Ecological effects of offshore wind farms on Atlantic cod (Gadus morhua) in the southern North Sea

Metagenomic biodiversity assessment within an offshore wind farm

Environmental DNA (eDNA) analysis can be a powerful tool for monitoring biodiversity and assessing human impacts on ecosystems. In this study, we employed a genome-wide metagenomic eDNA approach to assess the marine biodiversity within and around the Horns Rev 1 offshore wind farm in the Danish North Sea. Seawater samples were collected from both within the windfarm and surrounding control sites, sequenced, and analyzed using a combination of DNA k-mer matching and alignment-based classification methods. We identified a wide range of species across the tree of life-highlighting the species richness of this marine ecosystem. Our results revealed a high degree of species diversity congruence between the wind farm and control sites. While this could suggest minimal ecological disruption of the wind farm, we cannot rule out that the influence of ocean currents and water mixing the DNA from different regions dominate the species detection. We detected bioindicator species, such as Thalassiosira, Phaeocystis and Skeletonema, which can provide insights into water quality. Our metagenomic approach also enabled us to obtain population genomics insights for species, such as the European anchovy (Engraulis encrasicolus) and the diatom Rhizosolenia setigera, and genetically confirmed the origin of the invasive Sea walnut (Mnemiopsis leidyi) in the North Sea. This study highlights the potential of genome-wide eDNA metagenomics as a framework for assessing marine biodiversity and detecting population-level genetic signals, contributing to informed and scalable ecosystem monitoring strategies.

Offshore wind farms modify coastal food web dynamics by enhancing suspension feeder pathways

Given the global offshore wind farm (OWF) proliferation, we investigated the impact of OWFs on the marine food web. Using linear inverse modelling (LIM), we compared the OWF food web with two soft-sediment food webs nearby. Novel in situ data on species biomass and their isotopic composition were combined with literature data to construct food webs. Our findings highlight the prominent role of hard-substrate species on turbine foundations as organic material inputs for the food web. Hard substrate species account for approximately 26% of food source uptake from the water column and increase carbon deposition on the surrounding seafloor by ~10%. OWFs facilitate a novel food web with a higher productivity than expected based on standing biomass alone, as a result of numerous interactions between a diverse species community. Our study underscores profound effects of OWFs on marine ecosystems, suggesting the need for further research into their ecological impacts.

Site and species dependent effects of offshore wind farms on fish populations

The expansion of offshore wind energy capacity is changing the seascape with the large-scale introduction of turbines and associated infrastructure. Subsurface structures can influence the abundance, distribution and behaviour of some marine fish species by providing artificial habitat and food resources that supplements natural occurrence. At two of the highest latitude operational wind farms the abundance, biomass and size of haddock and flatfish was higher close to jacket turbine foundations, with the effect larger at the older and more complex foundations. The results provide further evidence of the fine-scale impacts of offshore wind turbines on demersal fish and illustrate their species and site-specific nature. Quantifying how these changes may have positive or negative effects on local ecosystems and scale up to networks of wind farms is a challenge, but will be required if potential future wind farm consenting policies are to be addressed.

Increased fish abundance, biodiversity, and body size near a North Sea oil and gas platform

In the North Sea, offshore oil and gas (O&G) platforms must be totally removed through decommissioning at the end of their productive life. However, the role of O&G platforms in marine ecosystems, especially for fish assemblages, is not well enough defined yet. Here, we document the association between an O&G platform in the North Sea and the fish assemblages along a distance gradient of 1-600 m from the platform. Scientific angling provided data on fish biodiversity, abundance, and body size. In addition, acoustic data on fish density and target strength were collected to explore spatial and diel fish distributions. The angling data comprised 1217 fish from 11 species, with the highest fish abundance, and all species occurring, within 20 m from the platform. Platform proximity was positively associated with fish biodiversity, and total fish abundance, as well as the specific abundances of Atlantic cod Gadus morhua, dab Limanda limanda, whiting Merlangius merlangus, and mackerel Scomber scombrus. Body sizes of Atlantic cod, whiting, and mackerel were also positively associated with the platform. Absent non-native or invasive species provided no support for stepping stone scenarios. This study highlights the attraction of a variety of fish species towards O&G platforms in the North Sea. Potential local loss of marine biodiversity following full platform removal should be considered in future discussions on platform decommissioning policies.

