Temporal, geographic, and density variations in the acoustic activity of snapping shrimp

The sounds produced by snapping shrimp (genus Synalpheus and Alpheus) are the main contributors to the ambient sound field of shallow‐water tropical and subtropical marine habitats worldwide. Despite this, relatively little is known about the temporal and spatial variability of snapping shrimp activity. To investigate this issue further, ecological acoustic recorders (EARs) were utilized to obtain time‐series records of the ambient sound field from multiple locations in Hawaii and American Samoa. Strong diel trends marked by sharp increases in acoustic activity during crepuscular periods were observed at all sites. However, sites varied greatly both in absolute sound levels and relative fluxes between day and night. In addition, fluctuations in snapping shrimp sound levels were found to track lunar cycles, with higher levels occurring during the new moon. To further investigate the reason for the higher levels observed during crepuscular periods, individual shrimp were localized using a three‐hydrophone line array on both a coral reef and a mud and algae habitat in Kaneohe Bay, Hawaii. The density of acoustically active shrimp was found to be higher during the sunset period than during the day or at night.