Relationships between dissolved free amino acids,chemical composition and growth of the marine diatom Chaetoceros debile

The release of dissolved free amino acids in axenic batch cultures of the diatom Chaetoceros debile during different growth phases was studied during the late summer of 1982. Variations due to ASP, HIS, ALA, SER, THR, PHE+NH⁴, LEU and ORN were observed. The proportions of each amino acid differed according to growth phase. Maximum release and accumulation in the medium, corresponding to a rise ranging from 10^-8 to 10^-6 M, occurred at the transition between the exponential and stationary phases, and coincided with a shift in the intracellular protein and carbohydrate concentrations, and in the chlorophyll: phaeophytin ratio. It is suggested that zooplankton grazers can benefit from the accumulation of phytoplankton standing stock and nutritious compounds at times when the concentration of extracellular amino acids is high enough to trigger chemosensory detection of algal food; i.e., at the end of the exponential growth phase.