Tapping Carbon Sequestration Potential of Blooming Macroalgae to Mitigate Climate Change

Abstract

Macroalgal mariculture is gaining global attention to achieve carbon neutrality due to its important contribution to ocean carbon sequestration. However, some wild macroalgal species (e.g., Sargassum and Ulva prolifera) exhibit strong environmental adaptability and can cause large-scale, recurrent blooms in global oceans, fueled by rising atmospheric CO2 levels and coastal eutrophication. Notably, massive Ulva prolifera green tides have occurred annually in the Yellow Sea for the past 17 consecutive years. At the late blooming stage, millions of tons of U. prolifera naturally sink to the shallow seafloor. The subsequent intense microbial aerobic degradation of sinking macroalgae results in coastal hypoxia and acidification, with most of the macroalgal carbon returning to the atmosphere. Preventing or reducing the intense degradation of massive sinking U. prolifera could enable more macroalgal carbon storage in the ocean in the long term and alleviate the harmful effects of green tide. Thus, ecological disasters from macroalgal blooms may be transformed into useful natural platforms to increase ocean carbon sequestration. We propose an integrated strategy using environmentally friendly minerals (e.g., montmorillonite and calcium carbonate) and coagulants (e.g., polyaluminum chloride), along with natural algicidal bacteria or substances, to induce rapid flocculation and sedimentation of blooming macroalgae, reduce the degradation of sinking macroalgae and its negative environmental impacts, and minimize the generation of macroalgal propagules or seeds and the potential risk for future green tide outbreaks. This integrated approach is potentially a promising approach to tap the carbon sequestration potential of macroalgal blooms to mitigate climate change.