Feeding Currents Generated by Upside Down Jellyfish

TL;DR

This study investigates the fluid flow generated by upside down jellyfish using experiments and simulations, revealing how their pulsing creates feeding currents and mixing around their oral arms.

Contribution

It combines videography, flow visualization, and numerical simulation to analyze the unique pulsing and flow patterns of upside down jellyfish, including the effects of porous oral arms.

Findings

Significant mixing occurs around oral arms and secondary mouths.

Numerical simulations agree with experimental flow visualization.

Porous oral arms induce net horizontal flow towards the bell.

Abstract

We present fluid dynamics videos of the pulsing dynamics and the resulting fluid flow generated by the upside down jellyfish, Cassiopea spp. 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, flow visualization, and numerical simulation. Significant mixing occurs around and directly above the oral arms and secondary mouths. Numerical simulations using the immersed boundary method with a porous layer representing the oral arms agree with the experimental results. The simulations also suggest that the presence of porous oral arms induce net horizontal flow towards the bell. Coherent vortex rings are not seen in the wake above the jellyfish, but starting and stopping vortices are observed before breaking up as they pass through the elaborate oral arms (if extended).