- Today's lecture will be about climate change and coral reefs. I'll be talking about how the ecology of coral reefs is changing, it's transforming, under climate change. What that means in terms of coral reef management, what it means in terms of coral fisheries. So the benefits that people are deriving from catching fish from coral reef. And finally I'll talk a little bit about the role of seabirds in transferring nutrients onto coral reefs and how that can bolster the resilience of this ecosystem to the impacts of climate change. Now early coral reef species existed with the dinosaurs. And then modern coral reef species have evolved and they've diversified. But through time, the ecosystem states and functions that coral reefs have performed, have remained remarkably consistent. However, the future is looking much less certain. We're now entering the Anthropocene where humans are the dominant driver of our ecosystems. And we're seeing dramatic changes in the functioning of coral reefs and in the benefits that humans are deriving from coral reefs or the existence services. A lot of the early work on coral reefs focused on how some biophysical processes were structuring the ecology and driving ecological patterns. So things like temperature primary productivity wave energy. And the human impacts on top of those drivers were thought to be relatively small. But there's a growing recognition now with an escalation of human threats that a myriad of human pressures operating at multiple scales are driving the composition of coral reefs. So there's obvious things like fishing and water pollution and climate change but underlying those pressures are things like finance and trade, human migration. So all of these different background or underlying social drivers are escalating our pressures to core of ecosystems. By far in the greatest impact that we're seeing to coral reefs is climate change. And we're seeing more frequently headlines such as these. So climate change is devastating coral reefs worldwide. And the Great Barrier Reef should be listed as in danger and sharks are functionally extinct from 20% of the world's coral reefs. Coral bleaching is very prominent and is probably the biggest threat the coral reefs are facing globally. Now coral bleaching occurs when the coral animal becomes stressed. So corals are animals and they live in a symbolic relationship with single-celled algae. Those algae give the corals their color and they also give them most of their energy. When corals become stressed, for example, when water temperatures become too hot, the corals eject the single-celled algae and you can see through the translucent animal tissue to the underlying skeleton that they've been building underneath. So that's why we term it coral bleaching. And within two to three weeks, the coral animal can die. So these mass bleaching events unfortunately have become quite frequent. I'm sure many of you saw in the news several years ago the Great Barrier Reef was very severely damaged by coral bleaching across two years. So in 2016 and 2017, about 18 months apart, two different vast areas of the Great Barrier Reef experienced very severe coral bleaching and coral mortality. You can see the photo on the top right there, those corals are now dead. You can see that they've lost their color and they're vulnerable to collapse. So it was estimated that about half of the corals on the Great Barrier Reef in the 18-month period were lost. So it really was a devastating event. And unfortunately, it wasn't just about the Great Barrier Reef. Coral reefs across the Indo-Pacific were very badly bleached in that event. So here's examples from Fiji, from Japan, from the Maldives, and a photo I took from the Seychelles where the corals have already died. And you can see that they, again, they've lost their color there. So really quite confronting images and the confronting reality unfortunately. We did this study around that time where we looked at about 100 different locations across the tropics and we estimated how severe the coral bleaching had been. And the red dots are where more than 30% of the corals have bleached severely. And you can see that about 75% of the world's coral reefs bleached in that one year in 2016. And we also looked at those locations through time at how frequently these bleaching events are occurring. In the 1980s, any individual location or any individual reef might be expected to bleach about once every 20 years. By 2016 they would be likely to bleach about once every six years. So the return time of these bleaching events is getting shorter. So the ability of coral reefs to bounce back and recover between these bleaching events is really critical and it's becoming more challenging. So why are these bleaching events happening, why are they becoming more frequent, more severe? Well, this image here is of an El Nino event where warm water is pooling in the eastern Pacific. So the red area is hot water. Now El Nino events cause changes in weather patterns all around the world. You can have fires in parts of the Amazon and floods in eastern, south and central America. So they're changing weather patterns around the world. They're also changing water temperatures around the world. So when these anomalies happen, we have spikes in warm water anomalies that occur in many parts of the tropics. What's key though is that these anomalies are happening on top of a background of warming temperatures. So as the oceans gradually warm, a smaller and smaller anomaly, warm water event, is more likely to push corals beyond their thermal tolerance. So corals live within a very narrow thermal tolerance depending on where they're situated. And it only takes one or two degrees warmer than their normal summer maximum for them to become stressed and to bleach. Now I've talked a little bit about the 2016 coral bleaching event which was extremely severe and globally. The last very severe coral bleaching event or very severe El