El-Dairi_2026_Mar.Environ.Res_216_107870

Underwater noise is an emerging physical stressor in the Baltic Sea, where strong seasonality coincides with peaks in recreational boating and continuous commercial shipping. While behavioural effects of noise are increasingly reported for marine invertebrates, Baltic mussels (Mytilus spp.) remain untested, and links to cellular physiology are scarce. We conducted controlled laboratory exposures of pre-recorded vessel noise with variable exposure durations, and quantified behavioural and biochemical responses in Baltic mussels. Individual valve-gape behaviours were recorded before, during, and after exposure; in parallel, we measured a suite of neurotoxicity and antioxidant biomarkers, including acetylcholinesterase, catalase, glutathione reductase, reduced glutathione, glutathione S-transferase, lipid peroxidation and superoxide dismutase. Compared with control mussels, noise treatments elicited significant changes in valve-gape behaviour and altered biomarker profiles. Elevated closure activity was linked with higher LPO and shifts in antioxidant enzyme responses, suggesting short-term trade-offs between defence and energy acquisition. Our results provide the first evidence for concurrent behavioural and biochemical effects of vessel noise on mussels from the Baltic Sea, demonstrating that noise can cause changes in their energy dynamics. Our results suggest that mussel behaviour depends strongly on the duration of noise exposure, in addition to its frequency pattern and intensity.