Fishermen had left reefs behind, and today science backs their value: natural or artificial reefs boost marine biodiversity. Preserving them and restoring them when possible has become a practical priority. A Danish study found that adding new reefs could trigger a dramatic increase in reef-dwelling fish for certain species.
Only six months after DTU Aqua at the Technical University of Denmark and local partners placed new reefs at Bredgrund in southern Denmark, researchers recorded a striking surge in cod populations, roughly a hundredfold higher than typical for that area.
The original Danish reefs declined due to decades of human activity. DTU Communications Director Christina Tækker noted that in the past century about 8.3 million cubic meters of stone were removed to widen ports and supply cement.
According to the university’s findings, removing that stone erased at least 55 square kilometers of habitat for plants and animals, an area roughly the size of Bermuda and nearly twice the area of La Graciosa in the Canary Islands.
The loss of stone reefs reduces hiding places for marine life and limits surfaces for algae and mussels to cling to. When algae decline, numbers of small marine creatures and fish like cod also dwindle.
A concrete reef is being tested in Copenhagen’s inner harbor. Wolfgang Kunther / DTU
The absence of stone reefs and kelp forests means fewer hiding spots for cod against predators such as cormorants and seals. The takeaway is clear: stone reefs should be restored.
Expensive and complex construction
To restore the reefs, DTU Aqua collaborated with local stakeholders, using rocks, mussels, and concrete in a series of component-focused projects.
One project aims to protect the coast and invite more marine life. The goal is to boost biodiversity by improving spawning and feeding grounds, creating benefits for sport fishermen and divers.
“We are amid a biodiversity crisis where species are slipping away at alarming rates,” said lead researcher Jon C. Svendsen. “I’m encouraged by results showing cod thrive around rock reefs and can hide and feed more effectively than before.”
“We are in a pilot phase, developing and testing various reefs and documenting how they perform. Progress is steady but slow because stone reef construction remains costly and intricate,” Svendsen added.
A reef installation in Santander Bay. University of Cantabria
Reef formation began in Denmark fifteen years ago. Today, there is growing attention to reefs across Europe as EU member states are obligated to protect and restore vanishing habitats under Natura 2000. There are two main reef types. Geogenic reefs consist of rocks quarried and transported to chosen sites. Biogenic reefs are built from living organisms such as oysters or mussels and provide vital habitats for various fish species.
Protection against climate change
Another DTU project, Barreef, explores whether artificial reefs can also shield coastlines while supporting biodiversity. DTU is testing the first coastal protection reef in the North Sea, with potential balancing and restorative effects on shorelines.
The project follows two sustainability principles: nature-inclusive design and nature-based solutions. Considering these, it could be advantageous to build reefs that also serve as coastal protection in the future, helping communities cope with rising sea levels caused by climate change, Svendsen notes.
Conscious of ecological aims, scientists hope a concrete reef could become a natural breeding ground for marine life by resembling coral reefs and seashell habitats.
“The hope is that the construction sector can apply what we learn to future coastal protection projects, potentially influencing bridges, tunnels, and offshore wind farms to incorporate new habitats for fish, mussels, and algae. Action is needed now,” Svendsen emphasizes.
Artificial reef installation off the coast of Valencia. EFE / Valencia City Council
Historically, the sea was seen as an endless resource to fish and dispose waste into. Yet material depletion and degraded living conditions threaten marine ecosystems. Svendsen warns, “We have relied on stone reefs as habitats for fish and small sea creatures, but we must restore balance. Oxygen depletion and sand extraction for coastal protection and construction threaten sea life. We need to give back, learn better, and act with care, or we risk a lifeless ocean.”
130 artificial reefs in Spain
Spain began installing artificial reefs in the early 1980s with pioneering projects such as Escorpora and Sa Riera-Begur in Catalonia. Through the 1980s, progress was modest, with ten new reef installations spread across Catalonia, Valencia, the Canary Islands, the Balearic Islands, and Andalusia.
In the 1990s, artificial reefs became a formal fisheries management measure, with 93 installations added that decade. Today there are 133 listed reef initiatives, with 17 overseen by the national government and the rest by autonomous communities.
Spain prioritizes artificial reef protection, while modules used in protection and production roles often double as ecological structures due to their weight and volume. The University of Cantabria reported three years ago, using a 3D printer under a European program, that 36 artificial reefs have been installed in Santander Bay and in three locations in France, the United Kingdom, and Portugal. Further details about reef stewardship are provided by the national and regional authorities through official channels. Marked citations explain these programs and installations in more depth, and public documentation is provided by the ministry and regional bodies for reference.
Note that references to specific external portals have been replaced with summarized attributions to official conservation authorities and research institutions to maintain a self-contained narrative while acknowledging source provenance.
The overarching message remains clear: reefs of all kinds play a vital role in sustaining marine life, supporting coastal resilience, and enriching recreational opportunities for Canadians and Americans alike. Ongoing projects across Europe and North America demonstrate that thoughtful reef restoration and protection can yield tangible ecological, economic, and cultural benefits.