RESEARCH INFORMATION

Since 2011, large quantities of Sargassum have overwhelmed various beaches, harming coastal ecosystems and the economies of coastal communities. Efforts are underway to understand the recent phenomenon and assist management strategies to minimize negative impact.

The Sargassum Information Hub provides up to date information on research focused on Sargassum distribution and movement, ongoing monitoring and forecasting efforts, biology and ecology, collection and use, management practices, as well as impacts.

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Distribution and movement

Various species of Sargassum are distributed in the global oceans. In the Atlantic, there are several benthic species, and at least two pelagic species. Historically, the largest concentrations of pelagic Sargassum had  occurred in the Sargasso Sea and northern areas of the Caribbean Sea, with strong seasonal influxes into the Gulf of Mexico. Starting 2011, large amounts of Sargassum have been found in the Caribbean Sea and tropical Atlantic, which reached maximum during summer months  (Wang et al., 2019). A continuous Sargassum belt formed between west Africa and Gulf of Mexico across the tropical Atlantic nearly every summer since 2011 except 2013. This belt contains the largest amount of macroalgae in the world during the peak months, representing possibly a new normal on Sargassum distributions in the Atlantic Wang et al., 2019). 

While the reasons behind the sudden changes in 2011 and the new normal are still under active research, several hypotheses have been proposed to explained the spatial distribution patterns and inter-annual  changes (Johns et al., 2020). Among these are physical transport and new nutrient supplies. Specifically, unusually strong winds associated with an anomalously negative North Atlantic Oscillation (NAO) during the northern winter of 2009-2010 could have transported Sargassum out of the Sargasso Sea to the eastern North Atlantic). These winds pushed Sargassum southward into the Canary Current along the coast of West Africa, southwestward into the North Equatorial Current towards the Caribbean Sea, and eastward into the North Equatorial Counter Current towards the Gulf of Guinea.  This displaced Sargassum contributed new Sargassum seed population to the existing population  in the tropical North Atlantic that has blossomed seasonally with some interannual variation since 2011. This population is now aggregated during the first few months of each year by the strong Trade Winds under the Intertropical Convergence Zone (ITCZ) to form a massive zonal (East-West) wind row that spans the tropical Atlantic. 

New nutrients supporting the growth of Sargassum in the tropical Atlantic may include dust deposition, vertical mixing, and land-based runoff, depending on the time and location (Oviatt et al., 2019; Wang et al., 2019). There is an increasing trend of nitrogen flux from the Amazon River in recent years, which may have contributed to the recent increases in Sargassum abundance, but riverine impact is only restricted to river plume regions. In the open ocean, vertical mixing by the strong Trade Winds provide an important nutrient supply mechanism to stimulate Sargassum growth. As seasons progress, the Sargassum wind row moves northward with the ITCZ. 

Growth of Sargassum may be further stimulated by surface layer mixing and eddy diffusion. As this wind row crosses the latitude and area of seasonal formation of the North Equatorial Counter Current around May, parts of the population near the continental land mass may derive some additional nutrients from runoff from the Amazon and Orinoco rivers. On the eastern side of the Atlantic, some of the nutrient requirements may be derived locally from the Congo River and the wind-driven upwelling off West Africa. Every spring-summer, Sargassum is advected to the Caribbean and the Gulf of Mexico by ocean currents and the wind (Wang and Hu, 2017; Books et al., 2018; Putman et al., 2018). 

A new regime is now established, and it is unclear how long the current situation will last. There is a need to monitor and forecast Sargassum blooms in order to mitigate its ecological, economic, and social impacts.

Gower, J., & King, S. (2020). The distribution of pelagic Sargassum observed with OLCI. International Journal of Remote Sensing, 41(15), 5669-5679.

