Purpose <p>This study investigates the covariation of soil organic carbon (SOC) and glomalin-related soil protein (GRSP) along a land-to-water gradient in mangroves, testing the hypothesis that these components are primarily derived locally rather than transported from land.</p> Methods <p>We measured SOC, total GRSP (T-GRSP), easily extractable GRSP (EE-GRSP), and soil conditions along a land-to-water gradient in Dongzhaigang Mangrove Reserve, Hainan, China. A nearby landward site served as a reference for comparison.</p> Results <p>SOC decreased significantly from the water side to the land side. Although T-GRSP and EE-GRSP did not vary significantly across the gradient, they exhibited a positive correlation with SOC. Soil water content and salinity strongly influenced the distribution of SOC and GRSP.</p> Conclusion <p>The findings suggest that SOC and GRSP are more likely locally derived rather than transported from land, supporting the hypothesis of native origin.</p>