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Bottom trawling can cause acute depletion of benthic invertebrate biomass, thus reducing competition among surviving organisms and increasing food availability by generating carrion. As ectotherms are generally smaller and grow faster with increasing temperature, they may be less vulnerable to trawling and quicker to replenish biomass in warmer waters. Therefore, the chronic effect of bottom trawling on benthic invertebrate biomass may depend on local sea temperature and, hence, be under the influence of climate change. We tested this hypothesis using benthic grab samples from 200 sites spanning the North Sea and data on trawling pressure in the areas where samples were collected. The relationship between benthic community biomass and swept area ratio (the average number of times the seabed is trawled per year) was negative where annual bottom water temperature was low (8°C), positive in relatively warm water (11°C) and approximately neutral at intermediate temperature (9.5°C). These relationships were attributed to changes in mean body mass, not community abundance. Our results are consistent with theoretical expectations and suggest that climate modulates the chronic effect of bottom trawling on benthic invertebrate biomass. Confirming causality and determining the broader consequences for community structure and ecosystem functioning should be priorities of future research.

The global issues of climate change and marine litter are interlinked and understanding these connections is key to managing their combined risks to marine biodiversity and ultimately society. For example, fossil fuel-based plastics cause direct emissions of greenhouse gases and therefore are an important contributing factor to climate change, while other impacts of plastics can manifest as alterations in key species and habitats in coastal and marine environments. Marine litter is acknowledged as a threat multiplier that acts with other stressors such as climate change to cause far greater damage than if they occurred in isolation. On the other hand, while climate change can lead to increased inputs of litter into the marine environment, the presence of marine litter can also undermine the climate resilience of marine ecosystems. There is increasing evidence that that climate change and marine litter are inextricably linked, although these interactions and the resulting effects vary widely across oceanic regions and depend on the particular characteristics of specific marine environments. Ecosystem resilience approaches, that integrate climate change with other local stressors, offer a suitable framework to incorporate the consideration of marine litter where that is deemed to be a risk, and to steer, coordinate and prioritise research and monitoring, as well as management, policy, planning and action to effectively tackle the combined risks and impacts from climate change and marine litter.

The blue growth agenda has spurred an accelerating exploitation and continued development of the coastal and marine environment. This is also driven by the increasing need to generate renewable energy. In most cases, this has resulted in a large number of man-made structures (MMSs) across several soft sediment environments. The nature of these structures ranges from oil and gas installations to harbour walls, anchored buoys, pipelines and offshore wind farms. These structures host fouling communities that are often new to offshore regions, potentially serving as stepping stones for range-expanding (non-indigenous) species and providing habitat and shelter for a variety of marine species. The altered local biodiversity also affects biological and biogeochemical processes from the water column to the seafloor, either directly (e.g. scouring, organic matter export from piles) or indirectly (e.g. closure or displacement of fisheries) and, hence, ecosystem functioning at various spatial and temporal scales. A proper understanding of the effects of artificial hard substrate and the consequences of its removal (e.g. through decommissioning) to marine biodiversity has yet to develop to maturity. This themed article set contributes to the scientific knowledge base on the impacts of MMSs on marine ecosystems with the specific aim to fertilize and facilitate an evidence-based debate over decommissioning. This discussion will become ever more vital to inform marine spatial planning and future policy decisions on the use and protection of marine resources.

Recent papers postulate that epifaunal organisms use artificial structures as stepping‐stones to spread to areas that are too distant to reach in a single generation. With thousands of artificial structures present in the North Sea, we test the hypothesis that these structures are connected by water currents and act as an interconnected reef. Population genetic structure of the Blue mussel, Mytilus edulis was expected to follow a pattern predicted by particle tracking models (PTM). Correlation between population genetic differentiation, based on microsatellite markers, and particle exchange was tested. Specimens of M. edulis were found at each location, although the PTM indicated that locations >85 km offshore were isolated from coastal sub‐populations. Fixation coefficient FST correlated with the number of arrivals in the PTM. However, the number of effective migrants per generation as inferred from coalescent simulations did not show a strong correlation with the arriving particles. Isolation by distance analysis showed no increase in isolation with increasing distance and we did not find clear structure among the populations. The marine stepping‐stone effect is obviously important for the distribution of M. edulis in the North Sea and it may influence ecologically comparable species in a similar way. In the absence of artificial shallow hard substrates, M. edulis would be unlikely to survive in offshore North Sea waters. Although we found an indication that FST was lower between connected locations, isolation by distance analysis showed no increase in isolation with increasing distance. Finally, we did not find clear structure among the populations.

Over the last years, the development of offshore renewable energy installations such as offshore wind farms led to an increasing number of man-made structures in marine environments. Since 2009, benthic impact monitoring programs were carried out in wind farms installed in the southern North Sea. We collated and analyzed data sets from three major monitoring programs. Our analysis considered a total of 2849 sampling points converted to a set of biodiversity response metrics. We analyzed biodiversity changes related to the implementation of offshore wind farms and generalized the correlation of these changes with spatial and temporal patterns. Our results demonstrate that depth, season and distance to structure (soft-bottom community) consistently determined diversity indicators and abundance parameters, whereas the age and the country affiliation were significantly related to some but not all indices. The water depth was the most important structuring factor for fouling communities while seasonal effects were driving most of the observed changes in soft-sediment communities. We demonstrate that a meta-analysis can provide an improved level of understanding of ecological patterns on large-scale effects of anthropogenic structures on marine biodiversity, which were not visible in single monitoring studies. We believe that meta-analyses should become an indispensable tool for management of offshore wind farm effects in the future, particularly in the view of the foreseen development of offshore renewable energies. This might lead to a better picture and more comprehensive view on potential alterations. However, this requires a modern open-source data policy and data management, across institutions and across national borders.

