Copepod behavior responses around internal waves

The purpose of this study is to further our understanding of the role of internal waves as a potential to influence the behavior and patchiness of copepods. A standing internal wave with a single dominate frequency of oscillation is generated using a laboratory-scale internal wave apparatus. One experimental configuration is presented with a density jump of 1 σ_t. The wave characteristics are quantified through flow visualization and signal processing. The analytical analysis of two layer stratification system based on the wave characteristics, that includes nonlinear effects, provided the target forcing frequency needed to generate a standing internal wave with a single dominate frequency of oscillation. Three physical arrangements are investigated to study the behavioral assays of marine copepods: (1) no density stratification, (2) stagnant two-layer density stratification, and (3) two-layer density stratification with internal wave motion. Digitized trajectories of copepod swimming behavior indicate that in the control (case 1) the animals showed no preferential motion in terms of direction. In the stagnant density jump treatment (case 2), copepods preferentially moved horizontally, parallel to the density interface. In the internal wave treatment (case 3), copepods demonstrated orbital trajectories near the density interface. Comparing the analytical back-and-forth oscillation trajectories of passive, neutrally-buoyant particles with the experimental orbital trajectories of copepods near the internal wave flow indicates a strong effect of animal swimming behavior on its trajectory in this region.