Sargassum Invasion: Frequently Asked Questions (FAQ)
Sargassum is a type of brown marine algae belonging to the Sargassaceae family. Unlike most algae, which are anchored to the seabed, certain species such as Sargassum fluitans and Sargassum natans float freely on the ocean’s surface, forming vast rafts. Unlike benthic algae, which attach to the seabed, these are known as pelagic algae.
At sea, Sargassum rafts provide habitats for many marine species, offering breeding and sheltering zones for fish, turtles, and other organisms. However, when these algae wash ashore in large quantities, they can disrupt coastal ecosystems and require proper management.
Among the many Sargassum species, three are primarily responsible for the massive beach strandings observed in recent years:
• Sargassum fluitans
• Sargassum natans I
• Sargassum natans VIII
These three forms of Sargassum are responsible for the extensive beach landings observed in the Caribbean Sea and the Atlantic in recent years.
For more details, visit our website: Sargassum Monitoring.
Floating brown macroalgae called Sargassum have historically been associated with the Sargasso Sea, a region of the North Atlantic where they form natural rafts that serve as habitats for various marine species. However, since 2011, a new proliferation zone distinct from the Sargasso Sea has emerged: the Great Atlantic Sargassum Belt. This belt spans approximately 8,850 kilometers (5,500 miles) from West Africa to the Gulf of Mexico, representing the largest accumulation of brown algae ever observed.
The formation of this new belt is attributed to changes in oceanic and climatic conditions. Sargassum, previously confined to the Sargasso Sea, now thrives in areas off the Amazon River’s mouth in the Atlantic Ocean. Driven by dominant ocean currents, it drifts toward the coasts of the Caribbean, French Guiana, and other regions, causing massive beach landings with significant ecological and economic consequences.
Thus, although Sargassum is originally linked to the Sargasso Sea, the bloom observed since 2011 mainly originates from this new Atlantic belt, resulting from recent environmental changes.
Scientists are still investigating various hypotheses regarding the cause of this first documented extreme event. One hypothesis suggests that during the winter of 2009-2010, the eastward winds that typically blow from the Americas toward Europe intensified and shifted southward more dramatically and persistently than at any time between 1900 and 2020. This wind shift triggered a long-distance eastward dispersion of Sargassum from the Sargasso Sea toward the Iberian Peninsula in Europe and West Africa. After leaving the Sargasso Sea, the Sargassum drifted southward in the Canary Current and entered the tropics. Once in this new tropical Atlantic habitat—with abundant sunlight, warm waters, and high nutrient availability Sargassum thrived and continued to grow.
Besides wind pattern changes, other hypotheses include a combination of factors such as variations in the flow of major rivers (e.g., the Amazon and Orinoco), the concentration of nutrients (nitrogen and phosphorus) in the ocean, increased phosphorus levels due to Saharan dust, water temperature fluctuations, and river runoff.
Having established a new population, Sargassum now clusters almost every year from January/February into a massive “belt” north of the equator along the trade wind convergence zone. By late winter and early spring, Sargassum shifts northward with seasonal winds and currents. By June, this belt may stretch across the entire tropical central Atlantic. Large portions of these algae are then transported into the Caribbean Sea and the Gulf of Mexico via the North Equatorial and Caribbean current systems.
Since 2011, large accumulations of Sargassum have occurred annually in the Caribbean Sea, the Gulf of Mexico, and the tropical Atlantic. The quantity of these brown algae varies from year to year, but the overall trend indicates a significant increase compared to pre-2011 levels. These Sargassum blooms extend for about 5,000 kilometers (3,100 miles), from the eastern tropical Atlantic to the Mexican coast in the Caribbean Sea. They float in patches of various sizes, ranging from a few centimeters to several hundred meters. Some of these patches reach coastal areas, affecting beaches, ports, and seawater pumping systems.
Several hypotheses have been proposed to explain this increase:
• Climate change: Shifts in ocean currents and rising water temperatures may favor Sargassum growth.
• Increased nutrient input: Nutrients from major rivers like the Amazon, along with particles from African wildfires, may enrich the water and stimulate Sargassum proliferation.
Research programs are underway to better understand these phenomena and improve predictions of future beach landings. Due to the complexity of ocean currents, the vastness of the affected area, and the available data, long-term predictions of this recent phenomenon remain uncertain.
Studies on the impact of Sargassum on human health have only recently begun, and further research is needed to fully understand the issue. However, it is already established that its decomposition releases gases such as hydrogen sulfide (H₂S) and ammonia (NH₃). H₂S, recognizable by its rotten egg smell, can cause eye and respiratory irritation, headaches, dizziness, and nausea, particularly in sensitive individuals.
A study conducted by the University Hospital of Martinique revealed that pregnant women living near Sargassum beach landings face an increased risk of preeclampsia a pregnancy complication characterized by high blood pressure and protein in the urine.
Additionally, Sargassum often contains heavy metals such as arsenic and cadmium, which can be toxic to humans and animals. The accumulation of these substances in the environment raises concerns about their long-term effects on health and ecosystems.
