Acoustic behaviour of the European spiny lobster Palinurus elephas

The acoustic behaviour of the European spiny lobster Palinurus elephas (Fabricius, 1787) was examined in the absence or presence of predators or conspecifics. Observations were conducted in a tank equipped with digital video and acoustic monitoring and recording systems using 25 adult lobsters and 5 common octopuses Octopus vulgaris. Single lobsters or groups of 4 lobsters were studied for 2 h. These were left alone during the first hour and exposed to a single specimen of the common octopus during the second hour. The lobsters' signals were acoustically analysed. Signal duration, number of pulses per signal, pulse rate, bandwidth, peak intensity, and peak frequency were measured. Single lobsters emitted a higher number of signals than lobsters belonging to a group. The signal (rasp) was audible to humans only in the presence of a predator and was always associated with specific behavioural events. In the absence of a predator, the lobsters produced ultrasound signals (screech) having lower duration, number of pulses per signal, bandwidth, and peak intensity and higher pulse rate and peak frequency. Audible rasps were produced in an anti-predator context, whereas the ultrasound screeches were also emitted under non-stressful conditions. Thus, these signals may play a role in intraspecific communication.