It’s possible that I shall make an ass of myself. But in that case one can always get out of it with a little dialectic. I have, of course, so worded my proposition as to be right either way (K.Marx, Letter to F.Engels on the Indian Mutiny)
Wednesday, March 11, 2026
How evolution shapes colour diversity in coral reef fish
An international study reveals that the incredible colour patterns of coral reef fish evolve rapidly, but according to common rules, regardless of oceans and regions of the globe.
Why does a Caribbean angelfish sometimes resemble its Indo-Pacific cousin, even though they have never lived in the same ocean? Why do coral reefs harbour such a wide range of stripes, spots and patterns? A study conducted by theUniversity of Liège y reveals that this explosion of colour patterns is not the result of chance. The more species a reef is home to, the more varied the patterns, and fish from different oceans often end up looking alike, guided by the same deep biological constraints.
Coral reef fish are among the most colourful animals on the planet. Horizontal or vertical stripes, round or eye-shaped spots, saddle or labyrinthine patterns... their visual diversity is breathtaking. But this explosion of patterns and colours is not the result of chance. For a long time, scientists wondered about the origin of this diversity, asking themselves whether it was the result of local ecological pressures (each ocean shaping its own diversity of pigmentation patterns) or whether it followed more universal evolutionary laws.
To answer this question, Bruno Frédérich and his colleagues analysed the pigmentation patterns of 918 species belonging to six large families of reef fish: surgeonfish (Acanthuridae), butterflyfish (Chaetodontidae), snappers (Lutjanidae), mullets (Mullidae), angelfish (Pomacanthidae) and damselfish (Pomacentridae). By systematically coding thirty different pattern types on photos of each species, the researchers compiled a unique database covering the five major biogeographic regions of the globe: the Atlantic, the Western Indian Ocean, the Central Indo-Pacific, the Central Pacific and the tropical Eastern Pacific.
The more species there are, the more varied the colour patterns
"The most striking initial finding is that we were able to link colour pattern diversity to the number of species present in a region," explains Bruno Frédérich, an evolutionary biologist at ULiège. The more species an ocean is home to, the more different patterns it contains. This finding suggests that speciation—the process by which new species appear —and the importance of visual recognition of conspecifics play a major role in the diversification of patterns, more so than local environmental conditions."
But the most surprising result obtained by the scientific team concerns the evolutionary dynamics of these patterns. "They evolve very quickly, but within a limited space," says the researcher. In other words, reef fish quickly explore the available decorative possibilities, but these possibilities are constrained by the biological mechanisms that produce colours and patterns. This combination of speed and constraint explains why species that are not closely related, living in different oceans, sometimes end up sporting visually similar motifs. This is called evolutionary convergence."
Patterns shaped from within
How can these evolutionary constraints be explained? Researchers point to cellular and developmental processes that govern the formation of pigmentation patterns. Patterns are not only shaped by the environment or predators, but also by biological 'internal rules' that limit the range of possible forms. Thus, across the oceans, reef fish converge on the same visual solutions, not because they are subject to exactly the same external pressures, but because they share similar developmental mechanisms.
This work is in line with research conducted by the ULiège's Laboratory of Evolutionary Ecology, which had already explored the evolution of colour patterns in clownfish. It opens up new perspectives for understanding the underlying mechanisms that generate and structure this visually striking facet of biodiversity. By mapping the pigmentation pattern diversity of nearly a thousand species on a global scale, this study provides an important answer: the colour patterns of reef fish are not simply a reflection of their local environment, they tell an evolutionary story shaped by speciation, convergence and deep biological constraints.
As any diver knows, oceans can be cloudy places. Even on sunny days, snow-like particles drift through the water column, obscuring the aquatic world below.
Scientists have long known that this “marine snow” carries inorganic calcium carbonate – the building block of shells – but couldn’t explain how the mineral dissolves in the upper part of the ocean.
New research from Rutgers University-New Brunswick points to the culprit: bacteria.
“Think of marine particles as the megacities of the ocean,” said Benedict Borer, an assistant professor of marine and coastal sciences at the Rutgers School of Environmental and Biological Sciences and lead author of the study published in the journal Proceedings of the National Academy of Sciences. “Within these tiny spaces, there are huge amounts of microbial activity. It’s here where calcium carbonate dissolves.”
The findings could reshape how climate scientists model carbon sequestration – the natural or engineered process by which carbon dioxide gas is removed from the atmosphere – and ocean carbon cycling (the exchange of carbon between the atmosphere and the ocean), Borer said.
“Oceanographers often think about the macro-scale, but in this instance, what’s happening in microscopic particles is controlling the entire ocean,” he said.
Oceans are central to the planet's biological carbon pump. At the surface, microscopic algae called phytoplankton absorb carbon dioxide from the atmosphere – including that released by the burning of fossil fuels – and convert it into biomass and, in the case of a phytoplankton called coccolithophores, calcium carbonate shells.
When marine organisms die and sink, billions of tons of organic and inorganic carbon are carried downward each year. The deeper the carbon sinks, the longer it is stored. Eventually, in the cold, acidic depths, calcium carbonate dissolves, carbon dioxide is released, and the cycle continues.