Johns, E. M., Lumpkin, R., Putman, N. F., Smith, R. H., Muller-Karger, F. E., Rueda, D., Hu, C., Wang, M., Brooks, M.T., Grammar, L.J.,  Werner, F. E. (2020). The establishment of a pelagic Sargassum population in the tropical Atlantic: biological consequences of a basin-scale long distance dispersal event. Progress in Oceanography, 102269.

Wang, M., Hu, C., Barnes, B. B., Mitchum, G., Lapointe, B., & Montoya, J. P. (2019). The great Atlantic Sargassum belt. Science, 365(6448), 83-87.

Putman, N.F., Goni, G.J. , Gramer , L.J.,  Hu,  C.,  Johns, E.M. , Trinanes, J., Wang, M. (2018).  Simulating transport pathways of pelagic Sargassum from the Equatorial T Atlantic into the Caribbean Sea. Progress in Oceanography, (165) 205-214.

Wang, M., & Hu, C. (2017). Predicting Sargassum blooms in the Caribbean Sea from MODIS observations. Geophysical Research Letters, 44(7), 3265-3273.

Franks, J. S., Johnson, D. R., & Ko, D. S. (2016). Pelagic sargassum in the tropical North Atlantic. Gulf and Caribbean Research, 27(1), SC6-SC11.

Gower, J., Young, E., & King, S. (2013). Satellite images suggest a new Sargassum source region in 2011. Remote Sensing Letters, 4(8), 764-773.

Smetacek, V., & Zingone, A. (2013). Green and golden seaweed tides on the rise. Nature, 504(7478), 84-88.

Gower, J., & King, S. (2011). Distribution of floating Sargassum in the Gulf of Mexico and the Atlantic Ocean mapped using MERIS. International Journal of Remote Sensing, 32, 1917–1929

Butler, J. N., & Stoner, A. W. (1984). Pelagic Sargassum: has its biomass changed in the last 50 years?. Deep Sea Research Part A. Oceanographic Research Papers, 31(10), 1259-1264.

Parr, A. E. (1939). Quantitative observations on the pelagic Sargassum vegetation of the western North Atlantic. Bull. Bingham oceanogr. Coll., 6, 1-94.

Monitoring

Sargassum rafts can be thousands of kilometers long and be made of millions of tons of biomass. Because of the extent of this phenomenon, in-situ and satellite observations, as well as citizen science efforts,  are needed to monitor the Sargassum at different scales. 

GIven the ongoing debate on which nutrient sources lead to the seasonal blooming of the Sargassum offshore in the tropical Atlantic, it is important to develop in situ and modeling studies that examine the relative contribution of various nutrient sources cited by different authors. There is substantial published speculation on different possible nutrient sources. Many papers have cited a possible compounded role of deforestation, pollution, and climate-driven changes in the discharge of the Amazon, Congo and Orinoco Rivers (reviewed by Johns et al., 2020). Others have emphasized upwelling off West Africa, and the possible role of African Dust (Oviatt et al., 2019; Wang et al., 2019). Johns et al. (2020) explain that these sources are smaller and not placed geographically to influence the aggregation and blooming of Sargassum during the first few years of the month in the central tropical Atlantic just north of the Equator. This debate could be better informed with observations and simulations from this region. In coastal zones, ship observations, video from remotely operated vehicles, net tows, and SCUBA divers provide small scale descriptions of Sargassum such as species composition, raft shapes and sizes, biomass estimates and depth of biomass submerged (Ody et al., 2019). 

Remote detection of floating Sargassum relies on satellite sensors capturing certain wavelengths of light reflected from the macroalgae. Known as the vegetation red-edge, different sensors capture reflectance in the near-infrared and use specific indexes to determine the presence of Sargassum. Sensors for detecting Sargassum include MERIS, MODIS, VIIRS, OLCI, MSI, and Landsat, each with different spatial and temporal resolution (Cuevas et al., 2018; Wang and Hu, 2016; Gower et al., 2013; Gower and King, 2011). 

Onshore, the general public can partake in science efforts, such as reporting beached sargassum. The public can take photos and upload location information into web and phone-based apps hosted by scientific organizations.

