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Two Sargassum Species
Two Sargassum Species
Caribbean Sargassum: Sargassum natans (left) and Sargassum fluitans (right).
University of South Mississippi
Beaching Event
Beaching Event 2015
Sargassum accumulates along Bathsheba Beach on the east coast of Barbados
(courtesy of Romel Hall/Barbados Today)

   SaWS Clickable Map

The Sargassum Watch System (SaWS) is designed to use satellite data and numerical models to detect and track pelagic Saragassum in near-real time.

Pelagic Sargassum seaweed (Image courtesy of Tracy Villareal) is a brown macroalgae floating on the ocean surface. Comprised primarily of two species, S. natans (Image courtesy of Amy Siuda) and S. fluitans (Image courtesy of Amy Siuda), it is abundant in the Intra-Americas Sea (IAS), the Atlantic, and along the coasts of British Isles and mainland Europe. In the ocean it serves as an important habitat for many marine animals as it provides food, shade, and shelter (from predators) to fish, shrimp, crabs, and turtles. Sargassum may serve as fertilizers for sand dunes and thus protects shoreline stability. It is also a marine resource for other uses such as biomass for food, fuel, and as a possible source of pharmaceutical materials.

However, excessive amounts of Sargassum on beaches in populated areas can cause a lot of problems and they must be physically removed. Sargassum decomposition on beaches smells bad, attracts insects, and causes many environmental problems (e.g., smothering turtle nesting sites, sea turtle mortality, fish kills) and economic problems (e.g., diminished tourism). The beaches along the Texas coast have experienced Sargassum inundation events annually, and since 2001 beaching events have also occurred on many Caribbean shores in nearly every spring and summer. Sargassum beaching events have also been reported in western Africa and northern Brazil. Monitoring Sargassum distribution and abundance in the ocean in a timely fashion is of great importance for studying ocean ecology, helping fishery management, and forecasting Sargassum beaching events. The SaWS is meant to provide such a function through producing and sharing customized satellite imagery in near real-time in a user-friendly way.

You may be interested in these links:

Sea turtles victims of Sargassum seaweed

Sargassum: The What, Where, and Why of this Seaweed

Sargassum is a genus of large brown seaweed (a type of algae) that floats in island-like masses

Gov’t allocates initial $5 million for removal of sargassums

   SaWS Clickable Map

The table below shows the four satellite sensors that are currently used in SaWS, with the first three sharing similar characteristics.

Sensor Revisit Frequency Spatial Resolution (m) Spectral bands for
floating algae (nm)
Spectral bands for
color index
MODIS/Terra Near daily 1000 667, 748, 869 469, 555, 645 2000 — present
MODIS/Aqua Near daily 1000 667, 748, 869 469, 555, 645 2002 — present
VIIRS Daily 750 671, 745, 862 443, 551, 671 2012 — present
Landsat 8 OLI 16-day 30 655, 865, 1609 443, 561, 655 2013 — present

The raw satellite data are provided by the U.S. NASA and USGS. These data are downloaded and processed through a Virtual Antenna System using both standard and customized algorithms. Of particular importance are the two customized data products, namely the floating algae index (FAI) to detect floating algae and other materials on the ocean surface, and the color index (CI) to trace ocean circulation features. Floating algae often appears in images as slicks over the relatively homogeneous background in the FAI imagery, while ocean circulation patterns may be inferred from the various eddy and plume features in CI imagery. Two examples are given below.

Examples of Satellite Imagery used in SaWS
Floating Algae Index Ocean Circulation CI
Floating Algae Index (left) reveals algae and Color Index (right) shows circulations patterns

   SaWS Clickable Map

SaWS covers the entire Intra-Americas Sea. To facilitate visualization and navigation, the imagery products are divided into different geographic regions, for example Central Atlantic, Eastern Caribbean, Central East Atlantic, Gulf of Mexico, etc. The "SaWS Clickable Map" at top of this paragraph shows the current coverage, where any region can be clicked to open a separate page unique to that region. A user may then select a specific date on the calendar, or use the “animate” function to browse through the image sequence quickly to determine the date of interest. The most useful image type may be the “FA_UNET_DENSITY”, which shows the Sargassum density over the past week. All images can be brought to the user’s Google Earth, together with ocean surface currents as a separate data layer. A screenshot of a typical web interface is presented below.

Virtual Antenna Web Interface
Virtual Antenna Web Interface
The information of each image type can be obtained by clicking on the “Information” link

   SaWS Clickable Map

Under each images icon in the VAS (previous tab) there is a small GE button in the lower right corner. When this is clicked, a KML file is generated for that image. In addition, surface currents from the Hybrid Coordinate Ocean Model (HYCOM — from the National Ocean Partnership Program (NOPP)) are obtained, updated nightly, and made available via the VAS as a layer within Google Earth. Thus, both the image and surface currents can be displayed in Google Earth with a simple mouse click (see example below), thereby facilitating visualization and navigation. Within Google Earth, once a Sargassum raft is identified with latitude and longitude, current speed and direction (available through a mouse click over the current vector) near the raft can be used to predict the movement of the raft and a possible beaching time, in essence, forming an early warning system.

