Multilevel governance of blue carbon: a narrative review of integration bottlenecks and pathways

Mangrove forests, seagrass meadows and tidal salt marshes store disproportionate amounts of carbon in coastal sediments while supporting biodiversity, coastal defence and livelihoods, yet the rapidly expanding blue-carbon policy field has not been matched by coherent governance across levels and sectors. This narrative review asks how, and how effectively, blue-carbon policy is integrated across governance levels and sectors in the post-2019 window, and disaggregates the question into documented integration bottlenecks, their structural, institutional and power-related determinants, and the governance pathways proposed to relieve them. We screened literature published from 2019 to 2026 and retained 24 empirical and policy studies; verbatim findings were extracted solely from Results sections and synthesised through a framework combining multilevel, polycentric and adaptive governance lenses. Horizontal fragmentation of mandates and regimes, institutional determinants, multilevel integration and polycentric participation each recurred in 21 of the 24 studies, whereas structural economic and biophysical conditions were documented least. Integration appears to fail institutionally before it fails technically: unclear carbon rights, missing or incompatible accounting and trading rules, and the non-recognition of sink preservation as mitigation strand initiatives between announcement and implementation, while expert-dominated knowledge interfaces, external and post-colonial dominance and elite capture skew who designs projects and who benefits from them. Local pilots and credits rarely scale into national markets, and bottom-up feedback lacks upward channels. Six recurring bottleneck–determinant–pathway chains indicate that effective responses align authoritative multilevel rules, equitable polycentric participation and adaptive public knowledge infrastructure, rather than relying on any single statute, market or financing instrument; politicisation, corruption and the upward feedback channel remain without documented responses. The review closes a descriptive–explanatory gap in blue-carbon scholarship and offers a sequenced, equity-sensitive basis for integrating coastal sinks into climate policy.