MCHENRY, M.J.; Harvard Univ.: Swimming in jellyfish (Aurelia aurita): ontogenetic scaling of morphology, motion and mechanics.

Many aquatic animals change their body shape as they grow larger and it is unclear how such change influences swimming performance. The scyphozoan jellyfish Aurelia aurita increases its mass by as much as three orders of magnitude in a lifetime and their bodies change from being prolate (more tall than wide) as juveniles to being oblate (more wide than tall) as adults. Does this change in body shape facilitate higher swimming performance than if these jellyfish maintained the same shape over their ontogeny? We addressed this question by measuring the body shape and swimming kinematics of jellyfish spanning nearly three orders of magnitude in body size and by mathematically modeling the hydrodynamics of their swimming. We found that larger jellyfish swam with a lower pulse frequency, a disproportionately slower speed and lower propulsive efficiency. Mathematical simulations of swimming suggest that having an oblate body shape throughout ontogeny would result in lower swimming speed and propulsive efficiency over a lifetime. However, our simulations also suggest that speed and efficiency would be greater if jellyfish maintained a prolate body shape throughout ontogeny.