Celestial patterns in marine soundscapes

Soundscape ecology is the study of the acoustic characteristics of habitats, and aims to discern contributions from biological and non-biological sound sources. Acoustic communication and orientation are important for both marine and terrestrial organisms, which underscores the need to identify salient cues within soundscapes. Here, we investigated temporal patterns in coral reef soundscapes, which is necessary to further understand the role of acoustic signals during larval settlement. We used 14 mo simultaneous acoustic recordings from 2 reefs, located 5 km apart in the Florida Keys, USA to describe temporal variability in the acoustic environment on scales of hours to months. We also used weather data from a nearby NOAA buoy to examine the influence of environmental variables on soundscape characteristics. We found that high acoustic frequencies typically varied on daily cycles, while low frequencies were primarily driven by lunar cycles. Some of the daily and lunar cycles in the acoustic data were explained by environmental conditions, but much of the temporal variability was caused by biological sound sources. The complexity of the soundscape had strong lunar periodicity at one reef, while it had a strong diurnal period at the other reef. At both reefs, the highest sound levels (~130 dB re: 1 μPa) occurred during new moons of the wet season, when many larval organisms settle on the reefs. This study represents an important example of recently-developed soundscape ecology tools that can be applied to any ecosystem, and the patterns uncovered here provide valuable insights into natural acoustic phenomena that occur in these highly diverse, yet highly threatened ecosystems.