Instant Genius - Corals, with Dr Jamie Craggs

Episode Date: April 10, 2022

Coral expert Dr Jamie Craggs tells us all about the biology of corals and reveals why they are so important for the planet. Once you’ve mastered the basics with Instant Genius, dive deeper with Instant Genius Extra, where you’ll find longer, richer discussions about the most exciting ideas in the world of science and technology. Only available on Apple Podcasts. Produced by the team behind BBC Science Focus Magazine. Visit our website: sciencefocus.com Hosted on Acast. See acast.com/privacy for more information. Learn more about your ad choices. Visit podcastchoices.com/adchoices

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the managing editor at BBC Science Focus magazine. In this episode, I talked to Dr Jamie Craggs, the aquarium curator at the Hornemone Museum and Gardens. He's a coral expert who founded Project Coral in order to research the ways that corals breed. He tells us all about corals

and explains why they're so important. So, Jamie, you're a coral expert. So just to start us off, what exactly is a coral? Is it a plant or is it an animal? Well, corals are one of those strangers. They are animals, but people think, you know, they're either rocks or plants or animals, but no, they are animals.

So they're closely related to sea and enemies and jellyfish. And they're predominantly made up of colonial animals. So they're made up of a unit called a polyp. And multiple polyps grow together to form the coral colony. but they are very much an animal. They have, you know, it's stinging cells and tentacles and a mouth. But what complicates it is the majority of corals also have a relationship with an algae that lives inside them. So an algae is a bit like a plant, plant-like animal that lives in the ocean.

And so these plants also inhabit the coral and live within the coral. And they complicates it even further is they build a skeleton which they live in. It's like a calcium carbonate cup that the polyp, the soft flesh, polypilip lives within this calcium carbonate cut. So they also build a rock-like structure. So they're interesting animals. So how many species of coral are there? So, I mean, certainly we're finding more as time goes on, but it's estimated around 2,000 species have been identified so far. And they inhabit all oceans of the world from shallow water in the tropics right the way to the deep Arctic Ocean. So,

they inhabit all areas of our oceans. Because that's quite surprising. I think people generally think corals only live in hot countries in tropical regions, but we do get them around the UK, don't we? And also you'll get them right in the bottom of the ocean. Yeah, very much so. So we have a number of species around the UK, and we have quite significant coral reefs, certainly off the coast of Scotland,

that form very big structures, yeah. So they are, yeah, they're significant in other. place of the world. Obviously, the tropics is where we have the most diversity and the most significant structures, things like the Great Barrier Reef that everyone knows. But yeah, there are corals all over. How long have corals been around for? When did they first evolve? So, corals as we know them now, so there's something called the Scleractinian corals. There are modern corals. They've been around a little over 200 million years, so they first appeared in the middle of the torsic period. Types of corals did survive before that, but they became extinct. But they evolved around

330 or million years ago, but became extinct. The modern corals that we now know, yeah, about 200 million years. So does that mean then the corals sort of died out and then evolved again? Ultimately, yeah. The new, the modern coral filled the niche that was left when the regos species became extinct. So you said earlier that corals have got these stinging cells. So what do corals actually eat? Corals consume a huge variety of prey. Everything from, they'll gain nutrients from the water itself. So things like nitrogen compounds and phosphorus compounds that they'll absorb from the water. They can consume small items like bacteria that are associated with the mucous layer, right the way up to larger items like zooplankton.

And even, you know, some species of corals can consume fish themselves. You know, they can actually hunt quite big, big prey items. So they have a big range that's on their diet, I suppose. And how do they actually kill that prey? Will it just be sort of floating past, they'll grab hold of it and sting it to death? Yeah, a number of different ways. You know, bacteria, they use the mucus that they secrete out of their mouth, covers the coral, and they can trap bacteria, all sorts of organic matter.

can stick to that and then they'll suck that mucous back in. But then bigger prey items, their tentacles are sort of armed with a battery of stinging cells, and much the same way as a jellyfish does this. You know, as a prey item comes in contact with the tentacle, they fire these batteries of stinging cells that are called pneumatocysts, and they ultimately inject venom into the prey item, paralyze it, and then they consume it. So, yeah, they sting. prodded a coral, would we feel the stings? First, we don't want to go around prodding corals, but no, you can, yeah, very much so, in sensitive areas. So if you were to get stung on your wrist, for instance, where the skin is quite thin, yeah, you can get stung, and it's a bit like a stinging

nettle sting. There's different strengths of sting, depending on the species. But unfortunately, my work, it's part and parcel of it. We get stung all the time, working with the corals. and it's one of those that's sort of three o'clock in the morning, that sting will be itching like crazy and keeping you awake for a couple of nights. But yeah, they, yes, they can sting you, definitely. And does anything eat them or do those stinging cells keep them pretty safe? They, you know, obviously that is predominantly there for prey capture, but they do also use the stinging cells to protect themselves

