Data from: Shear-induced orientational dynamics and spatial heterogeneity in suspensions of motile phytoplankton

Fluid flow, ubiquitous in natural and man-made environments, has the
potential to profoundly impact the transport of microorganisms, including
phytoplankton in aquatic habitats and bioreactors. Yet, the effect of
ambient flow on the swimming behavior of phytoplankton has remained poorly
understood, largely due to the difficulty of observing cell-flow
interactions at the microscale. Here, we present microfluidic experiments
where we tracked individual cells for four species of motile phytoplankton
exposed to a spatially non-uniform fluid shear rate, characteristic of
many flows in natural and artificial environments. We observed that medium
to high mean shear rates (1 – 25 s^-1) produce heterogeneous cell
concentrations in the form of regions of accumulation and regions of
depletion. The location of these regions relative to the flow depends on
the cells’ propulsion mechanism, body shape, and flagellar arrangement, as
captured by an effective aspect ratio. Species having a large effective
aspect ratio accumulated in the high-shear regions, due to shear-induced
alignment of the swimming orientation with the fluid streamlines. Species
having an effective aspect ratio close to unity exhibited little
preferential accumulation at low to moderate flow rates, but strongly
accumulated in the low-shear regions under high flow conditions,
potentially due to an active, behavioral response of cells to shear. These
observations demonstrate that ambient fluid flow can strongly affect the
motility and spatial distribution of phytoplankton and highlight the rich
dynamics emerging from the interaction between motility, morphology, and
flow.