Gracilaria edulis

Gracilaria edulis

Gracilaria edulis , the major raw material source for Indian food-grade agar, exhibits a gel strength of approximately 490 g cm−2 with 8% alkali treatment ( Meena et al. 2008). Although the Indian coastline has 32 species of Gracilaria ( Krishnamurthy 1971) View in CoL , G. edulis is the dominant alga with significant standing stocks. Indian agar industries annually harvest 100–200 dry tonnes of G. edulis from wild stocks along the southeast coast of India. Over-harvesting of this resource has led to depletion of wild stocks. Several technologies have been developed for G. edulis cultivation. The long-line rope method yielded approximately 20 tonnes dry wt ha−1 y−1 ( Raju and Thomas 1971) and increased to 30 tonnes dry wt ha−1 y−1 with the adoption of the Single Raft Floating Technique ( Subbaramaiah and Thomas 1995). Both methods experienced significant grazing pressure hindering their commercial scale adoption. Finally, the bamboo raft method was adopted for G. edulis cultivation as this method minimized seaweed drifting and herbivore grazing by covering the lower portion of bamboo raft below the planted ropes with fishing net.

In the bamboo raft method, young fragments of Gracilaria edulis (average 2.0 ± 0.25 g fresh wt) were tied to polypropylene ropes at 5-cm intervals. Each rope contained 25 seedlings with a total fresh weight of 50 g rope−1. A bamboo raft (2 × 2 m size) with 20 ropes had an initial seedling biomass of 1.0 kg fresh wt raft −1 ( Figure 12A View Figure 12 ). Seven harvests were completed in a year ( Figure 12B View Figure 12 ) and 35 tonnes dry wt ha−1 y−1 were harvested ( Ganesan et al. 2011).