Yields, photosynthetic efficiencies and proximate composition of dense marine microalgal cultures. III. Isochrysis sp. and Monallantus salina experiments and comparative conclusions

Yields and efficiencies of light utilization were determined for the Chrysophyte alga, Isochrysis (Tahitian strain), and the Xanthophyte, Monallantus salina. Under conditions of nitrogen sufficiency the maximum yield of the former alga was 47·9 g m^-2 day^-1 with an efficiency of light utilization based on PAR supplied (400-700 nm) of 11·6%. Nitrogen deficiency decreased these values to 7·6 g m^-2 day^-1 and 1·9% respectively. For Monallantus (N-sufficient) the maximum values were 13·9 g m^-2 day^-1 and 6·4% respectively; N deficiency reduced these values to 7·5 g m^-2 day^-1 and 3·7%, respectively. Deficiency reduced protein levels in both species and in Isochrysis metabolism was shunted towards the formation of carbohydrate. Carbohydrate yield was doubled by deficiency. In Monallantus, lipid content was not increased by deficiency; this is in contrast to previous reports. Rather an appreciable amount of some fraction 'other' than protein, carbohydrate, lipid or ash was formed. The results of all five marine microalgae studied in this series are compared. Phaedactylum gave the highest yield and efficiency, but similar values were obtained by Tetraselmis and Isochrysis. To produce the maximum amount of a high-energy component such as lipid, one would choose Isochrysis, and for high protein yield, Phaeodactylum or Tetraselmis would be chosen. The highest carbohydrate yield would be attained by Dunaliella, Tetraselmis, or Isochrysis under N-deficient conditions. These comparative results may be useful in choosing species and conditions for maximizing various biomass products in outdoor cultures.