Rumbling in the benthos: acoustic ecology of the California mantis shrimp Hemisquilla californiensis

Although much research has focused on acoustic mapping and exploration of the benthic environment, little is known about the acoustic ecology of benthic organisms, particularly benthic crustaceans. Through the use of a coupled audio-video system, a hydrophone array, and an autonomous recording unit, we tested several hypotheses about the field acoustics of a benthic marine crustacean, Hemisquilla californiensis. Living in muddy burrows in southern California, these large mantis shrimp produce low frequency 'rumbles' through muscle vibrations. First, we tested whether acoustic signals are similar in the field and in the laboratory, and discovered that field-produced rumbles are more acoustically and temporally variable than laboratory rumbles, and are typically produced in rhythmic series called 'rumble groups.' Second, we verified if the sounds were indeed coming from mantis shrimp burrows and explored whether rumble groups were produced by multiple individuals. Our results suggest that during certain time periods, multiple mantis shrimp in the vicinity of the hydro phone produce sounds. Third, we examined the relationship between behavioral and acoustic activity, and found that H. californiensis is most active during crepuscular periods. While these crustaceans make a substantial contribution to the benthic soundscape, omnipresent and acoustically overlapping boat noise may threaten their acoustic ecology.