Exploring the mysterious ocean realm of Sargassum seaweed and its potential to help capture carbon, combat acidification and create biomaterials

In the second in a series of posts created in partnership with local scientists, Brazil coordinator Thais Gonçalves delves into the mysterious world of Sargassum – the vast, floating mats of seaweed that give the famous Sargasso Sea its name. In this interview with Paulo Antunes Horta from Universidade Federal de Santa Catarina, we explore the potential for such seaweeds to capture huge quantities of CO2, improve ocean health and even create new biomaterials.

Q & A

What is Sargassum and where is it found?

Among seaweeds, Sargassum is one of the easiest to find. In a shallow dive, you are likely to see browny marine plants – and that is Sargassum. It is quite well known in the Caribbean and here in Brazil, and most of the “marine forests” underwater, specially in the west Atlantic, are formed by Sargassum.

The sargassum that lives in the open ocean – is it the same as that found on rocky reefs?

We now know, by molecular marker analysis, that we have different kinds of Sargassum species, but we don’t have full genomes yet. In Brazil, we couldn’t find significant differences between samples from rocky shores and on the floating Sargassum masses – these floating “islands” of 8000 km long in the Atlantic that start in Africa, pass in front of the Amazon and reach the Caribbean. Of course, that is always changing due to climate change and all the land uses we have in the Amazon. These huge masses are influenced by the runoff with all kinds of fertilizers that comes from the Amazon region.

Is the Brazilian Sargassum sea connected with the more famous North Atlantic region?

When it comes to species, some scientists believe that there are three species in the floating Sargassum masses in the Central-North blooms and only two species in the South Blooms. But they are quite similar overall, and we need to study them better. We really do not know if the Sargassum of the South Atlantic was always there, and now they are more or less connected, or if it has a different origin. We need to investigate the source of all the Sargassum seas – both the one in the South and the Sargasso Sea in the North Atlantic.

Are there a lot of species and endemic species associated with this sargassum sea?

Yes, we have a lot of invertebrates and a few fishes as well – but what we have the most are cryptic diversity, species that we do not know quite well yet. There is a lot to discover and research groups from Europe to the Caribbean and South America are getting together to investigate that. So we expect a lot of exciting news in the near future.

What is the relationship between Sargassum, carbon dioxide and climate change?

When Sargassum is growing, it is taking CO2 from the water and thus increasing the PH of the ocean, which helps with the problem of ocean acidification. By taking CO2 from the water, it also helps the ocean to absorb more carbon from the atmosphere. So we are learning that if we work well and get global collaboration, we can have Sargassum extracting CO2 and sinking, every year, removing the same amount of biomass that we have in all of the world's mangroves. That’s a lot of biomass that can sink and sequester carbon, but there is also a lot that can be done with that biomass, like bioplastics – shoes, masks, etc. It is a way of transforming a problem, because Sargassum blooms can also turn into a problem for tourism and for the economy, into a solution. In a way, it is also an opportunity to help local people and the government.

Would projects like that require more Sargassum to grow or could they use existing stocks?

We can start with the existing ones, but it is also possible to cultivate Sargassum – mainly on oil platforms. That was an idea that our research group discussed with MIT and I believe they are exploring it right now.

What is the relation between the Amazon and the Sargassum in the Caribbean?

Around 2010, when Brazil started to explore and export more iron from the Amazon, it increased deforestation as well. All that still happens today, as most people know about deforestation in the Amazon. With deforestation, the soil gets exposed and every time it rains, the runoff washes away nutrients from the soil. So the Amazon River water right now is leading to eutrophication — excessive input of nutrients — into tropical waters, causing the rapid proliferation of Sargassum blooms. Our research has shown that deforestation is deeply connected to the change in quality of the runoff and eutrophication of the ocean – which affects the marine ecosystem as a whole. It’s happening mostly in Brazil, but it affects Mexico, the Caribbean islands, the US, Africa – and really the entire globe. We have small islands that are ruined because of eutrophication problems, and to solve this problem will require global efforts to really find the origin and deal with the causes.

What benefits does Sargassum bring to the oceans?

These floating “forests” create many habitats. When we look to a forest on land, we see birds, monkeys, all different kinds of animals using trees. The Sargassum has the same role in the water. Fishes, invertebrates, a lot of animals, a lot of life needs and uses the Sargassum as food, as a home.

There are all the benefits of the biogeochemical process , the sink of CO2 and all that, and we have studies showing that Sargassum seas in a region lead to more fish, more life and that positively impacts the local fishing industry. Of course, when we upset the balance, and we have a Sargassum bloom, we are going to have to deal with the problems. And the problems are quite big – I’m talking about one meter tall piles of seaweed over an entire beach. That same amount of Sargassum covering a reef is going to mean no oxygen and no sun – and the reef dies. So the benefits are huge, but considering the fertilization and eutrophication of our oceans that we face right now, it is also a big problem.

What can we do about it?

First, we need to change each of us. Everyone is responsible for the pollution. Is your house plugged to the local sewage system? Are you doing your part? After we take care of our primary home, we need to talk about governments – from local and regional to national scale. It is all political and we need to remember we are always sending a message. Finally, we need agreements to give the local people the right tools to deal with the problem. There are a lot of new techniques to deal with Sargassum blooms now. People in Mexico, for instance, are building houses with Sargassum biomass! It can be a big problem – but there are lots of solutions as well that we need to make available.

Special thanks to Marcos de Lucena and Beatriz Mattiuzzo.