Nino that caused mass coral bleaching was in 1998. So that event in '98 had allowed us to really understand what the long-term ramifications of mass coral bleach of mass coral loss is for the ecology of coral reefs and what it means for fisheries. So here I'm going to take you to the western Indian ocean. It's a region that was the most severely impacted by the '98 bleaching event. About 45% of the coral was lost in that region, it's estimated in 1998. And you can see that the the impacts varied across the region. So the size of these bubbles determines how much coral was lost. So you can see that the island nations particularly the Seychelles but also the Maldives lost a substantial amount of coral. On the right hand side, I've plotted the percent change in coral cover on the horizontal axis and the percent change in the physical structure of the reef on the vertical axis. Now coral reefs build a remarkable three-dimensional structure. So the different species of coral all grown into intertwine and that provides the habitat and the space for all the other organisms, the fish and the invertebrates to co-exist and to avoid predators. So the vast diversity that we get on coral reefs is in a large part down to that physical structure that the corals are building. So we found that as more coral was lost, we saw more loss in the structure and this photo at the bottom there, you can see that looks a bit like a moonscape. So that's about five or six years after a major bleaching event and you can see my colleague in the background there surveying that reef. There's also impacts on the fish community of course. Now these fish are all coral feeding fish. Mostly butterfly fish but there's also some other species in there. And coral feeding fish have varying levels of specialization and how specialized they are in their diets. So facultative coral feeding fish feed on live coral but they will also feed on things like pollock heat worms and algae. Obligate generalists in the middle there will only feed on live coral but they've got a very generalist diet. They'll feed on most species of coral. And obligate specialists are very fussy eaters. They'll only feed on one two or three species of coral. They're not damaging the coral they're eating the mucus and some of the tentacles but that's how they survive. Now the black bars here represent the abundance or the number of these different groups of fish, there's four or five species in each group, that existed in the inner Seychelles prior to the '98 bleaching event, in 1994. And what you can probably see is that there was an advantage to being highly specialized Those obligate specialist feeders on the far right there, there was far more of them. There's not more species, there's more individuals. There's an advantage to being a specialist feeder. But if I bring the data in now following that '98 bleaching event, you can see that there was a small loss in the populations of the facultative feeders. A huge loss in the obligate generalists. And the obligate specialists all but disappeared. And we actually documented the local extinction of about four species of fish through that event. So really devastated those specialist populations and it really speaks as I'll go on to in a bit more detail in a moment, that there's winners and losers through these disturbance events. Now we've been following the trajectories of coral reefs in the Seychelles since that '98 bleaching event to try and understand what happens after these mass bleaching events. When all the coral gets decimated, in a very short space of time by climate change, what's the long-term trajectory for those reefs? Well, we looked at 21 reefs across the inner Seychelles and we found that just over half of them bounced back and recovered fairly rapidly. So those blue bars there represent the cover of live coral, the amount of live coral. And you can see by 2011 or 2014, the coral had returned to a very similar level that we saw prior to the bleaching event in 1994. So that's good news and you can see from the photos on the right there, the coral bouncing back. But the other half, some of the other reefs didn't bounce back and recover at all. They underwent what we call a regime shift. So the blue bars, the coral cover bounces along at about 5% so that there's very little coral left on those reefs. And the green bars represent macroalgae. And macroalgae are basically seaweeds. So they're fleshy brown seaweeds as you can see there, plants basically that come to dominate the dead reef space. Now these seaweeds are bad news because they dominate the space, they prevent new corals from settling. and they can actually use chemicals to kill any remaining corals. So they're very effective at maintaining their dominance on a coral reef once they've become established. And so it's very hard to return a coral reef to corals once it's become dominated by these seaweeds. And there's also winners and losers throughout the ecosystem. So as I mentioned, we looked at fish specialization just a moment ago. Well, corals also respond quite differently. There's hundreds of species of coral and they all have a different tolerance to stress, to heat stress. So you can see in these photos here, some corals have gone completely white and other corals have still got their color. And so there's winners and losers in terms of how easily corals die from climate change. There's also winners and loses in how quickly corals can bounce back and recover. So some corals are more effective at coming and settling and regrowing on dead reefs. And that's to do with their reproductive capacity but also their growth rates. So as I mentioned at the start of the lecture, the time between these coral bleaching events is getting shorter. So we're selecting for the species that not only don't die as easy but also those that can bounce back and recover more rapidly. So that's to do with the corals but we're seeing similar dynamics in the fish. So even those