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Seaweed Update: Florida beaches brace for ‘the bog’

Florida beaches have begun experiencing an onslaught of sargassum seaweed as an historic 5,000-mile-wide bog drifts our way from its origins in the central Atlantic.

Sargassum seaweed is not a new phenomena, but this year’s mass is the largest ever recorded.

Sargassum seaweed on Fort Laudedale beach at low tide April 8, 2023
Sargassum seaweed on Fort Lauderdale beach at low tide April 8, 2023. (Photo by Bonnie Gross)

Florida’s seaweed season typically runs from April until October, peaking in June and July. The seaweed comes in waves, depending on currents and wind direction.

The seaweed itself is not harmful to humans, but decaying sargassum on beaches releases hydrogen sulfide that can impact people with breathing issues. That said, even decaying sargassum is not considered harmful because the gases disperse quickly on breezy beaches.

You might think the seaweed would be removed from the water before it hits our beaches, but that’s against the law because of it’s value as a shelter and food source for marine life. Once the sargassum weed blob hits the beach, the seaweed can be removed.

Popular tourist beaches rake the seaweed each morning and remove it from beaches, but with the state’s 1,350 miles of shoreline, that’s not always possible.

Additionally, it may be an insurmountable task to keep up with the sheer mass of seaweed washing ashore during the day when beaches are crowded.

Latest NOAA Sargassum inundation assessment

sargassum florida map

The risk assessment was published by NOAA and the University of South Florida for the period May 16-22, 2023, and is the latest available. Red indicates full inundation of seaweed on beaches. Orange indicates a significant portion of the shoreline is affected. Blue indicates a lower level of inundation, though still well above 50%. Higher levels of concentration can be expected on beaches where there is no cleanup, such as Canaveral National Seashore and other state and national shoreline preserves. See our list of live beach cams for seaweed inundation on popular beaches that are routinely cleared in the morning. This map is updated weekly.

Seaweed Watch: Beach webcams

Sargassum seaweed arrives in waves, depending on wind direction and currents.

These links will take you to live beach cameras at Florida’s most popular beaches so you can check on conditions in real time near your destination.

Atlantic Beaches (North to South)

Surfing area at Deerfield Beach, north of the pier. Webcam hosted by City of Deerfield Beach. (Note: Pipes are part of a beach renourishment project.)

Gulf Beaches (Northwest to South)

Web cam hosted by the Wyndham Grand Clearwater. Book a room!

Latest sargassum headlines:

Sargassum FAQs

Source: National Oceanic and Atmospheric Administration (NOAA) Coast Watch

What is Sargassum?

Sargassum is a type of floating brown algae, commonly called “seaweed.” These algae float at the sea surface, never attach to the sea floor, and they can aggregate to form large mats in the open ocean.

Where does it come from?

Historically, the majority of Sargassum aggregated in the Sargasso Sea in the western North Atlantic, with some small amounts found within the Gulf of Mexico and Caribbean Sea. In 2011, the geographic range expanded, and massive amounts of Sargassum moved west into the Caribbean Sea, Gulf of Mexico, and south tropical Atlantic, washing ashore in Florida, Puerto Rico, the US Virgin Islands, and most islands and coastal areas in the Caribbean Sea.

What are the benefits of Sargassum?

Sargassum, in normal amounts, provides habitat, food, protection, and breeding grounds for hundreds of diverse marine species, including commercially important species, such as tuna and swordfish, which feed on the smaller marine life present in Sargassum mats. If Sargassum reaches the coast in small/normal quantities, it may help to avoid beach erosion.

What are some of the drawbacks of Sargassum?

As Sargassum accumulates close to the coastlines, it can smother valuable corals, seagrass beds, and beaches. As it washes ashore the seaweed begins to decay, attracting flies and other insects. During its breakdown, Sargassum produces hydrogen sulfide gas, which smells of rotten eggs, repelling beachgoers. Sargassum can also impact navigation, block water intake in desalination plants, and impact benthic ecosystems after/if they sink to the bottom of the ocean.

What threats, if any, does Sargassum present to human health?

