Roundup: Tardigrade, Glacier Modeling, and Eyjafjallajökull Eruption

Discovery of a New Water Bear Species

From BioOne: “Glaciers and ice sheets are considered a biome with unique organism assemblages. Tardigrada (water bears) are micrometazoans that play the function of apex consumers on glaciers. Cryoconite samples with the dark-pigmented tardigrade Cryoconicus gen. nov. kaczmareki sp. nov. were collected from four locations on glaciers in China and Kyrgyzstan… A recovery of numerous live individuals from a sample that was frozen for 11 years suggests high survival rates in the natural environment. The ability to withstand low temperatures, combined with dark pigmentation that is hypothesized to protect from intense UV radiation, could explain how the new taxon is able to dwell in an extreme glacial habitat.”

Learn more about the tardigrade population in glaciers here.

An image of a tardigrade (Source: Live Science).


Glacier Mass Change and Modeling

From Nature: “Glacier mass loss is a key contributor to sea-level change, slope instability in high-mountain regions, and the changing seasonality and volume of river flow. Understanding the causes, mechanisms and time scales of glacier change is therefore paramount to identifying successful strategies for mitigation and adaptation. Here, we use temperature and precipitation fields from the Coupled Model Intercomparison Project Phase 5 output to force a glacier evolution model, quantifying mass responses to future climatic change. We find that contemporary glacier mass is in disequilibrium with the current climate, and 36 ± 8% mass loss is already committed in response to past greenhouse gas emissions. Consequently, mitigating future emissions will have only very limited influence on glacier mass change in the twenty-first century.”

Read more about the glacier modeling here.

Image of mountain glacier model (Source: Antarctic Glaciers).


Glacierized Volcanoes and the Effect of Eruptions on Health

From NCBI: “More than 500 million people worldwide live within exposure range of an active volcano and children are a vulnerable subgroup of such exposed populations. However, studies on the effects of volcanic eruptions on children’s health beyond the first year are sparse. In 2010, exposed children were more likely than non-exposed children to experience respiratory symptoms… Both genders had an increased risk of symptoms of anxiety/worries but only exposed boys were at increased risk of experiencing headaches and sleep disturbances compared to non-exposed boys. Adverse physical and mental health problems experienced by the children exposed to the eruption seem to persist for up to a three-year period post-disaster. These results underline the importance of appropriate follow-up for children after a natural disaster.”

Find out more about the effects of the eruption in Iceland here.

Image of Eyjafjallajökull volcanic eruption (Source: Time Magazine).
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Life, Death and Predation on the Greenland Ice Sheet

The Greenland Ice Sheet is the world’s second-largest body of ice (Source: Krzysztof Zawierucha).
Mention the Greenland Ice Sheet, and chances are that you conjure up the image of a barren, white wilderness, dominated by ice and devoid of life. In fact, the ice sheet and its coastal outlet glaciers support thousands of small pools that teem with bacteria and animals. “A world of microbes exists in these tiny, frozen, cold pools on glaciers. There’s life, death, and predation happening,” marveled glaciologist Aurora Roth.

These little pools are called cryoconite holes, pockets in the surface of glaciers that are usually ovular or circular. Cryoconite holes can be quite small and shallow, or as wide as a meter and up to half as deep. “People first notice cryoconites because they look so odd, like honeycomb. The textures are visually striking,” says Roth. She added that they constitute such an extreme environment that scientists look to them to understand the evolution of simple life forms on Mars and other planetary bodies. A recent paper in Limnology by Krzysztof Zawierucha et al. analyzed cryoconite communities on the margin of the Greenland Ice Sheet and found that the distribution of microfauna at the edge of the sheet is random, without clear ecological determinants like water chemistry or nutrient availability.

Sediment lies at the bottom of cryoconite holes of various sizes (Source: Krzysztof Zawierucha).
Cryoconite holes (and their larger versions, puddles and lakes) are full of water, and contain debris deposited by wind, rockfall or water flow. Small debris particles can be bound together by cyanobacteria into granules, which eventually erode into mud. Both granules and mud foster communities of bacteria and animals that comprise the biotic hotspots of the ice sheet. Microorganisms are the top consumers in cryoconite food chains, a position impossible for them to occupy in most other ecosystems, where they are eaten by larger organisms. Such unusual dynamics make “this icy world more and more fascinating,” Zawierucha told GlacierHub. “Despite the fact that they are in microscopic size, they are apex consumers on the glacier surface, so they are like polar bears in the Arctic or wolves in forests,” he said.

Zawierucha conducted his fieldwork at the beginning of polar autumn and was struck by the changing colors of the tundra, the musk oxen and the impressiveness of the ice sheet, which together created a landscape that felt right out of a fairy tale. As he trekked through wind and rain to collect samples from cryoconite holes, puddles and lakes, he often felt as if he was in a science fiction movie about “icy worlds in other galaxies.”

