The Effects of Stream Flow on Invasive New Zealand Mudsnail, Potamopyrgus antipodarum, Dispersal
Authors:
Joseph Liao, Nicholas Novella, Craig SutterMentor:
Lee Kats, Vice Provost for Research and Strategic Initiatives, Pepperdine UniversityAuthors: Nicholas A. Novella, Joseph Liao, and Craig M. Sutter; Pepperdine University Mentor: Dr. Lee B. Kats, Natural Science Division; Pepperdine University New Zealand mudsnails (Potamopyrgus antipodarum) present ecological problems to the streams of the Santa Monica Mountains. The invasive snails may negatively affect the populations of native macroinvertebrate species and are resilient to predation. Preliminary observations have shown that populations of P. antipodarum decline in streams with high flow. The stream flow rates of the Santa Monica Mountain are extremely dynamic because their flow greatly fluctuates with rainfall. The purpose of this study was to investigate the differences in movement between native species, Physella sp., and invasive species, P. antipodarum, in a laboratory flow regime. A stream simulation apparatus with flow rates comparable to natural environments was used. It was found that native species exhibited a positive (upstream) average net displacement whereas invasive species displayed a negative (downstream) average net displacement. Secondly, the average number of positive taxes for P. antipodarum was notably higher than that of native snails. These findings suggest that the invasive P. antipodarum have inherent disadvantages in maintaining position in a stream post-rainfall; therefore, their ability to disperse in areas of high flow may be considerably inhibited. Additionally, the results are consistent with recent pre-rainfall and post-rainfall field surveys where the density of P. antipodarum noticeably declined whereas the density of native species was relatively unaffected. Our findings may shed light on the future dispersal of P. antipodarum in local streams, and the impact heavy rainfalls have on the stream population densities of native and invasive species.