Yields, photosynthetic efficiencies and proximate composition of dense marine microalgal cultures. II. Dunaliella primolecta and Tetraselmis suecica experiments

Yields and efficiencies of light utilization were determined in two species of green marine microalgae, Dunaliella primolecta and Tetraselmis suecica. Under nitrogen-sufficient conditions, the maximum yield of D. primolecta was 12.09 g dry weight m^-2 day^-1 and the corresponding photosynthetic efficiency was 4.3% (based on PAR supplied; 400-700 nm). When cells became N-deficient, the yield and efficiency decreased to 10.2 g m^-2 day^-1 and 2.8%, respectively. Under N-sufficient conditions the maximum yield of T. suecica was 19.1 g m^-2 day^-1 with an efficiency of 7.3%. Deficiency reduced these values to 12.7 g m^-2 day^-1 and 3.6%, respectively. Cellular protein levels in both species were very much reduced by N deficiency and photosynthetically fixed carbon was shunted into the production of carbohydrate, which increased to up to 65% of the dry weight. Carbohydrate yields increased about five-fold in deficient cells. Deficiency may be useful in manipulating cells in outdoor cultures to form carbohydrate, which in turn could be converted to useful biomass energy resources - methane or ethanol.