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Word on the Reef
Inspiring interviews with marine conservation legends.
Word on the Reef
S3 E6: Starfish vs. The Great Barrier Reef: Can We Stop Them? [EXTENDED VERSION]
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What has eyes on the tips of its 20 arms, venomous spines, is almost impossible to kill — and is munching the world’s largest reef?
Meet the crown-of-thorns starfish.
Professor Morgan Pratchett has spent years studying this formidable predator. He’s been on the pointy end of one more than once — and lived to tell the tale.
In this episode, he reveals new research that could help tackle this army of millions.
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20-Armed and Dangerous: Meet the COTS
SPEAKER_03You're listening to Word on the Reef, diving into marine science on the Great Barrier Reef and beyond with Tanya Murphy and Brett Goodban. Good morning and welcome to Word on the Reef. I'm your host, diver, and marine conservationist Tanya Murphy. And with me, as always, is Cairns Aquarium's marine educator and fish whisperer, Brett Goodban.
SPEAKER_02Good morning. Jeez, we dodged a bullet down here, didn't we?
SPEAKER_03Absolutely. We'll talk about that cyclone in a minute. But first, Brett, I want you to imagine that you have eyes on your arms.
SPEAKER_02Oh, okay.
SPEAKER_03And if that's not crazy enough, you also have 20 arms.
SPEAKER_02Oh, right, okay. At least I could see things coming.
SPEAKER_03From every direction.
SPEAKER_02From every direction, yes.
SPEAKER_03You also have venomous spines, hundreds of tiny sucker feet. Trikey. And you can eat up to half your body weight in coral polyps in a day by turning your stomach inside out and dissolving them with your stomach juices. Oh, lovely. Nice. If you could just stop doing it on the in the studio, that'd be great.
SPEAKER_02Yeah, I get in trouble walking down a street like that.
SPEAKER_03But can you guess what you are?
SPEAKER_02Oh, I know who that is. That's our Cranathorn Sea Star.
SPEAKER_03Yes, you're the infamous Cranathorn starfish or sea star, also known as Cots for short. They are a native animal in our oceans, but due to reasons that we'll explore in today's episode, their population has exploded. Millions of these spiny pests, which can be up to two feet in diameter, are munching their way through our reef. And to be honest, it's not great timing, considering our reef has also just experienced six mass bleaching events and is facing a bunch of other environmental threats at the same time. Those critters really are a thorn in our side. Joining us joining us in the studio today to unpack the latest research on these spiny pests and what we can do to stop them is Professor Morgan Pratchett, marine conservation ecologist at James Cook University. Good morning, Dr. Pratchett, and welcome to Wet on the Reef.
SPEAKER_00Very, very happy to be here.
SPEAKER_03Sorry, I didn't turn your microphone on.
SPEAKER_00You're on now.
SPEAKER_03Yes, great to have you on this.
Cyclone Narelle & Intro to Prof Pratchett
SPEAKER_03But before we dive into these coral munching critters, we do need to take a moment to talk about what the communities in Cape York are going through right now. As you heard on the weather a moment ago, Cyclone Norrell has crossed the coast of Cape York near Cohen this morning as a category four, which is the second most severe category of cyclone. It was a five up until it hit the coast, with peak gusts up to 270 kilometers per hour, possible heavy rainfall and flash flooding. It is a remote area and there's about 400 people who could be impacted. We'll be waiting for more updates as the day unfolds. But for now, our thoughts are with everyone up there. Hoping everyone is okay. Now, of course, here in the tropics, cyclones are a natural part of life, but thanks to climate change, they are becoming stronger and more destructive. The Coral Sea has just recorded its hottest summer on record following 2025, which was its hottest year on record, and warmer seas and hotter air tend to fuel more powerful storms. To put that in perspective, in the past 20 years we've had 15 severe cyclones, that's categories three, four, and five, compared with only eight severe cyclones in the 20 years before that. So the frequency of severe cyclones has effectively doubled. And if you overlay the tracks of all those cyclones, you can see that they have battered every corner of the reef. Professor Pratchett, you've been doing surveys all over the reef for a long time. Have you personally seen some of the impacts that cyclones can have on our reef?
SPEAKER_00Yes, we certainly have. So cyclones equivalent to Cyclone Norel have crossed the Northern Great Barrier Reef several times. So, you know, we saw back-to-back cyclones in 2014 and 2015 that impacted Lizard Island, and we were on site to see firsthand the destructive effects of those cyclones. The thing we need to realise, however, and it's quite important, is that these cyclones also have contributed to the fact that even though we were on track to have a really serious heat wave this summer and very high temperatures, the series of lows that we've had, even you know, soon after Christmas, have actually suppressed the ocean temperatures. And so I know it's not, you know, our thoughts are definitely with everyone who's being impacted by this cyclone, and there's no doubt that this cyclone will have localized impacts on the reefs in the path of that track. But it's also contributed to the fact that we've got lower temperatures than we might have otherwise expected at this time in the season, and that has meant that we are spared fortunately this year from having a serious mass bleaching event. Yeah, it's kind of like a double-edged sword, isn't it?
SPEAKER_03Yeah, if you're a coral, you've got an interesting choice. Either destructive cyclones or bake to death.
SPEAKER_02Yeah. Yeah, okay.
SPEAKER_03Okay, let's move on from cyclones for now and talk about some of your research, Professor Pratchett. To start off though, can you please tell us a bit about yourself and your background and how you came to be passionate about the marine world?
SPEAKER_00Yeah, so I was um very fortunate to end up at James Cook University back in the 1990s by virtue of the fact that my parents moved interstate. I went to school in Western Australia, grew up in remote part of the Kimberly's. So I grew up in Cunara. Oh, from the very far north. I did go to boarding school in Perth. Yeah. And then while I was at boarding school, my parents moved to Mackay. So I looked to JCU when the un time for university came. And at the time when I went to James Cook University, I was very much just can interested in science, but you know, everyone was talking about coral reef ecology, and it was of course, you know, fortunate to be on the doorstep of the Great Barry Reef, and so I fell into step with that and haven't looked back. So I am a JCU graduate. I spent a couple of years overseas for a while in France mainly, but also in the UK and the United States studying coral reefs, and then came back and have been at James Cook University ever since. Wow, that's a resume.
SPEAKER_03Well, you were already on the greatest reef in the world, so you can't really beat that. Yeah, that's
Name and Origins of the COTS
SPEAKER_03right. Now uh let's talk about the Crown of Thorns starfish. And by the way, they're not fish.
SPEAKER_02No, so I you have no idea how many times I say this in one day. Like I I have to bite my tongue. Otherwise, yeah.
SPEAKER_03Are they really called Crown of Thorns starfish or are they crown of thorns sea stars?
SPEAKER_00Um It depends where you're from, I think. So mostly if you take the sort of you know American perspective, then you should be calling them sea stars. But we encounter that on a regular basis because it depends on where we publish our research as to what they require us to call them. But generally, in sort of, you know, in Australia we tend to s stick with the sort of English vernacular and so starfish in my mind is the sort of you know is fine. Um and that's what I will refer to them as probably throughout this conversation.
SPEAKER_02I guess if you don't have a brain and a heart and blood, you sort of might not fall into the fish category, isn't that right, Professor?
SPEAKER_00Absolutely.
SPEAKER_02Yeah, okay.
SPEAKER_03So it's okay to call them a starfish then here. I believe so. Okay.
SPEAKER_00And we've got to be we've got to be a bit careful about calling them cots as well. Okay. Because I um got invited to talk at a um forum about animals. And everyone else there was talking about cats. And I'm sure I got invited because they thought I also worked on cats. Yeah, yeah, kind of different.
SPEAKER_03Oh goodness. Right. Well the methods Let's not do that.
SPEAKER_02Community announcement people, we're talking about COS, not cats.
SPEAKER_03The methods that we use on COTS might have a high a less um high approval rating if they were used on cats, that's for sure. So about these crownothorns starfish, when were these COT outbreaks first detected on the Great Barrier Reef?
