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Climate change is deeply affecting oceanographic, biogeochemical, and hydrological processes and consequently influencing the ecological patterns of ecosystems. Indeed, marine habitats and species are facing many alterations in their structure, functioning, and in their capacity of providing ecosystem services. To investigate and explore the distribution and potential variation of habitats and species under future climate change scenarios, Habitat Suitability Models (HSMs) have been widely applied during the last years for their recognized ability in predicting the suitability of a location for species and habitats in correlation with the environmental conditions.With the application of two of the best-known HSMs (Random Forest and MaxEnt), this research intends to investigate the distribution of the coralligenous, a widespread habitat in the Northern Adriatic Sea threatened by the effects of climate change, and identify its potential variation in a severe future scenario. The analysis consisted in examining the correlation between the habitat distribution with environmental parameters obtained from online databases and a set of dedicated ocean model simulations applied in recent past conditions and under RCP 8.5 climate change scenario. Furthermore, to explore the potential uncertainty of the environmental variables in future conditions, a sensitivity analysis has been implemented by running additional HSMs simulations set up with variables' increments and decrements resulting from projections modeled by other research.The models perform very well in predicting habitat distributions. The prediction under the climate change scenario shows that opportunistic species (e.g. turf-dominant algae) find more suitable conditions in the area being more tolerant to stressful conditions and alterations of the environmental variables. As a result, calcareous macroalgae appear to be more vulnerable to climate change effects, including increases in temperature, nutrient concentrations, salinity, and velocity. Overall, the results of the sensitivity analysis confirmed the results predicted by models; however, Random Forest also shows a higher sensitivity to uncertainty than MaxEnt.In conclusion, this study gives a sight of the likely ecological behavior in correlation with past environmental conditions and future alterations due to climate change. Besides, HSMs confirm to be very useful tools to develop adequate conservation strategies and/or identify priority areas to protect. Thanks to the sensitivity analysis, additional hints about the models’ behavior according to the environmental uncertainties are extrapolated, allowing to consider with consciousness the results and understanding of the potentialities of the models according to the data in possession.

Abyssal plains cover more than half of Earth's surface, and the main food source in these ecosystems is phytodetritus, mainly originating from primary producers in the euphotic zone of the ocean. Global climate change is influencing phytoplankton abundance, productivity, and distribution. Increasing importance of picoplankton over diatom as primary producers in surface oceans (especially projected for higher latitudes) is projected and hence altering the quantity of organic carbon supplied to the abyssal seafloor as phytodetritus, consequences of which remain largely unknown. Here, we investigated the in situ responses of abyssal biota from viruses to megafauna to different types of phytoplankton input (diatoms or cyanobacteria which were labeled with stable isotopes) at equatorial (oligotrophic) and temperate (eutrophic) benthic sites in the Pacific Ocean (1°N at 4277 m water depth and 39°N at 5260 m water depth, respectively). Our results show that meiofauna and macrofauna generally preferred diatoms as a food source and played a relatively larger role in the consumption of phytodetritus at higher latitudes (39°N). Contrarily, prokaryotes and viruses showed similar or even stronger responses to cyanobacterial than to diatom supply. Moreover, the response of prokaryotes and viruses was very rapid (within 1-2 days) at both 1°N and 39°N, with quickest responses reported in the case of cyanobacterial supply at higher latitudes. Overall, our results suggest that benthic deep-sea eukaryotes will be negatively affected by the predicted decrease in diatoms in surface oceans, especially at higher latitudes, where benthic prokaryotes and viruses will otherwise likely increase their quantitative role and organic carbon cycling rates. In turn, such changes can contribute to decrease carbon transfer from phytodetritus to higher trophic levels, with strong potential to affect oceanic food webs, their biodiversity and consequently carbon sequestration capacity at the global scale.

