[M-IS15] Mountain Science

[MIS15-P09] Diurnal vertical migration and seasonal change of snow-ice microorganisms on seasonal snow in Mt. Gassan, Japan

*MASATO ONO¹, Nozomu Takeuchi² (1.Graduate School of Science and Engineering, Chiba University, 2.Department of Earth Science, Graduate School of Science, Chiba University)

Keywords:snow ecosystem, seasonal snow, snow-ice microorganisms, diurnal vertical migration, seasonal change

In snow-ice environments such as glaciers and seasonal snow, we can see snow-ice microorganisms adapted to harsh conditions. Since these microorganisms form a food chain in the snow and ice environments, snow and ice can be regarded as an ecosystem containing these biological communities (snow ecosystem). Especially in seasonal snow, snow algae blooming occurred then snow surface is colored in various colors such as red, green, orange and yellow. So far, predators eating snow algae in red snow found in the alpine in Canada. In addition, it has been clarified that invertebrates such as tardigrades and rotifers concentrated and eat snow algae on green snow in the forest zone of the mountainous areas of Japan. While all of the studies focused only on the snow surface, it was also suggested that tardigrades and rotifers move actively in the vertical direction. The vertical movement of these organisms may be accompanied by daily cycles of the snow environments such as solar radiation, melting rate of snow, and temperature, or seasonal changes such as increase in nutrients and organic matter. However, diurnal cycle and seasonal changes in biological activity have not been investigated. In this study, we aimed to clarify the daily cycle, seasonal changes in the distribution of snow algae, microinvertebrates (tardigrades and rotifers), and fungi in the snow.
The fieldworks were carried out in the forest located in Mt. Gassan in Yamagata Prefecture, Japan. White snow and green snow on the snow surface and inside were collected from March 6 to May 20, 2021. It is known that green snow appears every year at this point. The samples shipped to Chiba university then processed to microscopic observation, measurements of organic and inorganic matter, and chemical analysis. It was clarified the samples were mainly contained various type of snow algae, morphologically two types of tardigrades genus Hypsibius, Bdelloid rotifer, and fungi. Microorganisms that can swim by themselves (snow algae, tardigrades, rotifers) had higher concentrations near the surface than the lower layers of snow from night to early morning (5:00 and 17:00 to 2:00). On the contrary, the concentrations were higher in the lower layer than on the snow surface from daytime to evening (from 8:00 to 20:00). Since these changes well matched with the timing of changes of solar radiation, it was suggested that snow algae in the snow move vertically to avoid strong solar radiation, and microinvertebrates are accompanied with food. Considering that these biomasses increased rapidly after opening of the leaf of beech forest, the propagation of the biological community in the snow may be triggered by the prolonged staying time on the snow surface due to the decrease solar radiation.