reefs where we see coral cover coming back, the makeup of those reefs, the types of species communities that we're seeing are quite different to what's existed there for hundreds of years. And that's led to a realization in the coral reef science community. The coral reefs are becoming novel ecosystems. They're changing in the Anthropocene. So quite a lot of bit has been written about this now trying to understand how reefs are changing, what species compositions are likely to emerge and what that means, what does it mean for how reefs function? What does it mean for how we manage them? What does it mean for the benefits that reefs are offering to humanity? Now there's lots of ways that reefs are changing. One of the most extreme is reefs on the move. Now what I'm referring to there is tropical reefs extending pole ward, so to higher latitudes into what was previously temperate rocky shores. So temperate reefs tend to look like the top left photo there in many parts of the world. That's a kelp bed. So a kelp forest and it's a type of algae. But what we're finding in many parts of the world, these photos are from southern Japan, is that as waters are warming, some of these kelp are dying off or they're being eaten by tropical herbivores of fish that feed on algae that are extending their range into cooler waters. And they're being replaced by corals. So corals are actually extending their range and in some places it's happening quite rapidly. These photos here were from the same reef across about a 20-year period. So they're now completely novel ecosystems. It's a mix of tropical and temperate species that are now living together. So you can imagine that now you're seeing completely new specific interactions in terms of predators and prey and competitors. And if you think about people that are living and using those coastlines, the types of fish that they're catching are changing as well. So there's a huge change in the makeup of these reefs. We're also seeing a change, as I mentioned through time, in how fish are recovering. So this is back to the Seychelles through time after that bleaching event. The horizontal dashed line, the flat line is the pre-bleaching baseline. The solid line is the return in species of coral feeding fish and algal feeding fish on the coral reefs that recovered. And the dash line is the change in those same groups of fish on the reefs that went to macroalgae, that underwent these ships to seaweed. And what you can see is that, for the coral feeding fish, we saw a recovery of the species makeup back to the pre-bleaching level. But on the macroalgal-dominated reefs, we didn't see that recovery at all for the coral feeding fish. For the algal feeding fish, we actually saw that they increased beyond what they looked like prior to that bleaching event. And that's because there's lots more algae on the reefs. Lots more seaweeds on the reefs. So those types of fish have done particularly well. But the message there is that, I've just shown you two groups of fish of course, there's many different types of fish on reefs. The makeup of fish communities is also changing dramatically in coral reef nations. Never mind at the extremes at high latitudes. Okay, so what does all of this mean for coral reef management? Well, I'm going to talk now a little bit about marine protected areas. Marine protected areas is a dominant management approach in lots of the oceans, it's particularly dominant approach to managing coral reefs. It's basically referring to setting aside an area of a reef mainly from fishing. So it means stopping fishing from either an entire reef or a section of reef and giving the populations a rest. The idea is that the fish populations will increase and that many of those fish provide really important processes such as controlling algae or taking away dead coral. So it increases a health of the coral reef. It also means that some fishing techniques and anchors aren't going to be damaging the corals as much. So it's a really dominant approach. And it's an approach that we've been using since the 1970s, 1980s in many in many places and there's been a huge amount of research on the effectiveness of protected areas and what they do. So much research that people have done studies of studies of marine protected areas to try and see if there's commonalities across different places and sure enough there were commonalities. And I'm going to now take us back to the Seychelles and first of all we're going to look at how the protected areas in the inner Seychelles were performing before that major coral bleaching event in 1998. So these data are from '94. And we looked at four different room protected areas and they were performing just as the literature that I've just been talking about said that they should be. So there was a huge benefit of marine protected areas in terms of the biomass or the amount of fish on a reef inside a protected area compared to a fished area, okay? So that dash line there zero, any of the data points to the right of that mean that there's more in the protected area than the fished area. So you can see the overall biomass that's the amount of fish you could expect to see around 250 kilograms per hectare of fish more in a protected area than a fished area. And that's consistent with expectations. What we also found again consistent with scientific understanding of protected areas is that most of that benefit was for fish that were higher up in the food web. So high trophic level fish we call them. So things like piscivores. Piscivores are fish that feed on other fish. And mixed-diet carnivores. So they're carnivorous fish that might eat invertebrates like crabs. They might also eat other fish. So a lot of this increase in biomass was these fish at the top of the food web, the top of the food chain. We also found that the species richness of fish was higher in protected areas than fished areas and the amount of coral was higher prior to the event. Now following