Hotwater physa (Physella wrighti) COSEWIC assessment and upate status report: chapter 5

Habitat

Habitat requirements

The common name of P. wrighti, the Hotwater Physa, suggests that this species is a habitat specialist, requiring a geothermally elevated water temperature. Although the dependence of P. wrighti on elevated temperature for life history requirements has not been studied, water temperature likely influences many aspects of its life history.

Table 2. Habitat parameters measured in Alpha Stream in Liard River Hotsprings Provincial Park (LRHPP) during surveys for Physella wrighti
Source Range of temperature in Alpha Stream (°C) pH Dissolved Oxygen
(% saturation)
Conductivity (μS/cm)
Te and Clarke 1985Table notea
23.0 - 35.0
7.9
-
1100
Lee and Ackerman 1997Table noteb
23.5 - 36.5
7.8
67
1155
Salter 2003Table notec
28.9 - 36.3
-
-
-
2006 surveyTable noted
35.5 - 40.0
-
-
-

The Liard Hotsprings area is unusual compared to other hotsprings in the region including Banff, Radium and Fairmont, in that it is considered a large-yield deep source, with a high flow rate of 81 L/s, and the chemistry is calcite-sulphite, not just calcite (Gilles Wendling, pers. comm.).

While Te and Clarke (1985) noted that snails occurred only on Chara plants in Alpha Stream, subsequent observations have located snails on the sediment surface, fallen leaves of Paper Birch (Lee and Ackerman 1999) and submerged debris, as well as on substrates within the pools (Salter 2001, 2003). Data for animals held in captivity suggest that a specific food requirement does not restricthabitat used by this species.

As pulmonates, physids use a pulmonary cavity for respiration. Some physids rely on aerial respiration and are somewhat amphibious (Brown et al. 1998) whereas others fill the pulmonary cavity with water and use it as a derived gill (Russell-Hunter 1978). Access to surface air is obtained by crawling along the substrate to the surface or by “spinning”, in which the snail attaches a mucus trail to the substrate or surface film and changes its specific gravity to enable movement up and down the water column (Pennak 1989). The relative reliance of P. wrighti on aerial or dissolved oxygen is unknown but snails are always found near the water/air interface in areas of little or no water flow.

Based on observations of P. wrighti in situ, the environmental requirements are a habitat that offers food and a secure anchoring surface near a water/air interface in areas of little or no water flow where the snails can position themselves and their eggs at temperatures optimal for life history traits (see Life cycle and reproduction). This habitat occurs in LRHPP along parts of the margins of Alpha Stream and at the perimeters of Alpha and Beta pools.

Habitat trends

The habitat in which P. wrighti lives has been highly modified to accommodate human use. Use of the hotsprings is recorded as far back as 1837 (Camsell 1954) and the area became a B.C. park in 1957. The original weir is thought to date back to the construction of the Alaskan highway completed in the 1940s (Sue Pollard, pers. comm.). LRHPP features a campground and two hot pools that are used by an estimated 40,000 bathers annually, with day use and camping statistics remaining reasonably consistent over time (A. Hansen, pers. comm.). Despite the building of change rooms, walkways and entry stairs, Beta Pool remains largely in its natural state. Alpha Pool has been modified by the diversion of cool water into the incoming springs, and by the construction of change rooms, walkways and entry stairs as well as a concrete dam. The outflow from Alpha Pool around the dam creates Alpha Stream. Some park users also explore Alpha Stream as evidenced by footprints along the margins noted in 2006.

