Red Algae (Rhodophyta)

Germany, Schleswig-Holstein, Baltic Sea, Red seaweed
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Of the more than 6,000 species of red algae, most are, not surprisingly, red, reddish, or purplish in color. Red algae are  protists in the phylum Rhodophyta, and range from simple one-celled organisms to complex, multi-celled, plant-like organisms. All algae get their energy from photosynthesis, but one thing that distinguishes red algae from others is that their cells lack flagella.

How Red Algae Get Its Color

When you think of algae, you might think of something that is green or brown. So what gives red algae a red hue? Red algae contain a variety of pigments, including chlorophyll, red phycoerythrin, blue phycocyanin, carotenes, lutein, and zeaxanthin. The most important pigment is phycoerythrin, which provides these algae's red pigmentation by reflecting red light and absorbing blue light. Not all of these algae are a reddish color, though, as those with less phycoerythrin may appear more green or blue than red due to the abundance of other pigments.

Habitat and Distribution

Red algae are found around the world, from polar to tropical waters, and are commonly found in tide pools and in coral reefs. They can also survive deeper in the ocean than some other algae, because the phycoerythrin's absorption of blue light waves, which penetrate deeper than other light waves, allow red algae to carry out photosynthesis at greater depths.


  • Kingdom: Protista
  • Phylum: Rhodophyta

Red Algae Species

Some common examples of red algae include Irish moss, dulse, laver (nori), and coralline algae.

Coralline algae help build tropical coral reefs. These algae secrete calcium carbonate to build a hard shell around their cell walls. There are both upright forms of coralline algae, which look very similar to coral, and encrusting forms, which grow as a mat over hard structures such as rocks and the shells of organisms like clams and snails. Coralline algae are often found deep in the ocean, at the maximum depth light will penetrate water.

Natural and Human Uses of Red Algae

Red algae are an important part of the ecosystem because they are eaten by fish, crustaceans, worms, and gastropods, but these algae are also eaten by humans.

Nori, for example, is used in sushi and for snacks; it becomes dark, almost black, when it is dried and has a green hue when cooked. Irish moss, or carrageenan, is an additive used in foods including pudding and for the production of some beverages such as nut milks and beer. Red algae are also used to produce agars, which are gelatinous substances used as a food additive and in science labs as a culture medium. Red algae are rich in calcium and sometimes used in vitamin supplements.