In Our Time - Corals

Episode Date: October 28, 2021

Melvyn Bragg and guests discuss the simple animals which informed Charles Darwin's first book, The Structure and Distribution of Coral Reefs, published in 1842. From corals, Darwin concluded that the Earth changed very slowly and was not fashioned by God. Now coral reefs, which some liken to undersea rainforests, are threatened by human activity, including fishing, pollution and climate change. WithSteve Jones Senior Research Fellow in Genetics at University College LondonNicola Foster Lecturer in Marine Biology at the University of Plymouth AndGareth Williams Associate Professor in Marine Biology at Bangor University School of Ocean SciencesProducer Simon Tilllotson.

BBC Sounds, music, radio, podcasts. Thanks for downloading this episode of In Our Time. There's a reading list to go with it on our website, and you can get news about our programs if you follow us on Twitter at BBC In Our Time. I hope you enjoy the programs. Hello, whenever shipwrecked sailors find sanctuary on a desert island under a coconut palm, they can thank coral. These tiny undersea creatures, once dead, leave behind stony skeletons.

And more corals grow on those until they form a mountain. its peak above the water, the sailor on that peak. Meanwhile, the submerged corals, sometimes called the rainforests of the oceans, team with life, or in the case of many, did team, until killed by rising water, acidity and temperatures, and the great storms that come with climate change. With me to discuss coral are Nicola Foster, lecturer in marine biology at the University of Plymouth,

Gareth Williams, Associate Professor in Marine Biology at Bangor University School of Ocean Sciences, and Steve Jones, Senior Research Fellow in Genetics, University College London. Steve Jones, what did Charles Darwin notice from the beagle when looking at coral islands?

I think it was a very important moment for him because nobody had before had really understood how a coral island could spring out from a deep ocean because corals need the light to grow. So how could they grow towards the surface

when it's obviously pitch black a long way down? And Darwin, as he was on the beagle, he went to pass. or he visited a coral atoll called Cocos Keeling. And he saw something which really formed his whole view of geology. And of course he was as much a geologist as he was a biologist. And also led to the idea of evolution.

Because he realized what was happening was a pattern of slow change over immense periods of time, which led to the appearance of new, in this case, new islands out in the deep ocean. And he got it right first time, really. How did you notice that, sir? How did he leap to that massive conclusion? You say it's a stroke of genius, but how did he arrive at it? Well, he went to Cocos Keeling, and he knew, for well, that corals were a living creature,

and yet, if you went too deep, they couldn't grow. So he postulated that actually what was happening was that below the coral reef itself, there was a foundation, a sea mount, as they sometimes called, which is a gigantic basaltic thing of hot rock that comes bubbling out of the earth's surface and then because it's heavy it sinks back in again okay Edinburgh Castle is on one of them and Edinburgh Castle is slowly sinking into the fourth I don't think we'll see that in our lifetimes but this is what these seamounts do so he realized what was happening was the seamount will come bubbling up Hawaii is a seaman

for example and then as it sank the reefs would be able to keep growing and keep up to the surface. So we realised that a very slow process of change by very unimpressive animals in some ways could have a massive geological effect. And that led him directly to the notion that in the same

way a very slow process of change in biology could lead to the emergence of new species, humans included. And hence his observation of this island was really the germ that sparked off the idea of evolution by natural selection. And it was his first book.

It was his first book. In fact, to be completely precise, his first book was a very boring book, was called The Zoology of the Beagle. But that was really more of an enormous journal than a book. But Coral, like most of Darwin's writings, is a surprisingly easy and good read. You get a feel for the excitement of seeing the stuff and understanding it for the first time. How do these tiny creatures make such enormous structures? We're told that the great Australian barrier reef can be seen from space and so on. How come?

Well, they do it in the same way that life does it by staying alive and sucking salts out of the water and fixing carbon. And the carbon, which comes from the air, carbon dark cell in the air, they can actually use that because they have within their bodies these corals, many of these corals,

have little green algae called zoosantheli, which are in their bodies and can pick up sunlight and use that to power the metabolism of the carbon animal, the polyp as it's known. It's a kind of symbiosis is the word that people use because the little green sections within the coral animal

were initially independent living creatures which came in and found a home there and they get nutrition from the coral animal and they soak up energy from sunlight and the coral animal uses that to drive its own machinery. How did it come about that what you keep calling a coral animal was for so long thought of as a rock. Well, nobody could really imagine

that animals could make rocks. I mean, it does seem a bit counterintuitive, but they can. Darwin's great insight was not just that that was true, but actually that a constant slow process could generate huge things like the Great Barrier Reef, okay? Nobody had an idea what the Barrier Reef was all about. I mean, Captain Cook was wrecked on the barrier reef,

but the idea that he was wrecked on something which made by a little bit, organism was completely alien to everybody. Nicola Postard, can you tell us what an individual coral? Can you describe their anatomy? Yes. So Steve has very nicely described how the corals form these large reef structures. But these corals are actually colonies. So they're formed of individual polyps, which are just a few millimeters in size.

