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Microplastics are now synonymous with human impacts on the environment and as a threat to marine organisms. Numerous taxa are at risk from microplastics including commercially valuable bivalves as seafood, which are also disproportionately important as biogenic reef-forming species that enhance biodiversity such that they are commonly protected under conservation actions. As a sessile filter-feeding organism, bivalves are highly susceptible to microplastic ingestion but despite their socio-economic and ecological importance, no research has been undertaken to assess how a reef's structural arrangement might affect plastic ingestion. Here, using a series of flume experiments, we examined how change in spatial arrangement of the blue mussel, Mytilus edulis, interacts with different flow speeds to effect retention of microplastic over reef surfaces and ingestion risk by individual mussels. Our results show that clumped spatial arrangements reduce boundary layer velocities, and increase turbulence, boundary layer thickness and plastic retention over reef surfaces under faster flow conditions, increasing plastic ingestion by 3-fold. Our findings suggest that the structural arrangement and rugosity of natural reef structures may create natural sinks of anthropogenic pollution, and species like Mytilus that are also important species for human consumption, while disproportionately susceptible to microplastic pollution, may be useful bioindicators of microplastic pollution.

In coastal habitats artificial structures typically support lower biodiversity and can support greater numbers of non-native and opportunistic species than natural rocky reefs. Eco-engineering experiments are typically trialed to succeed; but arguably as much is learnt from failure than from success. Our goal was to trial a generic, cost effective, eco-engineering technique that could be incorporated into rock armouring anywhere in the world. Artificial rock pools were created from manipulated concrete between boulders on the exposed and sheltered sides of a causeway. Experimental treatments were installed in locations where they were expected to fail and compared to controls installed in locations in which they were expected to succeed. Control pools were created lower on the structure where they were immersed on every tidal cycle; experimental pools were created above mean high water spring tide which were only immersed on spring tides. We hypothesised that lower and exposed pools would support significantly higher taxon and functional diversity than upper and sheltered pools. The concrete pools survived the severe winter storms of 2013/14. After 12 months, non-destructive sampling revealed significantly higher mean taxon and functional richness in lower pools than upper pools on the exposed side only. After 24 months the sheltered pools had become inundated with sediments, thus failing to function as rock pools as intended. Destructive sampling on the exposed side revealed significantly higher mean functional richness in lower than upper pools. However, a surprisingly high number of taxa colonised the upper pools leading to no significant difference in mean taxon richness among shore heights. A high number of rare taxa in the lower pools led to total taxon richness being almost twice that of upper pools. These findings highlight that even when expected to fail concrete pools supported diverse assemblages, thus representing an affordable, replicable means of enhancing biodiversity on a variety of artificial structures.

The marine environment is heavily exploited, but unintentional consequences cause wide-ranging negative effects to its characteristics. Linkage frameworks (e.g., DPSIR [driver-pressure-state-impact-response]) are commonly used to describe an interaction between human activities and ecological characteristics of the ecosystem, but as each linkage is viewed independently, the diversity of pressures that affect those characteristics may not be identified or managed effectively. Here we demonstrate an approach for using linkages to build a simple network to capture the complex relationships arising from multiple sectors and their activities. Using data-analysis tools common to ecology, we show how linkages can be placed into mechanistically similar groups. Management measures can be combined into fewer and more simplified measures that target groups of pressures rather than individual pressures, which is likely to increase compliance and the success of the measure while reducing the cost of enforcement. Given that conservation objectives (regional priorities) can vary, we also demonstrate by way of a case study example from the Marine Strategy Framework Directive, how management priorities might change, and illustrate how the approach can be used to identify sectors for control that best support the conservation objectives.

