MEPS 550:25-38 (2016)  -  DOI: https://doi.org/10.3354/meps11724

ABSTRACT: Underwater acoustic recordings can be used to measure the distribution and activity of sound-producing species and investigate variability in the physical and biological characteristics of marine ecosystems. This study characterized the summer soundscape of a coastal estuarine reserve, Middle Marsh, near Beaufort Inlet, North Carolina, USA. Passive recorders were deployed at 8 sites, within a mixture of seagrass, saltmarsh, oyster reef and soft-bottom habitats, and sampled for 2 min every 20 min between June and August 2014. Sound pressure levels (SPLs) in a high-frequency band (7-43 kHz) exhibited a periodicity of once per day, being 11 dB higher during the nighttime. This pattern is correlated with snapping shrimp sounds, with an average excess of ~12% more snaps detected at night. The same analysis for SPLs in a low-frequency band (150-1500 Hz) revealed a periodicity of twice per day, with diurnal sound levels varying by up to 29 dB. Temporal variability in the low-frequency soundscape is correlated with fish chorusing, as well as tidal water level, which may influence both the presence and absence of fish and the propagation of sound in the water column. The greatest SPLs are observed in association with periods of high biological activity during nighttime high tides. Sampling marine animals and their activities over ecologically relevant time scales is challenging using conventional techniques (trawls and throw traps) within complex shallow water habitats, particularly at night. Soundscape monitoring provides an additional method to assess spatiotemporal variation in essential fish habitat use within a complex mosaic of habitat types.

KEY WORDS: Passive acoustics · Habitat-related sound · Soundscapes · Estuarine habitats