Recent marine biology studies reveal a complex interplay between wind farm infrastructure and ocean inhabitants. While construction noise can temporarily displace marine mammals and affect fish behavior, the resulting artificial reefs often create thriving marine sanctuaries. Understanding these dynamics is crucial as we balance our urgent need for clean energy with our responsibility to protect ocean ecosystems.
When hard structures are introduced into the ocean, they often transform into artificial reefs. These are man-made structures deliberately placed in the sea to mimic the characteristics of natural reefs. Oceanographers and other researchers have long observed how submerged shipwrecks and bridges can become home to diverse and colorful arrays of marine species. Similarly, the underwater portions of many offshore wind turbines in Europe, China, and other parts of the globe have demonstrated this same phenomenon.
Offshore wind turbine foundations, along with their scour protection (such as rocks placed around the base), act as artificial reefs, attracting marine life and potentially enhancing local biodiversity. This “reef effect” occurs because these hard structures provide new surfaces for marine organisms to attach to, creating essential habitats for algae, shellfish, and various fish species.
Scour Protection: More Than Just Foundation Support
Scour, analogous to erosion, is the process by which waves and currents remove sediment from around the base of a structure. For offshore wind turbines and their connecting subsea cables, this phenomenon poses a significant threat to their stability and integrity. To counteract this, engineers frequently deploy scour protection measures, which are critical for the long-term viability of these projects.
These protective measures often consist of materials like rocks, concrete mattresses, or grout bags strategically placed around the turbine foundations and along unburied cable routes. Their primary function is to create a stable barrier that prevents currents from washing away the seabed sediment, which could otherwise undermine the turbine’s base. Additionally, scour protection safeguards the vital inter-array and export cables from exposure and potential damage.
Beyond their engineering purpose, these scour protection elements inadvertently contribute to the artificial reef effect of offshore wind farms. The varied surfaces and interstitial spaces created by the rocks, mattresses, and bags offer diverse habitats, shelter, and foraging grounds for a range of marine species. This secondary benefit is an important consideration in the ecological assessment of offshore wind projects, highlighting how essential infrastructure can also play a role in marine biodiversity enhancement.
How Offshore Wind Turbine Foundations and Scour Protection Create Thriving Marine Habitats
Offshore wind farm structures are more than just sources of renewable energy; they create unique artificial reef environments that often become thriving marine ecosystems. This phenomenon, known as the “reef effect” by marine biologists, arises as the turbine’s steel foundations and scour protection systems rapidly become colonized by various marine organisms.
These submerged structures quickly form the base of complex food webs. Organisms like mussels, barnacles, and diverse species of algae readily attach to the steel foundations, acting as “fouling organisms” and marking the start of a new artificial reef. The vertical pillars of the foundation provide ideal attachment points for these filter-feeding organisms, while the rocky scour protection at the base offers crucial shelter for bottom-dwelling species such as cod, lobsters, and crabs.
The introduction of these novel surfaces leads to the rapid colonization of various organisms, including mussels, macroalgae, barnacles, filter-feeding arthropods, and anemones, which often exhibit distinct vertical zonation. This can result in a significant increase in biomass, potentially up to 4,000-fold compared to original sediments, attracting larger species like crabs and lobsters. Studies have identified three successional stages for these biofouling communities:
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Pioneer stage (0-2 years): Initial colonization by opportunistic species.
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Intermediate stage (3-5 years): Increased diversity of suspension feeders.
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Climax stage (6+ years): Domination by species like plumose anemones and blue mussels, indicating a mature and stable community.
Different foundation types contribute to diverse habitats:
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Monopile foundations, the most common type, offer expansive vertical surfaces for mussels, barnacles, and other filter-feeding organisms to attach. These colonizing species form the foundation of a complex food web, attracting fish and crustaceans that seek both food and shelter.
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Jacket foundations, with their intricate lattice-like structure, create numerous hiding spots and breeding grounds for species like cod and pouting.
