Posts Tagged 'laboratory'

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

Published 3 September 2026 Science Leave a Comment
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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 Leave a Comment
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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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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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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.

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

Published 17 August 2026 Science Closed
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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.

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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
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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.

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

Published 12 August 2026 Science Closed
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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.

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

Published 11 August 2026 Science Closed
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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.

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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
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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.

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

Published 10 August 2026 Science Closed
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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.

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

Published 10 August 2026 Science Closed
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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.

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

Published 7 August 2026 Science Closed
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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.

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Multilevel impacts of ocean acidification on vision: retinal damage, optic tectum hyperexcitability, and behavioral dysfunction in marine medaka

Published 6 August 2026 Science Closed
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Ocean acidification (OA), driven by atmospheric carbon dioxide (CO2) emissions, significantly impacts marine organism. This study investigated OA effects on retinal structure and function in marine medaka (Oryzias melastigma) across life stages under controlled CO2 exposures (450 × 10−6, 1 000 × 10−6, and 1 800 × 10−6). Quantitative analyses revealed concentration-dependent retinal pathology, with larval incidence rising from 16.7% (450 × 10−6) to 50.0% (1 800 × 10−6). Significant structural alterations include progressive pigment epithelium thickening and concurrent atrophy in inner plexiform and ganglion cell layers. Electrophysiological recording demonstrated severe neural hyperexcitability, with larval and adult fish showing 91.3% and 154.9% increased firing counts respectively at 1 800 × 10−6. Behavioral analyses revealed significant CO2-induced locomotor dysfunction with distinct light-dependent patterns. Under illumination, larvae exhibited hyperactivity at 1 800 × 10−6, while adults showed progressive impairment (high-performance swimmers declining from 60% to 37.5%). Conversely, dark conditions intensified activity across concentrations, with adults displaying dose-dependent increases in swimming speed (23.5% to 68.8%). These results demonstrated that OA induces significant visual disruption and behavioral changes. The differential responses across life stages and light conditions suggest complex neurophysiological impacts that may have cascading ecological consequences for marine fish in acidifying ocean.

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Ocean acidification influence on Cymodocea nodosa seedling development

Published 5 August 2026 Science Closed
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Ocean acidification may positively affect seagrasses, although the response of the early life stages remains generally unknown. This study investigated the effect of OA and seed origin on the viability, morphometry, and chemical content of Cymodocea nodosa seedlings, using a field experiment along a natural-low pH gradient created by submarine vents in Vulcano Island, Italy. After four months of exposure, seedlings under increased pCO2 showed a reduction in the viability but a higher development exhibiting a lower C leaf content, independently of their origin. Results indicate compensating responses which may favour the plant acclimation in early life stages to future acidification scenarios.

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Isotocin receptor-adenylyl cyclase signaling mediates pH compensation in marine fish exposed to CO2-induced acidification

Published 4 August 2026 Science Closed
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Marine fish survival is threatened by ocean acidification, but the hormonal mechanisms for pH compensation are not well understood, limiting mechanistic understanding of stress responses in marine fish. We examined isotocin signaling in marine medaka (Oryzias melastigma) exposed to year-2100 ocean acidification conditions (Pco2 ∼0.14 kPa, pH 7.6). Our analysis demonstrated that isotocin receptor b (ITRb) was selectively upregulated at 6 h postexposure in adult gills, though it showed only a nonsignificant trend at 5 days postfertilization (dpf) embryos, whereas adenylyl cyclase 5 (ADCY5) showed hypercapnia responsiveness primarily at hatching. Using immunofluorescence and confocal microscopy, we found that both ITRb and ADCY5 proteins localize to the basolateral membrane of Na+-K+-ATPase-positive ionocytes, partially separated from apical H+-secretion machinery. Knockdown experiments showed that ITRb-ADCY5 coupling is crucial for pH compensation, with individual knockdown moderately reducing H+ secretion and combined knockdown causing severe impairment (>70% reduction) and decreasing transcription of acid-secretion genes (nhe3, ca2, and rhcgb) by 44%–60%. Paradoxically, double knockdown triggered a twofold cAMP increase that failed to restore function, whereas wild-type embryos maintained stable cAMP levels across pH conditions, consistent with the hypothesis that ITRb-ADCY5 coupling may organize cAMP production within specific basolateral microdomains, though direct subcellular imaging would be required to validate this compartmentalization model. The developmental asynchrony between ITRb (5 dpf) and ADCY5 (hatching) responses indicates life-stage-specific vulnerabilities. Our findings reveal that basolateral ITRb-ADCY5 coupling represents a critical control point for pH compensation capacity.

