Posts Tagged 'laboratory'

The response of coralline algae to cenozoic environmental change

Published 15 September 2026 Science Leave a Comment
Tags: , , ,

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.

Continue reading ‘The response of coralline algae to cenozoic environmental change’

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

Published 14 September 2026 Science Closed
Tags: , , , , , ,

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.

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

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

Published 14 September 2026 Science Closed
Tags: , , , , , , , ,

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.

Continue reading ‘Ocean acidification and nanoplastics disrupt mussel calcification in synergy: a multi-omics analysis’

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

Published 10 September 2026 Science Closed
Tags: , , , , ,

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.

Continue reading ‘Combined effect of ocean warming and acidification on the sea pen “Pennatula phosphorea”’

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

Published 9 September 2026 Science Closed
Tags: , , , , , , ,

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.

Continue reading ‘The impact of ocean acidification on the sorption of trace metals by diatoms’

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

Published 9 September 2026 Science Closed
Tags: , , , , , , , , ,

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.

Continue reading ‘Ocean acidification drives species-specific and time-dependent pigment responses in three phytoplankton taxa’

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

Published 8 September 2026 Science Closed
Tags: , , , , ,

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.

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

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

Published 3 September 2026 Science Closed
Tags: , , , , , ,

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.

Continue reading ‘Physiology and hydrodynamics influence the susceptibility of reef-building corals to ocean acidification’

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

Published 3 September 2026 Science Closed
Tags: , , , , , , , , ,

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.

Continue reading ‘Biological impacts of ocean change in upwelling systems: from organismal responses to fishery outcomes’

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

Published 26 August 2026 Science Closed
Tags: , , ,

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.

…

Continue reading ‘Early detection of coral reef acidification micro-hotspots driven by offshore energy development’

Witness to ocean acidification

Published 20 August 2026 Science Closed
Tags: , , , , ,

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.

…

Continue reading ‘Witness to ocean acidification’

Calcium isotopes link ocean acidification to Aptian–Albian foraminiferal extinctions

Published 19 August 2026 Science Closed
Tags: , , , , ,

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’

Short-term pH variability reshapes phytoplankton and microzooplankton communities in the northern Indian Ocean

Published 17 August 2026 Science Closed
Tags: , , , , , , ,

Phytoplankton and microzooplankton (MZP) are key components of marine food webs, driving carbon transfer through the microbial loop. Short-term laboratory microcosm bottle incubations using seawater from the Bay of Bengal (BoB) and Arabian Sea (AS) in 2022 examined the effects of reduced pH. Phytoplankton biomass (Chl-a) remained stable or increased by up to 12% under low pH, suggesting reduced grazing or improved prey quality. MZP diversity (Shannon index, H′) showed basin-specific responses. In the BoB (Exps. 1–2), H′ ranged 2.00–3.70 with high evenness (J′ = 0.93–1.00) and slight declines under medium acidification (ΔpH = 0.2). In contrast, the AS (Exps. 3–4) showed wider variability (H′ = 0.00–3.63) and greater sensitivity, with sharp diversity losses under stronger acidification (ΔpH = 0.4). AS assemblages showed pronounced richness declines (D′ = 2.85–0.00), whereas BoB communities remained stable. Regional and pH-related differences were linked to shifts in ciliates and dinoflagellates. Autotrophic bacteria sustained under low pH, while heterotrophic bacteria increased later, indicating altered microbial-loop functioning. Overall, pH, chlorophyll-a, and heterotrophic bacteria structured the community, accounting for > 65% of the variation. Thus, short-term acidification reshapes MZP assemblages and may modify trophic interactions across the northern Indian Ocean.

Continue reading ‘Short-term pH variability reshapes phytoplankton and microzooplankton communities in the northern Indian Ocean’

Biological modulation of shell δ13C in Mytilus galloprovincialis and Phorcus sp.: divergent responses between CO2 vents and laboratory mesocosms

