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Brown Algae (Phaeophyta)

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Knotted wrack (Ascophyllum nodosum), a species of brown algae / Blue Ocean Society

Knotted wrack (Ascophyllum nodosum), a species of brown algae.

© Blue Ocean Society

Description:

Brown algae is the largest, most complex type of algae. This type of marine algae is brown, olive or yellowish-brown in color. Brown algae contains contains chlorophyll a and c and a pigment called fucoxanthin, which gives it its color.

Fucoxanthin is not found in other algae or plants. Unlike red and green algae, brown algae are in the Kingdom Chromista.

Brown algae are often rooted to a stationary structure such as a rock, shell or dock by a structure called a holdfast, although species in the genus Sargassum are free-floating. Many species of brown algae have air bladders which help the blades of the algae float toward the ocean surface, allowing for maximum sunlight absorption.

Habitat:

Like other algae, the distribution of brown algae is broad, from tropical to polar zones. Brown algae can be found in intertidal zones, near coral reefs and in deeper waters, with a NOAA study noting them at 165 feet in the Gulf of Mexico.

Classification:

The taxonomy of brown algae can be confusing, as brown algae can be classified into the Phylum Phaeophyta or Heterokontophyta depending on what you read. Much information on the subject refers to brown algae as phaeophytes, but according to AlgaeBase, the brown algae are in the Phylum Heterokontophyta and Class Phaeophycea.

Brown Algae Species:

There are about 1,800 species of brown algae. The largest, and one of the most well-known, is kelp. Other examples of brown algae include seaweeds in the genus Fucus commonly known as "rockweed," or "wracks," and the genus Sargassum, which form floating mats and are the most prominent species in the area known as the Sargasso Sea, which is in the middle of the North Atlantic Ocean.

Natural and Human Uses:

  • Brown algae are eaten by herbivorous organisms such as fish, gastropods and sea urchins.
  • Benthic (bottom-dwelling) organisms also utilize brown algae such as kelp when pieces of it sink to the sea floor to decompose.
  • Brown algae are used to produced alginates, which are used as food additives and in industry. Common uses include food thickeners, stabilizers and fillers.

Sources:

  1. About.com
  2. Education
  3. Marine Life
  4. Marine Life Profiles
  5. Plants, Protists, Chromists
  6. Brown Algae - Profile of Brown Algae Including Seaweed

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