Stoneflies: western glacier stonefly (Zapada glacier)
Profile prepared by Sarah Foltz Jordan, Sarina Jepsen, Noah Greenwald, Celeste Mazzacano, Scott Hoffman Black, and Julia Janicki, The Xerces Society for Invertebrate Conservation
The western glacier stonefly (Zapada glacier) is a glacier meltwater-dependent stonefly known solely from a small area of Glacier National Park in Glacier County, Montana. Immature stoneflies, including the western glacier stonefly, have very narrow temperature requirements, making them especially vulnerable to extinction from increases in ambient water temperature. This narrowly endemic species is threatened by increases in water temperature and decreases in dissolved oxygen as a result of human-induced climate change in this region, specifically the loss of the glacial habitat on which this species depends. The glaciers within Glacier National Park are predicted to disappear by 2030. Loss of the glaciers, in combination with the species’ limited range, limited dispersal ability, and the inherent instability of small populations, collectively threaten this rare species with extinction.
Read the scientific petition to list the western glacier stonefly as Endangered under the U.S. Endangered Species Act.
Canada – Species at Risk Act: N/A
Canada – provincial status: N/A
USA – Endangered Species Act: N/A
USA – state status: Montana S1
IUCN Red List: N/A
Zapada glacier currently receives no federal protection. This species is rated by the Montana Natural Heritage Program (MNHP) as S1 (at high risk of range wide extinction or extirpation due to extremely limited and/or rapidly declining population numbers, range, and/or habitat) (MNHP, 2010). The NatureServe global ranking for this species has recently changed from G2 (Imperiled) to G1 (Critically Imperiled), based on the fact that climate change poses “an imminent and immediate threat [to this species], operationally occurring now and in the next couple years” (Stagliano, pers. comm., May 2010; Cordeiro, pers. comm., May 2010; Capuano, pers. comm., May 2010; NatureServe, 2009).
The western glacier stonefly is a member of the family Nemouridae, genus Zapada. Nymphs of the Nemouridae family are separated from other families by the small, stout body with numerous spines and the hairs on the dorsal surface and appendages (Baumann et al., 1977). Adults are readily distinguished by the distinctive nemourid “X” in the adult forewing (Baumann, 1975; Baumann et al., 1977). Zapada is a very distinctive genus in both the nymphal and adult stage (Baumann, 1975). Zapada nymphs are distinguished from other genera in the family by the very specialized whorls of large spines on all femora (Baumann, 1975). Adults of this genus have a single, simple gill on each side of the lateral cervical sclerites resulting in four single gills total, two on each side of the neck (Baumann, pers. comm., May 2010). Additionally, Zapada adults are characterized by large angular outer paraproctal lobes and a short, broad epiproct with the dorsal sclerite well developed (Baumann, 1975).
This species was described by Richard Baumann and Arden Gaufin in 1971 based on collections (largely by Gaufin) from 1963 to 1969. The species was originally described as Nemoura (Zapada) glacier (Baumann & Gaufin, 1971) and later classified as Zapada glacier (Baumann, 1975). The taxonomic status of this species is currently accepted as valid and is uncontested.
Zapada glacier is exclusively known from steep, high elevation, glacier-fed alpine streams below glaciers or glacial lakes (Baumann & Gaufin, 1971; Baumann et al., 1977; Newell et al., 2006). Like other lakes in Glacier National Park, the lakes that feed the streams where this species lives are oligotrophic (low productivity and very clear) due to very cold temperatures, extreme depth, and unique mineral composition from the surrounding rock (NPS, 2008). The limiting habitat requirement for Z. glacier is cold, glacial melt-water, since the species is only found in glacier-fed streams despite hundreds of other streams in Glacier National Park with similar substrate and riparian vegetation characteristics (Baumann, pers. comm., May 2010).
Baumann (pers. comm., May 2010) describes the streams where this species occurs as having a rocky (not sandy) substrate composed of variously sized cobble with some detritus. The stream microhabitat for Zapada larvae, in general, is described as leaf packs (accumulation of leaf litter and other coarse particulate detritus) and debris (e.g. logs, branches) in riffles (Stewart & Stark, 2008; Merritt et al., 2008). This species is found just below the alpine tree-line, and the riparian vegetation generally consists of grasses, bushes, and conifers (Baumann, pers. comm., May 2010).
Species in the family Nemouridae have a one to two-year life cycle with diapause occurring in the egg stage in some species (Stewart & Stark, 2008). After a given period of active feeding and growth, mature nymphs climb out of the water onto rocks, leaf packs, or pieces of wood that extend above the water-line and emerge as adults. Most species in the genus Zapada emerge very early in the year and are collected along with the winter stoneflies (Capniidae), but the emergence period varies with species and elevation (Baumann, 1975; Stewart & Stark, 2002). Zapada glacier emerges relatively late compared to others in its genus, and adults have been collected from July 9th to 30th (Baumann & Gaufin, 1971). Male stoneflies attract females by drumming, i.e. tapping specialized structures on their terminal abdominal segments on the substrate (Hynes, 1976; Stark et al., 1998; Sandberg & Stewart, 2006). The frequencies are transmitted through the substrate (not through the air), and females feel, rather than hear, the vibrations. Virgin females will drum in reply, followed by continued communication and migration towards each other until the two meet and mate. Shortly after mating, females extrude their egg mass over the stream surface or in the water (Hynes, 1976; Stark et al., 1998). Although both males and females in this species are macropterous (fully-winged), stoneflies in general are weak fliers with limited airborne dispersal ranges, and rely primarily on stream corridor connections to colonize new habitats (Hynes, 1976; Stewart and Stark, 2002). Like other stoneflies, adults of this species are collected near streams, walking on rocks or streamside vegetation.
