The sargassum invades the coasts due to marine currents and winds that push them towards the shores. These algae proliferate due to rising water temperatures and the presence of excess nutrients in certain oceanic areas.
The large invasions of sargassum often begin in the heart of the North Atlantic, specifically in an area called the Sargasso Sea. However, in recent years, a new hotspot has formed further south, between Brazil and West Africa, significantly increasing the accumulation on our beaches. Researchers believe that these immense floating mats mainly result from rapid proliferations due to a high availability of nutrients, such as nitrogen or phosphorus, which are present in large quantities in the water. These nutrients often enter the sea through rivers originating from agricultural lands or urban discharges. As a result, these algae grow quickly, drift in large compact mats carried by the currents, and ultimately wash up on Caribbean, American, or African coasts in large quantities.
Climate change is warming ocean waters, creating ideal conditions for sargassum, which thrives in this environment and reproduces at an astonishing rate. Additionally, our human activities, including intensive agriculture and the massive use of fertilizers, lead to the release of tons of nutrients such as nitrogen and phosphorus. These substances wash into the sea and become a veritable feast for these algae that were not asking for so much. As a result, they proliferate wildly, forming huge floating mats that later blanket our beaches and cause a lot of trouble.
Sargassum is carried by certain major ocean currents, notably the North Equatorial Current and the Gulf Stream, which act like oceanic conveyor belts, facilitating their movement towards the shores of the Caribbean and the Gulf of Mexico. And of course, the prevailing winds, such as the trade winds blowing from east to west, also push these floating algae towards the shores. When these currents and winds are strong and consistent, they promote a massive and regular influx of sargassum on certain specific coasts. In contrast, weaker currents or unusual atmospheric cycles can temporarily concentrate large quantities of sargassum in open sea, creating true floating "rafts" ready to reach land when conditions change.
These brown algae have an impressive ability to reproduce rapidly through fragmentation. A simple detached piece of algae can be enough to form new gigantic clusters. Their growth is particularly accelerated thanks to an excellent capacity to absorb nutrients, especially nitrogen and phosphorus, which are abundant in certain areas of the ocean. And that's not all: they benefit from a nearly total absence of significant natural predators in the open sea to curb their proliferation. Another serious advantage is their flotation system made up of small gas-filled vesicles that allows them to stay constantly on the surface, right in the perfect spot to capture maximum light essential for their photosynthesis. It’s safe to say they have all the cards in hand to joyfully invade our coasts...
Eutrophication is when the oceans receive far too many nutrients, primarily due to agricultural fertilizers, but also from domestic and industrial discharges. All these additional nutrients — especially nitrogen and phosphorus — stimulate rapid growth of marine plants, such as sargassum. As a result, these algae proliferate and have plenty of food to grow at an astonishing rate. Essentially, the more nutrients in the water, the more it becomes an all-you-can-eat buffet for sargassum, further accelerating their invasions on the beaches. This vicious cycle becomes a real problem for coastal ecosystems and tourism.
Currently, researchers are studying how to transform sargassum seaweed into useful resources, such as biofuels, natural fertilizers, or even biodegradable paper.
The gas produced from the decomposition of sargassum accumulated on the shoreline, primarily hydrogen sulfide (H₂S), can not only create a strong unpleasant odor but also cause eye and respiratory irritations in humans at high concentrations.
Once limited to the Sargasso Sea in the North Atlantic, recent massive blooms of sargassum mainly occur further south in the tropical Atlantic, linked to changes in oceanic and climatic currents.
Some community initiatives use stranded sargassum seaweed to create eco-friendly construction materials, thereby generating new local economic opportunities while cleaning up the beaches.
Satellite observation systems and predictive models currently exist to anticipate massive strandings. However, accuracy remains limited by the variability of ocean currents and weather conditions.
Currently, the management of strandings primarily involves the manual or mechanical removal of seaweed washed up on the beaches. Experimental techniques such as floating barriers or economic valorization (fertilizer or biofuel) are being developed.
Absolutely. Sargassum seaweed has potential to be transformed into natural fertilizers, bioenergy, or even cosmetic products, thereby providing a possible economic and ecological valorization of this resource, which has been particularly problematic until now.
No, not all regions are equally affected. The Caribbean region, the Antilles, and certain coastal areas of West Africa are particularly impacted by these invasions, mainly due to ocean currents, regional weather phenomena, and high nutrient inputs.
Yes, as they decompose on the beaches, sargassum releases hydrogen sulfide (H₂S), a potentially toxic gas that can cause respiratory and eye irritation, as well as headaches with prolonged exposure.
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