What Is Brown Algae?

Phylum Phaeophyta: Seaweed, Kelp, and Other Species

Seaweed- Ascophyllum nodosum - Brown Algae - Rockweed, Norwegian kelp, Knotted kelp, Knotted wrack, Egg wrack
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Brown algae are the largest, most complex type of marine algae and get their name from their brown, olive, or yellowish-brown color, which they get from the pigment called fucoxanthin. Fucoxanthin is not found in other algae or plants like red or green algae, and as a result, 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.

Like other algae, the distribution of brown algae is broad, from tropical to polar zones, but 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 of Brown Algae

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 Phaeophyceae.

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.

Kelp, Fucales, Dictyolaes, Ectocarpus, Durvillaea Antarctica, and Chordariales are all examples of species of brown algae, but each belongs to a different classification determined by their individual attributes and features.

Natural and Human Uses of Brown Algae

Kelp and other brown algae provide a number of health benefits when consumed by both humans and animals alike; brown algae are eaten by herbivorous organisms such as fish, gastropods and sea urchins, and Benthic (bottom-dwelling) organisms also utilize brown algae such as kelp when pieces of it sink to the sea floor to decompose.

Humans also find a variety of commercial uses for these marine organisms. Brown algae are used to produced alginates, which are used as food additives and in industrial manufacturing—common uses include food thickeners and fillers as well as stabilizers for the ionization process of batteries.

According to some medical research, several chemicals found in brown algae can work as antioxidants that are thought to prevent damage to the human body. Brown algae can also be used as a cancer suppressant as well as an anti-inflammatory and immunity booster. 

These algae provide not only food and commercial utility, but they provide a valuable habitat for certain species of marine life as well as significantly offsetting carbon dioxide emissions through photosynthesis processes of certain populous species of kelp.