Offshore wind farms (OWFs) are a rapidly expanding source of renewable energy, representing a significant global shift in power generation. This unprecedented scale of development has placed the environmental impact on marine ecosystems at the forefront of scientific and public inquiry. Understanding how these industrial complexes affect marine life requires examining both the temporary disturbances during installation and the chronic effects that persist over the farm’s multi-decade lifespan.
Effects of Construction Activities
The installation phase, particularly the placement of foundations, introduces intense, short-term disturbances to the marine environment. The most significant concern is the acute, impulsive noise generated by impact pile driving, which is necessary to secure large monopile foundations to the seabed. This noise can reach very high levels, making it one of the loudest human-made sounds in the ocean.
Such high-intensity noise acutely impacts marine mammals and fish that rely on sound for communication, navigation, and foraging. Exposure can cause temporary hearing loss, known as Temporary Threshold Shift (TTS), in marine mammals. Studies show that species like the harbor porpoise initiate avoidance behavior and flee the area, sometimes moving up to 20 kilometers away from the construction site.
Physical disturbance of the seabed also occurs during construction from activities like dredging and foundation placement. This results in the destruction of local seafloor habitats and the creation of large sediment plumes in the water column. Increased turbidity from these plumes can smother sessile benthic communities, such as corals and anemones, which cannot move away from the settling silt. The stirring up of sediment can also potentially re-mobilize contaminants buried in the seafloor over time.
Long-Term Operational Impacts
Once the turbines are operational, the impacts on marine life shift from acute to chronic, persisting over the 20-plus year life of the farm. The spinning turbines and their supporting structures generate continuous, low-frequency acoustic emissions that propagate into the water column. This operational noise is significantly quieter than construction noise, comparable to ambient background ocean noise.
While this constant humming is not loud enough to cause physical injury, it can mask the communication signals of marine mammals or influence the behavioral patterns of certain fish species. Another chronic effect is the electromagnetic field (EMF) generated by the subsea power cables transmitting electricity back to shore. These cables introduce artificial magnetic fields, concerning electroreceptive species, such as sharks, skates, and rays, that use the Earth’s natural magnetic field for orientation.
Scientific evidence suggests that behavioral changes in these sensitive species are likely limited to individuals in the immediate vicinity of the cable. Elevated EMF levels typically return to natural background levels within 100 meters or less of the cable. The constant presence of maintenance and service vessels required to operate the farm also introduces a persistent risk of vessel strikes for marine mammals.
Habitat Changes and the Reef Effect
The physical presence of turbine foundations introduces a change to the local seafloor ecosystem, particularly in areas that were previously soft-bottom habitats. This structural addition creates the “artificial reef effect,” which can be both beneficial and detrimental to marine life. The hard surfaces of the foundations and their surrounding scour protection provide a new substrate for sessile organisms, such as mussels, barnacles, and anemones, to colonize.
This colonization increases local biodiversity by attracting fish species, like cod, that prefer hard-bottom habitats for shelter, foraging, and reproduction. The aggregation of life around the foundations creates a localized “hotspot” of biological activity and biomass. Furthermore, many offshore wind farms restrict commercial fishing, which effectively creates a protected area that allows fish stocks to recover and potentially “spill over” into surrounding fished areas.
Conversely, the physical footprint of the infrastructure permanently displaces the original soft-bottom communities, leading to a net loss of that specific habitat type. The new hard substrates also risk facilitating the establishment and spread of non-indigenous or invasive species that thrive on artificial structures. The overall array of turbines can also act as a physical barrier for highly mobile or migratory species, altering their traditional movement corridors.
Regulatory Measures and Mitigation Strategies
Regulatory bodies and developers employ proactive measures to minimize the negative impacts of offshore wind development on marine ecosystems. To address the intense noise from pile driving, developers routinely use noise dampening technologies.
Noise Mitigation
Developers use double bubble curtains, which release a continuous stream of air bubbles around the piling site to scatter and absorb sound waves. Alternative foundation installation methods, such as vibratory piling or the use of suction bucket foundations, are also increasingly deployed to replace traditional impact hammers.
Temporal and Spatial Avoidance
Mitigation includes temporal avoidance strategies, such as scheduling construction activities outside of biologically sensitive periods. This involves avoiding times when marine mammals are migrating, fish are spawning, or sensitive species are calving in the area. To reduce the effects of electromagnetic fields, power cables are typically buried deep beneath the seafloor, increasing the distance between the EMF source and the water column. Furthermore, micro-siting, the practice of adjusting the exact placement of turbines and cables, helps developers avoid sensitive seabed habitats or known migration bottlenecks.