Blue Carbon Storage in Mangrove-Seagrass Ecotones

Abstract

Mangrove forests and seagrass meadows are recognized as globally significant blue carbon ecosystems, yet the transitional ecotones between these habitats remain largely uncharacterized in terms of their carbon storage capacity. This study quantifies sediment organic carbon stocks across 12 mangrove-seagrass ecotone sites spanning the Indo-Pacific and East African coastlines, using a combination of Sentinel-2 multispectral remote sensing for habitat delineation and sediment coring for direct carbon measurement. A Random Forest classifier applied to Sentinel-2 imagery achieved 84.6 percent overall classification accuracy across five habitat classes, with ecotone zones showing the lowest but still acceptable accuracies (producer's 78.2 percent, user's 76.8 percent) owing to their spectral similarity to adjacent habitats. Sediment cores to one-meter depth revealed that ecotone carbon concentrations are consistently intermediate between dense mangrove and seagrass values, ranging from 3.8 to 10.1 percent organic carbon by weight depending on depth. Extrapolated across mapped ecotone areas, these transitional zones store an estimated 142 ± 38 Mg C ha⁻¹ in the upper meter of sediment, representing a previously unaccounted carbon pool with implications for national blue carbon inventories and coastal conservation prioritization.