Baseline characterization of inshore reef soundscapes and noise dynamics along the southeast coast of South Africa

Underwater noise has risen in certain parts of the world, driven by continued growth of maritime economic activity. In South Africa, increasing economic development threatens to elevate underwater noise levels in marine habitats, yet knowledge of marine soundscapes remains very limited. This study characterized inshore soundscapes across four sites within the broader Algoa Bay region on the southeast coast of South Africa, including two within marine protected areas (MPAs) and two unprotected sites. Soundscapes across all the sites were characterized by broadband sounds associated with snapping shrimp, fish choruses, wave and wind-induced noise, and vessel traffic noise. Sound divergence analysis revealed clear spatial differences in soundscapes and site-specific temporal patterns. Biological sounds exhibited clear diurnal patterns across sites, with snapping shrimps detected both by day and night while fish choruses were predominantly detected in the late afternoon through the night and early morning. Vessel traffic had an effect on the soundscape across all sites; however, the magnitude of these effects was site-specific. This study demonstrates the usefulness of passive acoustic monitoring for soundscape monitoring and provides a baseline description for inshore soundscapes in the Algoa Bay region. This baseline provides a benchmark for future assessments of the impacts of ocean economy activities on marine soundscapes, ecosystem health and effectiveness of protected areas.