Distribution And Abundance

Algae are almost ubiquitous throughout the world and can be categorized ecologically by their habitats. Planktonic algae are microscopic and grow suspended in the water, whereas neustonic algae grow on the water surface and can be micro- or macroscopic. Cryophilic algae occur in snow and ice (see red snow); thermophilic algae live in hot springs; edaphic algae live on or in soil; epizoic algae grow on animals, such as turtles and sloths; epiphytic algae grow on fungi, land plants, or other algae; corticolous algae grow on the bark of trees; epilithic algae live on rocks; endolithic algae live in porous rocks or coral; and chasmolithic algae grow in rock fissures. Some algae live inside other organisms, and in a general sense these are called endosymbionts. Specifically, endozoic endosymbionts live in protozoa or animals such as shelled gastropods, whereas endophytic endosymbionts live in fungi, plants, or other algae.

Algal abundance and diversity vary from one environment to the next, just as land plant abundance and diversity vary from tropical forests to deserts. Terrestrial vegetation (plants and algae) is influenced most by precipitation and temperature, whereas aquatic vegetation (primarily algae) is influenced most by light and nutrients. When nutrients are abundant, as in some polluted waters, algal cell numbers can become great enough to produce obvious patches of algae called “blooms” or “red tides,” which can deplete the oxygen content in the water and poison aquatic animals and waterfowl.