- Sep 4, 2006
- Reaction score
- Gainesville, GA
This is of particular note to keepers and the observed period of activity of O. 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.
In field studies O. vulgaris was found to be nocturnal in the Mediterranean ( Altman, 1966, Kayes, 1974 and Woods, 1965), but diurnal ( Hanlon, 1988 and Hochberg and Couch, 1971) in the Atlantic, even showing crepuscular peaks (Mather, 1988). One might argue that this could be due to population differences, but Mediterranean animals held in the laboratory actually showed diurnal ( Meisel et al., 2003 and Meisel et al., 2006) or variable peaks of activity (Wells et al., 1983). Octopuses often rely on speculative foraging, using tactile and chemical, rather than visual cues. Although Mather (1988) was unable to time octopus activity to daylight, tidal level or tidal flow, light has some – albeit, probably not an exclusive – function as a zeitgeber for O. vulgaris (Meisel et al., 2006).
Observations on the behaviour of the common octopus Octopus vulgaris were made during daytime and night-time sampling on an unexploited rocky reef habitat in Baía dos Tigres, southern Angola. The relative numerical abundance sampled was 0.47 octopus person–1 h–1during the day and 5.33 octopus person–1 h–1 during the night, suggesting that the population under study was nocturnal. The activity patterns differed between sizes of octopus. Small octopus (<20 cm total length [TL]) were observed roaming during the night, whereas the large individuals (>20 cm TL) generally fed in their dens. This ontogenetic behavioural shift may be due to tidal constraints or could be a strategy to avoid cannibalism. Octopus inhabiting a shallow, small-boulder substratum made extensive modifications to their habitat, excavating dens of up to 1 m deep in the sand below the boulders. These dens were not visible during the day as the octopus appeared to retract the small boulders over their den entrances. This unique behavioural strategy is thought to be a means to reduce predation and reduce light intensity during the day. Octopus were not observed in the small-boulder habitat during the five hours of daytime sampling. With nocturnal activity and extensive habitat modification, it is likely that avoidance of predation may be an important driver influencing the behaviour of the octopus population under study.
Heartbeat frequencies and blood pressures were monitored in freemoving
Octopus vulgaris. Typical resting frequencies (for animals of 500 g ±
at 22° C) were 40-50 beats min"1, with resting pressures measured at the
dorsal aorta of 40 cm H20 in systole and 15 cm in diastole, rising to 100 cm
or more with a pulse of 50 cm in exercise. Beat frequency changes very little
and any increased oxygen demand results mainly in an increase in stroke
volume. Temperature affects heartbeat frequency with a Qio of about 3 over
the range 7-27 °C. Systemic heartbeat rate and pulse amplitude also
change with the oxygen content of the water, slowing as this decreases and
The common octopus (Octopus vulgaris Cuvier, 1797) is one of the most widely distributed species belonging to the genus Octopus as well as an important commercially harvested species and a model organism for behavioral biology of invertebrates. It has been described for the first time in the Mediterranean Sea but it is considered a cosmopolitan species inhabiting the temperate and tropical sea of the northern and southern hemispheres. In the last few years, several species previously considered as O. vulgaris have been recognized as new species, limiting the distributional range of “vulgaris” and reinforcing the thesis of a species complex. Where it is an important fishery resource, numerous studies have been conducted in order to define its genetic structure with the purpose of managing different stocks. However, many locations are still poorly investigated from this point of view and others are under taxonomic revision to exclude or confirm its occurrence. Here we provide a summary of the current status of knowledge on distribution and genetic structure in this species in the different oceanic regions.
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