Sargassum superblooms are choking coastlines around the Atlantic

What is sargassum seaweed

0:00Hey, it's Flora, and you're listening to Science Friday. An unwelcome visitor is arriving on beaches from West Africa to the Caribbean, Brazil to Florida. I will give you a hint. It's brown, it's stinky, and it's more abundant than ever. Sargassum, a type of free-floating seaweed. It's become a major problem for coastal ecosystems, communities, tourism, and infrastructure.

0:30So what is fueling the sargassum superbloom, and is there anything to do about it? Joining me now is Dr. Brian Barnes, satellite oceanographer at the University of South Florida, who studies sargassum. Brian, welcome to Science Friday. Thanks so much for having me, Flora. Thanks for being here. Introduce us to sargassum. What is this seaweed all about? How should I picture it? Yeah, so sargassum is a floating macroalgae. So it's macro meaning it's big enough you can hold it in your hand. And if you were to grab it, it kind of feels like a bunch of prickly blades of grass.

1:03And he's got these little like pea-sized floaty structures in it. And that's what keeps it at the surface of the ocean. It's been around for a long, long time. The first recorded observations that we have of it are from the Columbus days, the first trips across the Atlantic. And this is really a habitat in the middle of the wide, vast ocean. This is kind of like an oasis of life and activity in and amongst the sargassum rafts that are created. So is the Sargasso Sea its epicenter, its HQ?

1:35Yeah, historically, yes. So the Sargasso Sea is off the eastern coast of North America. And this is the area that was so named the Sargasso Sea because of this sargassum macroalgae. The little floaty bits in it are resembled to Columbus grapes. And so there's this grape in Portuguese is sargasso. The Great Atlantic Sargassum Belt is something that is a new occurrence. It's not this historical habitat that we know dates back to Columbus days. Instead, it stretches from the west coast of Africa through the Caribbean into the Gulf of Mexico and then out into that Sargasso Sea area.

2:14But we never saw before this type of bloom in the records that we have in the oral histories and the satellite data. Instead, in 2011 was the first time we observed this bloom, and it's really been getting bigger and bigger ever since. Yeah. So when you say bloom, what do you mean? I mean, how has its abundance changed in recent years? Yeah. So a bloom is an extension of the biomass, and it happens seasonally for most things. Just like a plant, you have a life cycle whereby you have a growth phase and then some die back in the wintertime, perhaps.

2:47The sargassum goes through the same type of cycle. And what we see now every summer is that there is an expansion, a growth of the sargassum, and impacts on the coastal environments in the Caribbean and so forth. And more so than just the seasonal expansion and decay, we now have kind of a trend where every year that expansion reaches higher and higher heights, larger and larger abundances. Do we know what's driving the boom? Yeah, it's really hard to tell. So there's evidence that suggests some of the initial growth may have been supported by some deep water mixing.

3:23So in the ocean, the deep water generally has more nutrients, and if you have a good wind blowing over it, it can mix some of those nutrients up into the surface water and make it available for sargassum. There's also tons of rivers in the area, like the Amazon and the Congo and the Orinoco. These rivers can provide nutrients that can be used by the sargassum. And then finally, that kind of community of life that exists in and amongst the sargassum, it kind of recycles nutrients within that own ecosystem such that sargassum can continually support and sustain its own growth.

3:58So like there could be a snowball effect, basically. Exactly. Hmm. It's complex. Always. So you mentioned this community of life that it supports. You mentioned that animals hide in it. Does anyone treat it like a salad bar? Like does anything eat it? Yeah. Yeah, of course. There are things that eat it, and there are, you know, secondary consumers that eat those things hiding in and amongst the sargassum. So it's a huge, as I said, an oasis of life in the middle of the Pelagic Ocean.

4:30There's structure, there's food, there's community and larger populations that span all the way from invertebrates all the way to fish and birds and mammals, marine mammals.

When seaweed becomes a problem

4:41So far, sounds great. When does it become a problem? Right. So this is the tricky problem. It's got a duality. Sargassum out in the open ocean, it's a beneficial habitat, and it's actually classified as essential fish habitat, which limits the amount that you can tamper with sargassum when it's out in the open waters. But the problem is, especially in these new environments that don't have a history of sargassum, at least not these levels of sargassum, that sargassum can wash ashore and start to have kind of cascading effects, negative effects on the local ecosystems, economies, and so forth.

5:18Give me some specifics around that. How does it become a problem? Yeah, so sargassum, it comes in sometimes to particularly beach communities or coastal communities in huge aggregations, thousands of tons of sargassum, and it kind of is just this floating mass. So if you have something like corals or seagrasses that are on the bottom, these can get shaded by the sargassum that's overlaying it, or if the sargassum's thick enough, it can get actually physically smothered by that sargassum biomass. Sargassum, as it kind of gets further up on the beach, piles up on the beach, we're talking feet high of sargassum just piled up on beaches, you know, all of those critters that lived in and amongst the sargassum are in trouble because they're no longer necessarily in the water, as well as, you know, for turtles.

