Algae are everywhere. The most famous algae, of course, are the seaweeds and kelps. But you don’t need an ocean to have algae. There are many different kinds, some of which exist as single-celled organisms. Some of these microscopic plants live in fresh water. Some live on or in the soil [see Lichens]. You’ve probably seen them in your pets’ water dishes, even inside the house. That’s because their single-celled reproductive spores are floating around in the air all the time.

In Carlsbad Caverns National Park, most kinds of algae are single-celled. As in many semi-arid and arid desert areas, the algal spore can survive being dried out for long periods of time. Then when water is available they grow into masses that are often visible. When the park gets a good rain, the water percolates down through the various limestone layers until it gets to a less-permeable layer. Then the water travels sideways and eventually runs down the sides of cliffs. You can see this on the Walnut Canyon entrance road. And along with the water running down are populations of algae that appear to stain the rocks black.

Some of these algae live in the caves, too. Under normal light conditions, they will grow on walls or in pools as far into a cave as the sunlight penetrates (the twilight zone). In caves with artificial light sources of suitable wavelengths, such as Carlsbad Cavern, algae will grow in the dark zones near the lights. These algae are considered pest plants, and are kept under control periodically by park staff.

Among the algae that live on the soil is a blue-green alga in the genus Nostoc. This plant, from a very ancient group that was among the first plants on earth, survives the dry periods as spores. After a rain, the algal cells hydrate, begin their biological functions, and begin to photosynthesize. They also make a gelatinous sheath that connects many cells together to form visible ribbons or balls of living algae. After the area dries out again, the Nostoc ribbons and balls dry up and look like black potato chip pieces.