Uncovering the acoustic ecology of sympatric coral-dwelling fish with portable audio-video arrays.

Acoustic communication plays an important role in fish ecology and behaviour. Understanding how acoustic signals vary across species and populations is central to questions of sexual selection, population divergence, and environmental modulation of communication. Yet many fish calls remain unattributed to species or behaviour, limiting their integration into broader ecological studies and monitoring. We deployed portable audio-video arrays at two coral reef systems to study the courtship calls of two sympatric damselfishes, Dascyllus aruanus and D. reticulatus. Arrays integrated four hydrophones with a video camera, enabling automated detection of pulse trains, 3D localisation, motion classification, and behavioural observations. We found interspecific differences and strong population-level divergence in call structure, with site effects often exceeding species effects. This suggests that local thermal conditions may influence the performance of sound production, potentially constraining communication under marine heatwaves. Our study shows that integrating small audio-video arrays with behavioural validation not only provides a tool for monitoring but also reveals how socially mediated courtship signals vary within and between species across broad spatial scales. This dual perspective strengthens the role of fish bioacoustics in ecological and conservation frameworks.