Researchers studying the floating wind turbine FLOATGEN off the shore of Le Croisic in France found that underwater mooring cables serve as artificial reefs.
Through surveys using cameras, it was found that blue mussels grew in the sunny parts of the cable, while anemones and soft corals grew in the darker parts.
The growth increased the line diameter by as much as 32 per cent.
Biofouling makes offshore industrial installations part of marine environments, but it poses mechanical problems to marine engineers.
Mapping biological zonation along floating turbine cables
The ocean currents carry microscopic larvae of invertebrates to the man-made cables 12 nautical miles away from the French coastline.
Penetration of light through shallow water makes the habitat suitable for the growth of mussels in the upper parts of the cable.
Groups of mussels in cascade offer a secure place to attach and become food for tiny crustaceans and young reef fish.
The middle layers of the cable that remain in shadow serve as a habitat for filter-feeding sea squirts and hydroids.
Plume anemones and cold-water soft corals grow on the lower cable parts, situated on the seafloor.
Depth differences lead to different biological habitats within one cable.
Calculating structural weight and underwater drag
Continuous deposition of marine life increases the cable size by up to 32 per cent.
Biofouling usually adds weight for floating mooring structures in sea water.
Greater cable diameter results in greater resistance by large ocean currents to drag forces applied to the base of the turbine.
The additional weight could end up pressing down on buoyant pontoons, while drag forces could increase the swaying of the platform in storms.
Biological accumulation could in the future necessitate the recalculation of dynamic tension on anchoring lines under the water surface.
Biological accumulation changes smooth engineered cables into ropes with high drag force.
Turning ocean energy platforms into artificial reefs
Offshore waters that are isolated lack hard substrates that allow sessile marine creatures to attach themselves and reproduce.
The artificial underwater cables and concrete anchor blocks act as artificial vertical reefs in the open ocean water areas that lack features.
Adding vertical structure elements has the potential to turn energy concessions into important marine refuges.
Offshore energy equipment offers habitat to marine life in coastal areas that are overfished.
Rethinking maintenance strategies for offshore wind farms
For many years, offshore energy production used to clean away biofouling from submerged structures to maintain the initial tolerances of mechanical engineering.
Frequent mechanical cleaning not only disrupts the marine ecosystems that have developed but also increases the operational cost of maintenance at wind farms.
Modern engineers create tough mooring cables with plenty of structural safety factors to account for extra weight and drag created by the biological community.
Building in marine growth into engineering models enables the biological community to develop without interference.
Biofouling left in place may well reduce operational costs in some ways and even help protect new marine ecosystems.
Proper design enables offshore energy production to live alongside artificial reefs.
Recognizing limits of initial demonstrator observations
Observations collected from one demonstrator structure cannot be used as evidence for identical biological colonization patterns in large-scale commercial farms with tens of wind turbines.
It is not clear whether cable biofouling contributes to faster deterioration of synthetic cables throughout their operational lifetime, lasting many decades.
Variation in water temperature and seasonal spawning may lead to changes in biological colonization compositions depending on ocean region.
Unknown effects of biological load on mechanical wear of mooring lines are the subject of ongoing investigation.
Thus, although FLOATGEN has demonstrated that mooring lines serve as habitat for vibrant marine life, further long-term observations are needed.
All the study information can be found here: Dubois, A., Schoefs, F., Cognie, B., Reynaud, M., Soulard, T., & Dumay, J. (2025). Spatio-temporal evolution and engineering implications of biofouling communities on floating wind turbines mooring lines. Estuarine, Coastal and Shelf Science, 320, 109302.
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