The 2023 Sargassum “blob:” dispelling myths

Over the course of the last month or so, talk of the sargassum “blob” has dominated local and national news headlines, and has even made it into pop culture television like The Daily Show. With all of the attention the “blob” is getting, it is important to understand just what is being discussed and what we can expect in south Florida over the coming months.

Sargassum: what is it?

As I outlined in my 2018 blog piece, sargassum, a free-floating seaweed or macroalgae, originates from an area in the Eastern Atlantic Ocean called the Sargasso Sea. However, there exists a second area of prolific sargassum formed in 2019 further south off the coast of South America (LaPointe et al. 2021, Wang et al. 2019). This area is referred to as the Greater Sargassum Belt (GASB) or Small Sargasso Sea. Water circulation patterns move similarly to a conveyor belt, and scientists theorize that some sargassum seeds traveled from the Sargasso Sea to this area between Brazil and West Africa and eventually created the GASB.

While sargassum is a naturally occurring species, many variables affect its abundance, or amount that it  grows. Sea surface temperature, freshwater inputs, increased deforestation in the Amazon River region, and nutrient inputs are all factors that can affect how much of a bloom occurs in a certain year (Wang et al. 2019).  The reference to the “blob” is simply describing the appearance of the 5,000-mile sized GASB when viewed via satellite imagery. The “blob” is not one contiguous mass, but rather multiple clumps and mats of sargassum that make up the GASB (USF Sargassum Outlook Bulletin, March 31, 2023).

An informational sign along the Rickenbacker Causeway, teaching beach patrons about sargassum. Photo: Ana Zangroniz

Why is sargassum coming here?

Ocean currents and gyres (large systems of circular ocean currents formed by global wind patterns and forces created by Earth’s rotation) work as an easy transport for sargassum. Since sargassum is a pelagic, free-floating seaweed, its travel remains dependent on hitching a ride on these currents or moving around with prevailing winds. Sargassum is transported to the western Gulf of Mexico via the Loop Current and Gulf Stream. The Gulf Stream is the warm, fast-moving current that hugs Florida’s coastline, transporting sargassum onto our beaches. Coastal Mexico and other Caribbean countries close to the source receive larger quantities of Sargassum than we see in Florida.

What should we expect?

The term “algal bloom” can be confusing and mistakenly used interchangeably with other phenomena. An algal bloom refers to an increase of biomass that becomes higher than average (Havens 2018). A “harmful algal bloom” or HABs are blooms that result in negative impacts to wildlife, people, and economics (Smyth et al. 2022). Unfortunately, sargassum is now being loosely considered a HAB due to now annual inundation and accumulation on local beaches. Under the HAB criteria, sargassum wreaks havoc. Although it floats freely in the water, sargassum can wash ashore and remain there, depending upon the local tides and slope of the beach.

Sargassum landings have been observed in Florida earlier than usual this year, and we can expect to experience a high and continuous amount of sargassum landings throughout the summer. At this point, the USF Sargassum Outlook Bulletin tentatively predicts the month of June for the peak of the Sargassum abundance in our area.

Left: the average of March sargassum influxes from 2011-2022. Right: the Great Atlantic Sargassum belt in March of 2023. Images: Optical Oceanography Laboratory at the University of South Florida College of Marine Science

Sargassum impacts

Environmental impacts

  • Large mats of sargassum have the potential to smother shallow coral reefs and seagrass beds by blocking needed sunlight.
  • Accumulation of sargassum along the shoreline can impede the ability of sea turtle hatchings to make their way to the ocean.

Recreational impacts

  • The continuous accumulation of sargassum brough in by daily tides results in large “carpets” of algae on local beaches. This can hinder beach access.
  • As the sargassum and the organisms living in it begin to decompose, hydrogen sulfide (a “rotten egg” smell) is released (Dierssen et al. 2015, Doyle & Franks 2015). In addition to smelling unpleasant, this gas can irritate individuals who have respiratory illnesses.
  • Large quantities of sargassum can clog motorboat intake valves.

Economic impacts

  • Beaches that are not easily accessible or don’t appear spotless can have ramifications for Florida’s tourist industry.
  • With more influxes of sargassum, the costs of both personnel as well as equipment for removal effort increases.

How is it being handled?

The National Oceanic and Atmospheric Administration (NOAA) classifies sargassum as essential fish habitat. This designation as well as other environmental legislation (the Endangered Species Act, Marine Mammal Protection Act, and others) makes it difficult, if not impossible to collect sargassum from the water. Therefore, sargassum may only be removed under permit after it lands on the shore.

Since sargassum season coincides with sea turtle nesting season, all beach cleaning operations must perform their work in accordance with the Florida Department of Environmental Protection & the Florida Fish and Wildlife Conservation Commission, as well as coordinate with local sea turtle monitoring programs. In Miami-Dade County, sargassum is either spread out with mechanized beach rakes or removed with front-end loaders. In some areas, it is mixed with or buried in the sand. In other areas, it is removed completely from the beach and transported to the local landfill (adding to the costs of removal).

In addition to permitted removal activities, coordination groups meet to discuss current events, response efforts, and sharing of best practices related to sargassum. These groups include, but are not limited to, stakeholders representing local resource managers, city planners, academic institutions, non-profit organizations, and others. Furthermore, several scientific studies are underway examining the viability of sargassum as a compost additive. The City of Fort Lauderdale has been composting their sargassum for 15 years, and uses it as fill for landscaping projects.

What can you do?

Whether you are a resident or visitor, if you enjoy going to the beach, you are likely to experience sargassum landings the summer. If possible:

  • Go to the beach early in the day, after beach cleaning has occurred.
  • Avoid accumulation hot spot areas, particularly if you have any respiratory illnesses.
  • If you like beach combing, carefully sift through some sargassum. You may find juvenile fish or other invertebrates hiding in the mats.
  • Report observed sargassum accumulations here via a citizen science project. The data submitted will help managers identify and respond to hot spots, as well as help track sargassum accumulation trends over time.

Para accesar a esta comunicación en español, por favor utilice este enlace.


Dierssen, H.M., Chlus, A., Russell, B. 2015. Hyperspectral discrimination of floating mats of seagrass wrack and the macroalgae Sargassum in coastal waters of Greater Florida Bay using airborne remote sensing. Remote Sensing of Environment 167, p. 247-258.

Doyle, E., Franks, J. 2015. Sargassum Fact Sheet. Gulf and Caribbean Fisheries Institute.

Havens, K. 2018. The future of harmful algal blooms in Florida inland and coastal waters. University of Florida Electronic Information Data Source. 4 pp.

Lapointe, B., Brewton, R., Herren, L., Wang, M. Hu, C., McGillicuddy Jr., D., Lindell, S., Hernandez, F., Morton, P. 2021. Nutrient content and stoichiometry of pelagic Sargassum reflects increasing nitrogen availability in the Atlantic Basin. Nature Communications 12: 3060. 10pp.

Smyth, A., Laughinghouse, D., Havens, K., Frazer, T. 2022. Rethinking the role of nitrogen and phosphorus in the eutrophication of aquatic ecosystems. University of Florida Electronic Information Data Source. 5pp.

Wang, M., Hu, C. Barnes, B., Mitchum, G., Lapointe, B., Montoya, J. 2019. The great Atlantic Sargassum belt. Science, 365 p. 83-87.

University of South Florida, March 31, 2023 Sargassum Outlook Bulletin:



Posted: April 20, 2023

Tags: Floating Ecosystem, Florida Sea Grant, Marine Science, Natural Resources, Sargassum, Sargassum Blob, Seaweed, Seaweed Blob

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