Published 17 August 2026 Science Closed
Tags: , , , , , , , ,

table isotopes are fundamental proxies for deciphering past environmental conditions and carbon cycle perturbations. However, applying these geochemical tools with a forward-looking perspective can also help predict the resilience of marine biota in future acidified oceans. This study investigates carbon uptake and biomineralization pathways under reduced pH in two ecologically keystone calcifying species: the bivalve Mytilus galloprovincialis and the gastropod Phorcus sp. To unravel these mechanisms, we adopted a dual approach, comparing isotopic trajectories (δ13C) under strictly controlled laboratory mesocosms with observations from natural CO2 vent systems in Ischia, Italy. Our results reveal a striking discrepancy between settings. Under laboratory conditions, both species exhibited a significant depletion in shell δ13C as pH decreased, directly tracking seawater carbonate chemistry. Conversely, specimens from the volcanic vents displayed a paradoxical δ13C enrichment at low-pH sites (pH ~7.4). These divergent trajectories indicate that in complex natural environments, the geochemical signal of ocean acidification can be overridden by metabolic overprints and trophically driven vital processes. Consequently, while laboratory experiments are essential to isolate kinetic fractionation, natural analogues remain crucial to capture the biological resilience and complex ecological feedback of future oceans. Future research combining these geochemical trends with direct, in vivo physiological assessments will be essential to precisely constrain the underlying metabolic kinetics and refine predictive metabolic models.

Continue reading ‘Biological modulation of shell δ13C in Mytilus galloprovincialis and Phorcus sp.: divergent responses between CO2 vents and laboratory mesocosms’

Preferential impairment of later mating stages and sex-dependent metabolic shifts in Japanese medaka exposed to acute acidification

Published 12 August 2026 Science Closed
Tags: , , , , ,

Highlights

  • Acute acid stress (pH 4.5) preferentially impairs later mating stages in medaka, rather than causing a generalized reproductive collapse.
  • Early initiation phases (following and courtship) are relatively less affected, whereas progression to the crossing stage and spawning is strongly suppressed.
  • General locomotion and territorial aggression show no detectable change under acute acidification.
  • Females exhibit increased ammonia excretion and oxygen consumption, indicating sex-specific physiological strain under acid stress.
  • The behavioral impairment is consistent with an energy reallocation toward acid–base homeostasis, reducing investment in energetically costly terminal mating behaviors.

Abstract

Environmental acidification poses a significant threat to aquatic organisms, yet the underlying mechanisms of how acid stress disrupts complex social and reproductive behaviors remain incompletely understood. In the present study, we investigated the behavioral and physiological responses of adult Japanese medaka (Oryzias latipes) under acute acid exposure (pH 4.5, 24 h). Our results showed that acute acid stress reduced mating success, with a stronger impairment observed in the transition to the crossing stage and subsequent spawning, while the earlier, male-driven stages of following and courtship were relatively less affected under the present experimental conditions. This reproductive impairment did not coincide with detectable changes in generalized emotional-like behavior. Fish showed normal performance in the novel tank test and maintained territorial aggression. Physiologically, we observed a clear sexual dimorphism. Under acid stress, males maintained relatively stable MO₂ and JAmm, whereas females showed elevated MO₂ and JAmm. These findings suggest that reproductive impairment may be more pronounced in energetically demanding mating stages and may be associated with sex-dependent physiological strain. We further propose that the increased metabolic cost of acid-base regulation in females could shift energy allocation, and that high-cost coordination behaviors may be reduced in order to maintain short-term survival. This study provides evidence linking bioenergetics, acid-base regulation, and reproductive behavior in a teleost model under acidification.

Continue reading ‘Preferential impairment of later mating stages and sex-dependent metabolic shifts in Japanese medaka exposed to acute acidification’

Invasive macroalgae exert stronger effects than elevated CO₂ on seagrass (Posidonia oceanica) seedling performance and associated microbiomes

Published 11 August 2026 Science Closed
Tags: , , , , , , , , , , ,

Highlights

  • Invasive macroalgae reduced P. oceanica seedling biomass and leaf development.
  • Macroalgal invasion depleted carbohydrate reserves in seedling roots and rhizomes.
  • Elevated CO2 increased rhizome starch but did not mitigate invasion impacts.
  • Root microbiome diversity declined markedly under macroalgal invasion.
  • Future CO2 enrichment unlikely to buffer invasion stress at recruitment stage.

Abstract

Seagrass seedlings are key to meadow recovery under global change, as they enable recolonization of degraded areas and provide genetic variability needed for adaptation. While invasive macroalgae increasingly threaten seagrass communities, elevated CO2 has been proposed to enhance seagrass performance and potentially buffer other stressors. Here, we conducted a mesocosm experiment to test the combined effects of two invasive macroalgae (Lophocladia trichoclados and Caulerpa cylindracea) and elevated CO2 on Posidonia oceanica seedlings. CO2 enrichment increased carbohydrate reserves in rhizomes and induced subtle shifts in root-associated microbiomes. In contrast, invasive macroalgae had consistently negative effects on seedling development and physiology and strongly altered both above- and belowground microbial communities. Despite its potential to stimulate seagrass productivity, elevated CO2 did not mitigate the detrimental impacts of invasive macroalgae. These findings indicate that future CO2 conditions may not offset invasion-driven stress at the recruitment stage, highlighting the need for targeted management efforts to limit macroalgal proliferation and support seagrass meadow regeneration.

