Substantial role of macroalgae in marine carbon sequestration

Journal name:
Nature Geoscience
Year published:
Published online


Vegetated coastal habitats have been identified as important carbon sinks. In contrast to angiosperm-based habitats such as seagrass meadows, salt marshes and mangroves, marine macroalgae have largely been excluded from discussions of marine carbon sinks. Macroalgae are the dominant primary producers in the coastal zone, but they typically do not grow in habitats that are considered to accumulate large stocks of organic carbon. However, the presence of macroalgal carbon in the deep sea and sediments, where it is effectively sequestered from the atmosphere, has been reported. A synthesis of these data suggests that macroalgae could represent an important source of the carbon sequestered in marine sediments and the deep ocean. We propose two main modes for the transport of macroalgae to the deep ocean and sediments: macroalgal material drifting through submarine canyons, and the sinking of negatively buoyant macroalgal detritus. A rough estimate suggests that macroalgae could sequester about 173 TgC yr−1 (with a range of 61–268 TgC yr−1) globally. About 90% of this sequestration occurs through export to the deep sea, and the rest through burial in coastal sediments. This estimate exceeds that for carbon sequestered in angiosperm-based coastal habitats.

At a glance


  1. Map of the locations where macroalgal carbon storage has been reported.
    Figure 1: Map of the locations where macroalgal carbon storage has been reported.

    The types of macroalgae are indicated for observations from sediment traps that are in the water column, on the sediment surface and buried in sediments. Inset, the frequency distribution of the water depths of macroalgae observations, with the majority representing the deep sea (<1,000 m). All references of observations are available in Supplementary Table 1.

  2. Conceptual diagram of the pathways for export and sequestration of macroalgal carbon.
    Figure 2: Conceptual diagram of the pathways for export and sequestration of macroalgal carbon.

    Air bladders are common among brown algal taxa and facilitate their long-range transport (i). Langmuir circulation forms windrows of macroalgae (ii) and can force the algae to depths where water pressure makes the air bladders burst and the algae then sink. Macroalgal carbon can be sequestered either via burial in the habitat or by transport to the deep sea where it is sequestered whether buried or not (iii).

  3. Pathways for the sequestration of macroalgal carbon in the ocean.
    Figure 3: Pathways for the sequestration of macroalgal carbon in the ocean.

    Each step of the carbon flow from global macroalgal net primary production (NPP) to carbon sequestration (in blue) is supported by the literature or inferred by a difference between a total and subcomponents supported by literature (Table 1). The means (with 25 to 75% quartile ranges in parentheses) shown are derived from an uncertainty propagation analysis (Methods), except for those fluxes not conducive to carbon sequestration (all values are in TgC yr−1). As the estimates have been derived independently, their total does not necessarily match to the mean global NPP estimate. Grazing (33.6% of the NPP) and remineralization (37.3% of the NPP) in the algal bed are adopted from a previous budget7.


