Acoustic and biological trends on coral reefs off Maui, Hawaii

Abstract

Coral reef soundscapes comprise a range of biological sounds. To investigate how the sounds produced on a given reef relate to the species present, 7 Hawaiian reefs that varied in their species assemblages were equipped with acoustic recorders operating on a 10% duty cycle for 16 months, starting in September 2014. Benthic and fish visual surveys were conducted 4 times over the course of the study. Acoustic analyses were carried out in 2 frequency bands (50-1200 Hz and 1.8-20.5 kHz) that corresponded with the spectral features of the major sound-producing taxa on these reefs, fish and snapping shrimp, respectively. In the low-frequency band, the presence of humpback whales (December-May) was the major driver of sound level, whereas in the high-frequency band sound level closely tracked water temperature. On shorter timescales, the magnitude of the diel trend varied in strength among reefs, which may reflect differences in the species assemblages present. Regression trees indicated that, at low frequencies, the relationship between species assemblages and acoustic parameters varied by season; however, at high frequencies, a given reef was generally most like itself over time. Thus, long-term acoustic recordings can capture and distill the substantial acoustic variability present in coral reef ecosystems.