General Impact
Potamopyrgus antipodarum may establish very dense populations, consume large amounts of primary production, alter ecosystem dynamics, compete with and displace native invertebrates, and negatively influence higher trophic levels. Its ecological plasticity, high competitive ability, high reproductive rate, high capacity for various dispersal methods, and ability to avoid predation make it a formidable colonizer capable of establishing abundant populations with significant effects on ecosystems (Alonso & Castro-Diaz, 2008). P. antipodarum and its impacts are similar to that of the extremely problematic invasive Zebra Mussel (Dreissena polymorpha) (National Park Service, undated).
P. antipodarum can establish extremely dense populations of tens to hundreds of thousands of individuals per square meter in introduced environments. In Australia densities of 50,000 snails/m2 have been recorded (Ponder 1988; Schrieber et al, 1998). In the United States densities of 200,000, 500,000 and even 800,000 snails/m2 have been recorded in several locations (Davidson et al, 2008; Dorgelo, 1987 in Brown et al, 2008; Crosier et al, undated; Hall et al, 20003; Levri et al, 2007).
These large populations undoubtedly have significant effects on ecosystems. P. antipodarum can consume up to 75% of gross primary production, dominate secondary production by composing up to 97% of invertebrate biomass, and excreting 65% of total NH4 thereby dominating C and N cycles as in the case of Polecat Creek, Wyoming. Its secondary productivity is one of the highest ever reported (194 g AFDM m-2 yr-1), being 7–40 times higher than that of any macroinvertebrate in Greater Yellowstone area (Hall et al, 2003; Hall et al, 2006; Richards et al, 2002). Such alteration of ecosystems likely results in far reaching cascading ecological impacts (Crosier et al, undated; Davidson et al, 2008; Alonso & Castro-Diaz, 2008). It has also been indicated that it may increase CO2 levels by precipitating calcium bicarbonate to calcium carbonate to produce shells (Chavaud et al, 2003 in NZMS Working Group, 2006).
P. antipodarum may displace, inhibit growth in, and compete with native invertebrates for resources in introduced locations (Alonso & Castro-Diaz, 2008; Cowie et al, 2009; Davidson et al, 2008; Hall et al, 2006; Kerans et al, 2005). High densities of P. antipodarum were believed to have negative interactions with native macroinvertebrates in several locations in Montana (Kerans et al, 2005). In the Snake River, Idaho, its site of initial introduction in the United States, it is believed to be a major cause of five species of native mollusks recently becoming endangered (Crosier et al, undated). This includes the endangered hydrobiid snail Taylorconcha serpenticola (Richards et al, 2004 in Brown et al, 2008). It is believed to limit absolute growth and the growth rate of the native desert valvata snail (Valvata utahensis) in the Snake River as well (Lysne & Koetsier, 2008). It dominates the Mont Saint-Michael Bay in western France and represented 80% of gastropods collected from all sites (Gerard et al, 2003). Similarly, P. antipodarum made up 83% of the mollusk community in a reservoir near an industrial area in Poland (Lewen & Smolski, 2006). P. antipodarum has been found to significantly inhibit growth in endemic snail Pyrulopsis robusta in Polecat Creek, Wymoing (Riley et al, 2008). A negative correlation has been demonstrated with P. antipodarum and important invertebrate species mayflies, stoneflies, caddisflies, and chironomids (Crosier et al, undated). It has also been to have a negative correlation with native hydrobiid snails in Tasmania (Poner, 1988).
P. antipodarum directly affects fish by being a poor and mostly un-digestible food source. Although rainbow trout Onchorynchus mykiss and brown trout Salmo trutta were found to feed on P. antipodarum in a study, about 80% of those consumed passed through their system undigested (NZMS Working Group, 2006). Not only does P. antipodarum replace energetic food sources, but it is believed to inflict poor health and reduce survivorship in fish that consume it based the significantly worse condition of fish with P. antipodarum in their guts (Vinsen & Baker, 2008). These direct as well as indirect impacts on fish by P. antiopdarum threaten fisheries in locations where it has established.
Additionally, P. antiopdarum has fouling potential as it is known to pass through water pipes, emerge from domestic traps, and may block water pipes, meters, or irrigation systems (Ponder, 1988; Cotton, 1942 in Zaranko, 1997; NZMS Working Group, 2006). P. antipodarum has also been found to be infected by blood fluke Sanguinicola sp. in Europe and represents a possible vector to new locations (Gerard & LeLannic, 2003).
