Red algae is one of the largest phyla of algae, with more than 5,000 distinct species. They are almost exclusively multicellular marine algae, and many of the common seaweed varieties people eat belong to this group. They can be contrasted primarily with brown and green algae, and should not be mistaken with the phylum Dinoflagellata, which are algae that cause the so-called red tide.
People may also talk about red algae when what they are referring to is red slime algae. This is actually a type of cyanobacteria, and not a true algae at all. Often, red slime algae is looked at as being a link between bacteria and the true algae, and it is more than three billion years old. Although red slime algae is not particularly attractive physically, it is one of the most important things on the planet. It is responsible for an enormous amount of oxygen creation, and it is thought that if red slime algae didn’t exist, the skies of earth would not be blue.
True red algae are red because they all contain a specific pigment, phycoerythrin. This pigment absorbs blue light and reflects red, giving the algae its color. This is an evolutionary device to allow it to grow at slightly greater depths than other types of algae, as blue light penetrates water better than longer-wavelength light. While a number of species are a deep red, so it is obvious what group they belong to, others have relatively small amounts of phycoerythrin, and high amounts of chlorophyll in them, which can make them look more blue or green.
There are certain types of algae that actually play a pivotal role in creating reefs. There are some atolls in the Pacific in which the reefs actually owe a great deal more of their development to red algae than to coral. These types, known as coralline algae, built up a layer of carbonate, much like coral, around themselves. This helps reefs to form around them, and in some cases these algae reefs can be enormous.
Many types are also used as food throughout the world, especially in Asia. They are consistently very high in nutrients and, like other algae, are extremely easy to grow. This makes them an ideal food source, as for a minimal level of upkeep huge amounts of food can be produced. Nori is one very famous species of red algae, and it is cultivated throughout the world, especially in Japan. Nori is an important seaweed in cooking, particularly in creating sushi rolls.
Irish moss, or Chondrus crispus, is another major food red algae, grown throughout the Atlantic ocean. It is one of the major sources of carrageenan, which is used in many foods and drinks as both a stabilizer and a thickener. People can find carrageenan in many things like ice cream and non-dairy frozen desserts. In the Caribbean, the red algae is used directly to make a drink with sweet and condensed milk and flavoring over ice.