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Phys Rev Lett. 2014 Jan 31;112(4):044502. Epub 2014 Jan 31.

Turbulent fluid acceleration generates clusters of gyrotactic microorganisms.

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Dipartimento di Fisica and INFN, Università di Torino, via P. Giuria 1, 10125 Torino, Italy.
Istituto dei Sistemi Complessi, Consiglio Nazionale delle Ricerche, via dei Taurini 19, 00185 Rome, Italy.
Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, United Kingdom.
Ralph M. Parsons Laboratory, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
Institut de Mécanique des Fluides, Université de Toulouse, INPT-UPS-CNRS, Allée du Pr. Camille Soula, F-31400 Toulouse, France.


The motility of microorganisms is often biased by gradients in physical and chemical properties of their environment, with myriad implications on their ecology. Here we show that fluid acceleration reorients gyrotactic plankton, triggering small-scale clustering. We experimentally demonstrate this phenomenon by studying the distribution of the phytoplankton Chlamydomonas augustae within a rotating tank and find it to be in good agreement with a new, generalized model of gyrotaxis. When this model is implemented in a direct numerical simulation of turbulent flow, we find that fluid acceleration generates multifractal plankton clustering, with faster and more stable cells producing stronger clustering. By producing accumulations in high-vorticity regions, this process is fundamentally different from clustering by gravitational acceleration, expanding the range of mechanisms by which turbulent flows can impact the spatial distribution of active suspensions.

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