Red Algae — Phylum Rhodophyta
Rhodophyta, or red algae, is a small phylum of predominantly marine plants. There are about 5000 species of red algae and, although they prefer warm waters, more than 20 species occur in the North. Red algae in the Arctic are mostly restricted to the coastal fringes, where the waters are warmer. They are a common sight in some intertidal areas, covering the rocks in a carpet of red. Their red colour is the result of a pigment, phycobilin, which is used in photosynthesis. This pigment allows red algae to capture blue light better than other types of algae, so some species are able to grow as deep as 200 m!
Some red algae are unicellular, but most species, such as the common arctic genus, Chondrus, form multicellular filaments, or long strands, with leaf-like feathery structures. Other red algae look very different. For example, rocks on the ocean floor are often coloured with pink or pinkish-grey splashes of encrusting algae. Also known as coralline algae, this group has walls composed of calcium carbonate. These coralline algae are important members of the arctic benthic marine community. They produce chemicals which promote the settlement of invertebrate larvae. In turn, these herbivorous invertebrates remove plants and algae that would otherwise grow on the coralline algae and block their light source. Coralline algae are also themselves an important food source for invertebrate algal scrapers.
The surface layer of most red algae is made of "slime", a gelatinous material that can be extracted from their cell wall with hot water. This material consists of complex sugars – agar and carrageenan – that are used in the production of everything from ice cream to makeup.