Habitat

The New Zealand Mud Snail (NZMS) is found in many water bodies, including estuaries, brackish waters, lakes, large rivers and small streams.

It occurs amongst stream beds and on submerged macrophytes; prefers littoral zones in lakes or slow streams with silt and organic matter substrates. NZMS can tolerate slightly higher flow environments in places where it can burrow into the sediment (Zaranko et al. 1997; Collier et al. 1998; Holomuzki and Biggs 1999; Holomuzki and Biggs 2000; Negovetic and Jokela 2000; Richards et al. 2001; Weatherhead and James 2001; Death et al. 2003; Schreiber et al. 2003; Suren 2005).

Beyond the broad theory that disturbed environments are more prone to the invasion of foreign species (Lodge,1993a,b; D'Antonio et al., 1999), environments that are near cities and susceptible to agricultural runoff may be also optimal for the NZMS because of their higher nutrient levels and fine sediment. (Quinn & Hickey, 1990a; Collier,1995; Quinn et al., 1997).  Even in its native habitat, the NZMS has been shown to become the most prolific macro-invertebrate in natural conditions that are reminiscent of those created by anthropogenic factors (Marshal and Winterbourn, 1979).
Some habitats are also more susceptible to NZMS invasion. Habitats relatively close to cities and/or fisheries in the mid and tail waters of streams seem to have the highest propensity of NZMS invasion (Harju 2007). 

Frenchman Flat, Piru Creek,Los Angeles County, CA

( photo by D. Bennett)

Velocity:

Fresh water systems that are supplied mostly from snowmelt runoff, or have a high water velocity usually do not have a high density population of P. antipodarum. Often vegetated areas with slower water velocity seem to provide refuge for small NZMS and may act as nurseries (Richards et al. 2001).

Water velocities are frequently related to possible passive distribution of this snail. Stream velocities over 0.6 m/s can be expected to facilitate the passive distribution of NZMS since at this velocity all NZMS were observed to detach from its substrate (Lysne 2003). In addition NZMS appear to have a greater attachment velocity then native snails (Lysne 2003).

Salinity:
The optimal salinity is probably near or below 5 ppt, but P. antipodarum is capable of feeding, growing, and reproducing at salinities of 0–15 ppt and can tolerate 30–35 ppt for short periods of time (Jacobsen and Forbes 1997; Zaranko et al. 1997; Leppakoski and Olenin 2000; Costil et al. 2001; Gerard et al. 2003). Populations in saline conditions produce fewer offspring, grow more slowly, and undergo longer gestation periods

Temperature:
Capable of tolerating a wide range of temperatures with upper thermal limits of 34°C and lower thermal limits near freezing (Zaranko et al. 1997; Cox and Rutherford 2000). NZMS reproduction is known to fail almost entirely at 24-27°C; and reproduction is being delayed and fecundity was reduced at cooler temperatures of 12°C relative to the optimum at 18°C (Dybdahl and Kane 2005, Bennett et al in press).  NZMS will probably not reach high densities in cold, headwater streams. Mudsnails will proliferate in cool springs and spring creeks, as well as in waters with moderate winter temperatures. Population of NZMS decreases during winter Gustafson (pers. comm.), Shinn (pers. com.), Kerans (pers. com.), but average water temperatures as low as 7º C (45º F) did not prevent survivorship, growth or reproduction of NZMS in the greater Yellowstone Area (Dybdahl, 2003).

Substrate preferences:
NZMS occupies a wide variety of substrates including silt, sand, mud, concrete, vegetation, cobble, and gravel.  Shinn (pers. com.) even reported them in high abundance at depths up to 60 feet in the Snake River. They do however appear to be limited by unstable substrates associated with spring runoff. New Zealand mud snail has been shown to display a preference for sediment-contaminated cobbles and the presence of filamentous green algae (Suren 2005).

NZMS frequently burrow into sand substrate, where they probably consume epipsammic algae (Holomuzki 2003).

Habitat disturbance

NZMS tolerates physical habitat disturbance and pollution well (Haynes et al. 1985, Dybdahl and Lively 1995, Schreiber et al. 2003, Suren 2005). The New Zealand mud snail has been associated with agricultural land-use disturbance (livestock grazing/pasture), where streams have been degraded by bank erosion, fine sediment, and elevated levels of nutrients and where streams often have higher SC (Harding and Winterbourne 1995, Schreiber et al. 2003). This mud snail has been found to become the dominant mollusk in environments that are rich in nutrients, so its close proximity to fisheries and cities may be due to their high level of nutrient runoff (dissolved inorganic N and P).

Where we are not finding NZMS

While the New Zealand mud snail seems to be invading nearly all types of fresh water bodies, there are some that seem more resistant to invasion.  Fresh water systems that are supplied mostly from snowmelt runoff, or have a high water velocity do not have a high density population of NZMS.  The fact that the NZMS is not present in waters that are supplied with fresh snowmelt runoff, (Statzner & Holm, 1989), as opposed to those that are feed by groundwater, may be due the low dissolved ions concentrations in these waters (Herbst, 2008).  Low ion concentrations, below an SC of 25µS per cm, may reflect the consequence of deficiencies in Na+, K+, and Mg++ for ionic and osmotic regulation.  The dependence on higher ion concentrations can be further supported by the snail's strong presence in brackish water.