Posts Tagged 'biological response'

The response of coralline algae to cenozoic environmental change

Published 15 September 2026 Science Closed
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Coralline algae, calcifying red algae of the orders Corallinales, Hapalidiales and Sporolithales, are important components of many marine ecosystems, providing stability and protection from high energy waves in coral reefs, and providing shelter, substrate and nutrients for many organisms across a range of marine environments. Corallines are thought to be amongst the most vulnerable marine organisms in the face of climate change, as their high-Mg calcite mineralogy makes them especially vulnerable to ocean acidification. Corallines also require light to perform photosynthesis and are therefore vulnerable to siliciclastic sedimentation which can reduce illumination and bury corallines. Lab based acidification experiments show most coralline species respond negatively to elevated CO2 conditions, but the nature and magnitude of effects vary between species, and the rate of experimental CO2 increase is much faster than natural rates, making it difficult to use experimental data to predict how corallines respond to acidification on time scales of thousands to millions of years. While most coralline groups are not directly affected by temperature changes, global warming can alter the hydrosphere, increasing precipitation intensity and therefore terrestrial runoff in some coastal areas. Increased runoff can directly lower illumination in the water column and can also cause phytoplankton blooms that significantly reduce illumination. The earth’s climate and ocean conditions have changed greatly throughout the Cenozoic, with significant effects on many marine organisms including corals, benthic foraminifera, bivalves, sponges, and many other groups. The response of coralline algae to Cenozoic climate change, however, has received less research attention despite their importance in marine ecosystems.

This dissertation uses the fossil record to assess how coralline algae responded to different types of Cenozoic environmental change at three different scales. Chapter 1 looks at coralline response to rapid warming, acidification and sediment influxduring the Paleocene-Eocene Thermal Maximum (PETM) in northeastern India and Tibet. The PETM is the largest hyperthermal of the Cenozoic, where a massive release of CO2 caused widespread ocean acidification and warming of ~5-8 °C over ~10,000 years. At both study locations, coralline abundance is high in the pre-PETM and remains high into the PETM onset. Corallines then disappear abruptly as carbonate sedimentation rapidly ends under heavy siliciclastic input. The results of this chapter suggest that coralline algae may be more tolerant of acidification, but less tolerant of sedimentation, than previously thought.

Chapter 2 uses the early Eocene Sierra Blanca Limestone in Santa Barbara County, California, as a case study for rhodolith bed construction in the early Eocene greenhouse. Elevated temperatures and CO2 in the early Eocene prevented rhodolith beds from developing in most areas, so the Sierra Blanca Limestone provides rare insight into the environmental conditions allowing a robust coralline deposit to form in a seemingly hostile ocean. The lithology, taxonomic assemblages, and characteristics of Sierra Blanca rhodoliths suggest they developed on an offshore uplifted block along an upwelling coastline, allowing rhodoliths to thrive in relatively cool water beyond the reach of siliciclastic sedimentation.

Chapter 3 examines what controls the partitioning of coralline algae into reef and non-reef habitats on carbonate platforms during the Paleogene and Neogene. Coral reefs are significantly impacted by climate change during this interval, but coralline algae are more resilient. Coralline algae occupy non-reef settings through the studied interval and their abundance in non-reef environments shows little variation. As coral reefs develop, corallines persist in non-reef environments and expand into reefs where they play a crucial role in cementing the framework. When coral reefs collapse, corallines do not take over reef building, but persist and even expand in non-reef settings, often constructing rhodolith beds that serve some of the same ecological roles as coral reefs.

Together, these chapters highlight the ability of coralline algae to adapt to changing environmental conditions despite their assumed vulnerability. The discrepancies between lab-based experiments and paleontological observations suggest that the rate of change is vitally important: corallines can adapt to even significant change if it occurs slowly enough but are less able to adapt to rapid environmental change.

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Brood chamber carbonate chemistry in the oyster Ostrea edulis is dynamically shaped by warming, acidification, and ventilation

Published 14 September 2026 Science Closed
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Brooding organisms can modify the chemical environment experienced by developing offspring, potentially altering their exposure to climate change. In marine systems, however, the carbonate chemistry of brood chambers, and the mechanisms governing it, remain poorly resolved. Here, we combine high-resolution pH and CO2 measurements of the empty brood chamber (i.e., mantle cavity above gills) in the European flat oyster (Ostrea edulis) while also tracking valve gape to quantify how warming, ocean acidification, and ventilation interact to shape the internal environment experienced by larvae during incubation. Brood chamber pH was consistently lower than that of the surrounding seawater and responded to external conditions in a state-dependent manner governed by ventilation and respiration. When oysters were actively ventilating, brood chamber chemistry tracked ambient seawater with a persistent offset, whereas valve closure led to rapid CO2 accumulation and pronounced declines in pH. These dynamics generated highly variable and behaviorally mediated exposure regimes, in which metabolic processes distorted ambient chemical signals over short timescales. Paired pH and CO2 measurements provided preliminary constraints on aragonite saturation state (Ωar), revealing that brood chambers can remain undersaturated (Ωar < 1) for prolonged periods even in ventilating oysters and while overlying seawater remains favorable. Together, these results demonstrate that brood chambers function as dynamic microenvironments in which larval exposure to ocean acidification is governed not only by external conditions, but also by behavior. Because warming enhances metabolic CO2 production and intensifies acidification within the chamber, future climate change is likely to amplify both the magnitude and variability of larval exposure. These findings help explain the apparent resilience of brooding species to ocean acidification, while also highlighting potential limits as environmental conditions move beyond historical bounds.

