Optimizing temperature, light intensity, and salinity for carpospore culture of Gracilaria fisheri

Gracilaria is a genus of economically important macroalgae that is widely cultivated worldwide. Currently, Gracilaria production relies on vegetative propagation, which is a labor-intensive method that leads to germplasm degradation and reduced yield. Spore-based seedling cultivation offers an effective solution to these issues. In this study, we conducted a series of orthogonal experiments to investigate the optimal temperature, light intensity, and salinity conditions for cultivation of Gracilaria fisheri carpospores. Through these experiments, we systematically explored the entire cultivation process to elucidate the variations in carpospore release quantity, attachment rate, and germination rate and in the carposporeling growth rate and pigment content under different combinations of conditions. We found that the optimal conditions for carpospore release were 25°C, 20 μmol·m^–2·s^–1, and 30 salinity. For carpospore attachment, the best conditions were 20°C, 40 μmol·m^–2·s^–1, and 30 salinity. The ideal conditions for carpospore germination were 30°C, 40 μmol·m^–2·s^–1, and 30 salinity. The most favorable conditions for carpospore seedling growth were 25°C, 40 μmol·m^–2·s^–1, and 30 salinity, and these temperature and salinity conditions were also favorable for pigment accumulation. However, chlorophyll a and carotenoids accumulation was higher under the lower light intensity condition (20 μmol·m^–2·s^–1). Under suitable conditions, visible carpospores of G. fisheri were observed within 4 weeks, and the maximum length reached 0.79 cm after 9 weeks. These findings provide a theoretical foundation and practical guidance for the cultivation, genetic breeding, and artificial spore propagation of Gracilaria species.