Sargassum seaweed on Florida beaches: Latest reports | (2024)

Sargassum seaweed has begun washing ashore at low-to-medium levels on Southeast Florida’s Atlantic beaches, according to observations by the Sargassum Watch database maintained by Florida International University.

And it’s likely to continue at low levels into May, according to the University of South Florida’s Optical Oceanography Laboratory.

In a normal year, the sargassum seaweed “season” on Florida beaches begins in April or May and continues into summer. Heaviest hit most years are the Florida Keys.

Sargassum seaweed on Florida beaches: Latest reports | (1)
Sargassum seaweed on Florida beaches: Latest reports | (2)
Sargassum seaweed on Florida beaches: Latest reports | (3)

Sargassum blooms arise in the Central Atlantic annually in December and drift westward into the Caribbean and Gulf of Mexico during spring and summer.

The floating seaweed provides beneficial shelter from the sun and food for fish offshore, but becomes a nuisance and potential health hazards after it washes up on beaches.

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Sargassum seaweed is not a new phenomena, but the 5,000-mile-wide mass recorded offshore during the spring and summer of 2023 was the largest ever recorded.

Florida’s seaweed season typically runs from April until October, peaking in June and July. The seaweed comes in batches, 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.

New research suggests the pathogen Vibrio sticks to microplastics that merge into sargassum clusters at sea, and while the bacteria has not been detected in sargassum washing ashore, beachgoers are advised to keep their distance from seaweed clusters.

Vibrio vulnificus,one of more than 100 species ofVibrio, sometimes referred to as flesh-eating bacteria, can cause life-threatening food-borne illnesses from seafood consumption as well as disease from open-wound infections, according to the national Centers for Disease Control.

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.

Indeed, these seaweed “lines” are popular targets for anglers who troll for mahi-mahi and other gamefish.

Once the sargassum 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.

Resource for you: Sargassum Information Hub

Beach Cams around Florida

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

These links will take you to live beach cameras at popular Florida beaches so you can see for yourself in real time.

Atlantic Beaches (North to South)

Gulf Beaches (Panhandle to South)

Sargassum FAQs

What isSargassum?

Sargassumis 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 ofSargassumaggregated 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 ofSargassummoved 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 ofSargassum?

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 inSargassummats.

IfSargassumreaches the coast in small/normal quantities, it may help to avoid beach erosion.

What are some of the drawbacks of Sargassum?

AsSargassumaccumulates 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,Sargassumproduces hydrogen sulfide gas, which smells of rotten eggs, repelling beachgoers.

Sargassumcan 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, doesSargassumpose to human health?

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

What about reports of ‘flesh-eating bacteria’ in sargassum?

In the open ocean, researchers at Florida Atlantic University discovered the pathogen Vibrio sticking to microplastics that merge into sargassum clusters at sea.

Vibrio vulnificus,one of more than 100 species ofVibrio, sometimes referred to as flesh-eating bacteria, can cause life-threatening foodborne illnesses from seafood consumption as well as disease, even death, from open-wound infections, according to the national Centers for Disease Control.

Kevin Johnson of Florida Tech’s marine sciences department, says the FAU research “has not demonstrated the sargassum coming onshore is especially dangerous with regard to bacterial infection for people.

Many of the bacteria that are associated with those plastics and sargassum are already present in our environment.”

What you should know about flesh-eating bacteria on beaches, CNN, 6/9/2023

“I don’t think at this point, anyone has really considered these microbes and their capability to cause infections,” says FAU biologist Tracy Mincer. “In particular, caution should be exercised regarding the harvest and processing ofSargassumbiomass until the risks are explored more thoroughly.”

Sargassum removed from beaches is frequently used in fertilizers.

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 forSargassumexpand in 2011?

Researchers arestill assessing various hypothesesabout the cause of this first documented extreme event.

One hypothesisproposes 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 ofSargassum, from the Sargasso Sea, toward the Iberian Peninsula in Europe and West Africa.

After exiting the Sargasso Sea, theSargassumdrifted 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, theSargassumflourished 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, theSargassumnow 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, theSargassummoves 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 ofSargassumin the Atlantic/Caribbean increasing?

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

The presence ofSargassumoccurs 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.

Sargassumdoes not extend as a blanket (or blob) covering the full surface of the ocean in these regions. Instead,Sargassumfloats 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

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Bob Rountree

Bob Rountree is a beach bum, angler and camper who has explored Florida for decades. No adventure is complete without a scenic paddle trail or unpaved road to nowhere. Bob co-founded with fellow journalist Bonnie Gross 14 years ago.

Sargassum seaweed on Florida beaches: Latest reports | (2024)
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