Aperture effects in squid jet propulsion

Abstract

Squid are the largest jet propellers in nature as adults, but as paralarvae they are some of the smallest, faced with the inherent inefficiency of jet propulsion at a low Reynolds number. In this study we describe the behavior and kinematics of locomotion in 1 mm paralarvae of Dosidicus gigas, the smallest squid yet studied. They swim with hop-and-sink behavior and can engage in fast jets by reducing the size of the mantle aperture during the contraction phase of a jetting cycle. We go on to explore the general effects of a variable mantle and funnel aperture in a theoretical model of jet propulsion scaled from the smallest (1 mm mantle length) to the largest (3 m) squid. Aperture reduction during mantle contraction increases propulsive efficiency at all squid sizes, although 1 mm squid still suffer from low efficiency (20%) because of a limited speed of contraction. Efficiency increases to a peak of 40% for 1 cm squid, then slowly declines. Squid larger than 6 cm must either reduce contraction speed or increase aperture size to maintain stress within maximal muscle tolerance. Ecological pressure to maintain maximum velocity may lead them to increase aperture size, which reduces efficiency. This effect might be ameliorated by nonaxial flow during the refill phase of the cycle. Our model's predictions highlight areas for future empirical work, and emphasize the existence of complex behavioral options for maximizing efficiency at both very small and large sizes.

Ocean acidification responses in paralarval squid swimming behavior using a novel 3D tracking system

“…Propulsive efficiency, of just the jetting contraction phase, has been shown to be quite high in D. pealeii paralarvae, greater than 80%, decreasing with growth to the juvenile & adult phases (Bartol et al, 2008(Bartol et al, , 2009a. Modeled hydrodynamic efficiency for squid, considering the whole jetting cycle, however, demonstrated that efficiency increases with growth from hatching to a peak efficiency of about 40% at 10 mm DML, decreasing slightly thereafter (Staaf et al, 2014). The decrease in time spent near the surface seen in high CO 2 -exposed paralarvae in the 2D analysis may have been caused by a reallocation of available energy by these paralarvae towards stress response resulting in decreased swimming activity, a reduction in jetting efficiency due to slightly smaller mantle size (seen in Kaplan et al, 2013), or a combination thereof, resulting in increased time spent sinking.…”

“…Paralarvae operate at intermediate Reynolds numbers (25 -90), balancing between the viscous world at low speeds and a more inertial world during their high speed jets (Bartol et al, 2009a). They are also negatively buoyant: slowly, passively sinking before jetting upwards in bursts, displaying a characteristic 'hop and sink' pattern, which is believed to conserve energy (Haury & Weihs, 1976;Staaf et al, 2014). Jetting is an energetically costly means of motion, but one that provides remarkable propulsive efficiency at the paralarval stage (Bartol et al, 2008(Bartol et al, , 2009b.…”

“…Early techniques of larval videography and tracking were enacted in simple, costeffective 2D systems, such as petri dishes or round aquariums, where the animal was recorded in the horizontal x, y plane from a camera directly above (Wassersug & von Seckendorf Hoff, 1985;Villanueva et al, 1997;Budick & O'Malley, 2000). These systems were limiting for a study with squid paralarvae given the dominance of vertical motions in their swimming behavior (Staaf et al, 2014). Stereoscopic camera systems are commonly used in the field to detect accurate depth and positional information of oceanic organisms (Klimley & Brown, 1983;Boisclair, 1992).…”

Multi-jet propulsion organized by clonal development in a colonial siphonophore

“…Although jet propulsion is common among animal swimmers 1 , the integration of multiple jets into a coordinated propulsive whole is rare within the animal kingdom. Directional control of a single jet typically relies on manipulation of the jet aperture to control orientation of thrust production during animal swimming 2 3 4 . Analogous directional aperture control during manoeuvring, termed thrust vectoring, is used for jet propulsion in human-engineered vehicles 5 6 .…”

Changing the habitat: the evolution of intercorrelated traits to escape from predators

“…Muscle mass and strength could interact in providing fish-lake species with a faster escape speed. Further, aperture size affects burst swimming in squid (Staaf et al, 2014). Dragonfly larvae can actively control the size of their anal valve (Pickard & Mill, 1974), but no studies so far measured the impact of the aperture size on burst swimming in larval dragonflies.…”