Global environmental change is increasing hypoxia in aquatic ecosystems. During hypoxic events, bacterial respiration causes an increase in carbon dioxide (CO2) while oxygen (O2) declines. This is rarely accounted for when assessing hypoxia tolerances of aquatic organisms. We investigated the impact of environmentally realistic increases in CO2 on responses to hypoxia in European sea bass (Dicentrarchus labrax). We conducted a critical oxygen (O2crit) test, a common measure of hypoxia tolerance, using two treatments in which O2 levels were reduced with constant ambient CO2 levels (~530 µatm), or with reciprocal increases in CO2 (rising to ~2,500 µatm). We also assessed blood acid-base chemistry and haemoglobin-O2 binding affinity of sea bass in hypoxic conditions with ambient (~650 μatm) or raised CO2 (~1770 μatm) levels. Sea bass exhibited greater hypoxia tolerance (~20% reduced O2crit), associated with increased haemoglobin-O2 affinity (~32% fall in P50) of red blood cells, when exposed to reciprocal changes in O2 and CO2. This indicates that rising CO2 which accompanies environmental hypoxia facilitates increased O2 uptake by the blood in low O2 conditions, enhancing hypoxia tolerance. We recommend that when impacts of hypoxia on aquatic organisms are assessed, due consideration is given to associated environmental increases in CO2.

The North Sea is one of the most studied and exploited ecosystems worldwide. The multiple uses from industrial, transport, as well as recreational activities have required researchers, regulators, and legislators to understand and, where possible, to minimize any expected negative environmental impacts. As with any international sea, assessing the current pressures and management actions resulting from these activities is centred on several national and international legislative instruments. This variety of co-existing legislations makes development processes and regulatory assessments cumbersome and time consuming. Hence there is a need to integrate environmental risk assessment and management across sectors, ensuring smart, cost-effective data generation, as well as supporting and standardizing environmental practices. This paper provides an overview of the changing regulatory frameworks regarding offshore chemicals used in the oil and gas industry, and the process of chemical risk assessment conducted under the Offshore Chemical Notification Scheme (ONCS) in the UK. Our view of methodological, research, and regulatory needs and challenges that should be addressed to ensure an adequate and sustainable assessment of offshore chemical use in the North Sea is discussed. Furthermore, we discuss the issues faced regarding chemicals used in the UK oil and gas sector with respect to declining hydrocarbon production.

Cumulative effects assessments are a legal requirement in many jurisdictions and are key to informing marine policy. However, practice does not yet deliver fit-for-purpose assessments relative to sustainable development and environmental protection obligations. The complexity of cumulative effect questions, which are embedded in complex social-ecological systems, makes multiple, methodologically diverse assessments a necessity. Using the expansion of marine renewable energy developments in European Union waters as a case study, this paper explores how social-ecological systems thinking and cumulative effects assessment theory can combine to structure CEAs that better support the management and regulation of maritime activities at regional scales. A general perspective for cumulative effects assessment is proposed to remove ambiguity of intent and to orient assessments towards a common objective. Candidate principles for practice are presented for consideration. These principles are integrated into a stepped assessment approach that seeks to improve cumulative effects assessments of localised activities relative to the information needs of decision-makers implementing the ecosystem approach.

Fish in coastal ecosystems can be exposed to acute variations in CO2that can approach 1 kPa CO2(10,000 μatm). Coping with this environmental challenge will depend on the ability to rapidly compensate the internal acid-base disturbance caused by sudden exposure to high environmental CO2(blood and tissue acidosis); however, studies about the speed of acid-base regulatory responses in marine fish are scarce. We observed that upon exposure to ~1 kPa CO2, European sea bass (Dicentrarchus labrax) completely regulate erythrocyte intracellular pH within ~40 minutes, thus restoring haemoglobin-O2affinity to pre-exposure levels. Moreover, blood pH returned to normal levels within ~2 hours, which is one of the fastest acid-base recoveries documented in any fish. This was achieved via a large upregulation of net acid excretion and accumulation of HCO3− in blood, which increased from ~4 to ~22 mM. While the abundance and intracellular localisation of gill Na+/K+-ATPase (NKA) and Na+/H+exchanger 3 (NHE3) remained unchanged, the apical surface area of acid-excreting gill ionocytes doubled. This constitutes a novel mechanism for rapidly increasing acid excretion during sudden blood acidosis. Rapid acid-base regulation was completely prevented when the same high CO2exposure occurred in seawater with experimentally reduced HCO3− and pH, likely because reduced environmental pH inhibited gill H+excretion via NHE3. The rapid and robust acid-base regulatory responses identified will enable European sea bass to maintain physiological performance during large and sudden CO2fluctuations that naturally occur in coastal environments.Summary statementEuropean sea bass exposed to 1 kPa (10,000 μatm) CO2regulate blood and red cell pH within 2 hours and 40 minutes, respectively, protecting O2transport capacity, via enhanced gill acid excretion.

Climate change causes warming, decreased O2, and increased CO2 in marine systems and responses of organisms will depend on interactive effects between these factors. We provide the first experimental assessment of the interactive effects of warming (14 to 22°C), reduced O2 (∼3 – 21 kPa O2), and increased CO2 (∼400 or ∼1000 µatm ambient CO2) on four indicators of aerobic performance (standard metabolic rate, SMR, maximum metabolic rate, MMR, aerobic scope, and hypoxia tolerance, O2crit), blood chemistry, and O2 transport (P50) of a marine fish, the European sea bass (Dicentrarchus labrax). Warming increased SMR and O2crit (i.e. reduced hypoxia tolerance) as well as MMR in normoxia but there was an interactive effect with O2 so that hypoxia caused larger reductions in MMR and aerobic scope at higher temperatures. Increasing CO2 had minimal effects on SMR, MMR and O2crit and did not show interactive effects with temperature or O2 for any measured variables. Aerobic performance was not linked to changes in blood chemistry or P50. Despite lack of effects of CO2 on aerobic performance, increased CO2 induced 30% mortality of fish exercised in low O2 at 22°C indicating important threshold effects independent of aerobic performance. Overall, our results show temperature and O2, but not CO2, interact to affect aerobic performance of sea bass, disagreeing with predictions of the oxygen- and capacity-limited thermal tolerance hypothesis.

