Red Snow, Green Snow

It's truly spring when those last white drifts go technicolor

Microbiologist Brian Duval hates this part, so let’s just deal with the snickering up front. Yes, he studies yellow snow.

No, it’s not a murder scene. A bloom of the alga Chlamydomonas nivalis reddens the snow beside a hip-high evergreen in the Sierra Nevadas of California. Duval

It takes an expert to tell, but this yellow stain revealed by digging in the snow comes from a bloom of a Chloromonas alga in Yosemite National Park. More delicate than its red relatives, it has not risen all the way to the sunblasted surface of the snow. Duval

What seems to be an as yet unnamed species of Chloromonas gives an orange tint to the last snow patches on Mount Washington in July. Duval

The plump cylinder of a rotifer (center) bends its lumpy head to the left as it grazes among Chloromonas algae. Duval

A microscopic water bear, or tardigrade, waddles on eight legs with no joints. Tardigrades root around the snowfield ecosystems that thrive on snow algae. John Crowe

He also studies red, green, and orange snow and would love to examine other colors if he were lucky enough to discover them. His palette comes from springtime blooms of algae that live only in deep, persistent snowfields.

And yes, even a professional sometimes gets fooled.

“I was outside a penguin rookery in Antarctica, and I thought I was collecting this greenish-yellow algae,” recalls the microbiologist now at the Massachusetts Department of Environmental Protection in Worcester. “I was  saying, ‘Yeah, yeah, this looks like the stuff.'” When he checked his treasures under a microscope, however, he diagnosed the obvious nonalgal origin. “It gets embarrassing,” he admits.

Despite the yellow-snow raillery, Duval and his colleagues stay with their studies of snow algae because of the marvels of the chilly lifestyle. Somehow the 350 species of snow algae thrive in the near-freezing, nutrient-poor, acidic, sun-blasted slush of melting snowfields around the world. The algae support a food web in the snow—a world of tiny, wormy, crawly beings as odd as Spielberg-movie creatures.

Algal life cycles combine the drama of salmon runs and the nightmare of icebound explorers. Snow-algae chemistry captivates biologists musing about life on other planets or prospecting for novelties on our own. These flashy algae are on their way to becoming glamour species in what Duval and like-minded specialists see as the dawning of a great era of snow ecology.

Plus, snow algae can be gorgeous.

In high Western snowfields, they blush red in footstep-size patches and meters-long streaks that hikers call watermelon snow. In northern New England, they give salmon-orange sunset streaks to the last mounds of snow at the season’s end.

Fie on snickering. Such wonders deserve awe.

“They’re amazing,” Duval sums up. He doesn’t say that they’re cool. That’s another one that he’s heard too often.

Not ice algae

Snow algae aren’t ice algae. Many of the ice species tolerate salt water and survive in solid ice packs at the poles. “They’re completely different species,” Duval says, sounding a little surprised that anyone would want to lump the groups together.

To find snow algae, look for serious snow, long lasting and several feet deep. William H. Thomas of Scripps Institution of Oceanography in La Jolla, Calif., goes to the high spots in Yosemite National Park and other snowfields at least 10,000 feet up in the Sierra Nevadas, the Cascades, and the Rocky Mountains. There, Thomas’ particular passion, watermelon snow, tinted mostly by Chlamydomonas nivalis, ripens around July in the same places year after year.

“The red snow gets all the publicity,” remarks Ronald W. Hoham of Colgate University in Hamilton, N.Y. “I find the green and orange more interesting.” The nonred species thrive where snow lingers longest in upstate New York and regions northward.

Massachusetts’ Berkshire Hills and Wachusett Mountain, New Hampshire’s White Mountains, Vermont’s Green Mountains, and Maine’s Mount Katahdin all harbor colonies of snow algae, Hoham and Duval report in a paper to be published in Rhodora.

These species never develop the extensive red pigments that protect watermelon snow algae from brilliant sunlight. The green snow algae, mostly in the genus Chloromonas, typically stick to high-elevation, shady forests of fir and spruce. These algae generally bloom several inches below the snow surface. Orange species tolerate a bit more light, and Duval and Hoham spotted their salmon-colored alga in the open snow of several New England ski resorts. They haven’t found the species in wilderness areas yet, and they speculate that it spreads in part by hitchhiking on skis.

As Duval and Hoham pored over their map of Northeastern algae sightings, they decided that Chloromonas algae were more likely to bloom where 80 inches of snow falls in a winter than in spots with less-extreme weather. This insight sent Duval algae prospecting in West Virginia, but so far, no luck.

If New Englanders have never noticed the colorful local snow algae high in their woodlands, Hoham is understanding, if a bit narrowly focused. “Nobody wants to go hiking when it’s miserable outside,” he says. “They miss everything.”

