Vertical acoustic stratification of tropical marine ecosystems

Vertical stratification shapes the structure and function of tropical marine ecosystems, yet its acoustic dimension remains poorly understood, especially in deeper zones. Extending our knowledge of reef dynamics across depth gradients is crucial not only to uncover the functioning of these largely unexplored ecosystems but also to advance non-invasive monitoring methods. This study provides the first insights into the soundscape of the lower rariphotic zone, revealing vertical acoustic stratification from altiphotic coral reefs, upper and lower mesophotic coral ecosystems (MCEs), to the rariphotic zone. Fish vocalizations decreased with depth overall but showed the reverse pattern at sunset, with sound activity rising from 20 m, 60 to 120 m, and peaking at 300 m. This sunset-driven surge was primarily driven by one dominant sound type, a phenomenon previously observed in environments such as MCEs and temperate seagrass meadows. This study represents the first exploration of vertical acoustic stratification, offering valuable insights into a region that remains largely unknown.