A numerical study of the effects of bell pulsation dynamics and oral arms on the exchange currents generated by the upside-down jellyfish Cassiopea spp

TL;DR

This study uses mathematical modeling and experiments to analyze how bell pulsation and oral arms influence fluid exchange currents in upside-down jellyfish, enhancing understanding of their feeding mechanisms.

Contribution

It introduces a novel numerical model incorporating oral arms as porous layers, validated with experimental data, to study feeding-related fluid dynamics in Cassiopea spp.

Findings

Oral arms increase fluid flux from substrate to bell.

Pulsation pauses significantly alter flow patterns.

Numerical results align with experimental velocity fields.

Abstract

Mathematical and experimental studies of the flows generated by jellyfish have focused primarily on mechanisms of swimming. More recent work has also considered the fluid dynamics of feeding from currents generated during swimming. Here the benthic lifestyle of the upside down jellyfish (Cassiopea spp.) is capitalized upon to explore the fluids dynamics of feeding uncoupled from swimming. A mathematical model is developed to capture the fundamental characteristics of the motion of the unique concave bell shape. Given the prominence of the oral arms, this structure is included and modeled as a porous layer that perturbs the flow generated by bell contractions. The immersed boundary method is used to solve the fluid-structure interaction problem. Velocity fields obtained from live organisms using digital particle image velocimetry were used to validate the numerical simulations. Parameter sweeps were used to numerically explore the effects of changes in pulse dynamics and the properties of the oral arms independently. Numerical experiments allow the opportunity to examine physical effects and limits within and beyond the biologically relevant range to develop a better understanding of the system. The presence of the prominent oral arm structure in the field of flow increased the flux of new fluid from along the substrate to the bell. The numerical simulations also showed that the presence of pauses between bell expansion and the next contraction alters the flow of the fluid over the bell and through the oral arms.