The expansion of offshore renewable energy developments (ORED) has prompted increasing concerns regarding their potential impacts on the marine environment and repercussions for ecosystem functions. A comparative assessment of benthic invertebrate communities associated with natural versus artificial hard substrates could provide insights for assessing ecological changes following the installation of such structures. This study evaluated the ecological functionality of offshore wind turbine foundations, scour protection layers, and geogenic natural reefs through a trait-based approach. The analysis focused on two regions (which we called 'Belgium' and 'Borkum') selected based on the availability of high-resolution invertebrate taxonomic data, comprising natural and artificial substrates at nearby geographical locations. Taxonomic data were sourced from the BISAR database, while functional trait data were compiled through an extensive review of the scientific literature. A total of six functional traits, encompassing 29 modalities, were assessed. The resulting data were analysed to determine both taxonomic and functional differences between artificial and natural hard substrates. Functional analyses were performed using a combination of functional diversity indices and latent variable models to elucidate underlying patterns in trait distribution and community functioning. The results constitute evidence, demonstrating that geogenic natural habitats support higher levels of biodiversity and harbour functionally distinct communities when compared to artificial structures. Analyses of functional diversity indices revealed significant differences in functional evenness and divergence between natural reef communities and those associated with artificial structures. These differences illustrate that natural rocks exhibit greater functional resilience to environmental disturbances. Furthermore, the majority of trait modalities exhibited significant responses to at least one substrate type, and several taxa displayed effect sizes that were positively or negatively correlated with specific habitat types, indicating substrate-driven shifts in community functional composition. Given the pronounced differences in biodiversity and functional attributes between natural and artificial hard substrates, enhancing the ecological sustainability of ORED requires a shift towards ecologically informed design. Artificial structures could potentially be engineered to mimic the multidimensional and heterogeneous properties of natural substrates, facilitating the establishment of more resilient benthic communities. These results have conservation and management implications when planning the introduction of such structures over local and regional scales.

Aim: We investigated how local-scale environmental heterogeneity influences biodiversity patterns across broad biogeographic gradients, using intertidal microhabitats as a model system within one of the most environmentally stressful ecosystems on Earth. Location: Intertidal habitats at 26 locations (two rocky shore sites per location) across six continents, spanning 98 degrees of latitude (38 degrees S to 60 degrees N). Time Period: 2019-2022. Major Taxa Studied: Algae, sessile and mobile invertebrates. Methods: We compared biodiversity and thermal environments across contrasting microhabitats (rock pools and adjacent emergent rock) along a latitudinal gradient, sampling during environmentally 'milder' and 'harsher' periods. Biodiversity was quantified using multiple richness metrics (mean, total, unique taxa) and functional diversity. Results: Microhabitat differences strongly influenced biodiversity patterns across latitude. Rock pools consistently supported higher taxonomic and functional diversity than emergent rock, irrespective of sampling period, reflecting their ability to buffer thermal extremes, particularly under harsher conditions. Mean species richness exhibited a non-linear, s-shaped latitudinal pattern, with lowest values near the equator and higher richness at mid-latitudes, diverging from classical Latitudinal Diversity Gradient expectations. Biodiversity differences between microhabitats were greatest in temperate regions and diminished at low latitudes, where extreme conditions constrained diversity across habitats. Main Conclusions: Local environmental heterogeneity can substantially modify, and in some cases obscure large-scale biodiversity patterns. By mediating exposure to environmental stress, intertidal microhabitats provide insight into how fine-scale variability interacts with latitudinal stress gradients to shape biodiversity distributions. Incorporating microhabitat variability into biogeographic frameworks is important for understanding global biodiversity patterns and predicting ecological responses to climate change.

North Sea human-made, offshore structures (e.g. oil/gas platforms, offshore wind farms) provide a hard substrate habitat for benthic marine species which can spread between sites during their larval stage. Here, we aim to address how the installation of additional human-made structures, like new wind farms, or decommissioning of existing ones, like oil and gas platforms at the end of service, contribute to changes in larval connectivity. We use particle tracking model simulations to assess the ecological connectivity of benthic species in the northern North Sea during two contrasting years to highlight seasonal to annual variability. The methodology of releasing an extensive set of particles over a wide area produces our Retrospective Particle Tracks dataset. The sets of simulations can be interrogated to understand if additional human-made structures placed in any locations in the northern North Sea could potentially affect the ecological connectivity. Network metrics were used to identify connectivity between sites. Clustering of existing structures identifies a region that acts as an interchange between other structures which may otherwise only be connected during intermittent periods. The addition of new human-made structures located in areas with stronger residual current flow would enhance the connectivity.

