Finnley W. R. Ross1*, Philip W. Boyd2, Karen Filbee-Dexter3a,3b, Kenta Watanabe4, Alejandra Ortega5, Dorte Krause-Jensen6a,6b, Catherine Lovelock7, Calvyn F.A. Sondak8a,8b, Lennart T. Bach2, Carlos M. Duarte9a,9b, Oscar Serrano10a,10b, John Beardall11a,11b, Patrick Tarbuck12, Peter I. Macreadie1
1 Centre for Integrative Ecology, School of Life and Environmental Sciences, Deakin University, Burwood Campus, Burwood VIC, Australia, 2Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia, 3aInstitute of Marine Research, 4817, His, Norway, 3bUWA Oceans Institute, University of Western Australia, Crawley, WA, 6009, Australia, 4Coastal and Estuarine Environment Research Group, Port and Airport Research Institute, 3-1-1 Nagase, Yokosuka, 239-0826, Japan, 5King Abdullah University of Science and Technology, Thuwal, Saudi Arabia, 6aDepartment of Ecoscience, Aarhus University, Ole Rømers Allé, building 1131, Aarhus C, 8000, Denmark, 6bArctic Research Centre, Aarhus University, Ole Worms Allé 1, Aarhus C, 8000, Denmark, 7School of Biological Sciences, The University of Queensland, St Lucia, QLD, 4072, Australia, 8aDepartment of Oceanography, Pusan National University, Busan, 46241, South Korea, 8bFaculty of Fisheries and Marine Science, Sam Ratulangi University, Manado, 95115, Indonesia, 9aKing Abdullah University of Science and Technology, Red Sea Research Center (RSRC), 9bComputational Bioscience Research Center (CBRC), Thuwal, Saudi Arabia, 10aCentro de Estudios Avanzados de Blanes, Consejo Superior de Investigaciones Científicas (CEAB-CSIC), Blanes, Spain, 10bSchool of Science & Centre for Marine Ecosystems Research, Edith Cowan University, Joondalup, WA, Australia, 11aSchool of Biological Sciences, Monash University, Clayton, Australia 3800, 11bFaculty of Applied Sciences, UCSI University, Kuala Lumpur, Malaysia, 12Sea Green Pte. Ltd., 60 Paya Lebar Road #06-12, Paya Lebar Square, Singapore 409051
* Correspondence: Finnley W. R. Ross, fwross@deakin.edu.au
A topical and contentious question is: Can seaweeds’ contribution to climate change mitigation be enhanced at globally meaningful scales? There are four categories where seaweed has been suggested to be used for climate change mitigation: 1) protecting and restoring wild seaweed forests; 2) expanding sustainable nearshore seaweed aquaculture; 3) offsetting industrial CO2 emissions using seaweed products for emission abatement; and 4) sinking seaweed into the deep sea to sequester CO2. Uncertainties remain about quantification of the net impact of carbon export from seaweed restoration and seaweed farming sites on atmospheric CO2. Evidence suggests that nearshore seaweed farming contributes to carbon storage in sediments below farm sites, but how scalable is this process? Products from seaweed aquaculture, such as the livestock methane-reducing seaweed Asparagopsis or low carbon food resources show promise for climate change mitigation, yet the carbon footprint and emission abatement potential remains unquantified for most seaweed products. Similarly, purposely cultivating then sinking seaweed biomass in the open ocean raises ecological concerns and the climate change mitigation potential of this concept is poorly constrained. Improving the tracing of seaweed carbon export to ocean sinks is a critical step in seaweed carbon accounting. Despite carbon accounting uncertainties, seaweed provides many other ecosystem services that justify conservation and restoration and the uptake of seaweed aquaculture will contribute to the United Nations Sustainable Development Goals. However, we caution that verified seaweed carbon accounting and associated sustainability thresholds are needed before large-scale investment into climate change mitigation from seaweed projects.