Soundscape as a proxy for seagrass meadow condition and anthropogenic activity

Abstract

Soundscape analysis has emerged as a relevant tool in functional marine ecology. However, how habitat-specific variables, environmental and biological components, and external pressures influence acoustic metrics requires further validation. This study investigates how soundscape structure and dynamics are influenced by seagrass meadow conditions, seasonal patterns, and anthropogenic disturbance. To this aim, the soundscape of P. oceanica meadows in 16 sites across two Mediterranean Marine Protected Areas was analysed (over 6,600 5-min recordings). The results revealed a multifaceted and highly site-specific soundscape. Diel cycles were the primary driver of the soundscape, with a significant nocturnal increase associated with fish sounds and the snapping rates of invertebrates. Meadow density and intermediate coverage positively influenced many acoustic metrics, suggesting that more structured meadows supported a more heterogeneous acoustic environment. However, denser meadows exhibited a reduction in low-frequency Sound Pressure Levels, indicating that the canopy acted as an acoustic attenuator. Furthermore, meadows on sandy substrates negatively influenced almost all acoustic metrics compared to those on rocky substrates, which provided more niches for soniferous species and acted as a reflective surface. Boat noise was pervasive and acted as the primary driver of low-frequency Sound Pressure Levels while significantly reducing acoustic complexity and diversity metrics. In conclusion, acoustic metrics reflected the dynamic interactions between habitat structure, biological processes, and human activity. These findings confirmed that soundscape analysis is a powerful complementary tool for assessing the functional state of P. oceanica meadows and that soundscape should be integrated into conservation strategies as a key functional attribute.