Stone Reefs in the Limfjord Show Rapid Impact on Biodiversity

Biodiversity in Danish waters is under pressure. Therefore, five students from Aalborg University have explored the use of the eDNA method to monitor the local impact of several nearshore stone reefs on biodiversity as part of a bachelor project.

eDNA is a method used to assess biodiversity levels. It doesn’t focus on the number of individuals of a particular species but rather on how many different species’ DNA are present. The method is well-suited for studying the potential of stone reefs to create natural habitats that serve as living and breeding grounds for marine life. The study’s conclusions are positive.

Surprisingly Rapid Impact

Six stone reefs were examined in the project, including one located at the East port, established by Port of Aalborg in 2023. An extensive analysis of conditions around the reefs was conducted, and several sampling efforts showed that within just one year, biodiversity at the reefs had increased compared to nearby barren seabed areas.

“The fact that we’re seeing results after just one year shows that the potential of stone reefs is greater than we initially thought. This is significant for promoting biodiversity in the Limfjord in both the short and long term – and even from an international perspective,” says Natalie Hvid Nielsen, who conducted the project together with Jens Emil Bigum Munck, Karl Klestrup Dam Andersen, Kasper Juhl Pedersen, and Kristoffer Baldur Jakobsen – all biology students at Aalborg University under the supervision of Professors Niels Madsen and Jeppe Lund Nielsen.

Supports Danish Fish Conservation

Different types of stone reefs can help support a wide variety of species. The reef at the East port is a cavity-forming reef, where large rocks are placed on or close to each other. This structure creates dark crevices between the rocks, providing hiding spots for both fish and their prey.

“In our project, we saw the greatest positive effects on species such as lumpsucker and eelpout, both of which are relevant to the Danish fish conservation discussion, and which are species we aim to increase in the Limfjord. Additionally, we expect the reefs to also support species like cod and eel, which are ecologically and economically important. These four species prefer nearshore, cavity-forming reefs with ample hiding spaces and light, enabling vegetation like seaweed to thrive,” says Jens Emil.

Beyond providing shelter and foraging grounds, nearshore stone reefs are especially important for the lumpsucker’s life cycle, as they lay and attach their eggs to rocks and in crevices. Moreover, these cavity-forming reefs offer good surfaces for seaweed, mussels, and other sessile animals and organisms.

Contributes to the EU Biodiversity Strategy

The EU Biodiversity Strategy aims to restore ecosystems and protect at least 30% of Europe’s marine areas by 2030. They might want to look to Aalborg, as the project by Natalie, Jens Emil, and Karl demonstrates how even small initiatives can make a difference.

“We can see that structure and hiding places are crucial for improving habitats and protecting species in coastal areas. If a reef is built with the right structure and under the right conditions, it can have a significant local impact,” says Karl.

“The project of measuring DNA in the water column has been important to us, as it provides evidence that even small-scale stone reefs make a difference for biodiversity in the fjord. That’s why we at Port of Aalborg will consider integrating stone reefs and stone placements in our future projects and initiatives,” says Brian Dalby Rasmussen, engineer and environmental coordinator at Port of Aalborg, and continues:

“At the same time, the work by Natalie, Jens Emil, and Karl has shown us how we can continuously measure species diversity and thus track the effects of, for example, a stone reef. It’s a valuable tool for our sustainability work.”

For further information, please contact:

• Jens Emil Bigum Munck, student, tel. +45 20 20 80 24, jebm@outlook.dk
• Brian Dalby Rasmussen, engineer and environmental coordinator, Port of Aalborg, tel. +45 29 20 72 52, bdr@portofaalborg.com
• Press contact: Maja Thordahl Schou, Head of PR, Port of Aalborg, tel. +45 22 61 83 08, mts@portofaalborg.com