Sound in motion: good vibrations? characterising the hearing in different decapod crustacean species

Abstract

Ambient underwater sound is a prominent feature of marine environments that is comprised of a variety of abiotic, biotic and anthropogenic sources. Many marine organisms, including crustaceans, rely on underwater sound for a number of important life strategies. Sound comprises of two components, particle motion and sound pressure, with crustaceans being most sensitive to the particle motion component. In decapod crustacean species, the statocyst has previously been identified as an organ that plays a crucial role in detecting particle motion. This study characterised and compared the hearing of five different decapod crustaceans from different habitats, using auditory evoked potentials (AEPs). Comparisons were made between the traditional AEP (dual-source, speaker) technique and the shaker table AEP (particle motion only) technique to determine the respective contributions of the two sound components to crustacean hearing. In order to study the importance of the statocyst to crustacean hearing, statocyst structures in paddle crabs were crushed after normal recordings were carried out using both methods. Experiments were repeated and showed that evoked responses disappeared after statocyst structures were crushed, which is indicative of their prominent role of sound detection in crustaceans. Overall, differences were found between species from different habitats (rocky shore vs soft sediment), with snapping shrimp and purple shore crab showing the most and least sensitive hearing respectively when tested using dual-source stimuli. In contrast, the sensitivity and frequency bandwidths between the five species were similar when tested using pure particle motion stimuli. These differences observed between species may be attributed to species-specific differences in life history or statocyst morphology and presence of unknown ancillary hearing structures, all of which might aid with achieving higher frequency sound detection. In conclusion, the results from this study provide the first comparison of the hearing abilities of marine temperate crustacean species and have greatly improved our general understanding of the hearing capabilities of these animals.