SPEAKER_00Okay, so when we count outbreaks of Crown of Thorns, we tend to refer to the scientific record. So the first documented outbreak of Crown of Thorns was in the early 60s and was first noticed on reefs around Cairns. But there is evidence that there were major infestations recorded on the Great Barrier Reef as far back as the 1930s. Wow. And it's quite possible, because you have to realize that you know there weren't a lot of people getting in the water and looking at the reef before that time, that Crown of Thorns outbreaks might actually be a natural phenomenon that have had a major influence on the function and structure of the Great Barrier Reef and all other reefs throughout the Indo-Pacific. Having said that, there's a high likelihood that human disturbances and especially overfishing and the introduction of nutrients may have made the situation worse. And fundamentally, the reef is subject to so many disturbances that they can't withstand the usual sequence of disturbances that they might have been exposed to in the distant past. Right, okay.
SPEAKER_03That's a good point. So even if there were COTS outbreaks in the distant past, the reef would have been in a healthier state to deal with those because it wasn't also dealing with bleaching and water pollution and things. So it makes sense why it's a bigger problem now. And it may be that the COTS outbreaks are bigger because of the things that humans are doing as well.
COTSon-Eyed Joe Outbreaks: Where Do they Come from? Where Do they Go?
SPEAKER_03How many outbreaks have there been since they sort of started scientifically recording them on the Great Barrier Reef?
SPEAKER_00Yes, so since the first documented one in the 1960s, we've had four major waves of outbreaks, and we have recently detected the start of the fifth. So it was widely predicted that we were going to see a fifth major outbreak commence in around 2024, and we actually have documented the increase in abundance since around 2021. But we now have higher than what we call outbreak densities on many reefs between Cairns and Lizard Island. And also I've just got back from the Torres Strait, and the densities of Crown of Thorns at many reefs up there are also above those outbreak thresholds. So the whole far northern Great Barry Reef is again being exposed to devastating size and density of these Crown of Thorn starfish.
SPEAKER_03I've been on and around the Great Barrier Reef for 15 years, and it feels like there's never a gap between them. Do all the outbreaks just sort of run into each other, into one continuous thing?
SPEAKER_00Yeah, it's important to realise that this sequence of outbreaks that we get travels down the Great Barrier Reef.
SPEAKER_03So they start in the north, do they?
SPEAKER_00They tend to start in the north. That we've had some interesting discussions of late about exactly where they start. We used to talk about this thing called the initiation box, which is the area of mid-shelf reefs between Cairns and Lizard Island, which is where a lot of the focus was in terms of understanding how or why we get these cranathons outbreaks. But in this recent event, we've been looking much further north, and we think that we probably have an issue where there's a lot of reefs in the vicinity from Lizard Island to Torres Strait, which are very poorly studied. And we found that we had elevated densities of very large starfish as far back as sort of 2019-2020, which might have been the precursor to this latest outbreak. So it's sort of changing our thoughts on how these things start and what we need to do about it.
SPEAKER_02So what constitutes an outbreak? Because we know that these animals are part of the ecosystem, and this is something I get at work a lot is people go, oh, they fell out of a helicopter or they came in in ballast water. So no, that's that's not true. They're part of it. So they're part of the ecosystem. So do we know what the controlled acceptable number is to have within an area and then constitute an outbreak?
SPEAKER_00So outside of outbreaks, and I should continue on, that we get this cycle where there's usually a 15-year gap between outbreaks on any given reef. But it like you have pointed out, that you know, they start in the north and they end up in the south. So just before we see the start of the new one, they're sort of petering out in the south. And there's all waves. Yeah, it's a big wave, and there's all sorts of questions about whether there's certain areas which are behaving independently like the swains. But outside of an outbreak, most people don't even realize they're there because the densities are really low and they're really, really cryptic, so they're hard for anyone to see. So there was an assumption that outside of outbreaks the densities were effectively nil. There were no starfish on the reef. But we've come up with a new method of surveying them, and we're consistently finding that outside of an outbreak, you've got about three starfish per hectare. Right, okay. And then when the density increases to around 15 starfish per hectare, that's when we consider that there's an outbreak. But you also get a fundamental change in their behaviour where they seem to be more visible and feeding a lot more during the day. Yep. And that's when they become really apparent to a lot of divers. Right. Okay.
SPEAKER_03The reef will just be seething with them, so to speak. I think the reefs that I've dived on, tourism reefs, have been very lucky in that they've had a lot of pest control done on them. So I actually haven't seen a seething amount of Crownathorn starfish, which goes to show that those areas are being tackled. Yeah. But of course, uh, in a reef that's nearly the size of Germany, there's there's going to be a lot out
COTS-Proof Wall?
SPEAKER_03there. That's so interesting that that you said that they always start in the north and they're even further north, this latest one, because that's not the area with the most water pollution, surely. And it's also it's very remote up there. So I would assume there is less fishing and less industrial and agricultural.
SPEAKER_00You're absolutely correct. So it questions the whole theory around what starts them. But we need to think very specifically about the initiation or what actually starts an outbreak, and it might just be a natural cycle versus the human disturbances which might be exacerbating or making the situation worse once an outbreak does get started. So they might start up there and then start progressing south, and then they uh you know, you've then you've got that area where there's parts of the reef which are heavily impacted by declining water quality and overfishing, and that's where we tend to get the highest density. So we need to separate that initiation versus the spread.
SPEAKER_03Yeah.
SPEAKER_00Okay.
SPEAKER_03Has anyone tried building a wall to stop the side?
SPEAKER_00We've had discussions about the fact that cyclones might create this area where there's very little coral, especially the particular corals that Crown of Thorns like to feed on. And so there was this notion of the yassy fire break, which was supposed to stop the last outbreak. But these things, as you say, are incredibly versatile, incredibly well adapted to their life on the reef. And so it wasn't really a surprise to me that the larval stage went straight over there and we saw the normal spread of outbreaks in this last event.
SPEAKER_03Yeah, the the tiny larvae will drift in the current and find their way straight over that fire break.
SPEAKER_02So if you is a lot, because I had eight sea stars in my touch tank the other day. Trevor went off just producing buckets of sperm, and the others went, oh, party time. And the whole the whole tank was just white with sperm and people coming up, what's that? Well you stick your hand in there if you like, but uh I had to go and put them over next to the filter. So yeah, it's a colossal amount.
SPEAKER_03You had to cool them down.
SPEAKER_02Yeah, I had to turn the barry white off.
SPEAKER_03Well, in case anyone's confused, the sea stars at the Cairns Aquarium are not crown of thorn stars.
SPEAKER_02No, they are not crown of thorns. We don't let you touch those.
SPEAKER_03No. Okay, so yeah, in case there are any people out there who are like, well, just blow a big hole in the reef and that'll stop the cots from marching across, not going to work because the larvae can drift across in the colour. Exactly.
How to Find COTS Faster... And How Many Are There?
SPEAKER_03Now I understand you've been using underwater scooters, Professor Pratchett, to help survey and detect cots. That sounds like fun. What can you tell us about that?
SPEAKER_00Yeah, so one of the problems in finding these cranothorns outside of an outbreak is there it's a lot of reef between the individual animals. And so the scooters are just helping us cover more ground so that we can now do transects which are up to two kilometres long on a single dive and provide much better ideas of what the densities are, and that's been important in detecting the very subtle increases that we see at the start of an outbreak. So we've seen in the areas around Lizard Island that the densities of Crown of Thorn starfish have been going up since 2019 and they exceeded those notional outbreak thresholds in the last couple of years. So we were we now have a method which lets us know that they're coming well before we get to those sort of devastating, unsustainable densities of crown of thorns.
SPEAKER_03Yeah, well, that's good. So you sort of predicted this was coming as you saw the numbers starting to climb. You must have a really good eye, knowing that they are so cryptic and they hide, and you're trying to see whether there's more than three per hectare.
SPEAKER_00Yep.
SPEAKER_03You must have your eye in after all the hours you've spent doing it.
SPEAKER_00Well, actually, the impact of crown of thorns, the feeding scars they produce, are really, really conspicuous. So you get to an area of reef where you see all these really stark bright white corals, which you can actually even see from the surface sometimes. And if there's no bleaching and there's no coral disease, it's a very high likelihood that it's one of a number of different coral predators. And so we then go down and look very carefully at those corals. We're looking for the little drupella or droop snails, which also will eat coral. And if there's none of those, we then sort of start thinking this gotta this has to be a crown of thorns, and then we look very intensively in the area of there and generally find the crown of thorns. Little cots neighborhood.