Ocean Currents Vectors Integrated with Satellite Imagery in Google Earth
Google Earth Interpretation
A KML file is created to provide Google Earth the image and ocean current data for visualization

   SaWS Clickable Map

Sargassum has impacted the Caribbean in so many ways. Here we show a few photographs that reveal the serious nature of the problem.

Capesterre Guadeloupe
Airborne survey during spring and summer 2015
(photo courtesy of Jean-Philippe Maréchal)
Desirade Guadeloupe
Airborne survey during spring and summer 2015
(photo courtesy of Jean-Philippe Maréchal)
Sargassum Beaching Event 2015
(photo courtesy of Jean-Philippe Maréchal)
Sargassum Beaching Event 2015
(photo courtesy of Jean-Philippe Maréchal)
Sailing Vessel Skipping Stone
Stranded boat in a Sargassum bloom off Admiralty Bay, Bequia, Grenadines
June 2015 (Photo credit: Sailing Vessel Skipping Stone)

  SaWS Clickable Map

Dierssen, H. M., A. Chlus, and B. Russell (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 Sens. Environ., 167:247-258.

Feagin, R. A. and A. M. Williams (2010). Sargassum: Erosion and Biodiversity on the Beach, Spatial Sciences Laboratory, Dept. Ecosystem Science & Management, Texas A&M University, pp23.

Franks, J., D. R. Johnson, D. S. Ko, G. Sanchez-Rubio, J.R. Hendon, and M. Lay (2011), Unprecedented Influx of pelagic Sargassum along Caribbean island coastlines during summer 2011, Proc. Gulf Caribb. Fish. Inst., 64:6-8.

Gower, J., C. Hu, G, Borstad, and S. King (2006), Ocean color satellites show extensive lines of floating Sargassum in the Gulf of Mexico, IEEE Trans. Geosci. Remote Sens., 44, 3619–3625.

Gower, J., E. Young, E., and S. King (2013), Satellite images suggest a new Sargassum source region in 2011, Remote Sens. Lett. 4, 764–773.

Hardy, R. F. (2014). Assessment of surface-pelagic drifting communities and behavior of early juvenile sea turtles in the Northern Gulf of Mexico. MS Thesis, University of South Florida, 118pp.

Hu, C (2009), A novel ocean color index to detect floating algae in the global oceans, Remote Sens. Environ., 113, 2118–2129.

Hu, C., B. B. Barnes, B. Murch, and P. Carlson (2014), Satellite-based virtual buoy system (VBS) to monitor coastal water quality, Optical Engineering, 53, 051402. doi: 10.1117/1.OE.53.5.051402.

Hu, C., L. Feng, R.F. Hardy, and E. J. Hochberg (2015), Spectral and spatial requirements of remote measurements of pelagic Sargassum macroalgae, Remote Sens. Environ., 167, 229-246. doi: doi:10.1016/j.rse.2015.05.022

Huffard, C. L., S. von Thun, A. D. Sherman, K. Sealey, and K. L. Smith Jr. (2014). Pelagic Sargassum community change over a 40-year period: temporal and spatial variability. Mar. Bio, 161:2735-2751

Lapointe, B. E., L. E. West, T. T. Sutton, and C. Hu (2014), Ryther revisited: nutrient excretions by fishes enhance productivity of pelagic Sargassum in the western North Atlantic Ocean, J. Exp. Mar. Bio. Ecol. 458:46-56.

Milledge, J. J., B. V. Nielsen, and D. Bailey (2015). High-value products from macroalgae: the potential uses of the invasive brown seaweed, Sargassum muticum. Reviews in Environmental Science and Bio/Technology. 15:67-88.

Parr, A.E. (1939), Quantitative observations on the pelagic Sargassum vegetation of the western North Atlantic, Bull. Bingham Oceanog. Coll., Peabody Museum of Natural History, Yale University, 6(7): 1-94. Oceanography 28(3):8–10

Sargasso Sea Commission (link: news/worldwide-sargassum)

The Journey of the Sargassum forum (link:

Smetacek, V., and A. Zingone (2013). Green and golden seaweed tides on the rise, Nature, 504:84-88.

Webster, R. K., and T. Linton (2013), Development and implementation of Sargassum Early Advisory System (SEAS), Shore and Beach, 81(3): 1 – 6.

Wang, M., and C. Hu (2016). Mapping and quantifying Sargassum distribution and coverage in the Central West Atlantic using MODIS observations. Remote Sens. Environ., 183:356-367.