However, while oceanographers have long known that calcium carbonate dissolves in the upper few thousand meters of the ocean, they could not explain the mechanism. The chemistry doesn’t favor it, Borer said.
Recent studies have provided clues, showing that acidic microenvironments in the guts of zooplankton enhance calcium carbonate dissolution, and suggesting that the interiors of marine snow particles may be additional hotspots for calcite dissolution, the crystalline form of calcium carbonate.
To test this theory, Borer and colleagues at the Massachusetts Institute of Technology and Woods Hole Oceanographic Institution studied how the chemistry of marine snow behaves in shallow seas.
In the lab, Borer built a three-layer microfluidic chip to mimic marine snow sinking through the water column. The middle layer held marine particles with calcite and marine bacteria. The top and bottom layers sealed the system, while artificial seawater flowed through the narrow channel between them, simulating particle sinking.
By controlling gas pressure, temperature, oxygen, and bacterial abundance, the team recreated the conditions within a sinking particle and measured how bacterial growth affected calcite.
As particles settled, bacterial respiration increased acidity around them, accelerating calcite dissolution. As a critical consequence, less calcite acting as ballast means that particles sink more slowly.
The results suggest that microbially driven changes in marine snow may dissolve enough calcite near the surface to slow sinking rates and reduce the efficiency of carbon sequestration. And because growing bacteria release carbon dioxide as a byproduct, the process may accelerate the return of heat-trapping gases to the atmosphere, Borer said.
More work is needed to confirm the findings in the open ocean, but the discovery clarifies bacteria’s role in carbon cycling and could improve future climate models and inform geoengineering approaches, he said.
“Our results provide a critical first step to decipher the influence of microbial-enhanced calcite dissolution in marine snow particles, and how it impacts the ocean's ability to sequester carbon at the global scale,” Borer said.
He added: “The question now is how the biological carbon pump will change in the future. Will the transport of carbon to depth become more efficient, or will bacteria respire the carbon more quickly, releasing carbon dioxide back into the atmosphere? To predict this, we need to understand all mechanisms that impact carbon transport to depth, such as the microbially enhanced dissolution of ballasting calcite. What I find quite scary, honestly, is that this process could go either way.”
Understanding how “marine snow” acts as a carbon sink
A new study finds hitchhiking bacteria dissolve essential ballast in ubiquitous “snow” particles, which could counteract the ocean’s ability to sequester carbon
In some parts of the deep ocean, it can look like it’s snowing. This “marine snow” is the dust and detritus that organisms slough off as they die and decompose. Marine snow can fall several kilometers to the deepest parts of the ocean, where the particles are buried in the seafloor for millennia.
Now, researchers at MIT and their collaborators have found that as marine snow falls, tiny hitchhikers may limit how deep the particles can sink before dissolving away. The team shows that when bacteria hitch a ride on marine snow particles, the microbes can eat away at calcium carbonate, which is an essential ballast that helps particles sink.
The findings, which appear this week in the Proceedings of the National Academy of Sciences, could explain how calcium carbonate dissolves in shallow layers of the ocean, where scientists had assumed it should remain intact. The results could also change scientists’ understanding of how quickly the ocean can sequester carbon from the atmosphere.
Marine snow is a main vehicle by which the ocean stores carbon. At the ocean’s surface, phytoplankton absorb carbon dioxide from the atmosphere and convert the gas into other forms of carbon, including calcium carbonate — the same stuff that’s found in shells and corals. When they die, bits of phytoplankton drift down through the ocean as marine snow, carrying the carbon with them. If the particles make it to the deep ocean, the carbon they carry can be buried and locked away for hundreds to thousands of years.
But the new study suggests bacteria may be working against the ocean’s ability to sequester carbon. By eroding the particles’ calcium carbonate, bacteria can significantly slow the sinking of marine snow. The more they linger, the more likely the particles are to be respired quickly, releasing carbon dioxide into the shallow ocean, and possibly back into the atmosphere.
“What we’ve shown is that carbon may not sink as deep or as fast as one may expect,” says study co-author Andrew Babbin, an associate professor in the Department of Earth, Atmospheric and Planetary Sciences and a mission director at the Climate Project at MIT. “As humanity tries to design our way out of the problem of having so much CO2 in the atmosphere, we have to take into account these natural microbial mechanisms and feedbacks.”
The study’s primary author is Benedict Borer, a former MIT postdoc who is now an assistant professor of marine and coastal sciences at the Rutgers School of Environmental and Biological Sciences; co-authors include Adam Subhas and Matthew Hayden at the Woods Hole Oceanographic Institution and Ryan Woosley, a principal research scientist at MIT’s Center for Sustainability Science and Strategy.
Losing weight
Marine snow acts as the ocean’s main “biological pump,” the process by which the ocean pulls carbon from the surface down into the deep ocean. Scientists estimate that marine snow is responsible for drawing down billions of tons of carbon each year. Marine snow’s ability to sink comes mainly from minerals such as calcium carbonate embedded within the particles. The mineral is a dense ballast that weighs down the particle. The more calcium carbonate a particle has, the faster it sinks.