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Ocean acidification and nanoplastics disrupt mussel calcification in synergy: a multi-omics analysis

Published 14 September 2026 Science Closed
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Highlights

  • Ocean acidification disrupts calcium homeostasis in the mantle of mussels.
  • Ocean acidification and N-NPs together intensify the inhibition of calcification.
  • Surface charge determines distinct, mechanism-specific response pathways.
  • Both omics reveal key roles for calcium transport, CA, and ECM synthesis.

Abstract

Ocean acidification (OA) and nanoplastics (NPs) increasingly co-occur in coastal ecosystems, yet their combined mechanistic impacts on calcifying invertebrates remain poorly resolved. Here, the mussel Mytilus coruscus was exposed for 30 days to factorial combinations of OA (pH 7.7 vs 8.1), surface-modified polystyrene NPs at a concentration of 100 μg/L (positively and negatively charged), and experimental shell damage to assess effects on shell repair, ion homeostasis, and energy metabolism. OA reduced shell repair quality by thinning repair layers, increasing porosity, and lowering calcium content, effects that were further enhanced by co-exposure to NPs, particularly negatively charged particles. OA and NPs jointly altered Ca2+ and Mg2+ levels, alkaline phosphatase activity, Ca2+Mg2+-ATPase activity, and key indicators of energy metabolism, including ATP content and cellular energy allocation. Transcriptomic and proteomic analyses revealed enrichment of ion transport, extracellular matrix, TGF-β signaling and other pathways, with divergent patterns linked to NPs surface charge. Together, these results suggest that nanoplastic surface charge under OA may impair mussel shell repair through associated alterations in ion homeostasis and energy metabolism. These findings highlight that particle surface properties shape how organisms respond to combined environmental stressors in acidifying marine environments.

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Long term monitoring of coral reef fish populations under increasing ocean temperature and acidification stress

Published 11 September 2026 Science Closed
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Coral reefs are especially sensitive to ocean warming and acidification caused by climate change and can have a major impact on reef-associated fish species and reef stability. This study analyzes the diversity of coral reef fishes over time using data from the National Coral Reef Monitoring Program (NCRMP) of NOAA from the year 2014 to 2024 from the Hawaiian Archipelago. The impacts of environmental factors such as sea surface temperature, ocean pH, and coral cover were evaluated on fish population structure. Shannon Diversity Index as the main statistical method to quantify the changes in biodiversity between monitoring years. The mean sea surface temperature (MST) ranged from 26.8°C in 2014 to 29.1°C in 2024, with a steady increase over the years, whereas the mean pH decreased from 8.12 to 7.95 over the years. During the same time frame, there was significant loss of coral cover, from 62% to 36%. The Shannon Diversity Index was then found to have decreased from 3.45 to 2.51, representing a loss of some 27.2% of biodiversity. The results indicate that the diversity of coral reef fishes is negatively correlated with environmental stress. Fish functional groups were further simplified, with habitat specialist fishes being more affected than generalist fishes under climate stress. The rising temperature and acidification of the oceans are important factors in the decline of coral reef fish. The continued monitoring and adaptive conservation strategies will be critical to ensure that reef biodiversity will persist into the future under different climate change scenarios.

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Combined effect of ocean warming and acidification on the sea pen “Pennatula phosphorea”

Published 10 September 2026 Science Closed
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Anthropogenic CO2 emissions are expected to increase ocean acidity and temperature over the coming century. Under the Shared Socioeconomic Pathway (SSP) 5–8.5 scenario, mean surface ocean pH is projected to decrease by approximately 0.39 units, while sea surface temperature is expected to rise by 2–4 °C between 2010 and 2100. Sea pens (Octocorallia) are important bioindicators of soft-sediment habitat quality and associated benthic communities; however, their responses to these stressors remain considerably less studied than those of their hexacoral counterparts.

This thesis investigates the individual and combined effects of ocean acidification and warming, based on SSP5–8.5 projections, on the sea pen Pennatula phosphorea (Linnaeus, 1758), collected from the Swedish Gullmarsfjord. During winter and summer 2025, four pH treatments (8.0, control; 7.8, present-day low value; 7.4, projected low value for 2100; and 7.0, extreme scenario) and four temperature treatments (7.7 °C, winter control; 14 °C, summer control; 17 °C, present-day high value; and 20 °C, projected high value for 2100) were assessed. Response variables included behavioural traits (colony burrowing, colony inflation, polyp opening and bioluminescence emission), survival, and bioluminescence substrate levels (coelenterazine concentration and maximum light intensity, Lmax). Three hypotheses were tested: (1) ocean acidification and warming would negatively affect all response variables, with stronger effects under combined exposure; (2) prolonged exposure would result in either progressive deterioration or acclimation of behavioural traits; and (3) larger individuals would be less affected by stressors than smaller individuals.

