Meeting Abstract
Cassiopea medusae (upside-down jellyfish) are observed in sheltered marine environments, with their bells resting on the substrate and oral arms directed towards sunlight. Unsteady pulsations of the bell are used to generate feeding and exchange currents, which are significant to these organisms as they inhabit areas with low background flow velocities (e.g., mangrove swamps, seagrass beds). We examine whether bell pulsations can generate sufficient force to release sediment-locked nutrients. 2D particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF) measurements were conducted on Cassiopea individuals of varying bell diameters, under initially quiescent flow conditions in a laboratory aquarium. PLIF measurements showed release of fluorescent dye, initially located 2 cm below the substrate, into the water column. Dye concentration was larger in high-shear regions in the medusa-induced flow above the substrate. Starting vortices formed during bell contraction were broken into small-scale structures when the jet was directed through the oral arms. Smaller individuals with higher pulsing frequency showed closer placement of vortices generated from multiple pulsing cycles that aided in augmenting concentration flux. Larger medusae with lower pulsing frequency appear to benefit from the increased time scale for suspension feeding and mixing of released pore water, on account of their wider and slower jets. Our results suggest that bell pulsations of Cassiopea medusae can facilitate nutrient cycling and benthic-pelagic coupling.
