Boom and bust of an aquatic invasive species? Population monitoring of the New Zealand mudsnail (Potamopyrgus antipodarum) and interactions with native species in Polecat Creek, WY

The invasive New Zealand mudsnail (Potamopyrgus antipodarum) has been found to reach densities exceeding 500,000 individuals/m2 in Polecat Creek, located in the Greater Yellowstone Ecosystem in Wyoming. The biomass of P. antipodarum in Polecat Creek has declined in recent years, suggesting the population “boomed and busted”; the population was booming in 2000-2001, but in 2011 the biomass had decreased by ~93%, suggesting a “bust” period for P. antipodarum. Native, net-spinning caddisflies (Hydropsyche spp.) have increased dramatically in biomass from 2001-2010, which may indicate that some native macroinvertebrates have increased in biomass due to release of suppression by P. antipodarum. I collected macroinvertebrate core samples in Polecat Creek to monitor any changes in macroinvertebrate biomass and performed field experiments to determine a possible mechanism by which P. antipodarum may have suppressed Hydropsyche caddisfly populations. I allowed Hydropsyche larvae to establish and build nets on tiles within experimental chambers in Polecat Creek and added “boom” and “bust” densities of P. antipodarum to chambers. Preliminary results showed no significant difference between the number of nets present in control chambers excluding P. antipodarum and chambers containing “boom” and “bust” densities of P. antipodarum. This suggests that P. antipodarum do not actively destroy nets, but may interfere with feeding by clustering upon nets. Featured photo from Figure 2 in report.

Testing Field Methods to Assess Interactions Between Native Caddisflies and the Invasive New Zealand Mudsnail (Potamopyrgus Antipodarum)

In Polecat Creek, WY, located in the Greater Yellowstone Ecosystem, the invasive New Zealand mudsnail (Potamopyrgus antipodarum) has been found to reach densities exceeding 500,000 individuals/m². At this extremely high density, P. antipodarum has been observed to consume most of the gross primary production and have a negative impact on native macroinvertebrates such as the Hydropsyche caddisfly. The current population of P. antipodarum in Polecat Creek has declined suggesting the population “boomed and busted”; the population was booming in 2000-2001, but in 2011 the population had decreased substantially suggesting a “bust” period for P. antipodarum. Native Hydropsyche caddisflies have increased dramatically in biomass during the 10-year span of data, which may indicate that some native macroinvertebrates have increased in biomass due to release of suppression by P. antipodarum. Consequently, during my research this summer I assessed several possible methods to test suppression of Hydropsyche by P. antipodarum. I devised a method to collect Hydropsyche and determined whether Hydropsyche can survive in experimental chambers for use in a future field experiment. I built wooden tiles to colonize Hydropsyche out of 4x4x2 inch wood blocks with 1/2 inch grooves along the length of the tile. Colonization was successful with approximately two Hydropsyche collected per tile in a 24-hour period. Based on low survival of Hydropsyche within experimental chambers, the use of different experimental chambers will be necessary. Specifically, chambers that are open on the upstream side should be used to better allow a fast flow of water, which is a requirement for Hydropsyche to collect food.