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Gravity-based foundations provide extensive horizontal surfaces near the seabed, becoming prime real estate for soft corals, anemones, and sponges.
Beyond the foundations, scour protection measures also create vital microhabitats. These rocky areas provide refuge for lobsters and crabs and suitable surfaces for kelp attachment, further contributing to the development of rich marine communities. Research consistently shows that these artificial reefs can support biomass levels up to 200 times greater than surrounding sandy areas, highlighting their significant potential for enhancing marine biodiversity.
The Oceanography Society
Offshore Wind Farms as De Facto Marine Sanctuaries
An additional benefit of some wind farms is their role as de facto marine sanctuaries. Fishing activities are often restricted within their boundaries, creating safe havens where fish populations can recover and flourish. This reduced fishing pressure around the wind farm structures frequently results in a “spill-over effect” into adjacent fishing zones, increasing available fish stocks for commercial fisheries.
This artificial reef environment attracts both resident and migratory species. Schools of fish commonly gather around turbine foundations, utilizing them as feeding grounds and nursery areas. Marine mammals, particularly seals, have also been observed foraging in these areas, indicating that the structures create productive hunting grounds.
Ecological Benefits and Research Findings
The colonization process typically follows a predictable succession pattern, with early colonizers like barnacles and tube worms preparing the surface for later arrivals. Over time, these communities become increasingly complex and stable, contributing significantly to local marine biodiversity and potentially enhancing fish populations in the surrounding waters. Scientists have specifically observed that juvenile fish greatly benefit from these structures, as they provide protection from larger predators and create crucial nursery areas.
Monitoring data from established wind farms in the North Sea consistently indicates a significant increase in fish abundance, with some sites reporting up to 50% higher population densities compared to surrounding areas. Species like cod, pouting, and various flatfish show a particular affinity for these structures, using them for shelter and feeding grounds.
Furthermore, the abundant suspension feeders on offshore wind farm structures act as “biofilters,” actively removing particles from the water column. This can lead to localized reductions in turbidity and increased light penetration, benefiting other marine life. These organisms also efficiently transfer pelagic food sources to the benthic community, potentially increasing overall secondary production. Studies have shown that sediments around turbines become enriched with organic matter from filter feeder fecal pellets, leading to increased macrofaunal densities and species richness.
Higher trophic levels, including various fish species, seabirds, and marine mammals, are also attracted to offshore wind farms for both shelter and food. Fish species such as Atlantic cod and black sea bass are frequently found associated with these structures, either aggregating due to the attraction of the enhanced habitat or experiencing increased production due to improved conditions. While some species prey on the biofouling community, others are attracted for non-trophic reasons like seeking shelter or social aggregation.
Nature Inclusive Design: The Artificial Reef Effect
Traditional scour protection, while effective for safeguarding underwater infrastructure, often overlooks its potential as a marine habitat. However, adopting a nature-inclusive design for scour protection can transform these necessary structures into thriving ecosystems, leveraging the artificial reef effect. This approach not only protects offshore wind turbine foundations but also significantly enhances the biodiversity of the surrounding marine environment, particularly in areas predominantly characterized by soft-bottom habitats.
To maximize the ecological benefits, the design of scour protection can be optimized to mimic the complexity of naturally occurring marine habitats. Incorporating a variety of structures—both large and small, with diverse hole sizes and an array of rock shapes and sizes—increases both the surface area and habitat complexity of the scour protection layers. This multifaceted approach provides essential shelter for larger, mobile species while also creating suitable refuges for smaller organisms, juvenile life stages, and attached species, thereby fostering greater biodiversity.
Further enhancing biodiversity can be achieved by modifying the overall shape of the scour protection. Irregular designs, featuring extensions in multiple directions, generate additional surface area for marine growth. Furthermore, diversifying rock sizes and shapes, incorporating more calcareous rocks, and enhancing surface roughness can significantly contribute to a richer ecosystem. The strategic introduction of specific species, such as ecosystem engineering species, can further accelerate the development of a robust and diverse community within the scour protection.
