May 31st 2011
Watermelon snow, also called snow algae, is snow that is reddish or pink in color, with the slight scent of a fresh watermelon. This type of snow is common during the summer in alpine and coastal polar regions worldwide, such as the Sierra Nevada of California. Here, at altitudes of 10,000 to 12,000 feet (3,000–3,600 m), the temperature is cold throughout the year, and so the snow has lingered from winter storms. Compressing the snow by stepping on it or making snowballs leaves it looking red. Walking on watermelon snow often results in getting bright red soles and pinkish pant cuffs.
Watermelon snow is caused by the presence mainly of Chlamydomonas nivalis, a species of green algae containing a secondary red carotenoid pigment (astaxanthin) in addition to chlorophyll. Unlike most species of fresh-water algae, it is cryophilic (cold-loving) and thrives in freezing water. Its specific epithet, nivalis, is from Latin and refers to snow.
Chlamydomonas nivalis is a green alga that owes its red color to a bright red carotenoid pigment, which protects the chloroplast from intense visible and also ultraviolet radiation, as well as absorbing heat, which provides the alga with liquid water as the snow melts around it. Algal blooms may extend to a depth of 25 cm (10 inches), with each cell measuring about 20 to 30 micrometers in diameter, about four times the diameter of a human red blood cell. It has been calculated that a teaspoon of melted snow contains a million or more cells. The algae sometimes accumulate in "sun cups", which are shallow depressions in the snow. The carotenoid pigment absorbs heat and as a result it deepens the sun cups, and accelerates the melting rate of glaciers and snowbanks.
During the winter months, when snow covers them, the algae become dormant. In spring, nutrients, increased levels of light and meltwater, stimulate germination. Once they germinate, the resting cells release smaller green flagellate cells which travel towards the surface of the snow. Once the flagellated cells reach the surface, they may lose their flagellae and form aplanospores, or thick-walled resting cells, or they may function as gametes, fusing in pairs to form zygotes.
Many species feed on C. nivalis, including protozoans such as ciliates, rotifers, nematodes, ice worms and springtails.
Is Watermelon Snow As Edible As An Actual Watermelon?
Although watermelon snow is a nickname of snow algae, it begs the question: Is watermelon snow actually edible?
In general, most algae is considered edible. Even the faint watermelon-like scent of snow algae might give that impression. The author of this SummitPost article has even tasted very small doses of snow algae, for testing purposes, without feeling sick. However, it is possible that snow algae might be contaminated by bacteria and toxic algae that are harmful to humans. Eating large quantities of watermelon snow has been known to cause digestive ailments, although the tolerance level of each person's digestive system might be different.
Although human consumption of watermelon snow is not wholely recommended, many organisms consider the algae as a delicacy and, for some, an essential food source. Most notably, ice worms, roundworms, snow fleas, and protozoans regularly consume snow algae. At high elevations, it is common to see millions of ice worms atop snowfields during early morning and late evening hours, especially near snow algae blooms.
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