The effects of acidification and warming varied among response variables, seasons, and whether stressors were applied individually or in combination. Overall, pH 7.8 produced few significant effects, except on burrowing behaviour, whereas pH 7.4 and 7.0 generated effects ranging from negligible (p > 0.1) to highly significant (p < 0.01), generally with greater impacts at pH 7.0. Similarly, temperatures of 17 and 20 °C elicited responses ranging from negligible to highly significant, with the strongest effects observed at 20 °C for quantitative measures of bioluminescence substrates. Combined exposure generally amplified the observed effects, suggesting that tolerance to one stressor may be compromised by the presence of another. No consistent evidence of behavioural acclimation or progressive deterioration was detected over time. Contrary to the initial hypothesis, larger individuals appeared more susceptible to environmental stressors than smaller individuals.

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Environmental regulation and disruption of shell biomineralization in bivalves and gastropods: a mechanistic review

Published 10 September 2026 Science Closed
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Molluscan shells are increasingly threatened by a complex array of environmental stressors—climate-related drivers, changes in seawater chemistry, contaminants, and biotic cues. This review provides a mechanistic synthesis of how these stressors disrupt the biomineralization process across life stages. We develop a conditional hierarchical response framework from the reviewed evidence. The framework links ionoregulatory and acid-base disturbances with molecular, microstructural, and shell-level responses, while allowing for compensatory, nonlinear, species-specific, and life-stage-specific outcomes. This molecular disruption manifests as defects in calcium carbonate (CaCO3) crystalline microstructure, which may in turn compromise shell macro-scale physical properties (strength, hardness, growth). We synthesize combined and context-dependent effects of co-occurring stressors and distinguish formally tested interactions from qualitative comparisons of combined treatments. Future research must leverage integrated multi-omics, advanced in vivo imaging, and multi-stressor experimental designs to unravel candidate molecular and physiological thresholds and predict adaptive potential. This framework may help identify testable mechanisms, evidence gaps, and context-dependent vulnerabilities relevant to conservation.

Highlights

  • A conditional framework links molecular, microstructural, and shell-level responses.
  • Early stages often show high sensitivity, although direct ontogenetic comparisons remain limited.
  • Energy limitation is a recurrent, but often indirectly inferred, physiological constraint.
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Parental CO₂-vent history does not improve larval performance of the sea urchin Arbacia lixula under copper and acidification

Published 9 September 2026 Science Closed
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CO₂-driven ocean acidification (OA) threatens marine calcifiers, while coastal ecosystems face increasing trace-metal contamination; their combined effects, and the modulating role of parental environmental history, remain poorly understood. We used the sea urchin Arbacia lixula from a naturally acidified CO₂ vent and a nearby ambient site at Ischia (Tyrrhenian Sea) to test how chronic adult exposure to low pH shapes larval responses to copper and low pH. Offspring from ambient (pH ~ 8.1) and vent (pH ~ 7.7) adults were reared for 48 h in a fully crossed design (two pH levels × three copper concentrations: 0, 5, 20 µg L⁻¹). At 24 hpf, development was dominated by parental history: ambient-derived larvae advanced rapidly, whereas vent-derived larvae showed higher arrest and slower progression, especially under low pH and high copper. By 48 hpf these effects diminished and pH and its interaction with copper became dominant, with both origins converging toward the echinopluteus stage. Nonetheless, malformations rose sharply under low pH regardless of copper, and skeletal-rod morphometrics revealed additional copper-related effects invisible to binary abnormality classifications. Chronic parental exposure did not enhance larval tolerance and sometimes increased sensitivity, underscoring the need to integrate multiple stressors and parental legacy.

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The impact of ocean acidification on the sorption of trace metals by diatoms

Published 9 September 2026 Science Closed
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Diatoms are a major phytoplankton group that plays a critical role in aquatic biogeochemical processes. Their metabolism relies on trace metals as cofactors for numerous enzymes, and changes in seawater pH may therefore influence metal sorption. Here, we investigated the effects of pH variability on diatom growth and trace-metal sorption using neutron activation analysis (NAA). Although NAA has rarely been applied to phytoplankton, we demonstrate its suitability for marine diatom samples. Overall, diatoms exposed to CO2 treatment exhibited higher cell abundance but lower intracellular elemental concentrations. In particular, Nitzschia navis-varingica showed significantly lower concentrations of Al, Ce, Co, Cr, Fe, Mg, Mn and Zn under the CO2 treatment. These trends are consistent with previous studies. For example, Zinc, which is a cofactor in many enzymes, plays a role in inorganic carbon acquisition; under lower pH, reduced enzymatic metal requirements likely explain the lower Zn concentrations observed. Nitzschia navis-varingica also had significantly lower levels of Co under lower pH. Both Thalassiosira pseudonana and Nitzschia navis-varingica showed lower Fe concentrations under CO2 treatment. As Iron is required for photosynthetic and respiratory processes that support the carbon-concentrating mechanism (CCM), reduced CCM activity at lower pH may decrease Fe demand. Overall, this study highlights NAA as a robust approach for quantifying metal sorption in marine organisms and provides new insight into the effects of ocean acidification on the growth and elemental composition of diatoms.

