Videos

Tradeoffs between swimming and feeding: The curious case of the upside down jellyfish

Presenter
June 2, 2010
Keywords:
  • Kinematics
MSC:
  • 70B10
Abstract
When studying the mechanics of swimming and flying, engineers and scientists often pose questions in the form of optimization strategies. This approach has been quite useful when trying to understand the kinematics of insect flight or the frequency that fish beat their tails. Understanding the kinematics and the morphology of animals that multitask is not as straightforward. For example, the elaborate tails of male guppy fish are likely not optimized for swimming efficiency or speed, but they do increase the likelihood of attracting a mate. In this presentation, the fluid dynamics of the currents generated by the upside down jellyfish *Cassiopea sp. *will be presented in the context of swimming and feeding. Medusae of this genus are unusual in that they typically rest upside down on the ocean floor and pulse their bells to generate feeding currents, only swimming when significantly disturbed. The pulsing kinematics and fluid flow around these upside-down jellyfish is investigated using a combination of videography, digital particle image velocimetry, and numerical simulation. There is no evidence of the formation of a train of vortex rings as observed in oblate medusae exhibiting rowing propulsion. Instead, significant mixing occurs around and directly above the oral arms and secondary mouths. Numerical simulations using the immersed boundary method agree with experimental measurements and suggest that the presence of porous oral arms induce net horizontal flow towards the bell and the absence of coherent vortex structures. The implications of these results on feeding and swimming efficiency will be discussed.