Artificial Reefs Deployed in Dutch North Sea to Boost Marine Life Around Offshore Wind Farms

Credit: TenneT
Credit: TenneT

Dutch transmission system operator TenneT, in collaboration with contractor Equans/Smulders,  has installed several artificial reefs near the offshore wind power transformer platform Hollandse Kust (west Alpha), which are meant to stimulate marine life.

TenneT said the artificial reefs were installed to gain further knowledge about nature-inclusive construction. 

This offshore transformer platform will connect the Ecowende consortium  (Shell/Eneco) wind farm to the high-voltage grid.

TenneT said the aim was to build this wind farm with a healthy ecosystem and as little impact on nature as possible.

"The artificial  reefs are part of a series of ecological measures by TenneT to monitor  and encourage underwater life around offshore wind farms," TenneT said.

"By 2050, energy production must be completely climate-neutral. One of the  main pillars to achieve this goal is offshore wind energy and the North  Sea is becoming our main power plant. However, all this infrastructure  may have an impact on the ecology of the North Sea," Tennet said.

Saskia Jaarsma, head of offshore development at TenneT: "We are aware of the potential  impact on the North Sea. That's why we pay a lot of attention in  researching what happens underwater. The installation of artificial  reefs is another step in researching, monitoring and stimulating marine  life.

To find out which form works best, two types of artificial reefs have been placed near the Hollandse Kust west alpha jacket, located about 50 kilometers off the coast of Egmond aan Zee. 

Earlier, similar structures were placed at the TenneT platform at Hollandse Kust north. Six reef cubes are attached to one frame. 

Hollow square blocks made of what has been described as "nature-friendly" recycled material with round holes in the walls. On the other steel frame are six reef balls, a similar structure but in the  shape of a ball.

"These artificial reef structures are meant to stimulate marine life. With these, you create potential spots where coral and algae settle. Earlier research shows that fish, crabs and  lobsters like to visit these spots for shelter and to look for food,"  says Annemiek Hermans. As a marine biologist, she advises TenneT on nature-inclusive construction at sea. 

Ball or Cube?

Credit: TenneT

The aim of the trial is to investigate which shape - ball or cube - works  best in the waters off the Dutch coast. The hollows provide protection for young fish, but are also meant to increase the structure's bonding surface. 

"In this way, we hope to provide a suitable place for numerous other animal and plant species in addition to juvenile fish, crabs, and lobsters," Hermans said. 

Jaarsma: "Only in this way can you gain the necessary knowledge and experience to build nature-inclusively. Otherwise, you never find out what the success rate  of a measure is. These pilots are relatively intensive to realize but  of great value for ecology. For example, the first effects of the  ecological cable crossings at wind farm Hollandse Kust zuid are already surprisingly good, we see a lot of life developing there."

Hermans said: "With the firm ambition for offshore wind, it is more than  understandable that there are concerns about the ecological effects.  After all, that roll-out comes with great responsibility for everything  that lives in our North Sea. Gathering knowledge quickly as we are used  to these days is unfortunately not going to work because nature will not be rushed in its development.”

Hermans expects that it will take up to three years to see clearly visible differences.

"Until then, we monitor annually whether the diversity of  life forms around the artificial reefs and fish hotels increases. Fish  lose scales and cells, for example, and faeces also end up in the water. By reading DNA in water samples, you can find out pretty quickly which  guests have checked in."

Jaarsma said: "A number of measures to stimulate marine life, such as the fish hotels on our jackets, are now standard at TenneT’s offshore assets, while we  always keep an eye out for innovation. We assess new nature-enhancing  proposals on technical feasibility, impact on planning, nature and on  costs and risks. 

"We monitor all measures for ecological success, in  order to learn more about what works well and what does not. We continue to experiment in this and exchange our knowledge with all stakeholders  in the North Sea, so that the whole sector can contribute to stimulating ecology around offshore wind farms."Credit: TenneT

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