Blue carbon

Blue carbon is the carbon captured by marine ecosystems — mangroves, seagrass, salt marshes and cultivated seaweed/kelp — together with the emerging industry of ocean farming, Sargassum valorization and marine carbon-dioxide removal (mCDR) that turns it into biomass products and durable carbon-removal credits. Giant kelp (Macrocystis pyrifera) grows 30–60 cm/day in the Benguela Current, and the Great Atlantic Sargassum Belt reached a record 37 million tonnes of biomass in 2025 — both vast natural carbon pumps. Yet 2026 science tempers the hype: a Nature Communications study finds iron limitation cuts seaweed-CDR potential ~3×, and a Biogeosciences model shows only ~27% of farmed macroalgae translates into additional CO₂ uptake. The credible business model therefore couples biomass revenue (biostimulants, biomaterials) with carbon credits, under strict MRV.

The key directions of blue carbon are:

1. Open-ocean kelp / macroalgae cultivation (Kelp Cultivation): offshore farms of fast-growing giant kelp — Kelp Blue holds a 6,400-ha, 15-year licence off Lüderitz and harvested >200 t in 2025.
2. Sargassum interception & valorization (Sargassum Valorization): harvesting invasive blooms for biostimulants, biochar, bioplastics and bio-leather — Carbonwave removed a record 20,300 t of Sargassum in 2025 (+129%).
3. Marine ranching & restoration aquaculture (Marine Ranching): seabed ranching of kelp, sea cucumber and shellfish as carbon sinks — Haohangjia runs a 50,000-mu marine ranch on the Shandong coast.
4. Marine CDR science & MRV (Marine CDR MRV): measurement, reporting and verification for durable credits — Kelp Blue is an XPRIZE CDR finalist with an independent atdepth MRV methodology.

Sectoral value chain#

[site licensing] ──> [seed/spore] ──> [cultivation] ──> [harvest & interception]
                            │
                  (kelp / Sargassum / mangrove / marine ranch)
                            │
                            ▼
[carbon credits] <─── [biorefinery processing] <─────┘

Value chain levels#

Cross-cutting technologies of the sector:

• Canopy-trim harvest (Canopy-Trim Harvest): trimming only the kelp canopy for healthy regrowth, continuous sequestration and biodiversity uplift.
• Sargassum interception (Sargassum Interception): floating barriers + Algaeponix paddocks intercept blooms before shoreline decay.
• MRV for marine CDR (Marine CDR MRV): POC/DOC export and deep-sea sinking models crediting >100-year sequestration.

The stack rests on three platforms: open-ocean macroalgae cultivation, Sargassum interception, and blue-carbon MRV/crediting.

1. Open-ocean macroalgae cultivation (Kelp Cultivation):
   • lab-cultured spores are wound onto twine and set on sub-surface ropes to grow giant kelp or sugar kelp, trimmed at the canopy for continuous regrowth and biodiversity uplift.
   • case: Kelp Blue’s Namibian farms lifted resident species from 135 to ~800 within months; Cascadia embeds spores for its Port Edward biorefinery.
2. Sargassum interception & upcycling (Sargassum Valorization):
   • floating barriers and in-water paddocks intercept free-floating Sargassum before it decays on shore, then mechanical pressing splits it into liquid (biostimulant/emulsifier) and pulp (bio-leather).
   • case: Carbonwave’s 20,300 t removed in 2025 and Seafields’ SeaClear/Algaeponix 60-paddock farm design.
3. Blue-carbon MRV & crediting (Marine CDR MRV):
   • monitored sinking of kelp/Sargassum biomass to the deep ocean, with POC/DOC export models crediting >100-year sequestration sold as durable removal credits.
   • case: Kelp Blue’s independent atdepth MRV assessment (XPRIZE finalist); Seafields’ permanent carbon-removal credits.