 I'm Pedro Cress, the managing editor of Conservation Letters, and I'm very pleased to be joined by Peter Mumby, who is the lead author of the feature article for the May-June issue entitled, Operationalizing the Resilience of Coral Reefs in an Era of Climate Change. Peter, welcome. Thank you. So, before we get started here, could you give us a little bit of information about the ecology of the Belize Barrier Reef in the context of conservation planning and ecosystem management? Sure. The Belize Barrier Reef is the second-largest reef system in the Caribbean, and it's of vast importance for the country in terms of tourism and people's livelihoods through fisheries. When I started working there in 1991, most of the fishery was focused on species like snapper and grouper that are highly desirable, and powderfish was not even considered. If you ask someone, do you fish powderfish, they'll just laugh at you and think you're crazy. But the grouper and snapper populations declined over time as they increasingly fished them, and by 2004, powderfish had become the number one species at the bottom of the food chain that was being harvested. And this was a real concern because powderfish play a very important role, grazing down seaweeds and helping corals recover. So there's growing concerns about the resilience of the reef, and the average health of the reef was declining, and to what extent could management help change that trajectory? So our plan was to say, can we understand the resilience of the Barrier Reef, and can we do two things? Can we, first of all, ask the question, are there certain parts of the reef where the implementation of a protected area that would actually protect powderfish through no fishing, would have a big impact on the future resilience of those reefs? Because in some places, you might have a relatively weak impact. And the second question was, well, if given that the police government, in fact, introduced a policy in 2009 to completely outlaw the fishing of herbivores, including powderfish, what effect has that had, would we expect that to have had, on the resilience of the Barrier Reef system? So we're asking these questions about the impact of the policy, and then also by identifying areas of protected areas that might actually have a big impact on resilience, those results are currently feeding into a new program that's going on in Belize right now to extend the protected areas. So although there's actually a complete ban on powderfish harvesting, at least the enforcement of that ban will be greatest, most likely, in areas that are already declared and managed as protected areas. So are there certain locations that perhaps should be prioritized? And you've been in Belize studying, or studying this research in Belize since 1991? That's correct. Yeah. The first time I ever saw a coral reef was in Belize, and I went to my next petition there and fell in love with it right there and then. And so it's been a bit of a sobering experience seeing the decline in the health of reefs that I used to know so well, even within that relatively short time period. And so anything that we can do to sort of help manage those reefs is a bonus. And when I was there in the early 90s, I was trying to assist the Fisheries Department in designing room protected areas. And we helped develop a management plan for one area that I know very, very well. And at the time of doing that, it was really clear that there was relatively little science available to guide our decision making. And so that's really what's motivated a lot of this research that's led up to this current paper. And so you've been looking at both what can be done locally as well as nationally and internationally. And so we'll get into this a little bit later. But one of the questions that I had was, can the work that you've done here sort of be extrapolated for coral reefs everywhere? Okay. So Belize is in the Caribbean, and Caribbean reefs are really very different to reefs in the Indian Ocean and the Pacific Ocean. In fact, Caribbean reefs have the lowest resilience of almost any coral reef region of the planet. And are we not entirely sure why? I mean, there's a bunch of factors. One is that seaweeds or algae on Caribbean reefs have a propensity to bloom very easily. And if you reduce the amount of herbivores that are trying to graze it down or if you add nutrients, the response by the algae is very rapid. In other parts of the world, the algae don't bloom quite so easily. And that bloom of algae is a problem for coral because the algae take up space that the corals would otherwise try and set it on and colonize and grow. And the algae can smother living corals so they can actually reduce the rate at which corals are able to recover after a disturbance. And then when they are trying to recover, the growth rates of individual corals decline and the fecundity declines when they're sort of battling away with seaweeds. So, the Caribbean seems to have a sort of seaweed problem and that was really became obvious in 1984 when the long-spined sea urchin, which was abundant throughout most of the Caribbean, died out because of a disease. And right around the Caribbean in one year, that really important herbivorous sea urchin almost became extinct. And as a result, all of the sort of control of seaweeds by herbivores was rather than it being a job for fish and sea urchins, it became just a fish job. And the fish have got a limit to how much they can cope with. So, in general, when you go and look at reefs in the Caribbean, you will see more seaweed than in any other parts of the world. So, I