Victoria:
Our guest this week is Susann Rossbach. She is a professional scientific diver and final year PhD candidate in Marine Science at King Abdullah University of Science and Technology in Saudi Arabia. She got her bachelor’s degree in Biology and her master’s degree in Biological Oceanography from Christian-Albrecht University of Kiel in Germany. As a marine biologist, she studies how animals and plants live underwater, and how they adapt to changing conditions like warming. She has studied cold water corals from the North Atlantic in Chilean Patagonia, but now she studies the warmer waters of the Red Sea investigating the ecology of giant clams. Giant clams live in a symbiotic relationship with tiny algae, just like tropical corals. Due to this relationship with plants, light is a very important environmental factor for these clams. That’s why her research focuses on how these clams and their algae can use the sunlight in a more efficient way without getting a sunburn.
This week’s questions were submitted by listeners through emails and on social media.
Thank you so much for joining us today.
Susann Rossbach
Yeah. Thank you very much for having me. Really excited to be part of this.
Victoria:
Is there anything you want to add to that little instruction?
Susann Rossbach
No. Perfect. Perfect introduction
Victoria:
(Katy – What does symbiotic mean?)
Awesome. So in that case, we can move on to the questions. This first question is from Katy. What does symbiotic mean?
Susann Rossbach
Okay. So symbiotic is a word that comes from Greek and means living together. And it describes a relationship in which two organisms, so animals and plants, are having such a close relationship that they’re actually living together. So in English, which is a bit different than in my natural language in German, where we have symbiosis only as a positive word, in English, it differentiate between three different forms.
So that’s the relationship can be a parasitic one: this is when only one partner has a benefit of this relationship and the other one is being harmed, in us humans for example, head lice are a good example.
Or a symbiosis can be commensalistic, where one partner has a benefit and the other one neither has a benefit nor is harmed in the relationship. For example in the sea or in the ocean, those are the barnacles tiny crustaceans that live on whales, and why the barnacles benefiting from it, being transferred all over the place, like on a fishy bus, the whale doesn’t really realize that the barnacles there. So it’s also not harm, but it’s very good for the barnacles.
And then there is also the mutualistic symbiosis. This is where both partners benefit from each other. And in the case of the giant clams by sample, they are living in such a mutualistic symbiosis with these tiny algae, so both have benefits of living together.
Victoria:
(Rhonda – What do the clams and algae each get from the symbiotic relationship?)
That’s so interesting. Okay. A good follow-up to that from Rhonda. What do the clams and algae each get from the symbiotic relationship?
Susann Rossbach
So the clam gives the algebra protected environment like a home where it is safe from being eaten, because the tiny algae sitting in tiny tubes inside the mantle, which is the colorful, outer part of the clam that you see when you see such a clam. And it also gives the algae some compounds and nutrients that they need to live better.
And then in return, the algae produce oxygen, because the clams need oxygen just as much as we do because they also breath. And then they help the clam also to remove waste. And most importantly, they share energy that they produce from sunlight and carbon dioxide.
Victoria:
(Tasmin – Why did you pick giant clams to study?)
Cool. Tasmin wants to know, why did you pick giant clams to study?
Susann Rossbach
I think I just have a big heart for animals that other people tend to ignore. Just a joke. In fact, many people study corals in a reef, and that makes totally sense because they’re building the majority of that. But clams also play a very important role in these reefs. And only very few people have looked into how they live, how they’re doing, and the different impacts of climate change, and all these things. So we know very little about these clams, although they might be very important for every or for many organisms that are living there. So I sometimes call them like the stepchild of coral reef research. And that is really not fair because they’re super cool and they have so many important interesting things to learn about.
Victoria:
(David – What are the differences between underwater plants and animals that live in cold water and those that live in warm water?)
Awesome. All right. This next question is from David getting at a couple of different aspects of your research. What are the differences between underwater plants and animals that live in cold water and those that live in warm water?
Susann Rossbach
Okay. So first and of course, the temperature they are living. The life in Arctic is also very different from life in the African savannah.
