Blueprinting the ecosystem health index for blue carbon ecotones

Blue carbon ecotones (BCEs) play a critical role in regulating abiotic and biotic ecological fluxes underpinning services which are also crucial for the protection of the land-ocean function. Here, we proposed a Benefit-Pressure-Transformation Risk model (BPT) to calculate the Ecosystem Health Index (EHI) for mangrove, salt marsh, and seagrass as core BCEs globally (at a resolution of 1° × 1 °lat-long), based on habitat structure, species morphological features and vulnerability, niche overlap, nature and human pressures, and ecosystem services. Our assessments identify that around 20% of BCEs as vulnerable globally. Specifically, with every 1° increase in latitude, the EHI values for mangroves, salt marshes, and seagrasses decrease linearly proportionally to a factor equal to 0.007, 0.003, and 0.004. We find that improving EHI of mangroves not only supports resilience but also enhances their carbon sink function (+68 Mg per hectare/0.1 EHI), making ecosystem health a critical factor in climate change mitigation.