The Laboratory at the Glacier’s Mouth

Glacier-fed rivers’ food chain can be used as a conceptual model

Glacier-fed rivers constitute a unique, harsh environment where only a few species are able to survive. Their study allows the establishment of very complete food webs that can be used as a model to understand those of other systems. In addition, glaciers are very sensitive to climate change. The observation of changes in the feeding habits of their inhabitants could lead to predictions concerning further glacial retreat.

Glacier-fed rivers constitute a unique, harsh environment where only a few species are able to survive. Their study allows the establishment of very complete food webs that can be used as a model to understand those of other systems. In addition, glaciers are very sensitive to climate change. The observation of changes in the feeding habits of their inhabitants could lead to predictions concerning further glacial retreat.

 

The Odenwinkelkees - ©Lee Brown

 

Glacier-fed rivers present unique, harsh living conditions

 

In general, in nature, a large number of species are linked together via the food chain. Thus, the study of food webs, and their evolution over time and as a function of various events, is rather complicated. Dr. Lee Brown, a freshwater ecologist from [email protected], University of Leeds, with a particular interest in river ecosystems, used a simpler system to study food webs. In his latest paper, published in PLOS One [available on MyScienceWork] with colleagues from the University of Leeds, he looked at food webs in rivers immediately downstream of a glacier outlet. Because of the unique, harsh conditions encountered here, only a few species are able to survive. Thus, these aquatic communities provide a simple model to learn more about food webs and to study how they change over time. Another interest of studying glacial areas is that the warming due to climate change occurs more rapidly in these regions. The consequent melting and shrinking of the glacier leads to less drastic living conditions in the river and leads to the appearance of new species that will compete for the same food.

Concretely, Dr. Brown’s team studied various samples taken from the Ödenwinkelkees River in the Central Austrian Alps in 2006, 2008 and 2011. They identified only 22 taxa: 11 unicellular algae (diatoms) and 11 macroinvertebrates, mainly some dipteral chironomids. To determine the feeding habits of the invertebrates, they dissected them to analyze directly the contents of their gut. Lee Brown was particularly interested in the observation of cannibalism developing in chironomids over the years.

After collecting all the data, food webs for each year and an overall web were established. According to Brown, “They do not yet permit any high level prediction of what might happen with further glacier retreat, but it is a start.” In addition, these food webs were compared to those of systems in less hostile environments and were found to be quite similar.

 

Food webs established in glacier-fed rivers represent a theoretical model

 

For Dr. Olivier Dangles, who studies biodiversity in a context of global change, at the IRD (Institut de recherche pour le développement) in Gif-sur-Yvette, “This conceptual approach removes some uncertainties when studying bigger systems, and thus is a great asset for the scientific community.” The model established in the glacier-fed rivers can be applied to other, completely different systems, mainly those with organic matter at the primary food chain level, also called the trophic level. For example, understanding trophic networks can help discriminate between two hypotheses concerning the disappearance of different species at the same time. Was it the change of conditions that was bad for both of them? Or was it the disappearance of the lower trophic level resource that led to the death of the higher that did not find enough food to survive?

The cannibalism observation is also a perfect example of the possible extrapolation of this model to other systems. Indeed, this survival mechanism can be seen as a malfunction of the trophic chain but is a great example of adaptation to the increasing scarcity of food.