SPEAKER_03Mm-hmm. And it's peeking out at you with its eyes on the end of its arms.
SPEAKER_02Sitting around a table playing poker.
SPEAKER_03So uh Brett sort of asked how many there are. I mean, you told us more than three per hectare areas starting towards an outbreak. I mean, uh over the whole Great Barrier Reef in total. Is there any estimate as to how many there might be?
SPEAKER_00Yeah, it's very hard to get an estimate. I mean, the last time we tried to really put a number on the total population across the Great Barrier Reef, the numbers were between seven and fifteen million starfish. Now, for this current outbreak, we're nowhere near that. Um, that's when you start to get the really high densities across a large range of reefs, mainly in the sort of central section of the Great Barrier Reef. But it does mean that, you know, if we're talking about culling, where you've got to individually find and inject all the starfish, we've got our work cut out for us.
What it's like to be Spined by a COTS
SPEAKER_02Yeah, I have a bit of a beef with the old sea stark cranathorns back in the day. I've been stabbed by them and I got the bends from them. They're they're not my best mate. Actually, we do have cranothorns at work, and we've got a big crown of thorns info wall. So if anyone wants to come in and say get a you can check them out. I give them a stink eye every time I walk past. Well, I remember you too.
SPEAKER_03Yeah, well, while Brett brings it up, that's that's one of the problems in dealing with Cots is their venomous spines.
SPEAKER_00Yes. Dr.
SPEAKER_03Pratchett, have you ever been stung by a crown of thorn starfish? And what does that feel like?
SPEAKER_00Yeah, unfortunately I have been spined or stung many, many times. It's a lot. Um in the worst case scenario, I was doing an experiment to see how fast they could walk over different reef substrates, and the tank we were using was so big you actually had to get in the tank. And I unfortunately stood on a spine and it you know went at least an inch or several centimetres into my foot, and that was the worst one I've ever had. And without the immediate sort of treatment, which is very hot water, and also, you know, we're realizing that it's not a it's not a risk of an infection, there's an actual allergic reaction, so you need to get cortisone on that side of the penetration pretty quickly and try and get the spine out, deal with it in all these different ways. Um, but it's still very, very painful.
SPEAKER_02Yeah, I don't I don't know what was worse, actually getting the stung in the thumb or sticking my hand in a bucket of hot water.
SPEAKER_03Oh yeah.
SPEAKER_02Yeah, it's just awful.
SPEAKER_03Yeah, you that's of course the treatment for the spin out the venom. Venom, yeah, is to put the affected area in very hot water.
SPEAKER_02Yeah.
SPEAKER_03Well, you're not supposed to have it hot enough that you can burn yourself though, Brett.
SPEAKER_02You might have Oh, I wasn't noticing anything at that point.
SPEAKER_03Yeah, wow. I have never been stung by Crown of Thorns, starfish. But is it true that if you get stung multiple times and it gets worse or that it builds up in your body?
SPEAKER_00Yeah, so I think the first thing to point out is that different people respond very differently. And there are some people who are very, very sensitive to being spined by crown of thorns. I have a previous student who experienced anaphylaxis following quite a serious spining. So there's that natural variation, but just based on my our experiences, it does seem that it's getting progressively worse. We don't really understand why that would be the case, but I'm much, much cautious now in handling crown of thorns than I used to be because of the potential risk. And we're always doing it at sea a long way from any sort of medical assistance, so we have to be super careful.
SPEAKER_02It's never next to Cairns Hospital, it's always out in the coral sea. There was a myth going around a lot. Well, I'm gonna say it is, but I'm gonna ask the professional that if you get stung a certain amount of times, then your dive career's over. Is there any truth to that?
SPEAKER_00Well, I've been spined many, many times. Yes. I do think it's getting worse, and I think we do need to make sure that divers realise that they shouldn't put themselves at risk when doing this. So I think it's important that we keep that message that leave it to the experts. And also if you are involved in the culling program, there's no reason that you should be anywhere near the starfish. The wands on those injection apparatus they use are quite long, and so you should keep your distance from them.
SPEAKER_02Do you know what ours was? We we were told as dive masters, right, this afternoon you're gonna get in, you're gonna go cot hunting. Here's a bag. They grabbed a pair of bags. Of tongs from the galley, just a normal pair of short barbecue tongs, no gloves. I said just go pick them up and chuck them in the bag. Well that was that was the level it was it was at back then.
SPEAKER_03OHS uh at C doesn't exist sometimes. And then they would go and um cook the sausages for the guests with the tongs, right? Yeah.
SPEAKER_02No.
SPEAKER_03Okay, so watch out, don't get stung, everyone. It makes sense because I feel like some other anaphylactic reactions, like even uh exposure to mango sap, apparently people end up becoming allergic to them over time because if the your body just builds up this stronger and stronger allergic reaction to some allergens.
SPEAKER_02There's my one thing I was going to learn today.
SPEAKER_03Yes, and that's all I know about mango sap. Right. Okay.
Impacts of COTS on Coral Reefs
SPEAKER_03So what impact do COTS outbreaks have on the Great Barrier Reef? How serious of an impact can they have? How much of the reef can they consume or damage?
SPEAKER_00Yeah, so the ecological impacts of Cranathorn starfish are directly related to both the size and also the local abundance or density of Cranothorne starfish. Now, we have had some unprecedented records of densities around the Pacific. So the highest densities recorded were in French Polynesia, where we had densities in the order of sort of like 1,500 per hectare. So that's sort of, you know, a hundred times higher than what we consider the outbreak density to be. And it's pretty obvious that when you've got those sort of densities, they're having a devastating impact because the coral cover at that particular location was around 40%, it went to less than 5% in three years. So they can have a very, very serious effect in areas where there's high densities. To put it into context, at the moment there is no denying that climate change is the biggest threat to the Great Barrier Reef, and these very large-scale mass bleaching events we've had cause devastating coral loss in many, many parts of the reef. But if we look at the sort of extended history, like we have good data for Lizard Island, I'd argue crown of thorns are still the biggest killer of corals on the Great Barrier Reef when you look at the history extending back sort of more than a decade. But in the recent years, there's no doubt that bleaching is a very important and increasing threat.
SPEAKER_03Yeah, it's only just started to overtake the cots as the biggest threat, yeah. Now, uh
Practically Indestructible: How to Kill COTS - Correctly
SPEAKER_03as we sort of touched on, the problem with controlling the crown of thorns starfish population is that they are really hard to kill. Can you explain to listeners why that is?
SPEAKER_00Yeah, so the foremost issue is finding them. So you've got to swim around very, very large areas of reef looking for these crown of thorns. So there's a very big surveillance issue to know where you should actually get in the water to start culling them. And even when you get in the water, I would argue that even the best divers, the people with the most experience, are probably only going to find around half, probably much less, of the crown of thorns that actually exist in that area. And that's just because the inherent behaviour of these crown of thorns is we've recently discovered is they can often go and have a really, really big feed and then go and hide in the reef for three or four days before they start feeding again. And no one's going to find those crown of thorns. So it's just this fact that you've got to keep going back to the same sites over and over again before you can really seriously affect the local population. And then we've got to think about what makes it really efficient and effective to cull these starfish at the moment. We're individually culling them. So, like I say, we've got our work cut out for us if we think we're going to, you know, effectively find and cull millions of starfish in a short space of time.
SPEAKER_03Yeah, the amount of people and boats and you know, dive tanks have a limited time on them, like you said. But also you can't actually stab them or chop them up, can you?
SPEAKER_00That's right. The way we cull stowerfish has evolved quite a lot and changed over the recent years. So in the past there was this idea that you could cut them up, and we've actually done that work now. It shows that you could cut them up into sort of, you know, as as many as eight pieces, and you do get eight new starfish. That's right. That's terrifying. The thing is, you have to cut through the oral disc. So it's, you know, we were doing it in a very rigorous, precise way. If you just like really cut it up into lots and lots of little pieces, there's a chance some of those pieces, but not all of them, will survive. So don't cut them up. Partly we recommend don't cutting them up because of that risk that you're going to get spined. It greatly increases that risk. So what we do now is we inject them with toxic chemicals. And even when I first got involved, um, we were using sodium bisulfate, and you needed to inject each starfish multiple times because if you inject certain chemicals, they just sort of like reject that chemical or they can drop that arm and continue to live. But we've now got indestructible. Like oh they're incredible.