Scientists had assumed based on thermodynamics that calcium carbonate should not dissolve within the ocean’s upper layers, given the general temperature and pH conditions in the surface ocean. Any calcium carbonate that is bound up in marine snow should then safely sink to depths greater than 1,000 meters without dissolving along the way.
But oceanographers have long observed signs of dissolved calcium carbonate in the upper layers of the ocean, suggesting that something other than the ocean’s macroscale conditions was dissolving the mineral and slowing down the ocean’s biological pump.
And indeed, the MIT team has found that what is dissolving calcium carbonate in shallow waters is a microscale process that occurs within the immediate environment of an individual particle.
“Most oceanographers think about the macroscale, and in this instance what’s happening in microscopic particles is what is actually controlling bulk seawater chemistry,” Borer says. “Consequences abound for the ocean’s carbon dioxide sequestration capacity.”
A sinking sweetspot
In their new study, the researchers set up an experiment to simulate a sinking particle of marine snow and its interactions at the microscale. The team synthesized particles similar to marine snow that they made from varying concentrations of calcium carbonate and bacteria — organisms that are often found feasting on the particles in the ocean.
“The ocean is a fairly dilute medium with respect to organic matter,” Babbin says. “So organisms like bacteria have to search for food. And particles of marine snow are like cheeseburgers for bacteria.”
The team designed a small microfluidic chip to contain the particles, and flowed seawater through the chip at various rates to simulate different sinking speeds in the ocean. Their experiments revealed that whenever particles hosted any bacteria, they also rapidly lost some calcium carbonate, which dissolved into the surrounding seawater. As bacteria feed on the particles’ organic material, the microbes excrete acidic waste products that act to dissolve the particles’ inorganic, ballasting calcium carbonate.
The researchers also found that the amount of calcium carbonate that dissolves depends on how fast the particles sink. They flowed seawater around the particles at slow, intermediate, and fast speeds and found that both slow and fast sinking limit the amount of calcium carbonate that’s dissolved. With slow sinking, particles don’t receive as much oxygen from their surroundings, which essentially suffocates any hitchhiking bacteria. When particles sink quickly, bacteria may be sufficiently oxygenated, but any waste products that they produce can be easily flushed away before they can dissolve the particles’ calcium carbonate.
At intermediate speeds, there is a sweet spot: Bacteria are sufficiently oxygenated and can also build up enough waste, enabling the microbes to efficiently dissolve calcium carbonate.
Overall, the work shows that bacteria can have a significant effect on marine snow’s ability to sink and sequester carbon in the deep ocean. Bacteria can be found everywhere, and particularly in the shallower ocean regions. Even if macroscale conditions in these upper layers should not dissolve calcium carbonate, the study finds bacteria working at the microscale most likely do.
The findings could explain oceanographers’ observations of dissolved calcium carbonate in shallow ocean regions. They also illustrate that bacteria and other microbes may be working against the ocean’s natural ability to sequester carbon, by dissolving marine snow’s ballast and slowing its descent into the deep ocean. As humans consider climate solutions that involve enhancing the ocean’s biological pump, the researchers emphasize that bacteria’s role must be taken into account.
“Insights from this work are vital to predict how ecosystems will respond to marine carbon dioxide removal attempts, and overall how the oceans will change in response to future climate scenarios,” says Benedict Borer, who carried out the study’s experiments as a postdoc in MIT’s Department of Earth, Atmospheric and Planetary Sciences.
This work was supported, in part, by the Simons Foundation, the National Science Foundation, and the Climate Project at MIT.
White water of Kueishantao: Sulfur-containing hydrothermal fluids make the sea appear milky. Photo: MARUM – Center for Marine Environmental Sciences, University of Bremen; S. Bühring
Credit: White water of Kueishantao: Sulfur-containing hydrothermal fluids make the sea appear milky. Photo: MARUM – Center for Marine Environmental Sciences, University of Bremen; S. Bühring
Hydrothermal vents on the ocean floor release carbon dioxide that is many million years old. This old carbon originates from the Earth's interior, and it escapes either directly from the Earth's mantle or is produced when rocks that contain limestone or other carbonate minerals are heated or transformed in geologically active zones. These processes primarily occur where tectonic plates converge or diverge, and hot, rising material heats the sea floor. However, the fate of this carbon after it enters the sea has so far been largely unclear.
The Path of Hydrothermal Carbon
In a new study, researchers from MARUM – Center for Marine Environmental Sciences at the University of Bremen, and the National Sun Yat-Sen University, and the Exploration and Development Research institutes in Taiwan investigated a hydrothermal vent system at a depth of about ten meters off the coast of Kueishantao island in Taiwan. They tracked the path of this carbon in the surrounding sea and its uptake by microorganisms and other living things.
“We were able to show that millennia-old carbon from hydrothermal vents can power life in these extreme systems,” says Joely Maak, the study's lead author and researcher at MARUM.