On 22 December 2019, the world of fisheries science and whale conservation lost one of its most ardent champions with the passing of Sidney J. Holt. His career began in 1947 at the age of 21. Ten years later, he and his colleague Ray Beverton published their authoritative monograph on quantitative fish population dynamics. In 1953, he joined the Fisheries Division of the United Nations Food and Agriculture Organization and soon became heavily involved in assessing whale stocks under the auspices of the International Whaling Commission, a role that eventually led to advocating for animal rights and the cessation of commercial whaling. Later in life, he returned to fisheries assessment and management, particularly issues pertaining to the Common Fisheries Policy of the European Union, where he advocated for fishing mortality less than that associated with maximum sustainable yield. This themed set consists of articles written by authors who knew and collaborated with Sidney, who may have met him once or twice at an international meeting, and who only knew of him via his reputation and massive and influential list of publications. Their articles address a wide range of topics relating to his work throughout his career and reflect, in part, the influence that his work has had on thinking about quantitative modelling of animal populations., SI

There is concern across the International Council for the Exploration of the Sea (ICES) region that a consideration of vulnerable components and the wider support mechanisms underpinning benthic marine ecosystems may be lacking from the process of marine protected area (MPA) designation, management and monitoring. In this study, MPAs across six European ecoregions were assessed from a benthic ecology perspective. The study included 102 MPAs, designated by 10 countries, and focused on three aspects regarding the role of the benthos in: (i) the designation of MPAs; (ii) the management measures used in MPAs; and (iii) the monitoring and assessment of MPAs. Qualitative entries to a questionnaire based on an existing framework (EU project ‘Monitoring Evaluation of Spatially Managed Areas’, (MESMA) were collected by 19 benthic experts of the ICES Benthic Ecology Working Group. A pedigree matrix was used to apply a numerical scale (score) to these entries. The results showed clear differences in scores between ecoregions and between criteria. The designation‐phase criteria generally achieved higher scores than the implementation‐phase criteria. Poor designation‐phase scores were generally reiterated in the implementation‐phase scores, such as scores for assessment and monitoring. Over 70% of the MPA case studies were found to consider the benthos to some extent during selection and designation; however, this was not followed up with appropriate management measures and good practice during the implementation phase. Poor spatial and temporal coverage of monitoring and ineffective indicators is unlikely to pick up changes caused by management measures in the MPA. There is concern that without adequate monitoring and adaptive management frameworks, the MPAs will be compromised. Also, there could be an increased likelihood that, with regard to the benthos, they will fail to meet their conservation objectives. This assessment was successful in highlighting issues related to the representation and protection of the benthos in MPAs and where changes need to be made, such as expanding the characterization and monitoring of benthic species or habitats of interest. These issues could be attributable to an ongoing process and/or an indication that some MPAs only have ‘paper protection’.

As the EU's commitment to renewable energy is projected to grow to 20% of energy generation by 2020, the use of marine renewable energy from wind, wave and tidal resources is increasing. This literature review (233 studies) (i) summarizes knowledge on how marine renewable energy devices affect benthic environments, (ii) explains how these effects could alter ecosystem processes that support major ecosystem services and (iii) provides an approach to determine urgent research needs. Conceptual diagrams were set up to structure hypothesized cause-effect relationships (i.e. paths). Paths were scored for (i) temporal and spatial scale of the effect, (ii) benthic sensitivity to these effects, (iii) the effect consistency and iv) scoring confidence, and consecutively ranked. This approach identified prominent knowledge gaps and research needs about (a) hydrodynamic changes possibly resulting in altered primary production with potential consequences for filter feeders, (b) the introduction and range expansion of non-native species (through stepping stone effects) and, (c) noise and vibration effects on benthic organisms. Our results further provide evidence that benthic sensitivity to offshore renewable effects is higher than previously indicated. Knowledge on changes of ecological functioning through cascading effects is limited and requires distinct hypothesis-driven research combined with integrative ecological modelling.

Ocean acidification may pose a major threat to commercial fisheries, especially those for calcifying shellfish species. This study was undertaken to estimate the potential economic costs resulting from ocean acidification on UK wild capture and aquaculture shellfish production. Applying the net present value (NPV) and partial equilibrium (PE) models, we estimate both direct and economy-wide economic losses of shellfish production by 2100. Estimates using the NPV method show that the direct potential losses due to reduced shellfish production range from 14% to 28% of fishery NPV. This equates to annual economic losses of between o3 and o6 billion of the UK’s GDP in 2013, for medium and high emission scenarios. Results using the PE model showed the total loss to the UK economy from shellfish production and consumption ranging from o23–o88 million. The results from both the direct valuation and predicted estimate for the economic losses on shellfish harvest indicate that there are regional variations due to different patterns of shellfish wild-capture and aquaculture, and the exploitation of species with differing sensitivities to ocean acidification. These results suggest that the potential economic losses vary depending on the chosen valuation method. This analysis is also partial as it did not include a wider group of species in early-life-stages or predator-prey effects. Nevertheless, findings show that the economic losses to the UK and its devolved administrations due to ocean acidification could be substantial. We conclude that addressing ocean acidification with the aim of preserving commercially valuable shellfish resources will require regional, national or international solutions using a combined approach to reduce atmospheric CO2 emissions and shift in focus to exploit species that are less vulnerable to ocean acidification.

Assessment of the effects of sediment metal contamination on biological assemblages and function remains a key question in marine management, especially in relation to disposal activities. However, the appropriate description of bioavailable metal concentrations within pore-waters has rarely been reported. Here, metal behaviour and availability at contaminated dredged material disposal sites within UK waters were investigated using Diffusive Gradient in Thin films (DGT). Three stations, representing contrasting history and presence of dredge disposal were studied. Depth profiles of five metals were derived using DGT probes as well as discrete analysis of total metal concentrations from sliced cores. The metals analysed were: iron and manganese, both relevant to sediment biogeochemistry; cadmium, nickel and lead, classified as priority pollutants. DGT time-integrated labile flux profiles of the metals display behaviour consistent with increasingly reduced conditions at depth and availability to DGT (iron and manganese), subsurface peaks and a potential sedimentary source to the water column related to the disposal activity (lead and nickel) and release to pore-water linked to decomposition of enriched phytodetritus (cadmium). DGT data has the potential to improve our current understanding of metal behaviour at impacted sites and is suitable as a monitoring tool. DGT data can provide information on metal availability and fluxes within the sediment at high depth-resolution (5 mm steps). Differences observed in the resulting profiles between DGT and conventional total metal analysis illustrates the significance of considering both total metals and a potentially labile fraction. The study outcomes can help to inform and improve future disposal site impact assessment, and could be complemented with techniques such as Sediment Profile Imagery for improved biologically relevance, spatial coverage and cost-effective monitoring and sampling of dredge material disposal sites. Additionally, the application of this technology could help improve correlative work on biological impacts under national and international auspices when linking biological effects to more biologically relevant metal concentrations.