Background The movement of animals in intertidal environments underpins community structure and is influenced by both abiotic and biotic factors within the environment. Whilst the effects of body size, tidal regime and temperature on the timing and ability of movement have been well-explored, physical features of the environment that generate complexity have received comparatively less attention. Given alterations to the topographic complexity of intertidal habitats associated with climate change and anthropogenic activities, understanding the effects of varying levels of topographic complexity on the movement of intertidal animals is critical to our understanding of biodiversity and ecosystem functioning in these habitats going forward. Methods We experimentally manipulated topographic complexity using bespoke concrete panels at two scales, the individual panel and configuration of panels in a modelled 2 × 4 m area, to explore the effects of topographic complexity on the movement of a key intertidal gastropod and ecosystem engineer, the common limpet Patella vulgata . Using a combination of time-lapse photography and correlated random-walk modelling, we ‘scaled-up’ these experimental results to model the effects of topographic complexity on movement and space-use at landscape scales. Results Results revealed a significant effect of topographic complexity on limpet movement, with greater distances travelled on ‘intermediate’ topographic complexity surfaces (surface areas = 0.08 m 2 and 0.09 m 2 ), but more frequent, shorter movements on lowest topographic complexity (surface area = 0.06 m 2 ). At landscape scales, panels with intermediate topographic complexity placed in random configurations at highest spatial cover induced the greatest path lengths of simulated limpets. Conclusions This study and its results represent the first experimental assessment of the direct effects of eco-engineered topographic complexity on the small-scale movements of intertidal gastropods and outline a first step towards the mechanistic extrapolation of results to heterogenous landscapes to explore the space-use of gastropods across larger spatial scales. With ongoing changes to intertidal environments resulting from climate change and anthropogenic activities, understanding how the movement of animals is impacted by variation in topographic complexity is essential to predicting future impacts on metapopulation dynamics and ecosystem functioning.

Dispersal is a primary driver in shaping the future distribution of species in both terrestrial and marine systems. Physical transport by advection can regulate the distance travelled and rate of propagule supply to a habitat but post-settlement processes such as predation can decouple supply from recruitment. The effect of flow-mediated recruitment and predation on the recruitment success of an intertidal species, the eastern oyster Crassostrea virginica was evaluated in two-replicated field experiments. Two key crab species were manipulated to test predator identity effects on oyster mortality. Recruitment was ∼58% higher in high flow compared to low flow, but predation masked those differences. Predation mortality was primarily attributed to the blue crab Callinectes sapidus, whilst the mud crab Panopeus herbstii had no effect on recruit mortality. Recruit mortality from predation was high when recruit densities were high, but when recruit density was low, predation effects were not seen. Under high recruitment (supply), predation determined maximum population size and in low flow environments, recruitment success is likely determined by a combination of recruitment and resource limitation but not predation. Four processes are demonstrated: (1) Increases in flow rate positively affect recruitment success; (2) In high flow (recruitment) environments, resource availability is less important than predation; (3) predation is an important source of recruit mortality, but is dependent upon recruit density; and (4) recruitment and/or resource limitation is likely a major driver of population structure and functioning, modifying the interaction between predators and prey. Simultaneous testing of flow-mediated recruitment and predation was required to differentiate between the role of each process in determining population size. Our results reinforce the importance of propagule pressure, predation and post-settlement mortality as important determinants of population growth and persistence, but demonstrate that they should not be considered mutually exclusive.

Negative impacts of global climate change are predicted for a range of taxa. Projections predict marked increases in sea surface temperatures and ocean acidification (OA), arguably placing calcifying organisms at most risk. While detrimental impacts of environmental change on the growth and ultrastructure of bivalve mollusc shells have been shown, rapid and diel fluctuations in pH typical of coastal systems are often not considered. Mytilus edulis, an economically important marine calcifier vulnerable to climate change, were exposed to current and future ocean acidification (380 ppm and 1000 ppm pCO2), warming (17°C; 20°C), and ocean acidification and warming (OAW) scenarios in a seawater system incorporating natural fluctuations in pH. Both macroscopic morphometrics (length, width, height, volume) and microscopic changes in the crystalline structure of shells (ultrastructure) using electron backscatter diffraction (EBSD) were measured over time. Increases in seawater temperature and OAW scenarios led to increased and decreased shell growth respectively and on marginal changes in cavity volumes. Shell crystal matrices became disordered shifting toward preferred alignment under elevated temperatures indicating restricted growth, whereas Mytilus grown under OAW scenarios maintained single crystal fabrics suggesting OA may ameliorate some of the negative consequences of temperature increases. However, both elevated temperature and OAW led to significant increases in crystal size (grain area and diameter) and misorientation frequencies, suggesting a propensity toward increased shell brittleness. Results suggest adult Mytilus may become more susceptible to biological determinants of survival in the future, altering ecosystem structure and functioning.

