Impacts of simulated infaunal activities on acoustic wave propagation in marine sediments

The activities of infaunal organisms, including feeding, locomotion, and home building, alter sediment physical properties including grain size and sorting, porosity, bulk density, permeability, packing, tortuosity, and consolidation behavior. These activities are also known to affect the acoustic properties of marine sediments, although previous studies have demonstrated complicated relationships between infaunal activities and geoacoustic properties. To avoid difficulties associated with real animals, whose exact locations and activities are unknown, this work uses artificial burrows and simulates infaunal activities such as irrigation, compaction, and tube building in controlled laboratory experiments. The results show statistically significant changes in sound speed and attenuation over a frequency range of 100-400 kHz, corresponding to wavelengths on the order of the burrow diameter. The greatest effects were observed for tubes constructed of hard shells which increased the attenuation by ∼30 dB m across the measurement band. These results highlight the importance of biogenic hard structures such as tubes on sound attenuation and suggest that organisms that create hard structures may be good targets for acoustic mapping of infaunal abundance and distribution.