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| Fig. 1: The Coastal Virginia Offshore Wind Pilot Project (Source: Wikimedia Commons). |
The rapid expansion of offshore wind energy is transforming open water seascapes into networks of artificial structures that increasingly function as artificial reefs. Fig. 1 shows the coastal Virginia offshore wind pilot project, highlighting this transformative time. Turbine foundations, scour protection rock, and associated subsea infrastructure introduce hard substrate into coastal and shelf environments that are otherwise dominated by soft sediments. As global offshore wind capacity has increased from tens of gigawatts in the early 2000s to tens of thousands of megawatts today, these engineered structures have begun to influence marine community structure and habitat connectivity. Offshore wind is also a key component of global decarbonization. Prospective life cycle assessments show that projected offshore wind deployment through 2040 emits far fewer greenhouse gases than generating the same electricity using the current global power mix. [1] At the same time, decades of artificial reef research demonstrate that purpose built reefs can support fish density, biomass, richness, and diversity comparable to nearby natural reefs, based on quantitative syntheses of 39 analyzed studies. [2] These findings motivate viewing offshore wind development not only as an energy transition, but also as a large scale ecological experiment in the creation of artificial reefs.
Offshore wind has shifted from a niche technology to a central element of global decarbonization. A prospective life cycle assessment estimates that from 2000 to 2018, global offshore wind capacity grew at an average rate of approximately 30 percent per year, reaching about 23 GW by 2018. [1] Under stated policy and sustainable development scenarios, global capacity is projected to increase to between 342 and 562 GW by 2040, representing a 15 to 24 fold expansion over two decades. [1] Each increment of capacity requires additional turbine foundations, subsea cables, and scour protection rock, all of which add hard substrate and vertical relief to continental shelf environments.
The 2023 Offshore Wind Market Report provides a detailed summary of current deployment patterns. By the end of 2022, global offshore wind capacity totaled 59,009 MW, generated by 292 operating projects and more than 11,900 individual turbines. [3] Newly commissioned capacity in 2022 alone amounted to 8,385 MW, including 5,719.6 MW in China, 1,386 MW in the United Kingdom, 480 MW in France, 342 MW in Germany, and 331 MW in Vietnam. [3] The global development pipeline expanded to 426,789 MW in 2022, an increase of nearly 16 percent compared to the 368,170 MW reported in 2021, indicating that the current fleet represents only a fraction of the structures expected to enter the ocean in coming decades. [3]
In the United States, similar trends are emerging. As of May 2023, the United States offshore wind pipeline reached 52,687 MW, a 15 percent increase relative to the previous year. [3] This expansion included 4,885 MW associated with three newly designated wind energy areas in the Gulf of Mexico and 1,826 MW resulting from updated capacity estimates at previously identified sites. [3] Thirteen coastal states now maintain offshore wind procurement targets that sum to 112,286 MW by 2050, supporting federal goals of 30 GW installed by 2030 and 15 GW of floating offshore wind by 2035. [3] These commitments imply continued growth in turbine foundations and associated infrastructure along United States coastlines.
Life cycle assessments place this structural expansion into a broader environmental context. Offshore wind deployment from 2020 to 2040 is expected to emit a cumulative 2.6 to 3.6 gigatons of CO2 across construction, operation, and decommissioning. [1] Generating the same amount of electricity with the 2020 global electricity mix would emit between 124 and 207 gigatons of CO2, meaning offshore wind reduces emissions by a factor of approximately 48 to 58. [1] Future deployment could displace 408 to 584 GW of fossil fuel generating capacity, underscoring the dual role of offshore wind foundations as climate mitigation infrastructure and long lived artificial structures with ecological consequences. [1]
The first Dutch offshore wind farm, OWEZ, was commissioned in 2005 and became fully operational by 2007. [4] Monitoring during the first two years showed that soft bottom benthos in surrounding sandy areas exhibited no measurable short term effects, while monopiles and scour protection rock served as new hard substrate that supported the establishment of new benthic communities. [4] The OWEZ area was previously a heavily fished region where beam trawl vessels regularly disturbed the seafloor. Once the wind farm was built, trawling was no longer allowed inside the turbine field. Monitoring during the first two years showed that early patterns of bivalve recruitment were not driven by the presence of the turbines. Instead, natural sediment conditions, specifically the amount of mud in the seafloor, explained most of the variation in where bivalves settled. In other words, sites with muddier sediments had lower recruitment and sandier sites had higher recruitment, regardless of turbine installation. [4] Fish communities remained spatially and temporally variable, though species such as Atlantic cod appeared to use turbine structures for shelter, and harbor porpoises produced higher rates of acoustic clicks inside the farm relative to reference sites. [4]
At the Lillgrund wind farm in the Oresund Strait, trawl survey data from 2003 to 2005, before construction, and from 2008 to 2010, after construction, were compared to assess fish community responses. [5] More than 95 percent of the fish community in the region is marine, and the area has been closed to trawl fishing since 1932. [5] Significant spatial and temporal patterns in abundance were detected, though these patterns were driven largely by environmental variation rather than turbine presence. [5] Overall, early studies indicate that while foundations function as artificial reefs at local scales, larger scale ecological effects remain uncertain.
