Motion of dinoflagellates in a simple shear flow

Abstract

Turbulence can be highly significant to dinoflagellates by affecting their swimming motion. We examined the effects of simple shear flow on swimming trajectories and orientations of two species of dinoflagellates Glenodinium foliaceum and Alexandrium catenella. In the absence of either shear or a cue that can cause directional motion, swimming orientations of both species were insignificantly different from random. Although cells of G. foliaceum maintained their random swimming orientations upon exposure to shear, swimming orientations of both single cells and chains of A. catenella were affected by shear. Magnitude of the effect increased with shear rate. Changes in decorrelation times, as a result of exposure to shear, were observed for both species, providing another indication that shear affects swimming behavior. Decorrelation times for the swimming directions of both species were of the same order as the characteristic time scale of turbulence that would produce shear rates comparable to those examined in this study. Theoretical models that assess the effects of turbulence on vertical migration of dinoflagellates and predator-prey interactions commonly assume that swimming motion of dinoflagellates in the presence of shear flow can be described by simple superposition of the flow on the swimming motion in the absence of flow. Our results suggest that this assumption is not universally true.