Amphiboreal taxa are often composed of vicariant phylogroups and species complexes whose divergence and phylogeographic affinities reflect a shared history of chronic isolation and episodic trans-Arctic dispersal. Ecological filters and shifting selective pressures may also promote selective sweeps, niche shifts and ecological speciation during colonization, but these are seldom considered at biogeographical scales. Here we integrate genetic data and Ecologic Niche Models (ENMs) to investigate the historical biogeography and cohesion of the polymorphic rockweed Fucus distichus throughout its immense amphiboreal range, focusing on trans-Arctic asymmetries, glacial/interglacial dynamics, and integrity of sympatric eco-morphotypes. Populations were sampled throughout the Pacific and the Atlantic, from southern rear-edges to the high-Arctic. They were genotyped for seven microsatellites and an mtDNA spacer, and genetic diversity and structure were assessed from global to local scales. ENMs were used to compare niche divergence and magnitude of post-glacial range shifts in Pacific versus Atlantic sub-ranges. Haplotypic and genotypic data revealed distinct and seemingly isolated Pacific vs Arctic/Atlantic gene-pools, with finer-scale regional sub-structuring pervasive in the Pacific. MtDNA diversity was highly structured and overwhelmingly concentrated in the Pacific. Regionally, Alaska showed the highest intra-population diversity but the lowest levels of endemism. Some sympatric/parapatric ecotypes exhibited distinct genotypic/haplotypic compositions. Strikingly, niche models revealed higher Pacific tolerance to maximum temperatures and predicted a much more consolidated presence in the NE Atlantic. Glacial and modern ranges overlapped extensively in the Pacific, whereas the modern Atlantic range was largely glaciated or emerged during the Last Glacial Maximum. Higher genetic and ecogeographic diversity supports a primary Pacific diversification and secondary Atlantic colonization, also likely reflecting the much larger and more stable climatic refugia in the Pacific. The relic distribution and reduced ecological/morphological plasticity in the NE Atlantic are hypothesized to reflect functional trans-Arctic bottlenecks, recent colonization or competition with congeners. Within the Pacific, Alaska showed signatures of a post-glacial melting pot of eastern and southern populations. Genetic/ecotypic variation was generally not sufficiently discontinuous or consistent to justify recognizing multiple taxonomic entities, but support a separate species in the eastern Pacific, at the southern rear-edge. We predict that layered patterns of phylogeographic structure, incipient speciation and niche differences might be common among widespread low-dispersal amphiboreal taxa.

Wave energy has the potential to contribute in the transition to decarbonized electricity generation. Extracting wave energy might be expected to have ecological impacts on rocky shore intertidal communities where exposure is one of the most important factors determining species structure and composition. With global climatic change, coastal exposure is predicted to increase with greater significant wave height. The wave-exposed west coast of Orkney, Scotland, UK, is the site of pre-commercial wave device testing. Surveys of 39 rocky shore sites along this coast identified key species and abundances, and quantified exposure-modifying topographic variables. A spectral wave model was constructed to compare baseline, wave extraction, climate change, and combined scenarios. Generalized additive modelling was used to describe the relationship between species, topography, and exposure. Results show that individual species differentially respond to exposure changes with 'winners' and 'losers' at site level. Overall, community responses are expected to be far greater following predicted climatic change than to industrial-scale wave energy extraction, depending on spatial scale. In combination, energy extraction may reduce the effects of climate-change-related increases in wave exposure of rocky shores. Predicting how location-specific biotic assemblages respond to changes in wave energy as a result of long-term forcing agents provides a valuable marine resource management tool.

