The snapping shrimp conundrum: Spatial and temporal complexity of snapping sounds on coral reefs

Snapping shrimp are abundant crevice-dwelling crustaceans worldwide. The short-duration broadband “snap” generated by the collapse of a cavitation bubble upon the rapid closure of their specialized claw is among the loudest bioacoustic sound in the sea. Because these shrimp form large high density aggregations, their colonies create a pervasive crackling in many coastal environments, and variation in shrimp acoustic activity substantially alters ambient sound levels at a given location or time. Despite their fundamental contribution to the soundscape of coral reefs, and probable influence on sound-receptive organisms, relatively little is known about snapping shrimp sound production patterns, and the underlying behavioural ecology or environmental factors. Recent advances in recording capacity and efforts to sample habitat soundscapes at high spatiotemporal resolution have provided datasets that reveal complex dynamics in snapping shrimp sound production. Our analyses of soundscape data from coral reefs show that snap rates generally exhibit diurnal and crepuscular rhythms, but that these rhythms can vary over short spatial scales (e.g., opposite diurnal patterns between nearby reefs) and shift substantially over time (e.g., daytime versus nighttime dominance during different seasons). These patterns relate to abiotic variables such as temperature, light, and DO, as well as life history processes, but the nature of these relationships and underlying causal mechanisms are only beginning to be explored.