Marine Biology

, Volume 162, Issue 10, pp 1939–1954

Zooplankton in flowing water near benthic communities encounter rapidly fluctuating velocity gradients and accelerations

  • Rachel E. Pepper
  • Jules S. Jaffe
  • Evan Variano
  • M. A. R. Koehl
Original Paper

DOI: 10.1007/s00227-015-2713-x

Cite this article as:
Pepper, R.E., Jaffe, J.S., Variano, E. et al. Mar Biol (2015) 162: 1939. doi:10.1007/s00227-015-2713-x

Abstract

The fine-scale temporal patterns of water velocities, accelerations, and velocity gradients encountered by individual zooplankters carried in ambient flow can affect their dispersal, behavior, and interaction with other organisms, but have not yet been measured in realistic flow environments. We focused on zooplankton in wavy turbulent boundary layer flow near benthic communities because such flow affects important processes, including larval settlement and prey capture by benthic zooplanktivores. Flow across fouling communities measured in the field was mimicked in a wave flume, where time-varying velocity fields over biofouled surfaces were quantified using particle image velocimetry (PIV). Trajectories of simulated zooplankters seeded into these flow fields were followed to quantify temporal patterns of velocity gradients and accelerations that individuals encountered. We found that such zooplankters are not subjected to steady velocities or velocity gradients, but rather encounter rapidly fluctuating accelerations and velocity gradients with peaks reaching several orders of magnitude above mean values and lasting fractions of a second, much shorter than the wave period. We calculated the proportion of time zooplankters spent affected (e.g., being damaged, changing behavior) by accelerations or velocity gradients and found that a small increase in mean velocity can cause a much larger increase in time affected. Animal reaction threshold and reaction time also changed the fraction of time they were affected by the flow. Using different PIV spatial resolutions showed that inter-vector spacing should be ≤0.5 Kolmogorov length (smallest eddy scale) to accurately capture velocity gradients along trajectories, but coarser resolutions (≤2–6 × Kolmogorov length) are sufficient for velocities, accelerations, and zooplankton trajectories.

Supplementary material

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Online Resource 1 An example of flow measured in a wave flume in the laboratory with vectors determined using PIV (particle image velocimetry). This is an example of the higher energy flow and is slowed down by a factor of two. (MPG 8618 kb)

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Online Resource 2Phestilla Sibogae (sea slug) larvae swimming in a petri dish. Larvae are about 200 microns long and 100 microns across. They swim using ciliated organs called velum. Note that one larva bumps into another and responds to the mechanical cue by retracting its velum. Slowed down by a factor of two. (MPG 1738 kb)

Copyright information

© Springer-Verlag Berlin Heidelberg 2015

Authors and Affiliations

  • Rachel E. Pepper
    • 1
  • Jules S. Jaffe
    • 2
  • Evan Variano
    • 3
  • M. A. R. Koehl
    • 4
  1. 1.Department of PhysicsUniversity of Puget SoundTacomaUSA
  2. 2.Scripps Institution of OceanographyUniversity of California San DiegoLa JollaUSA
  3. 3.Department of Civil and Environmental EngineeringUniversity of California BerkeleyBerkeleyUSA
  4. 4.Department of Integrative BiologyUniversity of California BerkeleyBerkeleyUSA