(IF 2.39; Q1); International audience; The expected increase of maritime activities in the North Sea and the growing awareness of its natural environmental value require enhanced science-based environmental advice for more efficient and effective marine management. The North Sea Open Science Conference organised by the Royal Belgian Institute of Natural Sciences and the Belgian Biodiversity Platform in 2016 aimed to take stock of the present-day scientific knowledge on the North Sea ecosystem, its interactions with human activities and its management. The conference was structured along three themes: (1) ‘the scientific backbone of the North Sea ecosystem: adequacy of the knowledge base?’, (2) ‘A new era in environmental monitoring and assessment: what is at stake?’, and (3) ‘Sustainability: one for all, all for one?’. Focusing on ‘open science’, we welcomed about 200 participants from around the North Sea with different backgrounds and interests in environmental sciences. The participants were challenged to reflect on current and future challenges for the North Sea management and, in particular, to explore possible nature-friendly solutions for addressing these challenges during a series of introductory oral (69) and poster (59) presentations, and World Café and Fish Bowl participatory sessions. The participants agreed on six main actions to (1) provide a solid scientific base for marine management decisions; (2) develop society-driven research; (3) increase interdisciplinary science; (4) recognise the need for system knowledge; (5) improve communication, knowledge exchange, and collective implementation of scientific knowledge; and (6) build integrated knowledge bases. For each of these, concrete action points were identified, and this review gives the most important and relevant ones for creating the knowledge base and managerial framework for a sustainable North Sea.

European research efforts to address concerns in relation to increasing levels of marine litter and potential effects on ecosystems and human health have been launched. We assessed a total of 52 European projects which researched or contributed to the implementation of European marine litter legislation. These projects ranged from national initiatives, to large scale programmes involving multiple EU member states. The best represented topics within those European projects were 'Policy, Governance and Management' and 'Monitoring'. Comparatively 'Risk Assessment', 'Fragmentation' and 'Assessment Tools' were underrepresented. The analyses showed that West-European countries have contributed more to marine litter research and therefore received more funding. As a result, thematic hotspots were present, and scientific capacity is concentrated by topic and countries. The results indicate the need to continue to support initiatives to cover clearly identified gaps, either geographic or thematic, to deliver risk assessments and recommendations to address the marine litter issue.

Benthic habitat condition assessments are a requirement under various environmental directives. The Marine Strategy Framework Directive (MSFD), for example, challenges member states in a European sea region to perform comparable assessments of good environmental status and improve coherence of their monitoring programmes by 2020. Currently, North Sea countries operate independent monitoring programmes using nationally defined assessment areas. Lack of an agreed OSPAR or EU scale monitoring method and programme has been identified as a priority science need. This paper proposes a method for the development of a coherent and efficient spatial sampling design for benthic habitats on regional level and gives advice on optimal monitoring effort to get more accurate assessments. We use ecologically relevant assessment areas (strata) across national borders and test spatial sample allocation methods. Furthermore, we investigate the number of samples needed in each stratum to reduce the variance for estimating mean number of taxa and abundance. The stratification needs to take into account the spatial heterogeneity of the entire ecosystem. The total sample effort is optimal when sample allocation takes into account the size and benthic variability within those strata. Change point analysis helps to find a balance between sampling effort and precision of the benthic parameter estimate. A joint sampling design for the North Sea could be generated by combining current efforts, and where needed adapting existing national programmes. This serves a coordinated, region-wide, benthic condition status assessment and strengthens regional cooperation to fulfil multiple monitoring tasks, with a scientifically underpinned common approach.

In this paper we outline the stakeholder-led approaches in the development of biological data products to support effective conservation, management and policy development. The requirements of a broad range of stakeholders and iterative, structured processes framed the development of tools, models and maps that support the FAIR (Findable, Accessible, Interoperable, Reusable) data principles. By structuring the resultant data products around the emerging biological Essential Ocean Variables, and through the engagement with a broad range of end-users, the EMODnet (European Marine Observation and Data Network) Biology project has delivered a suite of demonstration data products. These products are presented in the European Atlas of Marine Life, an online resource demonstrating the value of open marine biodiversity data and help to answer fundamental and policy-driven questions related to managing the natural and anthropogenic impacts in European waters.

Bioturbation is one of the key mediators of biogeochemical processes in benthic habitats that can have a high contribution to seafloor functioning and benthic pelagic coupling in coastal waters. Previous studies on bioturbation were limited to point locations and extrapolations in single regions, but have not accounted for regional differences under changing environmental conditions, though there are indications that species contributions will differ across regions or with biotic and abiotic context. To capture those differences and assess global patterns and commonalities, multi-regional analyses are imperative. Here for the first time, bioturbation potential (BPc), a functional indicator of benthic community bioturbation, was estimated based on macrofauna data from four regions (i.e. German Baltic Sea, German North Sea, Belgian part of the North Sea and the Eastern English Channel). For each region and sediment type we identified key species contributing to BPc. Comparison within and across regions demonstrated regional differences, and both overlap and mismatch between species that are functionally important and those that are dominant in biomass. Knowledge on the functionally important species is crucial when management objectives include the protection of certain ecosystem functions. Available environmental layers were used as predictors to model the spatial distribution of BPc for each area and to explore the underlying drivers of differences. Random forest models were trained using as response variables either i) BPc initially calculated per station; or ii) BPp – the species-specific contribution to BPc – for key species (with subsequent summation of their predicted full-coverage distributions to BPc). Maps of BPc distribution predicted by random forest were compared with those generated using natural neighbour interpolation. Overall, derived BPc values increased towards the German parts of the North and Baltic Seas. The relevance of BPc for ecosystem processes and functions, however, vary with biotic and abiotic settings. Results revealed a strong association of BPc with species diversity and region, but less with sediment grain size. A large range of BPc occurred when species richness was low. This suggests that the provisioning of high bioturbation activity is possible also under low diversity, where it is vulnerable due to reduced resilience. The executed multi-regional analysis allowed identifying regional differences in performance of macrofauna, suggesting the need for region-specific conservation and management strategies.

