Field demonstration of enhanced coral larvae settlement using acoustic enrichment, mesoscale artificial structures, and engineered biofilms

Broadcasting healthy reef sounds as acoustic enrichment (AE) has been shown to stimulate settlement behavior among coral larvae in captivity. In July 2024, a field test in Kāneʻohe Bay, Oʻahu, Hawaiʻi, evaluated AE during a natural coral spawning event. Nineteen Coral Settlement Modules (CSMs), mimicking reef roughness, were deployed at distances of 1–42 m from an underwater speaker on a 5-m-deep sandy seafloor. Additionally, synthetic biofilm-coated microhabitats, with Bacteria Reef Ink (“Brink”), were placed along a transect and around the AE setup. Healthy reef sounds were broadcast nightly for 3 weeks, centered on the new moon. Settlement was highest within 20 m of the speaker, peaking near it and declining to ambient levels beyond 20 m. A zero-inflated Poisson regression showed that Brink-coated microhabitats and speaker proximity significantly increased settlement densities. Distance effects were consistent across surfaces, with no significant relationship between algal cover and settlement. These findings highlight the potential of combining AE and synthetic biofilms to boost coral recruitment and accelerate reef restoration.