Studies of the impact of Sargassum on human health started very recently and this is a topic that needs more time to be fully understood. However, when decomposed, Sargassum releases hydrogen sulfide (a gas) that may cause respiratory health problems. Sargassum is also known to often contain heavy metals that can be toxic to humans and animals.

Does Sargassum cause skin rashes and blisters?

Sargassum does not sting or cause rashes. However, tiny organisms that live in Sargassum
(like larvae of jellyfish, sometimes called sea lice) may irritate skin if they come in contact with it.

Why did the geographic range for Sargassum expand in 2011?

Researchers are still assessing various hypotheses about the cause of this first documented extreme event. One hypothesis proposes that during the winter of 2009–2010, the winds that typically blow to the east, from the Americas to Europe, strengthened and shifted to the south more dramatically and persistently than any other time in the 1900–2020 record.

This shift in winds triggered a long-distance eastward dispersal of Sargassum, from the Sargasso Sea, toward the Iberian Peninsula in Europe and West Africa.  After exiting the Sargasso Sea, the Sargassum drifted southward in the Canary Current and entered the tropics. Once in this new and favorable tropical Atlantic habitat, with ample sunlight, warm waters, and nutrient availability, the Sargassum flourished and has continued to grow.

In addition to changing wind patterns, other hypotheses include a combination of factors, such as the variation in the outflow of major rivers (e.g. Amazon and Orinoco), nutrient (nitrogen and phosphorus) concentration in the oceans, increase in the amount of phosphorus due to saharan dust, water temperature, and river runoffs.

Having established a new population, the Sargassum now aggregates almost every year, starting in January/February in a massive windrow or “belt” north of the Equator, along the region where the trade winds converge.

During the late winter and early spring months, the Sargassum moves northward with the seasonal winds and currents. By June, this belt may stretch across the entire central tropical Atlantic. Large portions of this algae are then transported into the Caribbean Sea and Gulf of Mexico via the North Equatorial and Caribbean current systems.

Is the amount of Sargassum in the Atlantic/Caribbean increasing?

Since 2011, large accumulations of Sargassum have occurred every year in the Caribbean Sea, Gulf of Mexico, and tropical Atlantic, but the amount can vary from year to year.

The presence of Sargassum occurs over large areas from the tropical Atlantic in the east, to the Gulf of Mexico in the west, approximately 5,000 kilometers from the eastern tropical Atlantic to the west off the Mexican coast in the Caribbean Sea.

Sargassum does not extend as a blanket (or blob) covering the full surface of the ocean in these regions. Instead, Sargassum floats in patches that range in size from a few centimeters to hundreds of meters. Some of these patches reach the coastal areas, including beaches, ports, and even intake systems for drinking water.  The area that these patches cover has been significantly larger in recent years than prior to 2011.

Sources: National Oceanic and Atmospheric Administration (NOAA) Coast Watch,
Florida Department of Health Fact Sheet

Editor’s Note:

The information in this article was accurate when published but may change without notice. Confirm details when planning visits. 

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Friday 26th of May 2023

Greetings Bob, I wanted to draw your attention to a news program from today about the Sargassum Seaweed. According to WEAR NEWS, FAU has determined the bacteria vibrio is found in the seaweed. This bacteria is the dominant cause of death in humans from the marine environment. I am planning a trip to John Penningcamp State Park in a couple of weeks and was looking forward to snorkeling. Now I'm not sure it would be a good idea. I have Cancer so I have to be vigilant about such issues. Thoughts? Cheers, Susan

Bob Rountree

Sunday 28th of May 2023

Hi Susan: The original FAU press release about this issue seems to focus on beached sargassum, but the level of threat is unknown. It's likely you'd be snorkeling offshore from a boat at Pennekamp. At sea, sargassum comes in lines and clumps, not highly concentrated like it is on the beach, and it doesn't start rotting and releasing pathogens until it lands on the beach, or so we're told. My gut tells me the FAU research is very preliminary. But considering your other issues, I'd talk to your doctors. Good luck beating your cancer.

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