that '98 bleaching event, we looked at what happened through time. Well, the benefit of protected areas on coral cover disappeared and the recovery rate of coral on those reefs that recovered was no different between protected areas and fished areas. So it didn't seem to influence how reefs responded in the 20 years or so after the bleaching event. The species richness, the number of species diminished somewhat. What was really interesting though, I think, is what happened with the fish biomass. Now, these data here are the same as on the previous slide these are from prior to bleaching, okay? So again we're seeing a benefit of protected area for any data that's over to the right. And you can see that most of the benefit was for these high, these fish at the top of the food chain, these carnivorous fish. If we look on the right hand side, these are the protected areas that have now shifted to seaweeds. There's two things to take from that plot. One, is that the benefit of the protected areas. So the difference between the protected areas and the fished areas is greater. So the amount of biomass that's built up, was building up on those reefs that are now dominated by seaweed in the protected areas is quite substantial. The other thing to take away is that instead of these fish at the top of the food chain being the ones that are driving most of the change, it's now groups of fish that are at the bottom of the food chain. So all of those first three categories are fish that feed on algae or feed on seaweeds. So the browsers at the top there, they feed on the fleshy seaweeds. So those big mature seaweeds. Scrapers and excavators. They're basically parrotfish that are scraping away at sort of more turf algae we call it the algal film that grows on on dead bits of the reef. And grazers are the lawnmowers of coral reefs if you like. So the protected areas are still working in terms of fish biomass but the types of fish that they're benefiting has completely changed. And that's important'cause that means that what's happening inside the protected area in terms of the ecology is quite different and the trajectories that those reefs will now take. And what's happening at the boundaries of those protected areas has changed. One of the rationales for protected areas is the hope that fish populations will start spilling out and help fisheries in surrounding areas. Well, the types of fish spilling out are now going to be quite different. So that's important for thinking about management. Okay, next I want to think a little bit about fisheries. Our coral reefs are incredibly important across the tropics for food security and for fisheries. So what are the implications of climate change and the degradation of coral reefs for fisheries and food security in many tropical coastlines? Well, the expectation in the literature including some of the earlier work that I wrote was that when coral reefs degraded, we would see a collapse in many fisheries. It would be really quite bad news in terms of catch rates and the ability of people to be able to maintain enough catches and to fish sustainably so the populations could replenish. But what we've actually found is that if you look at the landings data, so these now aren't survey data that we've taken, they're actually the landings data from the fishermen themselves so a fisheries agency will go and monitor the fish that are being landed and understand the populations. So if you look at the landings data, CPUE is the catch per unit effort. So that means that a unit effort might be a boat trip or a trap. So you're standardizing how much effort is going into the fishery. So we know that the trend isn't to do with a change in how much fishing is happening because that's all standardized. What we're seeing is that after that '98 bleaching event in the inner Seychelles, we've actually seen an increase in the catch in coral reef fisheries, okay? So they're actually catching more which surprised us. And what's really interesting is that one of the groups of fish that's driving that increase are siganids or rabbitfish. Now rabbitfish are really interesting because they have a very fast life history. And that means that they grow and reproduce very quickly. So they can grow to a plate size, so a size that's ready to eat and have reproduced within about nine months. So they have this incredibly fast turnover. And that means that they can sustain the fishery but it also means that the fisheries can be quite sustainable because it's harder to collapse a population of a fast turnover species of fish. These siganids settle, the young of these fish settle into seaweed beds, into those algal beds and they feed on the seaweed. So this transformation that we've seen of the coral reefs of some of the coral reefs to algae has actually fueled this increase in the fishery and this productivity. Now this isn't to say that the demise of these coral reefs is good news. Far from it of course because there's a decline in biodiversity, decline in shoreline protection it's very bad news. But I think it's very important to reflect that when change happens, you know, when the coral reefs are degrading or other ecosystems are changing, it doesn't change to nothing. The ecosystem composition changes to something and that can bring up surprises. And if fisheries can be adaptive in this scenario then actually the yield and the food security can continue and that's a relief because those rates that have shifted to macroalgae as I said, it's very hard to return them to coral cover. Now we often think about fish as being very important for protein. But actually the importance of fish is about the micronutrients. So things like zinc, iron, vitamin A and calcium are found in fish in very high quantities, okay? Now that these micronutrients, if they're deficient in our bodies, cause all sorts of of developmental problems. They contribute to about 3 million premature deaths annually and all sorts of of issues within