Zawierucha poses against the dramatic landscape of the ice sheet during fieldwork (Source: Krzysztof Zawierucha).
Back in the lab, Zawierucha found rotifers and tardigrades swimming around in his samples, two hardy invertebrate groups that also live in freshwater, mosses, and for the tardigrade, extreme environments–tardigrades are the only animals that can survive outer space. The invertebrates were far more common in granules than mud. The paper suggests two reasons for this disparity: the mechanical flushing action of water that forms the mud and the food source the granules provide for the invertebrates. The samples boomed with other types of life, as well: they contained thirteen types of algae and cyanobacteria, plus different groups of heterotrophic bacteria.

The flushing process, and the way it affects the animals which it displaces, raises many questions for Zawierucha. How much wind or rain is required to remove the animals from the cryoconites? “How many of them are flushed to downstream ecosystems, and how many stay in the weathering crust on glaciers?” he wonders. And what happens once the animals are out of their holes? Zawierucha harbors what he calls a “small dream,” to find active animals in the subglacial zone (the hydraulic systems under a glacier). “If they are flushed to the icy wells, are they able to survive under ice?” he asks.

Tardigrades are found on all seven continents, in a range of extreme environments (Source: E. Schokraie et al./Wikimedia).
In the future, Zawierucha would like to continue to close what he calls the “huge knowledge gap” between the vast amount of research devoted to microbial ecology on glaciers and the dearth of information about animals. “Even if their distribution is random, they still may play an important ecological role in grazing on other organisms,” he believes.

Tardigrades, some species of which are black in color, may have an even bigger effect on glacial dynamics and global climate. Tiny though they are, populations of black tardigrades in cryoconite holes, which Zawierucha has found on alpine glaciers, can reduce albedo and increase melting of the glacier surface. This may constitute a positive feedback loop that hastens glacial melting, but more studies are required to prove this, Zawierucha says.

One positive feedback loop is clear. Higher temperatures increase the melting of glacier surfaces and spur microbial activity, which in turn speeds up the process of melting, according to Zawierucha. As the Greenland Ice Sheet continues to melt, the animals that call it home will be disturbed, though it is difficult to anticipate the end result. How tardigrades, especially species unique to glacial habitats, will respond to higher flushing rates and removal from glaciers is of particular interest. Perhaps the tardigrades will adapt, or perhaps they will go extinct, says Zawierucha.

Zawierucha prepares samples for transport off the ice sheet (Source: Krzysztof Zawierucha).
Faced with an uncertain future, glaciology projects that cross disciplines make Roth hopeful. “It’s a good example of what happens when you look at a system through an interdisciplinary lens,” she told GlacierHub. “When you bring in a biologist, you see the difference in the questions they ask and things they unearth.”

Now is the time for such interdisciplinary research: more studies of animals living on the Greenland Ice Sheet will help scientists understand how this important freshwater reservoir, and Earth’s climate, will respond to global warming.

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Could Cryoconites Hold the Secrets to Extraterrestrial Life?

In recent years, scientists have found other locations on planets, moons and exoplanets where life might exist. Different animals and organisms like tardigrades (eight-legged microscopic animals commonly known as water bears) have also been sent into space to explore the conditions for survival away from Earth. However, a recent paper published in the journal Contemporary Trends in Geoscience argues that we can look closer to home to understand survival strategies of extraterrestrial life.

More concretely, the authors propose we look to glacier cryoconites, which are granular or spherical mineral particles aggregated with microorganisms like cyanobacteria, algae, fungi, tardigrades and rotifera (another type of multicellular, microscopic animal). Glaciers are among the most extreme environments on Earth due to the high levels of ultraviolet (UV) radiation received and the permanently cold conditions. These factors make them analogous to icy planets or moons.

(Clockwise from top left) An ice sheet in Greenland, cryoconite holes, cryoconite granules, and cryconite granules in high resolution (Source: Zawierucha et al., 2017).

The associations of cryoconites and microorganisms on glaciers are held together in biofilms by extracellular polymeric substances (natural polymers of high molecular weight) secreted by cyanobacteria. They exist as sediment or in cryoconite holes (water-filled reservoirs with cryoconite sediment on the floor) on glacier surfaces.

Cryoconites have been found on every glacier where researchers have looked for them. Cryoconite holes form due to the darkening of color (also termed a decrease in the albedo, or reflectivity of solar radiation) of cryoconite-covered surfaces. The darker color leads to greater absorption of radiation, with an associated warming and increasing melt rates.

“Today we think that simple life forms might have survived on Mars in glacial refugia or under the surface. They can and could have evolved on Saturn and Jupiter’s icy moons,” Krzysztof Zawierucha, the lead author from Adam Mickiewicz University in Poland, shared with GlacierHub. “Imagine a multicellular organism, even a microscopic one, which is able to live and reproduce on an icy moon… It is a biotechnological volcano.”

