Revisiting the bioacoustics of European spiny lobsters Palinurus elephas: comparison of antennal rasps in tanks and in situ

Spiny lobsters (Palinuridae) are capable of emitting sounds called antennal rasps. In the bioacoustics literature, such broadband sounds have mostly been characterized from tank recordings where reverberation and resonant frequencies might strongly distort their features. Hence, in this study, we compared antennal rasps produced by European spiny lobsters Palinurus elephas in both tank and in situ conditions. We found significant differences in all sound features (temporal, intensity and spectral features) between tank and in situ recordings, confirming that antennal rasps-and broadband sounds generally -cannot be accurately characterized in tanks if sound reverberation is ignored. In recordings of antennal rasps made in situ, we show that the main acoustic power is located in the low frequency band (below 1 kHz), which was missed by all earlier studies done in tanks where such low frequencies cannot be properly measured. The hearing capacities of crustaceans suggest roles for intra-specific communication of these sounds, and their high levels indicate they could be heard above noise. Indeed, we outline that antennal rasps are among the loudest sounds known in the marine animal kingdom, with peak-to-peak sound pressure levels (calculated at 20 cm from the source) above 175.7 dB re 1 mu Pa-2, and peak-to-peak source levels (estimated at 1 m from the source) ranging from 154.2 to 160.6 dB re 1 mu Pa-2. These acoustic properties imply they could be detected in situ during passive acoustic monitoring. This study also highlights the importance of using appropriate measurement methods when characterizing sounds produced by marine invertebrates.