How Do Soundscapes Influence Settlement Patterns of Coral Reef Fish?

What does a coral reef sound like? Recent studies have shown that reef soundscapes are comprised of abiotic sounds (such as the breaking of waves), biological sounds (such as animals moving, mating, or foraging) and anthropogenic sounds (such as boat noise). Each reef has a unique “sound signature” which may be an indicator of habitat quality.  Several studies have demonstrated that settlement-stage larvae of various reef fishes may be attracted to reef sounds, yet few investigators have measured the temporal and spatial patterns of these sounds. Furthermore, to our knowledge, the linkage between acoustic signatures and natural settlement behavior of reef fish has not been examined. We selected two sites (Pickles and Sand Island Reefs, 8 km apart along the reef tract in the upper Florida Keys, USA) based on a time series of settlement data. Light-traps were used to collect settlement-stage reef fish during peak settlement times (new to third-quarter moon each month) during each of two summers (2007-2008). Significant differences in both mean number of individuals and mean number of reef fish families settling to the two locations suggest that the two sites may provide navigational cues of differing strength for the incoming larvae. To test this hypothesis, we chose these sites for long-term monitoring of reef soundscapes. Passive acoustic recorders were deployed within the reef framework at each of the sites at 6.5 m depth and were set to sub-sample for 12 seconds every 5 minutes at 20 kHz for a one year period. We characterized the sounds from each reef within relevant bandwidths based on larval fish hearing abilities, by analyzing the frequency distribution, amplitude, and temporal patterning of the sounds. Here we present acoustic data from the first months of our recording, and we examine the correlations between the soundscapes and the larval reef fish settlement data. This examination of long-term patterns in both soundscapes and settlement is a critical step towards understanding the navigational cues used by fish larvae as they seek suitable juvenile habitat.