Banff Springs snail (Physella johnsoni) COSEWIC assessment and status report: chapter 2

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COSEWIC
Executive Summary

Banff Springs Snail
Physella Johnsoni

Species Information

The Banff Springs Snail, Physella johnsoni (Clench, 1926), is a small, globe-shaped aquatic snail with a shell length up to 11 mm that coils to the left. Morphological and molecular analyses suggest that it is a valid species, although not all agree. It is suspected the species evolved within the past 3200 to 5300 years, which has resulted in limited genetic divergence from its ancestors.

 

Distribution

Physella johnsoni is confined to thermal springs near Banff, Alberta, within Banff National Park (BNP). The species was described in 1926 and collected from nine separate thermal springs. Two other historic sites were most likely the result of piped water or were erroneous. By 1996, the species was found living only in five thermal springs, four of which are in a high visitor-use area, the Cave and Basin National Historic Site. Two extirpated subpopulations were re-introduced, one each in 2002 and 2003 and are now self-maintaining subpopulations. These two re-introduced subpopulations are eligible for consideration in assessment of the species in accordance with COSEWIC guidelines on manipulated populations. All historic and current sites--100% of the global distribution--are found in Canada within BNP. If the seven sites are combined, all the snails live in a space similar in size to the area from the blue-line to the nearest end boards on a North American ice hockey rink.

 

Habitat

The Banff Springs Snail is a thermal spring habitat specialist dependent on a steady supply of warm thermal spring water (approximately 30–38°C) containing a high concentration of dissolved minerals, noticeably high levels of hydrogen sulphide and a complex microbial community that provides food and habitat structure. Most snails are found at the air-water interface, clinging to floating mats of algae, bacteria, woody debris, and leaves or on the edges of emergent rocks, concrete and rubber pool liners, and the riparian margin. Because the species is limited to thermal springs, the habitat is naturally fragmented and patchy with only the upper reaches of the thermal springs being preferred. All thermals springs historically or currently occupied by the Banff Springs Snail have been impacted by human development although some have returned to a more natural state.

 

Biology

Banff Springs Snails are hermaphrodites (both sexes within the same individual). In aquaria, snails as small as 3 mm shell length (nine weeks of age) can reproduce; small (approximately 2 mm × 5 mm), crescent-shaped, clear egg capsules contain on average 12 eggs and hatch within 6 days. Reproduction in the thermal springs most likely occurs year-round with the egg capsules being attached to substrates at the air-water interface. The snails feed on the microbial community. A white, filamentous, sulphur-oxidizing bacterium is the predominant food source. Adult snails added to aquaria have lived for an additional 11 months.

 

Population Sizes and Trends

There are no historic records of snail population levels. Regular surveys since January 1996 have counted snails once every three or four weeks. Snail populations undergo annual fluctuations of greater than two orders of magnitude. Population lows occur during the summer and highs occur during the late winter. Annual lows of 30 and 43 individuals have been observed in different springs since monitoring began. In contrast, nearly 34,000 snails were counted in December 2005, the highest peak. Significantly (P<0.05) increasing yearly population lows, highs, and averages were observed but only if results from the two re-introduced subpopulations are added to the original five. Population models using seven years of data from the original five subpopulations calculated extirpation probabilities ranging from 3% to nearly 30% after 40 years. If all five original subpopulations are combined, the probability of species extinction dropped to 0%. Population modelling results must be viewed cautiously given the assumptions inherent in the models.

 

Limiting Factors and Threats

Natural (N) and human-caused threats to the species and its habitat, whether incidental to facility operations (FO) at some thermal spring complexes or through other actions by people (Hu), have been identified and ranked from most to least severe as follows: thermal water flow stoppages (N), reductions/fluctuations (N/FO), redirections (N/FO); limited or low quality habitat (N/FO); soaking and swimming (Hu); population lows and genetic inbreeding (N); trampling/local disturbance (Hu); limb-dipping (Hu); stochastic events (N); others (predation, competition, collecting, twitch-ups) (Hu/N).

 

Special Significance of the Species

The Banff Springs Snail is endemic to thermal springs in BNP, one of four thermal spring complexes in Canada that are naturally occupied by aquatic snails of the family Physidae. It is an indicator of ecosystem health and may be a keystone species. Being confined to a national park enhances its importance as national parks have been identified as being key to meeting Canada’s national and international agreements on biodiversity and species’ preservation.

 

Existing Protection or Other Status Designations

Physella johnsoni is listed as Endangered on Schedule 1 of the Species at Risk Act (SARA) and is therefore protected under provisions of SARA as well as the National Parks Act. It also is assigned to the highest risk category both globally (G1) and provincially (S1 in Alberta). Direction for the species’ research and recovery program since January 1996 has been provided by the Parks Canada approved Resource Management Plan. Future direction is given in the national Recovery Strategy and Action Plan.

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