Fecundity and egg viability of Sargassum oligocystum Montagne, 1845 in Iligan Bay, Northern Mindanao, Philippines

Fertile thalli of Sargassum oligocystum were collected from the intertidal area of Naawan, Misamis Oriental, in northern Mindanao, Philippines. The early development, fecundity, egg viability, and recruitment of S. oligocystum were studied to gain insights into the species' biology in preparation for its future ecological and commercial applications. The embryonic development of S. oligocystum followed almost the same pattern as other Sargassum species found in the literature: 1) the presence of unfertilized eight-nuclei eggs, 2) zygotes undergoing division into embryos after fertilization, and 3) the development of dense rhizoids on embryos after 4–5 days from release. The fecundity of one thallus of S. oligocystum produced 0.5 million eggs and 746 ± 1.5 eggs per receptacle, with 94.72% viability of eggs developing rhizoids for attachment. Recruitment of zygotes ranged from 0.52 ind cm⁻² to 3.37 ind cm⁻², with clay bricks found to be the most suitable substrate with a significantly higher recruitment rate than nylon rope and plastic binder. The present study implies the high potential of producing S. oligocystum biomass through the mass production of seed stocks in the hatchery.