Effects of N/P Atomic Ratio on the Growth of Alexandrium Tamarense at Various Initial Phosphate Concentrations

To reveal the relationship between nutrient input and red tide outbreaks, the effects of N/P atomic ratio on the specific growth rate of Alexandrium tamarense is analyzed under various initial phosphate concentrations in laboratory cultures. The results show that both the cell density and the specific growth rate of A.tamarense first increased when the N/P atomic ratio ≤ (N/P)opt and then decreased when the N/P atomic ratio ≥ (N/P)opt in low-P-grown cultures, followed by those in medium-P-grown and high-P-grown cultures. And the highest cell density in low-P-grown, medium-P-grown, and high-P-grown cultures is 1776×104, 4094×104 and 6891×104 cells/L, respectively. The maximum specific growth rate is 4.022, 5.307 and 9.672 d-1, respectively. It seems that the higher the initial phosphate concentrations, the greater the probability of red tide outbreaks.