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Ocean acidification drives species-specific and time-dependent pigment responses in three phytoplankton taxa

Published 9 September 2026 Science Closed
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Phytoplankton are primary producers in marine ecosystems and play a central role in biogeochemical cycles, yet their physiological responses to altered seawater pH vary among taxa and over time. Here, we examined the effects of sustained pH manipulation on pigment composition, growth, and dark respiration in three ecologically important phytoplankton taxa – a diatom (Pseudo-nitzschia spp.), a dinoflagellate (Heterocapsa pygmaea), and a haptophyte (Emiliania huxleyi) – during a 15-day controlled laboratory experiment. Cultures were maintained at pH 8.1, 7.8, and 7.5, representing present-day and enhanced acidification conditions. Responses to pH were species-specific and strongly time-dependent. Growth and cell-specific respiration rates showed relatively small and often transient differences among pH treatments, suggesting short-term metabolic adjustment under altered pH. In contrast, pigment composition exhibited clearer and more consistent pH-related responses, primarily expressed as shifts in temporal patterns rather than uniform directional changes. In Pseudo-nitzschia spp. and H. pygmaea, several key pigments displayed pronounced pH-dependent trajectories, whereas E. huxleyi showed greater temporal variability and weaker separation among pH treatments. Overall, these results demonstrate that photophysiological traits respond sensitively to sustained pH changes even when population-level growth and respiration remain comparatively stable, highlighting pigment composition as a potentially sensitive indicator of short-term phytoplankton acclimation to ocean acidification.

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Elevated pCO2 impairs overall byssus attachment strength in the blue mussel (Mytilus edulis) without altering byssus thread quality

Published 8 September 2026 Science Closed
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Increasing atmospheric carbon dioxide (CO2) is driving global ocean acidification (OA). This process may threaten the persistence of bed-forming mussels by weakening the byssal system that anchors them to the seafloor. Here, blue mussels (Mytilus edulis) were exposed to present-day (∼460 ppm pCO2) normocapnic and projected end-century (∼1200 ppm pCO2) hypercapnic conditions for four weeks at 12 °C. Byssus production, thread morphology, whole-byssus mechanics and the underlying physiological condition index (CI) were quantified. Unlike previous studies, this study analysed the byssus as an intact functional unit. This approach better reflects its mechanical performance in situ. Median thread production fell by 50% under elevated pCO2 and the number of individuals producing no threads at all increased from 3% to 23% of the population. Thread diameter and plaque area were unaffected. Whole byssus tensile testing revealed a distinctive mechanical pattern (elastic loading, force plateau, and structural failure) regardless of environmental CO2 concentration. Whole byssus attachment strength scaled linearly with thread number in both treatments, and the mechanical work required to detach mussels under hypercapnia dropped by 42%. Elevated pCO2 reduced mussel condition index by 19% relative to the control, indicating an energetic burden. These results show that near-future ocean acidification weakens mussel attachment primarily by lowering individual physiological condition, which directly drives the reduction in total attachment energy, rather than by lowering individual thread quality. This likely results from a shift in energy use away from thread production, as seen in poorer mussel condition. As a result, mussels may become more prone to being dislodged by waves or predators. The findings of this study indicate that ocean acidification can reduce the overall strength of M. edulis beds, with important effects on rocky shore ecosystems and the viability of mussel farming in a changing climate.

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Shark responses to ocean acidification: physiological buffering, behavioural vulnerability, and comparative insights from teleost fishes

Published 8 September 2026 Science Closed
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Highlights

  • Sharks maintain acid-base balance under elevated CO₂ via effective buffering.
  • Physiological compensation carries energetic costs that constrain aerobic scope.
  • Olfactory-mediated foraging is more OA-sensitive than baseline locomotor function.
  • Multi-stressor effects (warming + OA) amplify biological impacts across life stages.
  • Evidence is biased toward benthic species; pelagic sharks remain understudied.

Abstract

Ocean acidification (OA), driven by increasing atmospheric carbon dioxide (CO₂), is a major component of global ocean change with widespread implications for marine organisms. Sharks (elasmobranchs) are often assumed to be relatively resilient to OA due to their distinctive physiology, including strong acid–base regulation and urea-based osmoconformation. However, empirical evidence evaluating this assumption remains limited and fragmented. This review synthesizes current knowledge on the physiological, behavioural, and sensory responses of sharks to OA within a comparative framework that incorporates insights from teleost fishes. A systematic literature search following PRISMA guidelines identified studies examining OA effects across shark species and life stages. Available evidence indicates that sharks generally maintain extracellular acid-base balance under elevated CO₂, demonstrating effective physiological buffering. However, this compensation is not without cost. Energetic trade-offs, reduced aerobic scope under multi-stressor conditions, and alterations in metabolic and oxidative responses have been reported. Behavioural and sensory-mediated processes, particularly olfactory-driven foraging, appear more sensitive to OA, with impairments emerging even in the absence of obvious physiological failure. Responses are highly species-specific and often amplified by co-occurring stressors such as warming. Despite these findings, current data are strongly biased toward small, benthic species, with limited representation of pelagic taxa and long-term responses. Sharks cannot be considered uniformly resilient to OA; rather, their responses are context-dependent, energetically constrained, and potentially consequential at population and ecosystem levels. Future research integrating long-term, multi-stressor, and mechanistic approaches will be critical for improving predictions of shark responses under ongoing ocean change.