A 2023 NOAA synthesis highlights these uncertainties, noting that turbine arrays alter near field flow, turbulence, and stratification, but that basin scale ecological effects, particularly regarding larval dispersal and fisheries production, remain unquantified in United States waters. [6]
Artificial reef science provides detailed quantitative evidence of how engineered hard structures affect marine communities. A systematic review of 115 peer-reviewed studies (89 on artificial reefs and 26 on offshore wind farms) found that 94% of artificial reef studies reported that fish abundance and biodiversity either increased or was unaffected by AR deployment. [7] Specifically, 49% of the literature reported locally increased fish abundances after AR deployment, while 31% found an increase in species richness in the AR area. [7] Long-term field studies provide additional high-value quantitative insights into how biological communities develop on artificial structures over time. A ten-year assessment of estuarine artificial reefs documented a more than two-fold increase in species richness between early (within 2 years) and recent (after 10 years) sampling periods, with this pattern particularly evident at artificial reefs. [8] The study also found that Simpson diversity increased even more substantially, indicating not just more species but greater evenness in their distribution. [8] Critically, recreationally important species such as yellowfin bream (Acanthopagrus australis) and snapper (Chrysophrys auratus) showed no decline in abundance after 10 years, with some target species like sand whiting (Sillago ciliata) showing significant increases only during the latter sampling period. [7]
At broader scales, offshore wind impacts exhibit similar ecological patterns. A systematic global assessment of 132 peer-reviewed studies synthesized 314 pieces of quantitative ecological evidence and found that during the operational phase of offshore wind farms, 34% of measured ecological responses were positive, 32% were negative, 26% showed no change, and 8% were inconclusive. [9] For fish specifically, operational phase studies reported increases in the abundance of commercially important species such as cod and pouting, while construction phase impacts were predominantly negative across subject groups (52% negative, 8% positive, 24% inconclusive), particularly affecting several species of fish including brill, cod, dab, and plaice, as well as some seabird species. [9] This structured distribution of positive and negative outcomes highlights the complexity of ecological responses, while reinforcing the potential for turbine structures to generate habitat value similar to that documented for dedicated artificial reefs.