And the corals are related to jellyfish and sea anemones. And so the best way to describe a coral polyp is that, It is an upside down jellyfish, basically. And it's this hollow sack, and inside the sack it has a kind of stomach with digestive filaments. And at the top of this sack, there is a ring of six tentacles around a central mouth. That mouth is the only entrance and exit into the polyp, so food and waste go in and out of this same opening. And this hollow sack actually sits within a limestone cup that the coral makes itself. This is known as the calyx

And it actually provides protection for the coral polyp So it can actually withdraw itself into this limestone cup To protect itself from predators and from the elements So at the top of the polyp it has these tentacles And it uses these to catch food at night So Steve is very nicely described the way that the corals Also use algae within their cells to generate food But they're also able to get a small amount of energy

from catching microscopic organisms. And they use these tentacles at night and they have small stinging cells within them called nematicists. And they use these to sting microscopic organisms and then they sweep these organisms or these animals into their mouth using their tentacles. So these individual coral polyps are very small. They're only a few millimeters across.

But they can actually form these really large colonies that actually work together as one organism. And they do this by connecting each of these polyps to the neighbouring polyps by a small piece of tissue. And the limestone cup that they sit in also cements together. And when hundreds of these coral polyps

cement together, they form a large colony. And these large colonies grow next to and on top of one another. And this is how they form these large coral reefs. Nicola, and for those who haven't had the opportunity to look up close, what should like to dive among these coral reefs? It's mesmerising.

I think the best way to describe it is like you're diving in a huge aquarium and it's just bursting with colour and with life. And I think the first thing you notice are actually the colours. All the colours you can imagine, all the colours from the rainbow are just right there in front of you. And you see this large three-dimensional structure. It stands up from the seabed, which is the coral reef, which is built from these stony corals. And they're just multitudes of shapes and sizes.

So you have branchy corals that look like trees with no leaves. You have table corals where the bruntary corals where the brachies. branches fuse together and they form sort of table-like structures. And then you have what we call folios corals that actually look like, they look like lettuces, heads of lettuces with leaves. And then you have corals that look like mushrooms and large, bolder-shaped corals. So there's this huge diversity of shapes and sizes. And in amongst these stony corals, you have soft corals.

And we have small ones that look like heads of cauliflower or broccoli. and again, there's such amazing colours, so pinks and purples and yellows and greens. And then we have sea fans that form these large tree-like structures that are again another type of soft coral. There are sponges amongst all of these of different shapes and sizes, and it's just teeming with life. So there are thousands of species of fish and invertebrates all around.

And then if you get closer to the reef, as you get closer and look in amongst the corals, there are hundreds of different species so you have these small Christmas tree worms that live with inside the coral limestone structure and they pop out they look like miniature Christmas trees on the corals and there are starfish and sea urchins it's just teeming with life

and I think one thing that you don't expect is the sound so you would expect diving on a reef to be actually quite quiet but it's actually really loud so there's a whole orchestra of bubbling and crackling and clicking and snapping and popping and this is noises made from the animals that are living there. So we've got snapping shrimp and fish feeding and it makes all these wonderful noises.

And I think the best way to describe the noise is very similar to the popping candy you have as a child that you would put on your tongue and listen to. And that's a very similar sound to what you hear when you're on the reef. Gareth, you're a deep sea diver. Have you anything to add to that vivid description of Nicholas? No, I mean, Nicola's done a greater description

for anybody that hasn't seen a coral. I think, you know, if you've never been privileged enough to visit a Corrieve firsthand and you've seen Coral reefs through nature documentaries, for example, on the television, you probably would expect the opposite. You're almost expecting, because of the overcues that are often played over the visions of the reef, you know, the sort of, ah, type music that often goes along with nature documentaries. You're expecting that kind of tranquil setting that Nicola's talking about. But she's absolutely right. I mean, there's all these noises going off around you. And, you know, the noises are those diverse array of organisms. that Nicola mentioned, eating and fighting and mating, all the things that organisms do,

and they're doing all those things. And because there are thousands of organisms, there are thousands of sounds that create this cacophony, as Nicola was mentioning. It's mesmerizing. You visited and dived in different coral reefs around deserted islands all over the world. What are the major differences? Reefs look really different from each other. I often say a reef is not a reef, is not a reef. They all have their own story to tell. They have different species and different abundances. As a consequence, no two islands look the same. And that's with the human kind of impacts removed.

There's all that variety. And that natural variety is caused by gradients and things like wave energy and food availability, like Steve mentioned. You know, with more waves, we see less coral perhaps because the waves can damage corals and break them up. And with more food, you know, supporting higher trophic levels like fish, so you see more fish and more fish biomass where there's more food. And these natural bounds shape the system that you see. and human impacts are then superimposed over the top of those natural bounds.

And the challenge then is to discern what variation is caused by these natural gradients and what is caused by us as humans. Is there such a thing as a pristine coral reef anymore, Garret. I'm afraid to say, I don't think there's a pristine ecosystem left on our planet, sadly. Human impacts are so ubiquitous on planet Earth that I don't think you can call any ecosystem truly pristine anymore. I do think, though, there are some near-pristine examples of corer reefs. Coral reefs are fascinating in the way that they provide example of some of the most degraded ecosystems on our planet, but at the same time provide example of some of the most near pristine.

