Feeding Rates of Sessile and Motile Ciliates are Asymptotically Equivalent

Ciliated organisms near the base of aquatic food chains either swim and use flows generated by swimming to encounter prey, or attach to a substrate and generate feeding currents from which to extract passing particles. To assess the hydrodynamic benefits of these "swim" or "stay" strategies, we combine mechanistic modeling with a review of published shape and flow data in ciliates. We find that, for both model and empirical results, nutrient uptake in both strategies converge and are essentially equivalent within flow regimes typically experienced by ciliates under high Péclet numbers. These results help resolve the long-standing dilemma of which strategy is optimal and explain patterns occurring in natural communities that alternate between free swimming and temporary attachments.