Growth kinetics and nutrient requirements of two tropical marine phytoplankters

Growth rates of nutrient-depleted cells of Biddulphia sinensis Greville and Ceratium furca (Ehrenberg) Claparède et Lachmann as a function of phosphate and nitrate, follow the hyperbolic expression of the Michaelis-Menten equation. variations in the half-saturation constants (K _s) for both species in each nutrient gave an index of their capacity to utilize these two nutrients when available either singly or in combination. The maximum growth rates (_max) of the two species did not follow the trends shown by K _s. Seasonal abundance of the two species in the Cochin Backwater (an Indian tropical estuary) showed that, at low concentrations of nutrients, C. furca becomes predominant; high nutrient concentrations present in the estuary during the monsoon months tend to increase the abundance of B. sinensis. The differences in the K _s values of the two organisms seem to reflect their observed seasonal abundance in the estuary.