Efficient mate finding in planktonic copepods swimming in turbulence

Abstract

Zooplankton live in dynamic environments where turbulence may challenge their limited swimming abilities. How this interferes with fundamental behavioral processes remains elusive. We reconstruct simultaneously the trajectories of flow tracers and calanoid copepods, the most abundant metazoans in the ocean, and we quantify their ability to find mates when ambient flow impose physical constrains on their motion and impairs their olfactory orientation. We show that copepods achieve higher encounter rates in turbulence than in calm water due to the contribution of advection and vigorous swimming. Copepods further convert encounters within the perception radius to contact events via directed motion toward nearby organisms. Inertial effects do not result in preferential concentration, reducing the geometric collision kernel to the clearance rate, which we model accurately by superposing turbulent velocity and organism motion. We suggest that this behavioral and physical coupling mechanism accounts for the ability of copepods to reproduce in turbulent environments.