Hydrodynamics of flow sensing in plankton

TL;DR

This paper models plankton as spherical particles with cilia to understand how they perceive fluid flow, revealing their ability to measure flow strain and the necessity of bottom-heaviness for vorticity sensing, enhancing understanding of plankton behavior.

Contribution

It introduces a physical model of plankton flow sensing, showing how cilia measure local shear and the role of bottom-heaviness in vorticity detection.

Findings

Plankton can measure certain flow strain components.

Bottom-heaviness is needed to detect horizontal vorticity.

The model clarifies how plankton perceive complex flow signals.

Abstract

Planktonic organisms, despite their passive drift in the ocean, exhibit complex responses to fluid flow, including escape behaviors and larval settlement detection. But what flow signals can they perceive? This paper addresses this question by considering an organism covered with sensitive cilia and immersed in a background flow. The organism is modeled as a spherical particle in Stokes flow, with cilia assumed to measure the local shear at the particle surface. This study reveals that, while these organisms can always measure certain components of the flow strain, bottom-heaviness is necessary to measure the horizontal component of vorticity. These findings shed light on flow sensing by plankton, contributing to a better understanding of their behavior.