Climate change drives oceanographic mechanisms at the global level and affects the functioning and structure of marine ecosystems by inducing shifts in species and habitats distribution. The coralligenous outcrops of the Northern Adriatic Sea (Eastern Mediterranean basin) are listed among the habitats of priority for conservation in the Habitats Directive (92/43/EEC) and in the Marine Strategy Framework Directive (2008/56/EC) for their importance as biodiversity hotspots and ecosystem services providers and are recognized to be needy of protection also due to their vulnerability to climate change impacts. This study aims at investigating how environmental variables predicted in future climate change scenarios could affect the distribution and composition of the coralligenous benthic assemblages in the northern Adriatic Sea, to inform management and conservation strategies in the area. A cutting-edge approach was adopted through the application of two predictive models (Maxent and Random Forest) in association with oceanic circulation modeling (ROMS) to deliver the most reliable projections. The present coralligenous habitat distribution and the different habitat typologies (based on the epibenthic assemblages structure inferred from literature) were correlated with historical (consisting in temperature, salinity, velocity, light, nitrogen and phosphorus concentration) and climate change scenario RCP 8.5 (temperature, salinity, velocity) variables in order to provide estimates of possible distribution shifts. Predictive maps showing the degree of habitat suitability across the basin were provided together with a potential shift in the structure of the associated communities. Predictive models are powerful decision-support tools (DSTs) to inform conservation strategies, and in this study they are applied to support the identification of new potential areas of conservation priority in the Northern Adriatic basin, where coralligenous outcrops will be still present in the future despite climate change. We emphasize the relevance of applying DSTs to help undertake science-based actions for conservation purposes in the face of future climate change effects on marine ecosystems.

Este artículo contiene 11 páginas, 2 figuras, 2 tablas., Local, regional and global targets have been set to halt marine biodiversity loss. Europe has set its own policy targets to achieve Good Environmental Status (GES) of marine ecosystems by implementing the Marine Strategy Framework Directive (MSFD) across member states. We combined an extensive dataset across five Mediterranean ecoregions including 26 Marine Protected Areas (MPAs), their reference unprotected areas, and a no-trawl case study. Our aim was to assess if MPAs reach GES, if their effects are local or can be detected at ecoregion level or up to a Mediterranean scale, and which are the ecosystem components driving GES achievement. This was undertaken by using the analytical tool NEAT (Nested Environmental status Assessment Tool), which allows an integrated assessment of the status of marine systems. We adopted an ecosystem approach by integrating data from several ecosystem components: the seagrass Posidonia oceanica, macroalgae, sea urchins and fish. Thresholds to define the GES were set by dedicated workshops and literature review. In the Western Mediterranean, most MPAs are in good/high status, with P. oceanica and fish driving this result within MPAs. However, GES is achieved only at a local level, and the Mediterranean Sea, as a whole, results in a moderate environmental status. Macroalgal forests are overall in bad condition, confirming their status at risk. The results are significantly affected by the assumption that discrete observations over small spatial scales are representative of the total extension investigated. This calls for large-scale, dedicated assessments to realistically detect environmental status changes under different conditions. Understanding MPAs effectiveness in reaching GES is crucial to assess their role as sentinel observatories of marine systems. MPAs and trawling bans can locally contribute to the attainment of GES and to the fulfillment of the MSFD objectives. Building confidence in setting thresholds between GES and non-GES, investing in long-term monitoring, increasing the spatial extent of sampling areas, rethinking and broadening the scope of complementary tools of protection (e.g., Natura 2000 Sites), are indicated as solutions to ameliorate the status of the basin., This article was undertaken within the COST Action 15121 MarCons (http://www.marcons-cost.eu, European Cooperation in Science and Technology), the Interreg MED AMAre Plus (Ref: 8022) and the project PO FEAMP 2014-2020 Innovazione, sviluppo e sostenibilita ` nel settore della pesca e dell’acquacoltura per la Regione Campania (ISSPA 2.51). M.C.U., A.B. have been funded by the project MEDREGION (European Commission DG ENV/MSFD, 2018 call, Grant Agreement 110661/ 2018/794286/SUB/ENV.C2). Aegean Sea data were retrieved from the project PROTOMEDEA (www.protomedea.eu), funded by DG for Marine Affairs and Fisheries of the EC, under Grant Agreement SI2.721917. JB acknowledges support from the Spanish Ministry of Science and Innovation (Juan de la Cierva fellowship FJC 2018-035566-I)., With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S).