Johns, E.M., Lumpkin, R., Putman, N.F., Smith, R.H., Muller-Karger, F.E., Rueda, D., Hu, C., Wang, M., Brooks, M.T., Gramer, L.J. & Werner, F.E., (2020). The establishment of a pelagic Sargassum population in the tropical Atlantic: biological consequences of a basin-scale long distance dispersal event. Progress in Oceanography, 102269.

Ody, A., Thibaut, T., Berline, L., Changeux, T., André, J.M., Chevalier, C., Blanfuné, A., Blanchot, J., Ruitton, S., Stiger-Pouvreau, V. & Connan, S. (2019). From In Situ to satellite observations of pelagic Sargassum distribution and aggregation in the Tropical North Atlantic Ocean. PloS one, 14(9).

Hardy, R. F., C. Hu, B. Witherington, B. Lapointe, A. Meylan, E. Peebles, L. Meirose, & S. Hirama (2018). Characterizing a Sea Turtle Developmental Habitat Using Landsat Observations of Surface-Pelagic Drift Communities in the Eastern Gulf of Mexico. IEEE J. Selected Topics in Applied Earth Observations and Remote Sensing, 11:3646-3659.

Wang, M., C. Hu, J. Cannizzaro, D. English, X. Han, D. Naar, B. Lapointe, R. Brewton & F. Hernandez. (2018). Remote sensing of Sargassum biomass, nutrients, and pigments. Geophysical Research Letters, 45(22), 12-359.

Hu, C., B. Murch, B. B. Barnes, M. Wang, J-P. Marechal, J. Franks, D. Johnson, B. Lapointe, D. S. Goodwin, J. M. Schell, and A. N. S. Siuda (2016). Sargassum watch warns of incoming seaweed, Eos, 97(22):10-15. 

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

Hu, C. (2009). A novel ocean color index to detect floating algae in the global oceans. Remote Sensing of Environment, 113(10), 2118-2129.

Forecasting

Forecasting Sargassum movement can help coastal communities prepare for inundation events, whether it is through beach closures or the deployment of Sargassum barriers. News archives are used to help scientists understand historical trends and identify the cyclical nature of Sargassum inundation (Webster and Linton, 2013). Information on previous Sargassum events and past and current satellite observations provide data to create inundation models. These models incorporate information from models of ocean current (HYCOM and CMEMS) and wind speed data with the distance of Sargassum to shore to predict the timing and location of Sargassum landings (Webster and Linton, 2013). Hindcasts of historical blooms from MODIS observations can also help predict the likelihood of future Sargassum blooms (Wang and Hu, 2017).

Currently, the Sargassum Watch System (SaWS; Hu et al., 2016) has been providing near real-time MODIS and VIIRS satellite images since 2016 to monitor Sargassum distribution and abundance. SaWS also provide HYCOM surface currents integrated with satellite images in Google Earth, thus providing a simple way for short-term forecasting. SaWS also provides monthly Sargassum Outlook Bulletins to nowcast current situation and forecast future 2-month outlooks. In addition, the Sargassum Early Advisory System (SEAS) provides interpreted Landsat images for short-term forecasts. However, these systems are limited by their spatial and temporal resolutions. Increasing forecasting accuracy is necessary for coastal communities to mitigate the effects of Sargassum.

University of South Florida Optical Oceanography Lab. (2018 – present). Sargassum Outlook Bulletins.

Johns, E. M., Lumpkin, R., Putman, N. F., Smith, R. H., Muller-Karger, F. E., Rueda, D., Hu, C., Wang, M., Brooks, M.T., Grammar, L.J.,  & Werner, F. E. (2020). The establishment of a pelagic Sargassum population in the tropical Atlantic: biological consequences of a basin-scale long distance dispersal event. Progress in Oceanography, 102269.

