Range expansion, sudden declines and unknown food web interactions of an aquatic invader

Background/Question/Methods

In western North America, the invasive New Zealand mudsnail (NZMS; Potamopyrgus antipodarum) is both expanding its range at the same time that established populations have recently declined in multiple streams. At present, comparatively little is known about the actual drivers or consequences of this invasion – the majority of efforts have focused on documenting changes in distribution. Studies of Potamopyrgus’ effect on nutrient cycling suggest dramatic alterations of stream ecosystems are possible. Since these these snails both dominate secondary production and do not have a terrestrial component to their life history, the consequences of this invasion have the potential to propagate across ecosystem boundaries, altering linked aquatic and terrestrial ecosystems. We used information about NZMS ecology in invaded and native ranges and time series data collected from three invaded sites to evaluate (1) likely shifts in connected stream and terrestrial food webs following NZMS invasion and (2) the plausibility of general drivers that could explain NZMS declines.

Results/Conclusions

We did not identify a single driver that could be linked to all locations where declines have been reported. However, we did find limited support for flow disturbance as a driver and strong support to eliminate temperature, predation, parasites, and genetics as isolated drivers. While food web effects from NZMS invasion are predicted to be strong, documentation of dramatic shifts remains sparse and populations appear to be declining. NZMS may represent an invasion that ultimately creates little functional change at the same time as it alters community structure and food web linkages across ecosystems.