What is Sargassum?

Mary McMahon
Mary McMahon

Sargassum is a large seaweed genus which prefers the open waters of the tropics, although some species can be found clinging to rocks closer to shore. Members of this genus are referred to as “Sargassum” by both biologists and laypeople, an example of a situation where the scientific name for something is also its common name. Many people are familiar with the concept of Sargassum, thanks to the fame of the Sargasso Sea, a remarkable feature in the Atlantic Ocean which has been a topic of discussion and commentary for hundreds of years.

Sargassum is a large seaweed genus which prefers the open waters of the tropics.
Sargassum is a large seaweed genus which prefers the open waters of the tropics.

Like other seaweeds, Sargassum is a form of algae which has developed a multicellular structure. Sargassum is characterized by long highly branched fronds which can make it appear almost leafy, and many have bladders filled with air which help them to float. In the open water, these bladders keep the Sargassum free floating near the surface of the water so that it can photosynthesize energy. In areas with Sargassum is anchored to the bottom, these bladders help the seaweed stretch towards the light, creating forests of seaweed which gently undulate with the waves.

The Sargasso Sea is named for its copious amounts of Sargassum seaweed.
The Sargasso Sea is named for its copious amounts of Sargassum seaweed.

There are a number of uses for Sargassum. In some regions, for example, it is collected as fertilizer. It is also a food source, especially in Japan, where it may be added to soups and fermented with the other ingredients in soy sauce to create a specific flavor. Many animals call Sargassum home, as the seaweed provides shelter with its abundant fronds, along with a hiding place from predators and a source of food.

The Sargasso Sea is a large section of the Atlantic Ocean which is often covered in mats of this interesting seaweed. Travelers were initially very confused by the region, which looked bizarre with mats of floating seaweed on it which were sometimes thick enough to choke a ship's progress, and they assumed that other than the seaweed, the Sargasso Sea was barren. This is not, in fact, the case. The seaweed hosts a number of animals, and the Sargasso Sea also plays an important role in the development of both European and North American eels, who travel to the area to lay eggs.

Closer to shore, Sargassum often occurs in combination with other seaweeds, creating lush underground forests which are filled with all sorts of fascinating animals. Sargassum is generally dark brown to green in color, with many branching fronds and a slightly sticky texture. You may also hear Sargassum called “gulfweed,” especially in the Southern United States.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments


@TreeMan - I grew up in the New England area, and you could find Sargassum there, too. At least that's what we were always told it was.

I never cared for it much, but I have known people who used it in salads if it wasn't too bitter. Apparently it is supposed to be a useful cure for goiters, too.

I am interested in the algal seas Sargassum can make in the ocean. What other things besides eels use the seaweed forests? Are there any popular fish that are there?


@cardsfan27 - Sargassum belongs in the brown algae group. If you have ever heard of kelp, it belongs here, too.

When I visited Florida, Sargassum would wash up on the shore, and you could use it in dishes. A lot of people considered it a nuisance, since it would wash up on the beach and start to rot after a couple of days. The smell wasn't pleasant.

You are right about the saltiness. Besides that, it was kind of bitter. I guess you could even compare it to biting into the white, bitter part at the bottom of a lettuce leaf. Every time I have seen Sargassum used, it has been in an Asian dish, but I'm sure there are other recipes it would work for.


Interesting, I always thought seaweed was a real plant, but I guess not. I know that there are a lot of different kinds of algae. Where does this one belong?

Has anyone ever eaten sargassum? What does it taste like? From the pictures of seaweed I have seen, I would guess it tastes like a salty leaf of lettuce. Is this something you can usually buy in a grocery store, or do you usually have to go to special Asian markets?

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