Acknowledgements: The Blue Growth Data Workshop was organised by the University of Edinburgh through the INSITE Data Initiative funded by the INSITE (INfluence of man-made Structures In the Ecosystem, www.insitenorthsea.org) research programme. The authors thank participants from BP, British Geological Survey, Gardline, DeepTek, theDataLab, Hartley Anderson, Marine Scotland Science, Heriot-Watt University, BMT Cordah, Shell, BEIS OPRED and Marathon Oil for their contributions. INSITE follows the 2012 Oil and Gas UK led “Decommissioning Baseline Study” joint industry project that identified data gaps in our understanding in the influence of man-made structures on the ecology of the North Sea. J. Murray Roberts and Katherine Needham acknowledge further support from the European Union's Horizon 2020 Research and Innovation Programme under grant agreement No. 678760 (ATLAS). David Billett was supported by funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 689518 (MERCES: Marine Ecosystem Restoration in Changing European Seas). Lea-Anne Henry was supported by the INSITE Project “Appraisal of Network Connectivity between North Sea subsea oil and gas platforms”. Kieran Hyder was supported by INSITE project “Assessing the ecological connectivity between man-made structures in the North Sea”. Silvana Birchenough was supported by the INSITE project “Understanding the influence of man-made structures on the ecosystem functions of the North Sea and the European Union's Horizon 2020 Project COLUMBUS (652690) ”Knowledge Transfer for Blue Growth”. This output reflects only the authors’ views and the European Union cannot be held responsible for any use that may be made of the information contained therein.

The EU Marine Strategy Framework Directive (MSFD) requires that GoodEnvironmentalStatus (GEnS), is achieved for European seas by 2020. These may deviate from GEnS, its 11Descriptors, targets and baselines, due to endogenic managed pressures (from activities withinan area) and externally due to exogenic unmanaged pressures (e.g. climate change). Conceptualmodels detail the likely or perceived changes expected on marine biodiversity and GEnSDescriptors in the light of climate change. We emphasise that marine management has toaccommodate ‘shifting baselines’ caused by climate change particularly during GEnSmonitoring, assessment and management and ‘unbounded boundaries’ given the migration anddispersal of highly-mobile species. We suggest climate change may prevent GEnS being met,but Member States may rebut legal challenges by claiming that this is outside its control, forcemajeure or due to ‘natural causes’ (Article 14 of the MSFD). The analysis is relevant tomanagement of other global seas.

Proponents of marine renewable energy worldwide highlight that regulatory and consenting procedures are a significant barrier to the upscaling of infrastructure required to transform the energy generation sector. Uncertainties about the cumulative effects of marine renewable energy developments cause substantial delays during the consenting process, which are exacerbated by the lack of clarity about how to assess cumulative effects. These obstacles have contributed to perceptions that this essential emerging industry receives disproportionate scrutiny relative to established maritime activities. However, alongside legislated targets to reduce carbon emissions, there are legal obligations to protect, maintain and improve the condition of the marine environment. As the imperative to halt the decline in the condition of the environment increases, so expectations of cumulative impact assessments grow and the risk of consenting delays persists. To investigate how robust current cumulative impact assessment practise is, a novel evaluation framework was developed and applied to Environmental Statements of the world's largest offshore wind farms, currently in United Kingdom waters. The framework was designed to evaluate cumulative impact assessments relative to the information needs of decision-makers tasked with managing cumulative effects. We found that current practise does not meet those needs, that there is dissonance between science and practise, and problematic variability between assessments was observed. Straightforward recommendations for improved practise are provided, which if implemented may ease the perceived regulatory burden by clarifying practise. We also highlight additional steps that could enable project-led cumulative impact assessments to better support regional marine management. The results and recommendations will be of interest to countries worldwide where marine renewable energy is emerging alongside ecosystem-approach and marine spatial planning aspirations.

Aquaculture is the fastest growing food production system in the world, generating more than half of the global seafood harvested today. These type of activities are crucial to provide key nutritional components for humanity in the future as populations worldwide are increasing and the demands for securing food resources are imperative. Multiple socio-ecological factors such as weak regulations and focus on maximizing production limit production and threaten the sustainable growth of aquaculture. We present a novel policy framework to evaluate and pursue growth in aquaculture considering four boundaries: biological productivity, environmental constraints to that productivity, policy that inhibits or promotes different kinds of aquaculture, and social preferences that determine aquaculture markets. Using a range of scenarios, we have shown that sustainable growth in aquaculture requires simultaneous consideration of all four boundaries and the potential interactions between all of these options. Our proposed conceptual framework shows that to further expand the boundaries of aquaculture production, the policy focus must remain flexible to enable the adaptation of from single-boundary approaches. Our approach takes account of the current boundaries, helping to consider the adaptive policy, which is deemed as a necessary tool for considering the dynamic interactions among boundaries, thus addressing the problem of defining the evolving limits of sustainable aquaculture.

This paper focuses on the difference between the value of some commonly used diversity indices (Simpson, Shannon, abundance, richness) calculated from benthic grab samples and their value in the population or region from which the samples are taken. The ability of the sample indices, as well as a recently derived relative Shannon index, to reflect change in biodiversity is examined in a short simulation study based on changing one of the diversity parameters (abundance, richness and evenness) in the population, whilst keeping the other two components constant. Our results suggest that, whilst their population equivalents do not always reflect biodiversity changes, the sample Simpson, Shannon and Richness indices perform well. We note that this will be true for any surveys where the sampling programme fails to detect many species in a population, and hence will be applicable for most benthic surveys. The use of sample indices to detect changes in biodiversity from long-running time series in the Thames and Tyne estuaries is illustrated.

