Type of infrastructure:
Location:
Country:
Denmark
Target species:
Implementation period:
2022, with ongoing monitoring
Implemented by:
Ørsted and WWF Denmark
TRL:
6
Funding:
Ørsted and WWF
Database Project

3D-printed reefs to help restore marine biodiversity in the Kattegat, Denmark

Objectives

To test how 3D-printed reefs can enhance marine biodiversity, by attracting various marine species, providing refuge and feeding grounds for cod stocks, among others.


Short description

In 2022, Ørsted and WWF Denmark deployed 12 3D-printed reef structures on the seabed between the wind turbines at Anholt Offshore Wind Farm in Kattegat. These structures complemented the boulder reefs installed in 2012 during the wind farm’s construction. The 3D-printed structures resemble wedding cakes with several levels connected by hollows that allow fish to swim in and out of hiding places. Designed specifically for cod as target species, the size and shape of the holes cater to their needs. The structures also provide surfaces and crevices for other marine organisms to attach to. Made from natural materials that are not harmful to the environment (70% sand, 30% pozzolanic cement), each structure is about one cubic meter in size and can weigh up to half a ton. The 3D-printed reefs were designed and developed in collaboration with WWF Netherlands and Reef Design Lab, and produced by the Italian company D-Shape.

The boulders placed during construction of the Anholt Offshore Wind FarmThe Anholt Offshore Wind Farm is in Kattegat, 21 km from the Danish shore. It comprises 111 turbines and a total capacity of 400 MW in 2012, have become attractive oases for various marine species. It is expected that the new 3D-printed reefs will complement the stone reefs and will quickly become populated with marine life. Environmental monitoring is ongoing, taking place from May 2022 until October 2025. Water samples are taken on quarterly basis on selected sites (covering both boulder reef and 3D reef areas). Environmental DNA (eDNA) is extracted from the water and the target species are analysed. Furthermore, several ROV surveys have been carried out during summer 2024 to record video footage in selected reefs.

As background information, Cod, the target species, is an important predator that helps maintain balance in the marine ecosystem. The stable presence of cod is also used as an indicator for a balanced marine ecosystem. Overfishing and the deterioration of habitats as main factors, have caused a significant decline in cod stocks over the past 20 years, leading to an overpopulation of their prey (e.g., green crab). In turn, this resulted in a decline of eelgrass, which is consumed by the crabs. Eelgrass is crucial for marine biodiversity and climate regulation due to its role as carbon storage.