Hop and escape behavior of Acartia tonsa in response to turbulent-like eddies

Copepods jump to escape predators or to relocate their position. The current study investigates the jump behavior of Acartia tonsa in presence of small-scale turbulent eddies. A Burgers vortex experimental model is used to study the interaction of A. tonsa with a single turbulent-like eddy structure. Tomographic-particle image velocimetry (PIV) experiments were performed at small-scale to quantify the velocity field of turbulent vortices modeling those that copepods encounter in their oceanic habitat. Turbulence intensities are discretized into four levels corresponding to dissipation rates of 0.002 to 0.25 cm²/s³. Three-dimensional swimming trajectories are retrieved from two orthogonal camera recording perspectives and overlaid on the Burgers vortex velocity structure to identify individual swimming kinematics and behavioral differences. Behavioral trials in apparatuses with the vortex axis in horizontal and vertical directions reveal the directional behavior of copepods to the vortex hydrodynamics. By comparing the behavioral changes in four turbulence intensity treatments and a control (stagnant) treatment, trends in behavioral responses may be identified. Escape jumps are differentiated from hops by their acceleration magnitude. Acartia tonsa exhibited escape jumps and hops in all treatments. However, the kinematics of the hops depended on the strength of the turbulent-like eddy flow. The frequency and acceleration of hops increase with increasing vortex strength. In contrast, the kinematics of escape jumps are uncorrelated with vortex strength.