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Marine soundscapes often differ among habitats; however, relatively little is known about whether soundscapes on naturally occurring habitats differ from soundscapes on human-made structures. To address this knowledge gap, we investigated whether temporal and spectral characteristics of biological sound production differ between natural and artificial offshore reefs. Specifically, we analyzed recordings from 5 week-long hydrophone deployments on 2 natural rocky reefs and 2 artificial reefs on the North Carolina, USA, continental shelf. Analysis of sound pressure levels (SPLs) on hourly and seasonal scales revealed similar temporal patterns between the reef types. These patterns were largely driven by 4 dominant fish vocalizers with seasonal chorusing patterns, including a toadfish Opsanus sp. Despite similar temporal patterns within reef types, soundscape spectral content was more similar within than between reef types, especially during the April deployment, which had the most acoustic activity. Our findings suggest that the soundscapes of shipwreck artificial reefs may differ from the soundscapes of natural rocky reefs, possibly due to differing community composition. As sound plays an important role in the navigation and settlement of many marine species, soundscape differences between natural and artificial habitats could affect ecosystem function through species behavior and interactions.

Settlement is a critical phase in the life history of most benthic marine organisms and has important implications for their survival and reproductive success, and ultimately for pop - ulation and community dynamics. Larval encounter with settlement habitats is likely facilitated through the use of habitat-specific physical and chemical cues, but the scales over which particular habitat-related environmental cues may operate are rarely measured. In Pamlico Sound, North Carolina, USA we used passively drifting acoustic recorders to measure the varia- tion in habitat-related underwater sound, a potential broad-scale settlement cue, at spatio - temporal scales relevant to dispersing bivalve larvae in the estuary. Sound levels increased by up to 30 dB during passage over oyster reefs compared to off-reef soft bottom areas, and sound level fluctuations in the 2000 to 23 000 Hz frequency range closely corresponded to the presence of oyster reef patches below drifters, indicating that sound characteristics could reliably provide a signal of benthic habitat type to planktonic larvae. Using these soundscape measurements and the known descent capabilities of oyster larvae, we demonstrate with a conceptual model that response to habitat-related sound cues is a feasible mechanism for enhanced larval encounter with settlement substrate.