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Marine Ecology Progress Series

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MEPS 660:53-67 (2021)  -  DOI:

Carbon sequestration potential increased by incomplete anaerobic decomposition of kelp detritus

Morten Foldager Pedersen1,*, Karen Filbee-Dexter2,3, Nikolai Lond Frisk1, Zsuzsa Sárossy4, Thomas Wernberg1,2,3

1Department of Science and Environment (DSE), Roskilde University, Universitetsvej 1, PO Box 260, Roskilde 4000, Denmark
2Institute of Marine Research, His, Arendal 4817, Norway
3UWA Oceans Institute and School of Biological Sciences, University of Western Australia, Crawley, WA 6009, Australia
4Department of Chemical and Biochemical Engineering, Technical University of Denmark, Søltofts Plads, Kgs. Lyngby 2800, Denmark
*Corresponding author:

ABSTRACT: Kelps are highly productive macroalgae that form habitats along one-quarter of the worlds’ coastlines. Emerging evidence suggests that kelps have the potential to sequester carbon through the export of detritus to deep marine sinks, yet how much of this detrital carbon is remineralized through grazing and microbial decomposition before it reaches these sinks remains a critical knowledge gap. We measured decay of Laminaria hyperborea detritus in shallow kelp forests (10 m) and adjacent deep fjords (300 m), and experimentally tested the effect of temperature and oxygen conditions similar to those at these habitats in ex situ experiments. Initial decay rate (k) was high (-0.107 to -0.183 d-1) with 40-60% of the original carbon biomass being lost within few weeks, after which decay rates slowed down (k = -0.009 to -0.038 d-1). Temperature had little effect on the rate and extent of decomposition within the temperature range tested (4-10°C). Blade detritus decomposed almost completely in 300 d under aerobic conditions. Anaerobic decay of both blade and stipe detritus ceased, in contrast, after 150-200 d, leaving 20-30% of the initial biomass to decompose extremely slowly or not at all. Decomposition was followed by changes in chemical composition; C:N ratios increased substantially, while mannitol and phenolics disappeared almost completely from the detritus matrix. Slow and incomplete anaerobic decomposition suggest that the potential for long-term burial and sequestration of kelp carbon will be enhanced if detritus is exported to nearby deep areas with permanent or periodic hypoxia near the bottom.

KEY WORDS: Laminaria hyperborea · Blue carbon · Carbon sink · Burial · Refractory compounds · Macroalgae

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Cite this article as: Pedersen MF, Filbee-Dexter K, Frisk NL, Sárossy Z, Wernberg T (2021) Carbon sequestration potential increased by incomplete anaerobic decomposition of kelp detritus. Mar Ecol Prog Ser 660:53-67.

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