The response of a freshwater copepod to small‐scale, dissipative eddies in turbulence

Abstract

The freshwater copepod Hesperodiaptomus shoshone was exposed to a Burgers vortex, a flow feature meant to mimic small‐scale, dissipative turbulent eddies found in the organism's environment, to determine how this copepod responds to microscale turbulent flow structures. Male and female H. shoshone were separately exposed to four turbulence intensity levels plus a negative control (i.e., stagnant flow) in two vortex orientations relative to gravity. H. shoshone demonstrates a mild behavioral change in the presence of a Burgers vortex that is dependent on both sex and vortex orientation. H. shoshone swim with fairly linear trajectories across all four levels of turbulence intensity, which is a notable difference from the swimming behavior of marine copepods exposed to the same flow feature. Variations in morphology, physical environment, or ecological niche between H. shoshone and marine copepods are potential factors that may explain the differences in how the species respond to a Burgers vortex. The setal array of H. shoshone differs from the setal array of the previously studied marine copepods, suggesting differences in sensory ability and response. The small pond habitat of H. shoshone is rarely or intermittently mixed, creating a different hydrodynamic landscape compared to the ocean, which may influence the copepod/turbulence interaction. H. shoshone has few, if any, naturally occurring predators whereas marine copepods have many, which may influence the difference in response to microscale turbulence.