The study, led by Erin Dillon and colleagues, examines reef shark communities that lived around Panama during the past 7,000 years. Panama provides a rare natural comparison because its Pacific and Caribbean coasts are geographically close but environmentally very different. The two regions share many shark species, yet their waters differ sharply in nutrient supply, primary productivity and historical human pressure. By comparing ancient sediments dating from approximately 7,000 to 3,000 years ago with sediments deposited during the past century, the researchers reconstructed both natural shark baselines and recent population changes. This approach helps solve a major problem in marine conservation: modern surveys often begin after decades or centuries of decline, making today’s depleted ecosystems appear normal. Fossil evidence can reveal the abundance that existed before those losses occurred.

The key evidence comes from dermal denticles, tiny tooth-like scales embedded in shark skin. Unlike the large teeth that are commonly associated with fossil sharks, denticles are produced across the entire body and differ in shape according to a shark’s body form, swimming style and habitat. Fast-swimming pelagic sharks, for example, possess denticle characteristics associated with reducing drag, while bottom-associated species may have scales adapted to a different hydrodynamic environment. When sharks die, their denticles can become concentrated in coral reef sediments, where they may remain preserved for thousands of years. The researchers extracted and identified these microscopic remains, using their abundance and morphology as clues to the composition and size of ancient shark communities. Because the number of denticles deposited in reef sediments closely tracks the number of sharks using those habitats, the fossils function as a biological archive of past abundance.

The ancient record revealed a dramatic ecological contrast. Before intensive commercial fishing, Pacific reefs in Panama supported approximately 20 times more sharks than Caribbean reefs. This difference existed thousands of years ago, when modern fishing fleets, industrial gear and global seafood markets were absent. The result indicates that productivity, rather than human pressure alone, played a decisive role in determining how many sharks each reef system could sustain. The Pacific coast of Panama experiences strong seasonal upwelling, a process in which winds and ocean circulation bring cold, nutrient-rich water toward the surface. These nutrients stimulate phytoplankton growth, supporting a larger food web that can ultimately provide more energy for predators such as sharks. The Caribbean coast lacks an equivalent level of seasonal nutrient enrichment and is therefore naturally less productive.

The study also shows that the ecological gap between the two regions has become far wider in the modern era. Since the period represented by the ancient sediments, Caribbean shark populations have declined by roughly 75 percent, with particularly severe losses among fast-swimming pelagic species. By contrast, shark populations on the Pacific coast have remained comparatively stable, even though Pacific sharks experienced greater historical fishing pressure. The researchers estimate that modern Pacific reefs now support about 100 times more sharks than comparable Caribbean reefs. That ratio is not simply a measure of different fishing histories. It reflects the combination of a naturally larger Pacific baseline and a much steeper Caribbean decline. The findings suggest that the same level of human exploitation can produce very different outcomes depending on the productivity and resilience of the ecosystem being exploited.

The apparent resilience of Pacific shark communities may be linked to the greater energy flowing through their food webs. In productive waters, prey populations can be larger and replenish more rapidly, potentially allowing predators to withstand some level of removal without suffering immediate collapse. This does not mean that Pacific sharks are protected from overfishing or that their populations are secure. Rather, it suggests that ecological conditions may give them a greater capacity to absorb disturbance or recover after declines. In less productive Caribbean waters, even moderate losses may represent a larger fraction of the available predator population and may be followed by slower recovery. The distinction is important because conservation models that ignore regional productivity could overestimate the number of sharks an ecosystem can support or misinterpret a naturally low baseline as evidence of severe human-driven depletion.

Fossil denticles also provide information that conventional fishery records cannot. Written catch records and underwater surveys generally cover only a small portion of the time during which humans have affected marine ecosystems. In many coastal regions, fishing pressure began centuries ago, long before scientists started counting sharks. As a result, historical surveys may already describe populations that have been substantially reduced. Sedimentary archives extend the timeline backward and allow researchers to separate long-standing ecological differences from recent changes. The technique can also distinguish broad groups of sharks through the microscopic structure of their denticles, helping reveal whether particular ecological types, such as pelagic hunters, reef-associated species or bottom-dwelling forms, have changed disproportionately over time.

