Feeding of planktotrophic squirmers: Effects of mobility and elongation of planktonic particles

Abstract

Ciliated micro-organisms feed on small planktonic and inorganic particles. Investigating their feeding ability is valuable for understanding corresponding ecodynamics. However, how the feeding ability is affected by the motility and elongation of their food particles remains unknown. In this study, we carry out numerical simulations based on a squirmer model and a point-particle model to represent the ciliated micro-organisms and planktonic particles, respectively. The feeding of the squirmer is accomplished by generating a flow field that attracts particles nearby. This squirmer-induced flow is described by the sum of multiple modes of Legendre polynomials. We adopt a 2-mode model, formed by the first mode and any other one, to investigate the influence of the flow structure on the feeding ability. The latter mode identifies the flow field under the two constraints of the constant maximum surface speed and the fixed vortex size. We find that the dependency of the feeding ability on the flow field varies with the mobility of food particles significantly. For non-motile particles, the feeding ability is little disturbed by the flow mode. While for motile particles, the feeding ability is negatively correlated with the flow mode, which suggests an efficient feeding strategy where the squirmer prioritizes enhancing swimming over attraction to capture more particles. Meanwhile, the elongation of food particles also plays an important role, as more elongated motile particles are more likely to be captured by the flows with high modes. This investigation advances the understanding of feeding on motile and elongated particles.