And here I'm really talking about, you know, in particular very remote systems that are many hundreds of miles away from the nearest human settlements that lack those local direct human impacts like fishing and pollution. And there are some, you know, really characteristic things that stand out. When you visit these remote reefs, you know, in my mind, there are three things that really stand them apart from reefs that are heavily degraded. First of all, there's an enormous amount of fish, in particular predatory fishes, big sharks, jacks, groupers, all those kinds of things. The second thing that really stands out is when you look at the reef floor, everything you're staring out on the reef just about is helping to build the coral reef. It's laying down that calcium carbonate. It's helping to grow the reef and keep pace with sea level change. And the third most striking thing for me when I visit these remote systems is the clarity of the water.

You can see as far as your eyes will let you, really. And it's because in degraded systems, we have a lot of bacteria and viruses in the water that create a lot of cloudiness. When you visit these remote systems, that's obviously not there. And in fact, some of the systems we visited, our group has visited an island, one, atoll, Millennium Atoll in the South Central Pacific that has a central lagoon that has so many giant clams that are filtering the water. It's almost impossible to detect any microbes or viruses. It's sort of like purified seawater. It's like diving in bottled seawater. So it's absolutely incredible.

Steve, what's the relationship between the coral polyps and the algae inside them? Well, the coral polyp is a classic example of something we call symbiosis, living together. And it was in, Darwin's there sometime later when this became clear. This was always seen as some kind of great, beautiful, charming friendship between two very different creatures, both of whom helped the other one to stay alive, okay? The Russian politician Kropotkin actually mentions corals as an example of a kind of semi-socialist system. It is a lot of tension between the little green structures inside the coral and the coral animal itself. Each one is interested only in its own future.

It's not interested in the slightest in the other one. It wants to extract as much as possible and give as little as possible. And you can see that particularly when you have... events where maybe there's an unduly sunny summer, shall we say, or there's been a big storm on a reef. What happens is that the little coral symbiots

in little green things, they just leave. They think, oh, the hell with this. They just go off and they live independently in the ocean until things get better back on the reef and then they'll come back in. And that's what that causes what we call coral bleaching.

And coral bleaching has always been seen as some kind of terrible sickness and it's all due to human effects. Now, some of it certainly is. You can't deny that. But there's a tension, there's a dynamism in this relationship. The Great Barrier Reef, for example, has bleached several times over the last five years. But it still survives and in time it may well regenerate itself.

Although I have to say, there's been so much pressure on that particular reef now that it's hard to know whether it ever come back to its pristine state. There's a constant battle going on. between the reef in the outside world and between the elements of the reef itself. And in some ways that's why they've become so fragile because anything which is an uneasy truce can easily break out into war.

And that's what we've been doing. We've disturbed the truce all over the place. And so war has broken out and the reefs are paying the price. Nicola, can we develop... Is there any way you can develop that? And not only about corals bleaching, but how great is the threat,

to reefs? Coral bleaching is a huge threat to reefs. And it's caused by a range of stressful conditions. So when the corals get stressed, they lose their algae. And when the algae are expelled from their coral host, this leaves the coral with, without their food source, basically. So they get the majority of their food source from the algae. And so they're literally starving to death.

And it makes them more vulnerable to diseases and to diseases and to degradation. And as Steve mentioned, the corals, they can recover if the stressful conditions are alleviated. It's a little bit like the coral is holding its breath. If the stressful conditions continue too long, so weeks or months, and the corals will eventually die, and they will starve to death. If the conditions return to normal, they can recover. They can take up algae again from the water.

Or if the bleaching was quite mild, they may still have a small population of algae within their cells, which they can then recover. But they will have, if they've experienced bleaching, they will have this reduced growth, reduced reproductive capacities that they won't be able to reproduce at the same level they could be previously. And they'll be susceptible to disease. And so this bleaching is caused by a range of stressful conditions, which could be land or marine-based pollution, so fertiliser runoff or ship discharges, changes in salinity and exposure to air or changes in water chemistry. but these stresses tend to cause bleaching quite localised, so just on tens of hundreds of metres. And the bleaching that is the real threat to corals is that which is happening on a much wider scale. So we call it is termed mass coral bleaching.

And this typically covers hundreds of kilometres. And the main cause of this mass coral bleaching is an increase in ambient sea water temperature. So corals live very close to their maximum temperature and just a one degree rise above this maximum temperature. for a minimum of four weeks can result in widespread bleaching. So they live in this very delicate balance. And when reefs bleach on this scale, it's over hundreds of kilometres. We're talking about entire reefs. Then there is a real risk that these reefs will become degraded

and that if it's over an extended period, they won't be able to recover. And that's when we start to see these reefs degrading. Gareth, I'm bred, though, from what you and others have written, that bleaching it looks terrible and then they rega, and their strengths and come back again. How true is that at the moment? Absolutely. There's certainly evidence that reefs can recover. I mean, over their geological history, they've been disturbed by storms naturally,

well before humans were around. And so there's been this natural development of reefs to regrow in response to the disturbance. In the same way that Steve was talking about that succession, reefs are always going through that ecological succession following disturbance. The challenge, I think, now is that these disturbance events, such as mass coral bleaching that Nicola was mentioning, are just becoming so frequent that that time window for recovery in between those disturbance events is closing and becoming less and less. Steve mentioned about the number of bleaching events on the Great Barrier Reef just in the last five years.