Environmental impact: Once stranded on the coast, Sargassum can smother coral reefs, seagrass beds, and marine fauna, while also covering beaches and contributing to coastal ecosystem degradation. Its decomposition attracts numerous flies and other insects.
Economic impact: Sargassum decomposition produces hydrogen sulfide, whose foul odor discourages beachgoers and harms tourism a key sector in affected regions. Cleanup costs are high for hotels and municipalities, and the image of beach destinations suffers long-term damage.
Sargassum can also disrupt navigation, clog seawater intake systems in factories, and, if it sinks to the ocean floor, potentially affect benthic ecosystems permanently.
Given these multiple impacts, effective management of Sargassum strandings is crucial to minimize consequences for public health, biodiversity, and economic activities.
It is recommended to harvest Sargassum at sea, near the coast, before it washes ashore. This approach helps limit the environmental and health impacts associated with massive beach strandings. When offshore collection is not possible, beach cleanup becomes necessary. However, heavy machinery should be avoided as it removes significant amounts of sand (up to 50%), exacerbating coastal erosion. Collection techniques should be carefully adapted to minimize sand loss and protect coastal vegetation.
Workers involved in Sargassum collection must be protected due to exposure risks to toxic gases released by decomposing algae. Preventive measures include wearing personal protective equipment (PPE), receiving training on toxic gas detection, and conducting regular air quality monitoring at collection sites.
Some local authorities are implementing actions such as regular cleanup efforts, deploying floating barriers to limit beach landings, and monitoring gas concentrations. Research efforts are also ongoing to better understand the phenomenon and develop sustainable solutions.
Yes, several initiatives aim to repurpose stranded sargassum. However, before starting a recycling business, it is important to consider several challenges:
• Irregular arrivals: Sargassum strandings vary in frequency and volume depending on the seasons and years, making the supply of raw material uncertain.
• Local specificities: Each island or country affected by sargassum has its own environmental, economic, and regulatory constraints. Adaptation to local realities is crucial.
• Heavy metal contamination: Sargassum can accumulate heavy metals, particularly arsenic and cadmium, which pose risks to human health and the environment. This contamination limits certain uses, such as food for humans or animals, and requires precautions during valorization.
Despite these challenges, innovative projects are being developed:
• Biogas production: Research is exploring the transformation of sargassum into biogas, providing a renewable energy source. However, the irregular availability of sargassum can make continuous production challenging. To counter this, hotels and other establishments can mix sargassum with plant and food waste, stabilizing the organic supply for anaerobic digestion while promoting sustainable waste management.
• Bioplastic production: Some companies are developing processes to convert sargassum into biodegradable bioplastics.
• Sargassum as compost and fertilizer – opportunities and challenges: Using sargassum as compost or fertilizer requires special attention due to its high salt content and the presence of heavy metals such as arsenic and cadmium, which pose risks to soil fertility and food safety. The salt acts as a natural herbicide, hindering plant growth. Therefore, rinsing sargassum with freshwater is essential before use. However, on islands, freshwater is a valuable resource. Traditionally, Caribbean people would collect small amounts of sargassum and hang them on tree branches to be naturally rinsed by rain before using them as fertilizer, mainly for fruit trees. This method effectively reduced salinity. However, since 2011, the massive influx of sargassum makes it difficult to apply traditional treatment and valorization techniques. In Puerto Rico, the use of sargassum in agriculture and composting has been banned due to soil contamination. To address these issues, some companies have developed processes to convert sargassum into organic fertilizers, offering an alternative to chemical fertilizers while ensuring strict protocols to eliminate toxic residues. The goal is to turn an environmental problem into an economic and ecological opportunity while minimizing risks to the environment and human health.
• Sargassum bricks – a viable solution? Making bricks from sargassum is an innovative way to repurpose these invasive algae. By mixing them with clay, it is possible to create eco-friendly building materials. However, sargassum contains a high amount of salt, which can attract moisture, potentially affecting the durability and strength of the bricks. Salt can also cause corrosion in metal reinforcements used in structures built with these bricks. To mitigate these effects, sargassum must be rinsed with freshwater to remove salt before use. However, in many island regions, freshwater is scarce, making this process less viable. Additionally, access to nearby clay sources is essential—transporting clay over long distances increases costs and the carbon footprint, reducing the potential environmental benefits of this approach. While sargassum bricks are a promising solution, challenges related to salt content and clay availability must be considered. Further research and feasibility studies are needed to determine whether this method can be implemented sustainably and profitably.
Researchers use satellite imagery to identify areas in the open ocean where sargassum density is high and estimate which coastal areas are most likely to be affected. While these observations do not provide exact predictions, they help communities better prepare for massive strandings.
To refine these estimates, scientists analyze ocean currents, winds, and wave conditions that influence sargassum drift. However, identifying these algae from space remains a challenge, as it relies on how light reflects off the ocean surface.
Research is ongoing, led by various organizations, to improve the accuracy of forecasting models and better understand the impact of oceanic phenomena on sargassum distribution.
