Flow disturbances generated by feeding and swimming zooplankton
Goncalves, Rodrigo Javier
Nielsen, Lasse Tor
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Interactions between planktonic organisms, such as detection of prey, predators, and mates, are often mediated by fluid signals. Consequently, many plankton predators perceive their prey from the fluid disturbances that it generates when it feeds and swims. Zooplankton should therefore seek to minimize the fluid disturbance that they produce. By means of particle image velocimetry, we describe the fluid disturbances produced by feeding and swimming in zooplankton with diverse propulsion mechanisms, and ranging from 10-µm flagellates to > mm-sized copepods. We show that zooplankton, in which feeding and swimming are separate processes, produce flow disturbances during swimming with a much faster spatial attenuation (velocity u varies with distance r as u ∝ r-3 to r-4), than that produced by zooplankton for which feeding and propulsion are the same process (u ∝ r-1 to r-2). As a result, the spatial extension of the fluid disturbance produced by swimmers is an order of magnitude smaller than that produced by feeders at similar Reynolds numbers. The ‘quiet’ propulsion of swimmers is achieved either through swimming erratically by short-lasting power-strokes, generating viscous vortex rings, or by ‘breast stroke swimming’. Both produce rapidly attenuating flows. The more ‘noisy’ swimming of those that are constrained by a need to simultaneously feed is due to constantly beating flagella or appendages that are positioned either anteriorly or posteriorly on the (cell) body. These patterns transcend differences in size and taxonomy and have thus evolved multiple times, suggesting a strong selective pressure to minimize predation risk.
Author Posting. © The Author(s), 2014. This is the author's version of the work. It is posted here by permission of National Academy of Sciences for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences of the United States of America 111 (2014): 11,738-11,743, doi:10.1073/pnas.1405260111.