Offshore wind turbines and biodiversity – science sets sail
With industrial offshore wind turbine projects multiplying along France’s four coastlines, a collaborative scientific expert review led by the CNRS and the Ifremer is taking stock of their impact on marine biodiversity and the mitigation measures that have been studied in the scientific literature.
In the spring of this year, a wind of change was sweeping through France’s offshore wind farms, with the Yeu-Noirmoutier wind farm off the coast of France’s Vendée region coming into full operation. This is the fourth such wind farm in France after those at Fécamp (Seine-Maritime), Saint-Brieuc (Côtes-d’Armor) and Saint-Nazaire (Loire-Atlantique). It is now fully operational and its 61 8 MW turbines are set to generate 488 MW of electricity, which is equivalent to the annual electricity consumption of the 800,000-strong population of the Vendée region. At the same time in spring, the first of the Dieppe-Le Tréport wind farm’s 62 turbines were being erected about fifteen kilometres off the Normandy coast. When this installation is fully operational by the end of this year, the wind farm could supply the equivalent of the electricity consumption of 850,000 people, which corresponds to two thirds of the population of the Seine-Maritime region.
Offshore wind power really does have the wind in its sails, in France and across Europe alike. Since the first offshore wind farm opened in 1991 in Denmark, Europe has established itself as a pioneering global leader in the sector1. By 2023, Europe’s total installed offshore wind capacity had reached 34 GW, with the North Sea at the heart of this industry. China’s ambitions have driven its rise to become the world’s leading producer, hosting half of the world’s offshore wind farms, in just under a decade. In response, Europe has renewed its support for this industry, which helps mitigate the effects of climate change and contributes to European energy sovereignty. In 2023, the European Wind Power Action Plan2 projected offshore wind capacity of 60 GW by 2030 and 300 GW by 2050.
Mainland France, with its four coastlines, is an integral part of this European revival. France accounts for a third of Europe’s potential for offshore wind farms, making it a key player in achieving the EU’s targets1. In February 2022, the President of the French Republic launched an 'offshore wind pact' between the State and the wind farm industry, aiming to establish around 50 wind farms by 2050. These would have an installed capacity of approximately 45 GW, which represents a fourfold increase in the number of jobs involved and a total investment of 40 billion euros over 15 years. One point in the pact attracted particular attention, namely the implementation of “exemplary projects in terms of integration into the environment – both human and natural – in which they are situated”.
The most comprehensive mapping of knowledge to date
In this context of a rapidly growing industrial sector supported by the State, the ministries responsible for energy, ecology and the sea have commissioned the CNRS – via its Mission for Scientific Expertise – and the French Research Institute for Exploitation of the Sea (Ifremer) to study the effects of these wind turbines on biodiversity and marine and coastal ecosystems. The State’s request followed on from the 2022 creation of a national observatory for monitoring offshore wind energy, and the subsequent national public debate on maritime issues in 2024. This expert review led by Cédric Bacher, an Ifremer researcher in marine ecology2, and Nathalie Niquil, a CNRS research professor in marine ecology3, led to the idea of a state-of-the-art review of the available scientific knowledge. Now the mission has been accomplished through a systematic review that analysed over 400 scientific publications identified following the initial screening of over 4500 publications by 25 experts from 13 French and Belgian research institutions. This constitutes the most comprehensive mapping of knowledge to date.
The expert panel analysed ten pressures exerted by offshore wind turbines on marine biodiversity, as described and analysed in the scientific literature. For example, “the structures of offshore wind farms constitute barriers to the movement of certain mobile species in the air and in the water. They also provide new underwater substrates that encourage the biological colonisation of species usually found on rocks”, explains Cédric Bacher. In tangible terms, where mussels attach themselves to the foundations, there is an increase in the abundance and size of the fish that feed on them, like the pollack. Similarly, the changes caused by wind farms to seabed habitats and the water column result in both “a change in turbulence within the water column and the filtration of plankton by the mussels”, details the researcher.
Furthermore, “the restriction or termination of certain fishing activities, like bottom trawling, leads to what the scientific literature describes as a ‘refuge effect’ in which an increase in the abundance and average size of certain species in the area is observed”, explains Nathalie Niquil. She goes on to explain that “the scientific literature discusses the effects of intense sounds at some length. For example, the pile-driving technique that is used to install certain foundations produces high-intensity sounds up to several tens of kilometres underwater, which causes marine mammals to flee. However, taking the appropriate measures can mitigate these effects”.
Avoiding, reducing and offsetting impacts
An analysis of the scientific literature highlights several courses of action to mitigate the effects of offshore wind turbines. In the case of certain identified effects, the literature suggests it would be beneficial to map marine habitats so turbines can be installed in areas where certain species are less sensitive to their effects. Similarly, the report notes a number of technical measures studied by researchers to reduce the intensity, extent or duration of the impacts, with most scientific studies on mitigation (85 per cent) focusing on these. “For example, to prevent collisions with birds or bats, the blades can be stopped at certain times of the day or during certain periods of the year”, explains Cédric Bacher. “To mitigate noise, we now have bubble curtains to limit the propagation of sound through the water, or a protocol on gradually increasing noise levels during construction so species have the time to move away”.
Following two and a half years of scientific research, it is now clear that the large-scale rollout of offshore wind turbines will bring about lasting changes to marine and coastal biodiversity, but “there are still gaps in knowledge to be filled, like understanding the effects linked to the introduction of non-native species or to chemical substances, or to the combined effects of various pressures, particularly on how ecosystems function”, emphasises Nathalie Niquil. She adds that “it would be important for scientists to focus on these issues in collaboration with industry so new mitigation measures can be proposed and tested”. Similarly, few studies have monitored wind turbines over the long term because wind farms have an average lifespan of twenty to thirty years and some are now nearing the end of their operational life.
To sum up a great deal of research remains to be carried out to reconcile European energy sovereignty, decarbonisation and the preservation of biodiversity.