Photo: Charles Boyer / FMN
In what has become a rite of summer, it’s nearly Sargussum season on Florida beaches. In many recent years, thick brown mats of a macroalgae named Sargussum start washing up on the shorelines, sometimes reaching several inches in depth in early summer, and those mats linger until well into the season.
Sargassum often comes with a pungent stench attached to it — something between sewage and rotten eggs — due to the mats off-gassing Hydrogen Sulfide and Ammonia, among others. Hydrogen Sulfide smells like rotten eggs, and ammonia is most commonly linked to a stale urine smell. This makes a sargassum-covered beach a wholly unpleasant experience, and that’s before the brown water is created in the surf by Sargassum decaying in the water.
So What Is Sargassum?
Sargassum is a naturally occurring seaweed that floats across the mid-Atlantic Ocean between the Americas and Africa in large island-like masses. Technically, it is a genus of brown macroalgae and has been present in the Atlantic for centuries if not millennia.
Early Portuguese explorers named it Sargassum after finding it in an area of the Atlantic that was later named the “Sargasso Sea.” The sailors thought Sargussum was like the wooly rock rose (Halimium lasianthum) that grew in their water wells at home, called sargaço in Portuguese.
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Christopher Columbus was the first European to mention the Sargasso Sea when he and the ships under his command crossed it on his initial voyage in 1492. Columbus and his crew thought the presence of the seaweed suggested the proximity of land and encouraged them to continue. Still, they were within the Sargasso Sea and nowhere close to land, save for the island of Bermuda.
Sargasso Sea? Where Is That?
The Sargasso Sea is a “sea within a sea” and is the only sea or ocean in the world without a coastline. Its borders expand and contract from year to year, but the center remains relatively constant. It is a gyre in the center of the Atlantic Ocean, where currents rotate around the edges and create an area with less currents — think swirling water with a calm center. That calmer center allows for the eponymous seaweed mats that are familiar to people in Florida, the Caribbean Basin, and other nearby regions.
Graphic: The Ocean Institute
Sargassum Is Harmless Until It Reaches Land
While floating, the sargassum has many benefits and provides shelter and food for marine life. But once the mass strikes land, it starts to decompose, creating a thick, stinking mess that is unpleasant to beachgoers and detrimental to turtle hatchlings trying to reach ocean waters as their life-cycle is just beginning. Sargasso mats on the shoreline also affect birds and other wildlife, and create an annual disruption to the normal shoreline ecosphere.
Decaying sargassum also creates “brown tides,” where the ocean’s water reduces light and oxygen and causes changes to the water chemistry, such as increasing nitrogen and phosphorus levels. Sargassum also contains high levels of arsenic and other heavy metals, organic contaminants, and marine debris.
“When the sargassum washes up on shore, it degrades and creates a brown tide. This impacts water quality,” says Javier Pizaña-Alonso, CORAL’s Program Manager in Cozumel. Put all together, Sargassum has other disruptive impacts on marine ecosystems, including methane emissions. In short, a thoroughly unpleasant experience for everyone and everything in or near the water.
The mass of Sargussum is huge: “In June 2018, the 8850-kilometer-long sargassum belt contained more than 20 million tons of sargassum biomass,” according to Menquiu Wang in a paper in the July 2019 edition of the journal Science.
Since 2010, Sargasso mats have been growing thicker, with theories ranging from excess fertilizer to raw sewage and soil runoff from farms, cities, and roadways flooding the ocean with nutrients that feed sargassum growth. Many scientists suspect nutrient runoff from the Amazon and Mississippi Rivers may play a role. Other theories say that Sargussum growth is fueled by dust blowing offshore from the Saharan Desert in Africa, and once the dust settles onto the surface of the water that iron and other nutrients in the dust are fueling the rise in the annual Sargassum coverage. Still other scientists claim that rising ocean temperatures caused by climate change create more ideal conditions for Sargassum growth.
You may need to click the photo to start the animation.
No matter the reason(s) for its happening, however, one thing is sure: more Sargassum is washing up on shorelines. Not only does the stinking stuff on beaches have an ecological impact, but it can also affect recreational and commercial fisheries by reducing the availability of essential species and preventing fishermen from catching the fish they are after.
In 2018, the estimated cost to clean up decomposing excessive Sargassum across the Caribbean was $120 million. In the United States, Miami-Dade County, Florida estimated $35 million dollars as the annual cost to collect, transport, and landfill Sargassum. A cost analysis by the city of Ft. Lauderdale, Florida, estimated an annual expenditure of $380,000 to clean beaches of Sargassum and maintain a Sargassum compost pile.
In 2022, the U.S. Virgin Islands Department of Planning and Natural Resources Commissioner estimated the daily cost of removing dense inundation of decomposing Sargassum at $25,000 per day. That same year, the U.S. Virgin Islands declared a state of emergency as excessive accumulation of Sargassum onshore and in coastal waters obstructed the water intake of a desalination plant on St. Croix. As a result, the plant struggled to produce sufficient water to meet the demands of the area, particularly during the time of a prevailing drought.
US Environmental Protection Agency, Sargassum Inundation Events (SIEs): Impacts on the Economy
The 2024 Sargassum Forecast
Map: NOAA / USF
From the University of South Florida:
Unlike most previous years, total Sargassum amount decreased from about 9 million metric tons in February to about 6.5 million metric tons in March. Most of the decline occurred in the eastern Atlantic where persistent cloud cover could cause some underestimation.
In the western Atlantic, slight decline could be due to weaker-than-usual winds. Nevertheless, similar February-March declines also occurred occasionally in previous years (e.g., 2018), and the total amount in March 2024 was still above the 75% of all previous March months, indicating that 2024 could still be a major Sargassum year.
As predicted earlier, the amount of Sargassum entering the eastern Caribbean Sea (CS) continued to increase from late February, and this trend will continue in the coming months. In contrast, negligible amount was found in the Gulf of Mexico (GoM) and the western CS. 6.5M 3.0M <0.1M <0.1M 0.4M 3.1M
Looking ahead: We interpret the February-March decline as an unusual anomaly, and expect increased Sargassum amounts in the central Atlantic and particularly in the eastern CS over the next few months.
By late April or early May, the coastal regions in the western CS may receive small to moderate amounts of Sargassum. The southeast coast of Florida (including the Florida Keys), however, will be largely free of Sargassum until late May.
We will closely monitor and track Sargassum throughout the central Atlantic, and will provide more summary updates at the end of each month.
Meanwhile, all previous monthly bulletins as well as daily updates through near real-time imagery can be found under the Sargassum Watch System (SaWS, https://optics.marine.usf.edu/projects/saws.html).
University of South Florida, Outlook of 2024 Sargassum blooms, March 2o24 Update
A Chance For Citizen Science
Readers in Florida and other affected regions can help forecasters hone their models by verifying the data scientists produce in the real world.
Sargassum Monitoring is a website that offers forecasts and observations. On the site, they say that
Whether there are few or a lot of algae, take photos/videos of the sargassum on the beach and share them on our social media.
Your photos are also so useful for the people dealing with this matter:
- Because they allow us to identify which of the 60+ models in the sargassum family, are these sargassum.
- It makes it clear where the affected areas are.
- We can estimate the quantity of sargassum that has washed ashore.
- We are able to calculate the direction and time it takes them to move.
- It helps to define the recurrence of arrivals, etc…
- It makes it easier to assess the damage caused to marine flora and fauna.
- It shows the effectiveness of the resources deployed.
To get started, click the link above and read through the information on the Sargassum Monitoring site.
