The effect of three cultivation methods and two seedling types on growth, agar content and gel strength of Gracilaria verrucosa

Gracilaria verrucosa is one of the Rhodophyta, it has an economic value and major aquaculture commodity in Indonesia which the production had increased between 2010 and 2014. Agar is one of the hydrocolloid extracts from Gracilaria, which the quality depends on the strain, cultivation methods and the water quality. This research compares three cultivation methods (broadcast, off-bottom and long-line) and two seedling types (local versus tissue cultured). After 60 days of cultivation, the Specific Growth Rates (SGRs), the agar content and gel strength were determined. The SGR (%d-1) of the local seedlings was higher than that of the tissue-cultured for all three culture methods: 1.2-1.3 and 0.5-1.1, respectively, probably due to adaptation problems. Overall, broadcasting resulted in a significantly higher agar content (9.6%) compared to off-bottom (6%) and long-line (3.2%), because of the low amount of light compared to photosynthesis, translating to less cell walls and more accumulation of carrageenan farther from the water surface. The gel strength of tissue-cultured seedlings in broadcast and off-bottom was significantly higher than that from long-line (505 compared to 201 g cm−2). The choice of seedlings and culture method may depend on the market price criteria and final use of the seaweed.