The discovery emerged from a research effort led by scientists at Sun Yat-sen University (SYSU) and the Southern Marine Science and Engineering Guangdong Laboratory in Zhuhai. Using modern deep-sea diving vehicles, including human-occupied vehicles and remotely operated vehicles, the team filmed deep-sea organisms in their natural habitat across three areas of the northern South China Sea. Among the animals they documented were three species of peristediid fishes, commonly called armored searobins: Scalicus engyceros, Paraheminodus murrayi and Peristedion liorhynchus. The footage captured not just still portraits of these animals but extended records of their benthic behaviors, allowing the researchers to describe, for the first time, how the fishes move and forage while alive on the seafloor.

Han Tian, the paper’s primary author and a doctoral researcher in the School of Marine Sciences at Sun Yat-sen University, described the finding as a paradigm-shifting revelation. S. engyceros belongs to a group of fishes characterized by highly specialized free pectoral-fin rays, finger-like appendages that extend from the pectoral fins and make contact with the seafloor. Scientists have long suspected that searobins use these rays to walk, but until now the behavior had not been directly confirmed with in situ footage. The species has even attracted popular attention for its appearance, which combines features of fish and shrimp so strikingly that U.S. local media have dubbed it a “fish-prawn hybrid.”

The walking itself proved more versatile than anyone anticipated. Searobins were first described by the zoologist Albert Günther in 1872, yet in the more than 150 years since, no one had predicted that these fishes could walk both sideways and backward. Locomotion in reverse has never been observed in other fishes, making the armored searobin’s gait a genuine first for the field. The finding illustrates how much basic behavioral information remains locked in the deep sea, inaccessible until organisms can be observed alive in their own environment rather than studied from preserved specimens hauled up in trawls.

The searobin’s body plan reveals a suite of adaptations that appear tailored to life on soft seafloor sediment. Beyond the walking rays, the fish sports outward-extending barbels that Tian compared to a farmer’s rake. While the structure may look awkward for getting around, it serves a foraging function: the barbels allow the searobin to sense and probe potential prey buried in the seafloor sediment, and even to dig into the surface sediment itself in search of food. Meanwhile, the animal’s main pectoral fins have evolved into flat, round plates, which appear to improve balance both during walking and while swimming. When threatened, the fish can deploy its shrimp-like fin rays and tail to make explosive, jerky leaps reminiscent of a startled shrimp, a rapid escape behavior that complements its slower, deliberate walking.

The filmed observations also yielded unexpected insights into the searobin’s sensory world. The fish’s large eyes could not resolve the approaching vehicle itself, indicating that its visual acuity is limited at close range. Yet when the vehicle’s light beam swept near, the animal rolled its eyes toward the light. This response suggests that the searobin’s eyes have retained some sensitivity to light, which, according to the researchers, may reflect a light history during the species’ life cycles. Many deep-sea fishes begin life in shallower, sunlit waters before descending to the abyss, and the eye-rolling behavior hints at vestiges of that developmental or evolutionary past, though the team presents the observation as a suggestion rather than a settled conclusion.

The fact that three different armored searobin species were observed at different locations in the South China Sea raised another question for the team. The distribution of these similar fishes across separate sites suggests, in the researchers’ view, the hypothesis that local specialization forces may be at work, shaping each population’s adaptations to its particular patch of seafloor. Testing that hypothesis will require further observation and comparison, but it points toward a research program that treats deep-sea fishes not as static curiosities but as dynamically evolving lineages responding to the distinct conditions of their habitats.

The methodological significance of the study lies in its approach. Classified as an observational study, the work rests on in situ filming rather than laboratory experimentation or dissection. Advances in deep-sea vehicle technology, including human-occupied vehicles and remotely operated vehicles, have transformed what is possible for deep-sea biology. Where earlier generations of scientists had to infer behavior from the anatomy of dead specimens, today’s researchers can watch living animals interacting with their environment. Tian emphasized that modern diving vehicles allow not only the discovery of new species but also add a new in situ, functional dimension to the study of species that were previously known only from preserved morphology. Observing deep-sea animals alive in their surroundings, the team argues, provides direct insight into adaptation and evolution that museum specimens alone cannot supply.