Johnson, D., & Franks, J. (2019). Final Report on Prediction of Pelagic Sargassum Incursions: Model Development. Report prepared for the Climate Change Adaptation in the Eastern Caribbean Fisheries Sector (CC4FISH) Project of the Food and Agriculture Organization (FAO) and the Global Environment Facility (GEF). Center for Fisheries Research and Development, The University of Southern Mississippi, School of Ocean Science and Engineering, Gulf Coast Research Laboratory, Ocean Springs, Mississippi, USA. 13 pp.

Putman, N.F., Goni, G.J. , Gramer , L.J.,  Hu,  C.,  Johns, E.M. , Trinanes, J., & Wang, M. (2018).  Simulating transport pathways of pelagic Sargassum from the Equatorial T Atlantic into the Caribbean Sea. Progress in Oceanography, (165) 205-214.

Maréchal, J. P., Hellio, C., & Hu, C. (2017). A simple, fast, and reliable method to predict Sargassum washing ashore in the Lesser Antilles. Remote Sensing Applications: Society and Environment, 5, 54-63.

Hu, C., B. Murch, B. B. Barnes, M. Wang, J-P. Marechal, J. Franks, D. Johnson, B. Lapointe, D. S. Goodwin, J. M. Schell, & A. N. S. Siuda (2016). Sargassum watch warns of incoming seaweed, Eos, 97(22):10-15. 

Wang, M., & C. Hu. (2017). Predicting Sargassum blooms in the Caribbean Sea from MODIS observations. Geophysical Research Letters, 44, 3265-3273. 

Webster, R. K., & Linton, T. (2013). Development and implementation of Sargassum early advisory system (SEAS). Shore & Beach, 81(3), 1.

Biology and ecology

There are over 100 species of Sargassum in the world. While the majority of Sargassum grow like most algae by anchoring onto hard substrate, two species in the Atlantic Ocean, Sargassum natans and Sargassum fluitans, form free-floating mats. It is nutrient limited in the Sargasso Sea; however, it is highly productive in the coastal zone, where nutrient sources like fish excretion and run-off from land may be more readily available (Lapointe et al., 2014). When it receives enough nutrients, it rapidly grows then breaks into smaller pieces, and the cycle repeats. 

Sargassum plays various roles in the marine and coastal environments. These floating algal mats provide food and habitat for over 200 species of fishes, invertebrates, mammals, and sea birds (Laffoley et al, 2011). Tuna and other commercially important fishes feed on the small fishes and invertebrates that live within the algae. As a nursery habitat, it shelters endangered and critically endangered sea turtles (Witherington et al., 2012). However, Sargassum species type can have an effect on the abundance and composition of marine life associated with the mats (Martin 2016).  It also serves as a carbon sink, sequestering carbon from the atmosphere (Laffoley et al, 2011). When it washes ashore, Sargassum stabilizes beaches, prevents erosion, and transports nutrients to land (Polis & Hurd, 1996). 

Though Sargassum is an important part of the ocean and coastal ecosystems, too much Sargassum can also act as pollution. Thick Sargassum mats reduce light, harming seagrass and corals and the fauna that rely on them (Rodríguez-Martínez et al., 2019). Ammonium and hydrogen sulfide released from Sargassum can create hypoxic areas that are lethal to marine life (van Tussenbroek et al., 2017). When large Sargassum mats wash ashore, it can prevent female turtles from laying in preferred nesting areas, which increases their probability of digging up other female’s eggs (Mauer et al., 2015). These mats also have a cooling effect on sand, which can lead to the increase in male sea turtles as temperature affects sex determination during development. More research is needed to understand the widespread effects of Sargassum blooms on marine ecosystems.

Cabanillas-Terán, N., Hernández-Arana, H. A., Ruiz-Zárate, M. Á., Vega-Zepeda, A., & Sanchez-Gonzalez, A. (2019). Sargassum blooms in the Caribbean alter the trophic structure of the sea urchin Diadema antillarum. PeerJ, 7, e7589.

