Feeding and exchange currents of epibenthic upside-down jellyfish

Through periodic bell pulsations, epibenthic Cassiopea jellyfish drive jets into the water column for suspension feeding, excretion and exchange of nutrients and gases. Hydrodynamic interactions of medusan jets with ambient low-speed flow can facilitate prey capture and enhance benthic nutrient fluxes. We conducted two-dimensional, two component (2D-2C) particle image velocimetry (PIV) measurements on Cassiopea individuals placed in a recirculating flow tank under continuous background flow speeds from 0.5 cm/s to 2 cm/s. Interaction of the background flow with the branches of the oral arms resulted in shedding small-scale vortices, with a larger spatial region where suspended particles can be brought closer to medusan feeding structures. With an advection-driven particle transport model that used PIV velocity fields as inputs, we observed that low background flow of 0.5 cm/s (characteristic of Cassiopea habitats) decreased escape efficiency and increased feeding efficiency of massless particles. Increasing background flow further to 2 cm/s increased escape efficiency and decreased feeding efficiency. Collectively, these findings suggest that suspension feeding is promoted by the interaction of unsteady medusan jets with low-speed, continuous background flows.