The results carry direct implications for conservation planning. Restoration targets are often based on comparisons with a nearby reef, a regional average or the best population measurements available from recent decades. But the study indicates that such comparisons can be misleading when ecosystems differ in nutrient supply and food-web structure. A target appropriate for a highly productive Pacific reef may be unrealistic for a less productive Caribbean reef, while a low target based on today’s Caribbean abundance could quietly institutionalize a severe level of depletion. Effective recovery plans should therefore combine fossil baselines with modern ecological data, including productivity, prey availability, habitat quality and fishing intensity. In practical terms, managers may need region-specific goals that recognize both the natural limits of an ecosystem and the extent to which its current shark population has fallen below its historical potential.

The research arrives as reef sharks face mounting pressure worldwide. Sharks are captured intentionally for their meat and fins, caught incidentally in other fisheries and affected by habitat degradation, climate change and the loss of prey. Their disappearance can alter reef food webs because sharks influence the behavior, distribution and abundance of other predators and prey. By showing that Pacific and Caribbean reefs began with profoundly different shark communities, Dillon and colleagues provide a more precise framework for understanding those losses. The fossil record does not offer a single universal number for what a healthy reef should contain. Instead, it reveals that shark conservation must be rooted in the history and productivity of each ecosystem. The microscopic scales left behind by ancient sharks may therefore become a powerful tool for setting realistic recovery goals—and for exposing just how much has been lost where modern reefs now appear deceptively quiet.

Subject of Research: Ancient and modern reef shark populations, ocean productivity, fossilized dermal denticles and conservation baselines.

Article Title: Fossil denticles reveal how ocean productivity shapes shark baselines and recovery potential

News Publication Date: 13-Aug-2026

Web References: https://doi.org/10.1126/science.aec2144

References: Dillon et al., “Fossil denticles reveal how ocean productivity shapes shark baselines and recovery potential,” Science.

Keywords: sharks, coral reefs, fossil denticles, dermal denticles, ocean productivity, Pacific Ocean, Caribbean Sea, Panama, upwelling, marine conservation, shark populations, reef ecology, paleobiology, overfishing, ecological baselines

Planktic foraminifera, the microscopic calcareous protists inhabiting the ocean’s upper layers, serve a vital role as paleoenvironmental indicators due to their sensitivity to surface water temperature, salinity, nutrient availability, and ocean circulation patterns. By scrutinizing fossil assemblages extracted from sediment cores dating from approximately 5.3 million years ago to roughly 0.8 million years ago, the researchers could trace shifts in species composition, abundance, and biogeographic distribution that coincided with major climatic events, including the onset of Northern Hemisphere glaciation and the intensification of cyclic ice ages.

The meticulous taxonomic identification and quantification of foraminiferal species were merged with geochemical proxies such as stable isotopes of oxygen and carbon, allowing the team to infer past sea surface temperatures and carbon cycling dynamics. These parameters are crucial in reconstructing the climatic milieu in which the communities thrived or declined. The analysis revealed clear patterns signaling a marked reorganization of planktic foraminifera biodiversity, featuring both species extinctions and emergences aligned with cooler, more variable climatic phases during the early Pleistocene.

One of the most striking observations was the spatial heterogeneity in community restructuring. Rather than a uniform biotic response to global climate shifts, distinct ocean basins exhibited variable degrees of diversity turnover. This regional specificity suggests that local oceanographic processes—such as changes in upwelling intensity, nutrient supply, and water mass redistribution—played critical modulatory roles in shaping community trajectories. Such findings challenge previous assumptions of homogenous global biotic responses to Pliocene-Pleistocene climate change, emphasizing instead the complexity of ecosystem responses to external forcings.

Beyond its paleontological implications, the study holds profound relevance for understanding future ecosystem responses in the face of ongoing anthropogenic climate change. The fossil record preserves a natural experiment dealing with rapid environmental perturbations, offering a valuable analog for predicting how modern marine microorganisms might react to current warming trends. The sensitive, yet regionally divergent, nature of foraminiferal community dynamics underscores the need for multifaceted climate models that incorporate ecological heterogeneity and localized feedback mechanisms.

The research also highlights the evolutionary adaptability and resilience of planktonic foraminifera as they navigated successive climatic upheavals. While certain species diminished or disappeared, others emerged or expanded their range, reflecting complex biotic interactions and evolutionary pressures. Such adaptive responses are, in part, mediated by morphological and physiological shifts enabling better exploitation of altered habitats. This evolutionary lens provides a richer understanding of the mechanisms driving biodiversity patterns through geologic time, integrating ecological, evolutionary, and environmental factors into a cohesive framework.

