An Annual Blue Carbon Budget for Kelp Forests and Seagrass Beds

Coastal vegetated ecosystems (e.g. kelp forests, seagrass meadows) potentially play a significant role in oceanic carbon sequestration, yet existing estimates have high uncertainty because they are compilations of few data from disparate species and regions, or focus on individual stocks or fluxes. We use empirical data and modeling to generate detailed carbon budgets for kelp forests and seagrass meadows in a single region (Nova Scotia, Canada). We estimate kelp forests to sequester more carbon (0.313 ± 0.144 Tg C y ^− 1 , 27 ± 19% of annual net primary production [NPP]) than seagrass meadows (0.011 ± 0.004 Tg C y ^− 1 , 9.5 ± 5.2% of NPP) by an order of magnitude. A substantially higher proportion of carbon sequestered by kelp forests is from the production and export of dissolved organic carbon (DOC) (98.5 ± 60.1% of carbon sequestered) than for seagrass meadows, which primarily sequester carbon through shelf burial and the export of particulate organic carbon (POC) to the deep sea (63.6 ± 43%). Our results show how detailed carbon budgeting can highlight undervalued or overlooked carbon pathways (e.g. POC to DOC conversion), and support more robust valuation and management of blue carbon ecosystems for carbon sequestration.