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The Conversation

Warm is the new norm for the Great Barrier Reef – and a likely El Niño raises red flags

The Bureau of Meteorology this week declared a 70% chance of an El Niño developing this year. This raises concern for the health of the Great Barrier Reef, which is under continuing threat from climate change. Recent summers have shown the devastating damage heat stress can wreak on the reef. We must act urgently to protect this underwater marvel – through this likely El Niño, and beyond. We are coral reef and climate scientists, and policy experts. We’ve seen how the Great Barrier Reef is nearing its tipping point. After this point, it will become unrecognisable as a functioning ecosystem. But the scale of climate threat is beyond the tools currently used to manage the Great Barrier Reef. New measures and sustained effort are needed – at local, national, and international scales – if we’re serious about saving this natural wonder. International treasure under threat The Great Barrier Reef is internationally renowned for its biodiversity, including more than 450 species of coral, 1,600 species of fish and 6,000 species of molluscs. It is also an economic workhorse, contributing about A$6 billion to the Australian economy and providing some 64,000 full-time jobs. Many industries and coastal communities in Queensland rely on a healthy Great Barrier Reef. But Australia’s reefs are in trouble and climate change is the biggest threat – bringing heatwaves, severe cyclones and more acidic oceans. The background temperature of the Great Barrier Reef has warmed by 0.8°C since 1910. This warming can couple with ocean temperature variability, such as from El Niño and its counterpart, La Niña. But because the Great Barrier Reef is already struggling under climate change, an El Niño could mean even more pressure. What the next Australian government must do to save the Great Barrier Reef The bathtub is filling We hope this analogy helps explain the situation. Imagine a bathtub. The water inside it represents global sea-surface temperature. When the bathtub was only half-full, temporary heat variability (from El Niño) caused splashes, but they were contained in the tub. Now fast-forward to the present day. For more than a century, humans have been heating the planet by burning fossil fuels. The background temperature has risen and the bathtub is now almost filled to the brim. Add a splash of heat from El Niño and the bath spills over. These splashes bring consequences: more mass bleaching of coral and, in severe cases, widespread coral death. El Niño and La Niña have become more variable in recent decades. This has meant more frequent and stronger events – bigger splashes in the bathtub – that pose a grave threat to the Great Barrier Reef’s health and biodiversity. All the while, the bathtub keeps filling. The World Meteorological Organisation reported that the next five years will be the warmest since records began. And 2023 will almost certainly be among the ten warmest years on record. Earth’s average temperature is predicted to exceed 1.5°C of warming in at least one of the next five years. This would produce a big splash – but it doesn’t represent the bathtub level reaching the brim. Under the global climate accord known as the Paris Agreement, nations are pursuing efforts to limit the average global temperature increase to 1.5°C above pre-industrial levels. Background warming beyond 1.5°C is widely considered by climate scientists as dangerous. We’re entering an era in which hot and more frequent splashes are imminent – and the survival of coral reefs is becoming increasingly threatened. Clearly, the global warming we’re seeing now is unprecedented. We must turn off the tap. An inadequate tool kit Unless global emissions are drastically reduced, frequent severe bleaching is projected this century for all 29 World Heritage-listed coral reefs. This would cause untold ecological damage. It would also reduce the reefs’ ability to support human communities that depend on them. Coral bleaching is not the only threat to the Great Barrier Reef. Other pressing problems include poor water quality from land-based runoff, crown-of-thorns starfish and unsustainable fishing and coastal development. So how do we deal with all of this? A range of management actions exists. Banning fishing in some areas and limiting exploitation elsewhere has benefited conservation, while also enhancing fisheries. But other actions have had mixed success. And not all available tools are being applied effectively. For example, “special management areas” were intended to restrict human use of the Great Barrier Reef for conservation or management purposes. But their use has been limited. And emergency implementations of these areas, allowed under the law, have never been used. Crucially, none of the available actions were designed to respond to climate threats. The reality is, the scale of climate disturbance is beyond the available management tools. We all know the Great Barrier Reef is in danger – the UN has just confirmed it. Again Source: Australian Academy of Science. What are we waiting for? The scientific evidence is unequivocal. We must work at local, national, and international scales to help the Great Barrier Reef better cope with climate change. The likely arrival of an El Niño makes this task ever more urgent. Australian and international governments must take immediate and decisive action on emissions reduction. This includes banning new coal and gas projects and rapidly shifting to renewable energy. Communities reliant on fossil-fuel industries should be helped to transition to new livelihoods. Reef management agencies need to tackle climate threats more effectively – at a scale commensurate with the problem. This requires a new way of managing key areas. That could mean, for example, temporarily closing off parts of the Great Barrier Reef affected by coral bleaching to give them a reprieve from other stressors such as fishing and tourism. And individuals must also ensure our everyday choices – in transport, consumption and elsewhere – help tackle the climate threat. It’s time for us all to double-down and ensure the survival of the Great Barrier Reef, and the planet. There is no room for complacency. So what are we waiting for? Adapt, move, or die: repeated coral bleaching leaves wildlife on the Great Barrier Reef with few options Scott F. Heron is receiving and has received funding from Australian Research Council, as well as from international government sources. Together with Jon Day, Scott developed the Climate Vulnerability Index (CVI) for World Heritage that has also been applied to assess climate impacts upon other areas of significance. Jodie L. Rummer has received funding from the Australian Research Council. She is the current Vice President of the Australian Coral Reef Society. Jon Day previously worked for the Great Barrier Reef Marine Park Authority between 1986 and 2014, and was one of the Directors at GBRMPA between 1998 and 2014. He represented Australia as one of the formal delegates to the World Heritage Committee between 2007-2011.