Acoustic telemetry suggests the lesser spotted dogfish Scyliorhinus canicula stays and uses habitats within a French offshore wind farm

Offshore wind farms (OWF) are a rapidly expanding renewable energy source, but their effects on marine wildlife need further investigation. These infrastructures form new artificial habitats that may modify the behaviour and spatial distribution of fish species. Among the species likely to be affected, benthic sharks occupying coastal habitats are particularly exposed to the development of OWF, especially as electrosensitive species. This study used passive acoustic telemetry to investigate the behaviour of a benthic shark, the lesser-spotted dogfish Scyliorhinus canicula, within France's first operational OWF. Most tagged sharks remained in the vicinity of the OWF post-release, exhibiting site fidelity and seasonal residency with reduced presence during winter when water temperatures are the lowest. The primary site frequented is a monopile with scour protection on soft substrate, offering potential shelters and food sources. This study provides new insights into the species' ecology and contributes to improving our understanding of how anthropogenic structure installation in the marine environment affects the behaviour of S. canicula.

Fish aggregations at oil and gas platform foundations in the North Sea

Globally, aging offshore oil and gas (O&G) platforms face resource depletion, and regulations often demand platform removal through decommissioning. In the North Sea, >€90 billion will be needed for decommissioning by 2060. However, the influence of O&G platforms on fish communities is poorly understood. This challenges predictions of possible fisheries scenarios associated with different decommissioning options. Here, we examined the role that North Sea platforms played on fish communities. We explored patterns of fish abundance and body size variation along transects from O&G platforms comparing catch per unit effort data. Fish abundance was positively associated with O&G platforms. Atlantic cod, plaice, saithe, and mackerel were most abundant near platforms. Similarly, larger Atlantic cod were near the O&G platforms. Our study provided information for decision‐making regarding platform decommissioning scenarios by evidencing O&G platform habitat provisioning for various commercial fish species.

Robust fisheries management strategies under deep uncertainty

Fisheries worldwide face uncertain futures as climate change manifests in environmental effects of hitherto unseen strengths. Developing climate-ready management strategies traditionally requires a good mechanistic understanding of stock response to climate change in order to build projection models for testing different exploitation levels. Unfortunately, model-based projections of fish stocks are severely limited by large uncertainties in the recruitment process, as the required stock-recruitment relationship is usually not well represented by data. An alternative is to shift focus to improving the decision-making process, as postulated by the decision-making under deep uncertainty (DMDU) framework. Robust Decision Making (RDM), a key DMDU concept, aims at identifying management decisions that are robust to a vast range of uncertain scenarios. Here we employ RDM to investigate the capability of North Sea cod to support a sustainable and economically viable fishery under future climate change. We projected the stock under 40,000 combinations of exploitation levels, emission scenarios and stock-recruitment parameterizations and found that model uncertainties and exploitation have similar importance for model outcomes. Our study revealed that no management strategy exists that is fully robust to the uncertainty in relation to model parameterization and future climate change. We instead propose a risk assessment that accounts for the trade-offs between stock conservation and profitability under deep uncertainty.

Strong site fidelity, residency and local behaviour of Atlantic cod (Gadus morhua) at two types of artificial reefs in an offshore wind farm

Globally, biogenic temperate reefs are among the most threatened habitats. In the North Sea in particular, large shellfish reefs were lost owing to fishing activities in the 1900s. The impact of offshore wind farms (OWFs) on marine wildlife is extensive, and it offers the possibility to reintroduce new hard substrate habitats that are protected from fisheries at a large scale. In addition to the submerged structures of OWFs, marine hard substrate habitat can be further enhanced by providing extra artificial reefs. In an operational OWF along the Dutch coast, four artificial reefs (two with a scour bed and two without) were deployed in the vicinity of a wind turbine. Acoustic telemetry was used to monitor the fine-scale movement of 64 Atlantic cod (Gadus morhua). The monitoring ran from July 2021 to January 2023. Detailed information on behaviour, area utilization and attraction to the structures was determined. Results showed strong attraction (high site fidelity and residency) to the artificial reef, with no significant difference between the two tested types of reefs, and only a few individuals staying over winter. Cod spent a large proportion of their time hiding in the artificial reefs, suggesting that adding pipes for shelter has a beneficiary effect.

