Offshore wind farms will change life in the sea

IN THE North Sea, wind power is booming. At the moment the world’s biggest offshore wind farm, with a capacity of 630MW, sits in the Thames Estuary. But the London Array, as this farm is known, will not hold the record for long. Another farm, over twice the size, is under construction off the coast of Yorkshire. Of the six countries with the most installed offshore capacity, five are part of the North Sea’s littoral. (The exception is China.) Bloomberg New Energy Finance, a research firm that keeps a close eye on the industry, reckons the world’s offshore wind-generation capacity will quadruple by 2025.

Given the need to cut carbon emissions, that is welcome news. But, just because wind turbines produce little carbon dioxide does not mean they have no environmental impact. In a study posted on the arXiv, an online repository of scientific papers, Kaela Slavik and her colleagues at the Helmholtz Centre for Materials and Coastal Research, in Geesthacht, Germany, explore the effects that the turbines might have on local wildlife.

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As every sailor will tell you, almost anything immersed in seawater for long enough will be settled by living creatures. Wind turbines—or, rather, the concrete pilings upon which they sit—are no different. Turbines in the North Sea provide a particularly enticing home for a type of tasty, edible mollusc called the blue mussel. FINO 1, a German research platform, for instance, was found to have an average of 4.3 tonnes of mussels clinging to each of its four piles. Dr Slavik and her colleagues wondered what might happen as more and more turbines proliferate across the North Sea.

One thing seems certain: there will be plenty more mussels. The team calculate that, if all the wind farms currently planned for the North Sea are built, they will provide extra habitat equal to about a fifth of the naturally occurring mussel beds along that sea’s coasts.

This will have consequences. Mussels eat plankton that they filter from the surrounding water. Dr Slavik’s computer modelling suggests plankton numbers around wind farms could fall by as much as 10%. Since plankton are at the start of most marine food chains, that will mean less of them for other animals, such as anemones, scallops and jellyfish, and thus less of those species and others that in turn depend on them. It will, however, mean more food for species that eat mussels, of which there are many—starfish, seagulls, seals and, not least, people, especially Belgians, who have already set up an experimental mussel farm on one of their wind farms.

Wind-farm piles may even increase the North Sea’s biodiversity, by providing homes for species that do not currently live there. One such is the marine splash midge, a fly originally from Australia. After hitching a ride to Europe on ship hulls, it has been found flourishing just above sea level on the piles of Danish and Swedish wind farms.

Whether local ecosystems will benefit from a new midge joining them remains to be seen. People, though, are unlikely to be inconvenienced. Unlike the midges that terrorise the Scottish Highlands, marine splash midges do not bite.

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