Strategy Dependent Swimming Dynamics Change among a Predatory Algae Species with Different Strains*

Digital holographic microscopic cinematography is used for measuring the 3D, time resolved, swimming behavior of toxic and non-toxic strains the marine dinoflagellate \textit{Karlodinium veneficum}. We focus on the response of predators of the same species, but with different predation strategy, to the presence of prey, \textit{Storeatula major}. Experiments are performed in a 3$\times $3 mm cuvette, at densities extending to 100,000 cells/ml. Holograms are recorded at 60fps and at 20X magnification. In each case, we simultaneously track 200-500 cells in the 3mm deep sample, at a spatial resolution of 0.4$\times $0.4$\times $2 $\mu $m. We show that responses are largely dependent on the predation strategy. \textit{K. veneficum} 2064, a toxic mixotroph, slows down and decreases the helix radius and clusters around the prey. Conversely, MD5, a non-toxic, autotrophic-like strain is completely oblivious to prey. Strain 1974, which is toxic and twice as motile, shows heterotrophic-like responses with characteristics of an active hunter. Also, on going spectral analysis of the 3-D motion provides quantitative insight on the swimming dynamics of microorganisms.