Witherington B., H. Shigetomo, and R. Hardy (2012), Young sea turtles of the pelagic Sargassum-dominated drift community: habitat use, population density, and threats, Mar Ecol Prog Ser 463: 1-22.

   SaWS Clickable Map


The information bulletin is meant to provide a general outlook of current bloom condition and future bloom probability for the Caribbean Sea and Gulf of Mexico. By no means should it be used for commercial purpose, or used for predicting bloom conditions for a specific location or beach. The authors of this bulletin, as well as USF and NASA, take no responsibility for improper use or interpretation of the bulletin. Any use of the image, data, or graph from this bulletin page in reports or publications should obtain permission from the USF OOL group.

This page provides links to Sargassum forecast or outlook bulletins (see bottom of this page), which are updated routinely. The bulletins started in early February 2018, and they are meant to give an outlook of Sargassum bloom probability in certain regions in the upcoming months, based on bloom conditions in previous months, and previous years.

Sargassum blooms in the Caribbean Sea

Since 2011, large amounts of Sargassum seaweed appeared in the Caribbean Sea every summer except 2013, creating many environmental, ecological and economic problems in many regions. The seaweed originated from the tropical Atlantic, and is believed to be a result of climate variability and other natural and unnatural processes. Based on satellite observations and statistics of historical events, in early February 2018 the Optical Oceanography Lab developed the first 1-page Sargassum outlook bulletin for the Caribbean Sea. Since then, the bulletins have been generated and distributed to subscribers by the last day of the month. These monthly bulletins are also made available at the bottom of this page. Further readings are also available under the Reference page.

Sargassum abundance in the Central Atlantic decreased overall from January to February, but substantial quantities in the Caribbean Sea continued to accumulate. In March, we expect Sargassum abundance increases in both the Caribbean Sea and Gulf of Mexico.


Sargassum Outlook Bulletin, February 2023

Sargassum Outlook Bulletin, January 2023

Sargassum Outlook Bulletin, December 2022

Sargassum Outlook Bulletin, November 2022

Sargassum Outlook Bulletin, October 2022

Sargassum Outlook Bulletin, September 2022

Sargassum Outlook Bulletin, August 2022

Sargassum Outlook Bulletin, July 2022

Sargassum Outlook Bulletin, June 2022

Sargassum Outlook Bulletin, May 2022

Sargassum Outlook Bulletin, April 2022

Sargassum Outlook Bulletin, March 2022

Sargassum Outlook Bulletin, February 2022

Sargassum Outlook Bulletin, January 2022

Sargassum Outlook Bulletin, December 2021

Sargassum Outlook Bulletin, November 2021

Sargassum Outlook Bulletin, October 2021

Sargassum Outlook Bulletin, September 2021

Sargassum Outlook Bulletin, August 2021

Sargassum Outlook Bulletin, July 2021

Sargassum Outlook Bulletin, June 2021

Sargassum Outlook Bulletin, May 2021

Sargassum Outlook Bulletin, April 2021

Sargassum Outlook Bulletin, March 2021

Sargassum Outlook Bulletin, February 2021

Sargassum Outlook Bulletin, January 2021

Sargassum Outlook Bulletin, December 2020

Sargassum Outlook Bulletin, November 2020

Sargassum Outlook Bulletin, October 2020

Sargassum Outlook Bulletin, September 2020

Sargassum Outlook Bulletin, August 2020

Sargassum Outlook Bulletin, July 2020

Sargassum Outlook Bulletin, June 2020

Sargassum Outlook Bulletin, May 2020

Sargassum Outlook Bulletin, April 2020

Sargassum Outlook Bulletin, March 2020

Sargassum Outlook Bulletin, February 2020

Sargassum Outlook Bulletin, January 2020

Sargassum Outlook Bulletin, December 2019

Sargassum Outlook Bulletin, November 2019

Sargassum Outlook Bulletin, October 2019

Sargassum Outlook Bulletin, September 2019

Sargassum Outlook Bulletin, August 2019

Sargassum Outlook Bulletin, July 2019

Sargassum Outlook Bulletin, June 2019

Sargassum Outlook Bulletin, May 2019

Sargassum Outlook Bulletin, April 2019

Sargassum Outlook Bulletin, March 2019

Sargassum Outlook Bulletin, February 2019

Sargassum Outlook Bulletin, January 2019

Sargassum Outlook Bulletin, December 2018

Sargassum Outlook Bulletin, November 2018

Sargassum Outlook Bulletin, October 2018

Sargassum Outlook Bulletin, September 2018

Sargassum Outlook Bulletin, August 2018

Sargassum Outlook Bulletin, July 2018

Sargassum Outlook Bulletin, June 2018

Sargassum Outlook Bulletin, May 2018

Sargassum Outlook Bulletin, April 2018

Sargassum Outlook Bulletin, March 2018

Sargassum Outlook Bulletin, February 2018

Sargassum Outlook Bulletin, January 2018