Mangrove (Avicennia marina) Conservation Contributed to a Higher Carbon Sequestration Rate at Protected Sites Compared to Overgrazed Mangrove Forests

Coastal mangrove ecosystems have been degraded due to changes in land use and grazing. Here, we assess the differences in population characteristics and sediment organic carbon (SOC) stocks and carbon sequestration rates (CSR) at Avicennia marina protected and grazed locations along the southern Red Sea coast, Saudi Arabia. Tree density per unit area were counted (tree 100 m^− 2) and maximum tree height and crown diameter (cm) were measured. Sediment bulk density (SBD, g cm^− 3), sediment organic carbon (SOC) content (g C kg^− 1), total SOC stocks (kg C m^− 2) to a depth of 75 cm, and CSR (g C m^− 2 year^− 1) were estimated. Protected A. marina trees had significantly (p < 0.05) higher tree height and crown diameter (119.5 ± 8.3 and 209.6 ± 17.1 cm, respectively) than those of the mangrove trees at the grazed locations (76.8 ± 7.5 and 148.0 ± 23.5 cm, respectively). Sediment of the A. marina trees that are growing at the protected locations had significantly (p < 0.05) higher SOC content, SOC density, SOC stock to a depth of 75 cm, and CSR (21.6 ± 0.5 g C kg^− 1, 30.5 ± 0.6 kg C m^− 3, 22.9 ± 1.1 kg C m^− 2, and 6.7 ± 0.1 g C m^− 2 year^− 1, respectively) than those of the grazed locations (9.6 ± 0.2 g C kg^− 1, 14.6 ± 0.2 kg C m^− 3, 10.9 ± 0.4 kg C m^− 2, and 3.2 ± 0.0 g C m^− 2 year^− 1, respectively). Our results provide strong evidence of the vital need to continue conserving A. marina’s population for accumulating more blue carbon for mitigation of global warming and offset greenhouse gas emissions.