‘Shrinking Nemo': Study finds clownfish can shrink to survive higher sea temperatures
Clownfish, a small orange and white species made famous by the 'Finding Nemo' movies, have been found to shrink in order to boost their chances of surviving marine heat waves, according to a new study.
Working at a conservation center in Papua New Guinea, a team led by scientists from Newcastle University, England, monitored 134 clownfish over a period of five months during a marine heat wave in 2023, according to a statement from the university published Wednesday.
Study lead author Melissa Versteeg, a PhD student at Newcastle University, measured the length of each fish every month, as well as taking the water temperature every 4-6 days.
Versteeg found that the fish would get shorter as temperatures rose, the first time that a coral reef fish has been found to shrink when environmental conditions change.
'I was very surprised by the findings,' Versteeg told CNN on Thursday, adding that the clownfish displayed 'incredible growth plasticity.'
'We're seeing that they have a great capacity to respond to what the environment throws at them,' she said.
This is particularly relevant because marine heat waves are becoming increasingly common as climate change intensifies, with serious impacts on coral reefs and other marine life.
Of the 134 clownfish studied, 100 got shorter, the team found, and this shrinking increased their chances of surviving the heat stress by up to 78%.
Senior study author Theresa Rueger, a marine ecologist at Newcastle University, told CNN that shrinking is not necessarily a good thing as small fish reproduce less, which could be bad for the population.
'But our study also found that because they can shrink and they have this great growth plasticity, they survive better during marine heatwaves,' she said.
'That could be a very positive thing, that they have that capacity and can adapt to their circumstances in that way.'
A small number of other animals are also capable of shrinking, including marine iguanas, which are able to reabsorb bone material to become smaller during times of environmental stress, said Versteeg in the statement.
The team also found that clownfish which shrank at the same time as their breeding partner had a higher chance of survival.
This is because of the balance of power between the female, which is the larger and more dominant, and the male, they explained.
If a female starts to shrink, the male will also shrink in order to prevent social conflict and reduce the possibility of a confrontation that he would always lose.
This is important because clownfish live symbiotically with either of two sea anemone species – Heteractis magnifica and Stichodactyla gigantea.
The anemones provide protection for the clownfish which are 'bad swimmers,' said Rueger.
'If they leave the anemone they have very little time before they get eaten, frankly,' she added, which means it is important for them not to fight with their partner and risk being forced out into the open sea.
The symbiotic relationship with their home anemone is another reason why clownfish are so fascinating, said Versteeg.
'They don't move, that's where they're at. You're able to just track them over time, and they're uniquely marked and they're relatively easy to catch,' she said.
'You really know who you're dealing with, and you can really follow them over extensive periods of time, which is unique,' added Versteeg.
Next up, the team plans to investigate the mechanisms behind this capacity to grow and shrink depending on environmental conditions, as well as looking into whether other fish species are also able to do so.
'If individual shrinking were widespread and happening among different species of fish, it could provide a plausible alternative hypothesis for why the size (of) many fish species is declining,' said Rueger in the statement.
The study was published in the journal Science Advances.
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A surprising study revealed biological activity on a distant planet. Weeks later, scientists say there's more to the story
Sign up for CNN's Wonder Theory science newsletter. Explore the universe with news on fascinating discoveries, scientific advancements and more. A tiny sign revealed in April seemed like it might change the universe as we know it. Astronomers had detected just a hint, a glimmer of two molecules swirling in the atmosphere of a distant planet called K2-18b — molecules that on Earth are produced only by living things. It was a tantalizing prospect: the most promising evidence yet of an extraterrestrial biosignature, or traces of life linked to biological activity. But only weeks later, new findings suggest the search must continue. 'It was exciting, but it immediately raised several red flags because that claim of a potential biosignature would be historic, but also the significance or the strength of the statistical evidence seemed to be too high for the data,' said Dr. Luis Welbanks, a postdoctoral research scholar at Arizona State University's School of Earth and Space Exploration. While the molecules identified on K2-18b by the April study — dimethyl sulfide, or DMS, and dimethyl disulfide, or DMDS — are associated largely with microbial organisms on our planet, scientists point out that the compounds can also form without the presence of life. Now, three teams of astronomers not involved with the research, including Welbanks, have assessed the models and data used in the original biosignature discovery and got very different results, which they have submitted for peer review. Meanwhile, the lead author of the April study, Nikku Madhusudhan, and his colleagues have conducted additional research that they say reinforces their previous finding about the planet. And it's likely that additional observations and research from multiple groups of scientists are on the horizon. The succession of research papers revolving around K2-18b offers a glimpse of the scientific process unfolding in real time. It's a window into the complexities and nuances of how researchers search for evidence of life beyond Earth — and shows why the burden of proof is so high and difficult to reach. Located 124 light-years from Earth, K2-18b is generally considered a worthy target to scour for signs of life. It is thought to be a Hycean world, a planet