Sharp turns and gyrotaxis modulate surface accumulation of microorganisms.

The accumulation of swimming microorganisms at surfaces is an essential feature of various physical, chemical, and biological processes in confined spaces. To date, this accumulation is mainly assumed to depend on the change of swimming speed and angular velocity caused by cell-wall contact and hydrodynamic interaction. Here, we measured the swimming trajectories of (a biflagellate marine alga) near vertical and horizontal rigid boundaries.