6:05Turtles use the sargassum when it's offshore, but if you have something, a huge barrier of sargassum preventing a young turtle hatchling from getting from the beach where it's hatching out into the water as it would start its next phase of life, there's another huge impact in these coastal ecosystems. It also starts to decay. When the biomass comes ashore, it starts to rot, decay, it releases a terrible smell that's awful for residents and tourists. And also that decay can also make a T or a brown tide, as we call it, that impacts the water quality for the local ecosystems as well.

6:42What's this year been like? This year was pretty bad. It was the second worst overall abundance that we've ever observed in the Great Atlantic Sargassum Belt. The largest bloom that we had ever seen was last year. But the difference between last year and this year is that instead of a lot of the sargassum being in the more offshore areas, there were a lot more sargassum in these areas that was available to wash ashore and impact the communities. So there are these negative effects on ecosystems, on infrastructure, fishing, tourism.

Solutions and satellite forecasting

7:15Are there solutions? Can it be used for something? Yeah, it's tricky. And there's a huge effort towards valorization, turning the sargassum problem into something positive, or at least reduce the negative aspects of the sargassum. But? Yeah. The problem is, you know, as we talked about the decay of sargassum, the more kind of a fresh material decays, the less value it has, the less ability you have to turn it into something of value. So you have to be very responsive to where sargassum is coming ashore.

7:48Sargassum impacts are generally pretty patchy. You may see a lot of sargassum in one beach and not on an adjacent beach. So you have to be very responsive to where the sargassum is coming from, how quickly you can pull it out of the water and try and translate it into any of these products. What about getting it before it reaches the shore? Yeah, that's often one of the best ways to really ensure that you're getting that fresh, the fresh part of the sargassum. But it does come with costs. You have to establish barriers, typically, that will kind of prevent the sargassum from coming directly into the shore.

8:24And then you have to go collect it offshore, which is much more costly than if you were to wait for it to come all the way to shore. But again, you're increasing the amount of value that you can potentially get out of your sargassum and reducing the impacts of the sargassum as it comes into the coastal ecosystem. I'm hearing a lot of challenges, Brian. Do these approaches seem viable to you?

8:46It's yes and no. It is something that we have to do. Essentially, necessity is the mother of invention in this scenario. We have to deal with this. And so we are trying to overcome these challenges in various ways by, for example, using satellite data to identify individual patches and make decisions as to whether or not those will come ashore. And thus, those would be the ones that we need to prioritize for offshore collection. There's also, in this context, there's a regulatory framework that is really difficult to deal with.

9:20Again, you have to make that decision of where sargassum, when is it going to change from being that essential fish habitat to being a harmful algal bloom. And this is your work, right, as a satellite oceanographer. Are you sargassum forecasting? Yes, absolutely. So we use two kind of broad scales of satellite data. So some of them are kind of global sensors that enable us to look at that entire sargassum belt domain, West Africa, all the way into the Gulf of Mexico, every single day. We can observe the sargassum current situation and make some broad projections on where sargassum may be moving.

9:55But again, with sargassum being very patchy, the kind of the forefront of research here is using high resolution satellite data. So between four and 10 meter resolutions that can identify really small patches. And if you couple that with models that show where the water is going, again, sargassum is floating at the surface. So it's responsive to where the water is moving. Coupling the hydrodynamic models with the satellite-based detections is really how we can start to make those predictions of where, not just where sargassum is, but where it's going to be going in the next couple of days.

10:29So you're in Florida. Does Florida have a plan for dealing with this? Oof. Each municipality in Florida has kind of its own different way of dealing with it. So, for example, the Florida Keys, much of it is a national marine sanctuary. So there's even more limitations on what exactly can be done to collect sargassum or otherwise remove from beaches. Some beaches, like in Miami Beach, they have regular beach raking that will collect any sargassum that washes ashore.

11:00And when they have exceptionally bad sargassum inundation events, they'll just send the rakes out more often and collect more of that biomass to keep it off of the shoreline. So the management response varies between these various entities. But the sense is that this is going to become a kind of recurring cost, a recurring need as the sargassum situation continues into the future. So doing nothing, it sounds like, isn't an option in your view.

11:31Yeah, from all of the partners, at least, that I deal with that handle sargassum, either on the detection, the modeling, the valorization, you know, everyone views this as a problem that needs to be solved because it will be something that we're going to be dealing with in the future. So we come up with the best solutions and, you know, try and implement them as effectively as possible. Dr. Brian Barnes is a satellite oceanographer and associate professor at the University of South Florida. Brian, thank you so much for joining me today.

12:03Thanks so much, Flora. Great chat. One more thing. Science Friday is a finalist for Best Science Podcast in the Signal Awards. And we need your vote. If you love the show, please vote for us. ScienceFriday.com slash signal. We'll take you right there. This episode was produced by Rasha Aridi. Thank you for listening. I'm Flora Linktman. I'm Flora Linktman. I'm Flora Linktman. I'm Flora Linktman.

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