Hybrid wind-solar energy resources mapping in the European Atlantic

The complementarity of offshore wind and solar resources can enhance the energy output of a hybrid farm and reduce its variability relative to a stand-alone, conventional offshore wind farm. In this work offshore wind and solar resources are characterised and mapped in a large study area covering the European Atlantic, the North and Baltic Seas, and the Canary Islands. The intra-annual and overall variabilities of wind power density and solar irradiance are investigated, and their complementarity is evaluated on the basis of their correlation. Negatively correlated regions include the seas around Ireland and Great Britain, with vast wind resources (mean wind power density ~1500 Wm-2 off W Ireland) and comparatively limited solar resources (mean solar irradiance ~100 Wm-2). Positively correlated regions include notably the Canary Islands, with the highest values of solar irradiance in the study area (mean values of ~280 Wm-2). Two study sites are chosen for more detailed investigation - one with a negative correlation, off W Ireland; the other with a positive correlation, off the Canary Islands. Even in the positively correlated regions, it is found that the correlation coefficient is never large (always under 0.2), which signals an opportunity for reducing power output variability through hybrid or co-located wind-solar farms. This, along with the other advantages of hybrid or co-located wind-solar farms (optimised use of scarce marine space, shared electrical infrastructure, shared O&M crews and vessels, etc.), attests to their potential in the European Atlantic. This potential could be realised through new hybrid or co-located wind-solar farms, or by retrofitting floating solar PV into existing offshore wind farms.

Operationalizing a fisheries social-ecological system through a Bayesian belief network reveals hotspots for its adaptive capacity in the southern North sea

Fisheries social-ecological systems (SES) in the North Sea region confront multifaceted challenges stemming from environmental changes, offshore wind farm expansion, and marine protected area establishment. In this paper, we demonstrate the utility of a Bayesian Belief Network (BN) approach in comprehensively capturing and assessing the intricate spatial dynamics within the German plaice-related fisheries SES. The BN integrates ecological, economic, and socio-cultural factors to generate high-resolution maps of profitability and adaptive capacity potential (ACP) as prospective management targets. Our analysis of future scenarios, delineating changes in spatial constraints, economics, and socio-cultural aspects, identifies factors that will exert significant influence on this fisheries SES in the near future. These include the loss of fishing grounds due to the installation of offshore wind farms and marine protected areas, as well as reduced plaice landings due to climate change. The identified ACP hotspots hold the potential to guide the development of localized management strategies and sustainable planning efforts by highlighting the consequences of management decisions. Our findings emphasize the need to consider detailed spatial dynamics of fisheries SES within marine spatial planning (MSP) and illustrate how this information may assist decision-makers and practitioners in area prioritization. We, therefore, propose adopting the concept of fisheries SES within broader integrated management approaches to foster sustainable development of inherently dynamic SES in a rapidly evolving marine environment.

Techno-economic assessment of potential zones for offshore wind energy: A methodology

This work presents a methodology for the techno-economic assessment and comparison of potential zones for the development of offshore wind energy. The methodology is illustrated through a case study in North Spain, using the high-potential zones designated by the Spanish government. The main elements considered include the bathymetry (water depths), energy production and total working hours based on the wind climate, maintenance windows based on the wave climate, and distance to selected port facilities that can accommodate the installation and operational and maintenance phases of an offshore wind farm. An interesting dichotomy arises moving from west to east along N Spain - energy production and working hours decrease, but maintenance windows increase. Given that both aspects play a role in the costs of an offshore wind project, pondering them adequately is crucial, and the selection of a particular zone for development may depend on project-specific cost models. Water depths may preclude the installation of bottom-fixed structures in certain areas; importantly, they may also represent a constraint for the deployment of certain floating concepts, particularly in the high-potential zones of the Cantabrian Sea. Finally, ports capable of servicing the offshore wind farms are identified and distances to all high-potential zones, calculated. By examining the unique properties of the high-potential zones, this methodology, which can be applied to other regions of interest for offshore wind, provides valuable insights into the advantages and challenges of offshore wind development at each site and thereby contributes to informed decision-making.