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Spring on Gold Ridge

Posted: July 13, 2012 - 7:34am
Sometimes called "watermelon snow", a reddish alga spreads across the snow surface. The inset photo shows a close-up of the spherical, resistant phase.  Photo by Bob Armstrong
Photo by Bob Armstrong
Sometimes called "watermelon snow", a reddish alga spreads across the snow surface. The inset photo shows a close-up of the spherical, resistant phase.

In June, we witnessed an explosion of tiny flies that swarmed in dense clouds. These mating swarms of March flies were so common that the Empire carried a story about them (http://juneauempire.com/outdoors/2012-06-22/love-air). The flies are short-lived, and their bodies accumulated on the surface of muskeg ponds and along the shores of Mendenhall Lake, where birds gobbled them up. Some of the March flies arrived, by choice or by wind, on the slowly dwindling snowbanks on Gold Ridge, above the tram. The surface of the snow was dotted with their tiny bodies and even with a few still living. Some were lively enough, however, to make their way to early flowers blooming in the snow-free areas.

Many of the remaining snowbanks had reddish streaks and patches. Going by the informal name of watermelon snow, both for the color and a faint aroma, it is actually an alga that lives on snow. It is common worldwide in alpine areas and polar regions.

Technically, the snow alga is a single-celled green alga, with chlorophyll that captures sunlight to fuel the process of photosynthesis, by which green plants build carbohydrates, releasing water and oxygen. However green it may be underneath, it ultimately turns red, from molecules that protect the green, photosynthetic pigment from intense UV radiation. In winter, the alga is dormant in the soil and contains antifreeze to protect it from freezing. But, come spring, the dormant cells release several smaller, green cells that have two whip-like hairs called flagella. Using the flagella, the little green cells recolonize the spring snow by swimming upward through the snow to the surface layers. At some point, they acquire the red color. At the surface, they may form thick-walled resting cells, capable of enduring desiccation and summer temperatures, while waiting for the next snow season. Or they may fuse in pairs to form zygotes — the product of sexual union — and then become dormant, later dividing into the swimming cells to recolonize a new layer of snow.

Snow algae build their carbohydrates for energy, but needed minerals are derived from wind-blown dust and bits of organic debris; they get needed water from slight melting of the snow. They are eaten by a variety of micro-herbivores, including protozoans, rotifers, nematode worms, ice worms and springtails. These grazers are, in turn, eaten by mites, spiders, and insects, which often end up in the stomachs of alpine songbirds. The pipits, rosy finches and occasional robins and sparrows also gorge on insects that are blown up the sides of mountains, eventually becoming immobilized by the cool temperatures at higher elevation. A condign fate for all those March flies too!

Gold Ridge had other things to offer that day, as well. There were long-abandoned ptarmigan beds, where the birds had spent the night in a snow-burrow that was now exposed by snow-melt. We found a strange pellet about two inches long, just lying on the snow. Close inspection revealed lots of little pebbles stuck together and — aha! — pieces of shell, including a recognizable fragment of barnacle shell. So the perpetrator was probably a raven that had been foraging along the shoreline and had unloaded this clump of indigestible bits.

A few flowers were blooming, such as the tiny primrose called pixie eyes, a mat-forming plant known as alpine azalea, some adventurous lupines and valerian, Cooley’s buttercup, hairy cinquefoil and caltha-leaved avens.

Our peaceful sojourn in the alpine was terminated by the temptations of dinner-time and rising winds that presaged a change from our brief spell of post-solstice sunshine.

• Mary F. Willson is a retired professor of ecology.

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