Application of environmental DNA methods for the detection and abundance estimation of invasive aquatic plant Egeria densa in lotic habitats

Estimating the presence and abundance of non-native species in the early stage of invasion is important to prevent further spread of non-native species in aquatic systems. Environmental DNA (eDNA) methods have been applied for aquatic plants; however, it is still questionable on the accuracy of the eDNA methods for the detection and abundance estimation of aquatic plants in lotic systems. Here, we studied the invasive aquatic plant Egeria densa in the tributaries of the Gonokawa River in Japan to compare the E. densa detection rate of the eDNA method with that of the three sampling methods and examine the relationships of the eDNA flux to the upstream plant coverage, plant stem fragment flux, and plant tissue DNA flux of E. densa in the study sites on each season. Our results indicated that the eDNA method better detected the presence of E. densa in our study sites than other methods. The eDNA flux was directly related to the coverage rank and the plant tissue DNA flux in the study sites in both months. These results suggest that the eDNA methods have a potential as monitoring tool for early detection and relative abundance estimation of invasive aquatic plants in lotic systems.