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

Switching from fossil fuels to renewable energy is key to international energy transition efforts and the move toward net zero. For many nations, this requires decommissioning of hundreds of oil and gas infrastructure in the marine environment. Current international, regional and national legislation largely dictates that structures must be completely removed at end-of-life although, increasingly, alternative decommissioning options are being promoted and implemented. Yet, a paucity of real-world case studies describing the impacts of decommissioning on the environment make decision-making with respect to which option(s) might be optimal for meeting international and regional strategic environmental targets challenging. To address this gap, we draw together international expertise and judgment from marine environmental scientists on marine artificial structures as an alternative source of evidence that explores how different decommissioning options might ameliorate pressures that drive environmental status toward (or away) from environmental objectives. Synthesis reveals that for 37 United Nations and Oslo-Paris Commissions (OSPAR) global and regional environmental targets, experts consider repurposing or abandoning individual structures, or abandoning multiple structures across a region, as the options that would most strongly contribute toward targets. This collective view suggests complete removal may not be best for the environment or society. However, different decommissioning options act in different ways and make variable contributions toward environmental targets, such that policy makers and managers would likely need to prioritise some targets over others considering political, social, economic, and ecological contexts. Current policy may not result in optimal outcomes for the environment or society.

Abstract The spread of the brown seaweed Sargassum muticum is one of the best documented invasions of a non-native marine species. Observation of a potentially established population of S. muticum in the Orkney Islands archipelago, located off the northern coast of Scotland, was reported by recreational snorkellers in 2019 and 2020. The present study summarises a focussed investigation to confirm its presence and current local distribution, using data from 46 survey sites monitored as a part of the Orkney Islands Council Harbour Authority monitoring programme. Findings in this study represent the most northerly record of an established population of S. muticum in the United Kingdom, extending the latitudinal range in this country by 1.44° (159 km) northwards, and indicate only localised presence of this species. Analysis of a partial cytochrome oxidase I gene sequence confirmed the visual species identification. Possible vectors of introduction, gaps in the geographic range, local ecological and economic impacts, and the potential ameliorating factor of deep rockpools on wave exposed shores for S. muticum are discussed.

Microsatellite data (12 loci) of 14 populations of Laminaria digitata covering the entire species range

Marine habitats are being targeted for the extraction of offshore renewable energy (ORE) as part of the drive to decarbonise electricity generation. Unmanaged biofouling impacts ORE devices and infrastructure by elevating drag forces, increasing weight, and accelerating corrosion, leading to decreased performance and survivability, and extending costly periods of maintenance. ORE deployments in high tidal flow locations are providing opportunities to study the biofouling unique to these habitats. In this study, surveys of numerous devices and associated infrastructure deployed at the European Marine Energy Centre in Scotland identified high tidal flow fouling assemblages. Substrate orientation relative to tidal flow appears to affect the abundance of key fouling species, including the massive barnacle Chirona hameri. This species is shown to recruit to a wide range of artificial substrates, over a prolonged period from mid-spring to mid-summer, and in maximum current speeds from 0.4–4.0 m/s. For the first time, C. hameri is reported in near-surface depths, on uncoated components of a floating tidal device. The highly gregarious settlement behaviour and rapid growth exhibited by this species may have important implications for managing fouling in the ORE industry, especially in ‘niche’ areas. Anti-fouling strategies and maintenance scheduling applicable to ORE and other marine industries are discussed.

A new record of an individual of the invasive sea squirt, Styela clava, is reported from Scapa Flow in Orkney, Scotland. This represents a 1.54° latitudinal extension (168 km) from the previous northern-most record in UK waters. Diver surveys of hard substrates in the immediate area, part of local biosecurity protocols, did not find any additional individuals. Possible transport vectors, likelihood of an established reproductively active population, and implications to local biodiversity are discussed.

ABSTRACTTemperature extremes are predicted to intensify with climate change. These extremes are rapidly emerging as a powerful driver of species distributional changes with the capacity to disrupt the functioning and provision of services of entire ecosystems, particularly when they challenge ecosystem engineers. The subsequent search for a robust framework to forecast the consequences of these changes mostly ignores within‐species variation in thermal sensitivity. Such variation can be intrinsic, but can also reflect species interactions. Intertidal mussels are important ecosystem engineers that host symbiotic endoliths in their shells. These endoliths unexpectedly act as conditionally beneficial parasites that enhance the host's resistance to intense heat stress. To understand how this relationship may be altered under environmental change, we examined the conditions under which it becomes advantageous by reducing body temperature. We deployed biomimetic sensors (robomussels), built using shells of mussels (Mytilus galloprovincialis) that were or were not infested by endoliths, at nine European locations spanning a temperature gradient across 22°of latitude (Orkney, Scotland to the Algarve, Portugal). Daily wind speed and solar radiation explained the maximum variation in the difference in temperature between infested and non‐infested robomussels; the largest difference occurred under low wind speed and high solar radiation. From the robomussel data, we inferred body temperature differences between infested and non‐infested mussels during known heatwaves that induced mass mortality of the mussel Mytilus edulis along the coast of the English Channel in summer 2018 to quantify the thermal advantage of endolith infestation during temperature extremes. Under these conditions, endoliths provided thermal buffering of between 1.7°C and 4.8°C. Our results strongly suggest that sustainability of intertidal mussel beds will increasingly depend on the thermal buffering provided by endoliths. More generally, this work shows that biomimetic models indicate that within‐species thermal sensitivity to global warming can be modulated by species interactions, using an intertidal host–symbiont relationship as an example.