and also defend themselves against neighbouring corals that are trying to encroach on their area. But there are lots of species that also feed on, on corals. So many butterfly fish will specifically feed on the coral polyps. Parat fish will be grazing that top layer of tissue off but also crunching away at the skeleton. And then there's lots of invertebrates as well from crabs and worms, right the way up to crown of thorn starfish, which are a huge problem for coral reefs around the world. You know, is we're destabilizing some of the population balances and the community balances in

reefs where we're overfishing potentially a species that will control crown of thorns starfish. That's allowing these crown of thorns starfish to explode in numbers and they feed on the coral themselves and they can cause huge destruction in a comparatively short period of time. And there's nothing we can do to stop the crown of thorn starfish? The first thing is to not remove the predator of the crown of thorns, but there's active removal programs where you get these big crown of thorns. at outbreaks, teams of divers ultimately with a spear, we'll just be spearing them and removing them. That's the best way of actually physically removing them from the reef and then they're brought

back to shore and disposed off. But it's that instability that's happened in the ecosystem that have allowed these crown of thorns to explode. Things like conchre, you know, a very large mollusk that feeds on the crown thorns. That's actually harvested for food. where we've taken too many of those out of the ocean, it's removed these top-down pressures that control the population of starfish naturally. And you said there's parrotfish that will eat the corals as well. I've heard before that white sand beaches that look all beautiful are actually parrotfish poo. Is that true?

Yeah, yeah, pretty much. So they get through a huge amount of this calcium carbonate material. So that's what the coral skeleton is made. of calcium carbonate. That's what the coral lays down itself. And as the parafish are taking chunks out of the coral, predominantly to get to the soft flesh and the algae that lives inside the coral, they also take that calcium carbonate structure into the gut and ultimately poo that out as nice, fine, white sand. So how long can corals live? You've said that they're quite threatened, but if they were just completely perfect and lovely and happy, how long could they live in the ocean?

There's differences depending on the species and the area of the world that they live in. Some can be short-lived, you know, 10 years could be the life cycle of a coral, whereas other species in different environments could live as long as 5,000 years. So they are the oldest animals that live on the ocean. So it's quite broad depending on where they come from. And I imagine those longer-lived ones, are they generally, the deep-water ones that are growing quite slowly and they've got the long lifespans. Yes, but also we do have some tropical species that form these colossal boulders,

and they're very, very slow at growing. But there's been some cores that have been taken, a bit like taking a core from a tree where you're looking at the tree rings. Corals can do the same thing, so we can look at the cores, and depending on the band that's been laid down, it tells you a huge amount of information about what the climate was doing in the year that that material was laid down. And some of these big colonies have been sort of looking at each of those bands.

You can then count and see how old they are and thousands of years old, some of these tropical species. So can they survive out of water, though? Again, it's species specific. So many corals live in the tidal zone. So obviously the tide's coming in and out twice a day. And those individuals, yes, they come out of the water twice a day every day of their lives. and they have mechanisms of coping with that. So they produce a lot of mucus,

which keeps the colony protected against the sort of harsh, midday tropical sun that's cooking them. That keeps them from dehydrating in essence. So they produce a huge amount of mucus to protect themselves. Because you'll see something similar with sea an enemies, won't you, when they'll sort of pull their tendrils in, if they're exposed and then sort of bead up into a little ball, and then when the water comes back again, just start opening up again.

Yeah, I mean, in the intertidal zone, it's, yeah, that's an incredibly harsh environment to live. You know, half the time you're submerged and it's oxygen-rich waters. And then that can disappear and you can be rained on. You can have a high amounts of sunlight. So you have to have coping mechanisms to deal with that, you know, those huge extremes. And the sea enemy pulls its, like you say, pulls its tentacles in and sort of hunkers down, a limpid sort of sucks onto the rock and protects itself that way. So there's different mechanisms to survive in that harsh environment. You said that the corals contain this symbiotic algae.

Now, are there lots of different types of this algae and can it exist by itself without the corals? The predominant strain, so there's about nine different genuses of these algies, but the predominant one is something called Symbudiniumasee. And rather than calling it species, they're called clades. So there's around eight clades of that symbedinium ac. They can live, open, you know, away from the coral. And in fact, we culture those in the lab just in conical flasks. So you can give them the nutrients and there's carbon dioxide light and they will grow independent of the coral. The benefit of living within the coral is it's a nice safe place to live.