SPEAKER_03Just throw one of my arms away.
SPEAKER_00Sorry, Frank, you're infected, you're off. Yeah. But we've changed the injecting apparatus and we're using new chemicals, and then we now have what's called the single shot injection method. It's safer to inject them probably two times instead of just one, just in case something goes wrong, but it's made it much more efficient. And so our capability to control starfish has increased, you can imagine, you know, many fold from having to inject them 20 times to just find them and give them a single injection.
SPEAKER_03Yeah. So I understand that one of the chemicals you can use to kill them with a single injection is oxbile. So that's from the stomach of cattle, basically, oxbile salts, or a single injection of vinegar. Is that right? What's the difference and and why does uh are both used in different situations?
SPEAKER_00Yeah, so we just fortuitously discovered that cranothorns are super allergic to bile salts. And it was an accidental discovery because bile salts isn't an agre in ingredient in this chemical we use to look at diseases that naturally occur in crownothorns. And so we're injecting them with this chemical compound and we are finding that they were dying really, really quickly. And so it just, you know, through a series of experiments and a lot of research, we found that the bile salts itself was what was killing the crown of thorns. Wow. And one of the things about bile salts is it's super acidic. And so then, you know, it resurrected a lot of discussions previously about using other acids, and so with some changes in the injecting apparatus, we've made it much more effective just to kill them with you know plain household vinegar. There's no denying that the bile salts is still more effective, but you can do things like change the concentration of vinegar. And we also did some work talking about, you know, their phenomenal reproductive capacity, each crown of thorns, you know, in this in the reproductive season can produce a hundred million babies. Yep. Oh my goodness.
SPEAKER_03Um there's 15 million starfish out there, and each one of those, at least half of them who are female, can release what did you say?
SPEAKER_00A hundred million per season. So the question is why don't we why aren't we just completely overrun with them all the time?
SPEAKER_01Yeah.
SPEAKER_00But the thing I was getting to with the chemicals is the bile salt seems to kill them faster still. We've still got a bit more work to do in that area. But that's why at the moment the recommendation is you use the bile salt, especially in the reproductive season, and then go back to using the vinegar outside of the reproductive season. Just because that bile salt is just a little bit more efficient still.
SPEAKER_03Yeah, so when you say reproductive system, you mean that if the starfish has been injected and it detects that it's going to die soon, does that actually trigger them to release their 100 million babies?
SPEAKER_00Yeah, that's exactly what we found. So sometimes when they've been injected with vinegar, they survive anything up to 48 hours and they still have that last gasp sort of chance to reproduce. Fortunately, it was only the males that were responding like this. They're the ones who seem to be r able to react really fast, so they were producing lots of sperm. But we know in the wild, just as you talked about in your tank experiment, the biggest cue for starfish to spawn is detecting other gametes in the water. So when one starfish spawns, the others in the area straight away go, Oh, this is a cue for me to get my act together. They all go off.
SPEAKER_02Isn't that incredible though that that something that doesn't have a brain goes, Oh, that's it, vinegar's in me, I've got one last crack and well there's one way of thinking about it that it doesn't have a brain, but in a way they have many, many brains.
SPEAKER_00So potentially we're underestimating their capability and adaptation.
SPEAKER_03Yeah, it's a nervous system. Yeah, for sure.
SPEAKER_00Yeah.
SPEAKER_03Okay. So and that so I understand I mean it says ox bile salts, so we're not able to get those from our native grown cattle where they come from overseas or something.
SPEAKER_00Yes, we are absolutely able to get them. The issue is that you know it's a very, very small market in the scheme of things, and so there's not currently abattoirs in Australia who will harvest the bile. Um, and so we're mostly importing it at the moment from New Zealand. And that's fine. There is a quite a substantial cost involved in making sure that it's refined appropriately. But there are issues with importing it, um, especially when there's concerns around mad cow disease and when there's bans on moving bovine products. But we could get it potentially from any other animal too. So we have been in discussions with a local abattoir for pigs because we could even get the bile from there.
SPEAKER_03Mm-hmm.
COTS Bot: The Robot Starfish Terminator
SPEAKER_03Now I was uh researching online and I saw a video about the Cotzbot, a Cotz terminator robot that was developed to help in the fight against COTS, but the video was quite old. Is that Cotzbot still going? Is it still a thing? What can you tell us about it?
SPEAKER_00Well, I'd argue that there's definitely a place for new technology in Crown of Thorns management, but probably the optimum use of the robots is to find the areas which are really severely affected by crown of thorns. Given the difficulty in actually finding a crown of thorns, let alone getting in amongst the coral and in ministering the injection, there's some a lot of work still to do before a cotspot will be able to outperform a diver in terms of the actual culling.
SPEAKER_03So the AI isn't coming for our jobs just yet?
SPEAKER_00Uh not in that sense, but I think that the the appropriate use of that technology, and especially you mentioned the AI, the machine learning, the ability to detect the crown of thorns, I think we should be using robots to make our surveillance um more efficient so that you know we're not analyze your divers better. We're not towing the divers around because their visual system isn't as good as a robot. But when it comes to actually killing them, their dexterity and their ability to find them in amongst the corals just still can't match what a robot can do.
SPEAKER_03Yeah, it was a really cool video. The robot had like an arm that would come flinging out and stab the starfish, but only if it was lying out in plain view, it couldn't get underneath the corner.
SPEAKER_02It had to be sitting in the middle of a sand coral sand bombing, perfect conditions, not tucked up underneath coral. Yeah.
Risks of Intervening on COTS
SPEAKER_03So with all of these humans and you know, scooters and robots zooming around trying to detect and kill Cranathorn's starfish, are there any possible risks to the reef associated with these types of interventions?
SPEAKER_00There is a concern that if we're not doing it well enough, we might just perpetuate the problem. So we do know that there's a natural boom and bust cycle, and so these densities increase really, really fast, and then they eat a lot of their preferred coral, which is the branching acropora, and then they disappear just as fast as they've come. And so there's that collapse in the population, which we think is due to a combination of things related to starvation and disease. So by culling them to a lower level all the time, we could be actually perpetuating the outbreak. So that's why it's important, and everyone recognises this, when we commit to culling at a certain reef, we've got to get them below that normal sort of threshold density and keep persisting with our effort until we do effectively do that.
SPEAKER_03Wow. So you're saying that by allowing them to overpopulate the area, they'll actually outcompete each other and just all die and collapse. And when you were saying about how they sort of just suddenly might disappear and everyone will be like, where did they go? And I just couldn't help but think they're like Cotton Eye Joe.
SPEAKER_02We should we should actually start little gangs of Cots, you know. One comes into their hood and they just take each other out.
SPEAKER_03Turn them against each other, you reckon.
SPEAKER_02Yeah.
SPEAKER_03Uh anyway, before I start breaking out into song about COTS,
The War on COTS: Who's Winning?
SPEAKER_03the Cot's problem is such a threat to the reef and its tourism industry that significant funding has been poured into having dedicated full-time COT eradication divers out on the reef. I have many friends who have worked on dedicated COT boats. It's a pretty cool job. They get to go diving and snorkeling all day and kill starfish and do scientific surveys. But how much effort in terms of staff, boats, and funding is being put into this war on COTS?
SPEAKER_00Yeah, it's a significant investment, and like I say, it requires persistent effort on the reefs where we decide to try and cull the crown of thorn starfish. And we are making headway. And so in the past, the the control efforts were really like you talked about previously, very localized around tourism areas. Where now, with changes in the way we do it, embracing the new technologies, the new surveillance methods, we're actually starting to have an impact at the scale of the entire Great Barrier Reef. But I believe there's still some way to go. And we need to sort of probably have an honest think about whether we're ever going to stop these outbreaks or whether the goal is just to suppress the density so that we can allow corals to survive and adapt to the other emerging threats like climate change. So there's a lot more work to do as well as continuing to invest in the culling program, I'd argue that there's still a lot more research that needs to be done. They're probably one of the most heavily studied animals on the reef, but it is critical we understand this animal as best as possible in order to effectively manage them.