The broader context makes the finding all the more compelling. The deep ocean is one of the most inhospitable places on Earth, characterized by crushing pressure, perpetual darkness and scarce food, yet many species have managed to survive there, often evolving specialized body structures and behaviors in the process. Armored searobins represent one such evolutionary experiment: a lineage that has repurposed its pectoral fins into a hybrid toolkit serving walking, balance, foraging and escape. The combination of rake-like barbels for probing sediment, plate-like fins for stability, free rays for stepping across the bottom and shrimp-style leaps for emergency escapes suggests a tightly integrated adaptive complex rather than a single isolated trait.

Looking forward, the team intends to push beyond this initial documentation. Tian said the researchers aim to explore the co-evolution of the fish’s unique rake-shaped appendages, its walking locomotion and its deep-sea foraging strategies, with the goal of establishing a new framework for understanding benthic fish adaptive evolution. Such a framework could reshape scientific perceptions of deep-sea biodiversity and illuminate how extreme marine environments drive the emergence of biological structures and behaviors seen nowhere else in the world’s aquatic ecosystems. In the team’s view, these walking fish harbor far more novel behavioral and evolutionary adaptations than previously assumed.

The research was a collaborative effort. Alongside Tian, contributors included Wei Xie, Mingting Li and Kedong Yin, affiliated with the School of Marine Sciences and the Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering at Sun Yat-sen University, and with the Southern Marine Science and Engineering Guangdong Laboratory in Zhuhai, China. The paper, titled “Walking Fish,” carries the DOI 10.34133/olar.0172, and the authors reported no conflicts of interest. As with any observational study, the findings describe what the cameras captured in a limited number of encounters and locations; the mechanisms underlying the backward gait, the developmental basis of the fish’s light sensitivity and the role of local specialization remain open questions for future work. Still, the footage marks a milestone: after a century and a half in the scientific record, the armored searobin has finally been seen doing what its anatomy always hinted at, walking, in every direction, across the dark floor of the South China Sea.

Corals, often thought of as mere marine organisms, are extraordinarily valuable recorders of environmental conditions. Their calcium carbonate skeletons grow incrementally, layer by layer, akin to the rings of a tree. Each layer encapsulates chemical and physical signatures of surrounding seawater, offering a window into historical ocean temperatures, salinity, and even sea level fluctuations. In this study, by meticulously analyzing samples from various coral species distributed across the Indian Ocean rim, the researchers reconstructed a detailed chronology of sea-level changes and climate shifts spanning the past century.

One of the striking revelations from the data is the marked acceleration in sea-level rise commencing in the latter half of the 20th century. While sea-level rise has been ongoing since the last glacial maximum some 20,000 years ago, the novel coral records underscore a sharp uptick during the period from around 1950 onwards. This acceleration correlates strongly with increases in global temperature and enhanced glacial melt rates, reconfirming the profound influence of industrial-era greenhouse gas emissions on the cryosphere and ocean dynamics.

The team employed geochemical proxies, particularly the ratios of strontium to calcium (Sr/Ca) and stable oxygen isotopes (δ18O), embedded within the coral skeletons to infer past sea surface temperatures and salinity. These parameters are crucial because they influence seawater density and circulation patterns, factors that ultimately affect regional sea-level heights. The observed patterns reflect a complex interplay of oceanographic phenomena including the Indian Ocean Dipole and the influence of the El Niño Southern Oscillation, which modulate monsoonal strength and precipitation regimes over the area.

