Huge carpet of algae drifts towards the Caribbean
Millions of tonnes of brown algae are approaching the coasts around the Caribbean and the Gulf of Mexico. The problem seems to be getting bigger every year.
The satellite images do not bode well: around 20 million tonnes of brown algae are drifting towards the coasts of the Caribbean, Florida and Mexico in March 2023. The algae belt already stretches over 8,000 kilometres across the Atlantic. The first carpets of Sargassum brown algae have already washed ashore - unusually early in the year. 2023 is also likely to be another year with strong brown algae blooms, write scientists led by Chuanmin Hu from the University of South Florida in the Sargassum Outlook Bulletin.
Floating Sargassum carpets are natural components of the Atlantic Ocean and provide food and shelter for many animals on the high seas. Since 2011, however, these carpets have spread enormously and regularly extend over thousands of kilometres from the West African coast to Brazil, Venezuela and further into the Caribbean and the Gulf of Mexico. 2023 could set a new record: From November to January, the area of flowering has doubled every month. And despite smaller declines until February, this expansion still corresponds to the distance from the east to the west coast of the USA.
On the high seas, trapped air bubbles ensure that the seaweed floats. On land, however, it rots quickly, releasing large quantities of hydrogen sulphide: a toxic gas that smells like rotten eggs. The spread and expansion of brown algae are subject to seasonal rhythms, with more brown algae now travelling in the water during the actual low point of the cycle than before 2011 at the peak of the spread. So far, 2018 and 2022 have set new records.
Scientists are still puzzling over the causes of the explosive increase in brown algae blooms. A study from 2019 suggests a connection with the rampant deforestation in the Amazon and the increase in agriculture there. Large quantities of fertiliser that are spread on the deforested areas for the newly planted soya fields end up in the sea via the Amazon. There, the nutrients fuel the growth of the algae and regularly lead to new blooms.
The Atlantic may have reached a tipping point for this in 2011: factors that previously kept brown algae out of the tropical area of the ocean now only play a role in influencing the size of the carpet, for example when the sea surface becomes too warm for the algae or rising deep water off Africa and the sediments of the Amazon provide few nutrients. In its current state, researchers fear that the Sargassum bloom will form an integral part of the ocean.
For countries in the Caribbean that depend largely on tourism, this is bad news: They have to spend a lot of money to dispose of the piles of stinking algae that wash up on the shore, and at the same time lose tourists who are put off by it.
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Cover photo: © jaminwell / Getty Images / iStock (detail) For about five years, brown algae have increasingly become an ecological and economic problem in the Caribbean. 2023 could bring a new peak.
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