The team used a special isotope in this study: radiocarbon (14C). This radioactive isotope is created in the Earth's upper atmosphere by cosmic radiation. The resulting 14C then enters the natural carbon cycle as carbon dioxide and is absorbed by plants, microorganisms, and, ultimately, animals. As long as an organism is alive, the proportion of 14C remains almost constant. However, once an organism dies and is no longer exchanging carbon with the atmosphere, the 14C gradually decays, and after several tens of thousands of years, it becomes virtually undetectable. Carbon from the Earth's interior is extremely old and has been separated from the atmosphere for a very long time, and therefore no longer contains 14C.
When this carbon enters the ocean through hydrothermal emissions, its signature differs significantly from that of modern atmospheric carbon. In fact, it is “radiocarbon-dead.” For the current study, the researchers are using this exact difference to trace the path of hydrothermal carbon through the marine ecosystem.
“Our approach was to use the old, 14C-free carbon from hydrothermal sources as a natural marker. We were surprised by how clearly the fingerprint could be traced through the entire food web, even into higher organisms,” says Dr. Hendrik Grotheer, geochemist at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research.
The team’s previous work has shown that specialized bacteria at these vents have a special “secret weapon,” namely, the reductive tricarboxylic acid (rTCA) cycle. This energy-efficient metabolic pathway enables microorganisms to incorporate carbon dioxide into their biomass even under extreme conditions. Building on these results, the new study now shows that the carbon from the hydrothermal vents actually accounts for up to 30 percent of the bacteria’s biomass in the hydrothermal system and is passed on in the local food web. Crabs living directly at the hydrothermal vents also contain this ancient carbon because they feed on the microbes living in the hydrothermal system. Consequently, their body tissue appears measurably older than it actually is.
Project manager Dr. Enno Schefuß of MARUM explains, “Only by combining the study of specific bacterial markers (so-called ‘fatty acids’) and radiocarbon analyses of these, we could obtain these new findings – a combination of state-of-the-art technology and meticulous laboratory work.”
Photosynthesis Also Uses Hydrothermal Carbon
Using additional hydrogen isotopes, the researchers were also able to determine whether the carbon was assimilated via chemosynthesis or by photosynthesis. Unlike photosynthesis, in which plants use sunlight to generate energy, chemosynthesis works completely without sunlight. In this process, microorganisms use reduced chemicals from the Earth's interior to generate energy. Until now, it had never specifically been demonstrated that photosynthesis plays a role in the uptake of old carbon from hydrothermal systems. The current study was able to show, by using several isotope systems, that hydrothermal carbon is assimilated by photosynthesizing organisms further away from the vent.
“At the same time, the results show that despite the various assimilation mechanisms, only a small proportion of the total carbon released actually remains in the local ecosystem. The majority of the CO2 escapes direct biological use and is distributed into the ocean with the surrounding water masses or escapes into the atmosphere,” adds first author Joely Maak. “On the other hand, the release of components not covered in this study, such as dissolved organic carbon and micronutrients from marine hydrothermal vents, may influence the biogeochemistry of the oceans. This will be investigated in more detail in several projects in the second phase of the Cluster of Excellence, which has just been launched," notes co-project leader Dr. Marcus Elvert from MARUM.
International Collaboration for Successful Exploration of Hidden Ocean Processes
The study emphasizes the importance of long-term international cooperation between Taiwan and Bremen, demonstrating how modern isotope methods can help to reveal previously hidden biogeochemical processes in the sea. “This study shows the importance of long-term international cooperation for understanding complex oceanic processes,” says Dr. Solveig Bühring. “My Taiwanese project partner, Prof. Yu-Shih Lin, and I led the fieldwork. This collaboration began with a jointly funded DAAD scholarship and has evolved into an extremely successful research partnership. I very much hope that we can continue this close exchange in the future and jointly gain further insights into the role of hydrothermal systems in the global carbon cycle.”
The study receives additional funding from and is an integral part of research in the Cluster of Excellence “The Ocean Floor – Earth's Uncharted Interface.” The cluster aims to better understand ocean floor ecosystems under changing environmental conditions, as well as central material cycles, such as the carbon cycle.
MARUM produces fundamental scientific knowledge about the role of the ocean and the seafloor in the total Earth system. The dynamics of the oceans and the seabed significantly impact the entire Earth system through the interaction of geological, physical, biological, and chemical processes. These influence both the climate and the global carbon cycle, resulting in the creation of unique biological systems. MARUM is committed to fundamental and unbiased research in the interests of society, the marine environment, and in accordance with the sustainability goals of the United Nations. It publishes its quality-assured scientific data to make it publicly available. MARUM informs the public about new discoveries in the marine environment and provides practical knowledge through its dialogue with society. MARUM cooperation with companies and industrial partners is carried out in accordance with its goal of protecting the marine environment.
A research group co-led by the University of Illinois Urbana-Champaign predicts that a surprisingly adaptable species of marine archaea will play an important role in reshaping biodiversity in the planet’s oceans as the climate changes.