Area-Based Management Tools (ABMTs) are spatial instruments for conservation and managing different forms of ocean use. A multitude of ABMTs exists in marine areas within and beyond national jurisdiction, ranging from tools for the regulation of specific human activities (e.g. fisheries, shipping, or mining) to cross-sectoral tools (e.g. such as marine protected areas, MPAs, and marine spatial planning, MSP). By applying expert elicitation and reviewing scientific and grey literature we evaluate the contribution of ABMTs to sustainable development goals (SDGs) as set out under the United Nations 2030 Agenda for Sustainable Development, including for SDG 14 that directly addresses the conservation and sustainable use of oceans, seas, and marine resources. We find that fisheries-related and conservation-related ABMTs, and MSP offer the greatest potential contributions to SDG 14 and to SDGs in general. Moreover, there is high complementarity and synergy among different ABMTs for most SDG 14 targets and other SDGs, with the exception of SDG target 14.6 Prohibit fisheries subsidies and SDG 7 Affordable and clean energy. We find that some ABMTs contribute directly to goal attainment, while others contribute in more nuanced or even unexpected ways. Furthermore, context-specific factors that relate to political and legal factors, enforceability, transparency, governance structure, and inclusivity are crucial for unlocking the full potential of ABMTs of attaining multiple SDGs, as shown through examples. The major challenge to face in the next decade is ensuring durable and equitable outcomes from ABMT implementation by coordinating ABMT initiatives established by different organisations and responsible authorities. It is also critical that outcomes are monitored and evaluated across environmental, social, economic, governance, and health dimensions, with indicators addressing management effectiveness and not only ABMT area coverage., This research was conducted in the framework of COST action on “Ocean Governance for Sustainability - challenges, options and the role of science”, CA15217, within the Working Group 2 “Area Based Management” activities. We would like to thank COST for the funding that made the cooperation amongst the authors, and thus this article, possible. EG partially acknowledges also funding from PORTODIMARE “geoPORtal of TOols & Data for sustaInable Management of coAstal and maRine Environment” (2018–2020), Adriatic-Ionian Programme INTERREG V–B Transnational 2014–2020, grant no. 205, and funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 893614-4, reflecting only the author's view ; AQ partially acknowledges the Project SIMAtlantic (grant no. EASME/EMFF/2018/1.2.1.5); MLF partially acknowledges the Portuguese Foundation for Science and Technology (FCT), with a Do*Mar programme PhD grant (PD/BD/113485/2015); MM partially acknowledges FCT, with a PhD grant (SFRH/BD/138422/2018). AQ, FA, MLF, LS, MM, CP partially acknowledge the financial support to FCT/MCTES for the financial support to CESAM (UIDP/50017/2020+UIDB/50017/2020), through national funds. CFS partially acknowledges funding from FCT research contract 2020.03704.CEECIND, research grant PTDC/CTA-AMB/30226/2017, and MARE strategic project UID/MAR/04292/2019. NV partially acknowledges also funding from the Romanian National Authority for Scientific Research and Innovation, grants no. CNCS-UEFISCDI PN-III-P1-1.1-TE-2016-2491, PN-III-P1-1.1-TE-2019-1444, and the project T4BS (grant no. EASME/EMFF/2019/863621). The work of CP was supported by FCT research contract 2020.02510.CEECIND. The work of BN and SU was supported by the German Federal Ministry of Education and Research (BMBF) through its Research for Sustainable Development program (FONA), and the Federal State of Brandenburg.

Industrial seabed mining is expected to cause significant impacts on marine ecosystems, including physical disturbance and the generation of plumes of toxin-laden water. Portmán Bay (NW Mediterranean Sea), where an estimated amount of 60 Mt of mine tailings from sulphide ores were dumped from 1957 to 1990, is one of the most metal-polluted marine areas in Europe and worldwide. This bay can be used to assess the impact on marine ecosystems of particle settling from sediment plumes resulting from mine tailings resuspension. With this purpose in mind, we conducted a field experiment there to investigate subsequent effects of deposition of (artificially resuspended) contaminated sediments on (i) prokaryotic abundance and meiofaunal assemblages (in terms of abundance and diversity), (ii) the availability of trophic resources (in terms of organic matter biochemical composition), and (iii) a set of ecosystem functions including meiofaunal biomass, heterotrophic C production and C degradation rates. The results of this study show that mine tailings resuspension and plume deposition led to the decline of prokaryotic abundance and nematode's biodiversity. The later decreased because of species removal and transfer along with particle resuspension and plume deposition. Such changes were also associated to a decrease of the proteins content in the sediment organic matter, faster C degradation rates and higher prokaryotic C production. Overall, this study highlights that mine tailing resuspension and ensuing particle deposition can have deleterious effects on both prokaryotes and nematode diversity, alter biogeochemical cycles and accelerate C degradation rates. These results should be considered for the assessment of the potential effects of seabed mineral exploitation on marine ecosystems at large.

