Belgian researchers deliberately installed a mussel longline inside a North Sea wind farm just before winter to expose it to the worst conditions; it survived waves more than nine metres high with only damaged sensor cables, and the project produced its first harvest the following May.

Belgium’s Edulis researchers put an instrumented mussel longline into the Belwind offshore wind farm in November 2017, deliberately ahead of winter. During December and January, waves exceeding nine meters were measured at the site. A university account reported that the installation survived, apart from damage to the force sensors’ cables.

The project also reported a first, limited mussel harvest in May 2018. These achievements came from a program with two distinct installations: a biological growth line at C-Power and a force-measuring line at Belwind. The university reported the harvest for the project as a whole, without identifying the winter-test line as its source.

Two installations answered different questions

Ghent University’s Edulis project description places the trials 30 to 50 kilometers off the Belgian coast. The first cultivation system entered the water at C-Power in May 2017 to investigate the capture of young mussels and their subsequent growth. Researchers repeatedly sampled the animals and compared their development with environmental conditions.

Belwind’s second installation followed six months later. Its integrated force meters measured the loads imposed by the sea. Comparing those measurements with waves and currents would help establish the requirements for a cultivation system capable of operating offshore.

The project brought together Ghent University, ILVO, OD Natural Environment and private partners spanning wind energy, marine construction and seafood. That mix reflected the practical problem: a successful biological trial would still need equipment and working arrangements compatible with an operating wind farm.

Winter supplied the test conditions

A July 2018 Ghent University account preserved by VITO’s EMIS service explains the seasonal decision. Winter increased the likelihood of storms and larger loads, giving the team a demanding test of its design.

The installations used a floating backbone roughly 50 meters long, supported between anchored buoys, with mussel-growing material suspended beneath it. At Belwind, measurements of force and buoy position were transmitted to shore through the wind farm’s communications network.

The report’s statement about surviving waves higher than nine meters applies to that winter and that experimental installation. It does not establish that every component of any offshore mussel farm can withstand every North Sea storm.

Even limited cable damage mattered to an experiment whose purpose included collecting measurements.

The load changes as the animals grow

A 2018 conference abstract by A.B.K. Pribadi and colleagues at Ghent University describes the modeling work behind the trial. It confirms that the Belwind force line was deployed with already-grown mussels, while the C-Power line studied mussel settlement and growth.

That detail prevents a misleading reading of the timetable. The November installation was not simply a batch of newly settled mussels that became a crop the following May. Loading a test system with grown animals allowed the researchers to examine forces acting on a structure that already carried biomass.

The abstract identifies waves, current, tides and changes in mussel size and weight as inputs to the model. Movement also had to remain limited enough to avoid interference with wind-farm activities. Anchors, ropes and floats therefore had to be assessed as a connected system.

A design that behaves acceptably at one stage of cultivation can experience different loading as its crop develops.

A harvest did not settle commercial feasibility

The 2018 university update describes the May harvest as limited and records the start of another production cycle. Later results added a longer view of the growing process. The project followed two growing seasons over three years, which helped the team assess whether initial observations were repeatable rather than relying on a single crop.

In its September 2020 project-results release, the consortium reported that marketable mussels averaging about six centimeters took approximately 15 months to grow in offshore suspended culture. It reported an average yield of around 10 kilograms per meter of cultivation rope.

Those measurements concern the trial’s growing conditions. The release explicitly cautioned that successful experimental production did not guarantee the same result across multiple lines, and that several assumptions needed for a commercial business case had not been sufficiently validated.

There were biological complications too. Seasonal growth of other organisms on the ropes added weight, requiring extra buoyancy. Maintenance, harvesting and trips to sites far offshore also affected the operating costs. Demonstrating that mussels could grow and that a structure could survive a winter left those questions open.

Later North Sea trials continue to test equipment

A separate June 2025 update from the Dutch ULTFARMS pilot shows why instrumentation and maintenance remain active subjects. That project installed five 200-meter mussel longlines with load cells in the Borssele wind-farm area in November 2024.

The update reported storm-related damage in March 2025, including missing load cells and a damaged chlorophyll sensor. Work resumed, with new lines and droppers installed and mussel-seed collection restarted by early May.

Borssele was a different installation from Edulis, so its experience is not a direct comparison of survival rates. It documents the continuing work required to keep offshore cultivation systems measurable, maintainable and productive through repeated seasons.