Christophe Eloy - Problems of Planktonic Navigation

Plankton face the challenging task of navigating oceanic turbulence using only hydrodynamic and chemical cues to escape predators or catch prey. This seminar focuses on one of such tasks: the problem of vertical navigation in turbulence or how a microscopic swimmer can move upward or downward using only local velocity gradients.

I first present a theoretical model showing that an optimal swimming direction can be derived under locally steady flow conditions. Numerical simulations reveal that organisms following this strategy can surf on turbulence, achieving vertical speeds of twice their own swimming speed. Experiments with larval snails support this mechanism. I then discuss how reinforcement learning recovers similar strategies in complex flows and conclude by showing how passive flexible bodies can reproduce these behaviours through fluid–structure interactions alone.