The design and establishment of Marine Ecological Observatories (MEOs) are fostered at the European level. MEOs should adopt a holistic view, integrating and harmonizing long-term oceanographic and ecological research and monitoring, and increasing conservation strategies effectiveness according to the ecological connectivity concept. The data and knowledge collected and made available through MEOs should inform policies dealing with conservation and management of the marine environment. We present and discuss these issues in the Adriatic Sea context, where the transnational ecological observatory “ECOAdS” is under development in the framework of the Interreg Italy-Croatia project ECOSS (Observing System in the Adriatic Sea: oceanographic observations for biodiversity), which aims to support Natura 2000 network implementation and cross-border coordination of multiple monitoring initiatives. We analyse the main EU directives that deal with marine conservation, notably the Habitats and Birds directives, the Water Framework Directive, and the Marine Strategy Framework Directive, as they are the primary instruments that can guide the development of the observatory while strengthening cooperation at the basin scale. We bring out the synergies and discrepancies among these legal instruments, and build on them ECOAdS as a monitoring platform that may respond and contribute to their requirements, boosting the synergies and overcoming the weaknesses. Finally, we provide some hints for the further development of this transnational MEO as a collector of the existing monitoring efforts aimed at harmonizing their approaches and incorporating the ecological connectivity to foster an ecosystem-based approach to conservation management.

14 pages, 5 figures, 2 tables, supplementary information https://doi.org/10.1016/j.scitotenv.2020.142564, Climate change (CC) is a key, global driver of change of marine ecosystems. At local and regional scales, other local human stressors (LS) can interact with CC and modify its effects on marine ecosystems. Understanding the response of the marine environment to the combined effects of CC and LS is crucial to inform marine ecosystem-based management and planning, yet our knowledge of the potential effects of such interactions is fragmented. At a global scale, we explored how cumulative effect assessments (CEAs) have addressed CC in the marine realm and discuss progress and shortcomings of current approaches. For this we conducted a systematic review on how CEAs investigated at different levels of biological organization ecological responses, functional aspects, and the combined effect of CC and HS. Globally, the effects of 52 LS and of 27 CC-related stressors on the marine environment have been studied in combination, such as industrial fisheries with change in temperature, or sea level rise with artisanal fisheries, marine litter, change in sediment load and introduced alien species. CC generally intensified the effects of LS at species level. At trophic groups and ecosystem levels, the effects of CC either intensified or mitigated the effects of other HS depending on the trophic groups or the environmental conditions involved, thus suggesting that the combined effects of CC and LS are context-dependent and vary among and within ecosystems. Our results highlight that large-scale assessments on the spatial interaction and combined effects of CC and LS remain limited. More importantly, our results strengthen the urgent need of CEAs to capture local-scale effects of stressors that can exacerbate climate-induced changes. Ultimately, this will allow identifying management measures that aid counteracting CC effects at relevant scales, This article is based upon work from COST Action 15121 ‘Advancing marine conservation in the European and contiguous seas’ [MarCons (Katsanevakis et al., 2017); http://www.marcons-cost.eu] – supported by COST (European Cooperation in Science and Technology, CA15121). EG partially acknowledges also funding from the project PORTODIMARE “geoPORtal of TOols & Data for sustaInable Management of coAstal and maRine Environment” (2018–2020), Adriatic-Ionian Programme INTERREG Vsingle bondB Transnational 2014–2020, grant no. 205; MC partially from the EU Horizon 2020 research and innovation programme under grant agreement no 817578 (TRIATLAS project). With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)

Portman Bay is one of the most contaminated and chronically impacted coastal marine areas of the world. Here, from the 1957 to 1990, about 60 million tons of mine tailings from the processing of sulfide ores were dumped directly at the shoreline. The resulting deposit provides a unique opportunity to assess the impact of mine tailings on coastal marine ecosystems after ca 30 years since the discharge has ceased. We investigated meiofaunal abundance, biomass and biodiversity along a gradient of metal concentration that overlaps with a bathymetric gradient from 30 to 60 m depth. Despite the localized presence of extremely high concentration of metals, the bay was not a biological desert, but, nevertheless, was characterized by evident signs of impact on benthic diversity. Meiofaunal variables increased significantly with decreasing metal contamination, eventually reaching values comparable to other uncontaminated coastal sediments. Our results show that mine tailings influenced the spatial distribution of meiofaunal taxa and nematode species composition. In particular, we report here that the bay was characterized by the dominance of nematode opportunistic species tolerant to high metal concentration. The effects of mine tailing discharge on meiofaunal biodiversity and composition were still evident ca 30 years after the end of the mining activities. Overall, this study provides new insights on the potential impact of mine tailings disposal and metal contamination in coastal sediments, and, can also contribute to predict the potential long-term consequences of ever-expanding deep-sea mining industry on benthic environments.

