This chapter presents a dynamic multi-scale model for macroalgae cultivation and marine nitrogen bio-sequestrationN bio-sequestration, integrating processes from the cellular metabolism of Ulva sp. to farm-scale nutrient dynamics. The model accounts for light extinction at the reactor scale (1 m) and nutrient absorption at the farm scale (1 km), offering a comprehensive simulation framework for optimizing seaweed farming for both biomass production and eutrophication mitigation. The calibration process was conducted using experimental data from a near-shore reactor system, refining parameters through a sensitivity analysis and optimizing growth function inputs. The model was then applied to simulate seasonal productivitySeasonal productivity, nitrogen sequestration potential, and the necessary farm size for reducing environmental nitrogen levels. Results indicate significant seasonal variations in both biomass yield and nitrogen uptake, highlighting the importance of adjusting farm operations throughout the year. Additionally, spatial effects such as dilutionDilution effects and airlift pumping were analyzed, showing their influence on nutrient availability, biomass composition, and overall farm efficiency. The findings emphasize that precision aquaculture techniques can enhance macroalgae farmingMacroalgae farming sustainability, maximizing economic and ecological benefits. This model serves as a decision-support tool for designing large-scale seaweed farms with applications in carbon sequestration, bioeconomy, and coastal water management.