Blue Reef Project: Rebuilding of Marine Cavernous Boulder Reefs in Kattegat

Area characterisation: 

Cavernous boulder reefs within an area of approx. 5ha on Læsø Trindel, a shoal in Kattegat, off the northeastern coast of Denmark/the Læsø Island. 


Restore the stone reef on Læsø Trindel (part of the Læsø Trindel and Tønnesberg Banke Natura 2000 site). Restore and stabilise the structure and function of cavernous boulder reefs; boost awareness among managers, planners and the general public about marine nature restoration, protection and management.


A number of preliminary surveys were conducted to ensure that the new reef could live up to the objective and would not have negative impacts on surrounding nature, local community, etc. Reef sections were restored using natural rock (quarrystone from the Krageø quarry in southern Norway). During the summer of 2008, a total of approx. 100,000 tonnes of boulders were laid out. Stone reef were restored and stabilised within a total area of 5ha. The area with stone reef was surveyed before the construction works in 2008 and, again, in 2012, in order to discover the significance of restoration efforts for ocean plants and animals. Fishing on and around the restored stone reef was banned throughout the monitoring programme.

Potential impacts/benefits: 

Increased abundance of crustaceans and cod (relevant for food security). Increased abundance and biomass of seaweed (relevant for biodiversity).

NbS benefits 
  • Better protection and restoration of coastal ecosystems
  • Developing climate change mitigation
  • Carbon sequestration and storage
  • Restoring ecosystems and their functions
  • Increase Biodiversity
Lessons learned: 

The reef was surveyed before construction in 2008 and in 2012. Abundance and biomass of seaweed, and abundance of crustaceans and cod had increased. Climate change mitigation and risk disaster reduction was not measured, but macroalgae are assumed to contribute to carbon storage and wave damping.


35,7 million DK. Supported from the Danish Nature Agency, Ministry of Environment and EU´s program LIFE.

NbS classification 
  • Biodiversity

Kristina Kvile (NIVA, Norway):

Further information

This project was added to the database as part of the Nordic S-ITUATION project (

Sustainable Development Goals 
  • 14. Life Below Water