Meeting Abstract

83.3  Thursday, Jan. 7  Characterization of the Fluid Motion Generated by Upside-Down Jellyfish Cassiopea SANTHANAKRISHNAN, Arvind*; DOLLINGER, Makani; MILLER, Laura; UNC Chapel Hill; UNC Chapel Hill; UNC Chapel Hill asant0@email.unc.edu

The fluid flow produced by bell pulsation in oblate medusan swimmers such as the moon jellyfish (Aurelia) has been examined in recent studies to understand the biomechanics of feeding via unsteady propulsion (see Dabiri et al., J. Exp. Biol., 2005). The upside-down jellyfish (Cassiopea) differs from the commonly observed swimming forms of scyphomedusae in that it is naturally found adhered to the muddy bottoms of shallow ocean waters in regions saturated with sunlight. While they tend to momentarily swim when significantly disturbed, these organisms prefer to otherwise attach their bell surface to the sand floor and direct their feeding appendages to the free surface in an ‘upside-down’ orientation. Filter feeding and prey capture are accomplished in these primarily non-swimming medusae by pulsatile contractions of the bell. The flow generated by the unsteady bell pulsations of these animals is examined herein using a combination of digital particle image velocimetry (DPIV) and videography measurements conducted in laboratory aquaria. The phase-averaged flow field closely resembles a blowing jet centered about the body, with fluid entrainment occurring near the bell surface. Reversed flow regions are identified during both the contraction and relaxation phases of pulsing. The effect of changing bell diameter on the jet characteristics as well as the production of flow structures is investigated. A qualitative comparison of the flow field between these organisms and swimming medusae will be presented.