Hydrurus-related golden algae ( Chrysophyceae) cause yellow snow in polar summer snowfields.

In polar regions, melting snow fields can be occupied by striking blooms of chrysophycean algae, which cause yellowish slush during summer. Samples were harvested at King George Island ( South Shetland Islands, Maritime Antarctica) and at Spitsbergen ( Svalbard archipelago, High Arctic). The populations live in an ecological niche, where water-logged snow provides a cold and ephemeral ecosystem, possibly securing the survival of psychrophilic populations through the summer. A physiological adaptation to low temperatures was shown by photosynthesis measurements. The analysis of soluble carbohydrates showed the occurrence of glycerol and sugars, which may play a role in protection against intracellular freezing. Although both populations were made of unicells with Ochromonas-alike morphology, investigation by molecular methods ( 18S rDNA sequencing) revealed unexpectedly a very close relationship to the mountain-river dwelling Hydrurus foetidus ( Villars) Trevisan. However, macroscopic thalli typical for the latter species were never found in snow, but are known from nearby localities, and harvested samples of snow algae exposed to dryness evolved a similar pervading, 'fishy' smell. Moreover, in both habitats tetrahedal zoospores with four elongate spikes were found, similar to what is known from Hydrurus. Our molecular results go along with earlier reports, where chrysophycean sequences of the same taxonomic affiliation were isolated from snow. This points to a distinct group of photoautotrophic, Hydrurus-related chrysophytes, which are characteristic for long-lasting, slowly melting snow packs in certain cold regions of the world. [ABSTRACT FROM AUTHOR]