Passive energy recapture in jellyfish contributes to propulsive advantage over other metazoans

Abstract

Gelatinous zooplankton populations are well known for their ability to take over perturbed ecosystems. The ability of these animals to outcompete and functionally replace fish that exhibit an effective visual predatory mode is counterintuitive because jellyfish are described as inefficient swimmers that must rely on direct contact with prey to feed. We show that jellyfish exhibit a unique mechanism of passive energy recapture, which is exploited to allow them to travel 30% further each swimming cycle, thereby reducing metabolic energy demand by swimming muscles. By accounting for large interspecific differences in net metabolic rates, we demonstrate, contrary to prevailing views, that the jellyfish (Aurelia aurita) is one of the most energetically efficient propulsors on the planet, exhibiting a cost of transport (joules per kilogram per meter) lower than other metazoans. We estimate that reduced metabolic demand by passive energy recapture improves the cost of transport by 48%, allowing jellyfish to achieve the large sizes required for sufficient prey encounters. Pressure calculations, using both computational fluid dynamics and a newly developed method from empirical velocity field measurements, demonstrate that this extra thrust results from positive pressure created by a vortex ring underneath the bell during the refilling phase of swimming. These results demonstrate a physical basis for the ecological success of medusan swimmers despite their simple body plan. Results from this study also have implications for bioinspired design, where low-energy propulsion is required.swimming efficiency | animal-fluid interactions

How the bending kinematics of swimming lampreys build negative pressure fields for suction thrust

“…Aquatic animals significantly outperform man-made aquatic vehicles because they are able to move in water with greater efficiency and maneuverability (Bandyopadhyay, 2005;Gemmell et al, 2013). Animals achieve these performance attributes by effectively transferring the momentum of body movements to the surrounding fluid in a manner that efficiently produces and controls thrust production.…”

Added mass energy recovery of octopus-inspired shape change

“…Moslemi & Krueger (2011) studied pulsed jet propulsion efficiency as a function of Reynolds number, Krieg & Mohseni (2013) studied non-parallel starting jets to better understand jellyfish and squid jets, and Linden & Turner (2004) discussed optimal vortex ring formation in salps, squid, and fish swimming. Gemmell et al (2013) illuminated the stopping vortex in the deceleration phase of jellyfish swimming as a passive mechanism that gives additional thrust to the jelly. In Gemmell et al (2013), the stopping vortex mechanism was previously overlooked in contributing to the optimality of the jellyfish jet formation; here, we highlight the distinct contribution and importance of the shape change mechanism in providing additional escape thrust during the octopus fast jet escape.…”

“…Gemmell et al (2013) illuminated the stopping vortex in the deceleration phase of jellyfish swimming as a passive mechanism that gives additional thrust to the jelly. In Gemmell et al (2013), the stopping vortex mechanism was previously overlooked in contributing to the optimality of the jellyfish jet formation; here, we highlight the distinct contribution and importance of the shape change mechanism in providing additional escape thrust during the octopus fast jet escape.…”

Self-repairing symmetry in jellyfish through mechanically driven reorganization

“…A stroke cycle in jellyfish consists of alternating fast muscle contraction (the power stroke), followed by a slow elastic response from the gelatinous mesoglea (the recovery stroke) ( Fig. 5D; Movie S1 shows an ephyra swimming in seawater) (52,59,60). Activation of the axisymmetric musculature produces symmetric bell contraction and a forward thrust.…”