Physics of shape-related external efficiency in sinking phytoplankton

Establish a mechanistic physical theory that explains the shape-dependence of external hydrodynamic efficiency in sinking phytoplankton, accounting for the observed discrepancy that spherical-shaped sinkers attain higher sinking speeds than non-spherical shapes, whereas prolate-shaped microswimmers achieve higher swimming efficiency than spherical or oblate swimmers.

Background

Throughout the paper, the authors discuss how geometric shape influences motility external efficiency differently for swimmers and sinkers. Empirical observations report that prolate shapes tend to improve swimming efficiency, while spherical shapes tend to enhance sinking efficiency.

This discrepancy lacks a comprehensive physical explanation. The authors explicitly identify this as an open problem, motivating the development of a theory that can reconcile the contrasting shape-efficiency relationships for swimming and sinking organisms.