CHAMPAIGN, Ill. — Deep-sea waters are warming due to heat waves and climate change, and it could spell trouble for the oceans’ delicate chemical and biological balance. A new study, however, demonstrates that the microbe Nitrosopumilus maritimus may already be adapting well to warmer, nutrient-poor waters. Researchers predict that these surprisingly adaptable iron-dependent ammonia-oxidizing archaea will play an important role in reshaping ocean-nutrient distribution in a changing climate.
The study’s findings are published in the Proceedings of the National Academy of Sciences.
Nitrosopumilus maritimus and its kin account for approximately 30% of the marine microbial plankton population, and many researchers agree that the oceans depend on these microbes to drive the chemical reactions that support marine life. The ammonia-oxidizing activity of archaea makes them key players in the oceans’ nutrient cycling. By altering the forms of nitrogen available in seawater, they control the growth of microbial plankton — the base of the marine food chain — and help sustain marine biodiversity.
“Ocean-warming effects may extend to depths of 1,000 meters or more,” said University of Illinois Urbana-Champaign microbiology professor Wei Qin. “We used to think that deeper waters were mostly insulated from surface warming, but now it is becoming clear that deep-sea warming can change how these abundant archaea use iron — a metal they depend on heavily — potentially affecting trace metal availability in the deep ocean.”
The study, led by Qin and University of Southern California global change biology professor David Hutchins, used controlled, trace-metal-clean experiments to expose a pure culture of Nitrosopumilus maritimus to a variety of temperatures and iron concentrations. They observed that increasing the temperature under iron-limited conditions reduced the microbes’ iron requirements and increased physiological iron-use efficiency, demonstrating that the microbes acclimate well to the stress of higher temperatures and decreased iron availability.
“We coupled these findings with global ocean biogeochemical modeling by Alessandro Tagliabue from the University of Liverpool,” Qin said. “The results suggest that deep-ocean archaeal communities may maintain or even enhance their role in nitrogen cycling and primary production support across vast iron-limited regions in a warming climate.”
This summer, Qin and Hutchins will serve as co-chief scientists aboard the research vessel Sikuliaq for a research expedition from Seattle to the Gulf of Alaska and then down to the subtropical gyre, stopping in Honolulu, Hawaii. Joining Qin will be 20 other researchers whose aim will be to validate the new experimental findings in a real-world setting and focus on the interactive effects of temperature and metal limitation on natural archaeal populations.
The National Science Foundation, Simons Foundation, National Natural Science Foundation of China, University of Illinois Urbana-Champaign and the University of Oklahoma supported this research.
The paper “Ocean warming enhances iron use efficiencies of marine ammonia-oxidizing archaea” is available online. DOI: 10.1073/pnas.2531032123
This summer, Qin will serve as co-chief scientist aboard the research vesselSikuliaq. He and 20 other researchers will work to validate the study’s experimental findings in a real-world setting.
Herring from different parts of the Baltic Sea belong to distinct populations genetically adapted to local differences in salinity and temperature. However, these populations can also mix with each other, according to a new study by researchers from Uppsala University, Stockholm University and the Swedish University of Agricultural Sciences. These results have important implications for the management of the Baltic herring. The study is published in the Proceedings of the National Academy of Sciences.
Spring- and autumn-spawning herring in the Baltic Sea as well as in the Atlantic Ocean are genetically distinct. This is well known. “Despite their striking genetic differences, we were able to identify hybrids between the spring- and autumn-spawning populations, thanks to the very large sample size in our present study,” says Leif Andersson, Professor at the Department of Medical Biochemistry and Microbiology at Uppsala University, who led the study together with Professor Linda Laikre, Department of Zoology, Stockholm University.
In other words, there are herring that, when they end up in a population spawning at the ‘wrong’ time of year, have been able to adapt their behaviour and spawn at the same time as the other herring in the surrounding population.
“Our interpretation is that genetics sets an optimal window for spawning, primarily spring or autumn, but water temperature and nutritional status influence when spawning happens. This would imply that there is a communication within the school, possibly due to hormones that set the spawning time for the school”, explains Leif Andersson.
The Baltic herring are not only split into spring- and autumn-spawning populations. Thanks to this new study, the researchers discovered that the spring-spawning herring, which are widely distributed in the Baltic Sea, are further subdivided into a Northern, Central and Southern cluster. There are also additional groupings within the major clusters of spring-spawning herring. Linda Laikre points to a striking example from the Stockholm archipelago, the so called ‘wild rose herring’: “We noticed that the genetic constitution of this population was more extreme than the populations from the Southern cluster. The explanation was that these herring was spawning in mid-July when the water is much warmer than in the spring. A population like this with adaptation to spawning in warmer waters may harbour gene variants of critical importance for future adaptation to a warming sea”, she says.
The locals call the fish ‘wild rose herring’ because it spawns when the wild roses are in bloom.
The researchers believe their results have very important implications for the management of Baltic herring.
