Nutrition and growth kinetics in nitrogen- or phosphorus-limited cultures of the noxious red tide dinoflagellate Gymnodinium mikimotoi

The dinoflagellate, Gymnodinium mikimotoi, causes severe red tides which ha ve been associated with mass mortality of marine fish and invertebrates in western Japan. To establish the background biological information to elucid ate the mechanism of red tide outbreaks, nutrition and growth kinetics in n itrogen (N)- or phosphorus (P)-limited semi-continuous cultures were examin ed using an axenic strain. G. mikimotoi is able to grow using organic and i norganic N compounds as sole N sources. Nitrate, nitrite, and ammonium were found to be good nitrogen sources. Urea and uric acid were not so well uti lized and none of the amino acids, except for glutamine and tryptophan, wer e utilized. G. mikimotoi was capable of using a wide variety of inorganic a nd organic phosphorus compounds of different molecular structure successful ly as a sole P source. Under N-limited steady state conditions, dilution ra te (= growth rate), as a function of cell nitrogen quota, followed the Droo p equation. Similarly, dilution rate, as a function of cell P quota, follow ed the Droop equation under P-limited steady state culture. Kinetic paramet ers D-m and K-q obtained for N- and P-limited cultures were 0.54 day(-1) an d 3.13 pmol . cell(-1), and 0.67 day(-1) and 0.25 pmol . cell(-1), respecti vely. The nutrient availability and kinetic parameters of G. mikimotoi were compared to other red tide organisms and the ecological implications of th ese characteristics were discussed.