The snow alga, Chlamydomonas nivalis is a good example of a microbe that survives under extreme environmental conditions. Typically it is found growing in melting snow and this alga is found on all continents with the possible exception of Africa. C. nivalis cells are orange-red in color because they contain large quantities of a carotenoid, astaxanthin. Under favorable conditions, C. nivalis forms dense algal blooms, coloring the snow pink, giving rise to the common name "watermelon snow".

Red color of Chlamydomonas nivalis cells is due to astaxanthin, a carotenoid with UV blocking characteristic. Cells average 35 µm in diameter.

C. nivalis populations occur commonly on the permanent snowfields in the alpine of the Rocky Mountains. Environmental conditions within the snow are harsh. Temperature fluctuates diurnally around the freezing point, from -8 to 1°C. In addition, the amount of visible light within the snow is very high. Snow is highly reflective to visible radiation and in combination with its highly light scattering properties, may create some of the highest natural photon fluence rates on Earth. The optics of snow may also enhance the fluence rate of UV-B radiation which is also naturally greater at high elevations. The simultaneous high fluxes of visible and UV-B radiation combined with low temperature may comprise one of the most extreme environmental conditions for photosynthetic organisms found on Earth. The purpose of the current research is to characterize the extreme light and temperature experienced by this snow alga and to determine the influence of these extremes on its photosynthetic O₂ evolution.

Colony of snow algae extending down into the snow. Hole is about 10 cm deep.

excerpt from http://uwadmnweb.uwyo.edu/botany/fac/tvogel/snowalg2.htm

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