Sargassum strandings show some seasonality, though this varies by region and climate conditions. Traditionally, massive sargassum landings on Caribbean and Gulf of Mexico beaches occur mainly between April and August, during the warmer months. However, in recent years, strandings have been recorded throughout the year, making predictions more complex.
For example, in 2023, sargassum arrived earlier than usual on some Mexican beaches. This variability highlights the importance of continuous monitoring and adapting management strategies to address this evolving phenomenon. The sargassum arrival maps from Sargassum Monitoring, enriched by citizen science contributions, now show strandings year-round.
Citizen science plays a crucial role in understanding and managing sargassum. By involving citizens in data collection and monitoring strandings, it helps to:
• Improve monitoring: Local observations provided by residents complement scientific data, offering a more precise and real-time view of affected areas.
• Raise community awareness: Citizen participation increases public knowledge of the environmental and health impacts of sargassum, encouraging collective actions to mitigate these effects. Initiatives such as the citizen science by Sargassum Monitoring encourage collaboration between scientists and citizens, contributing to more effective and inclusive management of the phenomenon.
• Support research: Data collected by citizens is a valuable resource for researchers, helping identify trends and develop management strategies.
• Enhance forecasting tools: Thanks to photos and observations provided by citizens, researchers can verify and refine their sargassum stranding prediction models. These data help identify trends, adapt algorithms to local conditions, and improve forecast accuracy, providing more reliable alerts to impacted communities.
Predicting the future of sargassum strandings is complex due to the variability of environmental factors involved. Recent observations indicate a trend of increasing massive strandings since the early 2010s. This rise is attributed to various factors, including climate change, changes in ocean currents, and nutrient enrichment in the water.
Research initiatives aim to improve understanding of sargassum blooms and develop short- and long-term forecasting models. These efforts are essential for anticipating strandings and implementing effective management strategies.
Despite ongoing research, the future of sargassum strandings remains uncertain. Continuous monitoring and flexible management strategies are crucial to adapting to potential variations.
To track sargassum strandings and impacted periods, visit the interactive maps on Sargassum Monitoring’s website. Since 2018, the site has provided annual maps of sargassum landings, enriched with geotagged and dated photos and videos from engaged citizens. These maps offer a visual record of past and present strandings across 43 countries in the Caribbean and beyond.
These resources are valuable for planning travel while considering areas that may be affected by sargassum.
Swimming in areas overrun by sargassum is not recommended for several reasons. As sargassum decomposes, it releases gases such as hydrogen sulfide, which can be harmful to health. Additionally, the large presence of sargassum can cause physical discomfort, such as skin irritation, making swimming unpleasant. It is advisable to avoid affected beaches and opt for those that are free from sargassum.
Walking your pet in areas covered with sargassum is not recommended. The decomposition of these algae releases gases such as hydrogen sulfide (H₂S), which can be harmful to both human and animal health. Additionally, decomposing sargassum emits a strong odor, making the experience unpleasant for you and your pet.
• Participate in citizen science: Report sargassum strandings by sending your photos to Sargassum Monitoring or sharing them in their Facebook groups.
• Reduce pollution: Limit chemical fertilizer use and avoid polluting waterways to reduce nutrient runoff that fuels sargassum blooms.
• Support Sargassum Monitoring by donating to help develop detection tools and share information.
• Join local cleanup efforts, following safety guidelines to avoid exposure to toxic gases.
• Educate your community on the impacts of sargassum and promote eco-friendly practices.
These actions allow you to actively contribute to sargassum management and environmental protection.
Currently, in 2025, 43 countries and islands are receiving massive arrivals of sargassum.
• Anguilla
• Antigua & Barbuda
• Aruba
• The Bahamas
• Barbados
• Belize
• Bermuda
• Bonaire
• Brazil
• British Virgin Islands (BVI)
• Canary Islands (Spain)
• Cayman Islands
• Colombia
• Côte d’Ivoire (Ivory Coast, Africa)
• Cuba
• Curaçao
• Dominica
• Dominican Republic
• French Islands: Guadeloupe, Martinique, Saint Martin, Saint Barthélemy, Marie-Galante
• The Gambia (Africa)
• Ghana (Africa)
• Grenada
• Guyana
• Haiti
• Honduras
• Jamaica
• Liberia
• Mauritania
• Mexico
• Montserrat
• Panama
• Portugal & Madeira
• Puerto Rico (USA)
• Saint Kitts & Nevis
• Saint Lucia
• Saint Vincent & the Grenadines
• Senegal (Africa)
• Sint Maarten
• Trinidad & Tobago
• Turks & Caicos Islands
• USA
• US Virgin Islands (USVI)
• Venezuela
Go further
• Regularly visit sargassummonitoring.com for maps, alerts, and forecasts.
• Join the Sargassum Monitoring movement to actively participate in sargassum monitoring and management—together, let’s protect our oceans.
IMPORTANT:
The science and management of sargassum are constantly evolving, leading to regular updates to our Frequently Asked Questions (FAQ). As an independent organization, Sargassum Monitoring is committed to providing reliable and up-to-date information on this complex phenomenon. We encourage you to check our FAQ regularly to stay informed about the latest developments and updated answers to your questions.