childhood development and stunting and so on. Now fish are packed dense with these macronutrients and they pack dense in such a way that they're bioavailable which means our bodies can absorb them quite easily. And this is an emerging area of science to do with fisheries to understand about how fisheries can contribute to food security from this sort of malnutrition perspective. So we've looked at this in the Seychelles where we were actually caught the same species of fish from reefs that bounced back and recovered to coral and those that went to seaweed. And what we've found is that the fish that are living on seaweed-dominated reefs their tissues become enriched in the minerals. So iron and zinc is found in high concentrations in this algae. That gets into the food web and the fish tissues become a lot more rich in these minerals on coral reefs with seaweeds. So we looked at the fishery potential on reefs before bleaching, on reefs that recovered and reefs that went to seaweed or to macroalgae. And we found that actually the amount of micronutrients available from these fisheries was either sustained or increased following the bleaching event. So as well as seeing this increase in the amount of fish being caught, we're actually seeing an increase in these important micronutrients from those fish. Okay, I want to change track a little bit now. I've talked a bit about how reefs are changing and unfortunately a lot of that change is already happening and some of it is inevitable. Not all reefs are going to degrade to macroalgae. Many are going to recover. But those that recover are changing in composition as well. We need to really think about how we can encourage as many coral reefs as possible to bounce back and to remain in a what we call a coral dominated state so there's more corals than other organisms. And we know broadly what we need to do. We need to limit warming to below 1.5 degrees centigrade and that's absolutely critical. If our planet warms to two degrees or more, the number of reefs that are going to be able to keep bouncing back and recover from bleaching becomes vanishingly small. Keeping warming below 1.5 quite a lot of reefs have got the possibility and the potential to keep recovering and to persist. We need to manage fisheries carefully and sustainably. Fisheries are important on coral reefs. And they can be managed carefully to maintain the role that those fish, enough fish to maintain the role that they're performing in the ecosystem as well as sustaining people's livelihoods and food security. And we also need to improve water quality. Now when I talk about water quality, I'm talking about the sediments that are entering reef ecosystems and the nutrients. And we typically think of problems with water quality. So things like lots of nutrients coming off farmland or from urban areas or from sewage. And that causing big problems for coral reefs. And that's certainly the case in many places. But what's something that's emerged in recent years is that most nutrients that are coming from humans, from farming, from fertilizers, from sewage tends to be very high in nitrogen but have very little phosphorus. It's phosphorus limited. So those nutrients we have an imbalance in nutrients in terms of nitrogen and phosphorus result in an impaired coral physiology. So the corals grow slower and they bleach more easily. So a smaller spike in temperature can cause them to bleach and die. If nutrients arrive in a more balanced fashion, so the amount of nitrogen and phosphorus is more balanced, coral physiology does a lot better. Corals grow faster and they can bleach at a higher threshold so they can actually withstand slightly higher temperatures. And there's been some really nice work looking at this mostly in aquariums, in labs. There's a group in Southampton in the UK actually that's been leading the way on a lot of this work. Now that got me interested in the potential role of seabirds and the nutrients that seabirds could be delivering to coral reefs. So I've been looking at a group of islands in the Indian ocean, some of which have got incredible seabird colonies. So these islands if you set foot on them are really noisy places, the skies are full of seabirds and they really smell. And that's the guano or the seabird droppings and if it's recently rained, you can smell the ammonia in the air. So these islands are really being fertilized, they're really pungent places. Islands very close nearby that of a similar size, similar height, similar geomorphology, have next to no seabirds. And that's because those islands have got introduced rats on them. The rats have been arrived on the islands through patterns of settlement all through shipwrecks over the years. Now, black rats will feed on seabird eggs, feed on the chicks and adult seabirds then tend to just avoid those islands and not visit them at all.(birds rattling) And it's really quite dramatic. So this is an island with no rats and as you can hear, it's a really loud busy place.(birds rattling) This is an island with rats. Just next door. And working here now are waves on the beach and you'll see in a moment the waves are tiny. So the contrast, you know, the skies are empty and you can just hear all of these small sounds around. It's completely different, it's chalk and cheese when you set foot on these two types of islands. It's really quite dramatic. Now what's important is that these seabirds are flying substantial distances out into the open ocean. Some of the species are going hundreds of kilometers for up to two days and they're feeding on what we call pelagic fish. They're small fish sardines and so on that live out in the open ocean, okay? So they're going quite long distances out into the open ocean and then they're returning to the islands to roost and to breed and they're delivering a lot of those nutrients, it's a bit like a conveyor belt if you like, they're delivering the nutrients from the open ocean back onto the islands