Environmental DNA identifies marine macrophyte contributions to Blue Carbon sediments

Estimation of marine macrophyte contribution to coastal sediments is key to understand carbon sequestration dynamics. Nevertheless, identification of macrophyte carbon is challenging. We propose environmental DNA (eDNA) metabarcoding as a new approach for identification of sediment contributors, and compared this approach against stable isotopes—the traditional approach. eDNA metabarcoding allowed high‐resolution identification of 48 macroalgae, seagrasses, and mangroves from coastal habitats. The relative eDNA contributions of macrophytes were similar to their contributions of organic carbon based on stable isotopes; however, isotopes were unreliable for taxonomical discrimination among macrophyte sources. Additionally, we experimentally found that eDNA abundance in the sediment correlates with both the DNA (84%, R2 = 0.71, p = 0.001) and the organic carbon content (76%, R2 = 0.58, p = 0.006) per macrophyte lineage. These results demonstrate the unparallel resolution of eDNA as a method for estimation of the organic carbon contribution of marine macrophytes to blue carbon stocks.