Glacier Loss Threatens Stoneflies in Glacier National Park

Glaciers in the Rocky Mountains are undergoing rapid retreat, threatening two remarkable insect species that live in streams fed by glacial meltwater. Lednia tumana (meltwater stonefly) and Zapada glacier (Western glacier stonefly) have recently been proposed for listing under the Endangered Species Act due to the threat that climate change poses to their habitats.

A recent study by J. Joseph Giersch et al. published in Global Change Biology offers insight into the factors that influence the distribution of these species, providing valuable information for conservation efforts. In an interview with GlacierHub, Giersch, a scientist at the U.S. Geological Survey (USGS), said, “Findings from our research were used by the U.S. Fish and Wildlife Service (USFWS) to inform the listing decision for the two species.”

The study took place in Glacier National Park, Montana, where regional warming has had serious effects. Surveys of glacial extent revealed that 80% of glacial mass within the park has been lost since the 19th century, with full recession predicted over the next two decades, according to Paul Carrara in the Canadian Journal of Earth Sciences. This creates the need for a better understanding of glacier-dependent species such as the stoneflies and ecological implications of species loss.

A researcher collecting samples from a stream fed by meltwater from Blackfoot Glacier (Source: Joe Giersch/USGS).
A researcher collecting samples from a stream fed by meltwater from Blackfoot Glacier (Source: Joe Giersch/USGS).

The team of researchers led by Giersch sampled the alpine stream network within Glacier National Park between 1996 and 2015, tracking the abundance of nymph (the immature form and second stage of the life cycle) and adult Lednia tumana and Zapada glacier. Samples of Lednia tumana were found in a total of 113 streams within the park, while Zapada glacier was only detected in 10 streams, six within the park and four within other parts of the Rocky Mountains in Montana and Wyoming.

Both species of stonefly are endemic to the region around Glacier National Park and are range-restricted. Their distributions were found to be related to cold stream temperatures and proximity to glaciers or permanent snowfields, with survival “dependent on the unique thermal and hydrologic conditions found only in glacier-fed and snowmelt-driven alpine streams,” according to the study.

A Lednia tumana nymph, which lives underwater (Source: Joe Giersch/USGS).
A Lednia tumana nymph, which lives underwater (Source: Joe Giersch/USGS).

An interesting feature of both Lednia tumana and Zapada glacier is that they are aquatic in the egg and nymph stages of their life cycles, before becoming terrestrial adults. The adult females lay eggs in short sections of cold alpine streams found directly below glaciers and permanent snowfields within the park. The whole life cycle can last from one to two years.

When the stonefly’s eggs hatch, the nymphs swim or drift along the alpine streams, feeding and growing until they emerge as fully grown adults in July or August. The short-lived adults are weak fliers, so they tend to be found on streamside vegetation. Male and female adult Zapada glacier communicate and find each other by drumming (tapping specialized structures in their abdominal segments on the material at the bottom of the stream). After finding each other, they mate and the females lay eggs in the streams, re-starting the life cycle process. Mature Lednia tumana nymphs tend to be about a quarter of an inch-long, while adults are slightly smaller, according to the USFWS.

An adult Zapada glacier, which is terrestrial (Joe Giersch/USGS).
An adult Zapada glacier, which is terrestrial (Joe Giersch/USGS).

As alpine glaciers in Glacier National Park disappear as a result of climate change, meltwater contributions to alpine streams will decrease, changing the temperature and hydrological regimes that both stonefly species, particularly in the egg and nymph stages, depend on.

The loss of permanent cold water to their native habitat may eventually result in the extinction of these species. Additionally, a shorter-term effect could be a decrease in population connectivity due to cold water dependent species migrating upstream in response to warming temperatures,” Giersch explained to GlacierHub. “In an area with steep topography such as Glacier National Park, upstream migrating populations become ever more geographically and genetically isolated. This will ultimately cause a decrease in the persistence of the species.”

Glacier National Park has many streams fed by glacial meltwater (Source: Joe Giersch/USGS).
Glacier National Park has many streams fed by glacial meltwater (Source: Joe Giersch/USGS).

According to Giersch, the implications of the loss of rare alpine insects like Lednia tumana and Zapada glacier are both abstract (the price of biodiversity) and concrete (glaciers are a source of water necessary for the survival of the species). As alpine streams in North America are not well studied, the effects of climate change on biodiversity and complex interactions within food webs in alpine streams are unknown. “However, the loss of the ice and snow masses feeding alpine streams will have far-reaching impacts, as many other species downstream rely on cold temperatures from melting ice and snow,” Giersch explained.