And some work by our group using global climate change models showing that potentially by the end of this century, all coral reefs on our planet will be exposed to bleaching-induced temperature stress every year, which means there'll be no time for recovery in between these disturbance events. And so it's that closing gap that worries me. Yeah. I mean, the interesting thing is, you know, we're so used to seeing coral reefs on television, as Gareth said, that you tend to assume that they're everywhere, okay? But in fact, the total area of coral reefs of the type that we associate with Hans and Lottie Hasse

and all those people and David Attenborough is only about twice the area of the British Isles. So actually, it's a pretty rare habitat. And they're sometimes called the rainforests of the sea, but the difference is that the area of the rainforest is hundreds of times the area of the British Isles. So these things really are fragile. And I think we tend to disregard that. Simply because you can't see them most of the time, you tend to forget that they are really being pushed over the edge.

Do you think, Steve, that if they disappeared, that would have a deleterious effect on us, humans? I think on some populations of humans it would. For example, if you take... When Captain Cook crossed the Pacific, and he found discovered Hawaii, he was astonished by the number of people

there. There were more people on Hawaii in Captain Cook's Day than there are now, and I've been to Hawaii, and it's a big, busy, rather spoiled part of the world. And that's what, because these people effectively lived off the sea, and they lived off, most of the time, the

reefs. And they had a very hierarchical structure. Queen Victoria was all favor of it because of course they had a monarch and monarch was in charge and that was the way that things ought to be. But the joy of the hierarchical structure was that there were very strict rules about who on Hawaii and elsewhere was allowed to go on to the reef.

And you had to be an aristocrat in some senses to go onto the reef and to go on to some of the most productive parts of the reef you almost had to be the royalty of the area and they were actually very good conservationists because before the appearance of Cook and people basically pillage the reefs. They were areas that were set aside not to be used for fishing, not to be trampled on, from year to year.

So they maintained a huge population. And of course, that huge population was devastated when the Westerners arrived, largely because they brought disease. And the disease roared through the coral islands, really depopulating them. So the coral islands that we see today are an absolute remnant of what would have been there before Europeans got into the Pacific? I think actually the loss of coral reefs will affect all people on our planet. And I think perhaps people in different ways.

So if you're, you know, for example, in the Pacific Island nations, about 90% of people live within five kilometres of the coastline. So they live within five kilometres often of a coral reef. And many of these people are obtaining all of their protein, their micronutrients from the reef, things like zinc and calcium and iron, things that stave off and prevent childhood diseases. So the food for these people coming from reefs is extremely important. And with the loss of reefs and the loss of the fisheries associated with these reefs,

many of these people will starve to death. But I also think that people living in inner city Manchester or London can be affected by the loss of coral reefs as well. I do. And I've been asked, how can that possibly be? And it's because everyone should care about the loss of coral reefs. If you care about biodiversity, then you're going to be impacted if coral reefs go away because we're going to see a loss of biodiversity. If you care about medicines, you're going to be impacted.

see many medicines discovered on coral reefs, anti-cancerous properties, for example. If you care, maybe you think you don't care about coral reefs and are disconnected from them completely. If you care about things like immigration patterns, you care about corarees. Because with the loss of these coral reef islands, hundreds of thousands, if not millions of people, will have to be rehomed, many of which are UK overseas territories that have tropical cor reefs around them. So I actually think that with the loss of coral reefs, everybody on our planet will be in some way affected. Nicola. Nicola Povos, can you take us into deeper waters, as it were? What are the corals like at great depths where there's much less sunlight?

So as you move deeper beyond the shallow reefs, you enter what's known as the mesophotic zone. And this zone sits between the brightly lit shallow waters and the deepest depths of the ocean. And mesophotic actually translates to middle light. And so it's between about 30 to 150 metres. depth and this is the furthest depths that the sunlight reaches into the oceans. And in the tropical waters, the tropical waters tend to be much clearer. And so the communities that rely on sunlight can actually live at these fairly deep mesophotic depths. And we've had stony corals recorded at around 100 to 170 metres. So the same coral species that we're finding on these shallow reefs are found on these deeper depths. But as you move deeper through the mesophotic zone, the coral communities change and so while sunlight is still present it's in much lower concentration than it is at the surface and so not all of the species can survive at these depths and so you get a shift in the

communities that you have there and you also get a shift in the size and shape of the corals and other organisms that live there so for the stony corals at these deeper depths they tend to have a plate-like growth form and so by doing this they're forming plates out of their limestone structure and they're doing this to maximise their surface area and to capture as much light as they can and this is for the algal symbionts that Steve previously mentioned that live within their tissues and so between about 30 to 70 metres the communities that you see are often an extension of shallow water reefs so it's quite similar species with just maybe a few less stony coral species than you would have at the shallow reefs but it's just as vibrant it's just as

