Divergent Patterns of Metabolite Expression in Red Seaweeds (Devaleraea mollis and Palmaria hecatensis) Following Nitrate and Ammonium Supplementation

This study investigates the species-specific metabolic responses of *Devaleraea mollis* and *Palmaria hecatensis* to different nitrogen-rich formulations, revealing distinct adaptive strategies. The effects of Von Stosch Enrichment (VSE, nitrate-only), F/2 (nitrate-only), and Jack’s Special (JS, nitrate and ammonium) on metabolic profiles were evaluated. *D. mollis* demonstrated elevated levels of energy storage and growth-related metabolites, with JS notably enhancing creatine production for energy storage and regeneration, alongside increased DNA/RNA synthesis and cell division activity. This suggests that *D. mollis* prioritizes rapid growth and energy demands, supporting its broader ecological adaptability.

In contrast, *P. hecatensis* exhibited higher expression of metabolites associated with amino acid metabolism and protein synthesis, indicating a focus on efficient nitrogen utilization for protein production. This strategy is likely advantageous in low-light, high-turbidity environments. Nitrogen sources significantly influenced amino acid metabolism, with JS promoting a broader range of amino acid production, while VSE and F/2 stimulated specific metabolites.

These findings reveal species-specific metabolic patterns, highlighting *D. mollis*’s flexibility in energy utilization and *P. hecatensis*’s adaptations to protein synthesis pathways. The results emphasize the importance of tailoring nutrient formulations to species-specific requirements to optimize seaweed growth and metabolic traits in aquaculture settings. Such tailored approaches could enhance productivity and sustainability in seaweed cultivation. JH-RE-06