Stéphanie Roy1, Christian Nozais2, Ladd E. Johnson3, Fanny Noisette1
1 Institut des Sciences de la Mer, Université du Québec à Rimouski, Rimouski, QC, G5L 3A1
2 Département de biologie, chimie et géographie, Université du Québec à Rimouski, Rimouski, QC, G5L 3A1
3 Département de biologie, Université Laval, Québec, QC, G1V 0A6
Kelp communities are major primary producers in subpolar and temperate areas, producing up to 39 Tg C year-1 in coastal zones. Kelp beds are not fully considered as blue carbon contributors in spite of their carbon storage capacity: indeed, local sequestration remains limited and most of the organic carbon is exported from the community. Certain limitations also prevent to correctly estimate their blue carbon potential: lack of measurements of organic carbon stocks, sub-optimal evaluation of carbon fluxes and uncertainties about the transport and sequestration of kelp-derived material. For instance, thorough measurements of primary productivity in subarctic kelp beds are scarce and almost never measured in situ. To fill in some gaps, we measured in situ primary productivity on individual kelps (Saccharina latissima) with incubation chambers during natural light and dark conditions, using oxygen flux measurements. As the seasonality is an important component of the sub-arctic systems, primary production was assessed from June to September (spring, summer, autumn). In June 2022, oxygen net production by individual kelp varied from 7.94 to 100.63 µmol O2 g-1 DW h-1. These rates exceed slightly the ones from in situ incubations of the kelp Laminaria hyperborea in Brittany where the maximum net primary production reached 72.13 µmol O2 g-1 DW h-1. From these oxygen fluxes, carbon fluxes will be calculated using the photosynthetic quotient extrapolated at the population scale to estimate the carbon storage capacity of kelp beds in the St. Lawrence Estuary.