Autonomous cameras reveal larval reef fish responses to acoustic enrichment and lunar phase

Acoustic enrichment (AE)-the playback of ambient sound from healthy coral reefs-shows promise in attracting fish larvae to degraded or artificial reefs, but previous evaluations have used invasive diver-based sampling techniques, limiting most studies to short deployments in benign and accessible environments. This study used fully autonomous cameras to non-invasively evaluate AE efficacy in attracting settlement-stage fish larvae and mature fish over large fractions of a lunar cycle. We deployed an AE system in Kāne'ohe Bay (O'ahu, Hawai'i) over three spawning events (August 2023, June-July 2024). Treatment (active speaker) and control (inactive speaker) sites were built by placing artificial structures, autonomous cameras, and hydrophones on a sandy seabed at 5 m water depth, with sites separated by 42-65 m. Treatment and control designations were alternated between deployments to remove potential spatial bias. Manual and semi-automated image analysis found larval counts at both sites peaking around the new moon, but the treatment site attracted 4-14 times more larvae. Both sites encountered similar numbers of mature fish. These results demonstrate that autonomous camera systems can non-invasively study fish larval presence and provide further support that AE can enhance larval fish response.