Continue reading ‘Invasive macroalgae exert stronger effects than elevated CO₂ on seagrass (Posidonia oceanica) seedling performance and associated microbiomes’

Tracing the imprints of dual stressors: eco-physiological and genotoxic insights from Mystus gulio under acidification and warming scenario

Published 10 August 2026 Science Closed
Tags: , , , , , , , ,

Global warming has caused a rise in ocean temperature and acidification, which collectively wreak havoc on marine animals. However, the combined ramifications of these stressors on energy metabolism, oxidative balance, and DNA integrity remain inadequately studied in teleosts. The present study aims to unravel the combined effects of warming (34°C) and acidification (pH 7.7) on energetic balance, antioxidant defense, and DNA stability in Mystus gulio at two intervals (15th and 45th day). Furthermore, the Effect Addition model was used to disentangle potential additive or non-additive effects of the combined stressors. Elevated temperature and acidification induced a marked energetic imbalance, as mirrored by suppressed ingestion and absorption rates, reduced scope for growth, and elevated excretion. Oxidative stress biomarkers revealed significant upregulation of SOD, CAT, and GST under combined treatment, which ultimately led to augmented lipid peroxidation. Genotoxic assessment delineated progressive upsurges in tail DNA (%) and olive tail moment, indicating compromised genomic stability. The integrated biomarker response consisted of six parameters, RR, ER, SOD, CAT, GST, and LPO, further corroborating that elevated temperature, alone and in combination with acidification, posed the highest cumulative physiological burden. Furthermore, the model assessment indicated that the interaction between warming and acidification varied among different biomarkers. Collectively, these findings corroborate that concurrent thermal and low pH perturbations destabilise physiological processes, oxidative instability, and DNA damage, which may undermine growth potential and jeopardise population structure and destabilise trophic relationships. The present study provides a mechanistic understanding of the impacts of multiple stressors and offers a robust integrative framework to predict fish vulnerability under future climate-driven oceanic vicissitudes.

Continue reading ‘Tracing the imprints of dual stressors: eco-physiological and genotoxic insights from Mystus gulio under acidification and warming scenario’

Warming and acidification shape zooplankton community dynamics in Jiaozhou Bay: evidence from an Acid-Heat Vector Intensity Index

Published 10 August 2026 Science Closed
Tags: , , , , , ,

Highlights

  • Warming and coastal acidification shape Jiaozhou Bay zooplankton dynamics.
  • AHIvec summarizes monitoring-oriented surface temperature-pH departure.
  • GAMs showed nonlinear, zone-specific zooplankton response patterns.

Abstract

Ocean warming and coastal acidification often co-occur in nearshore embayments, yet their joint associations with zooplankton remain difficult to characterize because responses are frequently nonlinear and spatially heterogeneous. In this study, we developed an integrated quantitative framework for characterizing joint warming-acidification exposure in Jiaozhou Bay. Based on six cruises conducted at nine stations in May (spring) and August (summer) from 2022 to 2024, we characterized zooplankton communities using abundance, biomass, Shannon-Wiener diversity (H′), and Pielou’s evenness (J). We further introduced a joint-exposure indicator, the Acid-Heat Vector Intensity Index (AHIvec), which summarizes joint temperature-pH departure based on standardized anomalies of temperature and pH. Generalized additive models (GAMs) were then applied to examine nonlinear response patterns and zone-specific associations between environmental gradients and zooplankton community attributes. Within the 2022–2024 observation window, sea surface temperature was generally higher in 2024 than in 2022, whereas surface pH was generally lower; however, these patterns should be interpreted as short-term observations rather than formal long-term trend estimates. Zooplankton also showed pronounced spring-summer and spatial variability. Notably, abundance showed pronounced temporal variation and generally increased with temperature, whereas biomass peaked at intermediate temperatures (∼20–22 °C) and declined thereafter, indicating a mismatch between abundance and biomass. Although pH-related associations were weaker than temperature-related associations, they became more evident at the lower end of the observed pH range (approximately 7.7–7.9). The AHIvec gradient was associated with contrasting zone-specific patterns in zooplankton community attributes. Overall, recent temperature-pH variations were associated with changes in zooplankton abundance, biomass, and diversity in Jiaozhou Bay. The AHIvec + GAM framework provides a monitoring-oriented complement to direct temperature-pH analyses for characterizing joint exposure in coastal ecosystems.