In a statement from the Center for Biological Diversity, endangered species director Noah Greenwald said, “Global warming is changing the face of the planet before our eyes, and, like these two insects, many species are seeing their habitats disappear.” With many biological and human communities dependent on the water that comes from glaciers, stoneflies serve as sentinels of climate change in mid-latitude regions, providing an indicator of changes that will also have serious effects downstream.

Glacier Retreat Threatens Insect with Extinction

As glaciers retreat, a species of glacier-dependent stonefly faces extinction.

In 2010, the Center for Biological Diversity petitioned for Zapada glacier, a western glacier stonefly only found in alpine streams of Glacier National Park, Montana, to be listed as endangered species under the U.S. Endangered Species Act. This species – one of more than 3500 species of stonefly –  is highly restricted to cold, glacial meltwater with limited dispersal ability.

Zapada glacier adult female from the Grinnell Glacier Basin in Glacier National Park (approximate length is 12 mm) (Source: Giersch et al./Freshwater Science).

Now, in an effort to save this endangered stonefly, the Center for Biological Diversity filed a lawsuit against the U.S. Fish and Wildlife Service to address the urgency of protecting this stonefly. The insect could potentially be taken to other clean cold streams outside its established range, perhaps further north or at higher elevation where it might survive – but time is running out.

Species evolve to survive in specific temperature ranges; however, when the environmental conditions have exceeded the range, species are unable to adapt to new conditions immediately. Climate change has put many species in danger, but this is the first time that an insect species has been threatened with extinction by glacier retreat.

“Protection can’t come soon enough for this stonefly,” said Tierra Curry, a senior scientist at the Center for Biological Diversity. “Glacier National Park will have no glaciers in 15 years if we don’t take action to curb climate change.”

Stoneflies are a particularly ancient order of insects that spend most of their lives in water. They are considered the most sensitive indicators of water quality in streams as they require fresh, clean water and don’t tolerate pollution. The insects have a one to two-year life cycle starting in the nymph stage in fresh meltwater. They usually emerge from the water in late spring when the stream is uncovered by melting snow. Z. glacier has a narrow temperature preference around 3.3 degrees Celsius. It is this narrow temperature preference that makes this insect especially susceptible to climate change.

Between 1960 to 2012, the average summer temperature in Glacier National Park has risen by approximately 1 degree Celsius. Additionally, since 1850, 125 of the 150 glaciers in Glacier National Park have melted away while the remaining 25 are predicted to disappear by 2030. The loss of glaciers as well as restricted suitable environmental conditions and limited dispersal ability of the stonefly threaten the species’ ability to survive.

Many Glacier in GNP (Source: Esther Lee/Flickr).
Glaciers in Glacier National Park (Source: Esther Lee/Flickr).

Few studies have investigated the impacts of climate change on alpine species distributions. To compensate for this knowledge gap, J. Joseph Giersch from US Geological Survey and other researchers looked at the current status and distribution of Z. glacier. Their results were published in Freshwater Science.

Giersch et al. sampled 6 alpine streams, where Z. glacier was historically known to live, to examine the relationship between species occurrence and environmental variations of temperature and glacial extent. In order to identify the current geographic distribution and distinguish Z. glacier from the other 6 Zapada species in Glacier National Park, the researchers used morphological characteristics, the outward appearance of adults and the DNA of nymphs.

Giersch et al. identified 28 suitable alpine locations in Glacier National Park as potential habitats for Z. glacier. From this study, Z. glacier was only found in 1 of the 6 historically occupied streams – the outlet of Upper Grinnell Lake. The results suggest increased temperature and glacier retreat have already caused local extinction of Z. glacier from several historical locations.

Upper Grinnell Lake in Glacier National Park, where Zapada glacier can be found (Source: GlacierNPS/Flickr).
Upper Grinnell Lake in Glacier National Park, where Zapada glacier can be found (Source: GlacierNPS/Flickr).

The stonefly was also detected in 2 new high-elevation locations in Glacier National Park. Therefore, only 3 out of the 28 potential habitats have Z. glacier. The results indicate that the historical distribution of this stonefly in Glacier National Park was already restricted and its distribution will be further reduced in the future due to increased stream temperatures and habitat loss.

“The plight of the glacier stonefly is a wakeup call that unless the United States takes major action to reduce our greenhouse gas emissions, this special insect and more than one-third of all plants and animals on Earth could go extinct by 2050,” said Curry.

For more stories on invertebrates near glaciers, read here and here.