Monroy-Velázquez, L. V., Rodríguez-Martínez, R. E., van Tussenbroek, B. I., Aguiar, T., Solís-Weiss, V., & Briones-Fourzán, P. (2019). Motile macrofauna associated with pelagic Sargassum in a Mexican reef lagoon. Journal of environmental management, 252, 109650

van Tussenbroek, B.I., Arana, H.A.H., Rodríguez-Martínez, R.E., Espinoza-Avalos, J., Canizales-Flores, H.M., González-Godoy, C.E., Barba-Santos, M.G., Vega-Zepeda, A., & Collado-Vides, L. (2017). Severe impacts of brown tides caused by Sargassum spp. on near-shore Caribbean seagrass communities. Marine Pollution Bulletin, 122(1-2), 272-281.

Schell, J. M., Goodwin, D. S., & Siuda, A. N. (2015). Recent Sargassum inundation events in the Caribbean: Shipboard observations reveal dominance of a previously rare form. Oceanography, 28(3), 8-11.

Lapointe, B. E., West, L. E., Sutton, T. T., & Hu, C. (2014). Ryther revisited: nutrient excretions by fishes enhance productivity of pelagic Sargassum in the western North Atlantic Ocean. Journal of experimental marine biology and ecology, 458, 46-56.

Rooker, J. R., Turner, J. P., & Holt, S. A. (2006). Trophic ecology of Sargassum-associated fishes in the Gulf of Mexico determined from stable isotopes and fatty acids. Marine Ecology Progress Series, 313, 249-259.

Lapointe, B. E. (1995), A comparison of nutrient‐limited productivity in Sargassum natans from neritic vs. oceanic waters of the western North Atlantic Ocean, Limnology and Oceanography, 40(3), 625-633.

Collection and use of Sargassum

Entrepreneurs can take advantage of inundation events through innovative uses of Sargassum (Milledge & Harvey, 2016). Its chemical properties can have agricultural applications, as it can be used as crop fertilizer and livestock feed. Amino acids and other extracts can be used for disease therapies, food supplements, and other pharmaceutical products. Due to its ability to absorb toxic metals, Sargassum can be an effective tool for wastewater treatment. However, this property may cause Sargassum to be unsafe for human or livestock consumption and may damage soil and crops. Sargassum can be refined and used as an energy source, but this benefit may be offset with high energy costs for drying and processing. Transportation, storage, and its seasonal availability are other challenges for turning Sargassum into a product. More information is necessary to understand the impacts of different mitigation and management strategies and the efficacy of Sargassum use.

Desrochers, A. 2020. Sargassum uses guide – A guide for researchers, entrepreneurs and policy makers. Report prepared for the Climate Change Adaptation in the Eastern Caribbean Fisheries Sector (CC4FISH) Project of the Food and Agriculture Organization (FAO) and the Global Environment Facility (GEF). Centre for Resource Management and Environmental Studies, University of the West Indies, Cave Hill Campus. Bridgetown: Barbados

Milledge, J. J., Maneein, S., Arribas López, E., & Bartlett, D. (2020). Sargassum inundations in Turks and Caicos: methane potential and proximate, ultimate, lipid, amino acid, metal and metalloid analyses. Energies, 13(6), 1523.

Rodríguez-Martínez, R.E., Roy, P.D., Torrescano-Valle, N., Cabanillas-Terán, N., Carrillo-Domínguez, S., Collado-Vides, L., García-Sánchez, M., & van Tussenbroek, B.I. (2020). Element concentrations in pelagic Sargassum along the Mexican Caribbean coast in 2018-2019. PeerJ, 8, e8667.

Thompson, T. M., Young, B. R., & Baroutian, S. (2020). Pelagic Sargassum for energy and fertiliser production in the Caribbean: A case study on Barbados. Renewable and Sustainable Energy Reviews, 118, 109564.