entirely covered in liquid water with a hydrogen-rich atmosphere, according to previous research led by Madhusudhan, a professor of astrophysics and exoplanetary science at the University of Cambridge's Institute of Astronomy. And as such, K2-18b has rapidly attracted attention as a potentially habitable place beyond our solar system. Convinced of K2-18b's promise, Madhusudhan and his Cambridge colleagues used observations of the planet by the largest space telescope in operation, the James Webb Space Telescope, to study the planet further. But two scientists at the University of Chicago — Dr. Rafael Luque, a postdoctoral scholar in the university's department of astronomy and astrophysics, and Michael Zhang, a 51 Pegasi b / Burbidge postdoctoral fellow — spotted some problems with what they found. After reviewing Madhusudhan and his team's April paper, which followed up on their 2023 research, Luque and Zhang noticed that the Webb data looked 'noisy,' Luque said. Noise, caused by imperfections in the telescope and the rate at which different particles of light reach the telescope, is just one challenge astronomers face when they study distant exoplanets. Noise can distort observations and introduce uncertainties into the data, Zhang said. Trying to detect specific gases in distant exoplanet atmospheres introduces even more uncertainty. The most noticeable features from a gas like dimethyl sulfide stem from a bond of hydrogen and carbon molecules — a connection that can stretch and bend and absorb light at different wavelengths, making it hard to definitively detect one kind of molecule, Zhang said. 'The problem is basically every organic molecule has a carbon-hydrogen bond,' Zhang said. 'There's hundreds of millions of those molecules, and so these features are not unique. If you have perfect data, you can probably distinguish between different molecules. But if you don't have perfect data, a lot of molecules, especially organic molecules, look very similar, especially in the near-infrared.' Delving further into the paper, Luque and Zhang also noticed that the perceived temperature of the planet appeared to increase sharply from a range of about 250 Kelvin to 300 Kelvin (-9.67 F to 80.33 F or -23.15 C to 26.85 C) in research Madhusudhan published in 2023 to 422 Kelvin (299.93 F or 148.85 C) in the April study. Such harsh temperatures could change the way astronomers think about the planet's potential habitability, Zhang said, especially because cooler temperatures persist in the top of the atmosphere — the area that Webb can detect — and the surface or ocean below would likely have even higher temperatures. 'This is just an inference only from the atmosphere, but it would certainly affect how we think about the planet in general,' Luque said. Part of the issue, he said, is that the April analysis didn't include data collected from all three Webb instruments Madhusudhan's team used over the past few years. So Luque, Zhang and their colleagues conducted a study combining all the available data to see whether they could achieve the same results, or even find a higher amount of dimethyl sulfide. They found 'insufficient evidence' of both molecules in the planet's atmosphere. Instead, Luque and Zhang's team spotted other molecules, like ethane, that could fit the same profile. But ethane does not signify life. Arizona State's Welbanks and his colleagues, including Dr. Matt Nixon, a postdoctoral researcher in the department of astronomy at the University of Maryland College Park, also found what they consider a fundamental problem with the April paper on K2-18b. The concern, Welbanks said, was with how Madhusudhan and his team created models to show which molecules might be in the planet's atmosphere. 'Each (molecule) is tested one at a time against the same minimal baseline, meaning every single model has an artificial advantage: It is the only explanation permitted,' Welbanks said. When Welbanks and his team conducted their own analysis, they expanded the model from Madhusudhan's study. '(Madhusudhan and his colleagues) didn't allow for any other chemical species that could potentially be producing these small signals or observations,' Nixon said. 'So the main thing we wanted to do was assess whether other chemical species could provide an adequate fit to the data.' When the model was expanded, the evidence for dimethyl sulfide or dimethyl disulfide 'just disappears,' Welbanks said. Madhusudhan believes the studies that have come out after his April paper are 'very encouraging' and 'enabling a healthy discussion on the interpretation of our data on K2-18b.' He reviewed Luque and Zhang's work and agreed that their findings don't show a 'strong detection for DMS or DMDS.' When Madhusudhan's team published the paper in April, he said the observations reached the three-sigma level of significance, or a 0.3% probability that the detections occurred by chance. For a scientific discovery that is highly unlikely to have occurred by chance, the observations must meet a five-sigma threshold, or below a 0.00006% probability that the observations occurred by chance. Meeting such a threshold will require many steps, Welbanks said, including repeated detections of the same molecule using multiple telescopes and ruling out potential nonbiological sources. While such evidence could be found in our lifetime, it is less likely to be a eureka moment and more a slow build requiring a consensus among astronomers, physicists, biologists and chemists. 'We have never reached that level of evidence in any of our studies,' Madhusudhan wrote in an email. 'We have only found evidence at or below 3-sigma in our two previous studies (Madhusudhan et al. 2023 and 2025). We refer to this as moderate evidence or hints but not a strong detection. I agree with (Luque and Zhang's) claim which is consistent with our study and we have discussed the need for stronger evidence extensively in our study and communications.' 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'Regardless of what any single author group says right now, we don't have a silver bullet. But that is exactly why this is exciting, because we know that we're the closest we have ever been (to finding a biosignature), and I think we may get it within our lifetime, but right now, we're not there. That is not a failure. We're testing bold ideas.'
