Sargassum is commonly thought of as a mass of seaweed, but it is actually a brown algae that floats in the ocean by gas-filled spheres, called pneumatocysts, found within the composition of its leaves and many branches. Sargassum is more than just a complex raft of seaweed; it’s a floating ecosystem in the open sea. It got its name from where it was originally discovered, by Portuguese sailors, in the Sargasso Sea.

Sargassum floating at the water surface
Sargassum is a type of free-floating brown algae

The Sargasso Sea spans over 600 miles wide and is over 1,800 miles long in the Atlantic Ocean. This sea is unique in that it has no land borders but is rather formed by dynamic ocean currents, called an ocean gyre. This unique sea contains a species of Sargassum that is called holopelagic, meaning that the algae is free-floating and reproduces in the Sargassum mats rather than on the ocean floor like most other seaweed.

Sargassum Biomass

The Sargassum mats house a vast diversity of marine species, all while free-floating in and about the Atlantic Ocean, the Gulf of Mexico, and the Caribbean. Providing a crucial habitat, within these masses, you can find an abundance of species of invertebrates, fish, turtles, fungi, and epiphytes. Over 100 species of invertebrates utilize the algae rafts as a food source and habitat.

Sargasso sea map showing the movements of the Sargasso biomass
Sargassum is a floating biomass of seaweed, forming an entire ecosystem in the Sargasso sea

Over 100 species of fish live in the Sargassum; many make use of the mats in varying ways, from nurseries for egg laying to foraging to the refuge to living their entire lives within the floating ecosystem. Some examples are the sargassum fish, gray triggerfish, sargassum frogfish, mahi mahi, amberjacks, marlin, tuna, and even sharks. These larger predators are attracted to the various other species for feeding and foraging but also use the Sargassum as part of the reproductive cycle.

The Sargassum biomass is home to the Sargassum fish
The Sargassum biomass is home to various species, including the Sargassum fish (seen above) named after it

There are four species of sea turtles (loggerhead, hawksbill, green, and Kemp’s ridley) that make their juvenile nurseries in the Sargassum, including foraging and seeking shelter.

Many other oceanic creatures call these floating mats home, such as eels, worms, crabs, shrimp, and snails. Some of the types of shore and pelagic birds include gulls, terns, plovers, godwits, and willets. Depending on where these birds live and forage, they may seek out the floating mats, or they might take advantage of the masses of algae that wash ashore.

Some species of sea turtles make their juvenile nurseries in the Sargassum
Some species of sea turtles make their juvenile nurseries in the Sargassum


Sargassum reproduction happens in two ways, vegetatively and sexually. By vegetative means, the process takes place by fragmentation, where the algae break into pieces. Each individual piece then becomes its own new plant with division and growth, remaining identical to the parent plant.

Sargassum uses the process of sexual propagation via oogamous reproduction. Much like in humans, the female gamete (egg) is enlarged and immobile, while the male gametes (sperm) are small and motile. This fusion of female and male gametes gives the occasion for a new organism.

Sargassum reproduces and grows faster in warmer temperatures.

Sargassum algae are capable of sexual reproduction, where the fusion of male and female gametes produces a new organism
Sargassum algae are capable of sexual reproduction, where the fusion of male and female gametes produces a new organism

When is Sargassum Good vs Bad?


If Sargassum doesn’t become too heavy and lose its buoyancy at the end of its life and sink to the bottom to become a food source for those below, it will invariably beach itself. During its normal life span, besides providing crucial habitat and refuge for hundreds of species, Sargassum purifies the water in its system and absorbs carbon dioxide. Once the mass has beached itself, depending upon the size of the beaching, the mass can help to prevent dune and sand erosion, encouraging plants in those habitats. In the long term, it can help to restore eroded beaches. In the short term, it helps by reducing wind and wave erosion.

Due to the increase in ocean temps, Sargassum has become more prevalent, which has allowed for the research, attempts, and ideas at using beached Sargassum for other more useful things, such as natural fertilizer, biofuels and ethanol, paper products, skincare products, livestock feed, and it has even been used in Chinese medicine all the way back to the 8th century.

Beached Sargassum with birds foraging
Beached Sargassum can prevent dune and sand erosion, helping to restore eroded beaches


Despite having some beneficial factors, it has become more common to have large, unmanageable tons show up on shorelines. If the rafts are big enough, they can block sunlight to seagrasses and coral reefs before washing ashore. After a few days, these mats of algae and biomass start to decompose, giving off a sulfuric acid and rotten egg smell. This can have detrimental effects on the resort and tourism industries. Hotel guests are deterred by the mounds of decaying algae, unpleasant smells, and even respiratory problems for those most sensitive. The depths and lengths of the beached mats can cause problems for nesting turtles being able to find stable sand to dig their nests. In addition, it can cause problems for hatchlings not being able to maneuver over and around the Sargassum.

Resorts and local authorities have worked to remove excess Sargassum by the least damaging means possible. Sometimes these wash-ups can be up to or more than three feet thick. Heavy machinery can compact the sand, damaging nesting areas for birds and turtles. If not removed, as it decays, the Sargassum releases nitrogen and phosphorous, polluting the groundwater. And in these large quantities, it can actually cause the beach to erode faster than usual. Most removal is done carefully by wheelbarrows to maintain the important habitat and coastal ecosystems.

Beached Sargassum for hundreds of feet down the beach
Large quantities of beached Sargassum release nitrogen and phosphorous, polluting the groundwater and causing disruption


Will Sargassum sting you?

The algae itself will not sting you. However, there could be larval stage species, like jellyfish, that could cause a stinging reaction.

What does Sargassum smell like?

Out in its normal habitat, Sargassum smells like any other seaweed. However, this changes when the raft of algae washes ashore and begins to decay. It is then that it starts to give off hydrogen sulfide gas, smelling like rotten eggs.

Can Sargassum be eaten?

Certain species of Sargassum can be eaten and have been used in Chines medicines for centuries. It can be boiled, fried, steamed, or dried. It can also be used in livestock feeds, as it’s rich in carbohydrates and amino acids.

Can Sargassum be burned?

Sargassum burns clean, producing less dust and smoke, making for a longer burn. In some Jamaican communities affected by large batches of Sargassum beaching itself, families are using the algae as a biofuel to cook the traditional jerk style or seasoning and cooking meat.

When did Sargassum start?

Sargassum has been estimated to have been around for 30 million years. However, in 2011 with oceanic changes, there began a dramatic increase in the floating algae, with unmatched amounts lining the shores of Brazil, the Caribbean, the Gulf of Mexico, and Florida.

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