Diel and tidal rhythms drive fish acoustic communities in a European kelp forest

Changes in marine animal communities shape ecological processes and ecosystem functioning. Monitoring temporal community dynamics is increasingly important under global change, yet remains challenging because community fluctuations can arise from multiple natural processes and are difficult to assess. Passive acoustic monitoring of signals produced by marine fauna offers a non-invasive means of tracking community dynamics, providing continuous, high-resolution data that capture temporal patterns often missed by traditional methods. Despite their potential as proxies for macrofaunal assemblages and associated dynamics, the responses of acoustic communities to environmental variability in marine ecosystems remain largely unexplored. This study aimed to characterize fish acoustic communities in a tidal European kelp forest and identify the environmental drivers shaping their temporal variability. Continuous acoustic recordings were combined with environmental measurements and underwater visual surveys to address these objectives. Generalized linear models revealed that diel and tidal cycles were the dominant drivers of acoustic activity, diversity, and community composition during the summer study period. Other environmental variables had weaker effects, reflecting the fauna's adaptation to marked short-term fluctuations in this dynamic ecosystem. Acoustic activity and richness increased at low water height, contrasting with higher visually observed fish abundance at high water height. This discrepancy suggests that sound production reflects behavioural interactions rather than fish abundance alone. The greater number of sound types (26) relative to observed species (19) indicates either behavioural sound diversity within species or the presence of undocumented soniferous taxa. Calmer sea conditions also promoted higher vocal activity and acoustic richness. This study provides an unprecedented description of kelp forest acoustic communities in Europe, demonstrating the value of ecoacoustics to complement visual surveys for capturing natural variability and establishing essential baseline information for detecting long-term ecological shifts in these climate-sensitive habitats.