Ancient phenomenon

Snow algae are hardly an exclusively North American phenomenon—or a new one. Greek philosopher Aristotle reported red snow more than 2,000 years ago.

An 1818 British expedition exploring off the northwest coast of Greenland spotted crimson streaks on snowy cliffs and brought home red meltwater for analysis. “Our credulity is put to an extreme test upon this occasion, but we cannot learn that there is any reason to doubt the fact as stated,” remarked the London Times.

Experts of that time decided that an iron deposit from a meteorite must have stained the explorers’ snow. Only a year later, however, biologist F. Bauer described living cells in colored snow. The snow dwellers turned out to be bona fide single-celled, chloroplast-carrying members of the green algae division. Zingy pigments mask the underlying green.

The greatest sense of the worldwide scope of snow algae came from a Hungarian botanist, Erzsébet Kol, who started publishing scientific articles on the subject in the mid 1920s. For the next 50 years, she described snow algae sent to her from Antarctica, New Guinea, and other far-flung snow fields and accumulated during her own wide-ranging travels. She collected specimens from Transylvania to Alaska and even managed to get into isolationist Albania to describe its algae in 1958.

With all these records, Duval wondered a few years ago why Africa remained the only continent where no one had reported snow algae. In 1998, he and Edilma Duval set off on an algae-prospecting jaunt on Mount Neltner in Morocco.

They brought an ice chest of Moroccan snow back to a laboratory in Spain. The next year, they and Hoham, their taxonomic collaborator, published the first report of snow algae in Africa.

Scientifically surveying for algae looks a bit like poking around in the snow. “People will come up to me and ask, ‘Did you drop something?'” Brian Duval says.

Blossoming colors

The colors blossoming on snowbank surfaces in springtime are just the tip of the life cycle for snow algae. The red of watermelon snow comes from pigments in algal cysts, resting cells protected by sturdy coats. Hoham has received healthy cyst samples shipped at -70ºC, a temperature that destroyed active algal cells. Using radioactive carbon, Thomas and Duval have shown that cysts photosynthesize, but otherwise they just wait for the next season’s action.

As snow vanishes in summer, the cysts settle onto the ground. “The red ones look like a crust of dried blood,” Duval says. Summer passes. Snow falls again. The cysts essentially just lie there as snow piles up on top of them week after week.

When the snow starts melting in the high-altitude spring, the cysts burst, releasing single cells, each with two whiplike tails. They swim upward, bucking the current of draining meltwater. “It’s a race against time,” explains Hoham. Like salmon on their final swim, the algal cells have to gain the upper reaches of their water world to reproduce. The cells, only 10 to 15 micrometers across, fight their way through several feet of snow in meltwater that hasn’t reached even 1ºC.

Because their snowy world is disappearing, the swimmers can’t afford to dally. Although the pH of most springtime snow hovers around 5, during the first flush of melting, it can sink to 3.5, about the same acidity as peat bogs, Hoham reports. The bogs’ well-known ability to preserve corpses stems from the death of most microbes in such an environment, yet snow algae swim through similar punishment.

When some of the swimmers near the surface, they mate and form the protective cysts. Others don’t mate when they reach the top, but they still form cysts. Hoham is trying to sort out why some algae he studies seem not to have sex at all, but others even in the same population reproduce sexually.

This month at the Eastern Snow Conference in Syracuse, N.Y., he and his students are scheduled to present results from their ongoing study of factors influencing algal mating. The researchers have established, for instance, that in the lab, New York Chloromonas mates most readily in a mild, blue glow, which resembles sunlight filtering through an evergreen forest and a layer of snow. These algae responded better to 20 hours of light followed by 4 hours of darkness than to New York’s 14-hour days. Hoham wonders if he’ll find the same strain at higher latitudes, such as Quebec, where spring days last much of the night.

He and his students will also describe a reproductive pattern that Hoham had never seen before in this group of green algae. When mobile cells of what seems to be a new species of Chloromonas start to mate, most have oblong shapes. Some 8 hours later, the oblong cells have blimped out, so the combining cells are spherical.

After mating, the snow algae drift back to the ground with the dwindling snow. In this spartan world, swift depletion of nutrients such as nitrogen jolts the cells into growing their protective coats and assuming a holding mode before their habitat melts away. In this way, they stay safe until the next spring rush.

Slush piles

Where an uninitiated person might see just a big pile of slush, snow biologists recognize a teeming, speck-eat-dot world. As primary producers, the algae capture energy from the sun. Bacterial colonies develop around the algae. Rotifers and other higher-level predators then move in.

