Assessing spatiotemporal variations in ecoacoustic indices and their relationships with indicators of ecosystem functions in coral reefs2023 · To ensure the sustained delivery of ecosystem services, monitoring methods that capture spatiotemporal dynamics are essential. Passive acoustic monitoring and the use of ecoacoustic indices have emerged as potential complements to traditional visual-based monitoring. However, their application to coral reef ecosystem monitoring is hindered by the limited understanding of the spatiotemporal variability in ecoacoustic indices and their reliability as proxies for ecosystem functions. This study aimed to elucidate the spatiotemporal variations in ecoacoustic indices across multiple sites and depth zones within coral reef habitats around Okinawa Island, Japan, and to explore their relationships with select benthic structure and fish functional groups in coral reefs. Two hours of acoustic recordings and biophysical data were collected concurrently at shallow and deep zones across 5 sites during summer of 2023 and spring of 2024. The acoustic complexity index (ACI, 0.5-1 kHz) and snap rate were quantified from the acoustic recordings, and their spatiotemporal patterns and correlations with the benthic structure variables and fish functional groups were analyzed. Analyses revealed that site, depth zone, and season significantly influenced ACI and snap rate. ACI tended to be higher, while snap rate was lower in shallow zones than in deep zones. Moreover, although significant Spearman correlations between ecoacoustic indices and functional groups were identified, partial correlation analysis revealed that these relationships were non-significant and most likely confounded by site, depth zone, and season. These results highlight that ACI and snap rate did not serve as consistent proxies for functional groups of fish and benthic structure.
