Digital holographic PTV analysis of the motile performance of the red-tides alga ``\textit{Cochlodinium polykrikoides}''*

The outbreaks of \textit{Cochlodinium polykrikoides }causes severe damages to fisheries in Korea and Japan. \textit{C. polykrikoides} actively makes chains in its exponential and stationary growth phase. The role of the chain formation has not been clearly known yet. In the present study, the motility characteristics of \textit{C. polykrikoides} was investigated using 3D digital holographic PTV technique. The moving trajectories and average velocities of the single and multi-chained \textit{C. polykrikoides} were compared to investigate the effect of the chain formation on the motile performance. Most of the multi-chained \textit{C. polykrikoides} exhibited zigzag or helical trajectory and the translational velocity of the 4-chained \textit{C. polykrikoides} was at least two-times larger than the single one.