Process development for scaled-up land-based cultivation of Ulva ohnoi (Hiraoka & S.Shimada) using spores-derived seedlings

Abstract Ulva is edible green seaweed with higher rate of productivity, and considerable nutritional benefits. However, its seasonal nature and reproductive behaviour hinder opportunities for continuous cultivation in land-based systems. In the present study, a scaled-up process was developed for the controlled production of spore-based seedlings of Ulva ohnoi. In a Phase I, production of ~ 100,000 seedlings (in 45 days) was achieved and while Phase II yielded two kg fresh biomass (in next 45 days) in systematic land-based cultivation. In phase I, various abiotic stresses, namely, different stocking densities of mother tissue as well as seedlings were standardized to ensure obtaining uniform and the highest number of seedlings available for farming. Fragmentation (~0.1 cm) induced 100% sporulation by Day 2, while 0.3 cm disks showed 37.2% sporulation by Day 2. Freshwater exposure (10 min) triggered 81.7% sporulation on Day 2, and desiccation (1 h) induced over 90% by Day 2. Salinity and temperature had negligible effects on sporulation induction. A stocking density of 0.1 g fragments per 100 ml seawater produced 5200 ± 200 seedlings by day 15. Through this method, mass production of ~ 100,000 seedlings was attempted and successful. The subsequent stepwise culturing protocol ensured production of seedlings of 0.97 ± 0.35 cm by Day 45. In Phase II, further stocking size, stocking densities of seedlings and light intensities for the land-based cultivation system were also standardized to scale-up the entire process to 250-L reactor. This yielded the production of 2 kg contaminant free biomass derived from ~ 100,000 seedlings. This scaled-up protocol recorded a growth rate of 14.26 ± 0.29% day −1 , and biomass yield of 33.54 ± 0.97 g ww m 2 day −1 . The nutritional compositions such as protein (35.25 ± 0.81% of dw), and carbohydrate (38.98 ± 0.55% of dw) were significantly improved during scaled-up production. This is the first attempt to produce spores-derived seedlings of U. ohnoi [at the scale of ~ 100,000] followed by biomass production in land-based cultivation system. This study would undoubtedly be helpful in food industries, seaweed farmers, stakeholders and Ulva biomass production industries for further scale-up. Graphical Abstract