But one of the most important differences in these two habitats is also the light. So animals and plants living in cold water often receive less light than those in the tropics, which is because tropical reefs are closer to the equator, and so they have often 12 hours of light in the day and throughout the entire year. So they don’t have seasons. But in other places of the world, there are sometimes only few or very few hours of light in a day, especially during the winter months. So that is also why, for example, the giant clams, which live in tropical sounded waters can have this symbiotic relationship with the algae, which also helped the clams to grow very fast and these big sizes. But clams in cold waters couldn’t live in such a symbiosis because there’s not enough light for some plants to live there. And this is also true for many coral species. So corals and the tropical reefs usually have algae symbionts, but those in cold water or deep sea where there’s no light or very little light, they don’t have symbionts.
Victoria:
(Julian – How has global warming affected the underwater plants?)
Okay. That makes sense. Okay. Julian wants to how has global warming affected the underwater plants?
Susann Rossbach
Well, so that’s a very complex question. And today we don’t only speak about global warming anymore, but we’d rather say global change, because in fact, it’s so much more than just warming up the earth, like changing CO2 levels in the atmosphere, seawater becomes more acidic, weather system is changing, regions that can have more or less rain than before, and many more things.
But, if we precise with how warming affects on the water plants, then, well, in some cases, submarine plants like tiny phytoplankton, a great sample, actually likes warmer waters, or some of them like warm waters and can grow better and faster. But that also means that we often end up with tons of it, which also unbalances the entire systems. Sometimes they even produce harmful compounds, and when there are too many of them, those can harm others, especially animals. So warming can then cause there’s too many of one type of underwater plant. And so others can’t live there anymore.
And if it’s too hot, plants, just like any other organism, has problems to live. Just like in high fever, humans can be dangerous. Temperatures that are too high can also cause damages and problems in plants and they might eventually die off.
And then the symbiosis such as the one with the clams and algae, or corals and algae, global warming is all messing up with a symbiotic relationship. Scientists are not fully sure yet what happens, but there are a lot of people working on this and studying how the, yeah, how this relationship changes under warming conditions. And we know now that if the water temperature is too high, the clam or the coral kick out the algae, because the relationship is becoming unhealthy for them. And then they get bleached. This is what we call them. So this process is called leaching because the clams and the reefs often look very white when they have kicked out the algae symbionts, just as if someone had put them in bleach.
In fact, this is way more complicated because there’s so many more things than just the warming that play a role here. And many of them are still not fully understood by the researchers, but in general, the warming is harming or is changing processes in the organisms, in plants as in animals, that are not good for them on a long term.
Victoria:
Oh wow. That’s scary. So the bleaching I’ve heard is really common in the Great Barrier Reef. Is that true?
Susann Rossbach
Yeah. Yeah. And then we also know today that it’s not only warming, because sometimes as well, for example, here in the Red Sea where I’m living, the temperatures are way higher than they are like Great Barrier Reef. That’s still corals don’t bleach that often. So it’s not necessarily the temperature, it’s also the different nutrients. So for example, like if it’s very high the stress, just as we humans, if we’re stressed and we get enough food still, it’s fine. But if we’re stressed and there’s not enough food, then we’re really struggling, and it’s kind of the same thing there. So if it’s a combination of stressful things that come together, that’s one problem.
Victoria:
(Ismael – Do you get to scuba dive in all the places you study?)
Yeah. Yeah. That makes sense. Okay, switching gears a little bit. We’ve got some questions about all of the scuba diving that you do. Ismael wants to know do you get to scuba dive in all of the places that you study?
Susann Rossbach
So, yes, luckily enough, I do. But I always also try to work on projects and in places where I can do scuba dive because I love it so much and because I think it’s really cool to use it for my work.
But you don’t need to be a scuba diver to be a marine biologist. So many people in marine science do not have to dive for the work. Sometimes because they’re working on organisms that are super small, like bacteria, and they won’t see them on the water anyways, or because they do not experiment on the water, but in an aquarium, and for many other reasons. So there are like the typical stereotype that people have in mind when they think of marine biology, they think of diving. But in fact, I know, I actually, I know more people that are in marine biology that do not dive than those that dive for the work.
Victoria:
(Franky – Do you ever see sharks and scary things when you dive?)