Milledge, J. J., & Harvey, P. J. (2016). Golden Tides: Problem or golden opportunity? The valorisation of Sargassum from beach inundations. Journal of Marine Science and Engineering, 4(3), 60.

Management

With information on Sargassum from monitoring and forecasting, as well as knowledge on its biology and ecology, coastal communities can implement clean up and management strategies, funding permitted. Management strategies can be implemented in the water as well as onshore

Beach managers can implement strategies in the water and onshore. Floating barriers redirect Sargassum movement to a removal site on the beach and near-shore collections can prevent Sargassum beaching events (Resilify Inc., 2019). When Sargassum is on the shore, the amount of beached Sargassum will determine the equipment necessary for its removal. Small amounts of Sargassum can be left alone to undergo natural processes. Moderate amounts of Sargassum can be raked and buried to stabilize beaches and reduce odor  or removed through organized beach clean up events. Large influxes may require mechanical removal with heavy machinery that may cause beach erosion and harm sand dwelling organisms.  Whether in the water or on the shore, mitigation and management strategies must consider the tradeoffs and potential impacts to beaches and marine life.

Ofori, R. O., & Rouleau, M. D. (2020). Willingness to pay for invasive seaweed management: Understanding how high and low income households differ in Ghana. Ocean & Coastal Management, 192, 105224.

Impacts

Large influxes of Sargassum can have negative impacts on human health and local economies. Sargassum produces hydrogen sulfide as it decomposes, releasing a gas that smells like rotting eggs. This pungent smell can deter tourists from beach activities or cause tourists to cancel beachfront rentals (Dutch Caribbean Nature Alliance, 2019). While a minor nuisance in small quantities, large amounts of Sargassum can result in high concentrations of hydrogen sulfide. Exposure to high gas concentrations could cause respiratory, cardiovascular, and neurological issues, and can lead to hospitalization and the associated costs (Mendez-Tejeda & Rosado Jiménez, 2019). Dense Sargassum mats in the ocean can also prevent tours or other ocean-based activities (Caribbean Alliance for Sustainable Tourism, 2015). Loss of tourism can lead to layoffs and an overall decline in revenue for the tourism industry and the surrounding community (Caribbean Alliance for Sustainable Tourism, 2015). The impact of Sargassum events will vary by region and an accurate assessment of these impacts will help coastal communities develop local

UNEP. (2018). Sargassum outbreak in the Caribbean: challenges, opportunities and regional situation. Sargassum White Paper, presented at 8th Meeting of the Scientific and Technical Advisory Committee (STAC) to the Protocol Concerning Specially Protected Areas and Wildlife (SPAW) in the Wider Caribbean Region, Panama City, Panama, 5 – 7 December 2018, UNEP(DEPI)/CAR WG.40/INF8..

Langin, K. (2018). Seaweed masses assault Caribbean islands. Science, 360(6394), 1157-1158.

Resiere, D., Valentino, R., Nevière, R., Banydeen, R., Gueye, P., Florentin, J., Cabié, A., Lebrun, T., Mégarbane, B., Guerrier, G., & Mehdaoui, H. (2018). Sargassum seaweed on Caribbean islands: an international public health concern. The Lancet, 392(10165), 2691.

Louime, C., Fortune, J., & Gervais, G. (2017). Sargassum invasion of coastal environments: a growing concern. American Journal of Environmental Sciences, 13(1), 58-64. 

Ramlogan, N. R., McConney, P., & Oxenford, H. A. (2017). Socio-economic impacts of Sargassum influx events on the fishery sector of Barbados. CERMES Technical Report 81.

Solarin, B. B., Bolaji, D. A., Fakayode, O. S., & Akinnigbagbe, R. O. (2014). Impacts of an invasive seaweed Sargassum hystrix var. fluitans (borgesen 1914) on the fisheries and other economic implications for the nigerian coastal waters. IOSR Journal of Agriculture and Veterinary Science, 7(7), 1-6.

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