colourful. We still have all of the sponges, the soft corals and these beautiful large sea fans. And it's also teeming with fish and other invertebrates at these depths. But as you move deeper beyond 90 metres, we have less stony corals because of the decrease in sunlight. And what happens is this leaves space for other species to occupy. And so from about 90 to 120, 130 meters, it's the soft corals and the black corals that really dominate these communities. So the soft corals I talked about earlier. There can be these small colonies or these huge tree-like structures, but the black corals, they're slightly different. So they're not black, as their name would suggest, but they're these large, bushy formations, often in vibrant colours of yellow and red and green, and they have a black

skeleton. And so this depth band has the most stunning communities with these huge sea fans and the large bushy black corals, which stand about a metre high from the seabed. And you also have an abundance of other organisms. And so these deeper reefs are really important communities in their own right. And it's estimated that they actually may cover the same surface area as the shallow water reefs. And they may actually provide some of those same services that Gareth was talking about. So they may actually be a source of food. So we get a large number of fish species, commercially important fish species down at these depths as well. There might be an important source of medicines, as Gareth talked about. And they also provide that barrier. So that protection.

to islands as well. And so these are really, really important reefs. So if you go beyond this depth, so if you go below 200 metres, you're officially entering the deep sea. And so you don't have the sunlight anymore. And what you have then is you have these deep cold water corals below 200 meters. And they don't have that relationship with algae, but you still have these really important coral structures at these depths as well. Thank you. Gareth. What's the relationship between corals and prevailing waves and currents around the globe? Waves are beyond corals is my second favorite thing. And of course, the two things interact. And waves shape coral reefs, quite literally. You know, corals change shape depending on the wave energy, as Nicola was alluding to.

So if there's high wave energy, you'll often see very low-lying corals, encrusting corals that reduce that drag. So they're not as vulnerable to breakage by things like waves. But corals, of course, can affect waves in turn and soak up that wave energy. So as the waves break over the corals, that dissipated energy is taken away. And in that sense, the corals protect the shorelines from those breaking waves. And of course, with the loss of corals, then leads the increase in things like coastal erosion as a result of that. There are also currents, as you mentioned, Melvin, and currents are extremely important for coral reefs

because they supply things like food. So there are deep water currents that move across our oceans. And when those deep water currents and deep water waves, when they bump into these giant underwater mountains that Steve is talking about, you know, they also break. So you get these deep water breaking waves that force energy up the reef slope and can cause localized upwiling

and bring that cold, deep, nutrient-rich water to the shallows to feed the corals. Currents also supply larvae across the ocean and connect reefs to each other that way as well. And the diversity patterns that we see on corries are somewhat reflective of probably of historical current patterns

delivering little larvae to different parts of the world. There's a phrase that came up in, when I was reading about this from what you three had written, that this was a teeming with life in a sterile sea. Can you just tell me more what you mean by that? Corals exist in this sort of oceanic barren landscape, this ocean desert. And Darwin talked about this, you know, sailed for weeks on end seeing these ocean deserts and then coming across one of the most diverse, if not the most diverse ecosystem he'd ever seen. You know, it was

puzzling. I mean, the actual technical term is called the island mass effect, this idea that there are these interacting forces that occur that actually increase primary production, increase a little microscopic algae in the waters, the surrounding waters of these islands, to create little halos of production. So when you look at these oceanic deserts, there are these little, you know, these little pockets that are hugely productive, and it's because of these nutrients coming up from upwelling, it's from fish pooping in the water and birds pooping and all these feedbacks that occur just from the fact that the island is there, river outflow, if it's a high island. And so it increases this primary production around the island and can cause

these little pockets of diversity. It's interesting when you look at a coral atoll, right? I mean, when we have this image of desert island disks and so on, of this heavenly place, which I can assure you that coral atolls are not heavenly places, but in many ways, but the actual lagoon and the inner slope of the reef are boring places. There isn't this constant import of nutrition that comes in on the ocean currents. There's far fewer fish in there than on the ocean sides, so that when we

we imagine living on a coral at all, we're actually missing the interesting stuff, which is the stuff on the outer reef, which you may not visit or even see. So they're very strange and isolated and interesting closed communities, and like many of those communities, of course, they're extremely fragile.

It's a pity that are so few of them, and it's even more of a pity, that there will be a lot less in the near future. While I'm with you, Steve, looking at what's changed over time. Can you take us from Captain Cook, what he noticed about coral islands when he was in the Pacific

in the 18th century to today what's the major change? Well, I mean, of course there's been a complete upheaval in our understanding of coral reefs. I mean, Captain Cook was trapped behind the Great Barrier Reef and he had no idea

that he would actually get a continent surrounded by a sort of protective wall of rock and he got trapped behind that and in fact was almost wrecked. The endeavour was his ship went to ground on the coral reef and in fact he threw over

to escape from it from it before it sank he threw over a number of cannon and anchors and the like which were rediscovered a few years ago so if you want to look at Captain Cook's canon they're in a museum in Sydney I believe so I think

understanding of reefs has been completely changed in some ways thanks to Darwin they had an effect in making us realise that tiny and unimportant, apparently unimportant creatures like coral polyps

can have an enormous effect. Karl Marx had comments on it in Das Capital. You don't often see that. He writes, we see mighty coral reefs, but each depositor is puny, weak and contemptible. And he makes the case that this puny,

weak and contemptible individuals, like humans, when they cooperate with each other, can make massive structures like the barrier reef. So being Karl Marx, of course, he took a political message from biology, which I think in general is usually a mistake. Yeah, and I don't like being lumped as puny, weak and whatever else he said about it. Anyway, never mind.

