The New Zealand mudsnail (Potamopyrgus antipodarum) (NZ mudsnail) is spreading rapidly in the western United States with several new populations being discovered every year. In Coastal Southern California national parks, NZ mudsnails can be found in the Santa Moncia Monica Mountains, specifically in Medea Creek, Malibou Lake, numerous sites on Malibu Creek, and in Las Virgenes Creek.

NZ mudsnails directly affect native biota by 1) consuming large quantities of the primary production, 2) competing with native gastropods, some threatened and endangered, 3) competing with other grazing and detritivorous invertebrates that are the foundation of aquatic food webs; and 4) negatively impacting both invertebrates and vertebrates at higher trophic levels in aquatic food webs that depend on the aquatic invertebrate food base. NZ mudsnails may displace native biota in aquatic food webs; hence their invasion has caused an alteration in the energy flow pathways among trophic level thus damaging aquatic ecosystems.

Since 2000, Santa Monica Mountains National Recreation Area - in partnership with Pepperdine University and the Resource Conservation District of the Santa Monica Mountains (RCD) - have annually surveyed park streams for crayfish and other non-native species as part of the aquatic amphibians long-term monitoring program. Monitoring helps park managers understand habitat and population changes in species over time.