Quantifying the distribution of tropical coastal blue carbon using environmental DNA

Tropical coastal blue carbon is stored in shallow-water ecosystems such as mangrove forests, seagrass meadows and macroalgal beds. Carbon is also exported from these ecosystems offshore and into sediment pools in the form of cellular organic carbon that comprises DNA among other components. Environmental DNA (eDNA) has recently shown promise in the identification and quantification of macrophytes such as mangroves, seagrasses and macroalgae from coastal sediment and seawater. This study tested an eDNA approach for detecting and quantifying tropical coastal macrophytes using a 18S-V7 mini-barcode from 60 seawater and sediment samples. The results demonstrated the ability of eDNA metabarcoding to detect significant temporal patterns in tropical coastal macrophyte communities. Spatial patterns of eDNA displayed high site fidelity but limited difference between depths. Furthermore, our study underscores important environmental constraints on eDNA monitoring of tropical blue carbon, including high temperature and rainfall that can impact eDNA residence time and detection levels. Not surprisingly, there remains a critical need to improve reference DNA databases and primers to more precisely characterise macrophyte communities. These findings contribute to the development of an eDNA-based monitoring system to track nearshore stocks and fluxes of tropical blue carbon and enhance blue carbon conservation efforts in a biodiverse region disproportionately affected by climate change.