SPEAKER_03Professor Pratchett, over the years, how has the tourism industry helped with efforts to fight COTS?
SPEAKER_00Well, the whole culling program that we have today was very much initiated by the tourism operators and a few select tourism operators around Cairns were very concerned about the threat posed by Crownathorns, and they really pioneered what we have today in terms of the culling program. So even before we had a you know integrated reef-wide program, they realized that we needed to move beyond sort of cutting them up or collecting them to an injection method. And so that paved the way for what we have today. Now there's been a number of improvements since to make it viable to attempt to control crown of thorns at the scale of the Great Barrier Reef, which is arguably, you know, the biggest reef system affected by Crown of Thorns. And so it has been important that we've made changes in the way it's done, and that has facilitated significant government investment, and it's it fortunately it is funded for quite a long way into the future now. Even though things like climate change are recognised as very, very significant threats, and we definitely need to do something about it. It also puts increased emphasis on the fact that we need to manage some of these other perennial threats, such as these outbreaks.
SPEAKER_02Yeah, well that was what twenty-seven years ago that I was doing that as a dive master trainee on Atlantic Clipper on the reef. That was part of our if you wanted dives, in you get.
SPEAKER_03How much impact are all these efforts making? Are we winning the war on COTS?
SPEAKER_00Yeah, so there was a um hope, and I probably was overly optimistic at the time that we could potentially stop or suppress the next outbreak. And you know, we're now seeing that we haven't managed to do that. The fifth outbreak is very much with us, and we're seeing high densities on many, many reefs. So we're not quite in the place where we could probably prevent or really contain future outbreaks. And so we have, you know, got our work cut out for us to try and protect as many reefs as possible and still have a clear focus on those really important reefs from the perspective of the tourism sector, but also reefs that are potentially important in terms of our future resilience. So anywhere where there's not sort of, you know, a high elevated risk of bleaching, then we want to try and keep those corals protected from crown of thorns as well. So on one hand, you can look at it, it's sort of, you know, that typical glass half-full analogy. On one hand, we are making progress. Um, in the last outbreak, there's evidence that the densities we saw at some of the really worst affected reefs didn't actually peak and cause devastating coral mortality because of the localized culling. But there's still some work to do before we can say that we've addressed or effectively stopped Crownathorn's outbreaks being such a huge threat to this system.
Root Causes: Solving the Problem at the Source
SPEAKER_03Okay. So given the difficulties in eradicating COTS, it's little wonder scientists have spent decades trying to learn more about what causes these outbreaks in the first place so we can try to prevent them. Professor Pratt, why has it been so difficult to understand the causes of these outbreaks?
SPEAKER_00I believe fundamentally the issue relates to the fact that it's very hard to study crown of thorns when there is no outbreak. So there was, as I said, that assumption that there are no crown of thorns on the reef in between the outbreaks. We've since proven that's not the case. It's just that they're very, very low densities, difficult to find, and so it's obviously hard to progress the sort of research we need to to understand what suddenly changes in the biology and behaviour of those animals that leads to the inevitable outbreak. There's still a lot of questions about the role of fishing and the role of water quality. I think there is no denying that our reef would be much better if we continue to improve management of all the various human disturbances. But it might not stop outbreaks of crown of thorns. What it possibly will do is reduce the severity of the outbreaks, but fundamentally it will allow the reef to be much more resilient to these disturbances that are inevitably going to keep coming.
SPEAKER_03Yeah, so speaking of those known or suspected causes of COTS outbreaks, what are they? What are the known or suspected causes?
SPEAKER_00So there's a lot of hypotheses out there. Essentially, you can reduce it down to three main theories. The first one being the natural causes, and you just got to recognise that they have this unbelievable reproductive capacity. And so, you know, you look at that and you go, well, why aren't we overrun by crown of thorns all the time? And then you know you start looking at well, what causes the collapse, what constrains the population certain times, and so I think there's this natural predator-prey dynamic in terms of they have an outbreak, they eat all the Acropora corals, which is their favourite coral, which you know provides the energy for their huge reproductive capacity, and then there's this inevitable population collapse. So that's the sort of natural theory, just broken down very, very quickly. Then there's two other human disturbances which are believed to either cause, if not exacerbate, the situation, the first one being overfishing. And so we've actually removed a lot of the key predators in certain parts of the reef. A lot of the focus early on was on the giant Triton, but we've just done some research showing actually probably the most important predator, at least in the northern Great Barry Reef, is Spangled Emperor.
SPEAKER_03Oh, is that right? And and is that a popular target because they don't fish or catch fish, is that a popular target for fishermen?
SPEAKER_00It's not a major target fishery species, but it is taken in large volumes by the commercial sector, but probably the biggest take is from recreational fishermen.
SPEAKER_03Wow. So throw your spangled emperors back, everyone.
SPEAKER_02Absolutely. Yeah, that was one of my favourite fish. I've had a connection with one of those out there called Tony.
SPEAKER_03They are beautiful fish. They always come up to you. They want to look in your mask and stuff.
SPEAKER_02I've got him on my wall at home. But isn't also the humphead marryrass.
SPEAKER_00Yeah, so we actually haven't witnessed predation on crown of thorns by humphead marry rass. I do believe that they're capable of it.
SPEAKER_01Yep.
SPEAKER_00Whereas there's other fish which have been on the radar in the past, like coral trout, which just haven't got the mouth parts or the behaviour where I would suspect they would ever eat crown of thorns.
SPEAKER_02So there was there's one of those other things I want to clear up now that my expert's next to me. Back in the the days when the humphead marryass was removed to high numbers off the Great Barry Reef, and then they were listed as endangered. There was this speculation that that helped with the outbreak of the crown of thorns back then because they were known to eat a lot of them, and now that there's less humphead marry rass. Is there any truth to that?
SPEAKER_00Yeah, like I say, I haven't got any personal evidence or verify the role of Marie Rass. We know that, you know, people have seen, have anecdotally reported them feeding on them. Yeah. But I don't think they're a major predator. I'd never seen Wally in 20 years eat a crown of thorns while I was with him. Absolutely. So the other one we're worried about is the inevitable decline in water quality on the Great Barrier Reef. And water quality poses many threats to the Great Barrier Reef and especially reef-building corals, and we absolutely will benefit from improving water quality. Now, the link to crown of thorns is such that they suggest that more nutrients going into the Great Barrier Reef lagoon will increase the availability of planktonic prey for the crown of thorns larvae, and then you have a higher survival of that phenomenal reproductive capacity. More of the crown of thorns are actually settling back on the reef. And that's what causes an outbreak. Now, we aren't really settled as a scientific community on which of those hypotheses is really true or not true. It's very likely that there's a combination of things going on, and so teasing all that apart is still going to require some more effort.
Now Entering: THE EXTENDED DIVE
SPEAKER_03You are now entering the extended dive. Exclusive content just for our subscribers. So
Animals That Can Help us Fight COTS
SPEAKER_03the predators that might be responsible for eating some of those Crown of Thorn starfish. You mentioned that you you found out that spangled emperors were some of the biggest consumers of Cranathorn starfish. How did you find that out? Were you did you set up cameras or were you just sitting on the seafloor watching cots to see what would come along and eat them?
SPEAKER_00Yeah, it might be surprising to learn that up until now we haven't actually measured rates of predation or more specifically predation risk on the Great Barrier Reef. So there's a lot of assumptions around the role of predators because we tend to find the worst outbreaks are in areas that are open to fishing, whereas you tend to get lower densities of crown of thorns in no-take areas. So that's why we think there's a role for fisheries species. And so what we did was actually tether or stake live animals in different reefs in different management zones, and did manage to show that the rates of predation were much, much higher in what we notionally call on the Great Barrier Reef the no-take or green zones. And we did have cameras deployed and found that over 90% of all the predation was actually caused by the spangled emperor. Now we had those traditional sort of candidates come in like giant triton, but they actually didn't do anything. And of all those other fish species, like the classic sort of fishery species like coral trout, we didn't see them get involved at all. We found a number number of other sort of species of puffer fish and ballistards which aren't really targeted by fisheries.
