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What is Sargassum?

Mary McMahon
Updated May 17, 2024
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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.

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.

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.

Frequently Asked Questions

What exactly is Sargassum?

Sargassum is a genus of brown macroalgae, which are large, complex seaweeds. This floating algae is notable for its dense, bushy fronds filled with gas bladders that allow it to float on the surface of the Atlantic Ocean. It forms vast mats that create unique ecosystems, often referred to as the Sargasso Sea.

Why is Sargassum important to marine ecosystems?

Sargassum serves as a mobile habitat for an array of marine life, including fish, sea turtles, and birds. It provides food, shelter, and breeding grounds for many species. According to the National Oceanic and Atmospheric Administration, the Sargasso Sea supports a rich biodiversity, including some species that are found nowhere else on Earth.

Can Sargassum be harmful?

While Sargassum is crucial for oceanic health, it can become problematic when it washes ashore in large quantities. Decomposing Sargassum on beaches releases hydrogen sulfide gas, which can be unpleasant and potentially harmful to coastal communities. Additionally, excessive amounts can smother coral reefs and seagrass beds, impacting local marine ecosystems.

How does Sargassum reproduce?

Sargassum reproduces through a process called vegetative fragmentation, where pieces break off and grow into new individuals. This asexual reproduction method allows rapid colonization and expansion across the ocean's surface. The algae can also reproduce sexually, but this is less common in the floating varieties found in the Sargasso Sea.

What causes Sargassum blooms, and are they increasing?

Sargassum blooms are influenced by nutrient levels in the ocean, water temperatures, and ocean currents. Human activities, such as agriculture runoff and sewage, increase nutrient levels, contributing to larger blooms. Recent studies suggest that Sargassum blooms are becoming more frequent and extensive, potentially linked to climate change and increased nutrient input.

How is Sargassum used by humans?

Humans have found various uses for Sargassum, including as a fertilizer and soil conditioner in agriculture due to its high nutrient content. It has also been used in traditional medicine and is being researched for its potential in biofuel production. However, managing excessive Sargassum on beaches remains a challenge for many coastal regions.

WiseGEEK is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Mary McMahon
By 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.

Discussion Comments

By jcraig — On Sep 04, 2011

@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?

By TreeMan — On Sep 04, 2011

@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.

By cardsfan27 — On Sep 03, 2011

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?

Mary McMahon

Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

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