Snake River Physa Snail

Physa natricina

Description

The Snake River physa snail, Physa natricina, is a "living fossil" in that it is a relict from Pleistocene-Holocene lakes and rivers in southeastern Idaho and northern Utah. This species possesses a 0.2 in (5-7 mm) long shell with 3-3.5 whorls. Fresh shells are amber to brown in color. Physids (bladder snails) have lungs and are quite similar to the Lancids. This family possesses a sinitral thin oval-shaped shell that spirals to the left and the body openings are on the left side. The final whorl contributes to about four-fifths of shell bulk. These snails have a broad tantaculate and the mantle margin covers the shell.

Behavior

Physids feed on algae, and delineate trails with mucus. The hermaphroditic reproduction of this species involves the exchange of spermatophores. Courtship entails investigation using tentacles and mouths. Slowly edging closer, the snails rear up at right angles to the ground with the bases of their feet in full contact. Supported by the tip of their shells and the hind part of the feet, the male and female open their orifices while caressing each other with their tentacles.

The detritivorous characteristics of this species restricts it to a diet of diatoms and plant debris. This snail grazes along mud surfaces, rocky surfaces and macrophytes.

Habitat

This snail occurs on the undersides of gravel to boulder substratum in swift current in the mainstem Snake River. Specimens have been recorded from boulders in the deepest accessible part of the river at the margins of rapids.

Distribution

Fossil records of the snail occur in deposits from Pleistocene-Holocene lakes and rivers from southeastern Idaho and northern Utah.

This species' current range is believed to be from Grandview upstream through the Hagerman Reach in Gooding, Idowyhee, and Elmore Counties, Idaho.

However, the native bottom fauna has been virtually eliminated in the Gooding County type locality and the species is believed to be extirpated from this region.

Threats

The free-flowing, cool water environments required by this species have been impacted by and are vulnerable to continued adverse habitat modification and deteriorating water quality from hydroelectric development, peak-loading effects from existing hydroelectric project operations, water withdrawal and diversions, water pollution, and inadequate regulatory mechanisms.

Water quality degradation continues from increased water use and withdrawal, aggravated by recent drought-induced low flows. The 121-mile (195-km) stretch of the Snake River is impacted by agricultural return flows; runoff from between 500 and 600 dairies and feedlots; effluent from over 140 private, state, and Federal fish culture facilities; and point source (e.g. municipal sewage) discharge. The ultimate impact of these factors are increased nutrient loads and concentrations which adversely affect the lotic fauna. Nutrient loading contributes to dense blooms of free-living and attached filamentous algae, which the species cannot utilize. This algae will often cover rock surfaces, effectively displacing suitable snail habitats and food resources.

A more recent threat is the discovery of the New Zealand mudsnail in the middle Snake River. The eurytopic mudsnail is experiencing explosive growth in the river and shows a wide range of tolerance for water fluctuations, velocity, temperature and turbidity. The mudsnail species seems to prefer warmer, polluted waters over pristine cold spring environments.

Conservation and Recovery

The U. S. Fish and Wildlife Service published a Recovery Plan for the Snake River Physa snail and other endangered mollusks in the Snake River Basin in 1992. Conservation of this endangered snail requires the protection of its surviving critical habitat in the mainstem Snake River from impoundment, diversion, pollution, and other threatening activities. Moreover, where possible, habitat quality must be improved if the Snake River Physa snail and other endangered species are to recover. The populations of the Snake River Physa snail should be monitored, and research undertaken into its biology and habitat needs.

Contacts

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
http://pacific.fws.gov/

Snake River Basin Fish and Wildlife Office
1387 South Vinnell Way, Suite 368
Boise, Idaho 83709-1657
Telephone: (208) 378-5243
Fax: (208) 378-5262

References

U. S. Fish and Wildlife Service. 14 December 1992. "Endangered and Threatened Wildlife and Plants: Determination of Endangered or Threatened Status for Five Aquatic Snails in South Central Idaho." Federal Register 57 (240): 59244-59257.

U.S. Fish and Wildlife Service. 1995. "Snake River Aquatic Species Recovery Plan." Snake River Basin Office, Ecological Services, Boise, Idaho.