Sargasses : le cauchemar des Caraïbes | Alerte Verte

Hello, I am Pascal Jean-Lopez and I would like to raise awareness about sargas. Are you familiar with Sargassum seaweed? In Brittany, we have green algae and in the Caribbean, we have their cousins, Sargas. Sargassum are brown macroalgae that live on the surface of the ocean. And so every year there are these phenomena where they leave from Africa, they come to make massive invasions across the entire Caribbean. The quantities are relatively monstrous. This natural phenomenon has exploded in recent years. According to satellite observations, the amount of sargas regularly exceeds 10 million metric tons per month. There are different hypotheses to explain these changes in Sargas's echem. It was 2011 with a change at that time in ocean currents, upwelling of deep currents, supply of nutrients, growth of algae. The other hypothesis is obviously the anthropization of the sea and in this case nitrogen from agriculture, such as off the coast of the Amazon river, which will be released into the marine environment. We can have piles of sargas that exceed the master and over increasingly longer periods. And the problem with these piles of sargassum is that it ferments and smells really bad. Therefore, the degradation of sargas, particularly the putrefaction of sargas, will lead to the production of two types of gas. Hydrogen sulfide smells like rotten eggs and ammonia H3, which is also an acidic gas. And so this acidity that is released by the gases can have consequences for humans. People who live or work on the sargas, for example, get headaches. It also has a rather surprising impact. This same acidity, which can potentially affect human health, will also affect household appliances. With corrosion of household appliances, refrigerators stop working. Sargassum seaweed has a huge impact on tourism. It has to be said that these brown algae on the white sand totally disfigure the paradise beaches. People will come less during the sargassum seaweed season, with consequences for the hotel industry, and obviously consequences for restaurants. There are ports where boats can no longer be taken out. This can also have consequences on property prices. Today, nobody is going to want to buy in areas that are invaded by Sargas for about 6 months of the year. So, what do we do with this sargassum? Essentially, they need to be removed. It's done with a tractor, mechanical shovel, it's done with a bulldozer, it's done, we should say, a little bit as best we can. It's also handmade. People used to come with pitchforks to remove the sargassum, and so once this sargassum is collected, well, we're going to store it on land at sargassum storage sites to let it degrade more or less naturally, but is this a long- term solution? Can we just let the sargassum degrade like that? We initially looked at the heavy metals that were present in these sargassums and we saw the presence of arsenic. Arsenic, that could give me some ideas. And so at these storage sites, obviously the arsenic that is present will flow from the sargassum as the sargassum degrades. And so this arsenic will obviously run off and then contaminate the soil locally. But that's not all. Sargassum seaweed comes with its microbiota, that is to say its bacteria, viruses, small cells, and associated microorganisms. And so this could potentially disrupt the environmental microbiota. The presence of bacteria potentially pathogenic to humans has been demonstrated. It is also contaminated by a pesticide that was widely used until the 1990s for banana cultivation. So, unfortunately, this is a characteristic of the past. Chlorine is a pesticide that's causing problems. This insecticide is now considered carcinogenic and harmful to the environment. What can be done with sargassum contaminated with chloreconium? The answer is nothing at all. If we want to make use of this sargas, it's possible, but we need to get rid of this chore of eco. Because what did you want to do with that sargassum? There are several ways to valorize it that have been considered. There are potentially organic amendments, there are fertilizers, there is the potential to make plastics, to use it as a material for construction, and so I think the future of valorization is important. However, the implementation of this valuation remains relatively complicated for small island states or for small islands on the scale of the Caribbean. Thank you Pascal Jean-Lopez. We now know much more about these brown algae. Have you ever seen sargassum seaweed? Tell us in the comments.