Hydrodynamics of cruise locomotion in the adult Euchaeta antarctica

Euchaeta antarctica is a key calanoid copepod species inhabiting the Southern Ocean surrounding Antarctica. In addition to basic propulsion considerations, the flow fields generated by Euchaeta antarctica are significant due to their ecological interactions with other organisms via hydrodynamic signals to predators and prey. In cruise swimming mode, Euchaeta antarctica generates thrust via metachronal stroking of swimming legs located on the dorsal side of their prosome. In the current study, a high-speed tomographic particle image velocimetry (tomo-PIV) system was employed to visualize and quantify the time-resolved 3D velocity field surrounding a free-swimming adult E. antarctica. Comparison of cruising swimming speed among adult E. antarctica and smaller species E. rimana and E. elongata, as well as smaller stage E. antarctica CV, demonstrate a linear dependence on organism length. The fluid velocity, vorticity, dissipation rate, and shear strain rate fields generated by adult E. antarctica during cruise behavior are quantified, with particular attention to turning. The flow fields reveal peak values of vorticity and shear strain rate within a proximity of 1 to 2 mm from the copepod body during straight motion, whereas significant increases in these quantities were observed along the animal tail during turning motion.