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Physiology and hydrodynamics influence the susceptibility of reef-building corals to ocean acidification

Published 3 September 2026 Science Closed
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Ocean acidification (OA) poses a major future threat to tropical coral reefs. This is primarily due to its effects on reef-building coral species, which vary in their susceptibility to this climate change stressor. However, the potential factors underlying the range of susceptibilities observed among reef-building corals remain poorly understood. Therefore, this doctoral thesis investigates the influence of species-specific physiology and water flow conditions on coral susceptibility to OA. Using an experimental, multi-scale approach, the present thesis addresses this knowledge gap in a total of four studies and focuses on the physiological response of three major reef-building coral genera (Acropora, Pocillopora, and Porites) to prolonged exposure of OA conditions (> three months).

The results showed that (1) variable decreases in coral growth under OA were mediated by differential changes in maintenance and cellular stress parameters. This physiological interplay was genus-specific for Acropora and Pocillopora, and was species-specific for Porites spp. Moreover, assessments of the combined effects of OA and changes in water flow conditions indicated that (2) temporarily reduced water flow may mitigate OA effects on Acropora and Porites spp. Still, simultaneous changes in seawater chemistry and flow led to changes in coral physiology with complex and species-specific patterns. Finally, at the microscale, characterisation of the effects of OA and water flow on the concentration boundary layer (CBL) at the coral surface revealed that (3) OA was an overall weak modulator of this layer, regardless of flow conditions and CBL variability among species. Despite minor OA effects, however, the results also suggested that the CBL had a limited OA-buffering capacity due to thin pH gradients across the CBL. Nonetheless, low flow potentially enhanced CBL sheltering from acidified seawater by elevating pH at the coral surface.

In summary, this thesis provides evidence that both species physiology and water flow conditions shape coral susceptibility to OA in species-specific patterns and contributes novel insights into the potential links, between colony and CBL levels, involved in shaping it. Furthermore, the findings of this thesis showcase the potential of low-flow environments as refugia for coral species under OA and highlight the importance of including reef hydrodynamics in future OA scenarios, which will require consideration of different spatial and temporal scales. Altogether, the knowledge provided here may help improve projections of coral community dynamics under future OA and inform conservation efforts.

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Biological impacts of ocean change in upwelling systems: from organismal responses to fishery outcomes

Published 3 September 2026 Science Closed
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Climate change is altering marine ecosystems through concurrent changes in temperature, carbonate chemistry, and dissolved oxygen. These changes are particularly important in coastal upwelling systems, where organisms already experience naturally variable environmental conditions. This dissertation integrates synthesis, experimentation, and modeling to evaluate how ocean change influences marine invertebrates and the fisheries they support. First, I conducted a meta analysis examining the effects of ocean acidification and deoxygenation on marine invertebrates. Both stressors produced broadly negative effects on fitness-related
traits, including survival, growth, development, and reproduction. Although vulnerability varied among taxa, responses were not strongly structured across broad taxonomic groups, suggesting that species-specific traits and environmental history are important determinants of sensitivity. Second, I investigated the effects of multi-stressor upwelling conditions on juvenile Dungeness crab (Metacarcinus magister). Crabs maintained net calcification across a range of moderate conditions but exhibited significant declines under the most severe treatments, indicating threshold responses to environmental stress. Short-term environmental variability had little effect relative to mean conditions, suggesting that exposure severity is a stronger driver of performance than exposure pattern. Finally, I incorporated experimentally observed reductions in calcification into a size-structured yield-per
recruit model to evaluate potential fishery consequences. Reduced growth delayed attainment of legal harvest size and decreased projected fishery yield, demonstrating how sublethal physiological responses can scale to population and management-relevant outcomes. Together, these chapters show that ocean change can affect biological systems across levels of organization, from individual performance to fishery productivity. By linking broad patterns of vulnerability to species-specific responses and applied fishery outcomes, this dissertation provides a framework for understanding and managing the impacts of global change in coastal
marine ecosystems.

