What's happening? The migration habits and biology of brown crabs are affected by underwater power cables that mesmerise the crustaceans, according to research conducted at the St Abbs marine station in the Scottish Borders. Researchers have found that the electromagnetism produced by the cables affects the creatures’ blood cells. The crabs are attracted to the cables, which are used for offshore renewable energy, when they emit an electromagnetic field of 500 microteslas or more, according to Professor Alastair Lyndon. Why does this matter? It’s important to recognise the lesser-known impacts of renewable energy infrastructure on marine biodiversity, given the key role clean energy has to play in the net-zero transition. While renewable projects are clearly a sustainable energy option, their impacts on ecosystems, marine habitats and the fishing industry should also be considered. The temporary stunning of crabs isn’t necessarily an issue in itself (though it may be uncomfortable), but it delays typical behaviour such as foraging for food or finding mates. Altered activity levels can also alter sugar metabolism rates in the crabs in a similar manner to humans. Changing blood cell levels within the crabs’ bodies could also increase their susceptibility to bacterial infections. Additionally, traditional migration patterns of male brown crabs, which typically move upwards along Scotland’s east coast, could be disrupted. This may result in a build-up of crabs in the south and scarcity in the north-east. Such abnormal distributions could influence marine ecosystem interactions and food webs, given brown crabs are active predators and feed on a range of crustaceans and molluscs, such as mussels, and are known to scavenge for food along the seabed. On a larger scale, migratory changes could increase the instability of catch levels for local Scottish fisheries in some areas, posing risks to the UK’s fishing sector. Crabs are the second-most valuable crustacean species across the UK fleet following the langoustine. UK fisheries caught around 60% of the 2019 global total catch of around 50,000 tonnes. Maintaining optimal crab and lobster populations for catches is also important to increase their quality and can contribute to longer-term benefits to the wider marine environment, according to researchers of a four-year University of Plymouth field study. Clean energy projects can result in other detrimental impacts for marine habitats. Conservation groups have raised concerns over the UK’s offshore wind projects, for example, which can disrupt vulnerable carbon-storing habitats such as saltmarsh, seagrass and deep-sea mud habitats. The acoustics of piling offshore wind turbines into the seabed as well as underwater sound generated from operational offshore wind farms are also a source of noise pollution for aquatic life. However, with the right planning renewable projects can be co-used to boost marine populations and reintroduce species. Van Oord, for instance, deployed oyster reef structures at its Borssele offshore wind farm in efforts to boost the North Sea’s oyster population amid a revival of Europe’s flat oyster beds. Increased monitoring and tracking of marine life populations will contribute to knowledge on the impacts of offshore renewable energy development. Scientists from the University of Plymouth recently deployed devices to track the movements of the endangered crawfish, which are important to small-scale coastal fisheries. Employing tech-based mitigation solutions can also help – Sercel recently launched Bluepulse, a marine acoustic source aiming to protect marine life from high-frequency noises.