Effects of irradiance and salinity on the growth of carpospore-derived tetrasporophytes of Gracilaria edulis and Gracilaria tenuistipitata var liui (Rhodophyta)

Gracilaria edulis and Gracilaria tenuistipitata var liui are agarophytes with high commercial value which are currently cultivated in countries like India and Thailand. They have great potential for mariculture in Malaysia. Experiments were carried out to study carpospore germination and determine the effects of irradiance and salinity on the growth of these two species. Both species showed the Dumontia type of carpospore development. Both species showed increased daily growth rate (% day(-1)) with increasing irradiance and tolerance for a wide range of salinity with a preference for low salinity. G. edulis grew best at 100 mu mol photons m(-2) s(-1) and 15 psu while G. tenuistipitata var liui grew best at 60-130 mu mol photons m(-2) s(-1) and 15 psu. The highest growth rate obtained for G. edulis and G. tenuistipitata var liui was 13.57 and 19.7 % day(-1) respectively. tenuistipitata var liui. ANOVA showed that both irradiance and salinity have significant effect on the growth of both species (P < 0.05). The results showed that G. tenuistipitata var liui is a good candidate for mass cultivation in Malaysian brackish waters. Besides, this study also showed the feasibility of using spore culture to provide stocks for sustainable farming of Gracilaria.