Growth characteristics of flagellated cells of Phaeocystis pouchetii revealed by diel changes in cellular DNA content

The specific growth rates (μDNA) based on the DNA cell cycle model were in close agreement with specific growth rates (μCell) determined from cell counts. The temperature affected the specific growth rates (multiple regression, p < 0.01) and were higher at 5 °C (μ ≤ 2.2 d−1) than at 10 °C (μ ≤1.6 d−1). Increasing the light:dark period from 12:12 h to 20:4 h affected the specific growth rate of P. pouchetii at the lower temperature tested (5 °C) (multiple regression, p < 0.01), resulting in higher specific growth rates than at 10 °C. At 10 °C, the effect of light:dark period was severely reduced. Neither light nor nutrients could compensate the reduction in specific growth rates caused by elevated temperature. The specific growth rates was not affected by the N:P ratios tested (multiple regression, p = 0.21). The experiments strongly suggest that the flagellated cells have a great growth potential and could play a dominating role in northern areas at increased day length.