Dancing Volvox: Hydrodynamic Bound States of Swimming Algae

TL;DR

This paper investigates how Volvox algae form stable bound states near surfaces due to hydrodynamic interactions, revealing mechanisms behind their clustering behavior.

Contribution

It introduces a hydrodynamic model explaining the formation and stability of Volvox bound states near surfaces, combining attraction and lubrication forces.

Findings

Hydrodynamic attraction causes Volvox to cluster near surfaces.

Lubrication forces stabilize the bound states.

Model explains observed Volvox clustering at surfaces.

Abstract

The spherical alga Volvox swims by means of flagella on thousands of surface somatic cells. This geometry and its large size make it a model organism for studying the fluid dynamics of multicellularity. Remarkably, when two nearby Volvox swim close to a solid surface, they attract one another and can form stable bound states in which they "waltz" or "minuet" around each other. A surface-mediated hydrodynamic attraction combined with lubrication forces between spinning, bottom-heavy Volvox explains the formation, stability and dynamics of the bound states. These phenomena are suggested to underlie observed clustering of Volvox at surfaces.