we detected molecular affinities between samples from APEI-6 and UK-1A, despite being separated ~800 km. Although our migration analysis inferred very little progeny dispersal of individuals between areas, the major differentiation of OMS-1A from the other areas might be explained by the occurrence of predominantly northeasterly transport predicted by the HYCOM hydrodynamic model. Our study suggests that although APEI-6 does serve a conservation role, with species connectivity to the exploration areas, it is on its own inadequate as a propagule source for P. craigi for the entire eastern portion of the CCZ. Our new data suggest that an APEI located to the east and/or the south of the UK-1, OMS-1, BGR, TOML and NORI areas would be highly valuable.

Geomorphological evidence of large vertebrates interacting with the seafloor at abyssal depths in a region designated for deep-sea mining.

Exploration licences for seafloor mineral deposits have been granted across large areas of the world's oceans, with the abyssal Pacific Ocean being the primary target for polymetallic nodules-a potentially valuable source of minerals. These nodule-bearing areas support a large diversity of deep-sea life and although studies have begun to characterize the benthic fauna within the region, the ecological interactions between large bathypelagic vertebrates of the open ocean and the abyssal seafloor remain largely unknown. Here we report seafloor geomorphological alterations observed by an autonomous underwater vehicle that suggest large vertebrates could have interacted with the seafloor to a maximum depth of 4258 m in the recent geological past. Patterns of disturbance on the seafloor are broadly comparable to those recorded in other regions of the world's oceans attributed to beaked whales. These observations have important implications for baseline ecological assessments and the environmental management of potential future mining activities within this region of the Pacific.

Potential Impacts of Offshore Oil and Gas Activities on Deep-Sea Sponges and the Habitats They Form.

Sponges form an important component of benthic ecosystems from shallow littoral to hadal depths. In the deep ocean, beyond the continental shelf, sponges can form high-density fields, constituting important habitats supporting rich benthic communities. Yet these habitats remain relatively unexplored. The oil and gas industry has played an important role in advancing our knowledge of deep-sea environments. Since its inception in the 1960s, offshore oil and gas industry has moved into deeper waters. However, the impacts of these activities on deep-sea sponges and other ecosystems are only starting to become the subject of active research. Throughout the development, operation and closure of an oil or gas field many activities take place, ranging from the seismic exploration of subseafloor geological features to the installation of infrastructure at the seabed to the drilling process itself. These routine activities and accidental releases of hydrocarbons during spills can significantly impact the local marine environment. Each phase of a field development or an accidental oil spill will therefore have different impacts on sponges at community, individual and cellular levels. Legacy issues regarding the future decommissioning of infrastructure and the abandonment of wells are also important environmental management considerations. This chapter reviews our understanding of impacts from hydrocarbon exploration and exploitation activities on deep-sea sponges and the habitats they form. These impacts include those (1) at community level, decreasing the diversity and density of benthic communities associated with deep-sea sponges owing to physical disturbance of the seabed; (2) at individual level, interrupting filtration owing to exposure to increased sedimentation; and (3) at cellular level, decreasing cellular membrane stability owing to exposure to drill muds. However, many potential effects not yet tested in deep-sea sponges but observed in shallow-water sponges or other model organisms should also be taken into account. Furthermore, to the best of our knowledge, no studies have shown impact of oil or dispersed oil on deep-sea sponges. To highlight these significant knowledge gaps, a summary table of potential and known impacts of hydrocarbon extraction and production activities combined with a simple "traffic light" scheme is also provided.

Metabolic rates are significantly lower in abyssal Holothuroidea than in shallow-water Holothuroidea.

Recent analyses of metabolic rates in fishes, echinoderms, crustaceans and cephalopods have concluded that bathymetric declines in temperature- and mass-normalized metabolic rate do not result from resource-limitation (e.g. oxygen or food/chemical energy), decreasing temperature or increasing hydrostatic pressure. Instead, based on contrasting bathymetric patterns reported in the metabolic rates of visual and non-visual taxa, declining metabolic rate with depth is proposed to result from relaxation of selection for high locomotory capacity in visual predators as light diminishes. Here, we present metabolic rates of Holothuroidea, a non-visual benthic and benthopelagic echinoderm class, determined in situ at abyssal depths (greater than 4000 m depth). Mean temperature- and mass-normalized metabolic rate did not differ significantly between shallow-water (less than 200 m depth) and bathyal (200-4000 m depth) holothurians, but was significantly lower in abyssal (greater than 4000 m depth) holothurians than in shallow-water holothurians. These results support the dominance of the visual interactions hypothesis at bathyal depths, but indicate that ecological or evolutionary pressures other than biotic visual interactions contribute to bathymetric variation in holothurian metabolic rates. Multiple nonlinear regression assuming power or exponential models indicates that in situ hydrostatic pressure and/or food/chemical energy availability are responsible for variation in holothurian metabolic rates. Consequently, these results have implications for modelling deep-sea energetics and processes.

