Organic Carbon Stocks in Earth's Most Remote Blue Carbon Ecosystems

Tropical coastal ecosystems are zones of important blue carbon sequestration, storing some of the highest carbon stocks per unit area and sequestering carbon on time scales exceeding centuries. However, mapping of these ecosystems using remote sensing is often hindered by cloud cover, inconsistent field methods employed between studies, and differences in the observation scale and frequency. High-resolution benthic habitat maps produced and ground-truthed by the Khaled bin Sultan Living Oceans Foundation's Global Reef Expedition (2005-2016) offer a unique opportunity to systematically assess the extents of blue carbon habitats in Earth's most remote tropical marine ecosystems. We present new map-based estimates of mangrove forests, seagrass meadows, and macroalgal habitats in 69 study areas spanning ∼15,970 km². Integrating these maps with regional carbon stock data suggests that these ecosystems store an average of 41.84 Tg C_org (range: 4.69-176.95 Tg C_org). The Solomon Islands, Bahamas, and Colombia were identified as potential blue carbon hotspots, while French Polynesian habitats exhibit the highest degree of fragmentation. Globally consistent mapping approaches and new stock estimates fill a critical knowledge gap for remote ecosystems, 82% of which have never been assessed. Our findings provide useful baseline data for management and conservation strategies of these vital ecosystems.