New paper: How do long-lived clams influence carbon cycling in the Baltic Sea?
We are pleased to share our new study published in Estuarine, Coastal and Shelf Science which investigates carbon cycling in habitats inhabited by the ocean quahog (Arctica islandica), a long-lived clam found in the Baltic Sea and North Atlantic.
Although these clams live largely hidden beneath the seafloor, their habitats contain substantial reserves of organic carbon. We found that sediments inhabited by Arctica islandica store approximately 1.5 kg of organic carbon per square metre in the upper 25 cm of sediment, comparable to carbon stocks found beneath eelgrass meadows in the German Baltic Sea.
Extrapolated across the species' distribution in German Baltic waters, these sediments could contain an estimated 12–13 million tonnes of organic carbon, highlighting an often-overlooked component of coastal carbon storage.
The study combined aquatic eddy covariance measurements with sediment sampling and laboratory experiments to investigate how carbon is stored, deposited and recycled within these habitats.
An important finding was that ecosystem metabolism varied strongly with oxygen availability. Oxygen concentration was highly dynamic, demonstrating the value of using non-invasive eddy covariance methods. Oxygen consumption at the seafloor was four to five times higher during periods with greater oxygen availability, demonstrating how changes in bottom-water oxygen conditions can influence oxygen uptake at the seafloor.
Interestingly, the clams themselves contributed relatively little organic carbon directly to the sediment. Instead, the large carbon stocks likely depend on additional inputs from sources such as sinking plankton and other organic material.
These findings highlight the importance of considering bivalve habitats in assessments of coastal carbon stocks. They also raise concerns about disturbances due to ongoing construction projects and bottom trawling, which may threaten stored sedimentary carbon. Whether these habitats provide long-term carbon sequestration remains an important question for future research.
Strengthening international research collaboration
The publication is the result of an ongoing close collaboration between the Department of Biology at the University of Southern Denmark (SDU) and the Leibniz Institute for Baltic Sea Research Warnemünde (IOW), Germany.
The study was jointly initiated by Fabian Wolf, Peter Holtermann, and Soeren Ahmerkamp at IOW and Karl Attard at SDU, bringing together expertise in benthic ecology, physical oceanography and aquatic eddy covariance.
Publication: Wolf, F., Schulz, L.A., Thiele, O., Ahmerkamp, S., Holtermann, P., Attard, K., & Zettler, M.L. (2026). Carbon fluxes within an Arctica islandica habitat in the German Baltic Sea. Estuarine, Coastal and Shelf Science.
