Abstract: Diatoms play an important role in the primary productivity of aquatic systems and in driving the global silicon and carbon cycles in biogeochemistry. Navicula (Navicula arenaria var. rostellata) is a widely distributed diatom species in polluted aquatic and coastal ecosystems. In this study, we treat Navicula as the research object, using f/2+Si culture medium 30 mg/L dSi concentration as a reference to set different dSi concentration gradients (1 mg/L, 15 mg/L, 30 mg/L, 60 mg/L, 120 mg/L, 240 mg/L); based on the Navicula experiments and tracking of cell trajectories and behavior analysis, we explore the effects of different concentrations of dSi on diatom movement behaviors and diffusion coefficients. We found that:Their trajectories display circular motion associated with stochastic disruption. The curvature of the circular arc remains unchanged, and the direction and speed of the motion change significantly at the reverse time point; when the angle is less than 90 degrees; moreover, the velocity decreases before and after the reverse. Their motions display ballistic behavior on short time scales, Brownian-motion on long time scales, and super-diffusion on intermediate time scales. Miniscule and high dSi concentrations effectively inhibit active dispersal, whereas low and intermediate dSi concentrations promote dispersal on diatom cells. Here, our study of individual movement behaviors on diatoms helps to improve our understanding of foraging strategy and aggregation behavior in diatom biofilms; in addition, it provides new ideas on the outbreak of algal bloom, the marine biofouling phenomena, and marine snow phenomena.

Key words: diatoms, Navicula, motion behavior, dissolved silicic acid