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. This extremely high density of P. antipodarum has been observed to consume much of the gross primary production and has 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"; it was observed in data collected in 2000-2001 that there was a "boom" period of P. antipodarum, and in 2011, a "bust" period of P. antipodarum. The 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. During my research this summer I assisted a graduate student, Daniel Greenwood in assessing several possible methods to test suppression of Hydropsyche by P. antipodarum. We devised methods to collect Hydropsyche and determined whether Hydropsyche can survive in experimental chambers for use in a future field experiment. We built Hydropsyche collection tiles out of 4x4x2 inch wood blocks with ~1/4 inch grooves along the length of the tile. Collection was successful with approximately two Hydropsyches collected per tile in a 24-hour period. Based on the 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 food collection.