Meeting Abstract
Body-vortex interactions are widely recognized as an important component in the effective locomotion of swimming and flying animals. It is less clear how vortex-vortex interactions contribute to animal movement in a fluid. Gelatinous zooplankton are a diverse group that exhibit a wide range of propulsive swimming modes. One of the most energetically efficient modes is a type of pulsation behavior, known as rowing, which is used by many species of jellyfish. Another type of gelatinous swimmer is the ctenophore, or comb jelly. These animals typically use a slow, cilia-based mode of propulsion. However species within the genus Ocyropsis have developed an additional propulsive strategy of rowing the lobes, which are normally used for feeding, in order to rapidly escape from predators. In this study, we used high speed digital particle image velocimetry (DPIV) to examine the kinematics and fluid dynamics of this rarely studied propulsive mechanism. This mechanism allows Ocyropsis to achieve size-adjusted speeds that are nearly double those of other large gelatinous swimmers. Investigation of the fluid dynamic basis of this escape mode reveals novel vortex interactions that have not previously been described for other biological propulsion systems. The arrangement of vortices during escape swimming produces a vortex configuration that behaves in the same manner as the well-studied ‘vortex rebound’ phenomenon, which occurs when a vortex ring approaches a solid wall. We discuss how this vortex arrangement can allow for a greater reaction force and overall thrust. These results extend our understanding of how animals utilize vortex-vortex interactions and provide important insights that can inform the bio-inspired engineering of propulsion systems.
