The effects of seawater temperature and irradiance on the sexual reproduction of Sargassum ilicifolium (Sargassaceae, Phaeophyta)

Sargassum ilicifolium, the dominant brown macroalgae in the northeast coastal area of Taiwan, is a crucial member in the marine ecosystem. Recently, various bioactive compounds and extracts within the Sargassum genus have been applied to disease treatment, health maintenance, the food industry, and agriculture. Therefore, the demand for this alga is increasing. To satisfy industry demand and to prevent the loss of natural stock due to harvesting without limits, the development of artificial cultivation is necessary. Following investigation of growth maturation in 2016, the present study aims to determine the optimal conditions for sexual reproduction. Our data showed that egg release and fertilization percentage were positively correlated with temperature, but sperm release was not. The optimal temperature for egg bearing and fertilization was 25 °C, which yielded 73.03 ± 10.94 eggs per receptacle over a period of 9 days and attained an 84.74 ± 6.59% fertilization percentage. Moreover, irradiance was the only stimulating factor on sperm bearing. The number of sperm released in a receptacle area (6.72 × 104 μm2) could be improved above 20% under an irradiance of 100 μmol photons m−2 s−1 compared with an irradiance of 20 or 50 μmol photons m−2 s−1. Thus, this study could provide the preliminary cultivation condition for developing the artificial technique of S. ilicifolium.