Life-cycle environmental burdens of cultivated seaweed as blue food: The case study of Wakame and Kelp in Dalian, China

Cultivated seaweed, known as typical blue food, benefits environmental sustainability like climate change mitigation when replacing land-based food with carbon-intensive fertilizer input. However, seaweed cultivation still generates environmental burdens that remain unclear, especially in China, where approximately 60 % of global seaweed is cultured. Here, we developed life cycle assessment (LCA) models to quantitatively compare the environmental performance of two seaweed species of wakame (Undaria pinnatifida) and kelp (Saccharina japonica) cultivated by floating rafts. We also developed scenarios to examine the environmental performance by controlling the seedling density and cultivation line inputs. Results show that the environmental loads of wakame are 10–40 % higher than those of kelp, with carbon footprints of 44–59 kgCO₂e and 37–58 kgCO₂e per ton wet weight, respectively. Seaweed cultivation at sea produces the most environmental burdens. The polyethylene cultivation lines are the crucial input influencing environmental performance. Extending the service time of cultivation lines by 10 % reduces the environmental load by ∼5 % on average. Lower seedling density with fewer cultivation line inputs slightly decreases the environmental burden but with less seaweed yield. Nitrogen and phosphorus removed by seaweed harvest are two orders of magnitude lower than fertilizers applied in land cropping systems of coastal provinces but are four orders higher than the life-cycle emissions of seaweed cultivation. We reviewed the carbon footprint of previous investigations on seaweed farming to compare with ours. Our study adds new knowledge to quantitatively understand the environmental burdens of cultured seaweed (especially for wakame Undaria pinnatifida) as a blue food alternative to land-based foods.