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Coastal vegetated ecosystems constitute very productive habitats, characterized by efficient C-org sequestration and long-term preservation in sediments, so they play an important role in climate change mitigation. The temporal evolution of C-org content, stocks and burial rates were evaluated in seagrass and salt marsh habitats in San Quintin Bay (northeast Pacific, Mexico) by using Pb-210-dated sediment cores. Salt marsh cores were characterized by fine-grained sediments, higher salinities, lower terrigenous input and lower mass accumulation rates (MAR: 0.01-0.03 g cm(-2) yr(-1)) than seagrass cores (MAR: 0.02-3.21 g cm(-2) yr(-1)). Accumulation rates in both habitats steadily increased throughout the past century most likely because of soil erosion promoted by land use changes in the surroundings. The C-org stocks were highest in salt marsh cores (12.2-53.6 Mg ha(-1) at 10 cm depth; 259-320 Mg ha(-1) at 1 m depth) than in seagrass cores (5.7-14.4 Mg ha(-1), and 80-98, Mg ha(-1), respectively), whereas C-org burial rates were considerably lower in salt marsh (13-60 g m(-2) yr(-1)) than in seagrass (9-144 g m(-2) yr(-1)) habitats, and the temporal variations observed in C-org burial rates were mostly driven by changes in the accumulation rates. The overall C-org stock (485 +/- 51 Gg C) for both habitats together was comparable to the carbon emissions of a major city nearby. Our results highlight the need to protect these environments as relevant carbon reservoirs. (C) 2019 Elsevier B.V. All rights reserved.