Abstract
Species of Sargassum are widely distributed along the coasts of Thailand. Sargassum oligocystum Montagne is a dominant species consisting of Sargassum beds, playing an important ecological role in a marine ecosystem along the east coast of the Gulf of Thailand. However, there is little information available on the early life stages of S. oligocystum . To fill the gap in this ecological knowledge, fertilized eggs obtained from the receptacles of wild matured individuals were cultured and morphogenesis in the early life stages of S. oligocystum due to their development was observed through laboratory culture. A fertilized egg divided transversely into one large cell and one small cell. The latter gradually induced rhizoidal cells after several divisions and many rhizoidal cells came out at the basal part of germling in 3 day culture. Finally, they became the holdfast of germling. In the large cell, cell divisions occurred and apical part came out in 1 day culture. It developed into the first cauline leaf in 7 day culture and the fourth cauline leaf was appeared in 30 day culture, which were lanceolate. Cauline leaves were lanceolate to spatulate in 60 day culture and broad spatulate in 90 day culture. Three-month-old juveniles of S. oligocystum were cultured in two 500 L fiberglass tanks set outdoor under a roof with translucent windows, and one was filled with seawater and another was filled with seawater with urea dissolved at a concentration of 4 g t-1. When juveniles cultured in two different conditions for five weeks, the growth rate of the germlings of S. oligocystum cultured in seawater was always higher than that of culture in seawater with urea dissolved. The results suggest that S. oligocystum has a potential to adapt to grow under lower nutrient environment.