More complex beasts, such as Mesenchytraeus ice worms, also come to graze. “You’ll know them if you see them,” chuckles Hoham. The dark squiggles, an inch-plus long, even have segments like earthworms.

Collembola, or snow fleas, hop about this nearly invisible zoo. Tardigrades, or water bears, also are on the prowl but more at a lumber than a hop. These flyspeck-size hunters have a blob of a body with a tiny head mounted low in front. Proportionally big claws adorn their eight stubby legs, which have no joints. “You wonder how on Earth they hold together, with part of them going one way and part another,” Hoham says.

With all these beings, fungi find plenty of material to decompose. They weave their strands through the snowfields. A white expanse of snow is far from barren, Hoham says. “Basically, you’ve got everything in it you would find in a freshwater ecosystem,” he explains.

But unlike idyllic rivers and streams, the snow ecosystem doesn’t offer people a fresh-caught meal. Duval says that after he explains that he hasn’t lost something in the snow, hikers often say, “I hear that watermelon snow can kill you.” Duval’s never even tasted it. While he doesn’t expect the algae to prove toxic, he fears the abundant bacteria. “I would advise people not to eat watermelon snow,” he says. “You don’t want to get diarrhea in an alpine environment.”

He does acknowledge the skimpiness of experimental evidence on this last topic. His extensive algae files include just one study, by physicians in Reno, Nev., who fed six people concentrated snow algae. Only one person developed diarrhea, the doctors reported in 1997 in Wilderness and Environmental Medicine.

While Thomas doesn’t recommend taking chances with bacteria either, he has tried a quick taste of colored snow. “It’s nondescript, a little tangy, like watermelon,” he says.

Withstanding cold

What hasn’t killed snow algae has made them stronger, or at least, more interesting to biochemists and physiologists.

A series of papers in the late 1970s and 1980s by British scientists reported chemical tricks for withstanding extreme cold. They described what Hoham calls “most peculiar” fatty acids in the creatures’ cell membranes. The compounds’ carbon chains have an unusually high ratio of double bonds to single bonds. These ratios make the fatty acids more fluid at low temperatures, just as margarines with polyunsaturated oils stay squishier in the fridge than lard with its heavy load of saturated fat. Membrane flexibility should help algal cells continue to function at low temperatures.

To withstand the intense sun burning down on snowfields, the algae display other chemical oddities. A red snow alga, for example, develops 12 carotenoid pigments. Harvey Marchant of the Australian Antarctic Division in Tasmania published electron micrographs of algae from the Snowy Mountains of Australia in 1982. The pictures and chemical analysis revealed carotenoids spread around the outer zone of the cell as if shielding the chlorophyll from sun overload.

The carotenoids protect against ultraviolet light, Thomas and Duval argued in 1995. Red algae in natural sunlight have 75 percent as much photosynthetic capacity as do those protected from the portion of the sun’s ultraviolet spectrum known as UV-B. Green snow algae, which lack these protective carotenoids, suffer much more from full sunlight. Those without artificial UV protection show only 15 percent of the photosynthetic power of protected cells. In nature, the green species shield themselves with a layer of snow.

Duval, Thomas, and Kalidas Shetty of the University of Massachusetts in Amherst have just published the first evidence for another potential algal strategy for protection against ultraviolet light. After 5 days of exposure to the radiation called UV-A, the classic watermelon snow alga of California pumped up the amount of its phenolic components by 5 to 12 percent.

“These are the compounds that are in red wine,” Duval explains. They’ve attracted interest as antioxidants, cellular police that capture potentially damaging singlet oxygen and free radicals. Likewise, UV-C juiced up the phenolic content, the research team reported in the Journal of Applied Phycology late last year.

Geneticist James Leebens-Mack, also at Colgate, has been examining snow algae. This month, he and Tomas Bonome are presenting their comparisons of genetic material from several species. The pattern of similarities, some strong and some weak, that they have described suggests that the snowy lifestyle evolved in algae at least twice, says Hoham.

He and three coeditors are putting finishing touches on a book with an unusually multidisciplinary approach to the topic. Cambridge University Press plans to publish Snow Ecology in August. With a sort of remembering-Woodstock glow, Hoham describes his first discipline-mixing experience at a snow scientists’ gathering in 1993. Sessions overran their scheduled times by at least 3 hours each night as snow chemists encountered microbiologists who’d never known what paleoecologists thought of snow physics.

“We didn’t want to stop because we’d never heard each others’ stories,” Hoham reminisces. Duval laments, “The whole topic of snow ecology has been overlooked.” Modern genetics could change that, he notes. He expects its tools to energize the field, untangling the chemistry and giving rise to new ways to use the discoveries.

Maybe then, at last, he’ll get through whole meetings where no one smirks about yellow snow.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.