Seagrass blue carbon stocks and sequestration rates in the Colombian Caribbean.

Seagrass ecosystems rank amongst the most efficient natural carbon sinks on earth, sequestering CO through photosynthesis and storing organic carbon (C) underneath their soils for millennia and thereby, mitigating climate change. However, estimates of C stocks and accumulation rates in seagrass meadows (blue carbon) are restricted to few regions, and further information on spatial variability is required to derive robust global estimates. Here we studied soil C stocks and accumulation rates in seagrass meadows across the Colombian Caribbean. We estimated that Thalassia testudinum meadows store 241 ± 118 Mg C ha (mean ± SD) in the top 1 m-thick soils, accumulated at rates of 122 ± 62 and 15 ± 7 g C m year over the last ~ 70 years and up to 2000 years, respectively. The tropical climate of the Caribbean Sea and associated sediment run-off, together with the relatively high primary production of T. testudinum, influencing biotic and abiotic drivers of C storage linked to seagrass and soil respiration rates, explains their relatively high C stocks and accumulation rates when compared to other meadows globally. Differences in soil C storage among Colombian Caribbean regions are largely linked to differences in the relative contribution of C sources to the soil C pool (seagrass, algae Halimeda tuna, mangrove and seston) and the content of soil particles < 0.016 mm binding C and enhancing its preservation. Despite the moderate areal extent of T. testudinum in the Colombian Caribbean (661 km), it sequesters around 0.3 Tg CO year, which is equivalent to ~ 0.4% of CO emissions from fossil fuels in Colombia. This study adds data from a new region to a growing dataset on seagrass blue carbon and further explores differences in meadow C storage based on biotic and abiotic environmental factors, while providing the basis for the implementation of seagrass blue carbon strategies in Colombia.