PERSPECTIVE • OPEN ACCESS You may also like - Effect of liquid seaweed extracts as Sinking seaweed in the deep ocean for carbon biostimulant on vegetative growth of soybean neutrality is ahead of science and beyond the Z A Noli, Suwirmen, Aisyah et al. - Kaizen implementation in seaweed ethics aquaculture (Gracilaria sp.) in Karawang, West Java: A productivity improvement case study To cite this article: Aurora M Ricart et al 2022 Environ. Res. Lett. 17 081003 F A Hasanah, M Nurhudah, M Mulyono et al. - Development and characterization of bamboo fiber reinforced biopolymer films H P S Abdul Khalil, Hazwan C I Che View the article online for updates and enhancements. Mohamad, A R Khairunnisa et al. This content was downloaded from IP address 83.43.242.15 on 12/09/2022 at 08:41 Environ. Res. Lett. 17 (2022) 081003 https://doi.org/10.1088/1748-9326/ac82ff PERSPECTIVE Sinking seaweed in the deep ocean for carbon neutrality is ahead OPEN ACCESS of science and beyond the ethics RECEIVED 2 June 2022 Aurora M Ricart1,∗, Dorte Krause-Jensen2,3, Kasper Hancke4, Nichole N Price1, Pere Masqué5,6,7 REVISED and Carlos M Duarte8 11 July 2022 1 Bigelow Laboratory for Ocean Sciences, East Boothbay, ME, United States of America ACCEPTED FOR PUBLICATION 2 Arctic Research Centre, Aarhus University, Aarhus, Denmark 21 July 2022 3 Department of Bioscience, Aarhus University, Silkeborg, Denmark PUBLISHED 4 Norwegian Institute for Water Research (NIVA), Oslo, Norway 12 August 2022 5 Institute of Environmental Science and Technology (ICTA) and Physics Department, Universitat Autònoma de Barcelona, Bellaterra, Spain Original content from 6 School of Science and Centre for Marine Ecosystems Research, Edith Cowan University, Joondalup, Western Australia, Australia this work may be used 7 International Atomic Energy Agency, Principality of Monaco, Monaco under the terms of the 8 Creative Commons Red Sea Research Center (RSRC) and Computational Bioscience Research Center (CBRC), King Abdullah University of Science and Attribution 4.0 licence. Technology (KAUST), Thuwal, Saudi Arabia ∗ Any further distribution Author to whom any correspondence should be addressed. of this work must E-mail: aricart@bigelow.org maintain attribution to the author(s) and the title of the work, journal Keywords: seaweed, carbon sink, aquaculture, governance, unintended consequences, carbon sequestration, sustainability citation and DOI. Abstract Sinking vast amounts of seaweed in the deep ocean is currently being proposed as a promising ocean carbon dioxide removal strategy as well as a natural-based solution to mitigate climate change. Still, marketable carbon offsets through large-scale seaweed sinking in the deep ocean lack documentation and could involve unintended environmental and social consequences. Managing the risks requires a number of urgent actions. The window to meet the goals of the Paris Agreement, artisanal to industrial scales. Farmed seaweeds, as well measured as remaining cumulative greenhouse gas as natural macroalgal beds, can export a fraction of (GHG) emissions to avoid trespassing the 1.5 ◦ C–2 ◦ C the carbon fixed during growth to adjacent environ- threshold of atmospheric warming, is narrow and ments (Fieler et al 2021) where a portion of this car- rapidly closing, leading to calls to urgently activate bon, either as entire thali or fragments, may occasion- all options. It is imperative to reduce emissions while ally sink to the deep ocean, and thus become removed implementing vetted carbon dioxide removal (CDR) from the short-term carbon cycle and sequestered strategies to remove excess carbon dioxide (CO2 ) (at (Krause-Jensen and Duarte 2016, Queirós et al 2019). the gigaton scale) from the atmosphere. However, Harvested seaweeds are used for human consump- most direct air carbon capture technologies are still tion and animal feed. This cannot be considered in their infancy and are operational at insufficient for carbon sequestration in the long-term, but can scale and/or involve too steep financial or environ- replace foodstuffs with higher carbon footprints, and mental costs. Many corporations and nations, com- potentially reduce enteric methane emissions from mitted to achieving carbon neutrality, are in search of ruminants (Vijn et al 2020). Seaweeds can also deliver investable carbon credits derived from nature-based high-value molecules for pharma and food industries, CDR strategies. Ocean CDR, especially related to the replace carbon intensive commodities like chemical expansion of blue carbon habitats (i.e. coastal and fertilizers and synthetic plastics, or generate biochar marine vegetated habitats), are in the spotlight. and biofuels (Duarte et al 2022). Each of these emer- In particular, seaweed