The Natura 2000 (N2K) network is a key conservation instrument in Europe, despite its many limitations concerning the efficacy in covering and adequately safeguarding the marine environment, mainly due to missing coordinated Governance and Management Systems (GMS). In this study, we present and discuss the main benefits, which could be provided by Marine Ecological Observatories (MEOs) to support N2K marine network implementation and related GMS. The conceptual design of the ecological observatory ECOAdS, under development in the framework of the Interreg Italy-Croatia project ECOSS, is described. ECOAdS, which focuses on marine N2K sites under jurisdiction of Italy and Croatia, is a first operative pilot proposal of MEO for the Adriatic Sea. It represents an opportunity to build a common knowledge and monitoring framework and shared data management practices at the transnational level, overcoming the N2K site fragmentation. The main challenges that ECOAdS should face in its implementation are discussed, with emphasis on the integration of the marine connectivity aspects and on the adoption of adaptive and participative GMS to address the main conservation issues in the area.

The deep sea covers about 79% of the Mediterranean basin, including habitats potentially able to deliver multiple ecosystem services and numerous resources of high economic value. Thus, the deep Mediterranean Sea represents an important frontier for marine resources exploitation, which is embedded within the European Blue Growth Strategy goals and agendas. The deep sea is crucial for the ecological functioning of the entire basin. For this reason, the deep Mediterranean deserves protection from the potential cumulative impacts derived from existent and developing human activities. Marine Spatial Planning (MSP) has been identified as key instrument for spatially allocating maritime uses in the sea space avoiding spatial conflicts between activities, and between activities and the environment. Indeed, MSP incorporates the ecosystem-based approach (EB-MSP) to balance both socio-economic and environmental objectives, in line with the Maritime Spatial Planning Directive and the Marine Strategy Framework Directive. Despite MSP is under implementation in Europe, the Directive is not applied yet for the managing and monitoring of the environmental status of the deep sea. In the Mediterranean, deep areas fall both in internal and territorial waters, and in High Seas, and its management framework turns out to be complicated. Moreover, a certain level of cumulative impacts in the deep Mediterranean has been already identified and likely underestimated because of paucity of knowledge related with deep-sea ecosystems. Thus, the implementation of scientific knowledge and the establishment of a sustainable management regime of deep-sea resources and space are urgent. This study aims at reflecting on the best available ecological knowledge on the deep Mediterranean to incorporate conservation objectives in EB-MSP. We propose a framework to include key ecological principles in the relevant phases of any EB-MSP processes taking in consideration existing socio-economic and conservation scenarios in the region. We add the uncertainty principle to reflect on the still unexplored and missing knowledge related to the deep Mediterranean. Here, we resume some guidelines to overcome limits and bottlenecks while ensuring protection of deep-sea ecosystems and resources in the Mediterranean Sea.

The abyssal plain covers more than half the Earth’s surface. The main food source to abyssal ecosystems is phytodetritus, which originates from phytoplankton in the surface ocean, and thus its variability to the seafloor is a major driver of abyssal ecosystem biomass and functioning. In this study, we conducted a comparative survey on organic matter (OM) quality and quantity in abyssal plain sediments and examined the distributions of megafauna, macrofauna, meiofauna, prokaryotes, and viruses in eutrophic (39°N), oligotrophic (1°N), and ultra-oligotrophic (12°N) areas of the western Pacific. We also analyzed stable carbon and nitrogen isotopic compositions of organisms at 39°N and 1°N to assess differences in benthic abyssal food-web structures with contrasting trophic states. Sediments collected at 39°N presented highest concentrations of total organic carbon (TOC) and labile OM, and high diffusive oxygen uptake rates. By contrast, the lowest values were found at 12°N. Vertical distributions of sediment macrofauna, meiofauna, and prokaryotes matched with labile OM profiles. There were prominent differences in abundances of macro- and megafauna among stations with different OM fluxes, whereas the abundance of meiofauna and prokaryotes showed smaller differences among stations. Such differences could be explained by higher turnover rates of smaller organisms. Food-web structures of abyssal plains are likely influenced by both the type and size of primary producers in surface ocean. Our results underscore the crucial importance of OM fluxes and their compositions to the abundances and vertical profiles of labile OM and benthic biota in abyssal ecosystems.

