The influence of seagrass traits and environmental controls on soil organic carbon stocks in Chrouy Pros Bay, Cambodia.

Seagrass habitats are valued for their ecosystem services, including organic carbon burial and storage, which has generated interest in their conservation as a nature-based solution for climate change mitigation. Globally, there is large variability in the magnitude and controls of seagrass carbon storage related to environmental conditions and seagrass traits. Here, we investigated seagrass soil and biomass carbon stocks alongside plant traits at Chrouy Pros Bay in the Gulf of Thailand, to present the first estimates of organic carbon storage in Cambodian seagrass meadows. The organic carbon stocks of 122 ± 52 Mg C ha in the top 1 m of soil are higher than the best available global estimate, and higher than recent regional estimates for other sites dominated by the seagrass Halodule pinifolia (Miki) Hartog. Seagrass traits differed with elevation in the tidal frame, where intertidal seagrasses had higher shoot density but lower biomass per shoot compared to shallow subtidal seagrasses, which undergo leaf etiolation in response to light limitation in this turbid bay. Interestingly, the sparser, subtidal meadows had larger organic carbon stocks than denser intertidal meadows, reflecting environmental conditions more conducive to organic matter burial and/or low remineralization rates. Organic carbon stocks increased with the proportion of allochthonous (mangrove and terrestrial) organic matter, which contributed 56 % to 95 % of organic carbon to seagrass-associated sediments across all sampling sites, highlighting that material fluxes connect the blue carbon ecosystems at this bay. This connectivity suggests that holistic approaches encompassing multiple habitats are needed to effectively manage coastal blue carbon ecosystems.