Drivers of Seagrass Meadow Sediment Organic Carbon Storage from Bioregional to Global Scales

Seagrass meadow ‘blue carbon’ stock is influenced by the meadow’s species composition and the environmental conditions in which they live. However, the influence of meadow organic carbon (OC) stock drivers can vary across seagrass bioregions. We used a meta-analytic approach to assess the influence of seagrass species, hydrologic setting, and tidal class on seagrass sediment OC storage and how it varied across bioregions using data from 39 studies published between 2011 and 2020. We leveraged a Bayesian hierarchical model approach that allowed us to use both aggregate values (mean ± error) and individual data points available in the literature. We provide a revised estimate of the global seagrass meadow OC storage of 573.67 [400.33—745.90] Tg and a mean local storage of 34.7 [27.5—41.8] Mg ha-1 within the top 30 cm of their sediments (mean [95% Credible Interval]). Globally, seagrass life-history had a strong influence on OC stock but this influence varied substantially across bioregions. Meanwhile, hydrologic setting and tidal class were weak predictors of OC stock at the global scale and across bioregions. Our study expands the evidence of variation in OC stock drivers across bioregions to a global scale and reaffirms the importance of considering bioregional settings. The limitations of our meta-analytic approach call attention to data gaps in the seagrass literature.