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Recovery Strategy for Hotwater Physa
Needs of Hotwater physa
1.4 Needs of Hotwater Physa
1.4.1 Biological needs
Physids are generally considered to be detritivores and/or bacterial feeders (Brown 1991) and the habitat in which Hotwater Physa is found suggest that this is true for this species. There have been no in-depth species-specific studies conducted on Hotwater Physa, although P. wrighti kept in captivity lived and reproduced on a diet of mixed brewer’s yeast and fish food (Lee and Ackerman 1998).
The snails in Liard River Hotsprings Provincial Park are found most densely on Chara vulgaris. C. vulgaris(orChara) is an algae which grows at the shallow edges of hotwater springs on rocks, submerged branches, introduced garbage and other submerged materials in the aquatic habitat (Salter pers. comm.) including rotting paper birch (Betula papyrifera) leaves(Lee and Ackerman 1998). This green algae (Class Charophyceae (Stoneworts)) and the outer cell layers are impregnated with calcium carbonate (Scagel et al. 1965) giving the plant a very crisp texture. Charagrows floating near the surface and forms dense mats attached at various intervals along the streamsides. When the spring water (high in calcium) cools, the calcium precipitates out onto the surface of the Chara and results in significant calcification of the plant, particularly those plants floating along the edges of the stream. Calcification of these plants and other surfaces eventually forms tufa, which is a crumbly and porous ‘rock’. The snails are probably not feeding directly on any of these substrates but are grazing on the aufwuch, which is the organic material that comes to encrust submerged substrates.
There is no known information regarding species-specific reproduction of Hotwater Physa. The Physid family, in general, replace generations annually, thus an individual snail will likely live approximately one year. These snails are oviparous hermaphrodites that breed once; the young overwinter, mature into adults, lay eggs in the spring, and die after eggs are laid. However, these observations are from temperate areas and it is likely that physids living at constant warm temperature may lay eggs continuously until senescence. Reproduction of P. wrighti has only been observed in captive specimens. In a heated aquarium with water from the hotspring, P. wrightilaid “clear crescent-shaped gelatinous egg masses containing 6 to 18 eggs laid above the water line in a temperature of approximately 25° Celsius with hatching after nine days (Lee and Ackerman 1998).
Physids are pulmonate snails, which use a richly vascularized pulmonary cavity in the mantle to extract oxygen from air or water. 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 (Russel-Hunter 1978). The relative reliance ofthe Hotwater Physa on aerial or dissolved oxygen is unknown but the snails are usually found on substrates near a water/air interface (Figure 2a & B) as these substrates offer secure anchoring surfaces, allow grazing on organic material, and allow access to the air/water interface for oxygen acquisition.
1.4.2 Biologically limiting factors
- Small and spatially isolated population:Globally, the Hotwater Physa is endemic only to the Liard River Hotsprings complex. At least until the taxonomic uncertainty is clarified, the Hotwater Physais a unique species and as such there is no possibility of a rescue effect from outside of this hotsprings complex. The population densities at sites within the Liard River Hotsprings complex vary, and the connectivity between these sites is limited.
- Small occupied area of population:Concentrated subpopulations of the snail within the Liard River Hotsprings complex occupy small areas on substrates at the edges of Alpha Pool, Alpha Stream and Beta Pool. Dispersal and occupancy of sites are likely due to temperature and substrate availability at depths where these pulmonate snails can access air and food.
- Habitat specificity: Hotwater Physa is associated with hotwater springs; which may also be in demand from development and human use. This species is restricted to its type locality, which makes it particularly susceptible to habitat disturbance. Changes to temperature and flow regime would undoubtedly affect reproductive success.
- Interspecificcompetition: Competition between Hotwater Physa and lymaeid and planorbid snails in other parts of the thermal spring ecosystem could be a limiting factor. However, the habitats of the physid and lymnaeid snails are distinct in cooler water habitats and appear not to overlap (Salter, 2003).
- Quality and quantity of food supply: Food supply is likely to be a limiting factor on a given population. Direct and indirect effects on food sources may be limiting to Hotwater Physa, including changes to riparian vegetation and habitat adjacent to the streamside.
1.4.3 Habitat needs
The specific habitat needs of Hotwater Physa and the dependent relationship the snails have on their hotsprings habitat has not been studied. However, there are conclusions that can be drawn from knowledge of physids in general, and observations of Hotwater Physa in situ. The continued health of both the riparian and instream habitats are undoubtedly of vital importance to the survival of this species.
Aquatic habitat factors thought to affect the habitat needs of Hotwater Physa are listed below.
- Water temperature: The geothermally heated water emerges from Alpha Pool at approximately 38o Celsius year round. The water will naturally cool as it flows away from the emergence point and is further cooled by purposeful mixing within the pool. The water temperature undoubtedly influences many aspects of the life history of Hotwater Physa.
