A Synthesis of Blue Carbon Stocks, Accumulation rates and Knowledge Gaps in Africa

Blue carbon ecosystems (BCEs), including mangroves, salt marshes and seagrasses, play a critical role in global climate mitigation by storing large amounts of atmospheric carbon. Despite Africa’s extensive and diverse coastal ecosystems, assessments of blue carbon stocks and accumulation rates are very scarce. We present a systematic review of blue carbon data in Africa, synthesizing data from 77 publications covering studies from 1 January 1993 to July 2025. Our analysis reveals marked regional variability in sediment organic carbon (SOC) stocks across Africa, based on depth-resolved sediment core data compiled from published studies. Median SOC values for cores extending from the surface to depths of 60, 100, and 200 cm show that mangrove sediments store substantially more carbon (320–372 Mg Corg ha⁻¹) than salt marshes (163 Mg Corg ha⁻¹) or seagrass meadows (86–157 Mg Corg ha⁻¹). Salt marsh and seagrass remain even more underrepresented and poorly quantified. Despite very limited empirical data, carbon accumulation rates in African seagrasses show substantial spatial variability, ranging from low values in Tanzania (24 g Corg m-2 y-1) to high rates in the Seychelles (107 g Corg m-2 y-1), underscoring that regionally comprehensive measurements are required. This study highlighted the need to strengthen technical capacity, expand regional studies, and integrate local knowledge to fully realize the potential of BCEs in supporting climate mitigation and coastal community resilience in Africa. Our findings underscore that this shall be accomplished with coordinated, continent-wide efforts to consolidate blue carbon data and inform policy frameworks, including Nationally Determined Contributions and emerging conservation finance markets. Building on existing open-access initiatives, standardizing methodology and consolidating data will strengthen blue carbon science and policy across Africa.