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

摘要

Different types of benthic habitats likely produce distinct soundscapes due to differences in the physical and biological contributors to ambient sound. Despite their potential importance to ecological processes such as larval settlement, the soundscapes of most coastal and estuarine habitats have not been characterized. We investigated whether an estuarine soundscape is a reliable indicator of habitat type by measuring the sounds of oyster reefs and nearby off-reef soft-bottom areas in Pamlico Sound, North Carolina, USA. Acoustic sampling in 3 areas across the estuary revealed distinct acoustic patterns in oyster reef habitats compared to surrounding off-reef areas, with reef soundscapes dominated by snapping shrimp sounds and the vocalizations of reef-dwelling fish species. Compared to soft-bottom habitat, oyster reefs had significantly higher sound pressure levels in the 2-23 kHz frequency band and higher acoustic diversity index values at each concurrent sampling event. Spectral differences between adjacent reef/off-reef habitats were present throughout the summer and fall sampling season and across 2 sampling years, but the acoustic signal strength differed between reef sites. Passive sound propagation surveys found that the distinct acoustic characteristics of oyster reefs within the 2-23 kHz frequency band were highly localized, with effective source levels of 108.8 to 120.0 dB re 1 μPa @ 1 m and transmission loss approximating a cylindrical geometric spreading model. This soundscape characterization study suggests that spatial heterogeneity in ambient sound could serve as a reliable indicator of habitat type and potentially convey habitat quality information to dispersing organisms.