Hydrodynamics of Jellyfish Swimming under High Hydrostatic Pressure

Jellyfish are well known for their highly efficient swimming and relatively simple body plans, which have made them an attractive model for locomotor hydrodynamics. However, studies of jellyfish swimming have generally been conducted under low hydrostatic pressure conditions. In the ocean hydrostatic pressure is almost directly proportional to depth, and organisms that swim in the bathypelagic or “midnight” zone experience hydrostatic pressures more than 100 times greater than organisms that swim at the surface. In this study we expose live moon jellyfish (Aurelia aurita) to hydrostatic pressures equivalent to 0-2000 m depth and examine how hydrostatic pressure affects their swimming kinematics and hydrodynamics. Under high hydrostatic pressures, both the contraction and relaxation rate are reduced relative to low hydrostatic pressure. The bell contraction is an active, muscle-driven motion subject to complex physiological interactions with hydrostatic pressure, while the relaxation is passively controlled by elasticity in the jellyfish bell. Using particle image velocimetry, we examine how these changes to jellyfish swimming kinematics affect both the hydrodynamics and swimming performance under high hydrostatic pressures.