You're not going to get eaten. And so that is the symbiotic relationship that has evolved over these tens of thousands of years. The algae lives within the coral, nice safe place to live, and in return, it gives food to the coral. So we know, again, depending on species, somewhere between 70 to 90% of the food for the coral comes from the symbiotic relationship with the zoosantheli. And we hear a lot in the news about the coral reefs bleaching where they eject their algae when they get stressed. So when they've bleached, will they die or can they get their algae back? It's sort of yes and no answer. It very much depends.

on how long that high and is predominantly driven by temperature. So as we hit above the maximum threshold of temperature in the summer, if we go above that threshold, that causes the bleaching. If that is a short episode of just a couple of weeks, then ultimately the coral can still capture enough food to maintain its energy level. If the temperature then drops back down, the algae can recolonize and that relationship can continue. What we're seeing, though, is these bleaching events are becoming more protracted. So we're getting longer periods of warming at the maximum temperatures of the summer. And ultimately, the coral then starves.

It just can't capture enough prey items to get it over that stress period. And in that sort of case, the coral dies, the skeleton that's formed, and the skeleton creates this huge three-dimensional structure that allows this explosion of life to occur on coral reefs. If the coral dies, that structure becomes very brittle, breaks down and it becomes very two-dimensional. So all that associated life on a coral reef actually disappears. It should be pointed out, coral bleaching is not a modern phenomenon. It has happened throughout the corals' evolution. What we are finding now is that these bleachy events are becoming more frequent, they're becoming more extreme. And we're, we're, we're,

We're not giving enough time for the corals to recover from one bleaching event before the next one slams into it. And it's the sort of constant onslaught of these temperatures that is causing the biggest concern for reefs around the world. And why are corals so important? What's their role in ecosystems? So corals are, they're a bit like the buildings of a city. They construct the reef themselves by laying down this calcium carbonate skeleton. And they make this three-dimensional structure of the reef that allows a huge variety of life to occur. So we know that they cover really small percentage of the ocean floor, less than 0.1% of the ocean floor is actually a coral reef. But within that 0.1%, a quarter of all marine species reside on coral

reefs. So they are absolutely jam-packed with life. And it's the coral making this three-dimensional structure that allows this explosion of life to occur. So they're really important for a a marine species point of view, but they're also really important from a human point of view. We get a lot of ecosystem services from reefs. So that three-dimensional structure that they build is really efficient at diffusing wave energy and stopping coastal erosion. So they're very important coastal barriers to stop coastal erosion. We know that a huge population of the planet, around 500 million people around the world rely on reefs for food security from fisheries increasingly because of tourism. So when you sort of tot up all these ecosystem services

that they provide, it's estimated about one trillion dollars they contribute to the global economy. So they're really important biologically. They're really important from a human perspective as well. So we said the warming can have an effect on the corals, but what else threatens them? Climate change is the biggest threat globally to corollies. And we know it's an anthropogenic driven climate change is the number one threat. And in order for reefs to survive into the future, we really need to be hitting those climate targets to stop CO2 emissions. But then there's lots of other threats that are compounding this pressure on reefs. And those, when we think about local threats, we think about issues of overfishing, local nutrient supplies, so things like

you're putting fertilizer onto agricultural land, to boost crop production. Ultimately, that excess nutrient makes its way into the oceans. And that causes, you know, phytoplankton to bloom and an increased nutrient is really bad for reefs. We've got lots of issues of sort of non-invasive species or non-indemic species and invasive species being introduced onto reefs. And all of these are putting increased pressure on corals themselves. You said that tourism is really important for coral reefs as that brings income to certain regions. So which reefs should I visit if I want to go and see one? Or should I even be visiting them in the first place?

Is it better if tourists leave them alone? It is a really difficult question, that, because we do know that if you value something, you're more like to protect it. We also know that the more people visit, the more pressures that puts on reefs from increased pollution, increased water use. All of the things that associated with overpopulation. So it is a really, that's a real double-edged sword, really is. If we empower people to look after their reefs, then, and that comes through generating income so that they can support their families, they're more likely to want to look after that.

But we have to do that in a responsible way where we think about which areas we want to want tourists to go to how we manage the pollution that ultimately people bring as part of that tourism. So it's a fine line to tread, definitely. What's the best reef that you visited? I think probably Palau, which is out in the Pacific, is just beautiful. And it's beautiful because it's very remote. It's a long way to travel to get there. It's relatively sparsely populated. And the reefs are an incredible condition there. What was quite interesting is, you know, I went there over a couple of years before the pandemic. In 2012, a typhoon hit and absolutely decimated the western side of Palau to the point that the coral coverage went down to less than 5%. It was really hit hard. But because

there's so little human influence, it has actually rebounded back so quickly that you will dive on a reef there and not know that there was an impact. It's incredible. And it just shows you that they are resilient reefs and corals can recover just as long as we give them, we remove the pressure to allow them to recover naturally. Thank you for listening to this episode of Instant Genius. That was Coral expert, Dr. Jamie Craggs. To hear him tell me even more about corals and how they breed, head over to the Instant Genius Extra podcast. The latest issue of BBC Science Foceroges, magazine is available now. Pick up a copy in store or visit sciencefocus.com. This podcast is sponsored by Name, Audio and Focal. The texture and emotional depth of music

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