- Water flow: At the site of the highest concentration of Hotwater Physa, in Alpha Stream,water enters over the weir at a rate of 80 – 81 litres/second (annual average)(Peepre 1990). While the initial observations of the Hotwater Physa’srestriction to Alpha Stream could have been correlated to habitat requirements found only in the flowing water, subsequent observation of the snails within the pools negates this relationship.
- Mineral composition and the content of dissolved substances in the water: The mineral composition of the water affects the amount of tufa formation and the surface area upon which bacterial and algal growth occurs.
- Chara, coarse woody debris and other substrates in the stream:Hotwater Physa has been observed grazing onChara, coarse woody debris and various other substrates. These substrates provide the surface area for the growth of algae and bacteria upon which the snail feeds, as well as an anchor in the water current of Alpha Stream. The abundance and distribution of these objects within the hotsprings habitat is likely important to the species.
- Stream dynamics: The width, length and the depth of water throughout the hotsprings is variable, and it is not known if the snails will inhabit areas according to the stream dimensions. The stream will likely not become ice-covered, although the greatest temperature variation will occur in the winter months and will largely be in the pools and eddies. Research on the factors that influence the distribution of the Hotwater Physa within the hotsprings complex are included under the schedule of studies (Section 1.6.1).
- Oxygen Requirements: The respiratory requirements of Hotwater Physa were previously described. Distribution throughout the hotsprings is probably influenced by the availability of suitable substrates at suitable depth for oxygen acquisition.
The habitat needs of the snail are both terrestrial and aquatic, and the quality of riparian habitat is as much a component to the health of the ecosystem as the water quality itself. Riparian habitat factors thought to affect the habitat needs of Hotwater Physa are categorized below.
- Streambank stability: Streambank stability and changes to this stability can affect Hotwater Physa habitat. Snails are known to congregate on Chara, which float in eddies as well as attach to the water bank edges. Soil compaction, disturbance and the removal of vegetation increases soil surface erosion into the hotsprings. In the first 60 metre section of Alpha Stream below the weir, there is a well defined, calcified channel with little sedimentation. However in the next 140 metres, the stream widens and slows due to an accumulation of sediment (presumably from Alpha Pool). This change may contribute to the habitat unsuitability for Hotwater Physa further downstream.
- Riparian vegetation and shade: The dependence of Hotwater Physa on allochthonous inputs, such as leaves, is unknown, but the snails have been observed grazing on the aufwuch on paper birch leaves within Alpha Stream (Lee & Ackerman 1998). The riparian vegetation also affects the amount of light reaching stream edges, which may influence the density and distribution of Chara, which appears to be a preferred substrate for Hotwater Physa.
- Ambient air temperatures: Outside air temperature will have an influence on the aquatic environment, although the effect on the temperature of the hotsprings is unknown.
Most threats to Hotwater Physa are a result of potential changes to the hotsprings habitat as a result of human activities, whether from recreational activities occurring within the park or the potential for industrial activities that could affect the source water entering the hotsprings complex. The threat from human activities is of particular concern given the biological factors that limit the species (Section 1.4.2).
- Change to the flow regime as a result of human activities:
- Weir maintenance. The natural flow of water from Alpha Stream to Alpha Pool has been changed due to the installation of the dam and weir prior to knowledge of the endemic snail. The mixed hot and cool water now exits through a narrow spillway in the top of the weir into the habitat colonized by Hotwater Physa. Failure of the dam or the weir could result in a large surge of water flowing down the stream, and this flash flooding could physically move snails into unsuitable habitat and significantly alter existing Hotwater Physa habitat. Alternately, a decrease in the flow of water during dam or weir maintenance activities could expose snails to drying and also result in altered water temperature in the area below the weir as the hot and the cold water sources would not be pre-mixed. Routine maintenance and repair of the dam and weir are conducted to maintain the integrity of Alpha Pool and Stream, and maintains Hotwater Physa habitat.
- Recreational activities. Blockages, erosion or alterations to the weir or pool banks from recreational users may alter the flow of the stream. While these destructive activities are prohibited, park visitors have, for example, been known to block the outflow to the lower Alpha Pool. Temperature loggers in Alpha Stream during the September 2005 Labour Day weekend showed that water levels fell below the height of the temperature logger (Rowe, pers. comm.).
- Drilling activities for oil and gas exploration. Although there is currently no specific application, drilling activities for oil and gas exploration could potentially affect the geothermally heated water from its source outside of the park boundaries to where it surfaces within the park. In the event an interest arises in oil and gas exploration in this area, a more detailed risk assessment will be required to determine specific high risk areas and to develop mitigation strategies.
- Hydroelectric development. There were historic hydroelectric evaluations in the Liard River in the early 1990’s and at least one site was identified outside the park boundaries on the Liard River. This proposal, titled Devil’s Gorge Project, would flood the Liard Hotsprings and most of the adjacent campground as it would raise the water elevation to greater than 420m. This flooding would also allow aquatic species to access the hotsprings marsh that is located on a bench above the Liard River and currently are not connected through waterways (Hill, pers. comm.). In the event there is a renewed interest in this or other projects in future, further assessment of the risk to Hotwater Physa and their habitat will be required.
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