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Anita’s Blog – From The Sargasso Sea

Updated: Jul 9, 2023


Polypropylene line floats and easily gets tangled in Sargassum, like the yellow depicted here, entwined in the beached vegetative sea debris. (Photo by Anita Westervelt)

Golden clumps of vegetation are washed ashore, left by the receding tide to dry on our beaches, to be picked at by shore birds for a tasty morsel of food or scooted around by beachcombers, hunting a rare shell, sea bean, piece of coral, sea critter or perhaps an ancient artifact that might have become entwined in the slick tangles.


Other than that, there’s not much use for beached seaweed – or is there? A lot of the vegetation that gets pushed up on our local beaches by the tide is sargassum, broad-leaved Gulfweed, Sargassum fluitans.


Interestingly, sargassum is not a sea grass, it’s a genus of large brown macroalgae in the order Fucales. It’s an important element in shoreline stability, helping to prevent sand erosion from wind and surf, even helping replenish areas affected by storms and hurricanes and an important element of dune construction. As it decomposes, it breaks down into vital nutrients that promote the growth of dune plants.


Broad-leaved Gulfweed, Sargassum fluitans. (Photo by Anita Westervelt)

It looks innocent enough, a small tuft of seaweed sitting by itself on an expanse of sand, but sargassum was in the news earlier this year with dire warnings of impending disaster when CNN and other media reported “a giant blob of seaweed twice the width of the continental United States” was headed to Florida and Mexico.


Media were rife with predictions and speculations about tons of seaweed rotting on the world’s beaches causing dangerous conditions. While it was worrisome, I thought it best to start my beach combing early – before the beaches were closed to the public – so, I’ve made a few trips to local beaches during the last couple of months.


In addition, I periodically checked in with our beach guru, Tony Reisinger, one of our Texas Master Naturalist chapter sponsors, the Cameron County Extension Agent for Coastal & Marine Resources with Texas Sea Grant at Texas A&M University and the Texas AgriLife Extension Service.


Tony’s most recent report was encouraging. “The amount of sargassum washing ashore up on our beaches lately has declined significantly.”


So, the threat has passed. Our beaches are safe from an extraordinary disaster – for now , so my photos, research and information from conversations with Tony Reisinger are for information instead of precaution and safety.


In and of itself, sargassum is pretty extraordinary. There are more than 300 species of brown algae in the genus Sargassum, but two species in the Atlantic are unique: S. fluitans and S. natans. They are holopelagic, meaning the alga not only floats around the ocean, it reproduces vegetatively on the high seas. Other seaweeds reproduce and begin life on the floor of the ocean.


But it’s really more fascinating than just a floating plant. As a matter of fact, sargassum has its own sea, named, interestingly enough, the Sargasso Sea, which has been called a golden floating rainforest because of the free-floating sargassum.


The Sargasso Sea itself is one of a kind. It is the only ocean in the world that is not bound by a landmass. While all other seas in the world are defined at least in part by land boundaries, the Sargasso Sea is defined by four ocean currents. The Sargasso Sea covers two million square miles of water and lies within the Northern Atlantic Subtropical Gyre.


The Gulf Stream establishes the sea’s western boundary, the north Atlantic Current is the north boundary, the east is bordered by the Canary Current and south by the North Atlantic Equatorial Current.


There is much mystique to this water-bound, becalmed sea; two of many informative accounts are here for you to peruse on your own:


But for now, the fascinating attributes of sargassum: Sargassum is composed of gas-filled structures that look like berries called pneumatocysts that keep it buoyant. It floats on the ocean’s surface, moving with the currents and wind.


Pneumatocysts (gas-filled berries) keep Sargassum buoyant. (Photo by Anita Westervelt)

Sargassum is more than just a floating island of vegetation, it’s home to an amazing variety of marine species, according to the National Oceanic and Atmospheric Administration (NOAA), whose site calls it a highly productive floating ecosystem. Loggerhead sea turtles use sargassum mats as nurseries where hatchlings have food and shelter. In the open sea, healthy patches of sargassum can soak up carbon dioxide and provide essential habitats for shrimp, crab, fish and other marine species that have adapted specifically to this floating alga. It provides refuge for migratory species and essential habitat for some 120 species of fish and more than 120 species of invertebrates.


The Sargasso Sea is a spawning site for threatened and endangered eels, as well as white marlin, porbeagle shark and dolphinfish. Humpback whales annually migrate through the Sargasso Sea. Important commercial fish, such as tuna, mahi mahi, jacks and amberjacks and birds also migrate through the Sargasso Sea and depend on it for food and prey.


Like most things, too much of a good thing can turn the tide – pun intended – and excessive amounts of sargassum can cause concern. Huge mats of it die and sink to the ocean bottom; large quantities can smother corals and seagrasses and alter the water’s pH balance. Great masses of it deposited on the world’s tourist beaches can strain economies and destroy tourist trade.


Sargassum and other sea vegetation drying on the beach. (Photo by Anita Westervelt)

Apparently, sargassum was once confined to the Sargasso Sea, however, recent studies suggest that changing wind patterns have caused it to multiply across the tropical Atlantic. Thousands of tons of sargassum end up on beaches; it releases gas that smells like rotten eggs, swarms with flies and other insects and causes respiratory problems. Mounds of algae on beaches and dense mats in the ocean harm marine ecosystems.


The study and research into sargassum accumulations is new. News feeds, quoting NOAA authorities, report that what is known today will most likely shift over time as scientific studies progress. Experts with NOAA contend that the proliferation of seaweed can shift year to year, depending on ecological factors affected by changes in nutrients, rainfall, wind conditions and sea currents. Phosphorus and nitrogen, elements that can be dumped into the ocean from world rivers, due to human activities like agriculture, can serve as food for the algae.


For now, appreciate sargassum as part of the beachcombing experience, but poke and explore it with a stick – even beached, it can be alive with sea creatures, debris, sharp plastics and bacteria.



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Many websites were helpful in compiling this information, including: www.npr.org, NOAA.gov, Wikipedia, www.sargassoseacommission.org, cnn.com, www.miamidade.gov,

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