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Algae flood in Mexico and the Caribbean – curse or opportunity?

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More brown algae are washing up on the beaches of the Caribbean and Mexico than ever before. This threatens coastal ecosystems and tourism. At the same time, the algae could help in the fight against the climate crisis.

Huge carpets of algae spoil the holiday mood on the beaches of Mexico

Anyone who wants to swim in the sea in the Caribbean or on the Gulf of Mexico at the moment has to first fight their way through a meter-wide carpet of algae , more precisely by brown algae of the genus Sargassum. Even barriers in front of the beaches or interception in the sea were not enough to cope with the immense crowd, reports the German Press Agency.

And so wide strips of algae pile up on many beaches and spread an unpleasant stench. It is hydrogen sulfide that is produced when they rot – and it can be life-threatening, as cases from Brittany show, where you also have to struggle with algae floods again and again. 

How dangerous is an algae flood the coast? 

If the brown algae were not properly dried and disposed of, further problems would arise, says Mar Fernández-Méndez from the Alfred Wegener Institute, the Helmholtz Center for Polar and Marine Research based in Bremerhaven, Germany. There she researches the carbon cycle of the sea.

“As the algae rot, they also release carbon dioxide (CO2) and methane, which fuels climate change. They also release toxic substances like arsenic that they picked up from the sea – and these can poison groundwater.” But especially in the poorer states of the Caribbean, it is often the case that you simply clear a piece of the jungle and leave the stinking masses there to themselves – the main thing is to stay away from the coast.

Not much is growing under this dense carpet of brown algae

The algae floating in the water also changed the coastal ecosystem, explains the scientist. “The washed-up Sargassum carpets hardly let any light into the water, and oxygen is also becoming scarce because bacteria consume oxygen when they rot in the water.” Not only did various sea creatures suffer, but also mangrove trees and corals. 

No end to the current algae plague in the Caribbean in sight

Satellite observations suggest there is more Sargassum than ever before this time of year. This is in the so-called Great Atlantic Sargassum Belt (GASB), which at peak times stretches from the coast of Florida through the Gulf of Mexico via the north coast of South America to West Africa. According to the University of South Florida, around 13 tons of the free-swimming brown algae drifted from the central Atlantic towards the Caribbean at the end of March.

“Sargassum populations increase in spring and summer, when conditions are more favorable for growth (from sun and heat – ed.'s note) so flowering this year is likely to be stronger than the peak year of 2018,” says Brigitta van Tussenbroek. She is a senior researcher in the Department of Reef Systems at the National Autonomous University of Mexico, specializing in seagrasses and macroalgae.

Peak flowering is expected in June or July. It is difficult to predict when and where the algae will later be washed ashore.

Overall, it can be said that the algal bloom has increased since the GASB was created in 2011, says van Tussenbroek. That means: The problem of the algae glut is likely to increase.

What is the reason for the strong algae growth in the Atlantic? 

Sargassum originally comes from the Sargasso Sea, east of Florida, where brown algae have always existed. Due to changes in the winds and currents in the North Atlantic caused by man-made climate change, part of the Sargasso Sea was pushed southwards in 2011 and reached the tropical Atlantic. There the brown algae found favorable propagation conditions: lots of sunlight, high water temperatures and nutrients. 

Scientists have not finally clarified why the algae spread so rapidly. However, it is clear that the increased CO2 concentration in the atmosphere alone increases the growth of algae – like that of all plants, according to Fernández-Méndez. In addition, global warming is accelerating all biological processes, including in the sea, emphasizes Florian Weinberger, who is responsible for the area of ​​marine ecology at the GEOMAR Helmholtz Center for Ocean Research in Kiel, Germany. 

The brown algae not only make walking on the beach tedious – dangerous substances are produced when they rot

“But in principle Nutrient inputs into the oceans are generally increasing. So far this hasn't been a problem in most parts of the world because the sea was able to dilute the nutrients – but eventually a limit will be reached here too.” 

A current study from the USA shows that in the past few decades, immense amounts of nitrogen compounds, mainly in the form of ammonia, have entered the oceans, mainly from excessive use of fertilizers in agriculture. The proportion of this gaseous nitrogen compound  was about 89 percent higher in 2018 than in 1970, the research team reports. 

How can algae growth be stopped?

Filter systems could help that fewer nutrients get into the ocean, explains Florian Weinberger. But even if all entry were stopped immediately, it would take many decades before this would lead to a measurable change in the marine environment. “In Denmark, it took more than 30 years for government-imposed fertilizer limits to improve coastal waters.” 

“We have to stop blowing so much CO2 into the atmosphere, i.e. stop global warming,” emphasizes Fernández-Méndez. But even then, the effects on algae growth would only set in very slowly. 

Algae farms in aquaculture: salvation against climate change?

As surprising as it may sound given the current situation: Mar Fernández -Méndez and Florian Weinberger want to ensure that even more brown algae grow in the oceans in the future. Because the two researchers are convinced that the algae could be important and perhaps decisive helpers in the fight against global warming and climate change. 

For one thing, floating algae reflect more sunlight than the open ocean, which could potentially lead to a drop in global temperature as the algae cover increases. On the other hand, according to Fernández-Méndez: “Sargassum absorbs a lot of CO2 and stores it very quickly. Its potential to draw carbon out of the atmosphere is extremely high.” An “afforestation” of the oceans with brown algae in aquaculture has the potential to absorb 64 gigatons of CO2 per year – if all suitable maritime cultivation areas could be used.

To classify: According to a special report by the Intergovernmental Panel on Climate Change (IPCC), the Paris climate target of curbing global warming to 1.5 degrees can only be achieved if CO2 is actively removed from the atmosphere. This so-called carbon dioxide removal, CDR for short, must therefore be between 100 and 1000 gigatonnes of CO2 over the course of this century.

In order for the CO2 stored in the algae to remain bound for a long time, the algae would be pressed into balls and then sunk into the deep sea, where over time the carbon would be covered by sediment on the sea floor and could remain for more than 1000 years.

However, the targeted and limited cultivation on the open sea has so far been technically difficult, above all because of the often high waves and strong winds, Weinberger admits. 

Brown algae as real all-rounders

But even if brown algae were cultivated on a smaller scale in aquaculture, there would be many advantages. “Brown algae contain certain polysaccharides that have very good gelling properties – this is of particular interest for the cosmetics and food industries,” explains Weinberger. Above all, they can be used to produce biogas and bio-oil, which can replace fossil raw materials such as natural gas or crude oil and thus also fossil plastic. 

Whether as a gelling agent or as a raw material for biogas: brown algae are interesting for many branches of industry

“There are already many small to medium-sized initiatives to produce commercial products from sargassum that washes ashore, such as building material and biomass,” says Brigitta van Tussenbroek of the National Autonomous University of Mexico. However, they have so far lacked sufficient support. 

And there is another very practical problem with using the biomass from the brown algae glut, reports Mar Fernández-Méndez. “You never know in advance exactly how much sargassum will wash up, when and where. This prevents these initiatives from being able to sign long-term contracts, for example with cosmetics or construction companies.” Here, too, according to the scientist, cultivation in aqua farms could help to keep the required minimum quantities available.

Editorial: Tamsin Walker


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