Seaweed-derived biostimulants differentially enhance growth, nutritional composition, antioxidant capacity, and sensory quality of cultivated Caulerpa racemosa

Abstract Seaweed-derived biostimulants offer a promising strategy to enhance the productivity and functional quality of edible seaweeds. This study evaluated the effects of aqueous extracts from Halymenia sp., Halimeda sp., Sargassum sp., Kappaphycus sp., and Gracilaria sp. on the growth, biochemical composition, nutritional quality, antioxidant properties, and sensory acceptance of cultivated Caulerpa racemosa under controlled 35-day laboratory culture conditions. All extracts contained detectable phytohormones (indole-3-acetic acid, kinetin, zeatin, and gibberellic acid) as quantified by HPLC. Among the treatments, Halymenia extract produced the highest absolute growth (155.02 ± 25.00 g), specific growth rate (4.02 ± 0.35% day −1 ), chlorophyll accumulation, total amino acids (50.12 mg g −1 DW), protein level (11.37% DW), mineral enrichment, and sensory acceptance, which correlates strongly with growth-oriented primary metabolism. In contrast, Sargassum and Gracilaria extracts were more strongly associated with secondary metabolic and antioxidant-related responses, including higher total phenolic content, carotenoids, polyunsaturated fatty acids, and radical-scavenging activity. Crucially, Halymenia extract optimized the dietary Na/K ratio to 1.12 (compared with 3.72 in control), highlighting its potential to produce health-beneficial, low-sodium edible sea grapes. These findings demonstrate that species-specific seaweed extracts correlate with distinct physiological and biochemical responses in C. racemosa , providing baseline evidence of biostimulatory potential for cross-phylum macroalgal biostimulation in controlled aquaculture systems.