A targeted review integrating artificial reef research into offshore wind planning argues that turbine monopiles and scour protection can be intentionally designed to support ecological function over multiple decades. [7] Scour protection typically consists of rocks positioned around turbine foundations with a radius reaching up to 20 m, with the filter layer usually about 0.5 m high and the armor layer about 1 m high. [7] These structures create complex three-dimensional habitat where only soft sediment existed previously, enabling colonization by diverse invertebrates, macroalgae, and reef-associated fishes. The ecological potential is substantial: one study estimated an average density of 14 pouting individuals per m2 on scour protection, yielding an estimated local population of 22,000 pouting individuals around one wind turbine foundation. [7]
Quantitative evidence from both artificial reef research and offshore wind monitoring shows that turbine foundations can support significant biological production. Scour protection at a Danish offshore wind farm provided a 50-fold increase in local food availability for fish compared to the previously sandy area. [7] Studies demonstrate that scour protection meets the requirements to function as an artificial reef, often providing shelter, nursery, reproduction, and/or feeding opportunities. [7] Fish species including Atlantic cod, pouting, goldsinny wrasse, rock gunnel, shorthorn sculpin, sole, and whiting have all shown locally increased abundances at offshore wind foundations. [7] Acoustic telemetry demonstrated that Atlantic cod exhibit strong residency, high site fidelity and habitat selectivity towards OWF foundations with scour protection. [7] The review of 132 studies found that approximately half of the offshore wind farm literature (46%) reported increases in fish abundance, particularly for species associated with rocky substratum. [9]
Despite these parallels, significant uncertainties remain. A global synthesis found that more than 86% of possible offshore wind farm impacts on ecosystem services are still unknown. [9] There was a particular paucity of studies on regulating services such as carbon sequestration and storage, with only a handful of studies available despite global net-zero ambitions. [9] Moreover, no peer-reviewed studies were found that empirically assessed the decommissioning of offshore wind farms. [9] Construction impacts during the operational phase showed that 14 ecosystem services are impacted either positively or negatively, with substantially enhanced services including commercial fisheries and experiential recreation, while substantially degraded services included existence values for culturally important groups and the spread of non-native species. [9] These gaps highlight the need for long-term monitoring programs with clearly defined ecological objectives, particularly in emerging markets and southern hemisphere countries with high future offshore wind deployment trends. [9]
By integrating artificial reef science with turbine foundation design, for example, using mixed-sized rocks to create varied crevice sizes, optimizing structural complexity, or incorporating purpose-designed concrete modules with multiple holes offshore wind development can create productive marine habitat capable of supporting ecological function over multidecadal time periods. [7] The potential is significant: using Reef Ball designs, the projected carrying capacity is approximately 385 kg of fish per unit within a year, suggesting that the annual carrying capacity of a scour protection area could approach 65,000 kg. [7]
The expansion of offshore wind is creating one of the largest additions of artificial hard substrate in the marine environment in modern history. Turbine foundations and scour protection rock introduce new habitat into soft sediment regions, and early ecological studies show that these structures rapidly attract benthic organisms, reef associated fishes, and marine mammals. Insights from artificial reef science demonstrate that engineered hard substrate can support biomass, species richness, and community diversity comparable to natural reefs when designed effectively. At the same time, uncertainties remain regarding basin scale ecological effects, larval dispersal, long term population dynamics, and cumulative regional change. Offshore wind also provides major climate mitigation benefits by replacing fossil fuel electricity and reducing global emissions. Taken together, the evidence indicates that offshore wind development represents both a significant environmental opportunity and a scientific responsibility. Understanding and guiding the ecological function of turbine foundations will be essential to ensuring that offshore renewable energy supports both climate goals and marine ecosystem health.
© Lauren Korsnick. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] C. Li et al., "Environmental Impacts of Global Ooffshore Wind Energy Development Until 2040," Environ. Sci. Technol. 56, 11567 (2022).
[2] A. B. Paxton et al., "Meta-Analysis Reveals Artificial Reefs Can Be Effective Tools For Fish Community Enhancement But Are Not One Size Fits All," Front. Mar. Sci. 7, 282 (2020).
[3] W. Musial et al. National Renewable Energy Laboratory, "Offshore Wind Market Report 2023 Edition," U.S. Office of Enegy Efficiency and Reliable Energy, DOE/GO-102023-6059, August 2023.
[4] H. J. Lindeboom et al., "Short Term Ecological Effects of an Offshore Wind Farm in the Dutch Coastal Zone; a Compilation," Environ. Res. Lett. 6, 035101 (2011).
[5] Bergström, F. Sundqvist, U. Bergström, "Effects of an Offshore Wind Farm on Temporal and Spatial Patterns in the Demersal Fish Community," Mar. Ecol. Prog. Ser. 485, 199 (2013).
[6] F. Hogan et al., "Fisheries and Offshore Wind Interactions: Synthesis of Science," NOAA Technical Memorandum NMFS-NE-291, March 2023.
[7] M. Glarou, M. Zrust, and J. C. Svendsen, "Using Artificial Reef Knowledge to Enhance the Ecological Function of Offshore Wind Turbine Foundations: Implications for Fish Abundance and Diversity," J. Mar. Sci. Eng. 8, 332 (2020).
[8] A. Becker et al., "Revisiting an Artificial Reef After 10 Years: What Has Changed and What Has Remained the Same," Fish. Res. 249, 106261 (2022).
[9] S. C. L. Watson et al., "The Global Impact of Offshore Wind Farms on Ecosystem Services," Ocean Coast. Manage. 249, 107023 (2024).
