Distribution and food chain assimilation of New Zealand mud snails in Spirit Lake, Washington, USA

Mount St. Helens National Volcanic Monument was designated by the U.S. Congress in 1982 to conserve the landscape for natural regeneration, scientific research, education, and cultural resource preservation. However, this designation has not eliminated threats from the introduction of non-native species. The non-native New Zealand mud snail (NZMS), Potamopyrgus antipodarum, was first observed in 2016 along the SW shore of Spirit Lake at the foot of Mount St. Helens, despite the lake’s closure to public recreation and isolation from other known sites harboring NZMS. Our study mapped native and non-native snails on aquatic macrophytes in Spirit Lake, analyzed NZMS eDNA in Spirit Lake and surrounding waters, measured stable isotopes in snails and their food sources, and analyzed rainbow trout (Oncorhynchus mykiss) gut contents from a twenty-year survey to examine the patterns of spatial distribution, habitat occurrence, and resource use. Our results show that NZMS colonies were likely firs..., eDNA Sampling
On two dates in October 2019 we gathered water samples from 18 sites for eDNA testing. Sites included nearshore waters along the SW shore of Spirit Lake (where NZMS had been observed annually since 2016), tributary streams flowing into Spirit Lake along this shoreline, nearby isolated ponds, and downstream in Coldwater Creek and Coldwater Lake. Flow rates in the tributary streams entering Spirit Lake were generally low in October (0.5-90 L s-1 measured in 2008; Gawel et al. 2018). Flow rates exiting the tunnel outlet and into Coldwater Creek were approximately 2800 L s-1 at the time of sampling (Gawel et al. 2018; US Geological Survey 2024).  At each site two replicate 1000 mL samples were collected in sterile one-liter Nalgene bottles following published protocol (Goldberg and Strickler 2017). Samples were placed on ice and filtered within 12 hours of collection. Both replicates were analyzed for 13 of the sampling sites with single samples run for the remaining 5 sites, ..., , # Distribution and food chain assimilation of New Zealand mud snails in Spirit Lake, Washington, USA

[https://doi.org/10.5061/dryad.6t1g1jx71](https://doi.org/10.5061/dryad.6t1g1jx71)

This data set contains measurements of snail (*Potamopyrgus antipodarum*, *Gyraulus deflectus*, and *Lymnaea* sp.) density per vegetation volume distributed spatially and per *Oncorhynchus mykiss* digestion track over time and distributed spatially in Spirit Lake, Mount St. Helens National Volcanic Monument, Washington, USA. *P. antipodarum* relative density is also measured using eDNA samples collected in Spirit Lake and surrounding water bodies. Stable isotope analyses (d13C and d15N) and %C and %N of the various food web members (periphyton, macrophytes, macroinvertebrates, amphibians, and fish) are also included.  

## Description of the data and file structure

All data are in one .XLSX file with 5 tabs as described below.

#### eDNA Data (New Zealand mud snail eDNA relative abundance in water sampl...