Sustainable cultivation of Gracilaria edulis in poultry manure-derived media: Evaluating growth, biochemical properties, and agar quality

Abstract

Present study investigates the potential of Gracilaria edulis, a red seaweed and a valuable source of food grade agar, to mass generate seedlings without stimulants, to grow and produce biomass in poultry manure derived nutrients, and to possess industry standard physico-chemical & proximate compositional biochemical attributes post-cultivation. From this study, for the purpose of producing clonal planting material, G. edulis explants showed near 100 % regeneration in seedling development in incubation in PES medium. Simple and yet efficient water-sonicate method extracted substantial amount of nutrients from the poultry manure, and the resultant formulated poultry manure aqueous-sonicate extract supplemented seawater, in short PMES, was enriched with significant levels of micronutrients (Cu–5.3 µM, Zn–11.7 µM and Mn–28.4 µM), and macronutrients (N: 311–1555 µM and P: 12–63 µM) compared to sole seawater. In incubation with various concentration of PMES (1–5 %, v/v), G. edulis seedlings exhibited robust growth characteristics across all the PMES, with the highest daily growth rate (9.9 ± 0.9 % day⁻¹) and biomass yield (202.5 ± 12.6 mg dry weight L⁻¹) observed in 2 % PMES, which significantly surpassing the growth characteristics of G. edulis seedlings grown in sole seawater as growth medium. Resultant G. edulis produced biomass from this study had superior oil-holding capacity (3.60 g/g dry weight), substantial soluble polysaccharide content (31.47 % of dry weight), and ash content (44.93 % of dry weight), alongside considerable crude fibre content (7.73 % of dry weight) compared to wild G. edulis and other commercially important seaweeds. Moreover, the biomass had 26 % agar which was substantial and higher than that of its wild counterparts, with the extracted agar displaying characteristic functionalities, as confirmed by infrared spectroscopy and thermal analysis, comparable to commercial agar. These findings demonstrate that G. edulis as novel macroalgae and PMES as a sustainable cost-effective growth medium for seaweed cultivation, offering promising implications in agar and seaweed food industry.