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Published April 2011 | public
Journal Article

Simultaneous field measurements of ostracod swimming behavior and background flow


Zooplankton swimming near the substratum experience boundary layer flow that is characterized by steep velocity gradients and turbulence. How do small swimming organisms navigate flows at this interface to forage and interact with mates? To address this question, we collected field measurements of the swimming behavior of the marine ostracod Paravargula trifax near complex living substrata, which were exposed to two conditions: slow "ambient flow" and faster "experimental flow." Ostracod trajectories and background flow were recorded simultaneously using a self‐contained underwater velocimetry apparatus (SCUVA). Particle image velocimetry (DPIV) produced instantaneous velocity vector fields in which the ostracods were swimming. Mean velocities, local shear stresses, turbulence intensity, and boundary shear velocity (u*) were greater in the experimental flow treatment. In slow ambient flow (u_(rms) = 0.39 ± 0.13 [mean ± SD] cm s^(−1)), ostracod swimming tracks were more tortuous and swimming angles corrected for background flow were randomly distributed compared with tracks in faster flow (u_(rms) = 3.49 ± 0.50 cm s^(−1)), indicating decreased maneuverability in rapidly flowing, turbulent water. Modeled, passive neutrally buoyant particles moved at substantially slower speeds, and their tracks were less tortuous than those of the ostracods, thus illustrating the importance of behavior as well as environmental flow in determining ostracod trajectories. Frequencies of encounters by ostracods with the benthos and with other ostracods were not different between treatments. However, in the experimental flow treatment, interactions with other ostracods occurred more frequently in the boundary layer than in the free stream, suggesting that microhabitats in the boundary layer may allow for enhanced mating encounters.

Additional Information

© 2011 by the Association for the Sciences of Limnology and Oceanography. Received: 7 March 2011. Amended: 13 June 2011. Accepted: 23 July 2011. We are grateful to the suggestions of three anonymous reviewers, which substantially improved the manuscript. We thank L. Kornicker at the Smithsonian for ostracod species identification, T. Cooper for field and data processing assistance, and M. Hadfield and F. Thomas for the use of facilities at the University of Hawaii Kewalo Marine Lab and Hawaii Institute of Marine Biology, respectively. This research was supported by the National Science Foundation (IOS‐0842681 to M.A.R.K.) and the Office of Naval Research (N000141010137 to J.O.D.).

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October 20, 2023