A vacant and an occupied shell of the masked duskysnail
Low-
Moderate
The masked duskysnail's population size in Washington is low and has a declining trend. They are currently found at only two lake sites in the state: one in Ferry County and one in Okanogan County. These snails are declining due mainly to habitat degradation and destruction, both in terms of populations and numbers of individuals.
Description and Range
Physical description
The masked duskysnail is an aquatic snail belonging to the family Hydrobiidae. Like all members of the Hydrobiidae family, the masked duskysnail possesses gills that make it dependent upon dissolved oxygen. Members of the Amnicola genus have high-spired shells measuring between 1/8th and 1/4 inch (4 millimeters) tall. The shells are of a brownish color, diffusely shaded, with up to 8 convex whorls. A whorl is the part of the shell that is one 360-degree section of the spiral.
All western populations of Amnicola species are masked duskysnails. Western populations may display subtle differences to those in the eastern United States.
Ecology and life history
This freshwater snail occurs in well-oxygenated kettle lakes among aquatic macrophyte vegetation beds, but is absent from dense aquatic vegetation areas. The species is found on soft oxygen-rich substrate at a depth of approximately two to six feet.
The snail is a detritivore, feeding on dead and decomposing organic matter. It grazes along the stems and leaves of aquatic plants, eating small organisms clinging to this material.
Members of Hydrobiidae cross-fertilize and breed only once during their life span of about one year. They reach sexual maturity a few months after hatching. Eggs are laid in the spring and hatch in between 2 to 4 weeks.
Geographic range
Masked duskysnails are a rare presence in the western United States, and small populations are currently found at only three lake sites: one in Ferry County, one in Okanogan County, and one in northwestern Montana.
According to a 2016 taxonomic study, all western populations of Amnicola are Amnicola limosa, the masked duskysnail. Nonetheless, Washington and Montana’s populations represent a significant westward range expansion of the species, and may warrant separate conservation management.
Climate vulnerability
Sensitivity to climate change
Low-
Moderate
There is limited information on the sensitivity of the masked duskysnail to climate change. The masked duskysnail occurs in Washington and Montana; in Washington, their habitat includes two large kettle lakes in eastern Washington: Curlew Lake in Ferry County and Fish Lake in Wenatchee National Forest. This species is considered to be a mud specialist, living on soft bottom substrates in highly oxygenated, cool lakes (preferring temperatures below 18°C); changes in water temperature and flow regimes that affect dissolved oxygen levels and stratification may therefore negatively affect the masked duskysnail. Changes in flow regimes that increase nutrient runoff may cause dense filamentous algae blooms that impair or prevent access to important food resources. This species occurs in low densities in isolated populations and therefore may be acutely vulnerable to diseases or other disturbance regimes causing mass mortality because they may not be able to quickly rebuild populations.
Exposure to climate change
Moderate
- Altered flow regimes leading to increased nutrient runoff
- Reduced oxygen
- Increased water temperatures
- Increased disease outbreaks
Conservation
For aquatic snails, limiting factors may include hardness, acidity, dissolved oxygen, salinity, high temperature, and food availability as associated with depth. Snails are uncommon in habitats with surface acidity greater than pH 5. Dissolved oxygen limits diversity, so severely polluted waters (oxygen consumed by algae blooms) are often devoid of freshwater snails excepting pollution-tolerant species. Most species live in the shallows, (depths less than 10 feet) where food abundance is greatest. As a result, drastic water fluctuations (draw-downs) may cause declines in snail populations.
Snails in the Hydrobiidae family are of conservation concern because they have specialized habitat requirements. They do not readily disperse and populations are isolated. They are vulnerable to alteration of their habitat. These snails are declining due mainly to habitat degradation and destruction, both in terms of populations and numbers of individuals.
Conservation Threats and Actions Needed
- Fish and wildlife habitat loss or degradation
- Threat: Pollution and siltation.
- Action Needed: Protect water quality.
- Resource information collection needs
- Threat: Taxonomic clarification.
- Action Needed: Inventory the species; determine taxonomic clarification.
See the Climate vulnerability section for information about the threats posed by climate change to this species.
Resources
References
Applegarth, J. S. 1999. Management Recommendations for Cryptomastix hendersoni, the Columbia Oregonian (land snail) v.20, Section 2, in T. E. Burke, J.S. Applegarth, and T. R. Weasma. Management Recommendations for Survey and Manage Terrestrial Mollusks (v. 2). USFS and BLM.
Burke, T. E. 2013. Land Snails and Slugs of the Pacific Northwest. Oregon State University Press, Corvallis, OR. 344 pp.
Burke, T., J. Applegarth, T. Weasma, and N. Duncan. 1999. Management recommendations for Survey and Manage terrestrial mollusks, ver. 2.0. USDA Forest Service, USDI Bureau of Land Management. Available online at https://www.or.blm.gov/surveyandmanage/MR/TM23Species/m2000-003.htm
COSEWIC. 2013. COSEWIC assessment and status report on the Oregon Forestsnail Allogona townsendiana in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. xii + 87pp. (https://www.canada.ca/en/environment-climate-change/services/species-risk-public-registry.html)
Duncan, N. 2009. Vespericola columbianus depressa. Species Fact Sheet. Interagency Special Status/Sensitive Species Program, Forest Service, Bureau of Land Management. (https://www.fs.fed.us/r6/sfpnw/issssp/documents/planning-docs/sfs-ig-vespericola-columbiana-depressa-2009-02.doc)
Edworthy, A., K. Steensma, H. Zandberg, and P. Lilley. 2012. Dispersal, home range size and habitat use of an endangered land snail, the Oregon Forestsnail (Allogona townsendiana). Canadian Journal of Zoology 90(7):875–884.
Frest, T. J., and E. J. Johannes. 1995. Interior Columbia Basin Mollusk Species of Special Concern. Final Report, Deixis Consultants, Seattle. Prepared for Interior Columbia Basin Ecosystem Management Project, Walla Walla, WA 362 pp.
Liu, H-P., Marceau D. and R. Hershler. 2016. Taxonomic identity of two amnicolid gastropods of conservation concern in lakes of the Pacific Northwest of the USA. Journal of Molluscan Studies. 82:464-471.
Monthey, R. and N. Duncan 2005. Conservation assessment for Lyogyrus n.sp.2, Masked Duskysnail. USDA Forest Service Region 6, and USDI Bureau of Land Management, Oregon and Washington. (originally issued in 1998 as management recommendations by R. Monthey; revised 2005 by N. Duncan). 10 pp.
Steensma, K. M. M., L. P. Lilley, and H. M. Zandberg. 2009. Life history and habitat requirements of the Oregon forestsnail, Allogona townsendiana (Mollusca, Gastropoda, Pulmonata, Polygyridae), in a British Columbia population. Invertebrate Biology 128:232–242.
USFWS. 2011. Endangered and Threatened Wildlife and Plants: 90-day finding on a petition to list 29 mollusk species as threatened or endangered with critical habitat: proposed rule. Federal Register 76 (No. 193, October 5, 2011): 61826-61853.
Washington Department of Natural Resources. 2005. Covered Species Technical Paper. Aquatic Resources Program Endangered Species Act Compliance Project. Prepared by Entrix and Battelle. Washington Department of Natural Resources, Olympia, WA.