“Our findings showing that herring are subdivided into different clusters and groups are of great importance for management, since herring along Sweden’s east coast are currently managed as two large populations, one in the Baltic Proper and one in the Gulf of Bothnia. The current management does not correspond to the genetic groupings we see, says Lovisa Wennerström from the Swedish University of Agricultural Sciences.
“We would like to see a much more restrictive industrial fishing for fish meal production to reduce the risk that important local populations and the genetic diversity they harbour get lost. Further, our results will constitute a basis for the Swedish Agency for Marine and Water Management’s monitoring program that aims at tracking genetic changes over time in key species such as herring”, says Linda Laikre, Stockholm University.
Background facts – how the study was made Herring has a key role in the Baltic Sea ecosystem. They are the most abundant fish in the Baltic Sea acting as a link between plankton production and other organisms, like predatory fish, sea birds, sea mammals, and humans. The Baltic Sea is home to many distinct local herring populations genetically adapted to when and where spawning takes place. These populations also migrate between spawning and feeding grounds. The present study concerns an extensive characterization of the genetic diversity of Baltic herring by analysing more than 4,500 fish collected during spawning at 150 different locations distributed along the Swedish east coast.
Geographic distribution of population samples included in the genetic study. Green dots mark samples of autumn-spawning herring while all remaining colours represent different clusters of spring-spawning herring. The size of dots reflects the sample size as indicated. STH36A, KAL05 and KAL06 are three outlier populations that genetically cluster with the Southern populations despite their geographic location.
Contrary to the popular belief that the species is mostly solitary, infant narrow-ridged finless porpoises in Ise Bay were observed to approach, parallel swim with, and even touch adults other than their mothers.
Credit: Assistant Professor Genfu Yagi from Mie University, Japan
A well-established fact of infancy in mammals is that the mother is the primary adult with whom an infant will interact. This holds true across species, from the tiniest shrew to the most massive blue whale. However, infants of many species also interact with adults who are not their parents. This is called “allomaternal behavior” and it is commonly seen in social mammals that move in groups or herds. One of the allomaternal behavior is when young females without infants of their own handle and care for infants. Young females learn to raise infants, while the mother can forage for food more effectively.
Allomaternal behavior has been observed in many species of odontocetes—toothed whales, dolphins, and porpoises. However, zoologists have long believed that the narrow-ridged finless porpoise, Neophocaena asiaeorientalis, is a solitary species with no allomaternal behaviors. Finless porpoises rarely form pods, and their primary social structure is mother-infant pairs or adults cooperating to swim or feed.
A new study led by Associate Professor Mai Sakai of Kindai University has cast shadows of doubt on this long-held belief regarding finless porpoises. Dr. Sakai’s team, which included Soeko Noro from the Marine Mammal Research Laboratory, Kindai University, and Assistant Professor Genfu Yagi from Mie University, observed porpoises in Ise Bay, Japan, and found examples of possible allomaternal behavior. Their findings were published on October 21, 2025, in the journal Mammal Study.
Earlier research has hinted at some kind of social interaction between finless porpoises. Dr. Sakai remarked that in a previous study, her team had observed synchronized diving by an adult and juvenile male pair. Dr. Tomoyoshi Terada, who is the member of the present study team, reported, “In Ise Bay, individuals within 15 m of one another engaged in social behaviors at a high frequency, suggesting that finless porpoises have a social structure where solitary and gregarious behaviors coexist (Terada et al. 2024).”
Using consumer-grade drones, Dr. Sakai’s team observed finless porpoises in Ise Bay over a period of 34 days between February and July 2023. They looked for infant porpoises interacting with more than one adult during an observation flight, as that was definite proof of interaction with an adult other than their mother.
The team found interactions between four “infant + two adult” sets. In most cases, the infant would approach or separate from an adult and spend periods parallel swimming (PS). The team found that in all cases, infants were on the lateral side of adults during PS. This position might reduce water resistance and allow the infant to keep pace with the adult with reduced swimming effort. Infants may approach adults for protection and reduced swimming effort.
Adults approached infants in two instances. These may be examples of young females without offspring learning to interact with infants before giving birth to their own. However, the sex of the adults was not confirmed. In all cases but one, the time spent in PS with any one adult was less than 40%. This is significantly lower than the mother-infant PS time seen in other dolphins and porpoises. Dr. Sakai highlighted, “The findings suggest that neonatal finless porpoises swim alone for extended periods compared with neonates of other odontocetes. The behavioral tendencies observed in neonates of narrow-ridged finless porpoises may be indicative of a comparatively weaker mother-calf bond when compared with other delphinid species.”
Put together, these observations reinforce the idea that N. asiaeorientalis may not be a mostly solitary species as was previously assumed. These findings are important for the conservation of finless porpoises. Orphaned or abandoned infants can be rehabilitated through allomaternal interactions with non-related adults. Lastly, this study proves the utility of relatively inexpensive and simple drones in wildlife monitoring studies.
“Allomaternal behaviors may be beneficial for neonates in the development of social relationships and/or as a supplement to the weaker mother-calf relationships that are typical of this vulnerable developmental stage,” remarked Dr. Sakai, adding, “To understand allomaternal behavior in species with simple social structures, future studies need to evaluate the cost-benefit relationship for mothers, calves, and non-maternal adults.”
