The energetics and mechanics of jet propulsion swimming in European common cuttlefish (Sepia officinalis)

The locomotive systems of animals play a key role in behaviours such as foraging, predator avoidance and migrations. The range of behaviours and morphologies exhibited by animals have led to a variety of locomotor strategies. This thesis investigates the jet propulsion of cuttlefish (Sepia officinalis), where water is taken into a compressible cavity, this is compressed by surrounding musculature, forcing water out and forming a jet. This process involves the transfer of chemical energy into mechanical energy, before mechanical energy is transferred into the wake, propelling the animal through the water. Here the energy transduction chain is investigated from the biochemical level through the mechanical and ultimately into the wake of the animal, providing the most complete investigation into the energy transduction chain during locomotion to date.
Investigations into the structure and function of cuttlefish jet propulsion swimming found cuttlefish produced two distinct jet modes. Jet mode use differed between hatchlings and juveniles. Differential use of jet modes may relate to flow environments inhabited by animals. Different flow environments may impact propulsive efficiency, where hatchlings are more efficient than juveniles. Juvenile propulsive efficiency was ~73 %, the highest reported value among cephalopods to date. Further investigations into the mechanical properties of mantle musculature found shortening velocities scale weakly with animal age, while cyclic measures revealed frequencies which produce the greatest net mechanical power decreased with age. Mechanical and hydrodynamic data reveal a transfer efficiency of ~26 %. Biochemical analyses of mantle muscle worked at three cycle frequencies revealed musculature heavily utilised ATP and phosphagen stores, however, no significant differences were seen between cycle frequencies, with the contractile efficiency being ~26 %. Taken together, these data revealed ~19 % of the available biochemical energy was successfully transferred into useful movement, this seems to question the idea of jet propulsion swimming being an inefficient mode of locomotion; this value does not account for recovery processes, suggesting efficiency may be lower.