SPEAKER_03That's a triggerfish, is it? Yeah, trigger fish.
SPEAKER_02Yep. Titan triggerfish, every diver's a nightmare.
SPEAKER_03Yeah, I saw your summary that you sent me. It had little illustrations on the graph, and the Spangled Emperors were involved in like 98% of feeding frenzies on that quotes, and the puffer fish was much less, and then the trigger fish, because I'm just based off looking at the picture. I was like, oh, that's a trigger fish, um, was much less, and then the triton was barely involved. I mean, they're they're always going to be late to a dinner party, aren't they? It's a snail.
SPEAKER_02Oh ha, nice. You know, this one thing that we usually say to people that you know if you look at the the head of an animal and you look at the way it's designed, we'll pretty much tell you what it can and it can't eat. And if the Spangled Emperor's got that beautiful long white sloped-down snout with the little lips at the front. So you'd be perfect to get in there and have a crack.
SPEAKER_03I wonder why the fish like the Spangled Emperor don't get stung.
SPEAKER_00Well, I think they are getting stung. They're probably, you know, resilient to it. Um we're not seeing them after that. But they've also got stronger mouth parts than a lot of other animals. So the spines are getting broken down rather than sort of, you know, sticking in their lips.
SPEAKER_03Okay, so uh so you found that no-take or green zones where fish are protected tend to have lower numbers of cots. So very strong Well, that's strong evidence. Very strong support for more green zones, perhaps, more no-take areas as a way of dealing with cots. And you also touched on water pollution, how the nutrients can sort of supercharge the larvae of the cots or are thought to. Do you think there's any impacts of water pollution also killing some predators like crabs? I read a report online, I think it's like new research, that there are certain types of decorator crabs that munch on baby crownathorn starfish. And uh I was just very briefly reading that crustaceans will be impacted by pesticides because any poison that's designed to kill an insect will also kill a crustacean. And so maybe there's some pollution, our pollution in the water is killing some of those cots predators close to shore or something. Is do you know anything about that?
SPEAKER_00I don't know about the direct effects of the pesticides on crustaceans. We do know that there's a lot of other potential predators at different stages in the life cycle of crown of thorns. So there's a lot of things that live within coral rubble and in amongst the interstities or spaces on the reef, which probably feed on the really small crown of thorns when they especially when they first settle. So those decorator crabs are incredibly effective at at removing the really small crown of thorns before they grow up and start eating corals. And so there's a lot more work to do to understand the role of all these different predators. I don't think that any one of these actions, like you know, even if we were to get to a point where we could possibly consider that there'd be a pro you know, a comprehensive ban on fishing, except for maybe some specific species across the entire Great Barry Reef, that it will stop the outbreaks. But all of these things have benefits for the reef aside from any benefits they might have in terms of suppressing crown of thorns. And so we do still need to be thinking about fisheries management and water quality improvement, especially given the overarching and increasing threat of climate change.
SPEAKER_03Yeah, I mean it even for fishermen, if COT outbreaks destroy a reef, then there's going to be less fish for you to catch. So having to have that that restraint in order to make your own passion for fishing sustainable is sort of self-beneficial, isn't it?
SPEAKER_00Absolutely. So, I mean, there's there's many different ways that humans interact with the reef and huge, enormous economic and social benefits from having a vibrant and flourishing Great Barrier Reef. So we just need to find that right balance.
Surprise Benefits of COTS!
SPEAKER_00I have a curveball question. Is there any benefits of the cranothorns? Yeah, it's it's a question we do actually get quite a lot because cranothorns are native and a natural inhabitant on reefs. Yep. And during the sort of you know, moderate outbreaks, the main thing they do is eat a lot of the fast-growing corals, and so a lot of people refer to those as weedy corals. And so they might actually be restoring some balance there and allowing for a greater diversity of corals to grow on the reef. It's sort of like the effect of a wildfire on land. The problem is that once those disturbances become too frequent or too severe, they're actually having a net negative benefit. So we don't want really, really severe outbreaks, and we do need to suppress the densities, otherwise, they'll just end up eating all the different corals.
SPEAKER_02I am so glad you said that because I've just had a professor back up the way my mind thinks because the way that I've been dissecting it for myself is the positivity of them is like our traditional owners burning off the bush to create new growth, which works before populations exploded, but now that balance isn't there anymore.
SPEAKER_00And it's the same with the wildfires. You got to you if you wanted to use it as a management tool, you'd want frequent low-intensity disturbances. You don't want really severe, sort of, you know, infrequent disturbances which have catastrophic impacts. And the problem we are facing with reefs all over the world, including the Great Barrier Reef, is just the ever-growing list of pressures that we have to deal with simultaneously.
SPEAKER_03Yeah, absolutely. And yeah, I loved that analogy as well by burning off the weeds and grass. Yeah. Or even just, you know, kangaroos eating all the grass and weeds maybe makes more space for the trees to grow,
Can COTS become a Commercially Viable Fishery?
SPEAKER_03right?
SPEAKER_02Do you remember remember when we had our expert on the show uh talking about the outbreak of the sea urchins? Yeah, in the Great Southern Reef. In the Great Southern Reef, right? And they were talking about profit made by removing them and selling them to Japan for food. Yeah. Is there any way that the cots could be removed and then used as fertiliser as a money filter to help me look at that?
SPEAKER_03On the same topic of what can we make them into to make a more profitable industry of removing the other. Could they be used as fertilizer or something? Could the toxins be leached out and people eat them? I mean, people eat types of uh spiny puffer fish which are highly toxic.
SPEAKER_00I can tell by the grill on your face that you've been you've had this question before, haven't you? So the issue for human consumption is this fact that we cannot predict who has this hypersensitivity to the toxin. And I don't think there's any way around that. The fact that they produce so many eggs and so much reproductive material, there is a lot of material there which could be useful as a carbon source for aquaculture or something like that. But the big issue is that toxicity. Now, there are places in the world where they take all of the crown of thorns out of the water and actually then sit them and weather them and then use them for improving soil. It's not that they're providing a fertilizer as such, but they're they are providing essential nutrients that can be put into the soil to help with growing crops like bananas. And the classic example of that is in um New Caledonia and Vanuatu, where they were doing that.
SPEAKER_03That must smell that must be a really good smell wherever they're doing that on their chest.
SPEAKER_00Well, the issue is you've got to get the salt out as well. So you need to weather them on the beach, let the rain pour all over them and wash the salt out before you can start using it for that. So it's a lot of work. And the problem is just the collection of the crown of thorns is much more time consuming than giving them a single injection. So it's gonna slow down the efficiency and effectiveness of the culling operation by trying to get them all out of the water.
SPEAKER_03Darn. It wasn't gonna be a quick fix, wasn't it?
SPEAKER_00Yeah, I was thinking of a new business plan.
Climate Change and COTS
SPEAKER_03How about climate change and coral bleaching? How do they interplay with the threat of cots? Do cots tend to move into areas that have been recently bleached or thrive better on degraded reefs?
SPEAKER_00We've only just started looking at the interactions between climate-induced coral bleaching and outbreaks of crownothorns. So we literally have just finished an experiment at Lizard Island showing that crown of thorns actually do not like to eat bleached corals. But moreover, we've got fussy eaters, ain't that? Yeah, but moreover, we've found that cranothorns are extremely sensitive to elevated temperature. So this work's been going on for a little while now. And the most noticeable thing I can say is during the mass bleaching and really hot temperatures we got in 2016, even though we're in the midst of an outbreak, I couldn't find any crown of thorns.
SPEAKER_03So is this the only positive of heat waves in the ocean?
SPEAKER_00Well, the problem is that, you know, with the escalating temperatures, we're going to lose the corals because of bleaching. So that's probably going to happen faster than we're going to stop the crown of thorns outbreak. So it's it is a positive in some ways, but climate change is going to cause greater devastation than these outbreaks of crown of thorns in the future.