The Conversation

Tiny aquatic athletes: how baby Nemo can ‘just keeping swimming’ from the open ocean to the reef

Kim Briers, Shutterstock If you’ve seen the hit animated film Finding Nemo, you might recall the character Dory singing the catchy tune “Just Keep Swimming” to help her clownfish friend Marlin make the long journey from the Great Barrier Reef to Sydney. In this case, art imitates life. Marathon swimming performances are a vital part of early life for the vast majority of coral reef fish. Baby (larval) reef fish – smaller than the size of your thumbnail – hatch from eggs laid on the reef and spend a few weeks in the open ocean before swimming back to the reef. But how does such a small creature make this impressive journey? Our research published today set out to answer this question. We found larval clownfish dramatically alter their physiology to complete their journey from the ocean back to the reef. In particular, they take in more oxygen per breath and at a faster rate than any other fish species studied to date. Essentially, this makes baby clownfish some of the smallest athletes on the planet. Just Keep Swimming from Finding Nemo. Read more: Dazzling or deceptive? The markings of coral reef fish Mini athletes swimming 10-50 body lengths per second Reef fish are vital to coral reef ecosystems. They play important roles in the food web, help keep the reef clean and recycle nutrients. Plus, their vibrant colours attract millions of tourists annually. Adult reef fish keep to a small patch. Their eggs are carried off by wave action into the open ocean, where they hatch and develop. Within a few weeks the tiny fish larvae must return to the reef. It’s a long, arduous journey that can last weeks to months. Depending on the species, they cover distances as far as 64 kilometres. So how do they do it? Until the 1990s, scientists believed the development of larval reef fish was like that of other fish such as herring, cod and flatfish. These species “go with the flow”, passively riding ocean currents until they become large and developed enough to actively swim on their own, against the currents. However, landmark studies from the early 1990s documented the impressive swimming capabilities of baby reef fish. It turns out reef fish are not passive particles after all. Previous research has provided overwhelming evidence coral reef fishes are capable of amazing swimming performance as babies. Some of these tiny athletes are capable of swimming 10-50 body lengths per second as a larva. For comparison, Olympic multi-gold medallist Michael Phelps races at just under two body lengths per second. When paired with well-developed sensory systems such as vision and the sense of smell, such impressive athletic performance enables these babies to “just keep swimming” with or against ocean currents until they find an optimal reef on which to settle. But 30 years after the discovery, we were still wondering how they manage it. Now we know. Clownfish eggs begin as tiny orange spots, but they soon start to lengthen and acquire visible eyes. Joe Belanger, Shutterstock Measuring the traits of an athlete My colleagues and I measured physiological traits required to be an athletic swimmer across the entire larval phase of a clownfish. These traits included swimming speed, oxygen uptake rates, gene expression patterns, and tolerance to low oxygen (hypoxia). Why hypoxia? At night, when it’s no longer possible to use sunshine and carbon dioxide to make energy by photosynthesis, corals and plants breathe in oxygen to make energy. This lowers oxygen levels on reefs. Larval reef fish returning home from the open ocean must prepare for such conditions. We found larval clownfish have the highest oxygen uptake rates of any fish to date. This supports elite swimming, growth and development. As they develop and swim faster, thousands of genes change. Genes that code for proteins that transport and store oxygen, such as haemoglobin and myoglobin (also found in our bodies), are especially important. They enable oxygen to be transported and stored during intense exercise and help retain oxygen in tissues when the fish experience hypoxia in their reef habitats. The changes in haemoglobin and myoglobin genes also correspond to when these baby fish start to increase their hypoxia tolerance. We’ve seen this before, in reverse. Salmon are one of the most studied fish of all time and, as adults, they’re pretty amazing athletes as well. However, baby salmon endure low oxygen conditions in the first few weeks of life, right after hatching, while they are hiding in the gravel of the freshwater riverbeds. And, sure enough, back in the 1980s, research showed salmon switch their haemoglobin too – right when the baby salmon have to transition from being hypoxia tolerant, to training to become elite swimmers. Why our research matters The changes in physiological machinery that we uncovered are key to survival for clownfish. It’s likely other coral reef fish follow similar developmental pathways. Reef fish – of all shapes, sizes, and colours – are integral for maintaining coral reef health and persistence of future coral reefs. This is crucial as climate change threatens these beautiful, delicate ecosystems. I studied what happens to reef fish after coral bleaching. What I saw still makes me nauseous Adam Downie receives funding from the University of Queensland, and the Goodman Foundation Research Grant Scheme through the Morton Bay Research station. He is a member of the Australian Society for Fish Biology. His past affiliations include the University of New Brunswick (BSc student) and James Cook University (PhD student). Jodie L. Rummer receives funding from the Australian Research Council and is the Vice President of the Australian Coral Reef Society.

