Underwater soundscapes in near-shore tropical habitats and the effects of environmental degradation and habitat restoration

Abstract

Most marine habitats have unique soundscapes and, among other potential ecological consequences, the larvae of many fish and invertebrates use habitat-specific sounds to locate appropriate settlement habitat. Anthropogenic stressors have degraded coastal ecosystems worldwide, but the effects of this degradation on the sounds emanating from deteriorated habitats are largely undocumented, as is the effectiveness of habitat restoration in reestablishing natural soundscapes. In this study, we investigated how ambient sound emanating from three near-shore, tropical habitats (subtidal mangrove prop-root habitat, seagrass, and sponge-dominated hard-bottom) in the Florida Keys, Florida (USA) varied with time-of-day and lunar phase. We also examined whether the destruction of sponge communities in hard-bottom habitats struck by cyanobacteria blooms alters the soundscape of that habitat, and if restoration of sponge communities can reestablish natural underwater soundscapes. Soundscapes of each habitat were examined using several acoustic metrics, including spectral analysis and counts of fish calls and snapping shrimp snaps. Mangrove, healthy hard-bottom, and restored hard-bottom habitats had higher soundscape spectra levels than seagrass and degraded hard-bottom whether at noon or dusk during new or full moons. Low-frequency sounds, most likely fish calls in the ~300Hz frequency range, were most prevalent in mangroves during dusk full moons. There were also higher numbers of snapping shrimp snaps in mangrove, healthy hard-bottom, and restored hard-bottom habitats than in degraded hard-bottom and seagrass beds, especially during the prominent dusk snapping shrimp chorus. Our results demonstrate that near-shore tropical habitats have unique soundscapes that are diminished by habitat degradation, but can be reestablished by habitat restoration, at least in the case of sponge-dominated hard-bottom.