SPEAKER_03Devastating. And, you know, you mentioned that cranothorns eat branching corals, the fast-growing weedy acrobera, and so on. And that's interesting because now that bleaching is happening so frequently, six times in the last decade, people tend to celebrate how fast corals can grow back between events, but the only corals, almost the only corals which can grow back that fast in just a couple of years between bleaching events, is those weedy branching corals. And so to know that they are the most vulnerable to cranothorns starfish is a sign that these two things are going to sort of interplay in a bad way, isn't it?
SPEAKER_00Absolutely. So yes, we're having a proliferation of weedy corals, and it's not just on the Great Barrier if it's far more advanced in other parts of the world. But because these corals are not only susceptible to bleaching, but also cranothorns and you know are really susceptible to these cyclone impacts, what's going to happen is we're going to have much greater volatility in coral cover. So, yes, we need to celebrate the fact that we've got really high coral cover on the Great Barrier Reef, but it's also really, really susceptible to all these disturbances that just keep coming.
SPEAKER_03Yeah, and a lot of coral restoration and coral planting projects are focusing mainly on the branching corals because they are the easiest ones to obtain a fragment, attach it to a frame, and it'll grow back quickly and make your tourism site look beautiful in a short space of time. But again, you were saying that those are vulnerable. So the not only do we need to be planting them, but then we need to be guarding them and being vigilant on them for the cots. It's um it's a tricky problem, isn't it?
SPEAKER_00Absolutely. So I mean, touching on the whole reef restoration thing, absolutely we want to, you know, be making sure that we protect those corals that are potentially really vulnerable to all those disturbances. But the flip side of that is that we can see where coral cover increases so fast on the Great Barry Reef, that those corals still have some resilience. So we do need to address what's killing the corals, but we also need to think about those corals such as the long-lived massive parieties which live for a hundred years and are being exposed to unprecedented events that are now killing them off. How are we going to get them back? Because they're also a key component of the Great Barrier Reef.
SPEAKER_03Yeah, that well, that's a whole other topic because we could probably get you back for multiple episodes, Professor Pratchett, and hopefully we will in the future, because it's not only Cranathorns that you are knowledgeable about, and it is obviously a big topic that you know restoration projects are only able to focus on so many species, and it's a lot harder to get a fragment of a boulder coral for your restoration project, isn't it?
SPEAKER_02I'm I've come up with another question. I know it's great. Yeah.
Brett's Wild Night-Time COTS Hunting Ideas
SPEAKER_02So have you looked for crown of thorns at night with the blue light or anything like that? Do they emit something that makes it easy to see them at night? Is there something we can inject into them into one and then when it spawns that travels to the next one and we chuck some goggles on at night and they all glow green? Wouldn't that be awesome?
SPEAKER_00Wow. Well, they are a lot easier to find at night, but it's got nothing to do with how easy you can see them. It's the fact that they come out of the reef. That's right. So they're quite nocturnal, are they? Well, there's a strong effect of food availability and size of the animal. So a lot of the smaller ones, especially when there's lots of that acropore around, will only feed at night. So our ability to cull might actually be greater at night, but then you've got the whole logistical challenge of actually navigating around and finding them at night. And when you add the two together, I think it's still on the whole better to do it during the day, but we definitely need to become more strategic about how we do it and where we do it.
SPEAKER_02Yeah, right. So imagine if you could inject half a dozen of them with a bright green dye or something within their system, and then when they spawn or they move around, it goes to the next one, and they'd be like little traffic lights. I've fixed everything.
SPEAKER_03Wow, what a novel idea. Very creative.
SPEAKER_02You're welcome. Oh, there's a lot going on in this ADHD brain, Tammy, you know that.
SPEAKER_03Well, ideally they kill it so it doesn't have any spawn.
SPEAKER_02Well, you could have your little well, you'd have your little, you know, your masters that are the spreaders. So you let you guys you're gonna let you live as long as you tell us where the other ones are. You're our informant. You're working for us.
SPEAKER_03Training them
Genetically Modified COTS
SPEAKER_03up. What about this genetic modification that we talked about during one of the ad breaks? You can genetically modify cats apparently so that they suppress breeding in the population once released. Is that something real for pests in general?
SPEAKER_00Yep, it's absolutely real. There's some obvious concerns about this sort of practice in marine environments, let alone freshwater environments. So if you think about it, we've been talking about genetically modifying the carp in the Murray-Darling Basin for many, many decades such that they can't reproduce. But there's a lot of concerns about the way that things spread in sort of aquatic ecosystems that have prevented us taking those steps at the moment.
SPEAKER_03It's like a Pandora's box. Once you release a genetically modified animal to start interacting with the others, once you release it out of the box, you know, it's like a cane toad, except a great decision.
SPEAKER_00It's hard to put it back in the box. That's absolutely right. And even the work we did to demonstrate the mobility of bile salts, when we were actually injecting them initially, we were inducing pathogenesis, which means that these starfish were not only dying because they were then exposed to naturally occurring diseases, but they were spreading that to all the starfish in the immediate area. Convenient. And so it was a step forward in the efficiency of culling, but the concern was that there could be other related organisms out there on the reef, and we did see some lesions occur in the really bright blue, pretty blinkier starfish.
SPEAKER_03Oh, I love that.
SPEAKER_00Which is the reason that research sort of had to be sort of wound down because there were going to be some unfortunate casualties of that approach.
SPEAKER_03Not the blue linky are got linel in my tank. People always ask if they're real, because they look like they've been made out of a million times a day by here. Yeah, they're they're real, mate.
SPEAKER_02So beautiful.
SPEAKER_03Yeah, well, there's a lot of other starfish out there on the reef, and we need to make sure that there's no flow-on effects to them. So,
COTS in Other Countries
SPEAKER_03all of this discussion about all the threats of COTS and climate change to the Great Barrier Reef, of course, is always at a risk of overstating the damage to the reef. It's still obviously a very beautiful place and very well managed, as they say, one of the best managed marine parks in the world. Yep. And this COT problem is not isolated to the Great Barrier Reef. Are there other countries experiencing COT outbreaks? And how do they compare to our outbreak?
SPEAKER_00Yeah, so we've recently realized there's at least five different species of crownathorns around the world. So the particular species affecting the Great Barrier Reef occurs mainly just in the western Pacific, and so we've had significant outbreaks of this same animal in Japan, Fiji, and a lot of other countries throughout sort of you know our neighbouring coral reef countries. And so it is an ever-present concern, and we do need to increase our capacity to manage this threat, especially given the myriad of other disturbances.
SPEAKER_02So if there's if there's 25, how much do they vary from those 25 species? Oh, sorry, five species. Oh, sorry, five species.
SPEAKER_00So how much would they vary? Is it much? Well, interestingly, nearly all the research we've done has because of where it's being conducted and where the outbreaks have been the worst, has been done here with this species, Achanthaster solaris, is the notional name we're using at the moment. There's been comparatively much less research to understand the biology and the behaviour of these same species in the Indian Ocean, but we do suspect that there's some fundamental differences which affect how important they are in reef disturbances.
SPEAKER_03Well, I think I've read that they're in the Red Sea. Are they in the Caribbean?
SPEAKER_00No, so they occur throughout the Indian and Pacific Ocean. So they are in the Arabian Gulf and also in the Red Sea. The one in the Red Sea has just recently been named a new species, Acanthastabenzi, in recognition of a researcher from Australia who did a lot of the pioneering research on crown of thorns. But they do not occur in the Caribbean or in the Atlantic.
SPEAKER_03Well, they've got enough of their own problems with the stony coral disease, which we we haven't actually talked about on the show yet, so many people won't know what that is. We'll have to bring that up on a separate episode. And you know, people releasing fish out of their aquariums. Yeah.
SPEAKER_00The lionfish.
SPEAKER_03The the the Caribbean is a topic for a whole separate show. You've been there, haven't you?
SPEAKER_00I haven't actually dived in the Caribbean except in the Florida Keys. But you're right, it's a very different system, and there's there's a lot that we can learn from the Caribbean, but we also have to realise that our system is very different. It's much more diverse and at this stage much more resilient, and there is still good reasons to come and visit the Great Barrier Reef.
SPEAKER_03Yeah, we do Yeah, we do still have a very healthy reef by comparison to some other parts of the world. And the fact that we know that we have so much focus on COTS here is because we have some of the best science facilities in the world, of course, on the Great Barrier Reef, some of the best research that's been going on for decades.