About Kindai University Kindai University was established in 1949 after the merger of Osaka Technical College (founded in 1925) and Osaka Science and Engineering University (founded in 1943). Over the past several decades, the university has transformed into a comprehensive educational organization with an ever-growing reputation. Kindai University has over 2,200 full-time faculty members, 6 campuses, and 18 research centers. As an academic institution offering a broad range of programs from across disciplines, Kindai University strives to impart practical education while nurturing intellectual and emotional capabilities. The university’s academic programs are fully accredited by Japan’s Ministry of Education, Culture, Sports, Science and Technology as well as by the National Institution for Academic Degrees and University Evaluation.
About Associate Professor Mai Sakai from Kindai University Dr. Mai Sakai is an Associate Professor in the Marine Mammal Research Laboratory, Department of Fisheries, Graduate School of Agriculture, Kindai University. Dr. Sakai completed her doctorate from Tokyo University of Technology in 2006. Her research focuses on the behavior of dolphins and other toothed whales. Dr. Sakai has authored 19 academic publications and has received awards from the Mammal Society of Japan. In addition to her research work, Dr. Sakai serves on the boards of several prestigious associations related to the study and conservation of wild mammals.
Funding information This research was partially supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI (Grant Number: 23K11793).
Infant narrow-ridged finless porpoises in Ise Bay primarily interact with the likely mother, but the mother-infant bond in this species appears to be weaker than in other dolphins and porpoises.
Credit
Assistant Professor Genfu Yagi from Mie University, Japan
Observations of Changing Partners During Parallel Swimming Behavior Between Neonatal and Adult Finless Porpoises (Neophocaena asiaeorientalis) in Ise Bay, Japan
Drones capture rare harbour porpoise mating behaviour off Shetland
Drones flying above the waters of Shetland have captured rare footage of harbour porpoises gathering in unusually large groups and engaging in mating behaviour.
Drones flying above the waters of Shetland have captured rare footage of harbour porpoises gathering in unusually large groups and engaging in mating behaviour.
The footage, gathered between 2019 and 2023, provides one of the most detailed records of harbour porpoise mating behaviour ever documented in UK waters.
They say understanding group sizes and mating behaviour could help manage and conserve harbour porpoises in the Important Marine Mammal Area of Shetland’s waters, and elsewhere.
Harbour porpoises are frequently spotted around Scotland and typically measure between 1.5 and 2 metres and weigh between 55 kg and 80kg.
Despite their abundance, their behaviour remains poorly understood because they are small, fast and spend much of their time underwater.
Research prompted by local sightings
Sophie Ariadne Francine Smith from UHI Shetland undertook the research as part of her PhD, and became a licensed drone pilot in the process.
A sighting by Karen Hall of NatureScot, Sophie’s PhD supervisor, helped kickstart investigations.
Sophie said: “Harbour porpoises are seen from land around Shetland all year round, but one sighting involved intense splashing at the surface. We realised it might be mating behaviour.
“It is incredibly difficult to film porpoises from boats or from land. They don’t spend much time at the water's surface, don’t follow a predictable line, like an orca, and they are incredibly fast.
“Drone technology means we can film them from above, which gives much more accurate accounts and a clearer interpretation of behaviour.”
Porpoise overtures caught on camera
The team analysed more than 79 minutes of usable footage from four coastal locations in the east and south of Shetland.
They recorded gatherings of up to 26 animals in a single bay, far larger than the small groups of two or three typically reported for the species.
Two types of sexual behaviour were observed. The first involved males rapidly approaching females in what researchers describe as copulation attempts, often ending with individual animals breaking the surface and creating the splashing seen from shore.
The second involved display behaviour, where males rolled to present their underside to a female.
Sophie said: “Harbour porpoises are fast and elusive. For much of this mating behaviour they only broke the surface for a few seconds - blink and you’d miss it, which is why using drones to capture footage has been such a boon.
“We can only fly the drone when Shetland’s weather allows; in an ideal world, we’d be able to observe the harbour porpoises all year round so that we can better understand why and when they gather in these larger groups, as well as a having a better understanding of harbour porpoise social behaviours.”
The harbour porpoises were filmed in four coastal bays: Gulberwick Bay, South Nesting Bay, Mousa Sound and Quendale Bay.
Dr Lauren McWhinnie from Heriot-Watt University, who co-supervised the research, said: “This work helps build a clearer picture of when and how porpoises use specific coastal areas.
“Although harbour porpoise populations in the North Sea are considered relatively stable, more detailed regional data and local observations, such as those gathered in Shetland, help us to better understand their potential exposure to human activities.
“This evidence allows us to plan more effectively and take proportionate action to reduce any impacts on them.”
Dr Rachel Shucksmith from UHI Shetland, co-supervisor said: “Shetland was identified as an Important Marine Mammal Area (IMMA) in 2024, based on vital local and community knowledge.
“This research forms part of a wider effort to understand where, when, and why whales, dolphins and porpoises use the Shetland coastline.
