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

Abstract

A new model of dinoflagellate diel migratory behavior and population dynamics is pre- sented using the Expanded Eulerian Method (Janowitz & Kamykowski 1999, Ecol Model 118:237-247) and adapting the concept of metabolism-influenced swimming orientation (Kamykowski & Yamazaki 1997, Limnol Oceanogr 42:1189-1202; Kamykowski et al. 1998a, in: Anderson et al. (eds) Physiolog- ical ecology of harmful algal blooms, Springer-Verlag, Berlin, p. 581-599; Yamazaki & Kamykowski 2000, Ecol Model 134:59-72). The model is constructed to simulate the observations in a 3 d laboratory mesocosm experiment (Kamykowski et al. 1998b, Mar Ecol Prog Ser 167:105-117; Kamykowski et al. 1998c, J Plankton Res 20:1781-1796) on autotrophic Gymnodinium breve (a red tide dinoflagellate species) under a nutrient-replete condition and in 12 h light:12 h dark cycle. A hypothesis of the accli- mations of the G. breve swimming orientation and speed to the internal biochemical and physiologi- cal state and external environmental conditions is proposed. A hypothesis proposed by Kamykowski et al. (1998b) on G. breve reproduction strategy is tested in the model by considering the 2 daughter cells coming from a parent cell to differ in internal biochemical composition. The model simulations are in good agreement 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 period and approximately uniform vertical distribution of the population through the water column during the dark period as well as the diel convergence and divergence patterns of the mean internal cellular carbon and nitrogen between the surface cells and mid-column cells. As expected, G. breve's internal biochemical and physiological states have a strong influence on its migratory behavior and consequently on its population dynamics. By com- parison to a simulation with a reproduction strategy producing 2 identical daughter cells, it is shown that the reproduction strategy producing 2 daughters different 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.