farming has entered the ging markets may represent meaningful GHG emis- family of blue carbon options with large expectations sions avoidance or sequestration opportunities else- due to its scalability, and the multiple socioeconomic where in extant supply chains (figure 1). The best path benefits that can be derived generating revenue at to activate the promise of seaweed farming likely is © 2022 The Author(s). Published by IOP Publishing Ltd Environ. Res. Lett. 17 (2022) 081003 A M Ricart et al Figure 1. Conceptual diagram of the pathways for seaweed as a CDR strategy. Seaweed from farms and Sargassum mats can naturally export carbon, where a fraction sinks into shallow and deep sediments. Harvested seaweed can be allocated for assisted sinking in deep sediments. However, scientific evidence on its effectiveness as a CDR strategy is lacking and it needs development of specific regulations to be implemented. Alternatively, uses of harvested seaweed can be optimized as a CDR strategy and utilization technology of low carbon footprint which also will help advance numerous UN SDGs. to develop it both as a CDR strategy and utilization (Fidai et al 2020), is also attracting attention in the technology of low carbon footprint. However, motiv- carbon crediting context (Bach et al 2021). ated by quick investment returns from carbon cred- Hence, the deliberate sinking of seaweed in the its and the desire to act quickly, some are eager to deep-sea has been proposed as a climate mitiga- purposefully sink the entirety of the harvested bio- tion strategy to capitalize on the scalability of sea- mass of seaweed, both farmed and wild, into the deep weed farming, including the growing masses of ocean (i.e. below 2000 m for maximized efficiency floating Sargassum (National Academies of Sciences based on Baker et al 2022). Engineering and Medicine 2021), and is garner- We reflect on risks stemming from scientific ing media, scientific, philanthropic, and commercial knowledge gaps and the lack of governance related attention. Coupled with a roaring demand for carbon to large-scale seaweed sinking, and consider ethical credits linked to the wave of carbon neutrality pledges concerns. in the private sector, many entrepreneurs and private companies are emerging that offer rapid solutions at scale from sinking seaweed in the deep sea (figure 2). 1. Seaweed carbon as an emerging The seaweed sinking strategy appears very attract- opportunity ive at first blush: a natural, but manipulatable solu- tion that reduces atmospheric CO2 levels, is easily Traditional natural blue carbon habitats (seagrass, measurable and can be valorized ($ ton−1 of CO2 - saltmarshes, mangroves) are the focus of conserva- equivalent or $ kg−1 of seaweed sunk), with expected tion and restoration projects for gaining carbon cred- increases in the value of carbon. The increasing uncer- its. However, these habitats are restricted to a nar- tainty surrounding terrestrial carbon capture options row belt along the shore and occupy <0.2% of the due to space limitations, wildfires and other cata- ocean surface (Duarte et al 2013). Seaweed aquacul- strophic events that release captured GHGs further ture represents a more scalable opportunity (Duarte points to farming and sinking seaweed as an appeal- et al 2017), since the areas suitable for seaweed ing alternative to investors. It has all the ingredi- cultivation can extend far offshore (Froehlich et al ents for success, and so, the seaweed sinking market 2019) within precautionary limits that avoid unin- has already emerged. The current discussion on CDR tended consequences on the environment (Duarte strategies is being capitalized on by Western coun- et al 2022). Additionally, floating Sargassum, which tries, and the US and UK are at the forefront regarding recently has been observed expanding across the trop- the number of companies offering seaweed sinking ical Atlantic Ocean causing unprecedented landings options for carbon removal (figure 2). Most of them of nuisance macroalgal mats in different continents have large institutional investors behind. 