An extremely specialized survivor
The Banff Springs snail, Physella johnsoni, is a tiny mollusc, with the largest individuals reaching only about one centimeter in length. First identified in 1926, this species has an incredibly restricted habitat, living only in a handful of thermal springs on Sulphur Mountain in Banff National Park. All known populations exist along the Sulphur Mountain Thrust Fault at elevations between 1,400 and 1,584 meters. The snail has adapted to an environment hostile to most other forms of life. The water it inhabits is low in oxygen but high in dissolved minerals and hydrogen sulfide, which produces a distinct rotten egg smell. It thrives in water temperatures maintained between 30°C and 38°C.
A physical feature distinguishes this snail from most others; its shell coils to the left, or sinistrally. Most other freshwater snails in North America have shells that coil to the right. Physella johnsoni feeds on the unique microbial communities that grow in the mineral-rich water, grazing on floating mats of bacteria, algae, and other microorganisms. These snails are hermaphrodites, meaning each individual possesses both male and female reproductive organs. They lay small, clear, crescent-shaped egg capsules containing an average of 12 eggs, which hatch in about six to eight days.
A precarious existence
This snail holds the distinction of being the first living mollusc to be listed as at risk by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) in 1997. By 2000, its status was updated to Endangered. Originally found in nine springs, the snail's range had shrunk to just five by 1996. The snail population fluctuates dramatically throughout the year, from highs of over 34,000 individuals in the winter to lows of just 30 in the summer. At its lowest point, the entire species population could fit inside a single ice cream cone.
Threats to the snail's survival are significant. Human activity has historically been a major issue; people bathing or dipping hands in the thermal springs can crush the tiny snails and their eggs. This has led Parks Canada to close some areas and increase surveillance. An even greater threat may be climate change, which is believed to contribute to the increasing frequency of the thermal springs drying up. The first recorded instance of a spring drying was in 1923, but it has become a more common occurrence. Parks Canada initiated a research and recovery program in 1996, which includes captive breeding and reintroducing snails to springs where they had previously vanished. These efforts have led to the successful re-establishment of self-sustaining populations in two springs.