How Loss Motivates Us... And Prof Pratchett's Fave Reef
SPEAKER_03Professor Pratchett, you've been diving on the reef for a long time. How has it changed just as your sort of general observation of it since your early years diving on the reef?
SPEAKER_00So, yeah, like many scientists, when we first started diving on the reef, it was, you know, because we loved the reef and it was an amazing place to work. But over time we've just become aware that it is a system under pressure and the research needs to. Be much more focused, not just in understanding the system, but also conserving the system. And so there's a lot of discussion about reef grief and the fact that you know we can be overwhelmed with the the issues we're facing, but if anything, it just makes me much more motivated because there's very good reason to protect this system. It is so critical to the Australian identity. It has really significant economic and cultural contributions, especially in Queensland. And so we owe it to ourselves to especially manage all the human disturbances and make sure there is a reef there in the future that we can be proud of, and many people will still come and visit. Absolutely well said.
SPEAKER_02Well, we had a last week's episode was all about managing mental health for people that have been diving the reef their whole lives and how to cope with what we're seeing and everything. So yeah. And that's a that's a valid point though, that's something we didn't cover last week, is is it does promote that extra push. And that's why we do this, right?
SPEAKER_03Spare us to act.
SPEAKER_02That's yeah, that's why I stand in front of thousands of people every week and sprook the reef and teach them about how beautiful she is, and it's why we do this show, and it's why you work so hard, you know. It makes sense.
SPEAKER_03That's why Professor Professor Pratch is putting his life on the line getting stabbed by a spiny starfish.
SPEAKER_02Yeah, oh yeah. Coral eating what do you call them? Coral eating pests. Coral eating little somethings.
SPEAKER_03I would never call them such a thing. So even just with this cyclone, I felt a pang for the reef as well as for all the people and that live up there. Lizard Island's obviously close to your heart. You've talked about it a lot. Are you feeling a bit nervous about what it'll look like the next time you go up there?
SPEAKER_00Yes, absolutely. So sincerely hope that everyone is well and hope also for the best for all the infrastructure on the islands and on in those coastal communities. And so, you know, Lizard Island's research station has been remarkably resilient to those previous disturbances. Unfortunately, the resort has been damaged quite significantly by past cyclones. So fingers crossed that they've escaped the worst off at this time. But I do believe that given how close this cyclone has passed to Lizard Island, there's a chance that this cyclone, just as this single sort of you know, two-day event, has probably undone all the amazing recovery in terms of the coral growth we've seen at Lizard Island since the lowest recorded coral cover in 2016. And that disturbance then was caused by the two cyclones in 2014 and 15, and then the major mass bleaching in 2016. Um and so when we were up there in January, February, the reef did look amazing. But unfortunately, my concern is that when we go back there and we're due to go back there in April, it might be a very different story.
SPEAKER_03Hmm. Yeah, it it it hurts to hear that.
SPEAKER_02Yeah, it does, it hits home. And we we've had um we had a guest on the show that worked at the Lizard Island Research Centre, didn't we?
SPEAKER_03Yeah, so we'll be checking in with them on slash you in a few months to see how it's how it's going after all of this. But Professor Pratcher, what would you say is your favourite spot to go diving on the reef that's still in a really good healthy condition?
SPEAKER_00Yeah, that's the problem. It keeps like the the because of this whole mosaic of disturbances, the different reefs are in different stages of recovery at different times, and so it's not like there's one spot that is immune to all these disturbances, and you I can guarantee is still going to be in amazing condition. So there's always some reefs which look stunning. There's always some reefs which you know can show you how bad things can potentially get. I'm fortunate that I see, you know, that broad cross section by seeing such large parts of the Great Barrier Reef. But I do feel for you know the tourism infrastructure, which isn't, you know, so mobile and things, and so they've got to do their utmost to manage those escalating threats in that location at all times. My favourite place to go is still very much Lizard Island. It seems like home on the Great Barrier Reef. It's unique because it does have the island system where the reefs built around the island system create such diversity of habitat. But there's also still nothing like diving out the front of the Great Barrier Reef when the weather allows it to see how different those systems are when you compare, you know, the inshore reefs to those offshore oceanic sort of exposed systems. Yeah, my favourite is still Osprey, which would have been right in the firing line of this thing.
SPEAKER_03That's off in the coral sea, but yeah, it's amazing.
SPEAKER_00We could have another whole discussion about the colour. We've got a couple of days about osprey. Yeah, we've spent a lot of time out there, but it's also not immune to these disturbances we're discussing.
SPEAKER_03Yeah, so you're lucky that you can go on these month-long research expeditions and visit hundreds of different reefs so you get to see the full cross section. But it's really uh comforting, I'm sure, for all our listeners to know that you can go a mere 45-minute ferry to Fitzroy Island off the coast of Cairns for a very affordable day trip and still see absolutely amazing things, turtles, sharks, rays, and and coral. Um you just need to know the right spots to snorkel in. And I'm going there next weekend for my birthday. Beautiful. So I am living my own advice. I'm not just um making it
First Nations knowledge of COTS
SPEAKER_03up. Are you aware of pre-European people, Aboriginal people, having any knowledge or interaction with the cots or I mean the indigenous people today are still involved with the protection of the reef, so do they have any knowledge around that that you're aware of?
SPEAKER_00Yes, absolutely. So have recently found out that the Torres Strait Island people do have terms for crown of thorns. So they're quite familiar with that animal throughout their history. And the fact that when there's not an outbreak, they're very hard to find, very hard to see, I would suspect means that they have been exposed to outbreaks in the past. And there is in the oral history of many places, including Torres Strait and the Solomons, concerns for the um local fishermen in terms of whenever they had to get out of their boat and walk across the reef, they were really concerned about the threat posed by these cranothorns. So they have been exposed to densities that were high enough to pose a real risk to what they were normally doing.
SPEAKER_03Hmm. That's really interesting. Okay, so we're getting close to winding it
How Can People Help?
SPEAKER_03up now. What can our listeners at home do to help protect the Great Barrier Reef and our oceans in general?
SPEAKER_00Yeah, this is a this is a very complex question and one we do got on a regular basis. The most obvious thing you can do is be very, very mindful of your carbon footprint because the foremost threat to the Great Barrier Reef and most natural ecosystems around the world is climate-induced coral bleaching and the other uh associated impacts of climate change. Now, the other thing you can also do is make sure that we still love our reef. So get out there and visit it and also make sure it stays on the agenda whenever we have, you know, these inevitable discussions about trade-offs between the decisions we have to make about where to invest limited resources, especially from the conservation perspective, so that we can put the Great Barry Reef front in centre of the decisions that the politicians inevitably need to make at the state and federal level. Yep, perfect.
SPEAKER_03All right, that's all we have time for for our extended chat. But Dr. Morgan Pratchett, Marine Conservation Ecologist at James Cook University, thanks for all your amazing work and thanks so much for joining us on Word on the Reef today.
SPEAKER_02It's been a pleasure today. We loved it. We'll have you back. You're not escaping that quick.
SPEAKER_03Oh, well, well, yeah, but you actually live in Townsville, so you're not in Cairns all the time. Are you here for something exciting? Anything interesting, any interesting plans up here?
SPEAKER_00Well, of course, this was, you know, a prime reason for coming here. But yeah, also loading equipment to go to Lizard Island for our next adventure up there, and just I'll let you know what we find. But I'm hoping for the best. Yep.
SPEAKER_03Well, all the best with it. And thanks to you, all our listeners, for joining us on Word on the Reef with me, Tonya Murphy, and co-host Brett Wood Ben. I'm actually away next Friday because it's my birthday though. And I'm spending it on Fitzroy Island. Of course you are. I can't wait. But we will be supplying a pre-recorded interview for that show. Um, one that's not been aired before. So make sure you tune in as usual to hear more Awesome Marine Science Adventures. This show is broadcast live from the Kans FM studio, which is on the land of the dingy people. We'd like to extend our respect to elders, past and present. And don't forget to follow us at instagram.com slash red on the reef podcast. That's all for this week. Best features. Happy diving. See you next time.
