Assessing light mediated behavioral response of the dinoflagellate Akashiwo sanguinea (Hirasaka) G. Hansen and Moestrup

Toxic phytoplankton blooms cause millions of dollars in economic and environmental damage each year. Environmental factors alone do not account for these toxic blooms; behavior plays an important role. Previous studies of phytoplankton behavior have captured population level behaviors but not individual swimming responses and their correlation to population level behaviors. Diel vertical migration may be altered in response to environmental stimuli such as light. To capture individual behaviors of Akashiwo sanguinea and isolate environmental stimuli stereo video analysis of a laboratory mesocosm under continuous light and dark treatments was performed. Eight vertical positions along the mesocosm were monitored every hour over 24 hours in each treatment to observe individual swimming behaviors such as speed, vertical velocity, declination, and turning rate as well as the population distribution throughout the tank. Comparisons of light and dark treatments indicated light leads to increased speed and orientation towards the surface. Average speed changed from 280 ± 100 &mgr;m/s in the dark to 380 ± 160 &mgr;m/s in the light. Downward vertical velocities of 23 ± 200 &mgr;m/s in the dark and upward velocities of 21 ± 260 &mgr;m/s in the light were observed. Speed, vertical velocity, and declination showed the mean was a coarse measurement of complex behavioral modulation found in non-Gaussian histograms. Changes in magnitude of speed or direction of vertical velocity on an individual level should dictate vertical migration changes, which were not observed, that can lead to population accumulation. Better understanding phytoplankton population changes can lead to understanding of the origin and persistence of toxic blooms