This species is restricted in distribution to a small area of Glacier National Park, Glacier County, northwest Montana. Of the 100 stonefly species documented from Glacier National Park, Z. glacier is one of just four species only found within the park on the east side of the Continental Divide (Newell et al., 2006).
Zapada glacier is not known to have been observed or collected since 1979, although macroinvertebrate surveys haven’t been conducted at the historic streams in recent years (Schweiger, pers. comm., May 2010), and the species is expected to be extant at most sites (Baumann, pers. comm., May 2010). Recent macroinvertebrate monitoring in Glacial National Park has documented several localities for the Zapada oregonensis group to which this species belongs, however, all collections were of the larval stage which makes further taxonomic resolution impossible, since only adults of this group can be positively identified (Schweiger, pers. comm., May 2010; Bollman, pers. comm., May 2010; Baumann, pers. comm., May 2010). According to Baumann (pers. comm., May 2010), the majority of these collections are thought to be Z. haysi, a very common species in the park and elsewhere. No localities other than those in the type series have been documented for Z. glacier adults (Stagliano et al., 2007; Newell et al., 2006; Baumann, pers. comm., May 2010; Newell, pers. comm., May 2010; Giersch, pers. comm., May 2010).
Since its establishment as a park in 1910, Glacier National Park has lost over 80% of its glaciers due to global climate change. And since snowpack is not adequate to counteract the regional temperature changes, the remaining 25 glaciers are continuing to shrink (USGS, 2010). Without a supply of glacial melt water, summer water temperatures are increasing in the Park and are expected to cause the local extinction of temperature sensitive aquatic species (USGS, 2010), including Zapada glacier (Baumann, pers. comm., May 2010). Zapada glacier belongs to a group of cold water obligate species (the Zapada oregonensis group) that have a preferred temperature of 8.8°C (Grafe et al. 2002), and this habitat requirement makes Z. glacier unlikely to survive increasing water temperatures. The most likely negative impact of global climate change on this species is larval mortality due to thermal intolerance of lethally high temperatures and/or lethally low oxygen concentrations caused by elevated water temperatures (Baumann, pers. comm., May 2010).
Zapada glacier is a narrowly endemic species, probably due to both its narrow habitat tolerance, which restricts it to very cold glacier-fed streams, and its poor flight capacity, which limits its airborne dispersal range (Stewart & Stark, 2008; Baumann & Gaufin, 1971). Stonefly dispersal from inhabited tributaries into new catchments is thought to occur primarily by means of larval drift down-stream to a confluence, followed by upstream migration of adults into the adjacent headwater (Griffith et al., 1998). Dispersal potential is of particular importance for this species, since dispersal is likely associated with the long-term persistence of freshwater taxa, and may present the only option for a species to avoid extinction in a changing climate (reviewed in Bilton et al., 2001). However, these species have nowhere to disperse to, as their habitat itself is going extinct.
Other than global climate change, its small population size, restricted distribution, and isolation, another major threat is the inadequacy of existing regulatory mechanisms. Despite being in danger of range-wide extinction due to climate change, Z. glacier currently receives no recognition or protection under federal or state law. The climate change regulations that currently exist are inadequate to protect Z. glacier from range-wide extinction.
Zapada glacier faces formidable threats which could be ameliorated or eliminated by regulatory actions. To protect Z. glacier‘s habitat, the reduction of greenhouse gas pollution is essential. This will slow global warming and ultimately stabilize the climate system, protecting the cold water habitat in Glacier National Park that Z. glacier depends upon.
Stricter international and U.S. regulatory mechanisms to reduce global greenhouse gas emissions are necessary to safeguard Z. glacier against extinction resulting from climate change.
Other necessary actions to conserve Z. glacier include conducting macroinvertebrate surveys over its historic range and researching more into its life history.
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Bilton, D.T., J.R. Freeland, and B. Okamura. 2001. Dispersal in Freshwater Invertebrates. Annual Review of Ecology and Systematics 32: 159-181.
Grafe, C.S., C.A. Mebane, M.J. McIntyre, D.A. Essig, D.H. Brandt, and D.T. Mosier. 2002. The Idaho Department of Environmental Quality Water Body Assessment Guidance, Second Edition-Final. Idaho Department of Environmental Quality; Boise, Idaho. Available at: http://www.deq.idaho.gov/water/data_reports/surface_water/monitoring/wbag_02_entire.pdf (Accessed 12 October 2010).
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U.S. Department of the Interior Geological Survey (USGS). 2010. Retreat of glaciers in Glacier National Park. Northern Rocky Mountain Science Center. Available at: http://www.nrmsc.usgs.gov/files/norock/products/GlacierRecession_infosheet2010_SRC_040910.pdf (Accessed 1 May 2010).