Earth’s glaciers could be analogous to environments like floating ice on Europa, one of Jupiter’s moons (Source: NASA).

Organisms that live in glaciated regions are adapted to survive in extreme conditions and could provide insights into the survival strategies of extraterrestrial life. Some possess lipids (organic compounds that are not water-soluble), and produce proteins and extracellular polymeric substances that protect them from freezing and drying. Others are able to enter cryptobiotic states in which metabolic activity is reduced to an undetectable level, allowing them to survive extremely harsh conditions.

The microorganisms in cryoconites cooperate and compete, affecting each other’s survival responses. Therefore, previous astrobiological studies, which have only been conducted on single strains of microorganisms, may not reflect the true survival mechanisms of these microorganisms.

Tardigrades can undergo cryptobiosis and survive in the vacuum of space (Source: UNC Chapel Hill/Creative Commons).

In addition, previous astrobiological studies involving some of these microorganisms used terrestrial or limno-terrestrial (moist terrestrial environments that go through periods of immersion and desiccation) taxa, such as moss cushions, which are less likely to be well-adapted to icy planets than their glacier-dwelling cousins.

Tardigrades found in cryoconite have black pigmentation, which probably protects them from high UV radiation. Along with tardigrades, glacier-dwelling rotifera, specifically Bdelloidea, also possess a great ability to repair DNA damage, which confers high resistance to UV radiation. Both may also be better adapted to surviving in constantly near-freezing conditions than terrestrial forms.

“So far, a number of processes analogous to those on Mars and other planets or moons have been found in the McMurdo Dry Valley as well as other dry valleys or brines in sea ice, both of which were considered to be extraterrestrial ecosystem analoguos. There is a great body of evidence that some bacteria and microscopic animals like tardigrades may survive under Martian conditions,” Zawierucha explained.

“Of course, to survive does not mean to be active and to reproduce. Undoubtedly, however, it triggers consideration regarding life beyond Earth, especially in close proximity or connection with permafrost or ice,” he added.

As such, further research about cryoconites could provide insight to mechanisms that enable organisms to survive such extreme conditions. At the same time, cryoconites could also be used in future astrobiological studies to understand how life on other planets functions.

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The Microscopic Life of Glaciers

Svalbard Glacier, courtesy of Airflore/Flickr.
Svalbard Glacier, courtesy of Airflore/Flickr.

Though it can be hard to imagine that cold, barren-looking glaciers are conducive to life, glaciers are actually teeming with organisms. Glacier surfaces are filled with cylindrical holes called cyroconite holes, in which melt water accumulates and micro-algae and cyanobacteria  thrive.

Now, a new study published in Biogeosciences has taken a closer look at these complex ecosystems to better understand the interactions between the organisms that inhabit this icy space. They found that Svalbard glaciers that received large quantities of deposits from local areas tended to have large amounts of microalgae. These microalgae can create large colonies to protect them from invertebrate grazers like tardigrades, minute animals also known as water bears, and other microscopic animals like rotifers and ciliates. Large microalgae colonies can protect themselves from the filtration feeding strategy used by rotifers.

The researchers studied these mini-ecosystems on four glaciers in Svalbard, a Norwegian Archipelago. Each sample had a different level of exposure to nutrients, water depth and the degree to which the cyroconite holes were isolated so that the researchers could separately analyze the effects of environmental factors and other biological interactions, such as animals grazing on the microalgae.

Under a microscope, the researchers identified the different species of tardigrades and rotifers. They also measured the density of microalgae clusters and the types of microalgae and cyanobacteria.

Colony of rotifers, courtesy of Specious Reasons/Flickr
Colony of rotifers, courtesy of Specious Reasons/Flickr

In glaciers farther away from glacier-free land, the microalgae species differed from glaciers closer to land. Species variability could be attributed to wind transport, the researchers suggest.

“We propose that selection occurs because polar cyanobacteria are often associated with dust in soil, and thus easily transported by 20 wind,” they wrote. Levels of nitrogen deposits from bird guano and tundra may also play a role in determining which species of microalgae lived where, but the researchers felt this factor was less important than wind transportation.

The species and quantities of grazers, on the other hand, did not vary much from site to site. Grazer types were also correlated with the types of microalgae found in different cyroconite holes. Rotifers tended to live around Zygnemales and Chlorococcales, while tardigrades were usually found around larger Zygnemales.

“The high abundances of tardigrades, rotifers, and ciliates, including genera with different feeding strategies, have been found and suggest a complex food web between more trophic levels than measured in the present study,” the authors wrote. “Feeding experiments and analysis of stomach contents may help to bring a more detailed picture of this yet hardly known food web.”

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