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Climatic factors effects on gastropods (Phylum: Mollusca): a review of the biodiversity of freshwater, marine, and terrestrial snails

Published 1 September 2026 Science Closed
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Climate change is altering ecosystems worldwide through rising temperatures, changing precipitation patterns, and more frequent extreme weather events, including heatwaves. Gastropods in freshwater, marine, and terrestrial environments are affected through changes in habitat characteristics, geographic distribution, abundance, physiology, and behavior. In freshwater systems, warming and drought can reduce dissolved oxygen and shrink suitable habitats. In marine environments, ocean acidification can impair shell formation and, under severe conditions, dissolve calcium-carbonate shells. In terrestrial habitats, increasing temperature and declining soil moisture can force snails into prolonged inactivity and increase desiccation risk. Effective climate information, predictive models, and early-warning systems are therefore essential for climate resilience, biodiversity conservation, and disease-risk management. Further comparative research is needed to clarify how phylogenetic history and adaptive variation influence heat tolerance and resilience among gastropod taxa.

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Coral reef community structure and photophysiology differ between upwelling and non-upwelling locations on the Pacific Coast of Costa Rica

Published 28 August 2026 Science Closed
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Reef-building corals and coralline algae form the calcium carbonate frameworks that underpin tropical coral reefs, yet in some locations, coral cover has declined by ~50% in recent decades due to marine heatwaves and other stressors. Identifying refugia environments, such as upwelling systems, that may buffer stress, promote recovery, and could enhance resilience by promoting physiological plasticity that supports thermotolerance is therefore critical. Here, we compared benthic community composition, coral percent cover, and photophysiology between an upwelling location in the Gulf of Papagayo and a non-upwelling location in Sámara on the Pacific coast of Costa Rica. Waters in Papagayo were cooler, more acidic, and had higher chlorophyll-a concentrations. Reefs at this location exhibited higher crustose coralline algae, higher sea urchin abundance, and lower macroalgae cover, compared to Sámara. Papagayo also showed higher stony coral cover, driven by Pocillopora spp., while Sámara was dominated by massive, heat-tolerant Porites spp. Photophysiological parameters were significantly different between locations. Specifically, photosynthetic efficiency (Fv′/Fm′) was 10–45% higher, and maximum photosynthetic rate (Pmax) was 20–40% lower in corals from Papagayo than in those from Sámara. These results reveal that two locations differing in environmental regime within a relatively small geographic area also differ in coral community composition and photophysiological features. Although further research is needed to resolve whether these environmental contrasts shape the observed biological differences, the observed patterns are consistent with the hypothesis that such regimes may support reef persistence or refugia, providing a basis for future work to test this hypothesis directly.

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Early detection of coral reef acidification micro-hotspots driven by offshore energy development

Published 26 August 2026 Science Closed
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Offshore energy development is a key measure to safeguard global energy security. At present, offshore oil and gas, wind power, tidal power and other offshore energy industries are expanding rapidly worldwide. However, large-scale energy activities have become a non-negligible driver of coastal ocean acidification. Carbon emissions generated throughout the full lifecycle of energy facilities locally alter seawater chemistry. This triggers ocean acidification of varying degrees and accelerates the corrosion and degradation of surrounding coral reefs.1,2,3 If population-averaged datasets are adopted to conduct environmental assessments of ocean acidification impacts, it will inevitably fail to identify fine-scale ecological risks to coral reefs induced by energy-related activities.4,5 Undoubtedly, this will become one of the critical bottlenecks restricting the green and sustainable development of offshore energy.

This study targets corals from the South China Sea. We adopt large-view macro-lens infrared thermal imaging. The technique reveals inherent microscale heterogeneity in coral skeletal corrosion susceptibility. The findings provide new technical references for ecological impact assessment, layout optimization and environmental risk control of offshore energy facilities. It also helps promote coordinated development between offshore energy exploitation and marine ecological conservation.

HIGH-PURITY PRIMARY ARAGONITE SKELETON OF GONIOPORA FROM THE SOUTH CHINA SEA

The coral sample used in this study was collected from Wuzhizhou Island, Sanya, South China Sea (Figure 1A). Whole-rock X-ray diffraction (XRD) analysis shows that aragonite is the dominant mineral phase, with a content of 88.5%. This matches the typical mineral composition of pristine coral skeletons. Minor impurities including halite (2.3%), clay minerals (2.3%), dolomite (1.9%), quartz (1.2%), K-feldspar (1.1%), calcite (1.1%), plagioclase (0.9%), and gypsum (0.7%) are also detected in the sample (Figure 1B). Plane-polarized and cross-polarized light micrographs show that the images display regular skeletal frameworks and unevenly distributed pore networks, which lay a structural basis for the spatial differentiation of lattice defects (Figure 1C & D).

Figure 1.  Early detection of coral reef acidification micro-hotspots driven by offshore energy development.(A) Photograph of the intact coral sample collected from the South China Sea; (B) X-ray diffraction pattern, showing dominant primary aragonite with a content of 88.5%, and some minor impurities; (C, D) Plane-polarized and cross-polarized light micrographs; (E) Large-view macro-lens infrared thermal image, with a measured temperature range of 23.60~25.60 °C. The color changes from red for high EBT to purple for low EBT. Dark green areas correspond to the coral pore system, including large corallite cavities, dendritic connected pores and scattered micro-pores. Orange areas represent skeletal matrix with high EBT, which features weak corrosion susceptibility. Bright yellow and light green areas represent matrix with low EBT, acting as acidification micro-hotspots with strong corrosion susceptibility. Sporadic blue spots are residual bubbles formed during thin section preparation, not native skeletal structures.

