The escape response of abalone (Mollusca, Prosobranchia, Haliotidae) to predatory gastropods

Abstract

Haliotis laevigata (Donovan, 1808) responds to contact with predatory gastropods by performing an escape behaviour. Once initiated, the escape response follows a pattern with recognizable sub‐units (Figure 2). Following stimulus contact, animals show considerable agitation and movement of the epipodial tentacles (Figure 1b and c). This is followed by elevation of the shell (Figure 1c), a thrusting in the direction of predator contact (Figure 1d), rapidly alternating shell twisting (Figure 1 el and e2) and rapid locomotion away from the predator (Figure 1f). Detailed analysis of the duration and variability of the sub‐units showed them to be temporally and spatially stereotyped, the exceptions being the predator directed elements. The probability of progression to subsequent sub‐units falls with completion of each sub‐unit (Figure 4b). Pedal muscle electrical activity associated with the escape response can be recorded only in the margins of the muscle. Differences in the threshold of initiation of the response in other species of Haliotis were noted and possible relationships to differences in habitat hypothesized. The organization of the escape response is discussed with reference to its adaptive significance. A comparison is made between this directional type of escape response and the non‐directional type seen in other gastropods such as the nudibranch Tritonia.