Ebb and flow of an aquatic invader: Density of the invasive New Zealand mud snail (Potamopyrgus antipodarum) over time and across diverse types of aquatic systems

Background/Question/Methods

The objective of this study is to describe changes in the density of the invasive New Zealand mud snail (Potamopyrgus antipodarum) and characterize recipient benthic invertebrate communities across a range of aquatic systems over time. New Zealand mud snails are tolerant of a wide range of environmental conditions, allowing them to invade many different habitat types. P. antipodarum reproduces primarily through parthenogenesis in its invaded range and is easily transported between water bodies due to its small size (5 mm) and desiccation tolerance. While P. antipodarum has been shown to reach extremely high densities in some systems, this is not always the case. In order to better understand how characteristics of aquatic systems, such disturbance level, physical factors and biological diversity are related to P. antipodarum density, I sampled benthic invertebrate communities at several sites throughout Oregon.  Sampling sites were located along four rivers, two of these were initially invaded (Deschutes and Umpqua Rivers) and two were initially uninvaded (John Day and Siuslaw Rivers), and also included one invaded estuary (Young Bay). Samples were collected during 2006 and 2007 and again in 2012. These systems differed in their level of disturbance and in native benthic invertebrate diversity.

Results/Conclusions

Preliminary analysis of P. antipodarum densities across systems show that mud snail density was negatively correlated with native invertebrate diversity (H’) and abundance across all regions, while at the local (within river) scale, the relationship was not significant. At the estuarine site where long-term data spanning the invasion of P. antipodarum were available, there was no evidence of a negative effect of high P. antipodarum density on benthic community density, diversity or structure. Between initial sampling events in 2006 and the most recent sampling (2012), P.antipodarum densities at some sites decreased dramatically (Deschutes River) and conversely, P. antipodarum were detected at new sites (Siuslaw River). P. antipodarum densities remained high at the estuarine site. All sites sampled were adjacent to boat ramps or fishing access sites which likely increases propagule pressure at all locations. I hypothesize that factors influencing both the success and impact of P. antipodarum differ between riverine and estuarine communities. In highly disturbed communities, such as estuarine Youngs Bay, highly variable abiotic conditions, rather that competition, may limit the abundance and diversity of the community. In systems with diverse native benthic invertebrate communities, such as the Deschutes River, competition may provide biotic resistance to invaders.