Okay. And a follow-up to that from Franky. Do you ever see sharks and scary things when you dive?
Susann Rossbach
I sometimes see sharks when I’m diving here in the Red Sea, by that’re never scary for me. So it’s quite the opposite because I’m always happy when I see one, because they actually quite rare in some places and seeing one shows me that they’re still around. And most of them, they’re very shy. Like when they see you, they will swim away very quickly. So it’s actually true that they are more afraid of you than you would be of them. And it’s very rare that they’re curious and come closer. But just because yeah, they want to know what kind of funny troublemaking thing you are. So, no, I don’t think that’s scary.
But what definitely is scary for me is when I see, for example, ghost nets on the water, which are abandoned fishing nets, that’s a thing to the bottom of the sea, and then they overgrown with things, but also fishes can get trapped in them and die.
So like those impacts the humans. Oh, when you see such a bleach reef, those are things that I think are really scary in that are stunning when I’m on the water.
Victoria:
(Eli – What’s the strangest sea animals you’ve seen in the water?)
Yikes. Eli wants to know what’s the strangest sea animal you’ve seen in the water.
Susann Rossbach
Well for me, jelly fish are and will be the strangest animals ever. Because some of them can become super big, and then there are times it goes up several meters of length. And then there are others that are super tiny, and some that are very one but a crowd of 1000 animals that are living together, a little bit like a bee and a beehive, and like build one giant organism. And then there’s some that have very wild life stages, which make me think they could be all, you could say immortal, because they only changed from one life stage to another and they don’t really die. So, yeah, jellyfish is definitely very big mystery for me and I think like the weirdest animals there.
Victoria:
(Grace – What’s the coolest fish you’ve ever seen in the water?)
Oh, wow. A good follow-up to that is from Grace. What is the coolest fish you’ve seen in the water?
Susann Rossbach
Oh the coolest fish I think, my absolute favorite is the ocean sunfish. So some of them like the ones you can see sometimes in the Mediterranean, I see them in the Mediterranean but they are in other places as well, they’re really round just like this time. And they’re actually the biggest fishes, the biggest bony fishes on Earth. And to me, they always looked a bit like if I’m outer space, because maybe that’s also the reason why I liked them so much. Again, my love for weird animals. But it’s also because they’re somewhat mystical mostly because we don’t know much about them.
And sometimes they just, pop out of the background and they look like they are from outer space and swim very fast away. They are really, really weird. And the funny thing is in English they are called sunfish, but in my native language, in German, for example, they called moon fish. So. And the Latin that called mola, which is the millstone. So it’s all referring to their own shape, but they have like very different names that are all referring to the shape of them. That’s the same.
Victoria:
Oh, that’s cool. I will get a picture of them that I’ll put it in the description of the podcast episode, so everyone can see them.
Susann Rossbach
Yeah they are really cool
Victoria:
(Zain – How big do the giant clams get?)
Switching gears again, back to some questions about the giant clams. Zain wants to know how big do the giant clams get?
Susann Rossbach
Ah so some species, like Tridacna gigas for example, which is the one that most people have in mind when they think about giant clam can be really really big. So like more than a meter in length, then we could easily use them as a sink in a bathroom, or you could use it as the bath tub for a baby.
The ones I’m working on don’t get that big, still about 30 to 40 centimeters. So like a magazine or a piece of paper, which I think is still pretty big for a clam.
Victoria:
(Ellie – Why do giant clams get so big?
Wow. A good follow-up to that is from Ellie. Why do giant clams get so big?
Susann Rossbach
Also we’re scientists think that one of the reasons the clams are getting so big is because they get all this extra energy from the algae symbiosis. So like other clams, they also filter tiny particles from the water, but the giant clams then get this extra energy, this extra food source, and then they basically double the energy that other clams have. So that’s why they can grow so big.
Victoria:
(Wyatt – What’s the biggest clam you’ve seen and what’s the smallest?)
Oh, cool. All right. And then Wyatt to know what’s the biggest clam you’ve seen and what’s the smallest.