A Study from Block Island
A groundbreaking, seven-year study, “Demersal fish and invertebrate catches relative to construction and operation of North America’s first offshore wind farm,” offers compelling insights into the ecological impact of the Block Island Wind Farm. This pioneering research, the first of its kind in the United States, meticulously tracked nearly 664,000 individual fish across 61 species around the wind turbines.
Contrary to concerns about potential negative effects, researchers found no adverse impacts on bottom-dwelling fish populations during either the construction or operational phases of the wind farm. Instead, they observed a remarkable phenomenon: fish populations were thriving around these new artificial reefs. The turbine foundations provided an unexpected boon, serving as a substrate for mussels, which became a readily available food source. Furthermore, the structures functioned as vital nursery habitats, offering shelter and protection for young fish.
The most significant and conclusive finding was a substantial increase in the congregation of black sea bass around the Block Island wind farm. This positive correlation is likely due to the species’ preference for physical structures, which the turbine foundations readily provide. While an increase in Atlantic cod was also noted, the frequency of these observations was not sufficient to draw definitive conclusions. The Block Island study strongly suggests that offshore wind turbines can, in fact, create flourishing marine ecosystems, acting as beneficial artificial reefs.
RWE and ARC Marine Pilot
RWE and ARC marine® have launched the world’s first full-scale pilot project, Reef Enhancement for Scour Protection (RESP), at the Rampion Offshore Wind Farm in England. This initiative involves deploying over 75,000 eco-engineered Reef Cubes, made from low-carbon, recycled materials, as a sustainable alternative to traditional rock scour protection. The project aims to simultaneously protect turbine foundations and enhance marine biodiversity through Nature Inclusive Design, fostering vibrant marine ecosystems while meeting critical engineering needs.
ARC marine and RWE view this as a flagship project to demonstrate and evaluate the potential for Nature Inclusive Design (NID) solutions to effectively meet both engineering and biodiversity requirements. The reef cubes® — designed and manufactured by ARC marine are engineered with rough surfaces and built-in shelter spaces that promote the settlement and protection of local marine species, such as European seabass, common starfish and brown crab.
The data and insights gathered from the RESP pilot will help to assess the potential benefits of using Nature Inclusive Design to increase biodiversity within future offshore developments while addressing a critical engineering issue. Deriving multiple benefits in this way delivers increased value and could lead to setting new practices for biodiversity integration across the renewables industry.
Examples of Nature-Based Design Products:
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Reef Balls: Reef Balls® can be added on top of, placed next to, or integrated into a scour protection layer. They can be customized to meet specific project needs and designed to attract use by specific focal species. They are designed to withstand movement and damage in storms and can be installed using a variety of methods. They are made from marine grade pH-neutralized concrete resulting in a pH similar to seawater. They can be customized to more closely resemble natural habitats and are constructed with a rough textured surface to promote colonization of marine epifauna.
Reef Balls, Reef Innovations -
Layer Cakes: Layer Cakes® are designed to provide increased horizontal surface area for colonization of benthic epifauna (when compared to Reef Balls®). They come in a variety of sizes and can be added on top of, placed next to, or integrated into a scour protection layer and are installed using a crane. Layer Cakes can be customized to meet specific project needs and designed to attract use by specific focal species by customizing the number, shape, and size of layers.
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Reef Cubes: The ARC Marine Reef Cubes are an advanced, versatile artificial reef solution made from 98% recycled, plastic-free materials, offering 91% carbon savings. Developed through extensive research, their patented design with textured finishes and adjustable passageways promotes the growth of local marine life. These cubes come in various sizes and can be used for coastal defense, fisheries, and offshore projects, including scour protection, artificial reefs, and fill-ins, with modularity allowing for diverse and stable reef system constructions.
