Edible macroalgal cultivation is increasingly promoted as a nature-based solution to mitigate coastal eutrophication and improve seawater quality. However, the species-specific impacts and spatial extent of these ecological effects remain poorly understood, particularly in semi-enclosed bays with complex hydrodynamics. This study aims to quantify the biogeochemical influence of two widely cultivated species—Porphyra haitanensis and Hizikia fusiformis—on seawater carbonate chemistry and nutrient levels in Yueqing Bay, eastern China. High-resolution field surveys were conducted at 52 stations, enabling direct comparisons between cultivated and non-cultivated waters. Geostatistical modeling, including spherical semivariograms and Empirical Bayesian Kriging, was applied to delineate species-specific influence zones and quantify changes in key water quality parameters. P. haitanensis farming induced broad, kilometer-scale improvements in seawater chemistry, including elevated dissolved oxygen (DO) (+ 2.72%) and pH (+ 0.09 units), and significantly lower partial pressure of CO2 (pCO2) (− 118 µatm), relative to distant reference sites (all p < 0.05). A slight increase in total phosphorus (TP) (+ 0.007 mg L− 1) was also observed, likely reflecting nearby riverine inputs. In contrast, H. fusiformis cultivation produced more localized (< 100 m) but significant changes, including reductions in dissolved inorganic carbon (DIC) (− 1.84 mg L− 1) and pCO2 (− 82.6 µatm), alongside increases in DO (+ 1.72%), pH (+ 0.02 units), and chlorophyll-a (Chl-a) (+ 0.72 µg L− 1) (all p < 0.05). These results provide the first fine-scale, species-resolved spatial assessment of macroalgal farming effects on water quality in a semi-enclosed bay. By quantifying distance-dependent ecological responses, this study offers science-based guidance for spatial planning, nutrient management, and blue carbon integration—particularly as the routine harvest of biomass facilitates net carbon export from coastal waters. These findings highlight the potential of macroalgal farming as a scalable, multifunctional nature-based solution for sustainable aquaculture and climate mitigation.
Wu Z., Cai C., Ye Z., Wang N., Zhu Y., Jin R., Christakos G., Chen S., Wang D., Zhu J., He J., Agusti S., Duarte C. M. & Wu J., in press. Macroalgae farming increases DO and pH, reduces pCO2 and nutrients, and enhances blue carbon potential. Earth Systems and Environment. Article.