Susann Rossbach
So the biggest clam I’ve seen was one of these Tridacna gigas clams, that I just talked about the big ones, and it was in a museum. So that one would have definitely worked as a bathroom sink or tub four for baby. And I really hope to see them on the water one day, but they’re not so many left, unfortunately, and they’re more common in Southeast Asia. So I hope that one day I will go diving there see one on the water.
But the smallest one, I definitely see frequently when diving in the Red Sea because they’re like a centimeter in length or so and they might start even smaller but this is like the first time when you can see them, like when they’re reach about the centimeter because before that would be hidden in between the corals. And it’s very hard to find them, but yeah, all the giants clams start small as a baby,
Victoria:
(Sierra – How long do the giant clams live?)
That’s cute. Okay. Sierra wants to know how long do the giant clams live?
Susann Rossbach
We actually don’t really know, but from the time we know that it takes to grow to these big size, it takes several decades and the big ones would be even a hundred years old or even older.
Victoria:
Wow. So do they continue growing throughout their whole life to get so big?
Susann Rossbach
Yeah. So the things at one point, they’re not getting longer anymore, but their shells getting thicker. So sometimes we don’t even have like, normally it’s like a, like a sink, part where you can put something inside, but at one point it’s just a thick brick of calcium carbonate. Sometimes you can’t even tell if they are getting bigger over time, just thicker
Victoria:
(Hayden – How much sun gets to the bottom of the ocean?)
Wow. Okay. transitioning a little bit. We’ll talk about some of the sunlight questions that you study. Hayden wants to know how much sun gets to the bottom of the ocean?
Susann:
What’s really at the bottom of the ocean? There’s no light at all. So that’s a place where it’s always dark.
But there are different zones or lanes, and the first about 200 meters, although it was just a bit dependent on the place and the ocean we’re talking about is the photic or the sunlight zone. So this is what almost all plants and animals that are living in the symbiosis with this, because at this point we can still have enough light to live on.
And we know that between about 200 and 1000 meters, this is the disphotic zone or the twilight zone. And this begins at a depth where about 1% of the light still reaching. And then it ends where there’s no light at all.
And the last zone is then the aphotic or a midnight zone. And as the name already gives it away, this is where it’s always dark. So animals that are living here must be able to live in complete darkness. And I’m saying animals, because if there’s no light, there can’t be any plant.
Victoria:
(Jarod – How close do clams have to be to the surface of the water to use sunlight?)
Oh yeah. That makes sense. Okay. Jarod wants to know how close do clams have to be to the surface of the water to use the sunlight?
Susann Rossbach
This is a very good question, and it depends a bit on species of the giant clams, but I would say that almost all of them live in shallow waters, so less than 20 meters, and some of them, most of them, less than 10 meters of water. And from the surface to about 10 meters it really depends on a lot of different, many different factors. Because although the clams, although they want and need light, they also have to make sure to protect themselves against too much light, just as we love it to be on the beach, but then at one point we have to put sunscreen on and I’ll go to the shade for a while. And actually most of my work is revolving around this topic. So how does a giant clam use the sunlight, but also how do they avoid getting sunburn when they’re sitting in the sun for too long?
Victoria:
(Ellie – How do clams get sunburned?)
And that leads in well to Ellie’s question, which is how do clams get sunburned.
Susann Rossbach
But actually that just as what humans do, because there’s too much sunlight and the clams always have to stay in one spot so they can’t move to the shade. The energy of the Sun can destroy parts of themselves. And then just like in us humans, when we have a peeling skin from a sunburn, parts of the clam can die off. And also the algae symbionts can die or are kicked out of them. So they loose their energy source. So this is also one of the factors, like if there’s too much light or too intense light can lead to that bleaching that I mentioned before, it cannot only happen if the water is to hot but also if there is too much light. And in the end the sunburn is very similar in all other organisms. The basic concept is that parts of the sunlight have so much energy, that they can destroy or damage cells all different kinds of problems.
Victoria:
(Julian – What do giant clams eat?)
(Franky – Could a clam ever get big enough to eat a person?)
Wow. Okay. some other questions about clams. These are a pair of questions that go together. The first one is from Julian, and Julian wants to know what do giant clams eat. And then Franky wants to know, could a clam ever be big enough to eat a person?
