Hoe kunnen we onze oceanen beschermen en duurzaam gebruiken?

Zijn onze oceanen gedoemd, zoals de Netflixdocu Seaspiracy doet uitschijnen?
Of biedt de wetenschap hoop?

Vast staat dat het leven onder water moet beschermd worden. Niet alleen om onze oceanen en zeeƫn duurzaam te gebruiken. Je ontdekt in deze aflevering waarom de gezondheid van het leven onder water ook belangrijk is voor het leven op land.

Beluister deze aflevering van 'Scientists With A Cause' in het Engels op Spotify, Apple Podcasts of Google Podcasts.


Biologie-professoren Farid Dahdouh-Guebas en Marc Kochzius en wetenschapper Tom van der Stocken zijn experten in ecologie en biodiversiteit in en rondom oceanen: van koralen tot mangroves.

Wetenschapper in ecologie en biodiversiteit

Farid Dahdouh-Guebas

Wetenschapper in de mariene biologie

Marc Kochzius

Wetenschapper kustwateren

Tom Van der Stocken


Verteller / narrator: [00:00:10] Scientists With A Cause is a podcast in which you discover how and what VUB scientists contribute to the Sustainable Development Goals. Those are 17 goals agreed upon by the United Nations as a part of sustainable development and development coordination. How do they work? What goes on inside VUB? The scientists take their turn in this podcast to tell you about their cause.

Farid: [00:00:35] Researchers, and academicians, always need to do more. They will never finish. And if it's not us, then it's the next generation that is going to finish it.

Verteller / narrator: [00:00:42] Farid Dahdouh-Guebas has been working on mangrove ecosystems since 1993, but as she says, the work is never done. He sometimes collaborates with Tom Van Der Stocken, a mangrove researcher at VUB and NASA.

Tom: [00:00:56] A system that appears colorful and sexy and is known by the people [00:01:00] might get more money for conservation than a system that people associate often with disease.

Verteller / narrator: [00:01:08] This episode puts the focus on the SDG 'life below water'. Conserve and sustainably use the oceans, seas, and marine resources for sustainable development. Talking about, for example, our beaches says Mark Kocsis, professor in marine biology at VUB.

Farid: [00:01:25] There's a problem with beaches, and I think most people are not aware of it. We're losing beaches.

Verteller / narrator: [00:01:31] And about why mangroves are a vital part of life below water.

Farid: [00:01:34] If mangroves are deforested, that carbon will not stay in the soil and evaporate and negatively contribute to climate change.

Verteller / narrator: [00:01:42] In this episode of Scientists with a Cause.

Farid: [00:01:49] We have a climate crisis. We have increasing temperatures due to high CO2 emissions. We have ocean acidification. So we must do something about climate change [00:02:00] and we have to decrease CO2 emissions. Then we have the factor of fisheries. It's a global business and many parts of the ocean are not regulated in terms of fisheries. Many countries have problems regulating the fisheries. For example, countries of the Global South, where a large part of the population depends on the marine living resources, on the fish they find in the coastal waters. So we need to find alternative livelihoods. Because you have to understand that poor people in countries of the Global South, if they don't have a job, if they don't have some land to do agriculture, the only thing that is left to do when they live on the coastline but also refers to lakes or rivers, then they go fishing. Because coastal waters are open access for small-scale fisheries and with increasing coastal population, you have an increase in fishing activity and fishing pressure on these coastal waters.

Farid: [00:03:00] And [00:03:00] then, on the other hand, we have industrial fishing, this industrial fishery. From my point of view, is mainly driven by profit. While on the other hand, you have the small-scale artisanal fishery and the countries of the Global South, which are driven by the need for food. And when we talk about fisheries, we always have to make this separation. There's not one fishery.

Farid: [00:03:23] The third point I think is important is pollution. Coastal waters are very much under pressure from land-borne pollution, and this comes usually from the rivers. So these are the three pressures of climate change, CO2 emissions, fishery, and pollution.

Verteller / narrator: [00:03:41] Researchers Farid Dahdouh-Guebas and Tom Van Der Stocken have been working together on a very specific project for VUB: analyzing Life Below Water.

Tom: [00:03:50] We have a two-year project where we investigate how the seeds and fruits in mangroves float in the water, and what the impacts of salinity temperature [00:04:00] on those floating dynamics are. And we organize a two-year experiment in Malaysia together with Farid and also Satyam, who is another colleague of ours. And so, in fact, we constantly collaborate or directly or just through the system because we need to interact to understand this very complex system.