Nicola, what clues are there that some corals are more robust than others in face of climate change? Well, there are a number of clues. So climate change is causing the atmosphere to become warmer, and it's causing the sea surface temperatures to become warmer, which is causing this bleaching that we talked about earlier when the corals lose their algae. But what we see is that the corals vary in their susceptibility to this bleaching, which tells us that some corals are perhaps more resilient or more robust

than other species or other individuals. So the fast-growing species with branching growth forms tend to bleach first if the sea surface temperatures increase, whereas the slow-growing species that have a more boulder-like growth form, they tend to bleach later or they don't bleach at all, so that suggests that these are more resilient. And so there are these natural differences in individual coral species that give them this inherent resilience.

And in addition to that, what's also been found is that corals can actually become more tolerant of bleaching stress if they're actually exposed to these warmer temperatures. So if you have coral species that live on the shore, shallow reef flats. These are actually more often able to tolerate higher water temperatures compared to individuals of the same species that live on the deeper reef slopes. And so it's these conditions that the coral develops and grows in that can actually influence the conditions at which it will bleach and provide these corals with its natural resilience.

Thank you. Garret, what impact can conservation efforts have on corals? Is there a one-size-fits-all approach? I would say there's evidence showing that if you mitigate local stresses, local human stresses, the sorts of things that we've been talking about like fishing and nutrient pollution. If you mitigate those, there's evidence that reefs can recover more effectively following disturbance events, things like ocean warming events triggering these mass coral bleaching events. And a common approach for people to do this is being through things like marine protected areas. So, you know, some kind of fisheries enforcement or regulation of activities within an area

or potentially fully closed off marine protection. areas. The problem is that in terms of as a conservation strategy, the problem is that reefs are now shaped by multiple cross-scale human impacts that can operate at global scales. So what I'm talking about there is that decisions made by banks, for example, or trade agreements made in one country can impact reefs many thousands of miles away. And so these stresses, you know, these sort of things like climate change, they don't recognize a marine protected area boundary. Ocean warming doesn't get to the edge of a marine protected area. I think, I better not go in, I might get fined.

It doesn't work like that, right? So, you know, that's a huge problem in the way that we've been thinking about how to protect these systems. And also, I'd like to come back to that point I made before, which is this idea of the time between disturbance events is becoming shorter, that there's this lack of time for recovery. And I think what that means is that climate change means that everything we thought we knew about Coralice and their effective conservation and governance really needs to be completely rethought in light of this. What about plastic?

Plastic, you know, there tends to be this war out there, doesn't it? You know, is it plastic or is it climate change? Is it climate change or is it plastic? And they're too often but heads, funny enough, particularly in the literature. And in fact, a PhD student of mine just a few days ago published a paper entitled The Fundamental Links Between Climate Change and Plastic Pollution. And it's because that plastic production, of course, contributes to global climate change. You know, generating all the plastic that we make contributes to greenhouse gas emissions.

the destruction of plastic contributes to greenhouse gas emissions, so they're actually quite intertwined. Whether or not plastic has large-scale direct impacts on marine life, I think is still out for debate. There's certainly evidence that at local scales, plastic can be ingested by marine organisms and cause them ill health. We've done some work looking at the ingestion of microplastics by tiny little coral reef larval fishes that in the first few days when nutrition is so vital for their survival, that they're consuming these non-nutricious, toxic-laden, particles. It can only probably be a bad thing, but evidence for that scaling up to impact populations, I think, is still out for debate at the moment. Steve, at the outset, you mentioned that Darwin examination of coral shows that slow changes could have enormous consequences. Do you think what's happening is that coral reefs are dying off slowly changing backwards, as it were?

Well, they're dying off pretty fast, if the truth were told. You know, they're sometimes called, in a rather banal way, the rainforests of the sea. But there's much more rainforests than that is coral reef. So I think we need to be much more careful of them than we usually are. The other thing about them is there's an awful lot to be learned from the animals that make them, the polyps.

I mean, most people at school would have looked down a microscope and seen this little hydra, as it's called, a little tiny, often greenish creature with its arms flailing around. And in fact, I vividly remember doing that. I couldn't be much older than 30,

I would say. I had a rather good biology teacher. And it seems perhaps an over-dramatic thing to say, but it was that moment, I was so amazed by this, that at that moment I made the decision I would become a biologist, maybe some liminally, maybe not. And it's a decision I haven't to get it for an instant. But it just, to see these things as a young person can be a very, very stirring thing. And in some ways, I guess we've had too much of it now. You know, I used to watch David Attenham programs with, I used to be riveted by them. Now you can't turn the television on without seeing yet another wonder of nature and reefs included. And there's a limit to one's power of wonderment.