Susann Rossbach
Well, so giant clams are lucky because they get most of the energy that they need and most of the food from the symbionts. So they don’t have to eat on their own very much, and that makes them also super special. So they’re not many other bivalves out there that can do this. But just like other bivalves, if they eat, they do this mostly by filter of feeding, which means that water streaming past their gills and its acting like a pump or a mesh or a filter filtering different particles, which are very tiny food items, or tiny animals out of the water. And then from the gill, it’s transported to the stomach and digested like us humans, and I know that’s the legend of the man-eating clam. But no, so even the big ones, would not be. Yeah, even the big ones, you might be able to just from the size to fit your arm or leg into this, but the bigger they are, the longer it takes them to close over. So if you don’t wait for it, you will still be able to put it out. So it’s not like this closing within a second and you’re stuck. This will not happen. But I would rather not test it with the smaller ones though, because you probably won’t be able to get your finger out, but it will definitely be heard. So like when you get your finger stuck in the door, but no, they can’t eat an entire human. A because they won’t get this big and B) because they’re very slow and stuff.
Victoria:
(Grace – How many giant clams are there in the world?)
That’s good to know. This next question is from Grace. How many giant clams are there in the world?
Susann Rossbach
Well, to be honest, we don’t really know. We usually give numbers of animals like these clams in animals per square meters. And this can be very different from region to region. And most places we find that there is less than one clam per square meter in a region, but then there’s some places in French Polynesia, for example, where they’re very abundant, and then many, many, many of them are found. They are even found in a reef where they are sitting on top of each other and building the reefs themselves but this is very rare. In most cases, we only find like single, single clams in there. and this is also because many places of the world they’re endangered, meaning we have to take care that they’re not getting extinct during the next year.
Victoria:
Wow. And are they endangered because of the climate change or like human activity and capturing them or hunting them?
Susann Rossbach
That’s different. In Asia, they harvested it a lot. So like people eat them. I can imagine it’s a very big animal, like a lot of meat that you eat. So they have a source for food. The shells are often used for ornamental purposes, so that carvings out of them and use them for all different kinds of things. They’re very commonly used in aquaria trade. There’s also farms of them like aquaculture there they don’t have to be taken from the wild, but then they’re still will be poached from some reefs where shouldn’t be, And definitely climate changes overall having a big impact.
Victoria:
(Rhonda – Are there multiple species of giant clams or just one?)
Yikes. Okay, another, a good follow-up to that from Rhonda. Are there multiple species of giant clams or just one?
Susann Rossbach
So at the moment we think there’re 13 or 14 species of giant clams. And this is also the reason why working on them is very interesting because in the last 10 or 15 years alone, there were a number of new species described or reselected, as we say. So that means they’ll have species that were described like four years ago and people just forgot about them. And now we realize, Oh, this is actually a species. Right. But it was never mentioned again. So I’m pretty sure that we update the number two times again during the last years, and during the next year.
Victoria:
(Eli – If you are scuba diving and you see a giant clam, can you touch it?)
Awesome. Okay. And Eli wants to know if you are scuba diving and you see a giant clam, can you touch it?
Susann Rossbach
Well, you could. But the best thing on the water is not to touch anything. Not necessarily because it might hurt you, but also because you can spread your germs or bacteria, something else to animal and touching, and then you could make the animal hurt or make it even sick. And that is why when we dive in just for fun and not working underwater, because when we’re working under water we sometimes have to touch animals, but in a just for fun dive we are looking at them and taking photos.
Victoria:
(Jarod -How old were you when you first scuba dived?)
Awesome. And we’ve got a bunch of questions now about you and your studies and everything. Jared wants to know, how old were you when you first scuba dived?
Susann Rossbach
I went scuba diving first time when I was 15 years old. And that was mainly because my dad used to dive when he was younger, but then he didn’t do it for a long time. So we kind of started together like me as a new diver and him being on the water for 20 years or so.
But I was always a water child from an early age on, I loved swimming. And snorkleing. So I guess like coming to the point where scuba diving comes up to the table was just the logical consequence.