Continue reading ‘Warming and acidification shape zooplankton community dynamics in Jiaozhou Bay: evidence from an Acid-Heat Vector Intensity Index’

Global genome-wide patterns of genetic diversity and population structure in Coryphaena hippurus

Published 10 August 2026 Science Closed
Tags: , , , , , , , ,

Highlights

  • Genome-wide SNPs reveal four discrete populations across ocean basins.
  • Mediterranean population forms a deeply divergent and isolated lineage.
  • Nuclear SNPs detect Pacific–Atlantic.
  • Environmental gradients (salinity, phosphate, pH, light) shape genomic structure.
  • Genetic connectivity varies within basins, revealing hidden substructure.

Abstract

The origin and maintenance of marine biodiversity remain poorly understood, particularly in highly connected oceanic environments where extensive dispersal is expected to limit population differentiation. Evolutionary processes driving population divergence or speciation frequently depend on a proper knowledge of species’ life history and its interaction with major environmental variables. Using a genome-wide approach, we investigated the global population structure of the cosmopolitan pelagic fish Coryphaena hippurus Linnaeus, 1758, generating a dataset of 8.7 million SNPs and complete mitochondrial genomes.

Our results reveal, for the first time, four genetically differentiated populations, corresponding to major oceanic basins: Atlantic, Pacific, Indian and Mediterranean Sea. The Mediterranean population exhibited a distinct genomic signature, likely resulting from historical isolation and restricted contemporary exchange through the strait of Gibraltar. Despite this structure, genome-wide analyses uncovered extensive signals of historical connectivity among basins. D-statistics and f4-ratio tests detected significant excess allele sharing, particularly between Indo-Pacific and Atlantic populations, while phylogenetic network reconstruction in TreeMix supported multiple migration events, highlighting the role of ancestral gene flow in shaping global genetic patterns.

At finer scales, a limited but significant intra-oceanic structure was detected within both Atlantic and Pacific basins. Seascape genomic analyses revealed that environmental gradients such as salinity, phosphate concentration, light availability (PAR, Kd), and pH are significantly associated with genomic variation, suggesting that ecological factors contribute to population differentiation across heterogeneous marine environments.

Continue reading ‘Global genome-wide patterns of genetic diversity and population structure in Coryphaena hippurus’

Vulnerability to low salinity but compensatory responses to low pH in an intertidal limpet

Published 7 August 2026 Science Closed
Tags: , , , , , , , , ,

Highlights

  • Low salinity linked to warming may intensify coastal pH reduction.
  • Low salinity reduced righting and emergence in the limpet Patelloida pygmaea.
  • Low salinity reduces Mg/Ca ratios in newly formed shell layers.
  • Low pH increases shell thickness and Mg/Ca ratios despite dissolution.
  • CHS2 upregulation suggests compensatory resistance to low pH.

Abstract

Rising anthropogenic carbon dioxide emissions have driven ongoing ocean warming and associated climate changes. In the Yellow Sea, this warming is associated with enhanced monsoonal rainfall, which increases freshwater inputs and lowers coastal salinity. Increased freshwater input can weaken seawater buffering capacity, thereby leading to lower pH conditions in coastal environments. Here, we examined the effects of low pH and low salinity on the intertidal limpet Patelloida pygmaea. Adult limpets were exposed for 31 days to four experimental artificial seawater conditions combining two pH levels (8.0 and 7.5) and two salinity levels (30 and 21 psu). Survival and condition factor were not influenced by pH or salinity. However, low salinity reduced righting and emergence behavior. In addition, the Mg/Ca ratio in the M + 1 layer was lower at 21 psu than at 30 psu. Low pH resulted in a thicker M + 2 layer with higher Mg/Ca ratios despite shell dissolution, potentially helping to maintain shell integrity. While there was no change in heat shock protein (HSP70) expression, these shell modifications were accompanied by an upregulation of chitin synthase (CHS2) genes under low pH. These findings suggest that P. pygmaea is negatively influenced by low pH and low salinity, but also demonstrate compensatory mechanisms that enhance resistance to low pH.

Continue reading ‘Vulnerability to low salinity but compensatory responses to low pH in an intertidal limpet’

Subscribe

Search

  • Reset

OA-ICC Highlights

Resources