THE ASCORBIC-ACID CONTENT OF 11 SPECIES OF MICROALGAE USED IN MARICULTURE

The ascorbic acid (vitamin C) concentrations in 11 species of microalgae commonly used in mariculture were determined. The species examined were 4 diatoms (Chaetoceros calcitrans (Paulsen) Takano, Chaetoceros gracilis Schutt, Skeletonema costatum (Greville) Cleve, Thalassiosira pseudonana (Hustedt, clone 3H) Hasle and Heimdal); 2 prymnesiophytes (Isochrysis sp. (clone T.ISO) Parke, Pavlova lutheri (Droop) Green); 1 prasinophyte (Tetraselmis suecica (Kylin) Butcher); 2 chlorophytes (Dunaliella tertiolecta Butcher, Nannochloris atomus Butcher); 1 eustigmatophyte (Nannochloropsis oculata (Droop) Green); and 1 cryptophyte (Chroomonas salina (Wislouch) Butcher). Duplicate cultures of each species were grown under defined conditions and analysed during both logarithmic and stationary phase of growth. Average values for ascorbic acid ranged from 9.4 fg cell-1 (N. oculata, stationary phase) to 700 fg cell-1 (S. costatum, stationary phase). This value was generally related to cell size. Levels of ascorbic acid cell-1 increased during the stationary growth phase for S. costatum and D. tertiolecta and decreased for C. gracilis, T. pseudonana, C. salina and N. oculata. Levels did not change significantly for the remaining species. Average values for per cent ascorbic acid ranged from 0.11% (T. pseudonana, stationary phase) to 1.62% of dry weight (C. gracilis, logarithmic phase). The per cent ascorbic acid was not related to algal class. Also, the percentage between logarithmic and stationary phase cultures differed for many of the species, but differences were unrelated to algal class. Chaetoceros gracilis, T. pseudonana, N. oculata and Isochrysis sp. (T.ISO) had higher per cent ascorbic acid during the logarithmic phase, whereas D. tertiolecta and N. atomus contained more per cent ascorbic acid during the stationary phase. Despite the differences in the composition of the different microalgae (0.11-1.62% ascorbic acid), all species would provide a rich source of ascorbic acid for maricultured animals, which can require 0.003-0.02% of the vitamin in their diet.