Cutting-edge analytical techniques were pivotal to these breakthroughs. High-resolution stratigraphic sampling allowed for unprecedented temporal resolution, enabling the researchers to detect even subtle community shifts that would otherwise be obscured in broader temporal bins. Coupling these data with machine learning algorithms facilitated sophisticated pattern recognition and robust statistical interpretations of the fossil assemblages’ complex compositional changes, ushering in a new era of paleoclimate and paleoecological research empowered by computational advancements.

Climate variability between the late Pliocene and early Pleistocene was marked not only by progressive cooling trends but also by increased frequency and amplitude of glacial-interglacial cycles. This oscillatory nature imposed fluctuating selective pressures on marine organisms, as evidenced by repeated cycles of expansion and contraction in foraminiferal populations. Such cyclical patterns crystallize the notion that ecosystem resilience is intricately tied to the timescale and variability of environmental perturbations, highlighting the importance of temporal dynamics in ecological forecasting.

Intriguingly, the study also touches upon the implications of these biotic shifts for ocean carbon cycling. Planktic foraminifera contribute significantly to the biological carbon pump through their calcitic shells, which, upon sinking, facilitate carbon sequestration in deep ocean sediments. Shifts in species composition and abundance thus potentially influenced carbon export efficacy during this interval, with broader feedbacks on atmospheric CO2 levels and climate regulation. Interpreting paleoecological changes within this biogeochemical context adds layers of complexity to our understanding of Earth’s carbon cycle stability amid climatic transitions.

The correlation between paleotemperature proxies and foraminiferal community turnover further elucidates the sensitivity threshold beyond which ecological reorganization becomes pronounced. Data indicate that once sea surface temperatures dropped below specific points, community composition reorganized markedly, revealing critical transition zones. These thresholds can inform models projecting how extant planktonic communities might respond to crossing modern climatic tipping points, reinforcing the notion that biodiversity shifts may be abrupt and transformative rather than gradual.

Throughout the research, the integration of paleoceanographic datasets with biological indicators demonstrated the power of interdisciplinary approaches in unraveling Earth’s climatic past. By combining geological, chemical, biological, and computational sciences, the study embodies a holistic methodology that transcends traditional disciplinary boundaries, setting a benchmark for future investigations into ancient ecosystems and their responses to environmental stressors.

Moreover, the study offers a detailed reconstruction of oceanographic conditions spanning multiple ocean basins, including the Atlantic, Pacific, and Indian Oceans, capturing the interconnected yet regionally idiosyncratic nature of global climate systems. Cross-basin comparisons expose the complexity of climatic teleconnections and localized ecological adaptations, suggesting that even in an era of widespread climatic upheaval, marine microfauna displayed remarkable heterogeneity in their responses.

Finally, the implications of this research resonate deeply with ongoing concerns over the sustainability of marine ecosystems in the Anthropocene. Planktic foraminifera contribute fundamentally to ocean ecology and global biogeochemical cycles, and understanding their past responses to climate volatility can illuminate pathways to resilience or collapse in current ecosystems. As modern oceans warm and acidify, insights gleaned from fossilized communities serve as cautionary tales and guideposts, emphasizing the urgency of integrating paleoecological knowledge into contemporary conservation and climate mitigation efforts.

Collectively, this pioneering investigation into planktic foraminiferal community restructuring during the Pliocene to early Pleistocene not only enriches our comprehension of marine microfaunal evolution in the face of climatic flux but also lays critical foundations for predictive ecological modeling in an era of unprecedented environmental change. The study symbolizes a monumental step forward in paleoclimate research, harnessing the power of ancient lifeforms to decode Earth’s climatic history and forecast its ecological future.

Subject of Research:
Regional restructuring of planktic foraminifera communities in response to climate variability from the Pliocene to early Pleistocene epochs.

Article Title:
Regional restructuring in planktic foraminifera communities through Pliocene-early Pleistocene climate variability.

Article References:
Larina, E., Woodhouse, A., Swain, A. et al. Regional restructuring in planktic foraminifera communities through Pliocene-early Pleistocene climate variability. Nat Commun 16, 5056 (2025). https://doi.org/10.1038/s41467-025-60362-8

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