Background Numerous man-made structures (MMS) have been installed in various parts of the ocean (e.g. oil and gas structures, offshore wind installations). Many are now at, or nearing, the end of their intended life. Currently, we only have a limited understanding of decommissioning effects. In many locations, such as the North Sea, regulations restrict decommissioning options to complete removal, with little consideration of alternative management options might offer. To generate a reliable evidence-base to inform the decision-making processes pertaining to marine MMS management, we propose a wide-encompassing systematic map of published research on the ecosystem effects (including ecosystem services) of marine MMS while in place and following cessation of operations (i.e. including effects of alternative decommissioning options). This map is undertaken as part of the UKRI DREAMS project which aims to develop a system to show the relative effects of implementing different decommissioning strategies in the North Sea. Method For the purpose of this map, we will keep our focus global, in order to subsequently draw comparisons between marine regions. The proposed map will aim to answer the following two primary questions: 1. What published evidence exists for the effects of marine man-made structures while in place on the marine ecosystem? 2. What published evidence exists for the effects of the decommissioning of marine man-made structures on the marine ecosystem? The map will follow the Collaboration for Environmental Evidence Guidelines and Standards for Evidence Synthesis in Environmental Management. Searches will be run primarily in English in at least 13 databases and 4 websites. Returns will be screened at title/abstract level and at full-text against pre-defined criteria. Relevant meta-data will be extracted for each study included. Results will be used to build a database of evidence, which will be made freely available. This map, expected to be large, will improve our knowledge of the available evidence for the ecosystem effects of MMS in the global marine environment. It will subsequently inform the production of multiple systematic-reviews and meta-analyses.

Background Many marine man-made structures (MMS), such as oil and gas platforms or offshore wind turbines, are nearing their ‘end-of-life’ and require decommissioning. Limited understanding of MMS decommissioning effects currently restricts the consideration of alternative management possibilities, often leaving complete removal as the only option in certain parts of the world. This evidence-base describes the ecosystem effects of marine MMS whilst in place and following cessation of operations, with a view to informing decision-making related to their potential decommissioning. Method The protocol used to create this map was published a priori. Systematic searches of published, literature in English were conducted using three bibliographic databases, ten specialist organisational websites or repositories, and one search engine, up to early 2021. A total of 15,697 unique articles were identified as potentially relevant to our research questions, of which 2,230 were screened at the full-text level. Of that subset, 860 articles met all pre-defined eligibility criteria. A further 119 articles were identified through “snowballing” of references from literature reviews. The final database consists of 979 articles. For each article included, metadata were extracted for key variables of interest and coded into a database. Review findings The vast majority of eligible articles related to the presence of MMS (96.2%), while just 5.8% considered decommissioning. Overall, articles mainly considered artificial reefs (51.5% of all articles) but increasingly oil and gas (22%), shipwrecks (15.1%) and offshore wind (13.1%). Studies were distributed globally, but the majority focused on the United States, single countries within Europe, Australia, Brazil, China, and Israel; 25 studies spanned multiple countries. Consequently, the bulk of the studies focused on the North Atlantic (incl. Gulf of Mexico, North Sea, and Mediterranean Sea) and North Pacific Oceans. A further 12 studies had a global scope. Studies in majority reported on fish (53%) and invertebrates (41%), and were disproportionately focused on biological (81%) and ecological (48%) impacts. Physico-chemical (13%), habitat (7%), socio-cultural (7%), economic (4%) and functional (8%) outcomes have received less attention. The number of decommissioning studies has been increasing since ca. 2012 but remains noticeably low. Studies mostly focus on oil and gas infrastructures in the USA (Gulf of Mexico) and Northern Europe (North Sea), covering 9 different decommissioning options. Conclusions This systematic map, the first of its kind, reveals a substantial body of peer-reviewed evidence relating to the presence of MMS in the sea and their impacts, but with considerable bias toward biological and ecological outcomes over abiotic and socio-economic outcomes. The map reveals extremely limited direct evidence of decommissioning effects, likely driven at least in part by international policy preventing consideration of a range of decommissioning options beyond complete removal. Despite evidence of MMS impacts continuing to grow exponentially since the early 1970s, this map reveals key gaps in evidence to support best practice in developing decommissioning options that consider environmental, social and economic effects. Relevant evidence is required to generate greater understanding in those areas and ensure decommissioning options deliver optimal ecosystem outcomes.

