Fish community structure, habitat complexity, and soundscape characteristics of patch reefs in a tropical, back-reef system

Marine soundscapes can provide information on the presence of soniferous species and, in some cases, habitat characteristics and biodiversity of certain marine organisms. Tropical back-reefs functioning as nursery areas provide essential fish habitat for juveniles and sub-adults moving to offshore coral reefs as they grow; yet little is known of underwater soundscapes in these habitats. We characterized the soundscapes of 7 artificial patch reefs within a seagrass-dominated, back-reef embayment in The Bahamas. Hydrophones were deployed at each reef and recorded simultaneously for 2 min every 20 min from March to July 2016. Sound pressure levels (SPLs) and acoustic complexity (ACI) were analyzed for low (0.1-1.5 kHz) and high (4-20 kHz) frequency bands to evaluate sounds produced by marine organisms. Low frequency SPLs associated with fish vocalizations peaked twice per day for some reefs, but showed no relationship with habitat complexity or fish community structure. High frequency SPLs and invertebrate snap rates peaked nightly and were positively correlated with structural rugosity of reefs but not fish community structure. ACI values for both high and low frequency bands showed no associations with habitat complexity or fish community structure. These findings suggest that high frequency SPLs and invertebrate snap rates may be more indicative of habitat complexity in back-reef nurseries than low frequency SPLs, and that neither ACI values for low or high frequency bands correlate with fish community structure in areas dominated by juvenile and sub-adult fish.