The Conversation

What the next Australian government must do to save the Great Barrier Reef

Getty Images Widespread coral bleaching has now occurred on the Great Barrier Reef for the fourth time in seven years. As the world has heated up more and more, there’s less and less chance for corals to recover. This year, the Morrison government announced a A$1 billion plan to help the reef. This plan tackles some of the problems the reef faces – like poor water quality from floods as well as agricultural and industrial runoff. But it makes no mention of the elephant in the room. The world’s largest living assemblage of organisms is facing collapse because of one major threat: climate change. Our window of opportunity to act is narrowing. We and other scientists have warned about this for decades. Australia has doubled down on coal and gas exports with subsidies of $20 billion in the past two years. When these fossil fuels are burned, they produce carbon dioxide and other greenhouse gases that trap more heat in the atmosphere that also warms the ocean. If our next federal government wants to save the reef, it must tackle the main reason it is in trouble by phasing out fossil fuel use and exports as quickly as possible. Otherwise it’s like putting bandaids on an arterial wound. But to help the reef get through the next decades of warming we’ve already locked in, we will still need that $1 billion to help reduce other stressors. Why is this new bleaching event such bad news? Past bleaching events have been linked to El Niño events. Stable atmospheric conditions can bring calm, cloud-free periods that heat up the water around the reef. That can bring extreme summer temperatures – and that is when corals bleach. This year is a La Niña, which can bring warmer-than-usual temperatures but also tends to bring more clouds, rain, and storms that mix up the waters. These usually spread the heat to the deeper parts of the ocean and mean lower temperature for corals. Not this time. Global warming means corals are already close to their bleaching threshold, and it doesn’t take much heat to tip the balance. Water temperatures across the reef have been several degrees hotter than the long-term average. And the corals are feeling the heat. Four times in seven years means that bleaching events are accelerating. Predictions have suggested that bleaching will become an annual event in a little over two decades. It may not be that long. You always remember the first time you see bleaching in real life. For co-author Jodie, that was in 2016, off Lizard Island, a previously pristine part of the reef far from human impacts or water quality issues. The water was shockingly warm. Looking at our dive computers, we saw that the temperatures we had been simulating in our laboratories for 2050 were already here. For a week, the marine heatwave pushed the corals to their limits. When corals experience heat stress, some initially turn fluorescent while others go stark white. Then the water goes murky – that’s death in the water. It’s heartbreaking to see. Grief is common among marine scientists right now. The $1 billion Great Barrier Reef funding is nonsensical. Australians, and their natural wonder, deserve so much better Corals can recover from bleaching if they get a recovery period. But annual bleaching means there is not enough time for proper recovery. Even the most robust corals can’t survive this year after year. Some people hope the reef can adapt to hotter conditions – but there is little evidence it can happen fast enough to outpace warming. While some fish can move to cooler waters further south, corals face ocean acidification, yet another problem caused by carbon dioxide emissions. As CO₂ is absorbed by the ocean, the changed chemistry makes it harder for corals to build their skeleton (and for other marine organisms to form a shell). There’s no safe place for corals to go. More acidic seawater makes it harder for coral polyps to build their skeletons. Shutterstock What does the next government need to do? The evidence is clear. We see it with our own eyes. We’re barrelling towards catastrophic levels of warming, and there’s not enough action. As it stands, policies on offer by our two major parties will not save the reef, according to new research by Climate Analytics. Current Coalition emissions reduction targets of 26-28% by 2030 would lead to a 3°C warmer world, which would be devastating for the Great Barrier Reef. Labor’s policies of a 43% reduction by 2030 still lead to 2°C of warming. The teal independents and the Greens have policies compatible with keeping warming to 1.5°C, though how to achieve those goals is unclear. What is clear is that every tenth of a degree matters. We need leaders who are serious about climate action. Who can acknowledge the truth that the problem is real, that we’re causing it, and that it’s hurting us right now. Australia's next government must tackle our collapsing ecosystems and extinction crisis There are still a few people sceptical that humans can change the climate. But today the changes are apparent. The words “unprecedented” and “record-breaking” are starting to lose relevance for natural disasters because they are used more and more. Australians faced the 2019/20 Black Summer of megafires. This year we’ve had major flooding. Marine heatwaves have killed off almost all of Tasmania’s giant kelp. But climate impacts are also being seen around the world – extraordinary drought gripping California, fires in melting Siberia and events scientists consider to be “virtually impossible without the influence of human-caused climate change”. That includes the accelerating impacts on coral reefs worldwide. We need government policies matching the scale and urgency of the threat. That means getting to net zero as soon as possible. It isn’t only about the reef – it’s about all land and sea natural systems vulnerable to climate change, and the people who rely on them. No developed country has more to lose from inaction on climate than Australia. But no country has more to gain by shifting to clean energy, through new economic opportunities, new jobs, and better protection for our natural treasures. Jodie L. Rummer has received funding from the Australian Research Council (ARC) and the ARC Centre of Excellence for Coral Reef Studies. She is also affiliated with the Australian Coral Reef Society. Scott F. Heron has received funding from Australian Research Council and NASA ROSES Ecological Forecasting.

The Conversation

Adapt, move, or die: repeated coral bleaching leaves wildlife on the Great Barrier Reef with few options