  1. Duarte, C. M., Middelburg, J. & Caraco, N. Major role of marine vegetation on the oceanic carbon cycle. Biogeosciences 2, 18 (2005).
  2. Nellemann, C. et al. Blue Carbon: a Rapid Response Assessment (United Nations Environment Programme, 2009).
  3. Mcleod, E. et al. A blueprint for blue carbon: toward an improved understanding of the role of vegetated coastal habitats in sequestering CO2. Front. Ecol. Environ. 7, 362370 (2011).
  4. Duarte, C. M., Losada, I. J. Hendriks, I. E. Mazarrasa I. & Marbà. N. The role of coastal plant communities for climate change mitigation and adaptation. Nat. Clim. Change 3, 961968 (2013).
  5. Blue Future: coastal wetlands can have a crucial role in the fight against climate change. Nature 529, 255256 (2016).
  6. Smith, S. V. Marine macrophytes as a global carbon sink. Science 211, 838840 (1981).
  7. Duarte, C. M. & Cebrián, J. The fate of marine autotrophic production. Limnol. Oceanogr. 41, 17581766 (1996).
  8. Hill, R. et al. Can macroalgae contribute to blue carbon? an Australian perspective. Limnol. Oceanogr. 60, 16891706 (2015).
  9. Hardison, A. K. et al. Microphytobenthos and benthic macroalgae determine sediment organic matter composition in shallow photic sediments. Biogeosciences 10, 55715588 (2013).
  10. Krumhansl, K. A. & Scheibling, R. E. Production and fate of kelp detritus. Mar. Ecol. Prog. Ser. 67, 281302 (2012).
  11. Filbee-Dexter, K. & Scheibling, R. E. Detrital kelp subsidy supports high reproductive condition of deep-living sea urchins in a sedimentary basin. Aquat. Biol. 23, 7186 (2014).
  12. Barron, C., Apostolaki, E. T. & Duarte, C. M. Dissolved organic carbon fluxes by seagrass meadows and macroalgal beds. Front. Mar. Sci. 1, 42 (2014).
  13. Barrón, C. & Duarte, C. M. Dissolved organic carbon pools and export from the coastal ocean. Glob. Biogeochem. Cycles 29, 17251738 (2015).
  14. Reed, D. C. et al. Patterns and controls of reef-scale production of dissolved organic carbon by giant kelp Macrocystis pyrifera. Limnol. Oceanogr. 60, 19962008 (2015).
  15. Sondak, C. F. & Chung, I. K. Potential blue carbon from coastal ecosystems in the Republic of Korea. Ocean Sci. J. 50, 18 (2015).
  16. van der Heijden, L. H. & Kamenos, N. A. Reviews and syntheses: calculating the global contribution of coralline algae to carbon burial. Biogeosciences 12, 64296441 (2015).
  17. Trevathan-Tackett, S. M. et al. Comparison of marine macrophytes for their contributions to blue carbon sequestration. Ecology 96, 30433057 (2015).
  18. Fraser, C. I. in Seaweed Phylogeography (ed. Fraser C. I.) Ch. 5, 131146 (Springer, 2016).
  19. Macaya, E. C., López, B., Tala, F., Tellier, F. & Thiel, M. in Seaweed Phylogeography (ed. Fraser C. I.) Ch. 4, 97130 (Springer, 2016).
  20. Garden, C. J. & Smith, A. M. Voyages of seaweeds: The role of macroalgae in sediment transport. Sediment. Geol. 318, 19 (2015).
  21. Wolff, T. The systematics and biology of bathyal and abyssal Isopoda Aselotta. Galathea Rep. 6, 1320 (1962).
  22. Fabry, V. J. & Deuser, W. G. Aragonite and magnesian calcite fluxes to the deep Sargasso Sea. Deep Sea Res. 38, 713728 (1991).
  23. Han, T. & Runnegar, B. Megascopic eukaryotic algae from the 2.1-billion-year-old Negaunee Iron-Formation, Michigan. Science 257, 232235 (1992).
  24. Sun, Y., Mao, S., Wang, F., Peng, P. & Chai, P. Identification of the Kukersite-type source rocks in the Ordovician stratigraphy from the Tarim Basin, NW China. Chinese Sci. Bull. 58, 44504458 (2013).
  25. Xie, X. et al. Petrology and hydrocarbon potential of microalgal and macroalgal dominated oil shales from the Eocene Huadian Formation, NE China. Int. J. Coal Geol. 124, 3647 (2014).
  26. Renaud, P. E., Løkken, T. S., Jørgensen, L. L., Berge, J. & Johnson, B. J. Macroalgal detritus and food-web subsidies along an Arctic fjord depth-gradient. Front. Mar. Sci. 2, 31 (2015).
  27. Chikaraishi Y. in Treatise on Geochemistry 5: Organic Geochemistry (eds Birrer, B. et al.) Ch. 12.5, 95123 (Elsevier, 2014).
  28. De Leo, F. C., Smith, C. R., Rowden, A. A., Bowden, D. A. & Clark, M. R. Submarine canyons: hotspots of benthic biomass and productivity in the deep sea. Proc. R. Soc. B. 277, 27832792 (2010).
  29. Canals, M. et al. Flushing submarine canyons. Nature 444, 354357 (2006).
  30. Harrold, C. & Lisin, S. Radio-tracking rafts of giant kelp: local production and regional transport. J. Exp. Mar. Biol. Ecol. 130, 237251 (1989).
  31. Palanques, A. et al. Downward particle fluxes and sediment accumulation rates in the western Bransfield Strait: implications of lateral transport for carbon cycle studies in Antarctic marginal seas. J. Mar. Res. 60, 347365 (2002).
  32. de Bettignies, T. et al. Phenological decoupling of mortality from wave forcing in kelp beds. Ecology 96, 850861 (2015).
