Abstract:Ulva prolifera is the main species in green tides and also an important marine carbon sink organism. It is characterized by fast growth, diverse reproductive modes, and strong resistance to stress. It can form a large-scale biomass in a short time. We review the carbon fixation features in the growth and drift of U. prolifera. It possesses a unique high pH induced HCO3– assimilation mechanism, which can promote CO2 absorption from the air by floating U. prolifera. Moreover, it utilizes the Hatch-Slack Cycle (C4) to enhance carbon fixation rate under high light irradiation conditions. The diverse carbon assimilation and sequestration mechanisms enhance photosynthetic carbon sequestration ability and help the quick accumulation of floating algal biomass. These abilities make the carbon sequestrating efficiency of U. prolifera significantly higher than that of Saccharina japonica, Undaria pinnatifida, and Porphyra haitanensis. Since 2007, the largest green tide in the world occurred in the Yellow Sea and persisted over 15 years. The average annual distribution area of U. prolifera was greater than 30 000 square kilometers, with an average annual coverage area in excess of 500 square kilometers. The average annual outbreak of U. prolifera had a biomass greater than 1.5 million tons. The net carbon sequestration from 2008 to 2020 was estimated to be 25 000~275 000 tons, averaging over 78 000 tons. This figure is higher than that of Gracilaria, P. haitanensis, and U. pinnatifida, and only second to that of S. japonica. The great biomass and strong carbon sequestration ability of U. prolifera has made it a potential new and important marine carbon sink and carbon storage pathway. We suggest strengthening the salvage and resource utilization of U. prolifera. This approach is a win-win situation for carbon utilization and eutrophication removal. These measures will promote the green tide U. prolifera carbon sink in joining the carbon market as soon as possible, to become a new low-carbon economic resource.
