Ten miles off the coast of Leucate, three floating platforms sit in the open Mediterranean, each carrying a turbine whose rotor spans more than 500 feet.
Below the waterline, something else is happening.
Bolted to the underside of just one float are 32 steel cages, each one packed with oyster shells.
Nobody put them there to catch anything.
They were built so baby fish would have somewhere to hide.
The question is why a wind farm would bother with fish at all.
Why a turbine float needed a nursery built into it
Floating wind farms anchor in water too deep for the fixed foundations used closer to shore, which means the steel structure that steadies the turbine spends its whole life mostly submerged. Ocean Winds, the offshore wind company formed by ENGIE and EDP Renewables, worked with the Montpellier ecological engineering firm Ecocean to fit one float with hardware meant to grow life rather than merely survive storms.
Each cage uses a double shell structure. The inner cage is filled with empty oyster shells, where algae and tiny crustaceans settle and become food for small fish.
Outer cages provide protection, their mesh sized to let small animals in while keeping larger predators out. That two part unit, called a Biohut, was developed for ports and marinas, places with plenty of concrete and steel but no real reef. The developer says no floating wind farm had previously been designed from the outset to diversify marine habitats this way.
Inside the cage a juvenile fish actually sees
Picture a mesh box packed with shells, submerged and swaying gently with the float above it. The cages are grouped along one side of the foundation, spaced roughly 20 inches apart, and the shells mimic the shelter that rocks or seaweed give juvenile fish closer to shore.
Algae and biofilm grow across the shells’ textured surfaces, so food accumulates where the shelter already is.
That stillness matters more than it sounds. Open water offers a young fish almost nothing to hide behind, so survival in the first weeks after settling often comes down to finding any structure at all, whether that is a harbor piling, a shipwreck, or a cage bolted to a turbine float.
Ecocean’s founder and president, Gilles Lecaillon, a company that has worked until now mainly in ports and marinas, has described putting these units on an offshore float as a world first.
What years of testing in the same patch of sea showed first
This was not a guess dressed up as an installation. From 2019 to 2023, a dedicated observation buoy fitted with the same shell filled cages was moored at the future turbine site in roughly 230 feet of water, years before any float arrived.
Scientists from the marine ecosystem research center at the University of Perpignan tracked what colonized it, alongside acoustic specialists, and the buoy also supported work by French marine research institutes. That trial gave the project real data, not a hope, on whether coastal species would use artificial nursery habitat this far offshore.
Reporting on the end of the four year mission noted up to 20 times more sea urchins per square foot on the structure than on natural bottom nearby.
The project also reported no invasive species on the buoy and a clear increase in the variety of life in and around it. Building on those results, 32 units went onto one WindFloat foundation while the floats were still alongside at Fos-sur-Mer, before the turbines were assembled at Port-La Nouvelle and towed out.
Data from the equipped float will be compared against an unequipped one to measure the difference in colonization. The same instinct for pairing turbine hardware with living systems has turned up elsewhere, including near Morris, Minnesota, where a wind powered ammonia plant adjusts output to the breeze.
A separate case off Northern Europe shows how much marine life a steel foundation can carry once left in the water long enough, where a North Sea foundation sheds thousands of pounds of mussel biomass every year.
Where the idea still has to prove itself
One float out of three is a small sample, and the farm itself produces just 30 megawatts across three 10 megawatt turbines, a pilot rather than a commercial project.
The project team reports that scientific dives in the first year after installation found about ten fish species using the equipped float, among them sea bream, salema, sea bass, amberjack and an octopus.
Those are early observations, and a full picture of the reef effect will take considerably longer to assemble.
What the next several years of monitoring show will decide whether this becomes standard practice on floating wind farms or stays a one off experiment. For now, in a patch of the Mediterranean that used to offer young fish nothing but open water, there are 32 small steel rooms where they can wait to grow up.
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