Grumpy Turtle Films, Author provided To our horror, another mass coral bleaching event may be striking the Great Barrier Reef, with water temperatures reaching up to 3°C higher than average in some places. This would be the sixth such event since the late 1990s, and the fourth since 2016. It comes as a monitoring mission from the United Nations arrives in Queensland today to inspect the reef and consider listing the World Heritage site as “in danger”. As coral reef scientists, we’ve seen firsthand how the Great Barrier Reef is nearing its tipping point, beyond which the reef will lose its function as a viable ecosystem. This is not only due to climate change exacerbating marine heatwaves, but also higher ocean acidity, loss of oxygen, pollution, and more. Scientists are at our own tipping points, too. The reef is suffering environmental conditions so extreme, we’re struggling to simulate these scenarios in our laboratories. Even though Australia has world-class facilities, we are proverbially beating our heads against the wall each year as conditions worsen. It’s getting harder for scientists to predict how these conditions will affect individual species, let alone the health and biodiversity of reef ecosystems. But let’s explore what we do know. Coral bleaching seen due to the current marine heatwave. Grumpy Turtle Films, Author provided What is coral bleaching and why does it happen? Corals are animals that live in a mutually beneficial partnership with tiny single-celled algae called “zooxanthellae” (but scientists call them zooks). Zooks benefit corals by giving them energy and colour, and in return the coral gives them a home in the coral tissue. Under stress, such as in too-hot water, the algae produce toxins instead of nutrition, and the coral ejects them. 5 major heatwaves in 30 years have turned the Great Barrier Reef into a bleached checkerboard Without the algae, the corals begin to starve. They lose their vibrant colours, revealing the bright white limestone skeleton through the coral tissue. If stress conditions abate, the algae can return and coral can recover over months. But if stress persists, the corals can die – the skeletons begin to crumble, removing vital habitat for other species. Water temperatures reaching up to 3°C higher than average in some places. Grumpy Turtle Films, Author provided We had hoped for a reprieve Scientists and managers had hoped for a reprieve this year. Much of the Great Barrier Reef was in the early stages of recovery following the 2016, 2017, and 2020 bleaching events. In the tropical paradise of northern Queensland, we’ve been wishing for cloudy days and cooler temperatures, hoping for rain and even storms (but not big ones). These conditions typically come with La Niña – a natural climate phenomenon associated with cooler, wetter weather, which has now happened two years in a row. But despite these effects of La Niña, climate change meant 2021 was one of the hottest years on record. Now, at the tail end of Australia’s summer, the reef is experiencing another marine heatwave and is tipping over the bleaching threshold. There’s not enough time for coral to recover between events. Even the most robust corals require nearly a decade to recover. There is also no clear evidence corals are adapting to the new conditions. To make matters worse, climate change is supercharging the atmosphere and making even the natural variations of La Niña and its counterpart El Niño more variable and less predictable. This means Australia will not only endure more intense heatwaves, but also flooding, droughts and storms. At least 1,625 species of fishes live in the Great Barrier Reef. Grumpy