The effect of predatory presence on the temporal organization of activity in Octopus vulgaris

Abstract

Studies of the daily activity patterns of Octopus vulgaris have shown varying activity in different habitats. This might stem from the octopus' ability to respond to influences such as predation pressure by adjusting its activity pattern. To test the hypothesis that a predatory threat could alter activity cycles, six octopuses were each held in a partitioned tank with a potential predator for a week. After we had determined the circadian activity of each undisturbed subject for two days, a nocturnal (moray eel, Muraena helena) and a diurnal fish (triggerfish, Balistes carolinensis) were alternately introduced into the second compartment of the tank for seven days. Each of these periods was then followed by a four-day period without eel or triggerfish. During the experiment, subjects had visual and chemical access but no physical contact. Octopuses showed an increase in activity in the presence of both species, but this increase was only significantly negatively correlated with the activity of the triggerfish. Attacks on the barrier by the octopus and the triggerfish decreased throughout the week, but this was not true for the octopus and the moray eel. We concluded that O. vulgaris can use temporal spacing of activity to respond to potential predators. This ability might be responsible for conflicting reports of activity patterns of O. vulgaris.