think the results can be extrapolated within much of the Caribbean. It's all pretty much all the same species, same processes going on around the region. But you can't directly extrapolate the results to places like the Great Barrier, for example. Sure. So, now, hurricanes is something that you talk about in the context of the article. And, you know, there's been a lot of natural disasters and tsunamis and hurricanes. And so, talk to us a little bit about kind of the recovery flexibility of the reefs in this kind of an acute disturbance. Yeah, I mean, hurricanes have been a part of coral reef dynamics forever. And so, hurricanes by themselves aren't a source of concern. However, because the recovery potential of reefs has declined for a variety of factors, principally because now it's so much easier for seaweeds to bloom because they're not controlled so well. Now what happens is that a hurricane would normally have hit a reef, killed coral, broken it up. That would have been followed by a period of rapid recovery of the corals. And that wouldn't have been a long-term problem. But now, because the recovery is so slow, in many cases doesn't even seem to occur very well, even a natural process like a hurricane will sort of, if you like, ratchet down the health of the reef. The first hurricane comes along and reef health declines a bit. It tries to recover a little bit and then bang, it gets hit again. So all this pushes the system down. And so when you take these acute disturbances and the other major acute disturbance that we're facing these days is coral bleaching, putting all these things together and we see that there's a sort of real trajectory downwards of many Caribbean reefs. Again, which raises concerns about their resilience. Now, you talked a little bit about the parrotfish. So they're playing a role, or it seems like a modest role in bioerrosion. So talk a little bit more, if you could, about their relationship to the coral reefs and some of your modeling efforts. Yeah. So the parrotfish do have, I mean, they're herbivorous. They eat seaweed. Some species of parrotfish are not all, but some also take a small proportion of their bites from the live coral. And also some of those species, when they're taking a bite from the reef, and when they have these hard beaks and as they scrape algae from the surface of the coral, they often include a little bit of that coral skeleton that gets bitten off as well. And that's actually loaded with all sorts of little algae inside it, which is perfectly natural. So they really see two things. One is that they're scraping the reef free of algae, which is a good thing, but they're also a natural source of erosion because every time they bite, basically they take a small sliver of reef with them. And so the concern that we and many other people have is that if you end up with too much erosion, and parrotfish are by no means the most important source of erosion, I mean, there's sponges that grow on corals and sort of essentially dissolve away the skeleton, and elections also dissolve a road away the skeleton, that you could actually end up with too much erosion and the whole reef starts to sort of begin to collapse. Now, no one's ever implicated parrotfish as creating so much erosion that they're effectively removing the entire skeleton. And most of the studies that have been done in the modelling studies where we take the measured impact of parrotfish as a source of erosion, and we also consider, of course, their role at scraping algae free. Because they're scraping algae free, they're facilitating corals, colonising the reef and growing relatively free of algae. So that's a positive thing on the reef, and they're sort of taking away a little bit, but they're facilitating the coral which is building the reef. And in every experiment we've ever done, we find that the positive role of parrotfish in helping corals grow outweighs their, if you like, negative role at removing substrate. So they're a net benefit to the reef, and it's very important. So in terms of the algae, you use the term in the paper, algae competition. Can you tell us a little more about that? Yeah, so seaweeds, there's a whole variety of different seaweeds in the reef, of course, but when we talk about seaweeds, we're really talking about some of the very conspicuous, often brown seaweeds. One group called dikteotra is really fleshy, it's like a big sort of fuzzy mess, and there's others called blaboffa, which is more of a sort of carpeting alga. And these seaweeds, the first thing that they do is that they pick up space, and it's very hard for a new coral larva, when it's coming to a reef and it's trying to settle and generate a new coral, it's hard for them to find a place that's free of algae to get established. Once they do get established, and the algae can grow, the algae can affect them in a number of ways, and they can reduce the amount of light which slows down the coral growth rate. They can touch the coral, and then the coral spends a lot of energy trying to fight off the algae, and because it's spending some energy doing that, it doesn't grow very quickly. And this is a problem, because when a coral is very, very small, it's extremely vulnerable to all sorts of disturbance. It could be getting rolled around, it could be getting sort of bit enough to keep it from being on the reef. And the bigger the coral is, the greater its knowledge for survival. So by the corals having these battles and competing with algae, it keeps them smaller and more vulnerable for longer. Then even the larger corals suffer when they're in contact