Farid: [00:04:22] Maybe to follow up on that. You know, when these propagules, they go around the world using the water currents. Sometimes they float, but they're not viable anymore and sometimes they don't float anymore, but they are still viable. So there is only a very small window of opportunity that the propagule has to spread and then establish somewhere. And nobody knows so far on the planet how long that period of viability really is. That's what this Malaysian experiment is about, where we started with thousands of propagules, and then every week we check how many are still viable while the rest is just [00:05:00] floating around in basins.

Verteller / narrator: [00:05:02] To talk about all of this, we've come to a very specific location together. You might have noticed in listening to this podcast, that there's some noise in the background. We're not just in the studio, we are at the Botanic Garden in Meise. Can we also call this some sort of office for you guys?

Farid: [00:05:17] It's more like a training site for students. Because that's the closest we can get to mangroves, is this place. Otherwise, we'll have to travel at least 4000 kilometers to get to the nearest ones somewhere in Mauritania. But this is where we show students, where we teach students about biogeography, and where we can show them the mangroves in real-time.

Verteller / narrator: [00:05:39] Can you briefly describe what mangroves are?

Tom: [00:05:43] Yes, mangroves are an intertidal ecosystem. So that means that they're thriving at the very edge of the land and the ocean. It's not a stressful environment for mangroves, by the way. You often hear that it's a stressful environment, no, it's a dynamic environment. So the tides [00:06:00] come in and out once or twice a day. Flooded once or twice a day by the tides. That's pretty spectacular. Everyone who has worked in mangroves will come up with stories that are pretty challenging. Also, you need to be a bit of Indiana Jones sometimes to walk through those forests. And they're also very important. They're often called the nurseries of the seas because a lot of fish species and other marine life go in between the very dense root systems to survive. And they also stabilize the coasts. They have very, very dense root systems which break the wave energy. And that's why they protect coastal communities against storm surges and tropical cyclones, for example. So they're important in many ways in tropical communities.

Verteller / narrator: [00:06:47] A quick, different question. Who of you two, is the best Indiana Jones?

Farid: [00:06:53] I mean, maybe more of a Tarzan, but.

Verteller / narrator: [00:06:56] Anything you like. It could be anything you like, of course. So in [00:07:00] hearing all of that, mangroves are incredibly important for a different number of reasons.

Farid: [00:07:04] Especially for people also. So the coastal protection function has been highlighted by Tom. But in many countries where mangroves grow and that's over 120 different countries, most of them are developing countries with a lot of fisher communities. And these fisher communities, depend not only on the fish but also on the wood resources, on the mangrove wood, which is very durable for constructing houses, for firewood, for medicinal products. So it offers a lot of ecosystem functions, benefits, goods, and services basically.

Tom: [00:07:42] Mangroves are the largest carbon stock, or they represent the largest carbon stock of all tropical marine and terrestrial ecosystems. And that has to do with the fact that it's a pretty particular environment. Again, we have a lot of sediment that is accumulating in those forests. Much [00:08:00] more than in a tropical rainforest. And so all the carbon that is there is stored and accumulated very quickly so that it doesn't oxidize and it can store four times as much carbon than other tropical forests.

Verteller / narrator: [00:08:21] So mangroves are incredibly important for not only life below water, but also other life on land, in their physical protection and their capabilities in storing carbon. Marc Kochzius has seen some positive evolutions over time in the attempts to conserve and sustainably use the oceans and seas. For example, with marine protected areas.

Marc: [00:08:42] There are people that rather have a vision that the oceans are doomed. If we think about the documentary 'Seaspiracy' that was on Netflix last year. You cannot do much about it except everybody becomes a vegan, which won't solve the problem. But on the other hand, I mean, there are studies [00:09:00] done. There are scientific publications that actually show how over the last decades there is an increase in, for example, areas of marine protected regions. There are many restoration projects for coral reefs, and for mangroves. There is a movement and there is something happening. There must be something done on the ground along the coastlines in all countries that have coastlines. And all countries must take their responsibility to do something about the increasing problem.

Verteller / narrator: [00:09:32] You mentioned marine protected areas. What does that exactly entail?

Farid: [00:09:38] There are many different views. What are marine protected areas? And this is a part of the problem. You can take it very strictly so that you say these are non-take zones. So basically there will be no extraction of living resources but also no extracting of other resources. The sand extracted fossil fuels like gas and oil. [00:10:00] And then you also have other marine protected areas where certain activities are allowed. And this is usually in the context of small-scale artisanal fisheries. So then you have to find a compromise between the needs of local populations and also the need of protecting marine biodiversity in general. And then you can allow certain methods of fishing, or you can have closure times when certain periods of the year you're not allowed to fish. If you talk about nets, for example, that are used, you can use different mesh sizes. So there are many different points of view about what is a marine protected area.