And I think perhaps to talk about the amazing properties of the animals that make the reefs would give them a new interest. Hydra, which is a relative of the reef animals, is immortal. In Edinburgh, where I was a student, there was a display cabinet of sea and enemies. It was set up in about, let me think, 1880. And when I was a student there, somebody knocked it over. And these creatures had been in this little tiny environment, happily multiplying themselves, for 80 years. And would have gone forever, probably, until somebody knocked it over. So the polyps are actually immortal.

And you can take a polyp, a little coral animal, and you can cut into two, and you'll get two polyps, and so on. But the one thing that tells you something very fundamental about life in general is that the polyps are immortal. But as soon as you get sexual reproduction and you get the sexual phases which are effectively the jellyfish, they die. So sex, age and death go together. So next time you look at a jellyfish, your heart should sink. Nicola, what does the health of coral reefs tell us about the health of the ocean more widely? I think the health of the reef can tell us a lot about the oceans in general. Coal reefs are very sensitive to even the smallest changes in temperature and water conditions or pollution.

And so I think they can give us an early indication of things to come of what's happening in other areas of the ocean, perhaps further offshore or in deeper areas. and because coral reefs they're located close to the shoreline and in shallow water, they're really visible. And so people see them frequently and we can see what's happening to them. And we can then use this information to give us an indication of what's happening in oceans in general. And we can use it like an early warning system, like a monitoring system. So as we observe the reefs and we see what's happening on these reefs,

so if we see coral bleaching, we can detect that something is wrong in the ocean. And it can demonstrate that there may be something. something wrong in other areas of the ocean, so further offshore or deeper areas that we can't really see. And so reefs really are an important indicator of the health of the oceans in general. Finally, Gareth, Gareth Williams, what gives you hope for that the coral reef is, are there enough of them and they're enough in robust shape? Does hope temper fear? Well, I think, I mean, as Nicola and Steve have pointed out, you know, there's so many things killing reefs. But I think that despite, you know, this widespread mass,

mass coral death that we're seeing across many parts of our planet, there are lots of corals still alive, you know, tens, maybe hundreds of billions at least. And we can save these individual corals and the coral reefs they build, I think, for future generations, but we need to act quickly. And, you know, I think we need global cooperation and very strong leadership to reduce greenhouse gas emissions, the things that are principally driving global climate change and causing these mass coral bleaching events. You know, the demise of coral reefs is the result of poor governance in my mind. But there are voices out there calling for change at the moment. I feel there's a momentum, perhaps more so than ever.

And I'm not just talking about scientists. I'm talking about members of the public. But, you know, we are running out of time and we need to act now. Well, thank you very much. Thank you, Karth Williams, Steve Jones, Nicola Foster, and our studio engineer, Sue Mayo. Next week, from the Middle Ages, it's The Song of Roland, a foundational text in French literature. Thanks for listening. And the In Our Time podcast gets some extra time.

now with a few minutes of bonus material from Melvin and his guests. What would you like to have said that you didn't get time to say? Who wants to kick off? Can I talk briefly about the coral animals themselves? Yeah, you can talk as long as you want. They're fascinating, well, of course they're fascinating animals.

They're the coral animals are the most primitive creatures that we know that actually go to sleep. They actually do seize it. cease that activity on a 24 basis. But what's striking about them is that they're a kind of

microcosm of development because they develop into this structure. And they're stem cells. The coral animal cells are stem cells. Most people have heard of stem cells now. In other words, you've got cells in your bone marrow

which are stem cells, which will generate different kinds of white cell the red cell and that kind of stuff. But most of the cells in a hydra, shall we say, or a coral reef polyp, they're all stem cells. So the people who are interested in stem cells, because of that importance in human health, shall we say, or in cancer, are actually beginning to concentrate on the cells of the coral animals and to look at the genetics of it. And this just shows the amazing connectedness of biology as a science. You know, you can, it's astonishing to me that you can, perhaps, perhaps, find a cure for cancer by understanding

the life and death of the stem cells of the coral animals. But this is certainly possible. So that I get very tired of people who used to say, they say it less now, they say, what you biologists or you scientists need to discover next is the following thing. It's not like that. Good science has always seen the triumph of the unexpected.

Something suddenly turns up you didn't expect it, and you have to be able to spot it. And I think the story of coral is a classic of that particular phenomenon. I completely agree, Steve. And we're still discovering, as you say, so much about the coral animal. I mean, to pick up on a point earlier about the reliance on photosynthesis by the coral holobiion, you know, the fact that it's the Zuzonthelia photosynthesizing. You know, it's only recently we've actually started to realize that in some cases

the corals are relying much more on predation, on the hetrotrophy part of their mixotrophic lifestyle. relying on that predation on things like plankton far more than we perhaps first thought. And I'm talking here about corals living in shallow depths where there's plenty of sunlight. People using new stable isotope type techniques to track energy flow and where the corals are actually obtaining their energy, finding that some corals meters apart. Some are almost entirely photosynthesizing and some are relying 80% perhaps on predation, just a few, you know, just on very small spatial scales. And people are now wondering whether this would help to explain some.

of the patchy mortality we see during bleaching events, because if you predate a lot as a coral, of course, you can store a lot of lipids, and those lipids can help you survive periods when you've lost your zoosantheli. If you have more lipids, you can perhaps survive for longer. So it's incredible to me, as Steve says, that we're still learning about what would be considered, perhaps, the basic biology of the corals. We still don't even really know which is the weakest link. The coral or the algae during coral bleaching is still debated, actually, by scientists. It's amazing. Nicola?

