Use of environmental DNA to survey the distribution of an invasive submerged plant in ponds

The first step toward solving the problems caused by an invasive alien species is to know the distribution of the species. However, species in underwater environments are difficult to investigate. The recent development of environmental DNA (eDNA) analysis has made it possible to investigate the distribution of a target species simply by analyzing the DNA in the water. To date, few investigators have used eDNA detection of aquatic plants. We established an eDNA detection method for Egeria densa, an invasive aquatic plant species in Japan; used eDNA detection to survey the species in aquaria; and applied this method to water samples from 23 outdoor ponds. We also used visual observations of the ponds. The aquarium experiments revealed that the eDNA concentration in the water increased rapidly and peaked 1 or 2 d after starting the experiment, after which it decreased rapidly, reaching its lowest point on the 5th day. In the field surveys, we visually observed E. densa at 5 ponds, and the eDNA of E. densa was detected from the same 5 ponds. Thus, the eDNA results perfectly matched the observational results. Our work confirms that detection of aquatic plants by eDNA analysis is feasible.