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Sign up for CNN's Wonder Theory science newsletter. Explore the universe with news on fascinating discoveries, scientific advancements and more. A tiny sign revealed in April seemed like it might change the universe as we know it. Astronomers had detected just a hint, a glimmer of two molecules swirling in the atmosphere of a distant planet called K2-18b — molecules that on Earth are produced only by living things. It was a tantalizing prospect: the most promising evidence yet of an extraterrestrial biosignature, or traces of life linked to biological activity. But only weeks later, new findings suggest the search must continue. 'It was exciting, but it immediately raised several red flags because that claim of a potential biosignature would be historic, but also the significance or the strength of the statistical evidence seemed to be too high for the data,' said Dr. Luis Welbanks, a postdoctoral research scholar at Arizona State University's School of Earth and Space Exploration. 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But two scientists at the University of Chicago — Dr. Rafael Luque, a postdoctoral scholar in the university's department of astronomy and astrophysics, and Michael Zhang, a 51 Pegasi b / Burbidge postdoctoral fellow — spotted some problems with what they found. After reviewing Madhusudhan and his team's April paper, which followed up on their 2023 research, Luque and Zhang noticed that the Webb data looked 'noisy,' Luque said. Noise, caused by imperfections in the telescope and the rate at which different particles of light reach the telescope, is just one challenge astronomers face when they study distant exoplanets. Noise can distort observations and introduce uncertainties into the data, Zhang said. Trying to detect specific gases in distant exoplanet atmospheres introduces even more uncertainty. 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But ethane does not signify life. Arizona State's Welbanks and his colleagues, including Dr. Matt Nixon, a postdoctoral researcher in the department of astronomy at the University of Maryland College Park, also found what they consider a fundamental problem with the April paper on K2-18b. The concern, Welbanks said, was with how Madhusudhan and his team created models to show which molecules might be in the planet's atmosphere. 'Each (molecule) is tested one at a time against the same minimal baseline, meaning every single model has an artificial advantage: It is the only explanation permitted,' Welbanks said. When Welbanks and his team conducted their own analysis, they expanded the model from Madhusudhan's study. '(Madhusudhan and his colleagues) didn't allow for any other chemical species that could potentially be producing these small signals or observations,' Nixon said. 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Meeting such a threshold will require many steps, Welbanks said, including repeated detections of the same molecule using multiple telescopes and ruling out potential nonbiological sources. While such evidence could be found in our lifetime, it is less likely to be a eureka moment and more a slow build requiring a consensus among astronomers, physicists, biologists and chemists. 'We have never reached that level of evidence in any of our studies,' Madhusudhan wrote in an email. 'We have only found evidence at or below 3-sigma in our two previous studies (Madhusudhan et al. 2023 and 2025). We refer to this as moderate evidence or hints but not a strong detection. I agree with (Luque and Zhang's) claim which is consistent with our study and we have discussed the need for stronger evidence extensively in our study and communications.' 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'Regardless of what any single author group says right now, we don't have a silver bullet. But that is exactly why this is exciting, because we know that we're the closest we have ever been (to finding a biosignature), and I think we may get it within our lifetime, but right now, we're not there. That is not a failure. We're testing bold ideas.'
