Protocol for scaling up biomass production of the green seaweed Ulva ohnoi from germling clusters

This study was carried out to develop a protocol for the biomass production and cultivation of Ulva ohnoi using germling clusters. The zygote germination was evaluated under different density conditions (10, 20, 30, and 40 × 104 gametes mL−1), nutrients (4, 8, and 16 mL L−1 of von Stosch standard solution), and irradiance (100, 200, and 300 μmol photons m−2 s−1). Afterwards, the formed germling clusters were cultivated in two pulse-fed treatments, one with nutrients offered once and the other on a daily basis, to establish a growth curve and evaluate the limiting factors. Once the optimal conditions for the cultivation were established, they will be evaluated for mature fronds based on the growth rate and productivity. Irradiance was the main factor that affected germling development. Moreover, the nutrient concentration did not present differences in their development. Germling clusters, at low densities had a significantly higher growth rate. Nutrient treatments with 8 mL L−1 was sufficient for the growth of germling clusters. The maximum cultivation period under the conditions tested was four days and thereafter the nutrients and density become limiting, and the renewal of the culture medium, harvest, and return to the initial density is recommended. Germling clusters are preferable over adult fronds, as they showed more significantly stable growth rates and yields, while adult fronds started to reproduce causing reduced growth and productivity.