2 Environ. Res. Lett. 17 (2022) 081003 A M Ricart et al Figure 2. Location of global seaweed aquaculture production and private companies offering seaweed sinking for carbon neutrality. Data for global seaweed production comes from FAO 2021 www.fao.org/fishery/statistics-query/en/aquaculture/ and is presented in two ways: fresh biomass (yellow bars) and economic value (blue bars). Yellow bars represent average production per year in the last five years (2015–2019) in tonnes of fresh weight using a logarithmic transformation. Blue bars represent average value per year in the last five years (2014–2019) in USD × 1000 using a logarithmic transformation. The vertical dotted line represents the amount of annual seaweed production required for the removal of 0.1 Gt of carbon dioxide (CO2 ), see details in main text. The subplot map highlights the number of countries (n = 54) with seaweed production reported to FAO in the last five years (2015–2019) and the number of countries (n = 6) with registered private companies or startups offering seaweed sinking for carbon benefits as of 21st of December 2021. For the latter, information comes from a search in CDR project databases (carbonplan.org, airminers.org, Stripe Negative Emissions Purchase, Microsoft Carbon Removal Request for Proposals) and Google (words: ‘seaweed sinking deep ocean carbon dioxide removal’). 2. Potential risks and lack of scientific Academies of Sciences Engineering and Medicine evidence 2021). Moreover, not all seaweed ecosystems, farmed or wild, may sequester carbon (Gallagher et al 2022) Currently, science cannot discern the impacts of and it is not known with confidence how much and large-scale seaweed sinking in the ocean for mar- for how long sunk seaweed will store carbon in the ine life or the carbon cycle. The ecological carry- deep ocean, and what will be the turnover rate, which ing capacity of both large-scale offshore farming and likely will depend on the location (Siegel et al 2021). large-scale sinking is unresolved. The consequences The scientific community, in a clear example of for primary productivity in the upper ocean and asso- producing demand-driven research, is in the process ciated food webs (e.g. from diverting nutrients into of identifying the best approaches to test the reliabil- large scale production of seaweed), as well as the ity and impacts of sinking seaweed. This is an essential impacts of large seaweed biomass to deep-sea bio- step forward. Here, we alert that the race to sink sea- logical communities (e.g. from oxygen depletion), weed in the ocean is outpacing the rate of progress of are largely unknown (Campbell et al 2019, National the essential science to assess risks, surging past even 3 Environ. Res. Lett. 17 (2022) 081003 A M Ricart et al perfunctory evaluation of the environmental impacts These include zero hunger (SDG2), good health and social benefits. This lack of scientific evidence and well-being (SDG3), affordable and clean energy and of peer-reviewed procedures to verify success of (SDG7), climate action (SDG13) and life below water the practice, however, has not prevented the private (SDG14); which provide integrative benefits contrib- sector from currently offering carbon removal from uting to additional SDGs (Duarte et al 2022). Despite sinking seaweed as an attractive marketable product its sustainability potential, social license for the sea- where millions $USD have already been invested. weed aquaculture sector hinders its growth (Billing et al 2021). Sinking seaweed for a poorly documented 3. Lack of governance regarding climate benefit will likely be met with increasing large-scale seaweed sinking social opposition. In recent human history, we have seen other Seaweed farming is a multibillion-dollar industry examples of natural food resources being deviated (figure 2) and the fastest-growing aquaculture sec- to climate-related actions with negative consequences tor worldwide. For the most part, seaweed cultiva- for communities that depend on them. The sudden tion activities in territorial waters are regulated in interest in sinking seaweed, that otherwise is usable the same way as shellfish farming (Wood et al 2017, and has market value, mirrors the biofuel race a few Billing et al 2021), and there are no explicit regula- decades ago, where the price of flour increased due tions regarding sinking seaweed in the deep ocean at to competing demands of crops for biofuel. Devel- any national or international level, although there are oping seaweed farming, both as a CDR strategy and international policy instruments that may apply: The an industry for resource production and use in par- United Nations Convention on the Law of the Sea, the allel, could have a positive social impact by enhan- Convention on Biological Diversity, and the London cing both the blue economy and the green shift, and Convention (1972) and its modernization under the possibly avoid negative social consequences. But the London Protocol (1996). Under the London Protocol, framework should be to achieve UN SDGs goals as a all dumping into the ocean is prohibited, except for whole, not solely climate action (Duarte et al 2022). acceptable wastes, including organic material of nat- ural origin. But, if the objective of farmed seaweed is 5. A call to action to sink it for financial gain through carbon credits, should the valued biomass be