New Zealand mud snail

The New Zealand mudsnail, Potamopyrgus antipodarum, sometimes previously known as Potamopyrgus jenkinsi, is a species of very small or minute freshwater snail with a gill and an operculum, an aquatic gastropod mollusk in the family Hydrobiidae.

This is an invasive species in many countries, where populations of this snail can reach phenomenal densities.

Contents 1 Forms 2 Shell description 3 Original description 4 Distribution 4.1 Nonindigenous distribution 4.2 Invasion in Europe 4.3 Distribution within the USA 5 Ecology 5.1 Habitat 5.2 Feeding habits 5.3 Life cycle 5.4 Parasites 5.5 Other interspecific relationship 6 References 7 Further reading 8 External links

Forms

• Potamopyrgus antipodarum f. carinata (J. T. Marshall, 1889)

Shell description

The shell of Potamopyrgus antipodarum is elongated and it has dextral coiling. The shell has 7 or 8 whorls. Between whorls are deep grooves.

This is an operculate snail, meaning it has a 'lid' that can seal the opening of its shell. The operculum is thin and corneus with an off-centre nucleus from which paucispiral markings (with few coils) radiate. The aperture is oval and its height is less than the height of the spire.

Some morphs, including many from the Great Lakes, exhibit a keel in the middle of each whorl; others, excluding those from the Great Lakes, exhibit periostracal ornamentation such as spines for anti–predator defense.^[2][3][4][5]

Shell colors vary from gray and dark brown to light brown.

The average height of the shell is approximately 5 mm ( in); maximum size is approximately 12 mm ( in). The snail is usually 4–6 mm in length in the Great Lakes, but grows to 12 mm in its native range.^[2][4][5]

Original description

This species was originally described as Amnicola antipodarum in 1843 by John Edward Gray:

"Inhabits New Zealand, in fresh water. Shell ovate, acute, subperforated (generally covered with a brown earthy coat); whorls rather rounded, mouth ovate, axis 3 lines; operculum horny and subspiral: variety, spire rather longer, whorls more rounded. This species is like Paludina nigra of Quoy and Gaimard, but the operculum is more spiral. Quoy described the operculum as concentric, but figured it subspiral. Paludina ventricosa of Quoy is evidently a Nematura."^[1]

Distribution

This species is endemic to New Zealand. It lives in freshwater streams and lakes in New Zealand and adjacent small islands.^[6]

Nonindigenous distribution

While endemic to New Zealand, the New Zealand mud snail has spread widely and has become naturalised and an invasive species in many areas including: Australia, Tasmania, Asia (Japan,^[7] in Garmat Ali River in Iraq since 2008^[8]), Europe (since 1859 in England), and North America (USA and Canada: Thunder Bay in Ontario since 2001, British Columbia since July 2007^[7]), most likely due to inadvertent human intervention.

Invasion in Europe

• England since 1859^[9] - probably the first introduction in Europe
• Germany
• Poland
• Western Baltic Sea since 1887^[10]
• Russia
• Azov Black Sea region, since 1951,^[11] Ukraine since 1951 in brackish waters, and since 2005 in freshwater^[12]
• Catalonia in Spain, since 1952^[13]
• Mediterranean region of France, since the end of 1950s^[13]
• Italy, since 1961^[13]
• Turkey^[13]
• Czech Republic, since September 3, 1981^[14]
• Slovakia, since 1986^[9]
• Greece, since November 2007^[13]
• and other areas

Potamopyrgus antipodarum occurs in nearly the whole of Europe. It does not occur in Iceland, Albania, Bulgaria and the former Yugoslavia.^[11]

Distribution within the USA

First detected in the United States in Idaho's Snake River in 1987, the mud snail has since spread to the Madison River, Firehole River, and other watercourses around Yellowstone National Park; samples have been discovered throughout the Western United States.^[15] Although the exact means of transmission is unknown, it is likely that it was introduced in water transferred with live game fish and has been spread by ship ballast or contaminated recreational equipment such as wading gear.^[16]

The New Zealand mud snail has no natural predators or parasites in the United States, and consequently has become an invasive species. It can reach concentrations above 500,000 per m², endangering the food chain by outcompeting native snails and water insects for food, leading to sharp declines in the native populations.^[17] Fish populations then suffer because the native snails and insects are their main food source.

The mud snails are impressively resilient. A snail can live for 24 hours without water. They can however survive for up to 50 days on a damp surface,^[18] giving them ample time to be transferred from one body of water to another on fishing gear. The snails may even survive passing through the digestive system of a fish.

Mud snails have now spread from Idaho to most western states of the U.S., including Wyoming, California, Oregon, and Montana. Environmental officials for these states have attempted to slow the spread of the snail by advising the public to keep an eye out for the snails, and bleach or heat any gear which may contain the mud snails. Rivers have also been temporarily closed to fishing to avoid anglers spreading the snails.^[19]

The snails grow to a smaller size in the U.S. than in their native habitat, reaching 6 mm (¼ in) at most in parts of Idaho, but can be much smaller making them easy to overlook when cleaning fishing gear.

