Macroalgal aquaculture is a globally important commercial industry, with increasing focus on farmed kelp as a marine carbon dioxide reduction (mCDR) strategy. Sinking kelp offshore could potentially sequester carbon in the deep sea, however this approach has several drawbacks, including unintended ecological consequences for the deep sea benthos. Alternatively, while nearshore sinking of kelp exposes it to higher remineralization rates, this approach mimics the higher organic matter regime of coastal ecosystems and is more feasible on a local scale. In Maine, up to 20% of farmed kelp is made up of less valuable biproduct (holdfasts/biofouled blades). To evaluate this mCDR potential, we incubated blades and holdfasts from Saccharina angustissima and Saccharina latissima under dark aerobic conditions at 19 ºC for 90 days to isolate microbial processing. Degrading kelp releases both dissolved and particulate organic matter (DOM and POM), which can contribute to recalcitrant carbon pools. Initial analysis of DOM optical properties showed a logarithmic increase of cDOM, with production and microbial degradation rates stabilizing after 30 days. Further analysis of fluorescent DOM and macromolecular composition is underway. The spectral slope ratio S_R (S_275-395:S_350-400), an inverse proxy for relative molecular weight (MW), rapidly increased to a maximum by day 17. This indicates that high MW compounds released during initial senescence were transformed into lower MW, the persistence of which suggests production of recalcitrant DOM under coastal conditions.

Authors:

Sarah Douglas, Bigelow Laboratory for Ocean Sciences  (sarahvdouglas@gmail.com)

Peter Countway, Bigelow Laboratory for Ocean Sciences  (pcountway@bigelow.org)

Peter Craig, Bigelow Laboratory for Ocean Sciences  (pcraig@bigelow.org)

Greg Drozd, Colby College  (gtdrozd@colby.edu)

David Emerson, Bigelow Laboratory for Ocean Sciences  (demerson@bigelow.org)

Brittney Honisch, Bigelow Laboratory for Ocean Sciences  (bhonisch@bigelow.org)

Sean O'Neill, University of Maine  (sean.oneill@maine.edu)

Nichole Price, Bigelow Laboratory for Ocean Sciences  (nprice@bigelow.org)

Charlotte Quigley, Bigelow Laboratory for Ocean Sciences  (cquigley@bigelow.org)

Jeremy Rich, University of Maine  (jeremy.rich@maine.edu)

Robin Sleith, Bigelow Laboratory for Ocean Sciences  (rsleith@bigelow.org)

Samuel Tan, University of Maine  (stan@bigelow.org)

Manoj Kamalanathan, Bigelow Laboratory for Ocean Sciences  (mkamalanathan@bigelow.org)