Hotwater physa (Physella wrighti) COSEWIC assessment and upate status report: chapter 11

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Technical Summary

Physella wrighti

Hotwater Physa – Physe d’eau chaude

Demographic Information

Population trend and dynamics

Number of mature individuals in each population

Values for different lengths of Alpha stream sampled

•      1,426 (Sep 1997)
•      5,186 (Aug 2000)
•      1,426 (Aug 2006)

Grand Total: Number of mature individuals in the total population unknown

Extent and Area Information

Quantitative Analysis

Not available

Threats (actual or imminent, to populations or habitats)

1. Recreational use of the hotsprings continues
2. The small population size and very limited geographic distribution makes this species extremely vulnerable to disturbance brought about by anthropogenic activities.
3. Rapid temperature change could occur in Alpha Stream if the outflow from Alpha Pool were diverted, exposing species to potentially lethal ambient air temperature. This would be most likely to occur through stochastic events or through the actions of recreational users altering the dam or creating alternative outflows.
4. Trampling caused by park users exploring Alpha Stream

Rescue Effect (immigration from an outside source)

Current Status

COSEWIC: Endangered, April 2008

Status and Reasons for Designation

Status: Endangered

Alpha-numeric code: B1ac(iv)+2ac(iv)

Reasons for Designation: This small snail is an endemic species living only within the hotsprings complex located in Liard River Hotsprings Provincial Park in British Columbia. The population is small, numbering fewer than 10,000 individuals and occupies an extremely restricted habitat around the margins of two pools and an outlet stream. Population size is believed to fluctuate by at least an order of magnitude in this short-lived snail (~1 year lifespan). The species is a habitat specialist requiring geothermally regulated water and substrates near the water/air interface in areas of no current. The hotsprings complex has been in use by humans for over 200 years. The species has survived structural modification and maintenance of the pools, the introduction of foreign substances such as soaps and shampoos, and trampling. However, a single event such as abrupt changes in water flow, chemical contamination or introduction of exotic species, could significantly affect persistence of this snail.

Applicability of Criteria

• Criterion A: Not applicable. There is no evidence that the population is declining or will decline over the next 10 years.
• Criterion B: Meets B1: EO ~ 0.02 km² (< 5,000 km²) for Endangered, and B2: 1 km² (< 500 km²) for Endangered a: Number of locations, 1 (less than or equal to 5, Endangered), c(iv): extreme fluctuations in mature individuals observed annually in a species that is believed to have a lifespan of ~ 1 year.
• Criterion C: Not applicable. The number of individuals is most likely > 2,500 but < 10,000, but the number of mature individuals is not believed to be in decline at present nor is it projected to decline in the next 10 years.
• Criterion D: Meets D2 for Threatened because: AO 1 km² (< 20 km²), there is only 1 locality (less than or equal to 5), the species is an habitat specialist, the locality is heavily used by humans for recreation, and a single catastrophic event could eliminate the entire population.
• Criterion E: Does not apply; not available.