Growth and mortality of flagellates and non-flagellate cells of Phaeocystis globosa (Prymnesiophyceae)

Two cell types of the same clone of Phaeocystis globosa, solitary non-flagellate cells and flagellates, were grown in batch cultures under identical conditions. The non-flagellate cells had a shorter lag phase (1.4 versus 2.8 days) and a higher growth rate (0.72 versus 0.65 day(-1)) than flagellate cells. The flagellates had a longer stationary phase (15.6 versus 9.5 days) and a lower death rate (0.07 versus 0.52 day(-1)) than non-flagellate cells. All differences were statistically significant. Biomass yield did not differ between the two cell types. The short lag phase and high growth rate of non-flagellate cells corresponds to field observations of rapidly developing non-flagellate Phaeocystis blooms that are typically observed in nutrient-rich environments such as temperate seas in spring. The flagellate cell type, with its longer stationary phase and lower death rate than non-flagellate cells, is better equipped for survival in oligotrophic environments. This explains why the flagellates of Phaeocystis are abundant after the spring phytoplankton bloom in temperate seas and in other nutrient-poor environments such as the open ocean.