For more than 10 years the coasts of the Caribbean Sea have been affected by the large amount of sargassum that arrives from offshore, occupying a central place in the lives of thousands of people.
But what is sargassum, where does this algae come from, why do these quantities reach the beach, what can be done with them, and many other questions become especially relevant, especially when we talk about the social and environmental impacts of Climate Change.
The economic and ecological consequences of sargassum in a region as important as the Caribbean Sea must be addressed based on scientific evidence, as well as with the support of authorities and affected communities, including the tourism sector and coastal communities.
At BioPlaster Research we work to develop a productive ecosystem driven by scientific innovation with the objective of an intelligent, responsible and sustainable use of this shared natural resource that adds to the efficient and effective management of these macroalgae.
What is Sargassum?
Sargassum is a brown macroalgae of the genus Sargassum, of which more than 350 species have been identified around the world (Guiry & Guiry, 2019).
The two species found in the Caribbean Sea are Sargassum natans and Sargassum fluitans, which were scientifically described just under 200 years ago in the tropical Atlantic Ocean (Agardh, 1821; Gaillon, 1828; Børgesen, 1914).
These two algae are unique within the genus Sargassum, as they are able to complete their entire life cycle floating on the sea surface, also called holopelagic (from "holow" 'all', and "piélagos" 'sea') (Smetacek & Zingone, 2013), so they have never been fixed to the bottom (they have no attachment organ like other types of algae, such as kelp).
Where does sargassum come from?
In a natural way these algae are distributed in the central region of the Atlantic Ocean, between The Bahamas and the Azores Islands (Deacon, 1942; Franks, et al., 2016), forming an area called the Sargasso Sea.
Due to the extent of area where these algae are found, they are important breeding grounds, refuge, habitat, food and transport for a great diversity of fish, mollusks and crustaceans (Farrel et al., 2014; Huffard et al., 2014), providing the oceanic ecosystem with environments conducive to connectivity between ecosystems and between species.
Unprecedentedly, since 2010 there have been immense upwelling of these algae, it is believed that the current conditions in the region cause these algae to multiply at an accelerated rate. The region is affected by the large amount of nutrients from both distant and nearby sources in the Caribbean Sea. From the tributaries of the Amazon and Niger Rivers, the mining industry in Central America, and the large amount of wastewater from coastal developments along the coasts.
Massive sargassum arrivals
The arrival of sargassum on the coasts of the Caribbean Sea and the Northern Gulf of Mexico in small quantities occurs naturally from an ecological point of view. The degradation of sargassum on beaches contributes to the biogeochemical cycle, contributing nutrients to coastal waters (Olabarria & Vázquez, 2018). In 2011, the first events of massive arrival of sargassum on the beaches of the Caribbean Sea were recorded, starting in the Lesser Antilles (North of Venezuela), which brought great local affectations, mainly to the tourism, fishing and environmental sectors.
Between April and August 2011, the first massive aggregations of sargassum appeared in northern Brazil, with peaks in July, returning to low levels in October.
For 2017 and 2018, sargassum growth was estimated at 15 million and 32 million tons, respectively. This concentration has been named The Great Atlantic Sargassum Belt (Wang et al., 2019), which reached maximum extensions close to 9,000 km, from the African coasts in Sierra Leone to the Gulf of Mexico.
Although the Sargasso Sea maintains populations in the Atlantic Ocean, the likely source of sargassum associated with the massive upwelling during 2011 is located northeast of Brazil, transporting the algae into the Caribbean Sea via the North Brazil Current, the Guyana Current, and the Antilles Current (Frank et al., 2012).
The Sargasso Sea Alliance seeks the conservation and protection of this unique ecosystem by considering it as 'a golden rainforest floating on the surface of the Atlantic Ocean, an oasis of marine life and the only landlocked sea, which contains endemic species such as Sargassum and many others that have specially adapted to life amidst this floating canopy' (Laffoley, 2011).