with algae. We've got evidence that shows that they're fecundity declines, and they produce smaller eggs when they're in contact with corals, with algae. They interact and there's been a whole bunch of exciting research by others looking at the mechanisms and the sort of chemical mechanisms by which these plants and corals interact. But it's pretty clear that there's this competition going on and that can slow coral recovery. Sure, it sounds like it. So in our final couple of minutes here, I wanted to have you touch on the concept of unstable equilibrium and then sort of give us these end summary points. So we have kind of a general sense of what readers can expect in this article. So we've really focused on resilience. Resilience is an ecological concept that's, I guess it's now 40 years old. It was originally developed by Buzz Hulling. And the coral reefs in the Caribbean at least, what we know and what we think we know is that under certain conditions for recovery to take place the recruitment of new corals and their growth has to be greater than the background rate of mortality. So you might have disturbance but then the corals can start to recover. But there are certain conditions where the recovery of corals and the recruitment and growth is so slow maybe because of seaweed that it's no longer able to sort of replace corals as they die naturally. And when that happens you essentially cannot sustain the population and the coral cover starts to spiral downwards. And the unstable equilibria are simply a set of if you like thresholds that sort of indicate the conditions which might be the amount of corals on the reef today, the type of environment that they're in and the amount of herbivorous fish, the amount of nutrients and so forth. So it defines whether or not the reef is likely to have enough natural capacity for recovery to replenish the population and recover over time. So by identifying where these areas are we can ask the question how likely is it that a reef of this state today may have let's say 25% living coral and what environment it's in it might be in an environment where algae grow very slowly or where algae grow very quickly and with a particular kind of disturbance environment. So some areas might have more frequent hurricanes than others or more likely to accept but putting all of that together and modelling it we can ask the question how likely are these reefs at the end of some period of time of interest and we've chosen the next 20 years, up to 2030 how likely are reefs at that location to still have an ability to show recovery by 2030 given the fact that they have all these impacts and everything else. And then we ask the question if you were to put in a marine protected area at that site and allow the parrotfish to recover then how would that influence that sort of potential for recovery which is the resilience. The resilience is the probability that reefs would show that kind of recovery by 2030. And we've mapped that through our beliefs by taking a whole series of real data sets, we've modelled the hurricanes we've modelled the climate change impacts and we've then shown essentially that without any coral reef management, any new coral reef management only a small proportion of reefs were actually predicted to be resilient by 2030. When beliefs introduced this complete ban on parrotfish fishing that increased the resilience six fold so that about more than half of the reefs still expected to show recovery by 2030. And this was a useful outcome because it really helps to verify that that policy decision appears to be borne out in terms of the potential resilience of the ecosystem. We also identify those areas where the ability of protecting parrotfish to affect resilience is greater than others and those areas that might be prioritised are being prioritised for conservation. And then the last thing we consider is how does this differ in terms of the action that humanity take in reducing greenhouse gas emissions and what we find is that if there's no action to reduce greenhouse gas emissions in other words we continue on our current trajectory then the outlook is of course very bleak and in fact that even if you want to protect parrotfish there is a benefit but it's a sort of modest benefit but if we take really assertive action on climate change and we follow some of the more ambitious and optimistic scenarios that have been considered by the IPCC then the impact of that local management is a lot greater in fact it's about three times greater and so it's not very surprising perhaps but the more we can do to sort of arrest the climate change problems the more likely our local management is to deliver a good outcome but it's important to bear in mind that even with the current climate change scenarios local management is really important in helping corals to maintain resilience it can certainly have a big impact on resilience and help coral populations turn over it doesn't mean we're going to be facing beautiful reefs in the future but it does mean that if they have enough resilience even if the amount of coral is generally not that great coral populations are still reproducing, recruiting, growing they'd be dying and that turnover keeps things open for adaptation and evolution and that's going to be critical and so this is one of the important considerations even if we have reefs that aren't as pretty as they were when many people including myself started diving well it's important research on WED we have the opportunity to speak with you and thank you so much for this contribution to conservation letters thank you