Ambient fluid motions influence swimming and feeding by the ctenophore Mnemiopsis leidyi
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Planktonic organisms are exposed to turbulent water motion that affects the fundamental activities of swimming and feeding. The goal of this study was to measure the influence of realistic turbulence levels on (i) swimming behavior and (ii) fluid interactions during feeding by the lobate ctenophore, Mnemiopsis leidyi, a highly successful suspension-feeding predator. A laboratory turbulence generator produced turbulence (epsilon = 0.5-1.4 x 10(-6) W kg(-1)) representative of a field site in Woods Hole, MA, USA. Compared with still water, M. leidyi avoided regions in the experimental vessel where turbulence was greatest (epsilon = 1.1-1.4 x 10(-6) W kg(-1)) by increasing its swimming speeds and accelerations. Both laboratory and in situ particle image velocimetry data demonstrated that feeding currents of M. leidyi were eroded by ambient fluid motions. Despite this, the overall flux to the feeding structures remained constant due to higher swimming speeds in turbulent conditions. Instantaneous shear deformation rates produced by background turbulence were higher than those produced by ctenophore feeding currents and frequently exceeded the published escape thresholds of copepod prey. Feeding current erosion and fluid mechanical signal noise within turbulent flows affect the mechanics of predator-prey interactions during suspension feeding by the ctenophore M. leidyi.