New life for stone reefs in the Baltic Sea

Launch event at the Marine Science Campus for the “Riffretter” project to restore a historic reef site

The “Riffretter” project kicks off with a launch event on September 22 at the Marine Science Campus of Kiel University. Over the next three years, scientists and experts from government agencies and educational institutions, under the leadership of Kiel University, will support the restoration of a historic reef site off the coast of Schleswig-Holstein near Waabs/Boknis Eck in Eckernförde Bay through a wide range of activities. Stone fishing, which continued until the 1950s, permanently altered the seafloor and ecosystems of the Baltic Sea. Where rocks from the Ice Age once formed a shallow stone reef, an important habitat is still missing today. A new compensation measure is now intended to restore this valuable habitat: The Kiel Canal Wasserstraßen-Neubauamt (WNA) plans to place stones and boulders on the seabed in the nearshore area by the end of the year to revitalize the former reef site. The German Federal Environmental Foundation (Deutsche Bundesstiftung Umwelt, DBU) is providing nearly 980,000 euros until August 2029 in funding for the “Riffretter” project through the DBU Marine Conservation Fund.

Researchers from the Center for Ocean and Society (CeOS) at Kiel University, together with colleagues from the Kiel University‘s Büsum Research and Technology Center (FTZ), the Baltic Sea Info-Center Eckernförde (OIC), and Environmental Action Germany (Deutsche Umwelthilfe e.V. DUH) are combining ecological research, socio-ecological analyses, and environmental education in this project and developing guidelines for future restoration measures.

“In this project, we bring together experts from research, the field, and state agencies. Together, we aim to examine the effectiveness of restoration measures — such as the restoration of a shallow stone reef in this case — as comprehensively as possible. In doing so, we are not only investigating the ecological consequences but also focusing on societal acceptance and environmental education,” says Dr. Christian Wagner-Ahlfs, coordinator of the “Riffretter” project and responsible for transdisciplinary research methods at the Center for Ocean and Society (CeOS) within Kiel Marine Science research priority area of Kiel University.

Rock fishing has severely altered ecosystems

Shallow stone reefs are among the most valuable habitats in the Baltic Sea. The rocks, deposited on the seafloor during the last Ice Age, provide a diverse habitat for flora and fauna. As recently as about 70 years ago, stones were extracted from the sea on a large scale — for example, for the construction of port facilities, dikes, or roads — until stone fishing was finally banned in 1974. As a result, an estimated 100 to 200 square kilometers of this habitat were lost throughout the Baltic Sea, and about 5.6 square kilometers in the Schleswig-Holstein section of the Baltic Sea. The consequences continue to affect the ecosystem to this day. Over the next three years, the reef is to once again provide a habitat for native species and biological communities. As a first step toward the planned restoration of the reef near Waabs/Boknis Eck, the stones excavated during the expansion of the Kiel Canal will now be deposited on the seabed.

Broad alliance of scientists, governmental partners and experts from the field

Scientists, government agencies, and partners from the field are conducting accompanying research on this initiative and systematically investigating the ecological and social effectiveness of such measures in the western Baltic Sea. The goal is to identify suitable methods for standardized monitoring and to use these to develop guidelines for the restoration of reefs in the Baltic Sea.

For the ecological research on the new reef, PD Dr. Katja Heubel, head of the Coastal Ecology research group (ECOLAB) at the Research and Technology Center (FTZ) Büsum of Kiel University, is using passive acoustic monitoring for the first time to track the development of fish populations at the reef site and is testing the possibilities of non-invasive long-term observation of the underwater world.

The socio-ecological research on societal perception, acceptance, opportunities, and potential obstacles to restoration measures is being conducted by Dr. Lotta Kluger, who leads the “Marine Food Security” team at the Center for Ocean and Society of CAU/Kiel Marine Science. The evaluation of how different user groups perceive the social and ecological impacts of stone reefs and their reintroduction is conducted through interviews and targeted surveys. The discussion of opportunities, risks, and conflicts related to reef establishment and long-term use will take place in focus group discussions.

The Baltic Sea Info-Center Eckernförde (OIC) is responsible for communicating this knowledge to the public. Under the leadership of OIC Director Till Holsten, environmental education programs are being developed to convey the ecological importance of nearshore stone reefs to various target groups. A particular focus is on recreational and leisure divers, for whom a practical guide on interacting with the reef habitat is being developed.

Another project partner is Environmental Action Germany (DUH). DUH’s “Lebendige Meere” team is responsible for building the network and conducting nationwide public relations work. The organization is also developing guidelines a practice guide for reef restoration in the Baltic Sea, drawing on experience from previous initiatives, including those in Germany and Denmark. The goal is to lay the groundwork for further reef restoration efforts.

“Riffretter” is intended to contribute to the long-term recovery of marine habitats. All relevant stakeholders were brought on board as associated project partners as early as the planning phase. The Kiel Canal Wasserstraßen-Neubauamt (WNA) is carrying out the restoration project. The Schleswig-Holstein State Office for the Environment (LfU) serves as the contracting authority and cooperates in ecological and geoscientific mapping activities carried out under European directives (Habitats Directive, Water Framework Directive, and Marine Strategy Framework Directive) in Schleswig-Holstein’s coastal waters The Ministry for Energy Transition, Climate Protection, Environment and Nature of the State of Schleswig-Holstein (MEKUN) supports the advancement of marine conservation policy in the state. As the project progresses, additional local stakeholders, such as diving clubs, will be involved.

Further information:

About the Center for Ocean and Society

About the priority research area Kiel Marine Science at Kiel University

About the ECOLAB working group at the West Coast Research and Technology Center (FTZ)

About Environmental Action Germany

About the Baltic Sea Info-Center

About the German Federal Environmental Foundation (Deutsche Bundesstiftung Umwelt, DBU)