Mytilus mussel patches and reefs as carbon modulators in the Baltic Sea: Insights from the STATUS project

Jahangir Vajedsamiei¹

¹Leibniz Institute for Baltic Sea Research (IOW), Germany

Temperate reef systems, such as biogenic mussel reefs, play a crucial role in the carbon dynamics of coastal ecosystems. In the Baltic Sea, Mytilus beds and patches influence carbonate chemistry and carbon fluxes through processes such as calcification, respiration, and bio-deposition. The STATUS project investigates these biogeochemical interactions to assess the net carbon sink or source behavior of these benthic communities. By combining in situ measurements, mesocosm experiments, and numerical modeling, we explore how mussel-mediated processes shape carbonate system dynamics, including pH and pCO₂ variations. Preliminary findings indicate that mussel reefs can act as localized CO2 sources, driven by high respiration and calcification rates that exceed primary production. Yet, these reefs also enhance sediment organic content and promote microbial processes that modulate alkalinity and CO₂ fluxes. We further evaluate how environmental variables such as hydrodynamics and substrate composition influence the interplay between mussel activity and sediment-water CO₂ exchange. This research highlights the dual role of mussel reefs as both emitters and modulators of CO₂ in marginal seas, with implications for regional carbon budgeting and ecosystem management. Future scenarios of warming and acidification will be integrated into our model to project the impact of climate change on reef carbon-storage capacities.