The North Sea region used to be full of biogenic reefs, but as intensive exploitation has deteriorated the marine environment, most of the native biogenic reefs have disappeared. That is why WWF-Denmark and Ørsted will establish a reef filled with horse mussels and native oysters – the Hirsholmene archipelago close to Frederikshavn in the northern part of Denmark has been identified as the prefered site for the project.
Ørsted and WWF-Denmark has chosen Hirsholmene archipelago close to Frederikshavn in the northern part of Denmark as location for their BioReef project.
Biogenic reefs – reefs made up of live organisms – are important habitats for many Danish marine animals. Unfortunately, both the number and quality of our native biogenic reefs have decreased significantly over the past century, in particular in the North Sea. Banks of European flat oysters and horse mussels have been hit hard in particularly. Therefore, WWF-Denmark and Ørsted initiated a large-scale project in 2022 with DTU Aqua as the scientific partner, the aim of which is to produce oysters and horse mussels with a view to restoring biogenic reefs in the Danish part of the North Sea region, including the northern part of the Kattegat Sea.
Several locations in the Danish seas, including Anholt Offshore Wind Farm and Thyborøn Stenvolde, have been considered as the site for the project. The site selected is Hirsholmene archipelago near Frederikshavn in the northern part of Denmark, which is ideal as European flat oysters have previously inhabited the area immediately to the north, and some scattered occurrences of horse mussels can still be found in the area – an important criterion for maximising the chances of survival of the reef.
Ingrid Reumert, Senior Vice President and Head of Global Stakeholder Relations at Ørsted, says:
“This is an important project that will benefit the marine environment, increase biodiversity and improve the water quality locally in the Danish part of the North Sea – which is why we’re delighted to have reached an important milestone by selecting a location for the project, allowing us to move it forward. Together with WWF, we’re dedicated to setting new standards for biodiversity-promoting work related to offshore wind development, and therefore innovative projects like BioReef are necessary to enlighten us on the possibilities.”
Mikkel Aarø-Hansen, Secretary General of WWF Denmark, says:
“We’re in the middle of a biodiversity crisis, which we can only solve through strong partnerships and new innovative solutions. The project with biogenic reefs is a good example of that. The reefs provide food and shelter for small fish and other marine animals. Our aim is that experience from the BioReef project in the North Sea region can be applied internationally, so that we’ll scale up efforts and share knowledge from our joint nature restoration project with the rest of the world.”
Pernille Nielsen, Project Manager and Senior Researcher at the Section for Coastal Ecology at DTU Aqua, says:
“This is the first time an attempt has been made to create large-scale banks of horse mussels and restore oyster banks in Danish waters. Viable fry of oysters and horse mussels of a certain size must be produced in order to reach the critical mass needed to realise the project. DTU Aqua has in-depth knowledge and experience of both hatchery and distribution of e.g. mussels and oysters in Danish inland waters, which is crucial for creating the biogenic reef for the BioReef project.”
However, as the creation of a biogenic reef at Hirsholmene is subject to a regulatory approval, the concrete deployment of oysters and horse mussels cannot begin until 2027 at the earliest. But experiments are already being planned with stocking in the Limfjord strait (connecting the North Sea and the Kattegat Sea) close to DTU Aqua’s facilities at the Dansk Shellfish Centre, where the experiments can be monitored on a continuous basis. Initially, the experiments will be performed with the species with which we made the most progress, namely European flat oysters, and the purpose of the experiments is to test materials and various designs to ensure good growth and protect the young oysters against predators such as crabs and starfish.
The creation of the biogenic reefs at Hirsholmene is intended to contribute to developing new innovative methods for the creation of similar reefs to be used for restoration projects in many other places in the world.