The assessment and mapping of ecosystem services (ES) has become an increasingly important instrument for environmental management and conservation priority-setting. As such, this practice can be used in ecosystem-based Marine Spatial Planning (MSP). MSP is recognized as an opportunity to achieve socio-economic and ecological goals simultaneously, to suggest solutions for sustainable management of marine environment and its resources. In this study, we propose an operational approach that includes novel spatial analysis in the marine field to quantify and map supporting ecosystem services. Such approach spans the 3D-dimension of the marine environment, considering all marine domains (sea surface, water column, seabed) separately. Our approach is focused on mapping supporting ES of the Adriatic Sea, to grant their preservation in order to guarantee the delivery of all other ES. Supporting ES provision in the Adriatic was quantified through the use of indicators that denote ES delivery and that are specifically related to the three marine domains. We identified areas of elevated provisioning levels of multiple supporting ES in the Adriatic, which is hypothesized to be priority areas of conservation. Our results confirm the importance of explicitly including the pelagic domain in planning and conservation processes. Areas that provide the lowest levels of supporting ES delivery were also mapped, to indicate possible ‘sacrificial areas’ for industrial or intensive use. The spatial coincidence of the determined hotspots areas of ES delivery associated with particular marine areas that are and are not under conservation regimes was analysed. This approach led us to test the applicability of the method for identifying marine areas for conservation purposes. Our methodological approach aims at producing relevant scientific knowledge for prioritizing marine conservation and sustainable management actions, to be used in MSP and marine management.

Extracellular DNA in deep-sea sediments represents a major repository of genes, which previously belonged to living organisms. However, the extent to which these extracellular genes influence current estimates of prokaryotic biodiversity is unknown. We investigated the abundance and diversity of 16S rDNA sequences contained within extracellular DNA from continental margins of different biogeographic regions. We also compared the taxonomic composition of microbial assemblages through the analysis of extracellular DNA and DNA associated with living cells. 16S rDNA contained in the extracellular DNA pool contributed up to 50% of the total 16S rDNA copy number determined in the sediments. Ca. 4% of extracellular Operational Taxonomic Units (OTUs) were shared among the different biogeographic regions revealing the presence of a core of preserved OTUs. A higher fraction of OTUs was exclusive of each region potentially due to its geographic and thermohaline characteristics. Ca. one third of the OTUs identified in the extracellular DNA were absent from living prokaryotic assemblages, possibly representing the signatures of past assemblages. Our findings expand the knowledge of the contribution of extracellular microbial sequences to current estimates of prokaryotic diversity obtained through the analyses of “environmental DNA”, and open new perspectives for understanding microbial successions in benthic ecosystems.

The United Nations Decade of Ocean Science for Sustainable Development presents an exceptional opportunity to effect positive change in ocean use. We outline what is required of the deep-sea research community to achieve these ambitious objectives. The health of the global ocean, on which society depends, is in decline. The importance of sustainable use to ocean health has long been recognized1, yet the United Nations (UN) First World Ocean Assessment2 from 2017 highlighted increasing ocean pressures from accelerated expansion of human activities, including climate change. These pressures affect all ocean regions, from the coast to the deep sea3. In response to this concern, and to align with several international policy commitments, the UN General Assembly proclaimed 2021–2030 the Decade of Ocean Science for Sustainable Development4. The roadmap for this Ocean Decade recognizes the deep sea as a frontier of science and discovery, and calls for research to advance understanding of deep-sea ecosystems, their functions, vulnerabilities and services to society. Published in March 2020, the draft implementation plan for the Ocean Decade guides the design and implementation of ‘Actions’ that underpin the desired move from ‘the ocean we have’ to ‘the ocean we want’ (Fig. 1). The draft plan calls on the scientific community to develop Actions, at programme, project, activity or contribution levels, to help deliver on four key objectives: (1) increase capacity to generate, understand, manage and use ocean knowledge; (2) identify and generate required ocean data, information and knowledge; (3) build comprehensive understanding of the ocean and its governance systems; and (4) increase the use of ocean knowledge.