Rethinking ocean noise: A cross-disciplinary lens on an emerging ecological stressor

The ocean is a complex acoustic environment in which sound plays a central ecological role. Many marine species rely on acoustic cues for vital functions such as navigation, foraging, social interaction, and reproduction. However, increasing anthropogenic noise has significantly altered marine soundscapes, introducing chronic and acute stressors for marine life. Noise can lead to acoustic masking, behavioral disruption, elevated stress, or area displacement, with effects that vary across species, life stages, and ecological contexts. This thesis explores underwater noise not merely as a pollutant, but as a multidimensional ecological and technological challenge. It integrates approaches from marine ecology, ocean acoustics, signal processing, and climate science, using desktop studies, field measurements, and numerical modeling. A major focus is on seismic survey noise. Using coupled propagation modeling and field data from the Ionian Sea, I examined airgun array signals and assessed emerging low-impact alternatives for different marine ecosystems. These findings will contribute to informing species-sensitive mitigation strategies. To account for environmental variability, a global dataset of underwater sound speed and its projected changes under a business-as-usual climate scenario was used. This provides a framework for evaluating how ocean warming will alter sound propagation, including the characteristics of the SOFAR channel, with implications for species that rely on long-range acoustic communication. The thesis also applies cross-disciplinary tools—from linguistics, information theory, and neuroscience—and new technology to bioacoustics. These methods enhance detection of subtle changes in vocal behavior that may signal disturbance or stress, offering additional tools to assess ecosystem health. Marine mammals, in this context, are reframed as diagnostic species, whose vocal capabilities can reflect broader environmental changes. Finally, this work contributes to a risk-based acoustic mitigation framework, combining species-specific data, regional ecology, and source characteristics into an acoustic risk matrix. This supports more effective and proportionate policy responses, particularly in vulnerable marine ecosystems. Overall, the thesis aims to propose a cross-disciplinary framework for understanding and managing the ecological impacts of underwater noise in changing oceans.