“Sanguina nivaloides” algae takes advantage of the first few centimetres of snow
The cellular structures of the algae that turns slush red in spring in the mountains and summer in the polar regions have just been described on a microscopic scale.
A red cell in shadowless white light. “Blood on the snow”: this phenomenon, which appears in spring on glaciers and in summer at the poles, has been observed and questioned by many people, hikers and scientists alike, over the course of time. In 300 BC, Aristotle was already wondering about its nature, long before the botanist and naturalist Horace Bénédict de Saussure, who proposed a description of it in the 18th century. In 1918, samples of colored snow were brought back to Europe by John Ross’s Greenland expeditions.
But it would be another hundred years before the origin of “snow blood” was actually described: it’s an alga called Sanguina nivaloides. And a few more years to unravel some of the mysteries surrounding this plant. A French research team, including Eric Maréchal from Grenoble’s Laboratoire de Physiologie Cellulaire et Végétale, has observed these algae in liquid water currents around ice crystals. “They are photosynthetic, can survive for months and are sensitive to frost”, we learn in the study published this November 18 in Nature Communication.
As laboratory cultivation of Sanguina nivaloides is not possible, snow samples containing the algae were collected on the Brevent and Galibier mountains in the Alps, on Mount Olympus and in the Trondheim region of Norway.
This is how they were able to see that this red algae evolved in tiny water circuits in the snow. In spring in the Alps, it contains 10-20% liquid water. “I went on an expedition this year in August to Scoresby Fjord with Greenlandia,” he recalls, to pinpoint the time of the Arctic Sanguina nivaloides bloom.
Counter-intuitively, these algae are sensitive to cold: stored at -4°C, they die overnight. Under the first centimeter of snow, they live at around the melting point (0°C), in this film of water that doesn’t freeze because it contains minerals, a bit like water on a mountain road, an ally against icy conditions. Algae multiply thanks to these minerals, although they are rare, as is phosphorus, which is essential.
“We analyzed the content of the snow with and without algae, and found that it had absorbed all the phosphorus,” notes Eric Maréchal. This result supports the hypothesis that revolves around the strange wrinkles on the outside of their single cell. “This increases the exchange surface by 10%, so they have more contact with their environment,” he describes.
In the cell, phosphorus is stored in lipids, which the researchers analyzed. “We deduce that they’re saving phosphorus, they’re in resistance mode,” he explains. To build these lipids and seal their cell walls, they break down water molecules using the sun’s energy during photosynthesis.
The anatomy of their photosynthetic organs is different from that of other plants. They are oriented in all directions, so that the chlorophyll captures the light arriving from all sides, reflected by the ice crystals.
This abundance of light is excessive, however, and leads to the production of free radicals that burn the cell’s molecules. To defend itself, Sanguina nivaloides produces a red pigment, carotenoids, which absorb this energy.
Once completely melted, the algae sink into the earth, but researchers still know very little about how they survive until the next snowfall.
Camille Lin, PolarJournal