considered waste? Spe- Managing the risks from the growing drive toward cific regulations designating harvested biomass status sinking seaweed as a CDR strategy requires a number are required, particularly if negative environmental of urgent actions: and social impacts are anticipated. Further, in-depth, third-party environmental impact assessments will be crucial. Similarly, accreditors of carbon credits should • Advance the scientific understanding of sinking enforce reliable verification processes and hold com- seaweed as a CDR strategy (scope and duration) panies accountable for the accuracy and precision of and the associated ecological impacts. The develop- estimations of carbon removal. ment of comprehensive estimates of regionally spe- Commensurate with emergent scientific evid- cific carrying capacity for large-scale seaweed farm- ence, urgently needed is a plural oversight approach ing, and informed assessments of where seaweed that embraces and coordinates the diversity of actors: sinking trials are best executed, are critical elements governments, managers, civil society (as consumers to inform regulations. and final beneficiaries) and the private sector. All of • Generate robust estimates of the spatial area neces- these play a vital role in climate action governance. sary to grow enough seaweed to sink in a way that is climatically effective, as well as estimates 4. Ethical considerations of area availability. A recent exercise in this sense (National Academies of Sciences Engineering and The disposal of a valuable, nutritional and biomater- Medicine 2021) suggests a required farming area of ial resource in the deep ocean in a world suffering 7.3 million hectares for CDR-worthy gigaton levels from hunger and a sustainability crisis needs care- (0.1 Gt CO2 sequestered per year = seaweed pro- ful ethical consideration. The agriculture capacity to duction of 0.033 PgC yr−1 ), which would require meet demands from the growing human population the entire current global annual aquaculture pro- for food and materials is forecasted to become lim- duction (figure 2) to be sunk. Estimates for carbon ited (Duarte et al 2009). Seaweed cultivation, for cen- neutrality suggest even larger areas and seaweed turies a common practice in East Asia, has recently production (Gao et al 2022a). However, the uncer- gained increased attention globally for its great poten- tainty around these estimates is very large, and tial to meet these challenges (Duarte et al 2022). layered seaweed cultivation systems are in develop- Seaweed farming has the capacity to meet multiple ment that would modify these estimates. goals contributing to advance a number of the United • Craft sustainability and ethical standards for large- Nations Sustainable Development Goals (UN SDGs). scale natural nuisance or farmed seaweed sinking 4 Environ. Res. Lett. 17 (2022) 081003 A M Ricart et al including socioeconomic and climate benefits that 2050 Seaweed Project. The IAEA is grateful for consider all applicable UN SDGs. the support provided to its Marine Laboratories • Develop and vet reproducible and species-specific by the Government of the Principality of Monaco. methodologies to verify carbon credits from sea- A M R and N P were supported by the World Wild weed sinking that considers various current farm- Fund (WWF) with support from Earth Bezos Fund. ing practices. Aside from sinking the entire crop, D K J was supported by the European Union H2020 seaweed farming presents other opportunities for (FutureMARES, Contract #869300). K H was sup- CDR through pathways not currently accoun- ported by the Norwegian Institute for Water Research ted for (figure 1). For instance, consideration for (NIVA). carbon sequestration purposes should be given to non-edible parts of the seaweed which are Author contributions currently culled and dumped during harvest as they are difficult to commercialize (e.g. holdfasts, All authors contributed to conceptualization and biofouled fronds, excess product). Similarly, sed- investigation. A M R led the writing of the original iments underneath farms could also be accumu- draft and all co-authors contributed to review and lating and storing carbon. Gaining carbon cred- editing. its from these pathways represents an unrealized, existing opportunity at no change in current activ- Conflict of interest ities and their impacts that needs to be explored. • Synthesize life cycle assessments (LCAs) to account Authors declare that they have no competing for total GHG emissions. These ‘sinking of farmed interests. seaweed’ LCAs need to be juxtaposed against the same assessments for sinking nuisance seaweed and against farmed seaweed biomass utilization ORCID iD strategies that avoid or sequester GHGs elsewhere in food, feed, plastic, or fuel supply chains to Aurora M Ricart  https://orcid.org/0000-0001- fully understand trade-offs and determine the most 7769-1661 cost-effective CDR strategies. • Consider all potential options that seaweeds offer References as a natural-based solution to reduce CO2 emis- sions. From integrating all seaweed uses (e.g. food, Bach L T, Tamsitt V, Gower J, Hurd C L, Raven J A and Boyd P W biofuel) and their specific temporal scale of car- 2021 Testing the climate intervention potential of ocean afforestation using the Great Atlantic Sargassum Belt Nat. bon sequestration in estimates of carbon neutral- Commun. 