Melting Glaciers and the Animals that Follow

Researchers taking soil samples to extract micro-arthropods (springtails and mites)(Source: Hågvar et al.).

Last week, GlacierHub reported on a study that followed the types of plants that colonize new areas exposed by glacier retreat. But what about animals that colonize de-glaciated regions? A recent study from a team of Norwegian ecologists led by Sigmund Hågvar explores 200 years of arthropod succession in a Norwegian glacier foreland, home to what the researchers described as “biological oases.” Arthropods are a phylum of invertebrates with hard outer shells and segmented legs, which includes insects, spiders, and many marine species like shrimp, lobsters, crabs, and even barnacles.

Headlines of melting glaciers and their implications aren’t new to anyone. “Melting glaciers all over the world are strong proof for global warming,” lead researcher Hågvar told GlacierHub. “If glaciers disappear, rivers which delivered water to people may dry up.” But for scientists like Hågvar, what’s left behind is ecologically fascinating. His team published their findings in a book titled “Glacier Evolution in a Changing World.”

“A melting glacier leaves large areas of barren ground, which is available for the colonization of plants and animals. How fast is this colonization, who are the pioneers, and how are plant and animal colonization connected? The sequence of organisms with time is called a succession, and in this case a primary succession because it starts on bare ground with no species present,” Hågvar explained.

Mauro Gobbi, research entomologist at the MUSE-Science Museum in Italy and a specialist on the ecology of alpine glacier forelands, shared similar sentiments. “The study of environmental changes occurring after the retreat of glaciers are giving us an extraordinary experimental opportunity to measure in space and time the temporal evolution of biotic communities, and how they are colonizing pristine areas,” he told GlacierHub.

Hågvar and colleagues Mikael Ohlson and Daniel Flø conducted their study close to the Hardangerjøkulen glacier in central southern Norway. Star Wars fans may recall how this glacier was the filming location for the iconic ice planet of Hoth, as GlacierHub reported earlier this year. Hardangerjøkulen has been receding for about 250 years since the end of the Little Ice Age, but “the melting rate has been especially high during the last two decades,” according to the study. Due to the rapid melting rate and good data on the glacier’s position, glacier forelands offer unique opportunities to study primary succession.

In general, previous studies dealt with plant succession, with few focusing on the animal’s story. However, this study is unusual because it provides an integrated account about animal succession near a melting glacier in Norway and how it is in accordance with findings in other parts of the world.

Which animals colonize retreated glaciers?

Researchers working at this 8-year old pond near the glacier, studying midge larvae (Source: Hågvar et al.).

Along the frigid slopes of the Hardangerjøkulen glacier foreland, few creatures call the treeless alpine region home save for an array of beetles (Coleoptera), spiders (Aranea), springtails (Collembola) and mites (Acari). These hearty, cold-tolerant arthropods utilize a wide variety of life strategies to survive in this harsh environment. Among these fighters is a “super-pioneer,” the biofilm-eating springtail. These animals closely follow the newly de-glaciated melting ice edge and are among the first organisms to colonize the barren ground, surviving on invisible diatom algae that attach to each other and the surface of the ground to form a biofilm. With the ice edge moving faster and faster each year, these organisms are put to the test to keep up.

Each species follows a distinctive successional pathway depending on the species, topography and moisture content of the physical environment. In this study, the researchers were able to distinguish the soil-living micro-arthropods and the surface-living macro-arthropods between a dry and moist succession. Among the first colonizers of the bare ground were large predatory beetles and spiders. But this is a bit odd. “According to common ecological theory, it is impossible to start an ecosystem with predators. A food web must start with plants, then herbivores, and finally predators,” Hågvar states.

The answer to the puzzle: a combination of long-distance aerial transport of prey unable to survive in the conditions as well as midge larvae colonizing in nearby ponds. The presence of these food sources allows for the predatory species to colonize much earlier than ecological theory may anticipate.

But what about the others?

With limited plant species or none available, how do so many of these observed species survive? In answering this question, the team analyzed the gut contents of these creatures and found three food sources that feed the arthropods: 1) biofilm with diatom algae, 2) tiny pioneer mosses, and 3) ancient carbon released from the glacier.

This figure demonstrates the food web of both dry and wet succession. The three colored frames represent the three sources of food supporting the colonizers (Source: Hågvar et al.).

Of these three, it is the third option that was the most “surprising” to the researchers. “We wondered whether ancient carbon was released also by our glacier, and if so, whether it could be used as a nutrient source for pioneer arthropods… We concluded that ancient organic material released by the glacier was assimilated by chironomid larvae [mosquito-looking flies], and transported further to aquatic and terrestrial predators,” the study noted.

But what was the source of the ancient carbon stored in the glacier? The likely source appears to be long-transported aerosols, including via heavily glaciated watershed. When predatory beetles, spiders, and harvestmen eat the adult versions of carbon-eating midge larvae, the predators would “achieve a radiocarbon age up to 1000 years,” according to Hågvar.

Looking Ahead

Despite widespread negative impacts of melting glaciers, the rise of “biological oases” present opportunities for scientists to explore the dynamics behind primary succession, a subject not easy to study. The resilience and persistence of the animals that survive in these harsh environmental conditions are remarkable. But cold-adapted species that enjoy sticking close to the ice edge may not be able to keep up if the rate of glacial retreat gets much higher, Gobbi told GlacierHub. “As the rate of glacial retreat is predicted to accelerate in the near future, recently de-glaciated areas will increase, therefore monitoring the uphill shift of the cold-adapted species chasing the glacier is one of the most important challenges for ecologists and conservationists. All of these cold-adapted species are in danger of extinction,” he said.

Besides the arthropods, other animals that rely on glacier forelands are humans. For instance, glacier meltwater supports a wide range of socioeconomic activities, including activities of the tourist industry, pastoralists, and hydrologists. Ultimately, “naturalistic components, social values, local perceptions and cultural beliefs are closely intertwined with the existence of glaciers in the regions, therefore it is mandatory to invest on research projects aimed at monitoring the changes of these habitats in relation to the ongoing glaciers disappearing,”states Gobbi.

As glaciers melt worldwide, it will be interesting to see what communities some of the planet’s toughest plants and animals build and the opportunities these communities present to scientists. Such organisms exemplify the tenacity of life. Even in the harshest circumstances, and despite the threat of climate change and its unknown effects, life still finds ways to survive.