Description:

Mimi A. R. Koehl

Professor of Integrative Biology
University of California, Berkeley

Swimming in a Turbulent World

How does the motion of small animals through aquatic habitats result from the interaction of their behavior and the ambient water flow? We address this question using microscopic larvae swimming in turbulent, wavy flow over spatially-complex benthic communities. Field measurements of water motion were used to design realistic flow in a laboratory wave-flume over different substrata, and particle-image velocimetry was used to measure fine-scale, rapidly-varying water velocity vector fields. We used individual-based models of small animals swimming and being carried in this unsteady flow to determine the temporal patterns of ambient velocity, acceleration, and shear they encounter, and to explore how their trajectories are affected by their active locomotion through the water, passive sinking or rising, rotation by local shear, and behavioral responses to and transport by ambient flow. We found that the velocities, shears, and accelerations encountered by small swimmers fluctuate rapidly, with peaks much higher than mean values. Although microscopic organisms swim slowly relative to ocean currents, their locomotory behavior in response to the rapidly-fluctuating flow they encounter can affect where they are transported by ambient water movement.