The Drejø stone reef – a mosaic of natural habitats
Creating a stone reef south-west of Drejø, in the middle of the South Fyn Archipelago.
Stone reefs and eelgrass are helping to revitalise the marine environment
Marine nature and biodiversity are under severe pressure. For decades, pollution, recurring oxygen depletion and intensive exploitation of marine resources have had serious consequences for Denmark’s coastal waters. In the South Fyn Archipelago, the ecosystem suffers not only from massive historical pollution from towns and industry, past overfishing and ongoing nitrogen emissions from agriculture, but also from the loss of stone reefs, which have been fished out to construct, amongst other things, the archipelago’s many marinas.
The fact that stone reefs have been fished out in the arcipelago is not unique in Denmark. It is estimated that over 83 million stones weighing between 0.5 tons and 5 tons have been fished out for the construction of harbour piers, promenades and other coastal structures.
Stone fishing has removed physical structures and, consequently, habitats for fish, crustaceans, molluscs and macroalgae. Restoring stone reefs will therefore not only create new habitats but also restore lost ecological functions – positive ecosystem services.
This project is realised thanks to substantial funding and broad collaboration
The South Fyn Archipelago UNESCO Global Geopark, which operates on behalf of the four South Fyn municipalities, has applied the Danish Marine Nature Fund to restore stone reefs in the archipelago in order to improve conditions for marine life – not least cod and flounder.
With the grant of EUR 1.4 million from the Marine Nature Fund and the Danish Nature Fund, marine nature restoration in the South Fyn Archipelago can now be realised.
The four South Fyn municipalities (Faaborg-Midtfyn, Langeland, Svendborg and Ærø) are co-funding the project at a rate of EUR 0.9 per citizen from 2025–27, and with the support from the Marine Nature Fund of EUR 1,4 million the project ‘Drejø reef – mosaic nature in the middle of the South Fyn archipelago’ can now become a reality. The project will be carried out from 2026 to 2027.
Restoration of the Drejø stone reef
Following a comprehensive ‘Archipelago Assessment’ (collection and interpretation of existing data), a geological report, a historical analysis and a physical survey of the seabed in the project area, the Geopark Secretariat has applied to restore a stone reef at Mads Jensens Grund, south-west of Drejø, in the centre of the South Fyn Archipelago.
There is evidence of extensive historical stone fishing in the project area, and from a geological perspective, the area is particularly well-suited for the restoration of cave-forming stone reefs.
Mads Jensens Grund is also historically known as one of the archipelago’s best fishing grounds for cod and flounder. The site is ideal, as it introduces a habitat type (stone reef) that is currently missing from the area’s mosaic landscape; furthermore, there are healthy eelgrass beds in the immediate vicinity, from which fish, amongst other species, will be able to migrate to the stone reef.
The primary objective is marine nature restoration, with a focus on mosaic habitats and ecosystem services across nearby healthy eelgrass beds and, in the long term, restoring robust food chains.
A secondary objective is to establish a permanent, competent project group which will serve as a basis for local engagement, visibility and commitment, and be able to take the lead on developing new projects and initiatives for marine nature restoration in the South Fyn Archipelago
Video
Come along beneath the surface and watch footage from the preliminary survey at Mads Jensen Grund in the South Fyn Archipelago.
Facts
What is a stone reef?
A stone reef is a cluster of large stones on the seabed. 'Large stones’ means stones big enough to remain firmly in place on the seabed despite the effects of waves and currents.
The stone reef creates new habitats for fish and many other marine species. By restoring natural habitats, the project helps to strengthen marine ecosystems and create a richer underwater wildlife.
Today, stone reefs can be constructed to provide shelter for fish, and their locations are precisely recorded using GPS equipment.
What is nature restoration?
Nature restoration is the restoration of lost habitat types at the site where they were previously known to occur, or of lost species within their original historical range and population densities.
Nature restoration thus restores natural habitats, hydrological processes, biological mechanisms and sustainable populations of species. In practice, however, it may be necessary to broaden the specificity of the location, as it will not always be possible to pinpoint exactly where a given habitat type was located or how widespread it once was.