A conceptual model of the main carbon and nitrogen flows through pelagic and benthic food webs was used to identify the key biogeochemical processes representing ecosystem functioning, and to select indicators of each of these processes. A combined fieldwork and modelling approach was used to provide the data required to evaluate the indicators in terms of their suitability for assessing and managing the impacts of climate change and demersal trawling. Four of our 16 proposed indicators (phytoplankton production and productivity, near-bed oxygen concentrations and oxygen penetration of the seabed) met the majority of criteria we used for evaluating indicators. Five indicators (depth of anoxic sediment, zoobenthos biomass, production, productivity and bioturbation potential) did not comply with sufficient criteria to be considered as good indicators. Six of our proposed indicators (zooplankton biomass, size structure, production and productivity; ecosystem productivity; ecosystem balance) could not be assessed for sensitivity and specificity using our models, and therefore need to be addressed in future work aimed at improving both the models and the fieldwork. Our results indicate that evaluation of indicators is difficult, because of the number and variety of human pressures which need to be considered in reality, and the interactions between these pressures and the ecosystem components which they affect. The challenge will be to establish if there are indeed any indicators which are able to meet the majority of criteria for good indicators in holistic ecosystem-based assessments.

Regime shifts are sudden changes in ecosystem structure that can be detected across several ecosystem components. The concept that regime shifts are common in marine ecosystems has gained popularity in recent years. Many studies have searched for the step-like changes in ecosystem state expected under a simple interpretation of this idea. However, other kinds of change, such as pervasive trends, have often been ignored. We assembled over 300 ecological time series from seven UK marine regions, covering two to three decades. We developed state-space models for the first principal component of the time series in each region, a common measure of ecosystem state. Our models allowed both trends and step changes, possibly in combination. We found trends in three of seven regions and step changes in two of seven regions. Gradual and sudden changes are therefore important trajectories to consider in marine ecosystems.

Current national (e.g. UK Marine and Coastal Access Act) and international (e.g. Water Framework Directive, Habitats and Bird Directives, European Marine Strategy Framework Directive) legislation and the recent UK state of the seas report Charting Progress 2 have focused on the quality and status of the marine environment. To this end, the UK has continued to work on the need to develop indicators which can assist with this process. This work has helped to identify the natural processes and man-made activities that are affecting marine systems. One of the marine descriptors within the MSFD is ‘seabed integrity’. This descriptor asks member states to ensure that the structure and function of ecosystems are safeguarded and benthic systems are not adversely affected. To date, we have furthered our understanding of the seabed by, for example, studying benthic systems. For this purpose indicator tools, such as a suite of benthic indices, have been employed as measures of ‘the health of benthic systems’. In most cases this information mainly relates to the structure of benthic populations. However, there is a gap in terms of what we can measure with regards to the function of the ecosystem and how individual benthic animals perform their roles within specific ecosystems. There is also a lack of data to assess if the functions of the seafloor are safeguarded. This work has combined two metrics, bioturbation potential (Bpc) calculated from quantitative information and apparent redox discontinuity layer (aRPD) derived from SPI images. Results indicated that both metrics provide valuable complementary information. The aRPD informed on the status of the sedimentary environment and these values were easily related to Bpc values. The Bpc values were used to quantify bioturbation activity and species’ identity at each site. The link between aRPD and Bpc can allow characterisation of 4 conceptual areas in relation to a key sediment function such as to carbon and nutrient cycling rates and control areas.

A regime shift is a large, sudden, and long-lasting change in the dynamics of an ecosystem, affecting multiple trophic levels. There are a growing number of papers that report regime shifts in marine ecosystems. However, the evidence for regime shifts is equivocal, because the methods used to detect them are not yet well developed. We have collated over 300 biological time series from seven marine regions around the UK, covering the ecosystem from phytoplankton to marine mammals. Each time series consists of annual measures of abundance for a single group of organisms over several decades. We summarised the data for each region using the first principal component, weighting either each time series or each biological component (e.g. plankton, fish, benthos) equally. We then searched for regime shifts using Rodionov’s regime shift detection (RSD) method, which found regime shifts in the first principal component for all seven marine regions. However, there are consistent temporal trends in the data for six of the seven regions. Such trends violate the assumptions of RSD. Thus, the regime shifts detected by RSD in six of the seven regions are likely to be artefacts caused by temporal trends. We are therefore developing more appropriate time series models for both single populations and whole communities that will explicitly model temporal trends and should increase our ability to detect true regime shift events.

Each year approximately 23–28 million tonnes of sand and gravel are removed from offshore sediments around England and Wales. This study was located in a licensed marine aggregate extraction site off Shoreham in the Eastern English Channel (EEC thereafter). Results from the multibeam survey showed the presence of dredged pits created by suction hopper dredging and elongated furrows created by trailer suction hopper dredging in the area where sand and gravel had been excavated. Electronic Monitoring System (EMS) contained the dredging intensity recorded annually at the site; this information was combined with particle size data providing interpreted maps, which informed the status of the sediments at the site. The aim of the current study was to explore the presence of marine habitats over a smaller area known as the ‘Shoreham Box’ in the EEC. Results showed some differences in the community composition produced by the two methods of extraction. There was also indication of enhanced number of species in the area dredged by suction hopper method. Notably, slipper limpets were also observed inhabiting dredged pits and creating permanent habitats in areas cratered by the dredging activity. This study has generated ecological information on the status of species and habitats inhabiting the dredged and undredged area. Management considerations are also discussed to ensure that sound aggregate extraction practices are in place to minimised the effects of aggregate dredging over licensed areas.