In all surveys in LRHPP, snails have been present in Alpha Stream. The structure of the habitat in Alpha Stream has changed over time. Te and Clarke (1985) described the type locality as “the reach extends from the mouth of Fern Creek (which enters Alpha Stream about 25 m below Alpha Pool) downstream for 34 m”. Later surveys have been unable to locate Fern Creek and snails have been found for a much shorter distance downstream from Alpha Pool (see Population sizes and trends). Te and Clarke (1985) reported the water temperature in the reach inhabited byP. wrighti to range from 23–35°C; Lee and Ackerman (1999) 23.5–36.5°C; and Salter (2001) 23-36°C in August 2000 and up to 33°C in January 2001 (see Table 2). In 1997, water temperature at the outflow from the dam was 36.5°C and while temperatures of 36°C were measured at some points up to 40 m downstream, the temperature was never higher than at the dam (Figure 4). In 2006, water at the dam was 36°C and with the exception of two points on the west bank, continued at this or greater temperature for the 95 m downstream that was surveyed, reaching a maximum of 40°C at a point on the east bank (see Figure 4). If the discharge from Alpha Pool were the sole source of water for Alpha Stream, the water temperature should decline with distance from the source. As previous surveys had found water temperature to be unchanged for some distance downstream of the dam, there must be hot water seepage into Alpha Stream.

It is unknown if this increased temperature might have changed the previously observed distribution of P. wrighti within Alpha Stream. All studies prior to 2006 reported the snails to be most abundant within the Chara on the margins of Alpha Stream. Te and Clarke (1985) noted that the snails occurred only on Chara, and Lee and Ackerman (1999) and Salter (2001) also found the snails to be most abundant within Chara. In 2006, there was no submerged vegetation in Alpha Stream, perhaps due to the increased water temperature. However, it is also possible that the tolerance of these snails to temperature was reached. An increase in temperature and loss of the submerged macrophytes could have reduced snail abundance in the upper portion of Alpha Stream but higher temperatures might also extend the reach of Alpha Stream that provides optimal conditions for P. wrighti (see Population sizes and trends).

Figure 4. Water temperatures measured in 1997 and 2006 along (a) west and (b) east banks of Alpha Stream in sections designated in 2006.

Figure 4.  Water temperatures measured in 1997 and 2006 along (a) west and (b) east banks of Alpha Stream in sections designated in 2006.

Water quality parameters of pH and dissolved oxygen have also been measured in Alpha Stream (see Table 2). Te and Clarke’s (1985) data came from water analysis and measured pH of 7.9. Lee and Ackerman (1999) measured directly in the stream at the dam and found pH of 7.8 and dissolved oxygen at 67% saturation.

Habitat protection/ownership

Both provincial and federal regulations protect P. wrighti and its habitat. Provincially, P. wrighti is protected under the B.C. Park Act (1996), which states that “natural resources … must not be granted, sold, removed, destroyed, damaged, disturbed or exploited except as authorized by a valid and subsisting park use permit”. The goals of the LRHPP Master Plan (Preepre 1990) are to preserve the outstanding natural hotsprings and warm swamp ecosystem while allowing for compatible recreational uses; natural processes will be allowed to occur without interference; existing water quality will be maintained; wildlife habitat enhancement will not be considered unless a species population is threatened, particularly by human activities in the park; and existing downstream water flow will be maintained by a policy of non-intervention in the hotsprings hydrology. The park’s master plan pre-dates the original status designation of this species, and any future plan for the park would undoubtedly have to fully consider this species. The park is now staffed 24 hours a day year round, although the hotsprings are not under constant surveillance (Doug Biffard, pers. comm.).

Federally, P. wrighti was listed and protected under Schedule 1 of SARA in 2003 based on the status designation of Endangered granted by COSEWIC in 2000. Actions that result in killing, harming, harassing, capturing or taking P. wrighti, or that result in the destruction of its critical habitat are legislated under SARA. SARA designates Fisheries and Oceans Canada as the responsible jurisdiction for P. wrighti. The Fisheries Act (Canada) prohibits works that may result in harmful alteration, disruption or destruction of fish habitat (Section 35) and prohibits the release of deleterious substances, such as contaminants, into fish-bearing waters (Section 36). In accordance with SARA regulations, a recovery strategy for P. wrighti has been developed (Heron 2007).

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