"Working closely with the local community, the project is advancing our understanding of cetacean movements and deploying innovative technology designed to operate within Shetland’s narrow weather windows.”
This PhD was additionally supervised by Professor Ben Wilson (SAMS) and Karen Hall (NatureScot), the wider project team included Dr Becky Giesler, Kate Allan, Dr Emily Hague, Dr Richard Shucksmith and Nick McCaffrey.
About harbour porpoises Harbour porpoises are the only porpoise species found in Scottish waters. They are widely distributed and commonly seen from shore around Shetland.
Important Marine Mammal Areas (IMMAs) are defined as discrete portions of habitat, important to marine mammal species, that have the potential to be delineated and managed for conservation. Shetland and Fair Isle were identified as an IMMA in 2024.
About the Shetland Islands Regional Marine Plan The Shetland Islands Regional Marine Plan sets out policies to guide sustainable use of Shetland’s marine environment and is supported by an evolving local evidence base, including research on marine mammals.
The RMIT team's 'Electronic Dolphin', a proof-of-concept minibot, collects kerosene oil from the surface of water, offering a safer and more targeted way to respond to spills in sensitive environments.
RMIT University engineers in Australia have built a remote-controlled minibot that hoovers up oil spills using an innovative filtering system inspired by sea urchins.
Oil spills are still a serious problem around the world. They can badly damage oceans and coasts, kill or injure sea animals and birds, and cost billions of dollars to clean up and repair the damage.
The team developed a minibot called the ‘Electronic Dolphin’ to address this global challenge, by collecting oil from the surface of water, offering a safer and more targeted way to respond to spills in sensitive environments.
The device, shaped like a dolphin and about the size of a sneaker, integrates a specially designed filter that repels water while instantly absorbing oil, allowing the robot to skim slicks and collect oil with high efficiency.
Lead researcher Dr Ataur Rahman, from RMIT’s School of Engineering, said the proof-of-concept minibot showed how small, adaptable platforms could support clean-up efforts without exposing responders to hazardous conditions.
“Oil spills can take a huge environmental and economic toll. We wanted to create a system that can be deployed quickly, steered accurately and used in areas that are too risky for people to access,” he said.
“We have a long-term vision of creating dolphin‑sized robots that can vacuum oil, return to base to empty their tanks, recharge, then redeploy automatically – repeating the cycle until the job’s done.”
The experimental minibot runs for about 15 minutes on its current battery, but the final version would scale up depending on pump size and oil‑storage capacity.
“Unlike past oil cleanup materials that often use harsh, hazardous chemicals and work only as fixed filters involving manual operation, our new technology is made using an eco-friendly coating for filter we developed.”
The minibot houses the coated filter at its front, with a small pump drawing oil through the filter into an onboard collection chamber. In controlled tests, it recovered oil at about 2 millilitres per minute with more than 95 per cent purity, maintaining performance without the filter becoming waterlogged.
The filter uses a special coating that grows tiny, sea urchin-like spikes you can only see under an electron microscope. These little spikes hold pockets of air that make water roll straight off, while oil sticks to the surface. That means the material can pick up oil without soaking up water, and because it is light and can be reused many times, it Is practical for real cleanup work.
PhD researcher Surya Kanta Ghadei, who led much of the materials development, said the project was driven by both technical ambition and personal experience.
“Growing up in India, I saw the impact oil spills can have on marine life, especially turtles,” he said.
“That stayed with me. When I began my PhD, I wanted to create something that could help responders act faster and keep wildlife out of danger.”
The team is now exploring how to scale the technology by increasing the filter area across the robot’s surface, which would require a higher capacity pump. Field testing and long-term durability assessments are planned as the next stage of development.
Rahman said the researchers were keen to work with industry or innovation partners to refine the design for specific applications and assess pathways for wider deployment.
Organisations interested in developing new products or collaborating further should contact RMIT at research.partnerships@rmit.edu.au
The research builds on extensive materials and environmental engineering work conducted in the broader group led by Distinguished Professor Madhu Bhaskaran and Professor Sharath Sriram, whose teams have developed a range of technologies and platforms for other applications, and Professor Ramasamy Sakthivel from India’s Academy of Scientific and Innovative Research.
Footage: robot skimming oil in a clear tank, researchers in‑lab, macro shots of water beading and oil uptake – Easy-preview MP4 version: Hightail - fTw6TEFzsD
Stills: hero action shots and clean portraits
Free use for news/editorial with credit: Peter Clarke, RMIT University
Interviews – Dr Ataur Rahman (Pronunciation “Ata-or Rar-man”)
The RMIT‑designed Electronic Dolphin minibot, fitted with a front‑mounted filter and pump system for skimming oil from water surfaces.
A researcher demonstrates the water‑repellent properties of the coated filter, showing water beading on the surface.
A researcher applies oil to the coated filter material to demonstrate its rapid absorption while remaining water repellent.
A macro view of the porous, sea‑urchin‑inspired filter material developed for the Electronic Dolphin minibot.
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