Abstract A novel system was developed to deploy settlement panels to monitor biofouling growth in situ and evaluate antifouling coatings at depths representative of operational conditions of full-scale marine renewable energy devices. Biofouling loading, species diversity, and succession were assessed at depths ranging from 25-40 m at four tests sites in Orkney (UK) featuring extreme wave and tidal current exposure to more sheltered conditions. Evaluations were carried out over a period of 8 months with intermediate retrieval of samples after 3 months. Early pioneer fouling communities, comprised of colonial hydroids, were succeeded by tube-forming amphipods across sites while solitary tunicates dominated in greater shelter. The highest biofouling loading was observed on high-density polyethylene (HDPE) panels (6.17 kg m−2) compared with coated steel (3.34 kg m−2) panels after 8 months. Distinct assemblages were present at exposed vs sheltered sites. Better understanding of fouling and antifouling strategies may provide guidance to more effectively manage biofouling impacts in this sector.

In the North-east (NE) Atlantic, most intertidal fucoids and warm-temperate kelps show unique low-latitude gene pools matching long-term climatic refugia. For cold-temperate kelps data are scarcer despite their unique cultural, ecological and economic significance. Here we test whether the amphi-Atlantic range ofLaminaria digitatais derived from past glacial survival (and vicariance) in both NE and North-west (NW) Atlantic refugia (as suggested by niche modelling), or post-glacial (re)colonization (as suggested by low mtDNA divergence). We screened 14 populations from across the species range for 12 microsatellite loci to identify and map major gene pools and refugia. We assessed if NW Atlantic survival was supported by unique endemic variation, and if genetic diversity and structure were, as predicted from larger hindcasted glacial ranges, higher in the NE Atlantic. Microsatellite data subdividedL. digitatainto three main genetic groups matching Brittany, northern Europe and the NW Atlantic, with finer-scale sub-structuring within European clusters. The relatively diverse NE Atlantic lineages probably survived the Last Glacial Maximum along unglaciated periglacial shorelines of the Armorican and Celtic Seas (Brittany cluster) and Ireland (northern European cluster), and remain well differentiated despite their relative proximity. The unique Brittany gene pool, at the contemporary European rear edge, is projected to disappear in the near future under high greenhouse gas emission scenarios. Low allelic diversity and low endemism in the NW Atlantic are consistent with recent post-glacial colonization from Europe, challenging the long-standing hypothesis ofin situglacial survival. Confusion withHedophyllum nigripesmay have led to underestimation of regional diversity ofL. digitata, but also to overestimation of its presence along putative trans-Atlantic migration routes. Partial incongruence between modelling and genetic-based biogeographic inferences highlights the benefits of comparing both approaches to understand how shifting climatic conditions affect marine species distributions and explain large-scale patterns of spatial genetic structure.

Submarine power cables (SPC) have been in use since the mid-19th century, but environmental concerns about them are much more recent. With the development of marine renewable energy technologies, it is vital to understand their potential impacts. The commissioning of SPC may temporarily or permanently impact the marine environment through habitat damage or loss, noise, chemical pollution, heat and electromagnetic field emissions, risk of entanglement, introduction of artificial substrates, and the creation of reserve effects. While growing numbers of scientific publications focus on impacts of the marine energy harnessing devices, data on impacts of associated power connections such as SPC are scarce and knowledge gaps persist. The present study (1) examines the different categories of potential ecological effects of SPC during installation, operation and decommissioning phases and hierarchizes these types of interactions according to their ecological relevance and existing scientific knowledge, (2) identifies the main knowledge gaps and needs for research, and (3) sets recommendations for better monitoring and mitigation of the most significant impacts. Overall, ecological impacts associated with SPC can be considered weak or moderate, although many uncertainties remain, particularly concerning electromagnetic effects.