12 2556 ity, to considering the role of all carbon pathways Baker C A, Martin A P, Yool A and Popova E 2022 Biological from seaweed cultivation, including lost particle carbon pump sequestration efficiency in the North Atlantic: organic carbon and excreted dissolved organic car- a leaky or a long-term sink? Glob. Biogeochem. Cycles 36 e2021GB007286 bon, which are usually overlooked (Duarte et al Billing S-L, Rostan J, Tett P and Macleod A 2021 Is social license 2022, Gao et al 2022b). to operate relevant for seaweed cultivation in Europe? Aquaculture 534 736203 In conclusion, the urgency to find solutions that Campbell I, Macleod A, Sahlmann C, Neves L, Funderud J, help stem climate change does not justify the delib- Øverland M, Hughes A D and Stanley M 2019 The environmental risks associated with the development of erate sinking of seaweed in the deep ocean without seaweed farming in Europe-prioritizing key knowledge gaps properly assessing the consequences. Investment is Front. Mar. Sci. 6 107 best spent on advancing practical knowledge, not on Duarte C M, Bruhn A and Krause-Jensen D 2022 A seaweed unfounded promises of carbon sequestration. aquaculture imperative to meet global sustainability targets Nat. Sustain. 5 185–93 Duarte C M, Holmer M, Olsen Y, Soto D, Marbà N, Guiu J, Data availability statement Black K and Karakassis I 2009 Will the oceans help feed humanity? Bioscience 59 967–76 All data supporting this study is publicly available and Duarte C M, Losada I, Hendriks I, Mazarrasa I and Marbà N 2013 The role of coastal plant communities for climate change data sources can be found in the main text and refer- mitigation and adaptation Nat. Clim. Change 3 961–8 ences. Duarte C M, Wu J, Xiao X, Bruhn A and Krause-Jensen D 2017 No new data were created or analysed in this Can seaweed farming play a role in climate change study. mitigation and adaptation? Front. Mar. Sci. 4 100 Fidai Y A, Dash J, Tompkins E L and Tonon T 2020 A systematic review of floating and beach landing records of Sargassum Acknowledgments beyond the Sargasso Sea Environ. Res. Commun. 2 122001 Fieler R, Greenacre M, Matsson S, Neves L, Forbord S and Hancke K 2021 Erosion dynamics of cultivated kelp, This work originated in a research workshop at Saccharina latissima, and implications for environmental the International Atomic Energy Agency (IAEA) in management and carbon sequestration Front. Mar. Sci. Monaco, November 2021, organized by the Oceans 8 632725 5 Environ. Res. Lett. 17 (2022) 081003 A M Ricart et al Froehlich H E, Afflerbach J C, Frazier M and Halpern B S 2019 National Academies of Sciences Engineering and Medicine 2021 A Blue growth potential to mitigate climate change through Research Strategy for Ocean-based Carbon Dioxide Removal seaweed offsetting Curr. Biol. 29 3087–93.e3 and Sequestration (Washington, DC: The National Gallagher J B, Shelamoff V and Layton C 2022 Seaweed Academies Press) ecosystems may not mitigate CO2 emissions ICES J. Mar. Queirós A M et al 2019 Connected macroalgal-sediment systems: Sci. 79 585–92 blue carbon and food webs in the deep coastal ocean Ecol. Gao G, Beardall J, Jin P, Gao L, Xie S and Gao K 2022a A review of Monogr. 89 e01366 existing and potential blue carbon contributions to climate Siegel D A, DeVries T, Doney S C and Bell T 2021 Assessing the change mitigation in the Anthropocene J. Appl. Ecol. sequestration time scales of some ocean-based carbon 59 1686–99 dioxide reduction strategies Environ. Res. Lett. 16 104003 Gao G, Gao L, Jiang M, Jian A and He L 2022b The potential of Vijn S et al 2020 Key considerations for the use of seaweed to seaweed cultivation to achieve carbon neutrality and reduce enteric methane emissions from cattle Front. Vet. Sci. mitigate deoxygenation and eutrophication Environ. Res. 7 597430 Lett. 17 014018 Wood D, Capuzzo E, Kirby D, Mooney-McAuley K and Krause-Jensen D and Duarte C M 2016 Substantial role of Kerrison P 2017 UK macroalgae aquaculture: what are the macroalgae in marine carbon sequestration Nat. Geosci. key environmental and licensing considerations? Mar. Policy 9 737–42 83 29–39 6