Soundscape analysis detects the presence of a keystone species on coral reefs

Passive acoustic monitoring (PAM) is a burgeoning technique in the underwater environment that can be used to monitor the acoustic profiles of communities and their interactions. Our study used PAM to examine whether the presence of the blue-streak cleaner Labroides dimidiatus is associated with distinct acoustic profiles. Labroides dimidiatus is f ound on coral reefs throughout the Indo-Pacific, where it is known to positively affect reef fish community composition. We analysed recordings from an ongoing 22-year experiment at Lizard Island, Great Barrier Reef, in which L. dimidiatus is either periodically removed from, or allowed to aggregate naturally on (control), a series of natural patch reefs. We compared sound pressure levels, acoustic indices, and counts of shrimp snaps between time of day (dawn, day, dusk, and night) on three control and five removal reefs. The presence of L. dimidiatus , time of day, and intra-site differences were important predictors of sound pressure levels, acoustic indices, and counts of shrimp snaps. Non-metric Multidimensional Scaling (NMDS) analysis revealed soundscape composition of removal reefs formed two distinct clusters that were separated from the control reefs, with patterns of variation differing across times of day. Entropy Index (H), Acoustic Diversity Index (ADI), and Patch Size-normalized snapping shrimp Snaps (PSS) had the largest influence on the distribution of individual reefs in the soundscape recordings. These findings act as an example of signature reef soundscapes and the importance of selecting suitable spatiotemporal scales for examining specific ecological events such as keystone species presence in the soundscape.