Verteller / narrator: [00:10:39] In trying to create those marine protected areas. How do you determine which areas are in need of that protection?

Farid: [00:10:48] There are many different ways of doing this. For example, in the last few years, the United States has implemented huge marine protected areas in the Central Pacific. And there it was easy because [00:11:00] these are almost uninhabited islands or just some reefs. There is a very small, or in some areas, just no population. So there you can easily say, okay, this is now a no-take zone and that's it, and we keep all fishers out. If you have coastal habitats, and coastal ecosystems with a human population, it's different or it's more difficult to handle this. And for example, if you talk about coral reef marine reserves to protect coral reefs. The approach, I would say until now is usually that surveys are done, first of all, to map where do we have coral reefs? And then make an assessment about the status, the health status of the coral reef, and then usually the reefs that are in the best state become protected.

Verteller / narrator: [00:11:58] Farid and Tom explained [00:12:00] that mangroves are a silent force in storing carbon. But what exactly makes them so exceptional at this?

Tom: [00:12:07] They're especially highlighted today by international climate organizations because they store disproportionate amounts of carbon. They cover only 1.5% of the tropical subtropical coastal area, but they represent 30%, three zero % of the carbon stock in the tropical/ subtropical region. So you see in terms of aerial coverage and carbon stock, there's a huge disproportion. And that's why they're so often highlighted as a climate solution. A natural nature-based climate solution.

Verteller / narrator: [00:12:45] Is there any counterpart on land or in the ocean that does the same or comes close, or is it really that exceptional?

Farid: [00:12:52] About ten, to 20 years ago, people were thinking the tropical rainforest and the next greenhouse we are in stored the most carbon. [00:13:00] But since about seven, or eight years ago, there was a paper that showed just how much carbon is not only in the trees but also in the soil - is stored in the soil. And it's three times, five times more than any other forest in the world. And so it's very important to keep that carbon there. It's a little bit like the permafrost in cold areas. If that starts to unfreeze, a lot of carbon is going to be emitted by the soil. The same in mangroves is if mangroves are not unfrozen but deforested that carbon will also not stay in the soil and also evaporate and negatively contribute to climate change.

Tom: [00:13:39] Between 1980 and 2000, there was a 35% areal reduction in mangrove coverage. That's about 2.1% per year, which is quite a lot. It doesn't sound a lot, but it is a lot. And that decline in mangroves has been reduced to point 30% in the last 15 years, [00:14:00] let's say, mainly due to restoration and conservation efforts and also awareness making by the scientific community. And it's interesting because when you ask people "What are coral reefs?" Or "Do you know what it is?", most people will say yes, or at least they will have heard something about it. For mangroves, it's totally different. It has this murky, muddy impression. It has this dangerous impression. It's dark. There are all these root systems with dangerous animals, or at least that's the perception. And I think that the perceived difference between corals and mangroves also has implications for conservation efforts. A system that appears colorful and sexy and is known by the people might get more money for conservation than a system that people associate, often with diseases also, the malaria mosquito. And that's something that we - Farid was the main author of that study [00:15:00] - that we outlined recently.

Farid: [00:15:03] Perceptions really matter for conservation. That was also the title. And if we are always saying that mangroves are dangerous and crocodiles and malaria and stinking, and so this public perception, it's important to show the beauty of an ecosystem so that when something happens like a tsunami, like a hurricane, there is the mangrove to protect the coast.

Tom: [00:15:23] Yes. And it's interesting because those ecosystems, mangroves, coral, sea grasses, kelp forests, they're often seen as disconnected, but actually they're very interlinked. A lot of fish species that thrive in coral systems move at some point in their life cycle and depend on mangroves. So take away the mangrove system and you will see shifts also in the coral reef system. And that's very interesting that people see it as different systems, but in fact, it's one large ecosystem, continuously interacting.

Verteller / narrator: [00:15:57] Interaction and connectivity. Very [00:16:00] important words in talking about life below water. Marc Kochzius also stresses how important that connectivity is amongst marine protected areas.