Turtle Films, Author provided How will this hurt marine life? A healthy Great Barrier Reef is home to at least 1,625 species of fishes, 3,000 species of molluscs, 630 species of echinoderms (such as sea stars and urchins), and the list goes on. Marine life in coral reefs have three options in warming waters: adapt, move, or die. Most shark species can’t adapt to warmer waters fast enough to survive. Grumpy Turtle Films, Author provided 1. Can they adapt? Over generations, species can make changes at the molecular level – their DNA – so they’re more suited to or can adapt to new environmental conditions. This evolution may be possible for species with fast generation times, such as damselfishes. But reef species with slower generation times can’t keep pace with the rate we’re changing their habitat conditions. This includes the iconic potato cod and most sharks, which take a around a decade or longer to reach sexual maturity. 2. Can they move? Some species of reef fishes may start moving to cooler waters before the harmful effects of warming take hold. But this option isn’t available to all species, such as those that depend on a particular habitat, certain resources, or protection. This includes coral, as well as coral-dwelling gobies and several damselfishes. A citizen science project called Project RedMap, has been documenting the poleward migration of reef fish species due to climate change. Studies have found that larger, tropical fishes with a high swimming ability are more likely to survive in temperate waters, such as some butterflyfishes. 3. They can die The third option is one we don’t like to talk about, but is becoming more of a threat. If marine life can’t adapt or move , we’ll see extinctions at a local scale, total extinction of some species, and dramatic declines in fish populations. UNESCO representatives are visiting the reef to assess its World Heritage status. Grumpy Turtle Films, Author provided Listing the reef as ‘in danger’ While the reef is bleaching, UNESCO delegates have arrived in Queensland to monitor its health, as the World Heritage site is once again being considered for an “in danger” listing. The visit will likely include seeing the bleaching currently occurring, the damage to the reef still apparent from past events, and they’ll hear firsthand from scientists and managers who’ve witnessed these impacts. Listing the Great Barrier Reef as “in danger” would raise the alert level for the international community and hopefully inspire climate action. Reducing the major source of stress the reef faces – climate change – will require ongoing collaborations between Australian and international governments, with work on local management issues also involving business owners, reef managers, Traditional Owners, scientists, civil society groups, and other stakeholders. The $1 billion Great Barrier Reef funding is nonsensical. Australians, and their natural wonder, deserve so much better We’ve known for a long time the most important step to save the reef: cutting emissions to stop global warming. Indeed, future projections of coral bleaching from the 1990s suggested that frequent and severe events would begin from the late-2010s – and they’ve been alarmingly prescient. The Great Barrier Reef’s continuing demise is one of the most visible examples of how our inaction as humans has profound and perhaps irreversible consequences. We are rapidly accelerating toward the tipping point. Jodie L. Rummer receives funding from the Australian Research Council Centre of Excellence for Coral Reef Studies. Scott Heron receives funding from Australian Research Council and NASA ROSES Ecological Forecasting.