through their droppings, through feathers, through dead chicks and eggs and so on. And this has been looked at in terms of island ecology and people have shown how the productivity of the plant life is enhanced, the diversity of insects or the growth rate of scorpions is faster. But there'd be very little understanding of what it meant for the near shore marine environment. So we studied what this meant for coral reefs next to these islands with or without seabirds. So here we've got six islands where there's no rats present and six islands where there's rats present. And we looked first of all at the amount or the number of seabirds on these islands. There's about 14 different species of seabirds and you could break them up into six different families. Now the darker colors, this is what we call a heat map, so the darker colors mean that there's more birds on that island, there's quite a lot of birds on that island. And you can see that most of the biomass most of the birds are on the islands with no rats. And the photos and the videos I just showed you, you know, really highlighted that probably, you know, a little bit better. If we run the numbers, there's about 750 times more seabirds on the islands with no rats. And people have spent a lot of time watching seabirds and how frequently they defecate and so on so we could work out that that translates to about 250 times more nutrients being deposited onto the islands. So there's a huge difference in the amount of nutrients that are being deposited onto the islands with no rats. Next, we wanted to see, well are those nutrients making it out onto the coral reefs and being used by coral reef organisms? Okay, so we use something called stable isotopes of nitrogen it's basically you can measure a signal of nitrogen in tissues. Of soil or leaves or anything you like, okay? So we took 10 samples of soil from the islands to the coastline. 10 samples of new growth leaves. This is from each of those 12 different islands. On the reef flat, this is about 100 meters away from the island, we collected filter feeding sponges and a macroalgae which is called halimeda. And on the reef crest, about 250 meters away from the island now and where the reef drops into deeper water and is mixing a bit more. We collected these sort of fuzzy turf algae and then some herbivorous fish that feed on that algae, okay? And then we looked at this signal, this signature of the nitrogen in all of these different samples. So this is the result for the soil. So these are the data for the samples of soil from islands with no rats and lots of seabirds. And these are the data for the islands with rats present. And you can see there's a huge difference. This signature here is characteristic of seabird droppings and it's actually what we call a heavier nitrogen signal which is associated with those fish that they're feeding in the open ocean. So you can actually be quite confident that this nitrogen signal is coming from the seabird guano. And we also looked at the amount of nitrogen. So this tells us where it came from. We looked at the amount of nitrogen and we saw a very similar pattern. So the amount of nitrogen, there's a big difference and the source of nitrogen is from the sea seabird droppings. Now if we look at the other tissues across that gradient, you can see that the difference gets smaller as you go across. Now that's to be expected because the nutrients are washing off the island through rainfall events and waves that are lapping on the shoreline. And dissipating and getting diluted in the water but it's also getting taken up by all of those organisms on the reef and getting used by those organisms. So the difference gets smaller but it's still there even right out on the reef crest. If you look at the muscle tissue of those fish, we're seeing a difference in the nitrogen signal. So fish living next to the islands with seabirds have got more and a heavier nitrogen signal than fish living next to islands with rats. Now, one of the things that's really useful with fish are their ear bones or otoliths. Now this is a cross section through an otolith of fish bone and they lay down growth rings very much like a tree does. So these rings you can see here are annual growth rings. So if you know the length of a fish, if you measure the length of a fish quite accurately and count the rings in its ear bone, you can look at how fast it's grown'cause you know the size of the fish and how old it is. You have enough species, enough individuals you can then start drawing a line through those data and looking at how fast they're growing. So we did just that and here the dashed line and the open symbols are the fish that we collected next to the islands with seabirds and the filled circles and the solid line are the fish that are living next to islands with rats. So you can see that the fish are growing faster when they're living next to the island with seabirds. And if you look at it for a given age, let's let's take four years old, they're larger for a given age than the fish that are living next to the islands with rats. So those nutrients mean that the fish are growing quicker. And we've looked at this in more species of fish now and we've found the same thing. Next, we surveyed the fish community. So using underwater survey techniques that are quite standard in coral reef science. And we looked at the amount of fish or the biomass again in different feeding groups. So coral feeding fish, plankton feeding fish, invertebrate feeding fish all the way through to those algal feeding fish again. Now, if the data are above this dash blue line, there's more fish adjacent to the islands with seabirds. If it's below, there's more fish adjacent to the islands with rats. And you can see that across the board, there was more biomass for the all of these feeding groups adjacent to the islands with seabirds. So these seabird nutrients are really fertilizing and bolstering the amount of fish throughout the