Effect of blue light on indoor seedling culture of Saccharina japonica (Phaeophyta)

Saccharina japonica is a brown alga that has been commercially cultured on a large scale in China. Integrating the light condition under seawater and the adaptation of Saccharina to this condition, it is expected that blue light would be beneficial to Saccharina culture system. Consequently, the detailed effect of blue light on the key stages during indoor seedling culture of S. japonica was investigated in this study. Irradiances and light qualities had little effect on zoospore attachment and germination. Egg formation occurred sooner under blue light than white light. Under optimum irradiances, 95 +/- 4% female gametophytes gave rise to eggs in 6 d under blue light, while it took 12 d for over 90% formation of eggs under white light. Over a culture period of 3 weeks, mean sporeling length and width under blue light was 1.39 and 1.56 times of that under white light, respectively, while the mean sporeling size obtained under red light was only 25% of that under white light. The higher growth rate under blue light was largely due to higher photosynthetic efficiency, as indicated by chlorophyll fluorescence of photosystem II. In addition, the mean ratio of sporeling width to length under blue light was significantly higher than that under white light. These results suggest that blue light would be superior to white light for indoor seedling culture of S. japonica. Based on these findings, an improved S. japonica seedling culture system is discussed.