Brown Algae — Phylum Phaeophyta
This phylum contains about 265 genera and 1500–2000 species. Most brown algae are multicellular organisms found in marine environments where they can be found attached to rocks. Flourishing in both arctic and temperate regions, they exhibit their greatest diversity in cold waters perhaps because competition for nutrients and light is reduced. Around the coastlines of the Arctic Ocean, multicellular brown algae grow in abundance below the ice scour zone forming large beds of vegetation. Strands of kelp, which grow up to several metres in length, are a prime habitat for many marine invertebrates in the Arctic!
All brown algae, including species of Fucus and Laminaria, are multicellular. Their structure, however, varies from microscopic, branched strands to long, leafy, plant-like forms. Brown algae owe their colour to a pigment, called fucoxanthin, which is contained in their ribbon-shaped chloroplasts.
In temperate regions, brown algae have commercial importance as a food or as a dietary supplement. Algin, a gel-like substance obtained from kelp, is used as a thickening agent in dairy products (e.g., ice cream) and in glues.