food web. And it's not a small effect. There's about 50% more fish adjacent to the islands with seabirds than adjacent to the islands with rats. Now that work was done in 2015. I already talked at the beginning of the lecture, the 2016 we saw this global coral bleaching event. And the reefs around these islands, unfortunately, bleached in that year as well. So we went back to those reefs in 2018 and we re-surveyed them to see what had changed through that bleaching event. And this is what we found. So here we have the pre-bleaching 2015 data and the post bleaching 2018 data. The blue dots are the surveys that we've done adjacent to islands with seabirds. The red dots are the surveys adjacent to the islands with rats. So let's first look at the change in higher coral cover. Well, both types of islands saw a very similar loss of live coral. So the presence of seabirds didn't alter whether coral was lost. This was a really severe coral bleaching event. The water temperatures got very hot for a very long time. So I think any benefit that the seabird nutrients might offer to the corals wasn't sufficient. What was really interesting though was what then replaced that dead space. Once the corals died, what took over that space? And we found that the top right there that's crustose coralline algae. This pink stuff here. Now crustose coralline algae is a calcifying algae and it's a bit like the cement of coral reefs. It holds reefs together. So when a reef has died it becomes more fragile more brittle and this crustose coralline algae can really cement the reef together, keep it stable and it's a really useful settlement site for juvenile corals. And we also saw an increase in halimeda. which is this green algae here which has little discs of carbonate. So these calcifying algae did very well on the reefs next to islands with seabirds. So it was enhancing these calcification rates. The reefs with with rats, it was turf algae and pavement. So they didn't get the the calcifying algae taking over. So that begs the question, well what happens to corals? Here's a really nice study by a colleague in New Zealand who's been working out in Fiji and she transplanted corals between islands with rats and birds. So she took some corals out and put them back on the same reef and took other corals out and she switched them around. So she took corals from a coral reef next to an island with seabirds and moved it next to an island with rats and vice versa. And she found that the seabird nutrients were increasing the growth rate of these corals four times. So these corals not only are the fish growing faster but the corals are growing faster as well. So we're now looking at that on the reef system that I've just described to you to see whether the corals are going to start growing faster and recovery patterns will be different. So the obvious conservation implication of this work is that eradicating rats from islands can have a huge benefit. We know that that has a big benefit on islands in terms of allowing all sorts of seedlings and plants to recover but also allowing seabirds to come back. And now we're showing that we'll also see an important benefit on natural marine ecosystems such as coral reefs including the potential for coral reefs to bounce back and recover more rapidly from climate change. Okay, so just to wrap up, coral reefs undergoing profound change. And unfortunately, that's a reality. Not all race will disappear but almost all reefs are changing. Climate change, no reefs are escaping climate change which is very sad. Scientific understanding and management therefore needs to be quite adaptive and to keep pace. Because a lot of the knowledge we've amassed over a number of decades is now changing. The species composition of reefs is changing. The rules of how coral reefs work and how they respond to management is also changing. Cutting carbon emissions and reducing local pressures is absolutely essential for the future of coral reefs. But there's also other things we can do and one of those things is to reinstate some of those natural ecosystem connections and the flow of nutrients and energy among ecosystems which can help bolster the resilience and the ability of these existence to cope with change. Thank you very much for listening.(audience applause)- Most reef studies are done close to urban areas where corals are already stressed. Is that the case? And if it is the case, how about the Pacific islands? Are are there differences in the coral being affected there?- Yeah, I don't actually know if it's true that most studies are done next to urban areas actually. I mean, a lot of research is done at research stations, a classic one is the Lizard Island Research Station on the Great Barrier Reef which is a long way from the nearest city. And the nearest big city would be Brisbane which is probably about, you know, two and a half thousand kilometers away. So a lot of coral reef science is actually done in research stations or on research vessels. But it's a good question. Yes, there's a lot of work done in the Pacific and the 2016 bleaching event absolutely devastated a lot of reefs in the Pacific. There were some islands in the Pacific that had incredibly healthy coral reefs and they were absolutely decimated by that 2016 bleaching event. So unfortunately, the patterns the warm water events are impacting reefs are not hugely predictable. There's some predictability but most reefs are getting impacted. Interestingly, some corals closer to human settlements can survive bleaching a little bit better. So the water's a bit more turbid then the light intensity doesn't get through to the corals quite as effectively and some types of corals are adapted and can cope a little bit more in these marginal environments than in the environments where they're less adapted to, you know, extreme impacts.- How are cold water corals such as those around the Scottish coast being affected?