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.
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.”