Environmental DNA Reveals Patterns of Biological Invasion in a Fjord

Abstract

Introduced species have the potential to cause ecological and economic harm to coastal and estuarine ecosystems. Understanding which habitat types are most vulnerable to biological invasions, where invasions originate, and the vectors by which they occur can help direct limited resources to prevent or mitigate harm. Data on introduced species occurrence can help guide interventions at all stages of invasion, from first introduction, to naturalization and invasion. Monitoring at an ecosystem scale requires considerable investment of time, resources, and taxonomic expertise. Environmental DNA (eDNA) metabarcoding samples coastal ecosystems at broad spatial and temporal scales to augment established monitoring methods. I use eDNA sampling to identify the presence of introduced species across distinct habitats in the Salish Sea in Washington State, USA. Sampling sites cross a range of habitats, from estuarine mudflats to marine rocky shores. The introduced species captured by my assay include both well-documented invaders and species not previously reported in the Salish Sea. I find an introduced assemblage dominated by shellfish and algae with native ranges in the temperate western Pacific. My results reveal a far greater invasion level in estuarine habitats than on marine rocky shores. I find an increase in invasion level with higher water temperatures in spring and summer across habitat types. This analysis contributes to a growing understanding of the biotic and abiotic factors that influence invasion level. eDNA surveys provide an effective means to monitor ongoing biological invasions and to better understand the factors that drive these invasions.