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Updated: Nov 17, 2025

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Chemotactic Response of Marine Micro-Organisms to Micro-Scale Nutrient Layers
Published on: May 28, 2007
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Hydrodynamic interactions between swimming microorganisms in a linearly density stratified fluid
Rishabh V More1, Arezoo M Ardekani1
1School of Mechanical Engineering, Purdue University, West Lafayette, Indiana 47907, USA.
Physical Review. E
|February 19, 2021
Summary
Density stratification in oceans and lakes significantly alters how swimming organisms interact. This study reveals distinct behaviors for puller and pusher types, impacting their collective motion and layering in aquatic environments.
Area of Science:
- Fluid dynamics
- Biophysics
- Ecology
Background:
- Marine organisms' motion drives significant ecological and environmental impacts in oceans and lakes.
- Vertical density stratification in aquatic environments alters swimmer interactions compared to homogeneous fluids.
- Organism size and finite inertia influence swimming dynamics and collective behavior.
Purpose of the Study:
- To numerically investigate the interactions between pairs of model swimming organisms with finite inertia.
- To analyze these interactions in two configurations: approaching and side-by-side, within a linearly density stratified fluid.
- To categorize squirmer (puller & pusher) interactions based on Reynolds number (Re) and Richardson number (Ri).
Main Methods:
- Utilized the archetypal reduced-order squirmer model for numerical simulations.
- Investigated interactions for different Reynolds numbers (Re: 1-50) and Richardson numbers (Ri: 0-10).
- Analyzed squirmer trajectories and contact times in approaching and side-by-side configurations.
Main Results:
- Observed distinct interaction categories for pullers and pushers based on Re and Ri.
- Pullers exhibited circular looping at high Re/low Ri and angle-dependent escape with stratification at low Re/high Ri.
- Pushers showed collision sticking and deflection at low Re or high Ri, and angle-dependent escape otherwise. Stratification increased contact time.
Conclusions:
- Squirmer interaction dynamics are significantly modified by density stratification and inertia.
- Findings elucidate mechanisms for planktonic organism accumulation in stratified aquatic layers.
- The study provides insights into collective motion and ecological patterns in stratified environments.
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