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Elucidating impact of ocean acidification on coral exoskeletons using an in-situ (S)TEM platform

Published 25 August 2026 Science Closed
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Scleractinian (stony) corals can build highly ordered aragonite (CaCO3) exoskeletons, which are vital for marine ecosystems, coastal stability, and of cultural and economic importance through supporting fisheries and tourism. However, they face multiple challenges through global climate change, unsustainable human activity, and coral-specific diseases. In the latter category, Stony Coral Tissue Loss Disease (SCTLD) has recently emerged as one of the most destructive coral diseases, spreading rapidly and causing widespread tissue mortality across many marine species [1]. We have recently started exploring remnant effects of this disease on Montastraea cavernosa exoskeletons, abundant throughout the Caribbean Sea, Gulf of Mexico, and Atlantic Ocean. Indeed, through use of multi-scale electron diffraction characterization techniques, we find that their skeletogenisis is impacted by this disease from the micro- through atomic scale [2]. Notably, at the nanoscale we observe pockets of more soluble amorphous calcium carbonate (ACC) within centers of calcification (CoCs; i.e. the center of the three-dimensional fans containing arranged elongated aragonite crystals) for healthy corals, which appear absent in STCLD-afflicted corals. At the atomic level, we reveal planar defects in diseased coral, which are much lower in density in healthy corals, presumably inflicted through dysregulation processes after tissue death.

Yet, the most severe threat to global coral reefs and their exoskeletons is climate change. As oceans increase the uptake of anthropogenic CO2 primarily from burning fossil fuels, ocean acidity has increased. The reduction in pH because of this Ocean Acidification (OA) not only reduces the rate of net ecosystem calcification, but also increases net dissolution of skeletons. At current trends, most coral exoskeletons are expected to dissolve starting in 2050 [3]. Currently, it is unclear how exactly (the onset of) dissolution proceeds and affects their aragonitic framework. Given our expertise in characterization of coral skeletons, herein we discuss a developed in-situ platform to investigate OA effects at the nanoscale.

As proof of concept, we sandwiched crushed geological aragonite nanoparticles between own fabricated SiNx-based chips, compatible with a Protochips Atmosphere gas cell holder [4]. Thereafter, we introduced water vapor at 14 Torr at room temperature (∼60% relative humidity) for 10 minutes to create a hydrated environment for the particles (Fig. 1b). In a third step, we introduced gaseous CO2 at a pressure of 1 atm (Fig. 1c). The formed unstable carbonic acid produces HCO3– and H+, which increases acidity (i.e. lowers pH). Indeed, we observe rapid dissolution of aragonite particles after CO2. While we expect roughly a pH ∼4 in this system, this experimental observation matches theoretical expectations that aragonite would dissolve under these conditions (Fig 1c-f). We further observe nucleation and growth of new particles in a dendritic fashion in the vicinity of the dissolved particles (Fig 1c-f). Likely, this is crystallization of calcite, the most stable crystalline polymorph of CaCO3, induced by local dissolution of aragonite [5]. Although pCO2 in the oceans is expected to be much lower (∼400 – 500 µatm) and thus dissolution timescales are expected to shift, this illustrates our platform can capture aragonite dissolution.

To expand our platform methodology, using conventional Ga+ FIB-methods, we prepared a lamella of geological aragonite with a thinned region (∼100 nm), which was then transferred on top of a SiNx-based chip, and attached this in one of the corners between the Si support and the SiNx layer (Fig. 2a). We were able to sandwich the lamella between both chips when observing the cell in the TEM (Fig 2b,c). Next, we will target healthy and STCLD-afflicted coral sections to investigate how nanoscale dissolution proceeds at/near more soluble areas including defects due to the devastating OA process. This understanding may allow for more accurate forecasting of marine ecosystem collapse, enabling targeted mitigation strategies, protecting food supplies, and predicting climate feedback loops [6].

Fig. 1. In-situ OA platform experiment showing TEM snapshots of: a) Initial geological aragonite nanoparticles. Inset: selected area diffraction pattern indicating aragonite spots. b) Introduction of water vapor (14 Torr) after 10 min. The white arrow indicates an apparent hydration layer surrounding the large particle. c) Introduction of CO2 at 1 atm pressure after 10 s. d) 60s e) 90s and f) 150s. White arrows in c-f) mark the outer layer of the large particle dissolving in time, red arrows illustrate growth of new crystals.

Fig. 2. a) SEM image of geological aragonite lamella attached to SiNx chip. b) TEM image of lamella after cell assembly (top and bottom chip). c) In-situ selected area diffraction pattern of the lamella.

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Calcium carbonate formation in coastal macroalgal ecosystems via multiple pathways

Published 24 August 2026 Science Closed
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Calcium carbonate formation in coastal macroalgal ecosystems via multiple pathways

Highlights

  • Focused on a novel inorganic carbon sequestration pathway of non-calcifying macroalgae.
  • Clarified algae-bacteria synergistic driving mechanism for calcium carbonate precipitation.
  • Systematically sorted out potential mineralizing microbial taxa within the phycosphere and their core metabolic pathways.