The success of the marine renewable energy (MRE) industry is dependent upon maximising energy capture and minimising down-time. Device performance is negatively impacted by the growth of fouling organisms, leading to reduced efficiency and reliability; anti-fouling strategies are costly and time consuming. Biofouling also reduces accuracy of data buoys and sensors used to assess the hydrodynamic resource and device performance. While biofouling has been a recognised problem for centuries, deployment of MRE devices creates several unique issues. Additional concerns exist over the role that MRE infrastructure may play as 'stepping-stones' promoting the spread of non-native and invasive species. A paucity of published studies exists concerning biofouling in this sector. With a general trend towards stricter environmental controls, it is essential that the MRE industry demonstrate commitments that minimise disturbance and promote positive impacts. Given small margins for MRE, there are potentially substantive benefits from tackling biofouling in terms of increased investor confidence. The BioFREE project (a collaboration between Heriot-Watt University and the European Marine Energy Centre (EMEC) in the UK) is addressing these issues by detailed characterisation of the biofouling communities from multiple habitats used by the MRE sector, and monitoring benthic impacts following deployment and decommissioning. BioFREE is developing a workable Standard Monitoring System designed to facilitate data collection using practical and effective methods. Frames are populated with settlement panels, data loggers, and components comprised of materials of greatest concern to MRE developers. Components of this system can be treated with anti-fouling coatings. Frames are being deployed in a variety of habitats at additional test centres and research institutes located in Japan, Chile, France, and the USA; organisms are recorded quarterly to identify the major foulants, determine the rate of settlement and growth, and study successional changes. These studies indicate strong species-specific seasonal settlement patterns. Fouling communities vary between deployment habitats depending on factors such as hydrodynamic conditions, water depth, and substrate type. These findings will allow recommendations for test centres and developers to minimise the impacts of fouling, chiefly through selective scheduling of deployments and maintenance, in different habitats, to times when the settlement of fouling organisms will be minimal or their removal will be least costly. In addition, BioFREE has created training materials to help inform the MRE industry of ways to better capture biofouling information when conducting operations at sea. Practical suggestions are informed by recent maintenance and decommissioning operations conducted on MRE infrastructure. These studies have identified structural areas and materials of particular concern from the impacts of biofouling. The lead role of EMEC, as a representative of MRE developers in the sector, is allowing promotion of project outputs within the industry and between test centres. These findings are being disseminated through conference presentations, technical reports, scientific publications, public engagement, and webinars planned for the near future.

Extensive marine growth on man-made structures in the ocean is commonplace, yet there has been limited discussion about the potential implications of marine growth for the wave and tidal energy industry. In response, the Environmental Interactions of Marine Renewables (EIMR) Biofouling Expert Workshop was convened. Discussions involved participants from the marine renewable energy (MRE) industry, anti-fouling industry, academic institutions and regulatory bodies. The workshop aimed to consider both the benefits and negative effects of biofouling from engineering and ecological perspectives. In order to form an agenda for future research in the area of biofouling and the marine renewable energy industry, 119 topics were generated, categorised and prioritised. Identified areas for future focus fell within four overarching categories: operation and maintenance; structured design and engineering; ecology; and knowledge exchange. It is clear that understanding and minimising biofouling impacts on MRE infrastructure will be vital to the successful development of a reliable and cost effective MRE industry. Crown Copyright (C) 2017 Published by Elsevier Ltd. All rights reserved.

Generating electricity from marine energy is a globally important industry and forms a vital part of several nations' objectives to decarbonise energy production. In the UK, the resource-rich waters around Scotland have led to world-leading developments of facilities and supporting infrastructure used in deploying and testing wave and tidal energy technologies. A major concern to industries working in the marine environment is biofouling on submerged structures, including energy converters and measurement instrumentation. In this study, marine energy devices, infrastructure, and instrumentation were surveyed to characterise biofouling organisms. Fouling communities varied between deployment habitats; key organisms were identified allowing recommendations for scheduling device maintenance and preventing spread of invasive species. A method to measure biofouling impact on hydrodynamic response is described and applied to data from a wave-monitoring buoy deployed at a test site in Scotland. Results are discussed in relation to measurement accuracy of resources for power generation. Further applications are suggested for future testing in other scenarios including habitats use for extracting tidal energy.