Freshwater Copepod Behavior in Turbulent Eddies

Previous studies have shown that marine copepod behavior is modulated by turbulence. We seek to expand on this observation by investigating a freshwater species, \textit{Hesperodiaptomus shoshone}, and how it responds to small-scale turbulent vortices. The calanoid copepod \textit{H. shoshone }is a dominant predator in high-altitude alpine lakes, ranging from 2-4 mm in length. The Burgers vortex model was used to simulate dissipative eddies with four levels of turbulent dissipation rates ranging from 0.002-0.25 cm$^{\mathrm{2}}$/s$^{\mathrm{3}}$, mimicking turbulent conditions found in natural habitats. Tomographic PIV was used to quantify the vortex circulation and axial strain rate of the vortices. \textit{H. shoshone }males and females were separately exposed to the four Burgers vortex treatments in a horizontal axis orientation plus a stagnant fluid control treatment. In comparison to the morphologically-similar marine copepod \textit{Calanus finmarchicus, H. shoshone }appears minimally responsive to the Burgers vortex. \textit{H. shoshone }swimming speeds remained similar under different turbulence conditions, showed no circular trajectories, and made minimal attempts to escape the vortex. These results were consistent between males and females and suggest \textit{H. shoshone }are not responsive to hydrodynamic cues of the vortex structure. The contrasting behavior will be discussed in the context of the ecology and environmental conditions of the different habitats.