Environmental DNA identifies coastal plant community shift 1,000 years ago in Torrens Island, South Australia

Anthropogenic activities are causing detrimental changes to coastal plants– namely seagrass, mangrove, and tidal marshes. Looking beyond recent times to past vegetation dynamics is critical to assess the response and resilience of an environment to change. Here, we develop a high-resolution multi-proxy approach, providing a new evidence base to decipher long-term change in coastal plant communities. Combining targeted environmental DNA analysis with chemical analysis of soils, we reconstructed 4,000 years of change at a temperate wetland on Torrens Island South Australia and identified an ecosystem shift that occurred ~ 1000 years ago. What was once a subtidal seagrass system shifted to an intertidal mangrove environment that persists at this site today. We demonstrate that high-resolution historical changes in coastal vegetation can be attained using these proxies. This approach could be applied to other ecosystems to improve the way we protect, conserve, and restore vegetated ecosystems.