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Snow algae are a group of freshwater micro-algae that grow in the alpine and polar regions of the Earth. Snow algae have been found on every continent but are restricted to areas with temperatures between 0°C-10°C. Snow algae are pigmented by
Snow algae undergo oxygenic photosynthesis and are primary producers on the snow. This allows other organisms to live on the snow along with the algae and feed on them to obtain energy. Tardigrades and rotifers have been shown to grow preferentially on green blooms but have been found on many different snow algae blooms across the globe.
Although the trophic webs of snow algae blooms are not generally complex, the microbial communities found in these blooms can play major roles in how nutrients are distributed in the environments they inhabit. These microbial and algal communities cycle globally significant amounts of carbon, nitrogen, iron, and sulfur.
Snow algae are a group of freshwater micro-algae that grow in the alpine and polar regions of the Earth. Snow algae have been found on every continent but are restricted to areas with temperatures between 0°C-10°C. Snow algae are pigmented by chlorophyll
Chlorophyll is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words (, "pale green") and (, "leaf"). Chlorophyll allows plants to absorb energy ...
and carotenoids
Carotenoids () are yellow, orange, and red organic compound, organic pigments that are produced by plants and algae, as well as several bacteria, archaea, and Fungus, fungi. Carotenoids give the characteristic color to pumpkins, carrots, parsnips ...
and can be a variety of colors depending on the individual species, life stage, and topography/geography. The pigmentation of snow algae reduces snow and ice albedo
Albedo ( ; ) is the fraction of sunlight that is Diffuse reflection, diffusely reflected by a body. It is measured on a scale from 0 (corresponding to a black body that absorbs all incident radiation) to 1 (corresponding to a body that reflects ...
, which can stimulate the melting of perennial snow and ice and exacerbate the effects of climate change
Present-day climate change includes both global warming—the ongoing increase in Global surface temperature, global average temperature—and its wider effects on Earth's climate system. Climate variability and change, Climate change in ...
. Snow algae are primary producers
An autotroph is an organism that can convert abiotic sources of energy into energy stored in organic compounds, which can be used by other organisms. Autotrophs produce complex organic compounds (such as carbohydrates, fats, and proteins) us ...
that form the basis of communities on snow or ice sheets that include microbes, tardigrades
Tardigrades (), known colloquially as water bears or moss piglets, are a phylum of eight-legged Segmentation (biology), segmented micro-animals. They were first described by the German zoologist Johann August Ephraim Goeze in 1773, who calle ...
, and rotifers
The rotifers (, from Latin 'wheel' and 'bearing'), sometimes called wheel animals or wheel animalcules, make up a phylum (Rotifera ) of microscopic and near-microscopic pseudocoelomate animals.
They were first described by Rev. John Harris ...
. Snow algae have also been carried great distances by winds.
Pigmentation
Snow algae produce two main classes of pigment molecules: chlorophylls and carotenoids. Carotenoids further split into two groups known as primary and secondary carotenoids and typically help give the snow algae cells their visible colors. Primary carotenoids, such as the yellowxanthophyll
Xanthophylls (originally phylloxanthins) are yellow pigments that occur widely in nature and form one of two major divisions of the carotenoid group; the other division is formed by the carotenes. The name is from Greek: (), meaning "yellow", an ...
, are typically used in low concentrations for photosynthesis while still offering some UV protection. Secondary carotenoids, such as the red astaxanthin
Astaxanthin is a keto- carotenoid within a group of chemical compounds known as carotenoids or terpenes. Astaxanthin is a metabolite of zeaxanthin and canthaxanthin, containing both hydroxyl and ketone functional groups.
It is a lipid-solu ...
, are used for UV protection by the cell and can be found in high or low concentrations depending on the strength of the UV light.
Different taxa of snow algae produce differing amounts of primary and secondary carotenoids, meaning the color of a snow algae bloom can give some indication of the composition of algae found there. The alga '' Chlamydomonas nivalis'' is a very abundant component of red blooms due to its high concentrations of astaxanthin and its derivatives. Many ''Chloromonas
''Chloromonas'' is a genus of green algae in the family Chlamydomonadaceae. It is closely related to the model green algae, ''Chlamydomonas'', and traditionally has been distinguished mainly through the absence of a pyrenoid.
Species of ''Chloro ...
'' species are associated with green or orange-yellow snow due to the primary carotenoids they produce. Similar colors of snow can also vary in composition by region, showing large scale biogeographical trends in the snow algae distribution.
The algae's life stage may also play a large role in the color of the snow. Many blooms are higher in chlorophylls and primary carotenoids during early stages of the bloom, causing the snow to appear green or yellow. Later in the summer, the bloom may switch to orange or red due high production of astaxanthin during low nutrient periods and the snow algae’s more stable cyst stage that they use to over-winter.
Role in ecosystem
Snow algae undergo oxygenic photosynthesis and are primary producers on the snow. This allows other organisms to live on the snow along with the algae and feed on them to obtain energy. Tardigrades and rotifers have been shown to grow preferentially on green blooms but have been found on many different snow algae blooms across the globe.
Although the trophic webs of snow algae blooms are not generally complex, the microbial communities found in these blooms can play major roles in how nutrients are distributed in the environments they inhabit. These microbial and algal communities cycle globally significant amounts of carbon, nitrogen, iron, and sulfur.
Effects on snow albedo and climate change
The pigmentation of snow algae can significantly reduce snow albedo, stimulating the melting of ice and snow on ice sheets. Larger snow grains allow light to penetrate further into the snow layer which increases light absorbance by snow algae and further reduces the albedo of the snow. Snow algae drive greater changes in snow albedo later in the summer when algae are more abundant. The different abundances of pigments present in snow algae, including chlorophyll and carotenoids, lead to differences in light absorption and therefore albedo changes based on algal community composition. The presence of mineral and organic particle impurities on snow also reduces the albedo of snow, which can sometimes overshadow the effects of snow algal community dynamics on the albedo. Under warmer conditions snow algae experience more growth, which can further reduce the albedo of snow and ice sheets. This positive feedback loop, similar to the ice-albedo feedback, can exacerbate the melting of perennial snow and ice by climate change.References
{{Reflist Algae Aquatic ecology Snow algae