Mapping the Climate Vulnerability and Carbon Potential of Global Seaweed Forests

Abstract

Coastal vegetated ecosystems are important global carbon sinks, capturing and storing organic carbon in vegetations and sediments. While macroalgal forests are increasingly recognized as significant contributors to marine carbon sequestration, they continue to receive relatively limited conservation attention compared to other coastal ecosystems. Here, recent literature on macroalgal distribution, productivity, carbon export, and sequestration, alongside current and projected climate-related threats, is synthesized to provide a global assessment of macroalgal forest vulnerability and conservation priority. Global macroalgal net primary production is estimated at approximately 1.3–1.7 Pg C yr⁻¹, with brown algal forests exhibiting the highest productivity rates (up to ~536 g C m⁻² yr⁻¹). A substantial fraction of this production is exported as particulate organic carbon (POC) to deep ocean sinks, with an estimated 56 Tg C yr⁻¹ being transported beyond 200 m depth. Of this, approximately 4–44 Tg C yr⁻¹ may be sequestered for timescales exceeding 100 years.

Using published data, the climate vulnerability and carbon potential of brown, canopy-forming macroalgal forests were mapped for each marine realm by integrating metrics of productivity, export, sequestration potential, and projected changes in habitat suitability. Polar regions and the Western Indo-Pacific currently represent lower priority areas, as recent warming and ice retreat have facilitated macroalgal expansion and direct human pressures remain comparatively low. Nevertheless, rapid environmental change in these regions necessitates monitoring to detect emerging vulnerabilities. Temperate regions, the tropical eastern Pacific and eastern Indo-Pacific systems remain key priorities due to their moderate blue carbon potential with medium-high sensitivity climate factors. The highest conservation priorities identified were the Central Indo-Pacific, Temperate Australasia, and the Tropical Atlantic realms, where high sequestration potential coincides with intense climate stress and dense human pressures. Key countries herein include Australia, Indonesia, Brazil and New Zealand.

In these areas, conservation and active reforestation are urgently needed. Long-term success will depend on addressing the root causes of macroalgal decline, including overgrazing, pollution, and ocean warming. Inclusion within existing blue carbon frameworks requires robust validation of carbon export and sequestration assumptions, which will require sustained monitoring and the broader application of oceanographic models. Formal recognition of macroalgae as blue carbon ecosystems could then unlock policy and financial support, positioning them as strong candidates for climate-adaptive conservation and restoration strategies.