Meeting Abstract
Patchy aggregations of Cassiopea medusae, commonly referred to as the “upside-down” jellyfish, are seen in sheltered marine environments such as mangrove forests and coral reefs in shallow regions saturated with sunlight. They exhibit a sessile, non-swimming lifestyle, and are oriented such that their bells are attached to the substrate and oral arms directed toward the free surface. Pulsations of their bells drive flow toward and away from the body, assisting in filter feeding and for exchange of inorganic and organic matter across the water column. While several studies have examined the basic functional morphology and fluid interaction in individual Cassiopea, the effects of body size and background flow on currents generated by these medusae are unclear. We investigate the effects of body size and background flow on currents generated using three experimental approaches. Bell pulsation kinematics was quantified from digitized videos. Fluorescein dye introduced underneath the substrate via gravity feed was used to investigate release of porewater via bell motion. Quantitative flow visualization studies of Cassiopea currents were conducted using 2D high-speed particle image velocimetry (PIV). The medusae were introduced in a low-speed recirculating water tunnel to replicate the background flows observed in their natural environment. The results of the study suggest an inverse dependence of bell diameter on pulsing frequencies and peak induced jet velocities. Vertical mixing of medusa-induced jets were observed in the presence of background flow. The implications of the study findings on organism-induced mixing in nearly quiescent flow habitats will be presented.