Background Under the threat of climate change populations can disperse, acclimatise or evolve in order to avoid fitness loss. In light of this, it is important to understand neutral gene flow patterns as a measure of dispersal potential, but also adaptive genetic variation as a measure of evolutionary potential. In order to assess genetic variation and how this relates to environment in the honeycomb worm (Sabellaria alveolata (L.)), a reef-building polychaete that supports high biodiversity, we carried out RAD sequencing using individuals from along its complete latitudinal range. Patterns of neutral population genetic structure were compared to larval dispersal as predicted by ocean circulation modelling, and outlier analyses and genotype-environment association tests were used to attempt to identify loci under selection in relation to local temperature data. Results We genotyped 482 filtered SNPs, from 68 individuals across nine sites, 27 of which were identified as outliers using BAYESCAN and ARLEQUIN. All outlier loci were potentially under balancing selection, despite previous evidence of local adaptation in the system. Limited gene flow was observed among reef-sites (FST = 0.28 ± 0.10), in line with the low dispersal potential identified by the larval dispersal models. The North Atlantic reef emerged as a distinct population and this was linked to high local larval retention and the effect of the North Atlantic Current on dispersal. Conclusions As an isolated population, with limited potential for natural genetic or demographic augmentation from other reefs, the North Atlantic site warrants conservation attention in order to preserve not only this species, but above all the crucial functional ecological roles that are associated with their bioconstructions. Our study highlights the utility of using seascape genomics to identify populations of conservation concern.

Background The presence of artificial structures in our marine environments is increasing rapidly, with negative impacts for biodiversity. Greening of grey infrastructure (GGI) - an eco-engineering method applied to the marine context - aims to increase the ecological value of traditional grey infrastructure, while still allowing it to perform its primary human-centric function. GGI is a rapidly increasing field of research, being tested and implemented worldwide by academics, private practitioners, governments, non-governmental organisations (NGOs), amongst others, using a variety of methods. Outcomes vary widely, and results are communicated across a range of peer-reviewed and grey literature, rendering the evidence base for the effectiveness of GGI fragmented. To inform future decision-making regarding GGI application, it is critical to consolidate and evaluate existing research. To do so, we propose a systematic review and meta-analysis that will answer the following primary question: “What are the effects of GGI interventions applied to marine structures on the diversity, abundance, biomass, composition, and functional diversity of species on or around these ecologically enhanced structures?”. Additionally, we will answer a series of secondary questions relating to intervention type, material use, geographic variations and other relevant associated variables. Methods This systematic review will follow the Collaboration for Environmental Evidence Guidelines and Standards for Evidence Synthesis in Environmental Management. Using a defined search string, literature searches will be run in English in at least five databases, three repositories and 10 websites, gathering both peer-reviewed and grey literature. Returns will be screened at title, abstract, and full text levels against defined inclusion criteria. Relevant metadata and effect data will be extracted from each study and used to write a narrative review and, where data allow, a meta-analysis of quantified effects. This review will provide a robust, up to date, consolidated and evaluated evidence base to inform future decision-making regarding the implementation of greening of grey infrastructure methods.