Effect of ambient medium viscosity on the motility and flagella motion of Prorocentrum minimum (Dinophyceae)

Abstract

The effect of ambient medium viscosity on the motility and flagellar beating motion of the dinoflagellate Prorocentrum minimum was experimentally investigated. Prorocentrum minimum is a thecate desmokont dinoflagellate with two flagella that emerge from the flagellar pore at the anterior end of the cell. A digital holographic particle tracking velocimetry technique was employed to capture the swimming trajectories of hundreds of P. minimum cells and to extract the kinematic motion parameters. The viscosity of the surrounding medium was changed from 1.12 cP (natural sea water at 22C) to 11.31 cP by adding methylcellulose to increase fluid viscosity. In natural sea water, the swimming speeds of P. minimum cells (n 77) in a helical motion ranged from 5.4 to 138.4 m/s with a mean speed of 51.3 27.9 m/s. The helix radius and pitch of the swimming trajectories are 3.08 0.64 and 25.34 7.96 m/s, respectively. The longitudinal flagellum beats with a planar wave at a beating frequency of 87.10 10.96 Hz. On the other hand, the transverse flagellum beats with a helical wave at a beating frequency of 45.38 13.61 Hz. As the ambient medium viscosity increases, the beating frequency of flagella decreased and consequently, the swimming speed of P. minimum was reduced.