Eyes in the sea: Unlocking the mysteries of the ocean using industrial, remotely operated vehicles (ROVs).

For thousands of years humankind has sought to explore our oceans. Evidence of this early intrigue dates back to 130,000BCE, but the advent of remotely operated vehicles (ROVs) in the 1950s introduced technology that has had significant impact on ocean exploration. Today, ROVs play a critical role in both military (e.g. retrieving torpedoes and mines) and salvage operations (e.g. locating historic shipwrecks such as the RMS Titanic), and are crucial for oil and gas (O&G) exploration and operations. Industrial ROVs collect millions of observations of our oceans each year, fueling scientific discoveries. Herein, we assembled a group of international ROV experts from both academia and industry to reflect on these discoveries and, more importantly, to identify key questions relating to our oceans that can be supported using industry ROVs. From a long list, we narrowed down to the 10 most important questions in ocean science that we feel can be supported (whole or in part) by increasing access to industry ROVs, and collaborations with the companies that use them. The questions covered opportunity (e.g. what is the resource value of the oceans?) to the impacts of global change (e.g. which marine ecosystems are most sensitive to anthropogenic impact?). Looking ahead, we provide recommendations for how data collected by ROVs can be maximised by higher levels of collaboration between academia and industry, resulting in win-win outcomes. What is clear from this work is that the potential of industrial ROV technology in unravelling the mysteries of our oceans is only just beginning to be realised. This is particularly important as the oceans are subject to increasing impacts from global change and industrial exploitation. The coming decades will represent an important time for scientists to partner with industry that use ROVs in order to make the most of these 'eyes in the sea'.

Direct evidence of an efficient energy transfer pathway from jellyfish carcasses to a commercially important deep-water species.

Here we provide empirical evidence of the presence of an energetic pathway between jellyfish and a commercially important invertebrate species. Evidence of scavenging on jellyfish carcasses by the Norway lobster (Nephrops norvegicus) was captured during two deployments of an underwater camera system to 250-287 m depth in Sognefjorden, western Norway. The camera system was baited with two Periphylla periphylla (Scyphozoa) carcasses to simulate the transport of jellyfish detritus to the seafloor, hereby known as jelly-falls. N. norveigus rapidly located and consumed a large proportion (>50%) of the bait. We estimate that the energy input from jelly-falls may represent a significant contribution to N. norvegicus energy demand (0.21 to 10.7 times the energy required for the population of N. norvegicus in Sognefjorden). This potentially high energetic contribution from jelly-falls highlights a possible role of gelatinous material in the support of commercial fisheries. Such an energetic pathway between jelly-falls and N. norvegicus could become more important with increases in jellyfish blooms in some regions.

Metabolic costs imposed by hydrostatic pressure constrain bathymetric range in the lithodid crab Lithodes maja.

The changing climate is shifting the distributions of marine species, yet the potential for shifts in depth distributions is virtually unexplored. Hydrostatic pressure is proposed to contribute to a physiological bottleneck constraining depth range extension in shallow-water taxa. However, bathymetric limitation by hydrostatic pressure remains undemonstrated, and the mechanism limiting hyperbaric tolerance remains hypothetical. Here, we assess the effects of hydrostatic pressure in the lithodid crab Lithodes maja (bathymetric range 4-790 m depth, approximately equivalent to 0.1 to 7.9 MPa hydrostatic pressure). Heart rate decreased with increasing hydrostatic pressure, and was significantly lower at ≥10.0 MPa than at 0.1 MPa. Oxygen consumption increased with increasing hydrostatic pressure to 12.5 MPa, before decreasing as hydrostatic pressure increased to 20.0 MPa; oxygen consumption was significantly higher at 7.5-17.5 MPa than at 0.1 MPa. Increases in expression of genes associated with neurotransmission, metabolism and stress were observed between 7.5 and 12.5 MPa. We suggest that hyperbaric tolerance in Lmaja may be oxygen-limited by hyperbaric effects on heart rate and metabolic rate, but that Lmaja's bathymetric range is limited by metabolic costs imposed by the effects of high hydrostatic pressure. These results advocate including hydrostatic pressure in a complex model of environmental tolerance, where energy limitation constrains biogeographic range, and facilitate the incorporation of hydrostatic pressure into the broader metabolic framework for ecology and evolution. Such an approach is crucial for accurately projecting biogeographic responses to changing climate, and for understanding the ecology and evolution of life at depth.