No, it's all fascinating and yeah, absolutely right, Gareth, that we still don't know. What really is driving that bleaching? Is it the host coral ejecting the algae or is the algae leaving of its own accord or is it a bit of both? And it's just fascinating that we still have so many questions that we need to answer. And what you were talking about in terms of certain corals on the reef using heterotrophy more than the food source from the algae itself is quite interesting. and I wonder if, as you said, the variation in mortality after bleaching is specific to certain species or certain growth forms. So we see that the branching corals bleach earlier and are more susceptible to bleaching.

Are these the ones that rely more heavily on photosynthesis, whereas the boulder corals that are more resilient to bleaching, do these rely more heavily on heterotrophy? Or is it just a mix? I was going to say, Melvin, the other thing we touched on very briefly was the idea of disease. I think it was Steve that mentioned it, and I mean, it had links to medicine. And, you know, we talk a lot about coral bleaching, but of course, corals suffer from other diseases, just like we do, that are caused by pathogenic microbes, bacteria viruses and things like that. And sadly, not to be more of the doom and gloom, but for some of those reefs that have been hammered by these mass bleaching events,

places like in Florida, for example, they're now being subjected to these large disease outbreaks. So those corals that have survived these bleaching events, some of them are now succumbing to these diseases, some of which people think are caused by bacteria, which of course are becoming more virulent, so they're able to take hold of the coral hosts more effectively under warming temperatures. That's why you put food in the fridge, of course, to hold that bacterial growth. And some of these diseases are causing this necrosis of the coral,

rapid tissue death. And what's so sad is that it can kill, you know, some of these diseases are killing corals over days, and some of these corals might have taken tens of years to grow. So I think it's important that we also remember that there's these disease outbreaks, which are also contributing to the death of course. But probably we can learn a lot about the disease ecology of the organisms by studying this.

When you talked about Hawaii, Steve, I was fascinated to read more about it in your notes. I'd love to hear a bit more about it. But Hawaii, as I mentioned, was tremendously populated. And they lived on the marine environment. And they actually conserved that marine environment with great enthusiasm. enthusiasm. And there were constant battles in Hawaii. Hawaii was a very, very bloodthirsty place, even before they killed Captain Cook. And a lot of those battles were about who owned the coral reef, who was allowed to go out and use them. And if you go down the great chains of reefs that

have been, you'll find that there's been, in the Pacific, there's been constant movement of populations along the reefs. And what they tended to do, on the smaller islands, they would exhaust the reef and they were forced to move on. And in fact, this is what drew people in the end towards Australia. And so, you know, they played really quite an important part in human history. When people were first exploring the oceans, one of the, a great threat to a mariner going across the ocean was, of course, a low-lying submerged coral reef.

If you were to run a ground, it would puncture the hull of your ship, and there weren't coast guards back then to come out and get you. I'm talking about hundreds of years ago. And sailing across the ocean later at night would have been very treacherous around these tropical submerged reefs. And so they used to put people out on watch at night. And sometimes what those people were actually doing is they were listening for sounds. So if you can imagine just sort of staring out over a very dark night in the middle of the ocean, knowing that you might run a ground on a coral reef and what it might be that you were listening for.

And all of a sudden you'd hear banging on the hull of the ship. And that sound would have been the banging of sea turtle shells. The sea turtles are so numerous back then prior to large-scale human exploitation that early mariners used to use them as a sort of early warning signal. They were approaching these shallow grounds. And of course, at that point, they would hold too and wake everybody up. And it just for me highlights how incredible that the number of these large organisms there were once, you know, many hundreds of years ago before we exploited them so.

And now, of course, most sea turtles are classified as endangered on the threatened species list. The thing I like about reefs is if you want to visit a reef, you can see them in Britain. Melvin, I assume that you were when you were a student in Oxford, he used to go to Whitesham occasionally. There's a nice pub in the village you may remember. Yeah, yeah. Well, that's on a coral reef. Whiteham Hill is a...

Yes, I've learned from your notes. Yeah. I didn't realize I was something half a bit from a coral reef. Yeah, and if you go to Malam Tarn in Yorkshire, she's a magnificent place, that too, was in part a coral reef. So the corals are all around us. You don't need to go to the tropics. You know, just get a bus, get to Oxford and walk up White and Hill.

And you'll be on a coral reef. Not quite as colourful as they are in the tropics, though. That's arguably true. Well, thank you all very much. I'm sure that a lot of people love that program. I did. Thanks a lot. In our time with Melvin Bragg is produced by Simon Tillotson. Thanks for listening to the podcast.

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