Form, Function and Flow in the Plankton: Jet Propulsion and Filtration by Pelagic Tunicates

Kelly Rakow Sutherland, Ph.D., 2010
Laurence Madin, Advisor

Trade-offs between filtration rate and swimming performance among salp species with distinct morphologies and swimming styles were compared.  Time-varying body volume calculated from in situ video sequences resulted in higher filtration rates than previous measurements, setting an upper limit on filtration capacity.   Though each species possessed a unique combination of body kinematics, normalized filtration rates were comparable across most species suggesting a common flow optimum.  In situ dye visualization and Particle Image Velocimetry measurements were used to describe jet wake properties and swimming performance variables.  All species swam via vortex ring propulsion.  Though Weelia cylindrica was the fastest swimmer, Pegea confoederata was the most efficient, producing the highest weight-specific thrust and whole-cycle propulsive efficiency.  Weak swimming performance parameters in Cyclosalpa affinis, including low weight-specific thrust and low propulsive efficiency, may be compensated by low energetic requirements. A low Reynolds number mathematical model using realistic oceanic particle-size concentrations, and feeding experiments with 0.5, 1 and 3 μm microspheres, showed that submicron particles are encountered at higher rates than larger particles.  Though 1- 10 μm-sized particles provide four times as much carbon as 0.1- 1 μm- sized particles, particles smaller than the mesh size (1.4 μm) can still satisfy salp energetic needs.