Abstract

Macroalgae are dominant primary producers that drive carbon sequestration in coastal ecosystems. Macroalgal carbon sequestration primarily refers to the long-term storage of macroalgae-derived organic carbon in the ocean. However, calcium carbonate (CaCO3) formation is frequently observed in non-calcifying macroalgal environments, suggesting the existence of an overlooked inorganic carbon process in macroalgal ecosystems. Here, we introduce multiple pathways that may drive CaCO3 formation in macroalgal ecosystems. These include the effects of macroalgal photosynthesis and carbon-concentrating mechanisms on the seawater carbonate system, the role of phycosphere interfacial properties in facilitating CaCO3 nucleation, and the macroalgae-bacteria synergy that promotes CaCO3 formation. We identified several current knowledge gaps—the unclear carbon sequestration or source effect of CaCO3 formation in macroalgal ecosystems and the stability of CaCO3 minerals in macroalgal ecosystems—that require further investigation. This review advances the understanding of macroalgal carbon cycling beyond organic pathways and emphasizes the importance of a comprehensive assessment of macroalgal carbon sequestration, including that of inorganic carbon.

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Witness to ocean acidification

Published 20 August 2026 Science Closed
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Foraminifera inhabit coastal and deep-sea marine environments. These microscopic, single-celled organisms are widely used as proxies for relative age determination and reconstructing past climates. The ratio of calcium isotopes (44Ca/40Ca) in their calcium carbonate shells depends on the amount of carbon dioxide (CO2) and carbonate saturation in seawater at the time of the shells’ formation. On page 527 of this issue, Chen et al. (1) report geochemical evidence that a rise in atmospheric CO2 concentration and ocean acidification at the end of the Aptian Stage [~113 million years ago (Ma)] may have caused the largest extinction of planktic foraminifera of the Cretaceous Period (146 to 66 Ma) (2–4), which is second only to the extinction event at the end of the Cretaceous Period (66 Ma) (5–7). The findings could be important for understanding potential effects of present-day increases in atmospheric CO2 levels on marine organisms.

Paraticinella rohri collected from the South Atlantic is a species of planktic foraminifera that went extinct at the Aptian–Albian boundary. IMAGE: HUBER AND LECKIE (3)

Seafloor-dwelling benthic foraminifera appeared more than 500 million years ago. It took at least 350 million years for them to evolve into planktic species that float in the upper ocean (8–10). The earliest species of planktic foraminifera lacked morphological diversity and were minor constituents of marine sediments. The first major morphological diversification of planktic foraminifera occurred (2, 11) during the Aptian Stage (125 to 113 Ma) of the mid-Cretaceous Period. New species of planktic foraminifera arose, with elongated chambers (Leupoldina) and larger, more heavily calcified shells (Globigerinelloides and Hedbergella), and the first species with a peripheral keel (Pseudoplanomalina cheniourensis) appeared by the late Aptian. Large increases in atmospheric CO2 concentration caused by massive volcanic eruptions triggered substantial depletion of oxygen in the oceans, including Oceanic Anoxic Event 1a and other similar events. Atmospheric CO2 likely drove warming of the atmosphere and water; warmer waters hold less dissolved oxygen compared to cooler water.

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Calcium isotopes link ocean acidification to Aptian–Albian foraminiferal extinctions

Published 19 August 2026 Science Closed
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Editor’s summary

About three quarters of planktic foraminifera species disappeared in the Aptian-Albian extinction event. What role might ocean acidification (OA) have played in this die-out? Chen et al. measured calcium isotope ratios in foraminifera, using them as a proxy for biocalcification and carbonate saturation (see the Perspective by Leckie). Their data reveal a dramatic reduction in calcification rates accompanied by decreases in the size, abundance, and diversity of planktic foraminifera. These results are consistent with the hypothesis that ocean acidification drove the extinctions of these organisms at the Aptian-Albian boundary. —Jesse Smith

Abstract

The second-largest extinction event in the evolutionary history of planktic foraminifera occurred at the Aptian–Albian boundary. This extinction may reflect ocean acidification (OA) associated with Oceanic Anoxic Event 1b. As calcium isotope ratios (δ44/40Ca) can track how biocalcification rates respond to OA, we measured δ44/40Ca records for planktic and benthic foraminifera, bulk carbonates, and authigenic calcite across the Aptian–Albian boundary in the South Atlantic. Benthic and bulk δ44/40Ca data display a distinct sequence of negative and positive excursions, similar to δ44/40Ca variations across other OA events. Planktic δ44/40Ca values increase markedly, tracking a reduction in calcification rates coincident with decreases in the size, diversity, and shell thickness of planktic foraminifera. These results suggest that OA drove extinctions of planktic foraminifera at the Aptian–Albian boundary.

Continue reading ‘Calcium isotopes link ocean acidification to Aptian–Albian foraminiferal extinctions’

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