sargassum

The Great Atlantic Sargassum Belt

October 17, 2025 By EarthWise Leave a Comment

Sargassum is a free-floating brown seaweed that can drift together in vast mats, sometimes stretching for miles across the ocean’s surface. For centuries, these blooms have been a natural part of the Atlantic, creating food and shelter for many marine creatures. Sargassum was once thought to be confined mainly to the Sargasso Sea in the western Atlantic, but scientists now know it grows rapidly and spreads widely, driven both by natural forces and by nutrients from human activities.

Scientists at Florida Atlantic University have reviewed 40 years of data on sargassum seaweed. Their study, which was recently published in the journal Harmful Algae, points to the rise of what is now called the Great Atlantic Sargassum Belt – a massive seaweed bloom stretching from West Africa to the Gulf of Mexico. First spotted in 2011, it has since appeared every year except in 2013. This past May, the bloom reached a record 37.5 million tons, a number that does not include the 7.3 million tons in the Sargasso Sea.

Sargassum thrives in nutrient-rich waters. Under ideal conditions, controlled studies found sargassum can double its biomass in just eleven days! According to the scientists, nutrient pollution from agriculture and wastewater has fueled these record blooms.

In the ocean, sargassum provides habitat for fish, turtles, and other marine life. But along the coast, it piles up in smelly heaps, clogs waterways, disrupts tourism, and can even threaten power plants.

Understanding why sargassum is spreading so rapidly is key to tackling a problem that now spans an entire ocean.

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A monster seaweed bloom is taking over the Atlantic

Photo, posted December 24, 2014, courtesy of Roban Kramer via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Seaweed On The Way | Earth Wise

April 28, 2023 By EarthWise Leave a Comment

A type of seaweed called sargassum has long formed large blooms in the Atlantic Ocean. It gets its name from the Sargasso Sea in the western Atlantic. Since 2011, scientists have been tracking massive accumulations of the stuff each year that starts out off the coast of Africa and works its way across the Atlantic to end up in the Gulf of Mexico.

The amount of sargassum present each year can shift depending on factors like changes in nutrients, rainfall, and wind conditions. But since the 1980s, nitrogen content in the Atlantic has gone up by 45%. This is likely due to human activities such as agriculture and fossil fuel production dumping materials into the rivers that feed into the ocean.

According to recent observations, the mass of seaweed now heading for Florida and other coastlines throughout the Gulf of Mexico may be the largest on record. The giant blob of sargassum spans more than 5,000 miles in extent. It is moving west and will pass through the Caribbean and up into the Gulf during the summer. The seaweed is expected to become prevalent on beaches in Florida around July.

The seaweed provides food and protection for fishes, mammals, marine birds, crabs, sea turtles, and more. But unfortunately, when sargassum hits the beaches, it piles up in mounds that can be difficult to walk through and eventually emits a gas that smells like rotten eggs.

Tourist destinations in the Caribbean region have their work cut out for them to remove seaweed that can pile up several feet deep. For example, in Barbados, locals were using 1,600 dump trucks a day to clean their beaches. Caribbean and Florida resorts spend millions of dollars each year to remove sargassum seaweed.

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A 5,000-mile-wide blob of seaweed is headed for Florida, threatening tourism across the Caribbean

Photo, posted February 24, 2020, courtesy of Bernard Dupont via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Making Use Of Invasive Seaweed | Earth Wise

June 26, 2020 By EarthWise Leave a Comment

In recent years, millions of tons of brown Sargassum seaweed have formed gigantic blooms stretching all the way across the Atlantic Ocean from West Africa to the Gulf of Mexico. The seaweed has become a problem for shorelines in the Caribbean, the Gulf of Mexico, and the east coast of Florida. The massive increase in seaweed populations is related to changes in ocean chemistry resulting from nutrients from fertilizer use entering the water as well as from changes to the climate affecting ocean currents and temperatures. The seaweed is harming the tourism industry as well as fisheries and ocean ecosystems.

Cleaning up the seaweed that washes ashore is labor-intensive and therefore expensive. A research team led by two British universities has developed a cheap and simple way to pre-process seaweed to facilitate making it into bulk chemicals and biofuels. With the new process, cleaning up the seaweed can be both economically and environmentally viable.

Previous techniques for processing seaweed generally required removing it from the saltwater, washing it in fresh water, and drying it – all of which add significant costs. The new technique makes use of catalysts to release sugars from untreated seaweed that feed a yeast to produce a palm oil substitute. At the same time, the process creates heat and pressure, turning the residual materials into a bio-oil that can be processed further into fuels, and a high-quality, low-cost fertilizer.

Apart from getting economic value out of the seaweed that is collected, any plastic collected alongside the seaweed can be converted to useful materials as well.

It appears that the seaweed scourge is here to stay, so finding an economically viable way to deal with it is a welcome development.

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Solve invasive seaweed problem by turning it into biofuels and fertilisers

Photo, posted August 10, 2015, courtesy of Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.