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First published online March 21, 2005
Journal of Experimental Biology 208, 1257-1265 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01519

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Flow patterns generated by oblate medusan jellyfish: field measurements and laboratory analyses

John O. Dabiri^1,*, Sean P. Colin², John H. Costello³ and Morteza Gharib¹

¹ Bioengineering and Graduate Aeronautical Laboratories, California Institute of Technology, Mail Code 301-46, Pasadena, CA 91125, USA
² Biology and Marine Biology, Roger Williams University, MNS 241, Bristol, RI 02809, USA
³ Biology, Providence College, Providence, RI 02918, USA

^* Author for correspondence (e-mail: jodabiri{at}caltech.edu)

Accepted 31 January 2005

Flow patterns generated by medusan swimmers such as jellyfish are known to differ according the morphology of the various animal species. Oblate medusae have been previously observed to generate vortex ring structures during the propulsive cycle. Owing to the inherent physical coupling between locomotor and feeding structures in these animals, the dynamics of vortex ring formation must be robustly tuned to facilitate effective functioning of both systems. To understand how this is achieved, we employed dye visualization techniques on scyphomedusae (Aurelia aurita) observed swimming in their natural marine habitat. The flow created during each propulsive cycle consists of a toroidal starting vortex formed during the power swimming stroke, followed by a stopping vortex of opposite rotational sense generated during the recovery stroke. These two vortices merge in a laterally oriented vortex superstructure that induces flow both toward the subumbrellar feeding surfaces and downstream. The lateral vortex motif discovered here appears to be critical to the dual function of the medusa bell as a flow source for feeding and propulsion. Furthermore, vortices in the animal wake have a greater volume and closer spacing than predicted by prevailing models of medusan swimming. These effects are shown to be advantageous for feeding and swimming performance, and are an important consequence of vortex interactions that have been previously neglected.

Key words: jellyfish, Aurelia aurita, flow pattern, flow patterns, vortex rings, jet propulsion

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