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.
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.
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.
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.”
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.