Rising seawater temperatures are known to reduce the productivity of Pyropia yezoensis aquaculture. Sargassum horneri extract (SHE), a seaweed-derived biostimulant, has been reported to enhance the heat tolerance of P. yezoensis. This study was conducted to examine whether the enhanced heat tolerance conferred by this biostimulant can be retained after asexual reproduction.
P. yezoensis thalli were treated with four concentrations of SHE (0, 0.001, 0.005, and 0.1 g/L) for 10 days, with the untreated group serving as the control. After treatment, archeospore release was induced at 20 °C. The control group (0 g/L) showed rapid and complete sporulation, reaching 100 % by Day 6 and maintaining that level through Day 10. In contrast, SHE-treated groups exhibited delayed onset and lower overall sporulation rates. By Day 10, sporulation rates were 75 %, 87.5 %, and 60 % at 0.001, 0.005, and 0.1 g/L, respectively, with the 0.005 g/L treatment showing a partial mitigation of the inhibitory effect.
Thalli from each treatment group were subsequently cultured at 10 °C and 20 °C. Specific growth rates and physiological parameters—including chlorophyll a, total protein, phycoerythrin, and phycocyanin—were measured to evaluate the biochemical effects of the biostimulant treatment. The findings of this study are expected to provide insights into the appropriate stage of the P. yezoensis life cycle for biostimulant application, with particular reference to enhancing heat tolerance, and its potential benefits for stable seedling production and sustainable aquaculture management.