Location Specific Impacts:Tasmania (Australia) 
Competition: A negative correlation has been found between Potamopyrgus antipodarum and nnative hydrobiid snails in Tasmania (Ponder, 1988). France
Ecosystem change: Of gastropods collected in the Mont Saint-Michael Bay in western France Potamopyrgus antipodarum represented 80% collected from all sites (Gerard et al, 2003). Poland
Ecosystem change: Potamopyrgus antipodarum was found to comprise 83% of the mollusk community in a reservoir surveyed in Poland (Lewin & Smolinski, 2006).
Reduction in native biodiversity: The introdocution of Potamopyrgus anitpodarum significantly reduced biodiversity in Upper Silesia, Poland (Strzelec et al, 2006). United States (USA)
Competition: The National Park Service (Undated) states that "preliminary baseline surveys indicate that the mudsnails may be impacting the invertebrate community . . . not only through physical displacement or crowding, but also through competitive interactions such as food availability."
Modification of hydrology: "Because the West is known for abundant trout and productive fishing spots, there is concern that P. antipodarum will impact the food chain for native trout and the physical characteristics of the streams themselves" (USGS-FISC, Undated).
Modification of natural benthic communities: The National Park Service (Undated) states that "these small molluscs have the potential to 'cover the stream bottom,' similar to impacts observed with the Zebra Mussel (Dreissena polymorpha) in the midwestern U.S. "
Modification of nutrient regime: "P. antipodarum has been shown to drastically alter primary production in some streams" (Richards et al 2002). "Because the West is known for abundant trout and productive fishing spots, there is concern that P. antipodarum will impact the food chain for native trout and the physical characteristics of the streams themselves" (USGS-FISC, Undated). Idaho (United States (USA))
Competition: Potamopyrgus antipodarum is believed to compete with and may displace native molluscs in the Snake River. Five species of native molluscs have recently been listed as endangered in part because of the establishment of the P. antipodarum and its potential impacts (Crosier et al, undated).
Other: The presence of increasing densities of Potamopyrgus antipodarum are believed to limit absolute growth and the growth rate of the native desert valvata snail Valvata utahensis in the Snake River (Lysne & Koetsier, 2008).
Threat to endangered species: Potamopyrgus antipodarum was the dominant snail species in three habitats in Banbury Springs, Idaho and is believed to outcompete and displace native snails including the threatened Taylorconcha serpenticola (Richards et al, 2001). Montana (United States (USA))
Ecosystem change: Densities of Potamopyrgus antipodarum of over 28,000/m2 in a spring creek of south western Montana have been found to have a negative correlation with mayfly, stonefly, caddisfly, and chironomid populations (Crosier et al, undated). Oregon (United States (USA))
Ecosystem change: High densities of Potamopyrgus antipodarum established in Oregon alter ecosystems and affect native benthic invertebrates (Bersine et al, 2008). Utah (United States (USA))
Other: Rainbow trout Onchorynchus mykiss and brown trout Salmo trutta were found to consume Potamopyrgus antipodarum in the Green River Utah. P. antipodarum is a poor quality food source and is often not even digested at all by these fish. Trout with P. antipodarum in their guts were in signifacntly worse condition than those without. P. antipodarum may result in poor health and other negative effects on fish that consume them (Vinsen & Baker, 2008). Wyoming (United States (USA))
Competition: High densities of Potamopyrgus antipodarum were associated with low colonization of other macroinvertebrates. Negative interactions between native macroinvertebrates and P. antipodarum may have the potential to compete with and influence the large scale distribution of other macroinvertebrates (Kerans et al, 2005).
Ecosystem change: Potamopyrgus antipodarum was found to consume nearly all primary production in the highly productive Polecat Creek, WY and dominated flows of C and N (Hall et al, 2003). Also the production of P. antipodarum was found to be one of the highest for any stream invertebrate ever reported and constituted 65-92% of total invertebrate productivity. It also dominated secondary production and had extremely high rates of secondary production in the Firehole River and Gibbon River(Hall et al, 2006).
Reduction in native biodiversity: Potamoyrgus antipodarum was found to significantly inhibit the growth of endemic snail Pyrulopsis robusta in Polecat Creek, WY (Riley et al, 2008).
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