The growth response of a model Gymnodinium splendens in stationary and wavy water columns

Abstract

A computer model is used to investigate the simulated growth of a theoretical dinoflagellate resembling Gymnodinium splendens in response to a variety of field conditions. Literature data on G. splendens are combined with probable estimates of organism response (where direct data are lacking) to yield light-and temperature-dependent production curves. These production curves are superimposed on a physical model characterized by a diurnally variable light cycle, by a two-layered water column (16°C water overlaying 12°C water) of variable layer thicknesses, and by variable extinction coefficients in the upper layer. The water column is either stationary or perturbed by a semidiurnal (12.4 h) internal wave. Organism behavior ranges from the continuous occupation of selected strata (stationary or wavy) to diurnal vertical migrations within the upper layer or across the thermocline. In stationary water columns, species patchiness depends on spatial differences in the depth preferences of nonmigrating organisms or in the details of the behavior of migrating organisms. In water columns perturbed by a semidiurnal internal wave, spatial differences in the phase relationship between the wave form and daylight supplement organism behavior as a source of patchiness. The models result in their most complex spatial patterns when a population migrates through a thermocline perturbed by a semidiurnal internal wave.