Half a million tonnes of sewage sludge was disposed annually over an 18-yr period at a licensed area off the Northumberland coast, UK. The disposal operation ceased in December 1998, providing the ecological opportunity to study macrobenthic changes in relation to theoretical succession models. A transect from the centre of the disposal site to a control station was monitored three times a year (i.e. March, August and December). This study provides a description of the changes in the macrobenthos and physical environment in the initial ‘3 years’ (i.e. 1999 – 2001). During the period of sewage sludge disposal there were indications of an impact on the macrobenthic community with a high total abundance of individuals ( N ) and high total number of species ( S ) at the stations located in the centre of the disposal ground. During the immediate post-disposal phase the site continued to show a localised increased of individuals and species in the disposal area. Over time the communities showed signs of successional changes when the reduction of organic matter source was eliminated from the natural system. Multivariate analysis demonstrated a clear gradient of change in the community composition between impacted and control stations. While most benthic studies assess re-colonisation and succession stages of macrobenthos by using manipulative field experiments, this study provides an in situ long-term assessment in the offshore environment. This study contributes with information on: i) initial colonization and succession of macrobenthic communities over a large scale and real world data; ii) macrobenthic data into existing successional models and iii) resilience of benthic communities following the cessation of sewage sludge disposal. This information has the potential to contribute to an effective management of the marine communities in the North Sea.

Data support for GES assessment under the MSFD will require subregion-scale Joint Monitoring Programmes (JMPs). These JMPs must be cost-efficient and produce the necessary evidence-base to support management decisions. This review summarises the outputs of a 2.5-day multidisciplinary workshop where scientists and programme managers developed monitoring scenarios as examples of how current sampling activities could be extended and combined into framework JMPs. The objective was to explore opportunities for improved i) integration of monitoring, ii) international collaboration and iii) multi-disciplinary use of platforms. The workshop identified opportunities to upgrade current monitoring programmes, to include additional sampling activities, and to support integration of resources and activities. We found that developing JMPs using this bottom-up approach has potential benefits but requires commitment and expert coordination. Coordination needs include definition of data requirements, common sampling methodologies and data exchange.

There is growing evidence that climate change could affectmarine benthic systems. This review provides information of climate change-related impacts on the marine benthos in the North Atlantic. We cover a number of related research aspects, mainly in connection to two key issues. First, is the relationship between different physical aspects of climate change and the marine benthos. This section covers: (a) the responses to changes in seawater temperature (biogeographic shifts and phenology); (b) altered Hydrodynamics; (c) ocean acidification (OA); and (d) sea-level rise-coastal squeeze. The second major issue addressed is the possible integrated impact of climate change on the benthos. This work is based on relationships between proxies for climate variability, notably the North Atlantic Oscillation (NAO) index, and the long-term marine benthos. The final section of our review provides a series of conclusions and future directions to support climate change research on marine benthic systems.

Marine benthic ecosystems are difficult to monitor and assess, which is in contrast to modern ecosystem-based management requiring detailed information at all important ecological and anthropogenic impact levels. Ecosystem management needs to ensure a sustainable exploitation of marine resources as well as the protection of sensitive habitats, taking account of potential multiple-use conflicts and impacts over large spatial scales. The urgent need for large-scale spatial data on benthic species and communities resulted in an increasing application of distribution modelling (DM). The use of DM techniques enables to employ full spatial coverage data of environmental variables to predict benthic spatial distribution patterns. Especially, statistical DMs have opened new possibilities for ecosystem management applications, since they are straightforward and the outputs are easy to interpret and communicate. Mechanistic modelling techniques, targeting the fundamental niche of species, and Bayesian belief networks are the most promising to further improve DM performance in the marine realm. There are many actual and potential management applications of DMs in the marine benthic environment, these are (i) early warning systems for species invasion and pest control, (ii) to assess distribution probabilities of species to be protected, (iii) uses in monitoring design and spatial management frameworks (e.g. MPA designations), and (iv) establishing long-term ecosystem management measures (accounting for future climate-driven changes in the ecosystem). It is important to acknowledge also the limitations associated with DM applications in a marine management context as well as considering new areas for future DM developments. The knowledge of explanatory variables, for example, setting the basis for DM, will continue to be further developed: this includes both the abiotic (natural and anthropogenic) and the more pressing biotic (e.g. species interactions) aspects of the ecosystem. While the response variables on the other hand are often focused on species presence and some work undertaken on species abundances, it is equally important to consider, e.g. biological traits or benthic ecosystem functions in DM applications. Tools such as DMs are suitable to forecast the possible effects of climate change on benthic species distribution patterns and hence could help to steer present-day ecosystem management.

This study presents the results of a trial assessment based on a combination of sampling techniques at a dredged material disposal site located off the North East coast of the UK, over 2001 to 2004. The site was surveyed with a high-resolution sidescan sonar system producing a mosaic with 100% coverage of the survey area. Benthic communities and sediments were ground-truthed using a Hamon grab with a video camera. Additionally, the area was also sampled in 2003 with a Sediment Profile Imaging (SPI) camera, which complemented other techniques by providing in situ information on sediment quality, and biogenic activities. An assessment is made of the benefits of combining the results from conventional methods, principally using grab samples, with those from acoustic techniques and optical imaging devices to determine seafloor and macrobenthic conditions. This information has the potential to contribute to the enhancement of routine monitoring programmes within UK waters.

Macrofaunal assemblages inhabiting stable offshore muddy sand substrata responded predictably to the effects of mild organic enrichment arising from sewage-sludge disposal off the north-east coast of England (western North Sea). At the disposal site, densities were elevated up to two-fold, but classical ‘indicator’ species were only marginally enhanced and there was no evidence of a significant waste-induced change in assemblage structure. The response following cessation of disposal was equally predictable, with a decline in densities to ‘reference’ levels some three years later. However, physical manifestations of disposal, including tomato pips and non-biodegradable artefacts, were still evident after this time.Changes in diversity at selected monitoring stations tended to track each other over time and the employment of treatment/reference ratios and limit values for acceptable change provided a useful model for the simplified expression of trends. Predictions concerning the limited scale and intensity of the effects of sewage-sludge disposal appear to have been met, indicating that the management option of sea disposal was, at the time, an environmentally acceptable one.Temporal trends in the benthic fauna were also correlated with winter values of the North Atlantic Oscillation Index for the preceding year. The densities and variety of species tended to be lower in response to warmer winters characterized by westerly airflows which were commonly encountered in the 1990s. Finally, the increasing importance of extended time-series data for the investigation of man-made impacts on the marine environment is highlighted, along with the accompanying requirement for continuity and quality assurance of sampling programmes.

