All sorts of things are blown onto the glaciers by wind: small plants, seeds, pollen, tiny insects, sometimes even birds! Most of these things freeze and eventually die, but some things manage to survive on the snow and some even spend their entire lives on the glaciers. Glaciers in Denali are covered with algal cells, minute plants so small that they can’t be seen with the naked eye. These algal cells, or algae, provide food for other organisms. Food chains on the glacier are very simple when compared to food chains in other habitats, but they provide an elegant example of how energy flows through a system. The sun shines on the snow and the algae. The algae use the sun to produce food for themselves and are eaten by insects, such as springtails. The springtails may die, decompose and return their nutrients to the glacier, or they may become food for larger animals, such as beetles.
One thing all organisms living on the glaciers share in common is size. They are all tiny! This is because resources, such as nutrients, are in short supply. Larger animals could not survive on such meager rations. Temperatures on the ice and snow are always at or below freezing. This means that there is usually very little free water. All organisms need water to survive. But if ice forms inside an animal’s body it can cause tissue damage or death. Glacier organisms have many adaptations that help them to cope with freezing temperatures. When the temperature drops, some types of invertebrates can isolate water in their bodies and cause it to form ice crystals in non-critical areas of their system. This prevents their tissues from being damaged. They may also produce a type of glycerol that acts as an antifreeze in the cells, keeping them from freezing completely.
But that’s not all! When the sun shines on the glacier, the ultraviolet rays bounce on the ice crystals and subject organisms to heavy doses of radiation. To help prevent damage from the radiation, glacial organisms have developed different types of "sunscreen". For example, one type of algae is colored red (causing "watermelon snow"). The red pigmentation is a type of kerotene, a substance that acts as a sunscreen for the algae.