Beyond reconstructing physical changes, the coral chronologies provide unprecedented insights into extreme climate variability events. The researchers detected distinct signatures of anomalous warming and cooling episodes, droughts, and cyclonic activity that mirror historical meteorological records. Such fine-scale resolution offers valuable information on the frequency, intensity, and duration of past climate extremes, which are particularly relevant for modeling future climatic scenarios under continued greenhouse warming.

The importance of this research extends beyond its academic novelty; coastal populations around the Indian Ocean are among the most vulnerable to rising seas and climatic perturbations. Nations such as India, Indonesia, Madagascar, and parts of East Africa face mounting risks including coastal erosion, saltwater intrusion, and habitat loss. By providing a high-resolution historical baseline, the coral-derived data enhances predictive models essential for effective policy-making, coastal planning, and disaster preparedness.

A key technical challenge the study overcame was the calibration and validation of coral proxies against instrumental sea-level records. The team cross-referenced their coral-based reconstructions with tide gauge data and satellite altimetry, achieving robust congruence that validates coral growth rates as reliable indicators of relative sea-level changes. This methodological advance sets a benchmark for future paleoclimate reconstructions using biological archives.

Moreover, the spatial distribution of coral sampling sites allowed the researchers to capture regional heterogeneity in sea-level rise and climatic shifts. The data revealed that certain locales experienced amplified rates of change, likely influenced by regional ocean currents, tectonic activity, and local climatic feedbacks. Such nuanced understanding challenges the traditional notion of uniform sea-level rise, highlighting the necessity for localized adaptation strategies.

Notably, the research also sheds light on the potential feedback mechanisms linking coral reef health to climate change. Accelerated sea-level rise and thermal anomalies stress corals, leading to bleaching and reduced calcification rates. The historical record thus serves as a dual function: it chronicles past environmental conditions and signals biological thresholds that could inform conservation priorities under escalating climate threats.

Advanced analytical techniques, including laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and secondary ion mass spectrometry (SIMS), were instrumental in resolving fine-scale geochemical variations within coral skeletons. These innovations enable temporal resolutions down to seasonal or even monthly scales, capturing the dynamic environmental fluctuations that traditional sediment or ice core archives often miss.

The study’s interdisciplinary approach, combining marine biology, geochemistry, climatology, and oceanography, exemplifies the collaborative science necessary to unravel the complexities of Earth’s climate system. It underscores the indispensability of natural archives for extending observational records beyond the limited span of instrumental data, which typically cover only the past century or less.

Looking forward, the findings invite further exploration into how coral reef ecosystems themselves might evolve in tandem with ongoing sea-level rise and climatic variability. Understanding how corals have historically responded to changing environments can illuminate their resilience thresholds and the potential for natural adaptation versus the need for human intervention, such as assisted gene flow or habitat restoration efforts.

Finally, the study serves as a clarion call to the global community about the urgency of mitigating greenhouse gas emissions. The clear fingerprints of anthropogenic influence on regional sea-level dynamics, as recorded in coral archives, paint a sobering picture of accelerating environmental change. It compels scientists, policymakers, and the public to recognize the interconnected fates of marine ecosystems and human societies in the Anthropocene epoch.

In conclusion, this pioneering research not only advances our scientific understanding of historical sea-level rise and Indian Ocean climate variability but also provides actionable knowledge critical for addressing the grand challenges posed by climate change. Corals, silent sentinels of the sea, continue to tell the story of our planet’s shifting past and offer warnings and lessons essential for securing its future.

Subject of Research: Historical sea-level acceleration and climatic variability in the Indian Ocean as recorded by coral growth patterns.

Article Title: Coral growth records 20th Century sea-level acceleration and climatic variability in the Indian Ocean.

Article References: Kench, P.S., Morgan, K.M., Owen, S.D. et al. Coral growth records 20th Century sea-level acceleration and climatic variability in the Indian Ocean. Nat Commun 16, 5872 (2025). https://doi.org/10.1038/s41467-025-60972-2

Image Credits: AI Generated