Victoria:
(Katy – What’s the closest place in Saudi Arabia that you go scuba diving?)
And Katy wants to know what’s the closest place in Saudi Arabia that you go scuba diving?
Susann Rossbach
Actually, it surprises people often because when they think of Saudi Arabia, they only think of the desert, but actually Saudi Arabia has a lot of coastlines, like the biggest proportion of the Red Sea is part of Saudi Arabia. And I’m actually living right at the sea. So when I walk for five minutes I’m at the ocean. Like, yeah, I technically could go swimming. It’s a bit complicated with the regulations, but I’m really, really close to the sea. And I think within 15, 20 minutes, if I go on a boat, I would be out on the reef.
Victoria:
(Jevan – What’s your favorite place that you’ve been scuba diving?)
Oh, cool! Jevan wants to know what’s your favorite place that you’ve been scuba diving.
Susann Rossbach
So my favorite diving spot is the underwater part of a bridge pillar of the Danish Straight so in Denmark. And that sounds a bit odd, I know, but it’s really amazing because the walls of the pillar are overgrown with corals and anemones. And so they’re fully covered in these fluffy coral relatives.
And because the visibility is not so good that the water was really green and you kind of see them until you’re like five or 10 meters away from the pillar. This is everything like the spooky atmosphere, but I really liked it a lot. And it’s also a bit like a, like a reef and a place where you wouldn’t expect so many animals and like such a nice setting.
Victoria:
(David – Do you speak a lot of different languages?)
Sounds incredible. David wants to know do you speak a lot of different languages.
Susann Rossbach
But I don’t think it’s a lot. But yeah, so I’m originally from Germany, I speak of course German. And then there’s English, some French because I took French in school, but to be honest, I feel like I forgot quite a lot, cause I never practiced. I think I still understand quite a bit, but yeah, speaking, not so well. And then after working in Italy a few times I understand some Italian, but also pretty bad in speaking it. And I still try to learn Arabic and only know some basics, but it’s also to be fair, very hard to learn a language where you can’t read the letters.
Victoria:
(Tasmin – How many years of school have you done?)
Yeah. I imagine that it’s very challenging. Tasmin wants to know how many years of school have you done?
Susann Rossbach
Feels like too many, but this is my last year in school, hopefully. And this is the 21st. Because so many federal States in Germany, like the one that I went to school, you have 13 years of normal school, like of high school. And then I went to University and I did a bachelor’s for three years, and a master’s for two. And now I’m finishing up the third year as a PhD student.
Victoria:
(Ismael – Do you go scuba diving for fun or just for work?)
Nice. That’s exciting. Ismael wants to know do you go scuba diving for fun or just for work?
Susann Rossbach
Definitely both. Although there are times when I have to dive a lot for work. I still love doing it in my free time, especially when I’m stressed out about work about other things. It’s really like a short vacation when I go in the water. And then, there’s also like this combination of both, I would say, because I also teach diving which is just kind of work and fun at the same time. But, well I think that’s a saying, like, if you, if you choose the right job, then it’s never really work. I think for the diving part that might be true, not for everything else I have to do, and the diving is just a very small part of what I have to do, but for the diving part kind of a mix between work and fun, always.
Victoria:
(Jenny – Do you have to hold your breath for a long time underwater?)
Oh, that’s good. Okay. And this is our last question from Jenny. Do you have to hold your breath for a long time underwater?
Susann Rossbach
Oh, so as a diver, it’s always good when you’re able to hold your breath for some time. So in case something happens, and you can always stay calm, knowing that no matter what you have enough time to reach the surface even when your tank is empty or when something else is happening.
So the important thing is more to be healthy and fit. And then the more you train and try to be fit for diving, the longer you can also hold your breath. So it’s nothing that I really practiced for it, but it’s like I try to be fit for diving. So I know that I’m always safe on the board.
Victoria:
Oh, that’s good. So that is all of our questions. Do you have any questions of your own for the listeners or any comments or anything?
Susann Rossbach
Honestly, I never actually thought about this before.
Victoria:
That’s ok
Susann Rossbach
I think the questions already covered everything and all the stuff that is good to know
Victoria:
Yeah. Awesome.
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