A study of grazing behavior of copepods using digital holographic cinematography

Generating proper feeding currents for entraining prey is one of the important features in the grazing behavior of (∼1 mm) copepods. These feeding currents vary with the copepod species, as well as with the species or strains and concentration of prey (∼10μm) dinoflagellates. Calanoid copepods also hover for a while, while slowly sinking, and then intermittently jump to a different location. In our study, we employed high speed digital holographic cinematography to measure elements of the flow field around copepods in an environment seeded with dinoflagellates. In most cases, the flow field and feeding currents were characterized based on the trajectories of the dinoflagellates. However, in some of the tests we also added neutrally buoyant 20 μm particles as independent flow tracers. At low magnifications, we simultaneously recorded two perpendicular views to obtain the same spatial resolution in all directions. Data were recorded at varying magnifications and frame rates. In recent experiments, we exposed the copepods to different strains of the same dinoflagellate species that have varying levels of toxicity, and measured the resulting changes to the grazing behavior of the copepods. Here we present results from two of these experimental setups: Acartia tonsa with Karlodinium veneficum (non toxic strain) and Acartia tonsa in particle seeded flow. Issues such as swimming characteristics, feeding classification (raptorial vs. filter feeding approaches) and copepod response to different environmental settings were addressed.