Navigating the soundscape: The role of acoustic cues in the settlement behavior of larval reef fishes

Nearly all coral reef fishes pass through a pelagic larval stage that concludes when they locate and select appropriate reef habitat. At least some species use the reef soundscape—the collection of sounds produced by reef-dwelling organisms—to achieve this task that is necessary for survival. Since larval fishes in the open ocean are inherently difficult to study, investigating their acoustic environment can allow predictions about their behavior in response to these cues. Further, we can predict the roles of different frequency bands in aiding long-distance navigation or short-distance habitat selection. We recorded the soundscapes at four reefs in Caribbean Panama for six weeks to inform the identity and variability of the most common sounds. We next predict the frequency-dependent transmission loss using an acoustic propagation model calibrated with acoustic transects. Including knowledge of source sound levels allows us to elucidate the sound fields created by low frequency fish and high frequency invertebrate sounds originating at the reef. We find that larval fishes are likely to encounter highly complex acoustic environments as a result of frequency-dependent acoustic structure in the water column coupled with temporal and spatial variation in the sources of the potential cues.