- Well, the big concern with cold water corals is ocean acidification. So temperature is a less of a problem because the warm water anomalies are really happening in the sort of surface waters and in the shallower water. Cold water corals grow very slowly and they're very susceptible to what we call ocean acidification. And that's where the oceans absorbing a lot of the CO2 that we're emitting into the atmosphere and that's creating a slightly more acidified ocean chemistry. And that can reduce the growth rates of all sorts of animals including corals and cold water corals are particularly vulnerable to that. So the worry is that the ocean chemistry is going to alter to such an extent that it's going to affect hot water corals.- [Attendee] Could you elaborate slightly on one how those rats ended up on these islands and also why they have such an effect on the seabird population?- Yeah, so rats stow away on boats basically and they've decimated seabirds populations from about 90% of the world's island archipelagos. So they're almost everywhere. And they think, you know, if a boat more than a jetty quite often rats will run down the ropes or jump off the boat. On remote islands, sometimes there's been historical patterns of habitation that through time, all there's been shipwrecks where boats have actually ended up on the coastline. So rats have made it onto some islands but not other islands. And the rats basically are eating, they eat bird eggs. They'll actually eat chicks and occasionally adult birds you know, they're predators. So rats is the main problem but there's also cats. Sometimes foxes, so when predators mammal predators make it onto islands, they devastate the the wildlife on the islands. And adult birds very quickly learn to avoid those islands and they won't try and raise chicks on the islands because they know they've got very little chance of survival.- [Attendee] When you're talking about the fisheries and when the seaweeds take over a coral bed, what's to stop the fisheries from taking up even more space with the way the kelp, or whatever it is, that's increasing into the coral area? Sorry, I don't remember.'Cause I was worried about the protection of the corals versus consumer based fisheries and finding an excuse to go into coral protected areas that are declining.- Right yeah. Well, so the protected areas are managed usually by local government, sometimes by local communities. And so the line's drawn on a map and fishers are not allowed to cross those lines and fish within the boundaries. So that's a bit different to what's happening in the ecology of the system. What we've found is that, so those protected areas are really about managing fishing. But because they're just lines on a map, it doesn't mean that warm water doesn't go into the protected areas or sediments or whatever is stressing a coral reef. So the the corals in the protected areas are just as vulnerable to the corals the fished areas to bleaching or being damaged by things like warm water and climate change. And are transforming and some of them are getting dominated by seaweeds in protected areas as well as in fished areas. So the fish populations are changing inside and outside of the protected areas. And as I showed, in the protected areas we're seeing more fish biomass, there's more fish in there than the fished areas but the types of fish has changed. And in the fished areas, the very productive algal feeding fish are now actually increasing the amount of fish that can be caught and the nutrients that are coming from those fisheries.- [Attendee] The Great Barrier Reef coral, I was astonished that it didn't create a reaction in Australia in terms of their approach to climate change. It seems to be one of those, you know, what is Australia if it is not the Great Barrier Reef. You know, and if that is under threat, I was astonished that that didn't create an enormous reaction amongst the Australian public in terms of what do we expect from our government in terms of coral extraction or more defensive measures against climate change.- Yeah, yeah you're not alone. I think and it's been a source of deep frustration from scientists particularly scientists in Australia. That there hasn't been a change in policy in Australia. It's not just about the bleaching the Great Barrier Reef has caused as well, you know, they've been horrendous wildfires, horrendous flooding. You know, the the continent is really on the front line of some of the dramatic impacts of climate change and yet they, for the time being are not changing course. And in terms of policy, yeah.- I wondered if you think that it's possible to fish sustainably. I don't know if you've seen the documentary "Seaspiracy" but it was like arguing that it's not possible and I just wondered what you think about that.- Yeah, I do believe you can fish sustainably. I mean, the definition of being sustainable is that, you know, something's replenishing itself. And it's the basis of fisheries science for hundreds of years is to is to try and manage what they call maximum sustainable yield where you're sustainably extracting fish without collapsing the population. There's also ecosystem-based approaches to fishing which is what we've been looking at more so on coral reefs. Which is where you can see changes in the functions that the fish populations are providing to the ecosystem and staying above the reference points or the targets to maintain those important existing processes while still taking some fish. So yeah, I absolutely do believe you can fish sustainably and fish are incredibly important for food security in many many parts of the world. So that you know they, you know, fisheries are important and they can't, you know, stopping them in many places is just not possible. Yeah.- I'm afraid we have to draw it to a close there. I wanted to thank you all for coming and thank you for your attention and our online audience as well. And I hope you'll join me in thanking the professor for his lecture.(audience applause)