SUSTAINABLE COMMERCIAL CULTIVATION OF Gracilaria edulis THROUGH SPORE PRODUCTION IN THE LABORATORY

Gracilaria  edulis  has been traditionally used for extraction of food grade agar. Demand for raw material outstripped the supply of seaweeds from wild stocks. Therefore, several vegetative propagation methods have been developed in open sea water to augment its resources.  However cultivation through vegetative fragments requires large quantity of seed materials and seasonal dependency and ageing of thallus are other impediments. Therefore,  cultivation through spore production was tried. 2g fresh wt. of cystocarpic  G. edulis plants were suspended over  1L conical flasks containing 800mL sterile seawater with 35 ±1 ppt salinity,  7.9 ± 2 pH,  4000 lux light intensity and 10:14 (light : dark) hrs photoperiod. Spores released and attached on the bottom of the flasks.  Sporelings were cultured in the laboratory under MP1 medium for  20 - 25 days and reached an average size of 0.9 - 1.3 cm. The sporelings were then transferred to outdoor tanks and maintained for 20 - 25 days, where they attained an average length of 2.0 - 2.5 cm. The plantlets were then seeded on 1 × 1m bamboo rafts at sea, each carrying 10 ropes.  Each rope had 10 seedlings (each has approx. 0.025g fresh wt) with 3 plantlets per seeding.  300 plantlets were seeded on a single raft with an initial seedlings of 10.g fresh wt. The rafts were kept at subsurface water for acclimatization. Biomass reached to 1 kg fresh wt. per raft in 25 days. The spore plants acclimatized at sea conditions were harvested and seeded on 2m × 2m rafts with initial seedling of 1.5kg.fresh wt per raft and kept on the seawater surface. The final biomass obtained was around 20kg.fresh wt. per raft after 45 days. This technique ensures seedling production throughout the year.