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Clean energy, fresh mussels: Scandinavia’s experiment to harvest seafood and wind power together

From a boat, workers check seaweed and mussels crops at Kriegers Flak offshore wind farm in the Baltic Sea, Denmark.
From a boat, workers check seaweed and mussels crops at Kriegers Flak offshore wind farm in the Baltic Sea, Denmark. Copyright AP Photo
Copyright AP Photo
By James Brooks with APTN
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Denmark is serving up a side of mussels alongside renewable power.

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In a small boat bobbing in the waves between towering offshore windturbines, researchers in Europe’s Baltic Sea reach into the frigid water and remove long lines stretched between the pylons onto which mussels and seaweed are growing.

It’s part of efforts to explore multiple uses for remote wind parks far out at sea, such as fresh seafood production.

Run by the Swedish state-owned power firm Vattenfall and Denmark’s Aarhus University, the four-year project started in 2023 off the Danish east coast at Scandinavia’s largest wind farm, Kriegers Flak. With its first harvest just 18 months later, it’s already showing signs of early success.

The race for space beneath the waves

“There’s an increasing competition for space on land and in the sea,” says Aarhus University senior scientist Annette Bruhn, who leads the project. “We can, in one area, produce both fossil-free energy and food for a growing population.”

With a capacity of over 600 megawatts, Kriegers Flak can power up to 600,000 households. Its 72 turbines deliver clean energy to nearby Denmark and Germany to the south.

But researchers saw other potential within the park’s 132 square kilometre area.

The water between its spinning blades has been transformed into an experimental underwater seafood farm.

Four hundred-meter lines spread between the turbines grow seaweed and mussel crops. The seaweed was recently harvested for the first time.

A wind turbine, part of Kriegers Flak offshore wind farm, off the Danish coast, Baltic Sea, Denmark.
A wind turbine, part of Kriegers Flak offshore wind farm, off the Danish coast, Baltic Sea, Denmark.James Brooks/AP

The carbon capture benefit of mussel farming

“Seaweed and mussels are low trophic aquaculture crops, which means that they can be produced without the use of fertilisers. They take up nutrients from the sea and produce healthy foods,” Bruhn says.

Recent Aarhus University modelling suggests tonnes of fresh seafood could be produced annually by utilising just a tenth of Denmark’s wind park area. Researchers say the benefits could go well beyond food production - mussel and seaweed crops could help improve water quality and capture carbon.

“These are non-fed crops that live from what they take up from the sea, they capture emissions instead of having emissions,” Bruhn says.

There’s an increasing competition for space on land and in the sea. We can, in one area, produce both fossil-free energy and food for a growing population.
Annette Bruhn
Aarhus University senior scientist, project leader on the Kriegers Flak experiment

Europe’s drive to quadruple production of wind power

Researchers say now is the time to develop guidelines to encourage companies to plan for multiple uses of the ocean as European nations massively ramp up production of clean energy from wind turbines in the North Sea.

In 1991, Denmark became the first country in the world to install a commercial offshore wind park. More than 30 years later, nearly half of the Danish electricity production derives from wind turbines.

Driven to meet climate targets and reduce energy dependence on Russia, nine European countries, including Denmark, last year announced plans to quadruple current production to 120 gigawatts by the end of the decade and move to 300 gigawatts by 2050.

Vattenfall bioscience expert Tim Wilms says there’s “huge potential. We have so much untapped area within our turbines that is not being used.”

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“In some areas, it makes a lot of sense to combine with sustainable food,” he adds, while in other areas, “we might look into offshore solar.”

What impact do offshore wind farms have on underwater ecosystems?

A growing body of research shows that offshore wind farms can have both positive and negative impacts on local ecosystems.

Offshore projects have been criticised for damage caused to the sea floor during construction, noise pollution and now-debunked claims they caused whale deaths.

Meanwhile, the large boulders laid at the base of the turbines to prevent erosion can also act as artificial reefs attracting more marine life and protect from large-scale fishing operations.

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Wilms says underwater surveys of older wind farms revealed structures “completely transformed”, overgrown with different species.

A deep dive into research is needed

Liselotte Hohwy Stokholm, CEO of Danish think-tank Ocean Institute, says more “knowledge about multi-use” developments is needed to understand how to combine human activities so that great areas of the ocean could become “strictly protected areas”.

Currently, efforts are on a limited scale, but researchers hope to soon take their knowledge to the extreme conditions of the North Sea, eventually upscaling to commercial food production.

“It’s very vital that we do it now because there’s so many questions we still need to have answered before we can do this in the right way,” says Bruhn.

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