Clonal species like the New Zealand mud snail can often develop clonal lines with quite diverse appearances, called morphs. Until 2005, all the snails found in the western states of the U.S. were believed to be from a single line. However a second morph has been identified in Idaho's Snake River. It grows to a similar size but has a distinctive appearance. (It has been nicknamed the salt-and-pepper mud snail due to the final whorl being lighter than the rest of the shell.) This morph has apparently been present in the area for several years before being identified correctly as a distinct morph of Potamopyrgus antipodarum. It dominates the typical morph where they overlap, and has a much higher prevalence of males.^[20]

In 1991 the New Zealand mud snail was discovered in Lake Ontario,^[21] and has now been found in four of the five Great Lakes. In 2005 and 2006, it was found to be widespread in Lake Erie.^[22] By 2006 it had spread to Duluth-Superior Harbour and the freshwater estuary of the Saint Louis River.^[23] It was found to be inhabiting Lake Michigan, after scientists took water samples in early summer of 2008.^[24] The snails in the Great Lakes represent a different line from those found in western states, and were probably introduced indirectly through Europe.^[20]

As of 26 November 2009 (2009 -11-26)^[update] Olympia Washington's Capital Lake is infested with the New Zealand Mud Snail. All three Boat Launches at the lake have been temporarily closed to pleasure boat traffic by the State's Department of General Administration.^[25]

In 2010, the Los Angeles Times reported that the New Zealand mud snail had infested watersheds in the Santa Monica Mountains, posing serious threats to native species and complicating efforts to improve stream-water quality for the endangered steelhead trout. According to the article, the snails have expanded "from the first confirmed sample in Medea Creek in Agoura Hills to nearly 30 other stream sites in four years." Researchers at the Santa Monica Bay Restoration Commission believe that the snails' expansion may have been expedited after the mollusks traveled from stream to stream on the gear of contractors and volunteers.^[26]

As of 21 September 2010 (2010 -09-21)^[update] In Colorado, Boulder Creek and Dry Creek have infestations of New Zealand Mud Snails. The snails have been present in Boulder Creek since 2004 and were discovered in Dry Creek in Sept. 2010. Access to both creeks has been closed to help avoid spread of the snails.

Ecology

Habitat

The snail tolerates siltation, thrives in disturbed watersheds, and benefits from high nutrient flows allowing for filamentous green algae growth. It occurs amongst macrophytes and prefers littoral zones in lakes or slow streams with silt and organic matter substrates, but tolerates high flow environments where it can burrow into the sediment.^{[2][5][27][28][29][30][31][32][33][34][35]}

In the Great Lakes, the snail reaches densities as high as 5,600 m² and is found at depths of 4–45 m on a silt and sand substrate.^[2][4][5]

This species is euryhaline, establishing populations in fresh and brackish water. The optimal salinity is probably near or below 5 ppt, but Potamopyrgus 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.^{[2][5][36][37][38][39]}

It tolerates temperatures of 0–34°C.^[2][5][40]

Feeding habits

Potamopyrgus antipodarum is a nocturnal grazer, feeding on plant and animal detritus, epiphytic and periphytic algae, sediments and diatoms.^{[2][5][41][42][43][44]}

Life cycle

Potamopyrgus antipodarum is ovoviviparous and parthenogenic. This means that they can reproduce asexually; females "are born with developing embryos in their reproductive system."^[5][15]

Native populations in New Zealand consist of diploid sexual and triploid parthenogenically cloned females, as well as sexually functional males (less than 5% of the total population). All introduced populations in North America are clonal, consisting of genetically identical females.^[5]

Each female can produce between 20 and 120 embryos.^[16] The snail produces approximately 230 young per year. Reproduction occurs in spring and summer, and the life cycle is annual.^{[2][5][6][39][45][46]}

The rapid reproduction rate of the snail has caused the numbers of individuals to increase rapidly in new environments. The highest concentration of New Zealand mud snails ever reported was in Lake Zurich, Switzerland, where the species colonized the entire lake within seven years to a density of 800,000 per m².^[5][47]

Parasites

In their native habitat, the snails pose no problem because of a trematode parasite which sterilizes many snails, keeping the populations to a manageable size. However they have become an invasive pest species elsewhere in the world in the absence of these parasites.^[5]

The parasites of this species include at least 11 species of Trematoda.^[5][48]

Common parasites of this snail include trematodes of the genus Microphallus.^[5][49][50]

Other interspecific relationship

Potamopyrgus antipodarum can survive passage through the guts of fish and birds and may be transported by these animals.^[51]

It can also float by itself or on mats of Cladophora spp., and move 60 m upstream in 3 months through positive rheotactic behavior.^[2] It can respond to chemical stimuli in the water, including the odor of predatory fish, which causes it to migrate to the undersides of rocks to avoid predation.^[5][52]

References

This article incorporates public domain text (a public domain work of the United States Government) from the reference.^[5]

Further reading

External links

• Pesticides Database - Chemical Toxicity Studies - [1], [2]
• CISR - New Zealand Mud Snail Center for Invasive Species Research, Summary of New Zealand Mud Snail
• Species Profile- New Zealand Mud Snail (Potamopyrgus antipodarum), National Invasive Species Information Center, United States National Agricultural Library. Lists general information and resources for New Zealand Mud Snail.