Biological value estimation is based on a set of assessment questions and several thresholds to delineate areas of ecological importance (e.g. biodiversity). An existing framework, that was specifically designed to assess the ecosystem biodiversity, was expanded by adding new questions on the productivity, functionality and biogeochemical status of benthic habitats. The additional ecological and sedimentological information was collected by using sediment profile imagery (SPI) and grab sampling. Additionally, information on the performance and comparability of both techniques is provided in this study. The research idea was tested at a site near the harbor of Zeebrugge, an area under consideration as a new disposal site for dredged material from the harbor entrance. The sedimentology of the area can be adequately described based on the information from both SPI and Van Veen grab samples, but only the SPI revealed structural information on the physical habitat (layering, a-RPD). The latter information represented the current status of the benthic habitat, which was confirmed by the Van Veen grab samples. All information was summarized through the biological valuation framework, and provided clear evidence of the differences in biological value for the different sediment types within the area. We concluded that the installation of a new dredged material disposal site in this area was not in conflict with the benthic ecology. This area has a low biological value and the benthic system is adapted to changing conditions, which was signaled by the dominance of mobile, short living and opportunistic species. This study showed that suitable sedimentological and ecological information can be gathered by these traditional and complementary techniques, to estimate the biological value of an area in the light of marine spatial planning and environmental impact assessments.

Metal behaviour and availability at a contaminated dredge material disposal site within UK waters has been investigated using Diffusive Gradient in Thin films (DGT) passive sampling technology. Three stations representing contrasting history and presence of maintenance dredge disposal, including a control station outside the disposal site, have been studied and depth profiles of fluxes of different metals (Fe, Mn, Pb, Cu, Cd, Cr, Ni, Zn) to the binding gel (Chelex 100) have been derived. Higher flux rates and shallower mobilisation of metals (Mn and Fe) to the binding gel were observed at the disposal stations compared to the control station. Here we describe metal mobilization at different depths, linking the remobilization of Fe 2+ and Mn 2+ to the sediment (re)supply of other heavy metals of interest with a focus on Cd, Ni and Pb and as they are on the Water Framework Directive (WFD) list of priority substances and OSPAR list of priority pollutants. Results showed that Cd, Pb and Ni exhibited signs of resupply at the sediment-water interface (SWI). There was a potential increased mobilisation and source to the water column of Pb and Ni at the disposal site stations, but there was no Cd source, despite higher total loadings. This information has the potential to improve our current understanding of metal cycles at disposal sites. This work can be used as an indication of likely metal bioavailability and also assist in determining whether the sites act as sources or sinks of heavy metals. This information could assist disposal site monitoring and dredge material licensing.

Bioturbation, the biogenic modification of sediments through particle reworking and burrow ventilation, is a key mediator of many important geochemical processes in marine systems. In situ quantification of bioturbation can be achieved in a myriad of ways, requiring expert knowledge, technology, and resources not always available, and not feasible in some settings. Where dedicated research programmes do not exist, a practical alternative is the adoption of a trait-based approach to estimate community bioturbation potential (BPc). This index can be calculated from inventories of species, abundance and biomass data (routinely available for many systems), and a functional classification of organism traits associated with sediment mixing (less available). Presently, however, there is no agreed standard categorization for the reworking mode and mobility of benthic species. Based on information from the literature and expert opinion, we provide a functional classification for 1033 benthic invertebrate species from the northwest European continental shelf, as a tool to enable the standardized calculation of BPc in the region. Future uses of this classification table will increase the comparability and utility of large-scale assessments of ecosystem processes and functioning influenced by bioturbation (e.g., to support legislation). The key strengths, assumptions, and limitations of BPc as a metric are critically reviewed, offering guidelines for its calculation and application.

Ocean acidification (OA) may alter the behaviour of sediment-bound metals, modifying their bioavailability and thus toxicity. We provide the first experimental test of this hypothesis with the amphipod Corophium volutator. Amphipods were exposed to two test sediments, one with relatively high metals concentrations (Σmetals 239 mg kg(-1) ) and a reference sediment with lower contamination (Σmetals 82 mg kg(-1) ) under conditions that mimic current and projected conditions of OA (390-1140 μatm pCO2 ). Survival and DNA damage was measured in the amphipods, whereas the flux of labile metals was measured in the sediment and water column (WC) using Diffusive Gradients in Thin-films. The contaminated sediments became more acutely toxic to C. volutator under elevated pCO2 (1140 μatm). There was also a 2.7-fold increase in DNA damage in amphipods exposed to the contaminated sediment at 750 μatm pCO2 , as well as increased DNA damage in organisms exposed to the reference sediment, but only at 1140 μatm pCO2 . The projected pCO2 concentrations increased the flux of nickel and zinc to labile states in the WC and pore water. However, the increase in metal flux at elevated pCO2 was equal between the reference and contaminated sediments or, occasionally, greater from reference sediments. Hence, the toxicological interaction between OA and contaminants could not be explained by e ffects of pH on metal speciation. We propose that the additive physiological effects of OA and contaminants will be more important than changes in metal speciation in determining the responses of benthos to contaminated sediments under OA. Our data demonstrate clear potential for near-future OA to increase the susceptibility of benthic ecosystems to contaminants. Environmental policy should consider contaminants within the context of changing environmental conditions. Specifically, sediment metals guidelines may need to be reevaluated to afford appropriate environmental protection under future conditions of OA.

The Water Framework Directive (WFD) and the Marine Strategy Framework Directive (MSFD) are the European umbrella regulations for water systems. It is a challenge for the scientific community to translate the principles of these directives into realistic and accurate approaches. The aim of this paper, conducted by the Benthos Ecology Working Group of ICES, is to describe how the principles have been translated, which were the challenges and best way forward. We have tackled the following principles: the ecosystem-based approach, the development of benthic indicators, the definition of 'pristine' or sustainable conditions, the detection of pressures and the development of monitoring programs. We concluded that testing and integrating the different approaches was facilitated during the WFD process, which led to further insights and improvements, which the MSFD can rely upon. Expert involvement in the entire implementation process proved to be of vital importance. (