Soundscapes and living communities in coral reefs: temporal and spatial variation

Acoustic landscapes, or soundscapes, can vary due to biological ('biophony'), geophysical ('geophony') and anthropogenic ('anthrophony') components, and in some environments, such as many coral reefs, biophony dominates the soundscape. We compared 126 sound recordings from 3 different times of day (day, dusk and night) at 42 locations with concurrent fish and habitat surveys to investigate the relationships of acoustic parameters with biological and physical characteristics of coral reefs in the Gambier Archipelago, French Polynesia. Principal Component Analysis revealed that most of the variability in soundscapes could be described using only 4 factors: (1) full bandwidth root mean squared sound pressure level (SPL; 0.01 to 22.5 kHz in dB re 1 mu Pa); SPL of frequencies (2) > 0.63 kHz and (3) between 0.16 and 2.5 kHz; and (4) the number of snaps made by snapping shrimp. Number of snaps in a recording and SPL above 0.63 kHz were negatively related to live coral cover, and the density and diversity of adult and juvenile fish, but positively related to dead coral cover and time of day (as the day progressed from day to dusk to night). Full bandwidth SPL and midrange SPL were positively related to sea state, depth, Porites coral, the coral forms 'branched' and 'massive' and whether the bottom was coverd by coral (live or dead). Soundscape recordings can contribute to a more complete assessment of ecological landscapes and, in cases where logistical constraints preclude traditional survey methods, passive acoustic monitoring may give valuable information on whether habitats are changing over time.