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Reef Matts: The ARC Marine Reef mat is an environmentally friendly, low-carbon concrete alternative to traditional subsea mattresses. It promotes biodiversity through its Nature Inclusive Design with 3D textures, is made from 98% recycled materials, offers significant carbon savings, and provides cost benefits by avoiding decommissioning.
Ørsted Deploys 3-D Printed Reef Structures at the Anholt Offshore Wind Farm
Recognizing the urgent need to address the drastic decline in cod populations within the Kattegat, a sea area between Sweden and Denmark, an innovative project was launched in 2022 by Ørsted and WWF Verdensnaturfonden / WWF Denmark. This initiative saw the deployment of a dozen 3D-printed reef structures on the seabed between the wind turbines at the Anholt Offshore Wind Farm. Developed through a collaboration between WWF Netherlands and Reef Design Lab, and produced by the Italian company D-Shape, these biocompatible reefs are designed to create much-needed habitats for cod. Years of overfishing, oxygen depletion, and habitat loss have severely impacted the Kattegat’s cod stock, which is now 90% lower than in 1990. As a vital top predator, the scarcity of cod disrupts the delicate marine ecosystem, leading to an overgrowth of species like green crabs that negatively impact crucial eelgrass beds—important habitats and carbon sinks. The hope is that these uniquely shaped, wedding cake-like structures, approximately one cubic meter in size, will provide varied hiding spaces for fish and hard surfaces for other organisms, ultimately contributing to the recovery of the cod population and the overall health of the marine environment.
Offshore Wind & Aquaculture
The co-location of offshore wind farms (OWF) and aquaculture, often referred to as a Multi-use Setting (MUS), has emerged as a strategy to optimize the use of marine space and potentially benefit marine wildlife and fish populations. Beyond the artificial reef effect, integrating aquaculture, especially with shellfish or seaweed farming, within OWFs can be a nature-based solution that supports threatened species and contributes to wider ecosystem services.
For example, co-locating wind farms with farming of blue mussels and sugar kelp can deliver emission free energy, nutritious seafood, and positive ecosystem services through emission (CO2 and nutrients) capture and utilization. The diagram below shows how the integration of low-trophic aquaculture (LTA) can benefit the surrounding ecosystem.
Low Trophic Aquaculture, which involves farming shellfish and seaweed, provides a sustainable method for food production with a significantly smaller carbon footprint than land-based agriculture. These aquatic organisms naturally purify the water by absorbing surplus nutrients and carbon dioxide, leading to improved water quality and a reduction in ocean acidification. By offering a protein source with minimal environmental impact and enabling the recirculation of nutrients from marine to terrestrial environments, LTA can provide a multitude of benefits when co-located with offshore wind farms.
Conclusion: A Symbiotic Future for Energy and Ocean Life
The journey towards a sustainable energy future is intrinsically linked with our stewardship of the marine environment. As this article has explored, offshore wind farms, far from being mere industrial installations, are proving to be dynamic contributors to ocean ecosystems. The “reef effect,” driven by the very foundations and essential scour protection of wind turbines, transforms these structures into vibrant artificial reefs, fostering biodiversity and providing crucial habitats for a myriad of marine species. Innovative approaches, such as the deployment of 3D-printed reefs and the adoption of nature-inclusive designs, further amplify these ecological benefits, actively contributing to the restoration of vulnerable populations. Moreover, the de facto marine sanctuaries created by restricted fishing zones within wind farms offer a vital reprieve for marine life, leading to spill-over effects that benefit surrounding areas. Looking ahead, the potential for co-locating offshore wind with sustainable aquaculture presents an exciting frontier, promising not only clean energy and food production but also enhanced ecosystem services. Ultimately, the evolving understanding of the “reef effect” underscores a powerful truth: with thoughtful design and a commitment to ecological integration, offshore wind development can indeed forge a symbiotic future, where our pursuit of renewable energy actively contributes to a healthier, more resilient ocean.
Interested in learning more? Check out this video by The Nature Conservancy