Field application of environmental DNA techniques to detect early stages of invasion by the destructive New Zealand mud snail

Species transported by humans that cause damage to ecosystems to which they are introduced are considered invasive. Restoration of the original ecosystem after an invasive population has arrived is expensive and difficult but more likely to succeed when invasions are discovered early. Containment efforts to prevent the spread of invasions also benefit from earlier knowledge of invaded sites. A new tool that can identify invasive species without needing to physically locate them is currently being developed. This tool uses DNA collected directly from the environment rather than from an organism itself, called environmental DNA (eDNA). By using a probe to identify this eDNA, we can tell whether a species has recently been present in a given location. I collected water samples from eight sites near a known invasive population of the freshwater New Zealand mud snails (NZMS). These sites plausibly could be invaded by NZMS and may lead to further spread due to their popularity with fly-fishermen. After filtering these samples to collect eDNA, I found evidence for NZMS invasion at five of the eight sites, with later physical confirmation of mud snails at one of these sites. This study is the first example of successful application of eDNA to detect new invasions of the freshwater New Zealand mud snail, setting the stage for further monitoring of at-risk sites to detect and control new invasions of this destructive snail.