Assessment of carbon sink potential and methane reduction scenarios of marine macroalgae(Gracilaria)cultivation

Marine macroalgae cultivation is an important part of the effort to address climate change through carbon sinks.Gracilaria,especially Gracilaria lemaneiformis and Gracilaria lichenoides are the major macroalgae cultivated in China.This study proposes a method to assess the net carbon sink of marine macroalgae(Gracilaria)cultivation.First,the net carbon sink of Gracilaria cultivation in China is calculated based on the yield of annual cultivated Gracilaria recorded in China Fishery Statistical Yearbook from 2011 to 2020.Next,we predict the net carbon sink trend of Gracilaria cultivation from 2021 to 2030 using the autoregressive integrated moving average model(ARIMA).Finally,the potential carbon sink increase and methane reduction related to Gracilaria cultivation in China is explored through a scenario analysis.We find that the net carbon sink of Gracilaria cultivation in China was about 32.1-92.4 kilotons per year from 2011 to 2020,and shows a great annual growth trend.Moreover,the predicted net carbon sink of Gracilaria cultivation would increase to 77.8-191.4 kilotons per year from 2021 to2030,thereby could contribute considerably in the achievement of China's carbon peak goal.Under a scenario of producing ruminant green feed with additional Gracilaria cultivation,each ton of macroalgae is predicted to reduce carbon emission(i.e.,methane)by 0.33-0.68 tons.Thus,marine macroalgae cultivation might form a synergistic chain of"carbon sink increase-water purification-economy-methane reduction".This study proposes a synergistic new model that operates through marine macroalgae cultivation,economic aquaculture,and green feed production.