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These worms stack together to form living towers, new study finds
Sign up for CNN's Wonder Theory science newsletter. Explore the universe with news on fascinating discoveries, scientific advancements and more. Nature seems to offer an escape from the hustle and bustle of city life, but the world at your feet may tell another story. Even in the shade of a fruit tree, you could be surrounded by tiny skyscrapers — not made of steel or concrete, but of microscopic worms wriggling and writhing into the shape of long, vertical towers. Even though these miniature architects, called nematodes, are found all over Earth's surface, scientists in Germany recently witnessed their impressive building techniques in nature for the first time. After months of closely inspecting rotten pears and apples in local orchards, researchers from the Max Planck Institute of Animal Behavior and the University of Konstanz were able to spot hundreds of the 1-millimeter-long (0.04-inch) worms climbing onto one another, amassing structures up to 10 times their individual size. To learn more about the mysterious physics of the soft, slimy towers, the study team brought samples of nematodes called Caenorhabditis elegans into a lab and analyzed them. There, the scientists noticed the worms could assemble in a matter of hours, with some reaching out from the twisting mass as exploratory 'arms' sensing the environment and building accordingly. But why the worms formed the structures wasn't immediately clear. The team's findings, published Thursday in the journal Current Biology, show that even the smallest animals can prompt big questions about the evolutionary purpose of social behaviors. 'What we got was more than just some worms standing on top of each other,' said senior study author Serena Ding, a Max Planck research group leader of genes and behavior. 'It's a coordinated superorganism, acting and moving as a whole.' To find out what was motivating the nematodes' building behavior, the study team tested the worms' reactions to being poked, prodded and even visited by a fly — all while stacked in a tower formation. 'We saw that they are very reactive to the presence of a stimulus,' said the study's first author, Daniela Perez, who is a postdoctoral researcher at the Max Planck Institute of Animal Behavior. 'They sense it, and then the tower goes towards this stimulus, attaching itself to our metal pick or a fly buzzing around.' This coordinated reaction suggests the hungry nematodes may be joining together to easily hitch a ride on larger animals such as insects that transport them to (not so) greener pastures with more rotten fruit to feast on, Perez said. 'If you think about it, an animal that is 1 millimeter long cannot just crawl all the way to the next fruit 2 meters (6.6 feet) away. It could easily die on the way there, or be eaten by a predator,' Perez explained. Nematodes are capable of hitchhiking solo too, she added, but arriving to a new area in a group may allow them to continue reproducing. The structures themselves may also serve as a mode of transport, as evidenced by how some worms formed bridges across gaps within the petri dishes to get from one surface to another, Perez noted. 'This discovery is really exciting,' said Orit Peleg, an associate professor of computer science who studies living systems at the University of Colorado Boulder's BioFrontiers Institute. 'It's both establishing the ecological function of creating a tower, and it really opens up the door to do more controlled experimentation to try to understand the perceptual world of these organisms, and how they communicate within a large group.' Peleg was not involved in the study. As the next step, Perez said her team would like to learn whether the formation of these structures is a cooperative or competitive behavior. In other words, are the towering nematodes behaving socially to help each other out, or are their towers more akin to a Black Friday sale stampede? Studying the behaviors of other self-assembling creatures could offer clues to the social norms of nematodes and help answer this question, Ding said. Ants, which assemble to form buoyant rafts to survive floodwaters, are among the few creatures known to team up like nematodes, said David Hu, a professor of mechanical engineering and biology at Georgia Tech. Hu was not involved in the study. 'Ants are incredibly sacrificial for one another, and they do not generally fight within the colony,' Hu said. 'That's because of their genetics. They all come from the same queen, so they are like siblings.' Like ants, nematodes didn't appear to display any obvious role differentiation or hierarchy within the tower structures, Perez said. Each worm from the base to the top of the structure was equally mobile and strong, indicating no competition was at play. However, the lab-cultivated worms were basically clones of one another, so it's not clear whether role differentiation occurs more often in nature, where nematode populations could have more genetic differences, she noted. Additionally, socially cooperative creatures tend to use some form of communication, Peleg said. In the case of ants, it may be their pheromone trails, while honeybees rely on their ritual dance routines and slime molds use their pulsing chemical signals. With nematodes, however, it's still not clear how they might communicate — or if they are communicating at all, Ding said. 'The next steps for (the team) are really just choosing the next questions to ask.' Notably, there has been a lot of interest in studying cooperative animal behaviors among the robotics community, Hu said. It's possible that one day, he added, information about the complex sociality of creatures like nematodes could be used to inform how technology, such as computer servers or drone systems, communicates.
