Artificial reefs from offshore wind and wave energy sites



Offshore wind generation and wave energy foundations can step-up local abundances of fish and crabs. The reef-like structures also favor for example blue mussels and barnacles.

What's more, it is possible to increase or diminish the abundance of various species by altering the geomorphological blueprint of foundation. This was demonstrated by Dan Wilhelmsson of the Department of Zoology, Stockholm University. 

A major enlargement of offshore wind generation is underway on European coasts, and the interest is growing in countries such as the US, China, Japan, and India. Moreover, wave power technologies are being developed very rapidly. Many thousand wind and wave power stations grouped in large arrays that each cover many square kilometers can be anticipated. How marine life will react to this is not clear, but numerous research projects looking into the affects of noise, shadows, electromagnetic fields, and changes in hydrology etc. are underway.

Dan Wilhelmsson studied how offshore wind turbines constitute habitats for fish, crabs, lobsters, contaminating animals, and plants. He demonstrates that wind turbines, even without scour protection, function as artificial reefs for bottom dwelling fish.

The seabed in the vicinity of wind turbines had higher densities of fish compared to further away from the turbines and in reference areas. This was despite that the natural bottoms were rich in boulders and algae. Blue mussels dominated on the wind turbines that appeared to offer good growth conditions.

Wave power foundations, too, comprising of large concrete blocks, proved to attract fish and large crabs. Blue mussels fall down from the surface buoys and become food for animals on the foundations and on the adjacent seabed. Lobsters also settle under the foundations. In a mass experiment, holes were drilled in the foundations, and this dramatically increased numbers of crabs. The placement of the holes also demonstrated to be of importance for the crabs.

However, aggregations of certain species may have a negative impact on other species. The number of predatory animals on artificial reefs can sometimes become so large that the organisms they prey on, such as sea-pens, starfish, and crustaceans, are eliminated in the surroundings, and certain species can disappear altogether.

'Hard surfaces are often hard currency in the ocean, and these foundations can function as artificial reefs. Rock boulders are frequently located around the structures to prevent erosion (scouring) around these, and this strengthens the reef function.' Dan Wilhelmsson, Department of Zoology, Stockholm University.

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