What Creatures Live in Floating Sargassum?

Did you know that the rotting, smelly brown seaweed that scatters beaches all over the world is actually the remnants of a vital marine ecosystem?

Jul 9, 2023By Abigail van der Hoeven
what creatures live in floating sargassum

This seaweed is called floating sargassum, and it creates one of the most unique and important marine habitats. Before breaking up and being washed up onshore, these mats of floating brown seaweed make up the home of thousands of sea creatures. Some species of marine life live their whole lives in sargassum, while others just spend their juvenile years in the protection of the dense, nutrient-rich seaweed.

What is Sargassum?

floating yellow seaweed

What exactly is sargassum? Sargassum is a type of pelagic brown macroalgae. Pelagic seaweed is unique in that it floats on the open sea, not attached to the ground in any way. They are floating islands of seaweed, creating one of the only open-water habitats. Sargassum is kept afloat by little gas-filled “berries” or bladders called pneumatocysts. The sargassum will slowly sink as these bladders slowly deflate over weeks and months.

Sargassum is most commonly found in shallow waters and coral reefs and usually originates in the Atlantic Ocean. It used to be believed that all sargassum flats originated in the Sargasso Sea, a sea named after a large amount of seaweed found there. However, these various species of these floating mats are found all over the world.

Sargassum can stretch for miles along the ocean’s surface. Sargassum can reach depths of 9 feet. Most of the time, sargassum looks brown or dark green. Sargassum has the unique ability to propagate itself and regenerate itself from any part of the plant into an entire and fully functioning new float.

What Animals Live in Floating Sargassum?

floating red seaweed

Sargassum floats are one of the only marine habitats available for ecosystem development. They serve as a home and nursery to a huge number of fish, invertebrates, and sea creatures. A few species found in sargassum floats are rarely found anywhere else in the ocean. A few creatures endemic to sargassum floats are pipefish and sargassum frogfish. Both fish can camouflage with the sargassum for further protection.

A great number of sea creatures live their juvenile years in the floating seaweed. A few examples include loggerhead sea turtles, American and European eels, pufferfish, skeleton shrimp, crabs, sea spiders, snails, squid, dolphins, flatworms, and triple fins. But juvenile fish of all kinds can be found within sargassum floats, including flying fish, triggerfish, plane head filefish, amberjacks, and tuna.

Why Do Sea Creatures Live in Brown Seaweed?

shark in seaweed

Sargassum provides food and protection to all these species as they are in the most vulnerable years of their lives. Small fish, turtles, invertebrates, and animals are at great risk of becoming some larger animal’s meal when they are juveniles. Sargassum floats not only offer plenty of nutritious food but also protection from predators. Common predators of small fish and juvenile sea creatures include sea birds (like gulls, terns, and pelicans), mammals (like dolphins, porpoises, and seals), crustaceans (like crabs and lobsters), and other seas creatures (like sharks or squid).

Is Sargassum Good for Oceans and Beaches?

brown seaweed

Sargassum serves a lot of beneficial purposes beyond that just providing a vital environment for marine life development. Sargassum provides vital nutrients such as carbon, phosphorus, and carbon. Beached sargassum can reduce coastal erosion and can help bring greater health to nutrient-poor waters.

What Happens When Sargassum Washes Ashore?

seaweed and sand

Sargassum grows and decays seasonally. Sargassum that doesn’t sink may eventually wash up on beaches. This is usually not a real problem, though it can make for a less fun vacation. However, over the past years, annual blooms have been bigger, leading to some new issues. Due to fertilizer runoff from the Congo and Amazon rivers, sargassum blooms have been much larger. There is usually a bloom event every 2-3 years, but since 2011, these events have been much larger than usual. In 2018, the largest sargassum float measured 1600 square kilometers. This was more than three times the usual size!

The increase in sargassum creates a few issues. For one, large amounts of beached seaweed affect tourism. This is especially devastating for Caribbean countries that depend on tourism. Beached sargassum can also lead to oxygen depletion, which can lead to fish kills. Decomposing sargassum creates sulfide gas which can cause some health issues in some humans. Large floats can block sunlight from getting to corals and seagrasses. They can also entangle sea turtles and sea mammals.


seaweed waves

Sargassum is a vital, unique marine ecosystem that is important to the development of other ecosystems. Thousands of sea creatures make these floating mats their home while they grow and develop. While there is an increase in the number and size of sargassum floats every year, they still serve an important role in the health of marine and coastal ecosystems. While they may seem a bit unsightly strewn across the beach and may not smell too great, they serve as safe havens for a thriving ocean.

So, this year on your summer beach vacation, pluck off some of those seaweed “berries” you find strewn on the beach and stick them on your sandcastles with pride.

Abigail van der Hoeven
By Abigail van der Hoeven

Abigail grew up with many pets, from a sweet Golden Retriever to raising her school of tadpoles. She has three years of experience writing for the animal and pet niche. She has a lifetime of hands-on experience with all animals, including dogs, cats, birds, fish, rabbits, frogs, and more. She has three adorable guinea pigs: Guinevere, Tater Tot, and the most recent addition - baby Duncan! Abigail enjoys being outside, writing fiction, or kicking it back with a good tv comedy.