Media Coverage

Featured interviews, news coverage, and public engagement in marine science and conservation.

Latest Media Coverage

The Conversation

Mais pourquoi certains requins « freezent » lorsqu’on les retourne ?

Lorsqu’on retourne certains requins, ils se figent totalement. Rachel Moore Vous avez peut-être déjà vu cette scène dans votre documentaire animalier préféré. Le prédateur surgit brutalement de sa cachette, gueule grande ouverte, et sa proie… se fige soudain. Elle semble morte. Cette réponse de figement – appelée « immobilité tonique » – peut sauver la vie de certains animaux. Les opossums sont célèbres pour leur capacité à « faire le mort » afin d’échapper aux prédateurs. Il en va de même pour les lapins, les lézards, les serpents et même certains insectes. Mais que se passe-t-il quand un requin agit ainsi ? Dans notre dernière étude, nous avons exploré ce comportement étrange chez les requins, les raies et leurs proches parents. Chez ce groupe, l’immobilité tonique est déclenchée lorsque l’animal est retourné sur le dos : il cesse de bouger, ses muscles se relâchent et il entre dans un état proche de la transe. Certains scientifiques utilisent même cette réaction pour manipuler certains requins en toute sécurité. Mais pourquoi cela se produit-il ? Et ce comportement aide-t-il réellement ces prédateurs marins à survivre ? Le mystère du « requin figé » Bien que ce phénomène soit largement documenté dans le règne animal, les causes de l’immobilité tonique restent obscures – surtout dans l’océan. On considère généralement qu’il s’agit d’un mécanisme de défense contre les prédateurs. Mais aucune preuve ne vient appuyer cette hypothèse chez les requins, et d’autres théories existent. Nous avons testé 13 espèces de requins, de raies et une chimère – un parent du requin souvent appelé « requin fantôme » – pour voir si elles entraient en immobilité tonique lorsqu’on les retournait délicatement sous l’eau. Sept espèces se sont figées. Nous avons ensuite analysé ces résultats à l’aide d’outils d’analyse évolutive pour retracer ce comportement sur plusieurs centaines de millions d’années d’histoire des requins. Alors, pourquoi certains requins se figent-ils ? Chez les requins, l’immobilité tonique est déclenchée lorsqu’on les retourne sur le dos. Rachel Moore Trois hypothèses principales Trois grandes hypothèses sont avancées pour expliquer l’immobilité tonique chez les requins : Une stratégie anti-prédateur – « faire le mort » pour éviter d’être mangé. Un rôle reproductif – certains mâles retournent les femelles lors de l’accouplement, donc l’immobilité pourrait réduire leur résistance. Une réponse à une surcharge sensorielle – une sorte d’arrêt réflexe en cas de stimulation extrême. Mais nos résultats ne confirment aucune de ces explications. Il n’existe pas de preuve solide que les requins tirent un avantage du figement en cas d’attaque. En réalité, des prédateurs modernes, comme les orques, exploitent cette réaction en retournant les requins pour les immobiliser, avant d’arracher le foie riche en nutriments – une stratégie mortelle. Du lundi au vendredi + le dimanche, recevez gratuitement les analyses et décryptages de nos experts pour un autre regard sur l’actualité. Abonnez-vous dès aujourd’hui ! L’hypothèse reproductive est aussi peu convaincante. L’immobilité tonique ne varie pas selon le sexe, et rester immobile pourrait même rendre les femelles plus vulnérables à des accouplements forcés ou nocifs. Quant à la théorie de la surcharge sensorielle, elle reste non testée et non vérifiée. Nous proposons donc une explication plus simple : l’immobilité tonique chez les requins est probablement une relique de l’évolution. Une affaire de bagage évolutif Notre analyse suggère que l’immobilité tonique est un trait « plésiomorphe » – c’est-à-dire ancestral –, qui était probablement présent chez les requins, les raies et les chimères anciens. Mais au fil de l’évolution, de nombreuses espèces ont perdu ce comportement. En fait, nous avons découvert que cette capacité avait été perdue au moins cinq fois indépendamment dans différents groupes. Ce qui soulève une question : pourquoi ? Dans certains environnements, ce comportement pourrait être une très mauvaise idée. Les petits requins de récif et les raies vivant sur le fond marin se faufilent souvent dans des crevasses étroites des récifs coralliens complexes pour se nourrir ou se reposer. Se figer dans un tel contexte pourrait les coincer – ou pire. Perdre ce comportement aurait donc pu être un avantage dans ces lignées. Que faut-il en conclure ? Plutôt qu’une tactique de survie ingénieuse, l’immobilité tonique pourrait n’être qu’un « bagage évolutif » – un comportement qui a jadis servi, mais qui persiste aujourd’hui chez certaines espèces simplement parce qu’il ne cause pas assez de tort pour être éliminé par la sélection naturelle. Un bon rappel que tous les traits observés dans la nature ne sont pas adaptatifs. Certains ne sont que les bizarreries de l’histoire évolutive. Notre travail remet en question des idées reçues sur le comportement des requins, et éclaire les histoires évolutives cachées qui se déroulent encore dans les profondeurs de l’océan. La prochaine fois que vous entendrez parler d’un requin qui « fait le mort », souvenez-vous : ce n’est peut-être qu’un réflexe musculaire hérité d’un temps très ancien. Jodie L. Rummer reçoit des financements de l’Australian Research Council. Elle est affiliée à l’Australian Coral Reef Society, dont elle est la présidente. Joel Gayford reçoit des financements du Northcote Trust.

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.