On the origins of ambient biological sounds in shallow water tropical ecosystems

Abstract

Although discovered more than 60 years ago, the origins of much ambient underwater biological noise remain unclear. Snapping shrimp sounds dominate some environments but elsewhere the shallow-water biological sound field is often heterogeneous. Here we show that dominant components of underwater ambient noise recorded on coral reefs around five islands in the central Pacific may be caused by the interaction of hard-shelled benthic macro-organisms with the substrate. Recordings show a consistent, nightly 4.7 to 6.9 dB increase in estimated pressure spectral density level in the 11 to 17 kHz band with a spectral peak centered between 14 to 15 kHz. Underwater time-lapse photography reveals a marked night-time increase in benthic invertebrate activity at most locations, temporally consistent with the increase in pressure spectral density level. Intensity-filtered recordings of an example species, the hermit crab Clibanarius diugeti, in quiet aquarium conditions reveal that transient sounds produced by interaction between the crustacean’s carapace, shell, and coral substrate are spectrally consistent with the central Pacific recordings. Passive acoustic monitoring of such ambient noise may be useful as a complementary ecological survey technique to SCUBA-based visual observations, which are typically poor in estimating the abundance and diversity of cryptobenthic organisms.

Estuarine soundscapes: distinct acoustic characteristics of oyster reefs compared to soft-bottom habitats

“…Although sound levels in the higher frequency band appear to be driven primarily by the abundance of snapping shrimp sounds, other acoustic sources unique to oyster reefs likely also contribute to the difference in spectral characteristics and acoustic diversity between reef and off-reef soundscapes. Certain invertebrates, such as urchins, can be a dominant sound source in New Zealand coastal habitats, creating a distinct chorus via their feeding activity (Radford et al 2008a), and in a Pacific Ocean coral reef system, the interaction of hard-shelled crustaceans with coral substrate can produce a consistently detectable spectral peak (Freeman et al 2013). It is possible that the activity of abundant oyster predators such as mud crabs (Panopeidae) and stone crabs Me nippe mercenaria could similarly represent a significant sound source to our estuarine oyster reef soundscape as they crush oyster shells and interact with the hard substrate.…”

Ecoacoustic indices as proxies for biodiversity on temperate reefs

“…; Freeman et al . ). Marine habitats are complex and interconnected due to the highly dispersive larval stages of many species, and their boundaries are often less distinct than those on land (Gray ; Cowen et al .…”