Effect of seaweed-based liquid extracts on biomass production and lipid accumulation in Nannochloropsis oculata and Dunaliella salina

: Seaweed liquid fertilizers (SLFs) contain macronutrients, micronutrients and trace nutrients essential for microalgal growth. The study aims to evaluate the efficiency of SLFs on the biomass production, biochemical and physiological processes; and the study was carried out at different SLF concentrations of selected seaweeds i.e. Kappaphycus alvarezii, Gelidiella acerosa and Turbinaria ornata . The comparative analysis of the growth performance of two unicellular green alga on three different organic media suggest that the liquid fertilizer from red seaweed was highly efficient than the SLF prepared from brown seaweed. The growth rate of N. oculata and D. salina in K. alvarezii SLF as culture media resulted in 1.25 and 1.21 times higher growth than the control whereas in G. acerosa SLF it was 1.17 and 1.1 times higher than the control, respectively. In contrast, in T. ornata SLF treated groups, the growth rate of N. oculata and D. salina was 0.59 and 0.68 times lower than the control, respectively. The maximum biomass concentration values recorded for N. oculata in different SLFs were 0.474, 0.422, and 0.194 g/L whereas the maximum productivity obtained was 0.034, 0.030, and 0.014 g/L/d, respectively. D. salina grown in three different SLFs of K. alvarezii, G. acerosa and T. ornata resulted in biomass concentration of 0.534, 0.497, and 0.305 g/L and the production values obtained were 0.038, 0.035, and 0.021 g/L/d, respectively. The biochemical analysis also suggests that pigments, protein, carbohydrate and lipid contents were significantly higher than the control. Given the growth performance, physiological and biochemical response of the algae in the SLFs, the best concentration of K. alvarezii, G. acerosa and T. ornata for N. oculata growth and biomass and lipid yield were 10%, 8%, and 1%, respectively. However, for D. salina it was 10%, 6%, and 2%, respectively. Overall, the findings suggest that SLFs from red seaweeds were more efficient in enhancing the biomass production, pigment, protein, carbohydrate and lipid yield than the SLF prepared from brown seaweed signifying their potential application as an alternative to the commercial culture media.