Aquatic organisms release a constant amount of DNA into the water, known as environmental DNA (eDNA). The Danish Environmental Protection Agency, in collaboration with NIVA Denmark and the Natural History Museum of Denmark, has been monitoring eDNA from non-indigenous species in Danish waters.

Previously, eDNA analyses were performed using a method called quantitative Polymerase Chain Reaction (qPCR), but this method had limitations, particularly in detecting low levels of eDNA.

A newer method called digital droplet Polymerase Chain Reaction (ddPCR) has shown to be more precise in detecting low levels of DNA. In this project, filtered water samples from Danish waters were collected by the Danish Environmental Protection Agency in two seasons annually from 2017 to 2022, and were analyzed using both qPCR and ddPCR. The aim was to determine whether ddPCR could provide higher precision and greater sensitivity to low levels of eDNA in water samples while reducing the working time.

The results showed that for 17 out of the 19 tested species, ddPCR was as accurate as qPCR when eDNA levels were sufficiently high. However, ddPCR was more precise in assessing the uncertainty at low levels of eDNA. One advantage of ddPCR was that it required fewer reaction tubes per water sample compared to qPCR.

Based on these results, it is recommended to use ddPCR for future monitoring of eDNA from marine invasive species in Danish waters. This will result in improved precision and time savings. This technology offers the possibility of more effective identification and mapping of non-indigenous species and their distribution in Danish waters.

Read the full report in Danish here.