Influence of Light Quality on the Initial Development in Edible Brown Alga Cladosiphon okamuranus

The impact of light quality on pre-germling formation was studied in the edible macroalga <i>Cladosiphon okamuranus</i>, cultivated in subtropical Japan. While the conditions for germination remain unclear, successful cultivation typically occurs in deeper nursery sites where light quality might play a crucial role. Initially, we compared light wavelengths at various depths, revealing that blue light (400-500 nm) predominated at approximately 7.5 m, where aquaculture nets were used for germination. Two experiments were conducted using discoid thalli. In the first, thalli were grown under four light conditions (white, blue, red, and a combination of blue and red) in sterilized seawater or nutrient-enriched PESI medium. Blue light resulted in the highest pre-germling formation rates in sterilized seawater, and notable rates were observed in the PESI medium across all wavelengths except red. The second experiment involved culturing thalli in sterilized seawater under white, blue, and red light at varying intensities (25 or 100 µmol photons m^-2 s^-1). The consistent promotion of pre-germling formation was observed with blue light, whereas red light produced no effects. These findings highlight the importance of blue light for germination in <i>C. okamuranus</i>, which can aid in optimizing nursery site and incubation conditions.