Who legally controls carbon stored in seabed sediments and coastal waters — tenure regimes, marine property rights and what they mean for carbon projects.
Ask a seabed-carbon project developer who owns the carbon under their site, and you will often get a confident answer followed, a beat later, by a longer one. The confident answer is usually "the state does." The longer answer — about leases, licences, customary rights and registries — is the truthful one. Tenure is the bundle of rights over a place: who may use it, exclude others, claim benefits from it and transfer those rights. For carbon stored in sediments, drifting in the water column or growing on seeded lines, the bundle is rarely whole in any single pair of hands, and understanding the gaps is now basic project hygiene.
This article maps the tenure question as a working issue for blue-carbon projects on kelp coasts. It deliberately complements two companion pieces: who owns blue carbon and how sea country shapes the answer, which centres Indigenous and customary tenure, and consent before credits, which covers the consent process. Here the focus is the formal legal architecture — and where it is silent.
Marine jurisdiction is layered, and carbon inherits the layers. Under the United Nations Convention on the Law of the Sea, coastal states hold sovereignty over their internal waters and territorial sea — generally twelve nautical miles, including the seabed, subsoil and water column above. Further out lies the exclusive economic zone, to 200 nautical miles, where states hold sovereign rights rather than sovereignty: rights to explore, exploit, conserve and manage natural resources, plus jurisdiction over certain activities. Beyond that, states exercise sovereign rights over seabed resources on their continental shelf, which can extend past 200 miles, while the water column there becomes the high seas.
Why this matters for carbon: most coastal kelp blue-carbon work sits inside national jurisdiction where domestic law fills in the picture, while offshore carbon pathways — kelp detritus exported beyond twelve miles, for instance — begin crossing legal regimes with the current. A tonne of carbon can change governing law while decomposing.
Within national waters, the detailed answer varies by country, in ways that surprise project teams moving between jurisdictions:
No serious project should infer tenure from a cadastral map alone. The map shows formal grants; the case law, statutes and customary practice show the rest.
The complication specific to blue carbon is that "the carbon" is not one thing in one place — and different pools sit inside different rights.
Carbon buried in seabed sediments attaches most plausibly to whoever controls the seabed itself — typically the state, subject to lease rights and customary rights. This is the pool wetland-style methodologies credit, and it is the pool where the "landlord" logic of terrestrial carbon projects transfers most cleanly.
Kelp's distinctive pool — detritus exported as particulate and dissolved carbon, some reaching deep water — lives in the water column, which is characteristically a common-pool space even inside national jurisdiction. The closer a project moves from "carbon stored in sediment under our site" toward "carbon our forest exported somewhere the current took it," the weaker the tenure intuition becomes, because the storage location sits outside any one right-holder's bundle, and attribution joins the open methodological debates in where kelp carbon actually ends up.
Where kelp is grown on seeded lines in a leased farm or restoration site, the standing biomass is usually the clearest ownership case: the lease-holder typically owns the crop, as a matter of ordinary aquaculture law. That clarifies who owns the fronds — while, notably, saying nothing automatic about who may claim ecosystem-level carbon effects in the surrounding sediment.
The crucial finding from comparative reviews is that most coastal states have not legislated who owns blue carbon as such. On land, several jurisdictions created explicit carbon-sequestration rights over the past two decades — severing carbon rights from land titles so they can be registered and traded separately. Equivalent statutory treatment for marine carbon is rare. Aquaculture leases talk about gear and stock; foreshore licences talk about occupation; environmental approvals talk about impacts. Carbon benefits sit in the seams between these instruments.
In that silence, practice improvises: project contracts allocate "environmental attributes" between landlords and leaseholders; registries define a "project area" over which the named project proponent claims carbon ownership rights, requiring evidence of those rights at registration; and governments contemplating blue-carbon revenue are beginning to ask, reasonably, whether seabed carbon in state hands should behave more like a royalty-bearing public resource. Governance questions of this shape — who decides, under what authority — are the subject of our piece on who governs ocean carbon removal.
Tenure is not a paperwork afterthought; it is a design constraint on the same level as the ecology. Teams that handle it well tend to do five things, in order:
The trajectory in land-based carbon was clear: ambiguity was legislated away, one jurisdiction at a time, usually in favour of the resource right-holder with statutory carbon rights layered on top. Expect the sea to follow, more slowly, with added public-interest doctrine. Developers who build tenure schedules and consent processes now will find they were building compliance infrastructure ahead of the regulation; those who treated the ocean as ownerless will find, when the laws arrive, that nobody ever thought it was.
In most jurisdictions the state owns or controls the seabed, so sediment carbon attaches first to state control — but leases, licences and customary rights all modify who may use and benefit from it. There is no universal answer; there is only the jurisdiction-specific one.
Not automatically. A lease typically conveys rights to occupy water and to the crop, while ecosystem-level carbon rights are usually unaddressed in statute and must be allocated contractually or evidenced to a registry.
It is the hardest claim in kelp blue carbon: the storage may occur outside any rights-holder's bundle, and permanence and attribution are methodologically contested. Serious projects either evidence the chain conservatively or decline the claim.
Formal ownership varies, but customary tenure and Indigenous rights overlay formal titles in many jurisdictions; legitimate projects proceed through partnership, benefit-sharing and consent. Our dedicated piece on sea country and carbon rights treats this properly.
Unlikely. Land-based carbon went through the same ambiguity before statutory carbon rights arrived. Coastal states eyeing blue-carbon revenue have every incentive to legislate, and early movers in project contracting will find their paperwork becomes the template.
The ocean is not empty and neither are its rights. Tenure, jurisdiction and Indigenous sea country decide who can claim coastal carbon — before any science does.
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