Activity pattern as a mechanism of predator avoidance in two species of acmaeid limpet

Activity patterns in the foraging activity of two species of acmaeid limpet, Collisella limatula (Carpenter, 1864) and Collisella scabra (Gould, 1846) were documented over the entire tidal cycle. Collisella limatula was found to be active only while awash by the tide and during nighttime emergence; periods of inactivity were spent in crevices and on the undersides of boulders. Collisella scabra, which homes to a scar on the upper surfaces of rocks, foraged only while awash in daylight. In laboratory experiments both species of limpet were shown to orient their movement relative to light and gravity stimuli, while turbulence was necessary to elicit a response in C. scabra and produced an increased intensity of response in C. limatula . The activity pattern of C. limatula was demonstrated to be an effective mechanism for avoiding predation by octopus sp., a major visual predators of limpets, in both laboratory and field experiments. The homing habit of C. scabra was also shown to reduce the rate of predation in the laboratory. Fishes and birds, other visual predators, were also found to prey on limpets during the submerged and emerged portions of the tidal cycle respectively. It is suggested that the observed activity patterns have evolved in response to predation pressure from swift-moving predators which locate their prey visually.