A biophysical model of population dynamics of the autotrophic dinoflagellate Gymnodinium breve

A new model of dinoflagellate diel migratory behavior and population dynami cs is presented using the Expanded Eulerian Method (Janowitz & Kamykowski 1 999, Ecol Model 118:237-247) and adapting the concept of metabolism-influen ced swimming orientation (Kamykowski & Yamazaki 1997, Limnol Oceanogr 42:11 89-1202; Kamykowski et al. 1998a, in: Anderson et al. [eds] Physiological e cology of harmful algal blooms, Springer-Verlag, Berlin, p. 581-599; Yamaza ki & Kamykowski 2000, Ecol Model 134:59-72). The model is constructed to si mulate the observations in a 3 d laboratory mesocosm experiment (Kamykowski et al. 1998b, Mar Ecol Frog Ser 167:105-117; Kamykowski et al. 1998c, J Pl ankton Res 20:1781-1796) on autotrophic Gymnodinium breve (a red tide dinof lagellate species) under a nutrient-replete condition and in 12 h light:12 h dark cycle. A hypothesis of the acclimations of the G. breve swimming ori entation and speed to the internal biochemical and physiological state and external environmental conditions is proposed. A hypothesis proposed by Kam ykowski et al. (1998b) on G. breve reproduction strategy is tested in the m odel by considering the 2 daughter cells coming from a parent cell to diffe r in internal biochemical composition. The model simulations are in good ag reement with the observations. Consistent with the observations, the model predicts the surface aggregation of a portion of the population during the light period with decreasing surface aggregation intensity over the 3 d per iod and approximately uniform vertical distribution of the population throu gh the water column during the dark period as well as the diel convergence and divergence patterns of the mean internal cellular carbon and nitrogen b etween the surface cells and mid-column cells. As expected, G. breve's inte rnal biochemical and physiological states have a strong influence on its mi gratory behavior and consequently on its population dynamics. By comparison to a simulation with a reproduction strategy producing 2 identical daughte r cells, it is shown that the reproduction strategy producing 2 daughters d ifferent in biochemical composition appears to be the one adopted by all or at least a large portion of the G, breve population in the experiment.