  33. Dierssen, H. M., Zimmerman, R. C., Drake, L. A. & Burdige, D. J. Potential export of unattached benthic macroalgae to the deep sea trough wind-driven Langmuir circulation. Geophys. Res. Lett. 36, L04602 (2009).
  34. Hobday, A. J. Abundance and dispersal of drifting kelp Macrocystis pyrifera rafts in the Southern California Bight. Mar Ecol. Prog. Ser. 195, 101116 (2000).
  35. Rowe, G. T. & Staresinic, N. Sources of organic matter to the deep-sea benthos. Ambio Special Report 1, 1923 (1979).
  36. Kingsbury, J. M. Christopher Columbus as a botanist. Arnoldia 52, 1128 (1992).
  37. Johnson, D. L. & Richardson, P. L. On the wind-induced sinking of Sargassum. J. Exp. Mar. Biol. Ecol. 28, 255267 (1977).
  38. Harrold, C., Light, K. & Lisin S. Organic enrichment of submarine canyon and continental shelf benthic communities by macroalgal drift imported from nearshore kelp forests. Limnol. Oceanogr. 43, 669678 (1998).
  39. Bauer, J. E. & Druffel, E. R. Ocean margins as a significant source of organic matter to the deep open ocean. Nature 92, 482485 (1998).
  40. Josselyn, M. N. et al. Composition, export and faunal utilization of drift vegetation in the Salt River submarine canyon. Estuar. Coast. Shelf Sci. 17, 447465 (1983).
  41. Hardison, A., Canuel, E. A., Anderson, I. C. & Veuger, B. Fate of macroalgae in benthic systems: carbon and nitrogen cycling within the microbial community. Mar. Ecol. Prog. Ser. 414, 4155 (2010).
  42. Wernberg, T. et al. Seaweed communities in retreat from ocean warming. Curr. Biol. 21, 18281832 (2011).
  43. Smale, D. A., Burrows, M. T., Moore, P., O'Connor, N. & Hawkins, S. J. Threats and knowledge gaps for ecosystem services provided by kelp forests: a northeast Atlantic perspective. Ecol. Evol. 3, 40164038 (2013).
  44. Poloczanska, E. S. et al. Global imprint of climate change on marine life. Nat. Clim. Change 3, 919925 (2013).
  45. Krause-Jensen, D. & Duarte, C. M. Expansion of vegetated coastal ecosystems in the future Arctic. Front. Mar. Sci. 1, 77 (2014).
  46. Krumhansl, K. A., Lauzon-Guay, J. S. & Scheibling, R. E. Modeling effects of climate change and phase shifts on detrital production of a kelp bed. Ecology 95, 763774 (2014).
  47. Duarte, C. M. Global change and the future ocean: a grand challenge for marine sciences. Front. Mar. Sci. 1, 63 (2014).
  48. Smetacek, V. & Zingone, A. Green and golden seaweed tides on the rise. Nature 504, 8488 (2013).
  49. Duarte, C. M. et al. Will the oceans help feed humanity? BioScience 59, 967976 (2009).
  50. Olsen, Y. How can mariculture better help feed humanity? Front. Mar. Sci. 2, 46 (2015).
  51. Gattuso, J. P., Frankignoulle, M. & Wollast, R. Carbon and carbonate metabolism in coastal aquatic ecosystems. Annu. Rev. Ecol. Syst. 29, 405434 (1998).
  52. Whittaker, R. H. & Likens, G. E. Carbon and the biota. Brookhaven Symp. Biol. 24, 281302 (1973).
  53. Gattuso, J. P., Gentili, B., Duarte, C. M., Kleypas, J. A., Middelburg, J. J. & Antoine, D. Light availability in the coastal ocean: impact on the distribution of benthic photosynthetic organisms and their contribution to primary production. Biogeosciences 3, 489513 (2006).
  54. Cebrian, J. & Duarte, C. M. The dependence of herbivory on growth rate in natural plant communities. Funct. Ecol. 4, 518525 (1994).
  55. Duarte, C. M. Nutrient concentration of aquatic plants: patterns across species. Limnol. Oceanogr. 37, 882889 (1992).
  56. Charpy-Roubaud, C. & Sournia, A. The comparative estimation of phytoplanktonic, microphytobenthic and macrophytobenthic primary production in the oceans. Mar. Microb. Food Webs 4, 3157 (1990).
  57. Baines, S. B. & Pace, M. L. The production of dissolved organic matter by phytoplankton and its importance to bacteria: patterns across marine and freshwater systems. Limnol. Oceanogr. 36, 10781090 (1991).
  58. Ciais, P. et al. in Climate Change 2013: The Physical Science Basis (eds Stocker, T. F. et al.) Ch. 6, 465570 (IPCC, Cambridge Univ. Press, 2013).
  59. Hardison, A., Canuel, E. A., Anderson, I. C. & Veuger, B. Fate of macroalgae in benthic systems: carbon and nitrogen cycling within the microbial community. Mar. Ecol. Prog. Ser. 414, 4155 (2010).

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  1. Department of Bioscience, Aarhus University, Vejlsøvej 25, DK-8600 Silkeborg, Denmark

    • Dorte Krause-Jensen
  2. Arctic Research Centre, Department of Bioscience, Aarhus University, Ny Munkegade 114, bldg. 1540, 8000 Århus C, Denmark

    • Dorte Krause-Jensen
  3. King Abdullah University of Science and Technology (KAUST), Red Sea Research Center, Thuwal 23955-6900, Saudi Arabia

    • Carlos M. Duarte

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