ADAPTATION OF CERATIUM FURCA AND GONYAULAX POLYEDRA (DINOPHYCEACE) TO DIFFERENT TEMPERATURES AND IRRADIANCES: GROWTH RATES AND CELL VOLUMES 1

Growth rates and cell volumes of Ceratium furca Ehrenberg and Gonyaulax polyedra Stein were determined during the log phase of growth in cultures which had been extensively adapted to one of three temperatures and five irradiances. At each temperature, curves for the growth rate vs. irradiance for both species had light‐limited and light‐saturated regions. Three properties of these curves characterized the response of each species to temperature: the light‐saturated growth rate, the irradiance at which growth became light‐saturated and the compensation irradiance for growth. For both species, the first two properties generally decreased with declining growth temperature, while the compensation irradiance declined for Ceratium but had a V‐shaped response pattern for Gonyaulax. The light‐saturated growth rates were generally higher for Ceratium than for Gonyaulax , while the irradiance at which growth became saturated and the compensation irradiance were lower for Ceratium. The changes in cell volume associated with the irradiance and temperature of growth were very different for Ceratium and Gonyaulax. The cell size of Gonyaulax increased as irradiance and temperature decreased, while cell volumes of Ceratium did not change with temperature but were smallest at the highest and lowest growth irradiances. In general, the growth rate patterns were similar for Ceratium and Gonyaulax , while those for cell size were different. The maximum growth rate, the irradiance at which growth became saturated, the compensation irradiance, and the cell volume all showed that Ceratium grew at the same rate or faster than Gonyaulax over the entire range of irradiances and temperatures examined.