Continual migration of patches within a Massachusetts seagrass meadow limits carbon accretion and storage

Seagrass meadows facilitate the capture and storage of organic carbon, but spatial variability in carbon has been observed among and within meadows. Here we combine sediment and seagrass data with aerial images collected near the Annisquam River, Massachusetts, USA to examine spatial variations in carbon retention across a patchy seagrass meadow. Tidal velocities were reduced within patches and elevated in bare regions, which was expected to promote carbon accumulation within the patches. However, organic carbon was not correlated with the spatial distributions of seagrass or velocity. Historical aerial images showed continual patch movement, with vegetation persistence of less than a decade throughout the meadow. The highest carbon stock occurred in the largest area of recent vegetation persistence. Though present for >45 years, the meadow accumulated negligible carbon, likely due to the migration of patches. Overall, we provide insight into a potential limitation on carbon accretion and storage in patchy meadows. The spatial variation in sediment organic carbon stocks in a patchy seagrass meadow is linked to the temporal stability of the patches, according to an analysis of sediment samples and historical aerial imagery collected in Massachusetts, USA.