Decomposition dynamics and long-term persistence of seagrass and macroalgal litter carbon: insights from mesh-bag experiments and modeling

Authors:
  • NHNatsuki Hasegawa
    Natsuki Hasegawa
  • DMDaisuke Muraoka
    Daisuke Muraoka
  • SSShuhei Sawayama
    Shuhei Sawayama
  • HSHiromori Shimabukuro
    Hiromori Shimabukuro
  • GYGoro Yoshida
    Goro Yoshida
  • SKSetsuo Kiyomoto
    Setsuo Kiyomoto
  • KFKurumi Fujino
    Kurumi Fujino
  • HSHuamei Shao
    Huamei Shao
  • TMToshihiro Miyajima
    Toshihiro Miyajima
  • MHMasakazu Hori
    Masakazu Hori
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Abstract
Understanding the decomposition kinetics of organic carbon (OC) is key to accurately assessing blue carbon sequestration by seagrass and macroalgal beds. In this study, mesh-bag decomposition experiments were conducted in flow-through tanks supplied with natural coastal seawater across multiple coastal regions of Japan. Temporal changes in bulk OC remaining in the mesh bags, representing its persistence, were determined over 2 years for numerous seagrass and macroalgal species, and decomposition dynamics were subsequently modeled to estimate carbon persistence in long-term litter at annual, decadal, and centennial timescales.,Seagrass species exhibited substantially slower decomposition than most macroalgal species, retaining greater than 20% of initial bulk carbon after 1 year. In contrast, brown macroalgae of the order Laminariales, particularly edible species, showed rapid initial decomposition, losing more than 90% of bulk carbon within 3 months. Green and red algae exhibited relatively limited initial decomposition but ultimately declined to levels comparable to those of brown algae at the end of the 2-year experiment.,Statistical analyses indicated that taxonomic order influenced early-stage decomposition, whereas environmental effects, particularly water temperature, on residual proportions after 1 month and 1 year remained limited. Decomposition dynamics were successfully reproduced using a dual-exponential Multi-G model and a mixed model incorporating a reactivity continuum framework. Although estimated residual proportions during the 2-year experimental period were similar between models, projections diverged markedly at longer timescales of 10 and 100 years.

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