Marc: [00:16:10] If you protect a certain area, then this certain area should be able to act as a source of, let's say, keep it simple new fish for other areas which are not protected, where fisheries can go on. And the dispersal of fish, for example, but also almost all other organisms living in coral reefs, happens with the larval stages. So what are the animals doing? They spawn their eggs into the water. Fertilization takes place in the water column. And then the eggs, they just drift with the current somewhere. The larvae hatch and they also become part of the plankton that just drift with the ocean currents. And once they find a suitable habitat, [00:17:00] they will settle down and then they become juveniles. And then they grow and they become adults. And then they could eventually reproduce again. So the dispersal which maintains connectivity between different regions is very important when you want to set up networks of marine protected areas. You need to know if what you protect, this population is replenished, has input from elsewhere, or can replenish itself by so called self recruitment. And this is something we investigate in our research team. So a large part of the offspring will just settle to the same reef where the parents live. Or is it what we call an open population? That means all the offspring will go away elsewhere. And then the question is, where are they going? And depending on how much time they spend drifting as planktonic organisms in the ocean, they [00:18:00] can drift tens of kilometers, maybe hundreds or even thousands. There are organisms that spend more than a month just drifting, and if they catch a strong current, yeah, there will be swept away for hundreds or even thousands of kilometers. And this is also something to consider if you set up networks of marine protected areas.

Tom: [00:18:37] Let's imagine here in the room where we are, if we would make it warmer and warmer, so we increase the temperature and we keep doing that and we would remove all the drink water. At some point we probably will all leave the room because it's no longer viable for us. And the same is happening with climate change. We humans are impacting the environments, we [00:19:00] are impacting the conditions to which species are adapted. And as we change those conditions, species need to go somewhere. They want to survive and they escape their locations where it's unsuitable, but maybe new places become suitable. Of course, if it's suitable, the question is, do those species get there? Can they colonize those areas? And that's where that movement part comes in. Studying stuff that is moving at the ocean surface is very challenging because there are millions, billions of those seeds floating around at this very moment on the ocean surface. You can maybe follow two of those, but you can't follow all those seeds globally. And that's why we collaborate with NASA. They have these very high resolution ocean current models in which we can release every hour virtual seeds and see where they go. And that way we use those MIT simulations [00:20:00] to see how forests of mangroves globally are connected through oceanic movements. We're mapping the highways or the transport system of mangroves.

Farid: [00:20:11] And to link it back to to conservation. Sometimes people are saying, yeah, it's just a small mangrove forest, so it's not so important. But sometimes these small patches, maybe somewhere in the Maldives, it's very small patches. There can be stepping stones for those propagules to arrive and then when they are big, send other propagules further. So the small patches also have very much value. Every part of it, every puzzle piece of it can be done within a couple of months, within a year. But then there is putting all the pieces together. And that, of course, sometimes brings new questions, which you didn't think of. And like that, we continue and we continue. And also the context, the climate change context, it's something which was already there 20, 30 years ago, but not nearly as much as [00:21:00] now. And also the fact that people become more poor and have to rely sometimes more on on getting things from nature instead of from a store that is also more and more current and was less there, I think, so many years ago.

Verteller / narrator: [00:21:18] I have one final question for actually both of you. Are you still able to very much enjoy the ocean on a holiday or does your mind always go to the research and everything you know about it?

Farid: [00:21:28] Well, it depends. If you're in the mangrove science, it's always we always think about mangroves. But if we are on the Belgian coast, then I can relax.

Tom: [00:21:38] I find it hard to disconnect it or to see the part because I think also because I'm trained as a physical geographer, I like to be in desert environments, polar environments, all the ecosystems globally I'm very interested in. So as soon as I arrive somewhere, I have this tendency and will to explain things and understand them.

Verteller / narrator: [00:21:58] It's understandably not [00:22:00] always that easy to cool down your mind and thoughts. When talking about a holiday Marc Kochzius immediately thinks about another problem we are facing.

Marc: [00:22:09] So everybody likes to be on the beach. There's a problem with beaches, and I think most people are not aware of it. We're losing the beaches. And why is that? Because we have a growing population on the planet. There's an immense need for sand for construction. To make concrete. And when you see in booming countries like China, but also there's a lot of construction in the Western world and industrialized countries, there's a huge hunger for sand. And usually, this is dug out in front of the coast. But if you remove sand in front of the coast, this must be refilled from somewhere. And in many cases, it's coastal erosion. So the beach will be eroded [00:23:00] away to fill the gap. The big hole you dig out in front of your coastline. And in some countries, even complete beaches disappear because the local population in the global south needs an income. They're just removing the beach. And also in rivers, a lot of sand is removed. This means this sediment is no longer reaching the coastline to replenish the beaches. This is also a huge problem, which is in connection with the construction boom. Booming cities, megacities that build more and more skyscrapers and buildings. And for this, you need sand. And it must come from somewhere. And we need to find other ways to construct buildings because we can't go on with digging out sand from the ocean.

Verteller / narrator: [00:23:58] This was Scientists with [00:24:00] a Cause, a podcast series of VUB created by the Podcast Planet.