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Swimming Patterns of the Octopus Vulgaris

Conference Paper · April 2012

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Asimina Kazakidi

University of Strathclyde

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Michael J Kuba

Okinawa Institute of Science and Technology

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Alex Botvinnik

Hebrew University of Jerusalem

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Michael Sfakiotakis

Technological Educational Institute of Crete

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1. Background Swimming is an important means of locomotion for the benthic common octopus (Octopus vulgaris) whenever the animal needs to cover distances at greater speed. Although swimming does not appear to be the predilected mode of locomotion for octopuses in captivity—possibly due to the limited available space and the large amount of energy consumption required—, the behavior has been previously observed in nature.

Swimming patterns of the Octopus vulgaris

Asimina Kazakidi1, Michael Kuba2, Alex Botvinnik2, Michael Sfakiotakis1, Tamar Gutnick2, Shlomi Hanassy2, Guy Levy2, John A. Ekaterinaris3,4,

Tamar Flash5, Binyamin Hochner2, Dimitris P. Tsakiris1

3. Results By defining swimming as any type of locomotion of the octopus that involves no attachment to the aquarium walls or other objects and substrates, three different patterns of swimming were observed:

2. Methods Six adult animals (Octopus vulgaris, 200-400 grams of weight) were used. The animals were filmed in an aquarium of dimensions 150x70x48 cm3, filled with artificial sea water (average temperature 18oC, pH 8.38, density 1034 kg/m3 and salinity 37 ppt). Three synchronized, high-definition cameras were used during the filming, and a fourth one for side viewing. A calibration body of size 30x30x30 cm3 was used to calibrate the cameras. Jet swimming, in which the octopus uses the siphon, while the arms trail tightly

together, behind the mantle; Head-first swimming, where the octopus swims using the siphon, with the head in front, and the arms trailing and undulating behind; Arm swimming, that involves undulations of the arms in synchrony, with a power (closing) and a recovery (opening) stroke of the arms. In Figure 1, arrows indicate the approximate swimming direction.

4. Discussion This is the first time that the swimming patterns of Octopus vulgaris have been recorded systematically in the laboratory. Three-dimensional reconstructions of individual or multiple arms show the underlying mechanisms involved, and may assist in the design and control of robotic arm prototypes. Based on the collective observations of the video sequences involving octopus arm swimming movements, a simplified schematic representation of the power stroke (closing of the arms) was produced (Figure 2). The octopus appears to generate thrust by using those parts of the arms that are at incidence angles greater than zero with the direction of movement.

Figure 2. Schematic representation of the power stroke during the Octopus vulgaris arm-swimming movement. Blue arrows indicate local direction of movement while the entire octopus

moves from left to right. Interconnected solid and dashed lines indicate the location of the web during the movement.

Acknowledgments This work was partially supported by the EU via the ICT-FET OCTOPUS Integrated Project, under contract No. 231608.

Swimming direction

1 Institute of Computer Science, Foundation for Research and Technology - Hellas, Heraklion, Greece 2 Department of Neurobiology, The Hebrew University of Jerusalem, Jerusalem, Israel 3 Institute of Applied and Computational Mathematics, Foundation for Research and Technology - Hellas, Heraklion, Greece 4 School of Mechanical and Aerospace Engineering, University of Patras, Patras, Greece 5 Department of Computer Science and Applied Mathematics, Weizmann Institute of Science, Rehovot, Israel

Parts of the arms that become parallel to the direction of movement do not appear to contribute to thrust generation. Furthermore, the web of the octopus appears to be active during the movement. At the initial steps of the power stroke, the web, which is already under tension, starts to contract, contributing to the generation of forward thrust. At the final steps of the stroke period, the arms are almost fully in parallel with the direction of movement and the web is relaxed. Hence, no further directional thrust can be generated with the arms or the web; instead, the octopus uses the siphon to avoid sinking. Further work in analyzing the kinematics and the thrust generation mechanisms of the octopus swimming is in progress.

Head-first swimming

Arm swimming

Figure 1. Observed swimming patterns of the Octopus vulgaris

Jet swimming

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