NEW & NOTEWORTHY Isotocin signaling, through ITRb-ADCY5 coupling, enables marine fish to compensate for ocean acidification via compartmentalized rather than global cAMP production. Paradoxically, disrupting this pathway doubles cAMP levels yet abolishes H+ secretion, revealing that signal localization determines function. The developmental asynchrony between ITRb and ADCY5 responses suggests that pH-stress vulnerabilities are specific to each life stage and require further investigation.

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Ocean acidification alters phytoplankton diversity and community structure in the coastal water of the East China Sea

Published 4 August 2026 Science Closed
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Anthropogenic CO2 emissions and their continuous dissolution into seawater lead to seawater pCO2 rise and ocean acidification (OA). Phytoplankton groups are known to be differentially affected by carbonate chemistry changes associated with OA in different regions of contrasting physical and chemical features. To explore responses of phytoplankton to OA in the Chinese coastal waters, we conducted a mesocosm experiment in a eutrophic bay of the southern East China Sea under ambient (410 µatm, AC) and elevated (1000 µatm, HC) pCO2 levels. The HC condition stimulated phytoplankton growth and primary production during the initial nutrient-replete stage, while the community diversity and evenness in both pCO2 treatments were reduced during this stage due to the rapid nutrient consumption and diatom blooms, and the subsequent shift from diatoms to hetero-dinoflagellates led to a decline in primary production during the mid and later phases under nutrient depletion. HC treatment suppressed the diatom-to-dinoflagellate succession and enhanced the subsequent remineralization of organic matter, thereby facilitating smaller phytoplankton to dominant and sustaining primary production. Our findings indicate that, the impacts of OA on phytoplankton diversity in the coastal water of the southern East China Sea depend on availability of nutrients, with primary productivity and biodiversity of phytoplankton reduced in the eutrophicated coastal water.

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Seasonal variations in the bulk density of planktic foraminiferal tests in response to oceanographic changes in the western North Pacific

Published 3 August 2026 Science Closed
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Ocean acidification (OA) is a major component of ongoing global environmental change, yet its biological impacts on open-ocean calcifiers remain insufficiently quantified. Here, we investigate seasonal variability in the individual test density of the planktic foraminifer Globigerina bulloides in the western North Pacific. Test density was determined using high-resolution microfocus X-ray computed tomography, enabling micron-scale structural assessment. Time-series samples collected by sediment traps moored at 150 m and 540 m at station K2 (2008–2009) reveal pronounced seasonal variability, with test density reduced by ~ 20% during winter relative to other seasons. Seasonal reductions were associated with enhanced vertical mixing and positively correlated with mixed-layer pH, carbonate-ion concentration, and temperature. Additional plankton-tow samples collected between 2010 and 2016 further support a strong linkage between carbonate chemistry and calcification intensity. Multiple regression analysis shows that carbonate-ion concentration independently explains 46.6% of the variance in test density, whereas temperature accounts for only 0.25%, indicating that carbonate-ion availability exerts a dominant control on test density. Given the ongoing decline in carbonate-ion concentration in the North Pacific (~ 0.77 µmol kg−1 yr−1), our results imply an annual decrease of ~ 2 µg mm−3 in foraminiferal test density. Continued OA may therefore reduce biogenic CaCO3 shell density, potentially weakening the efficiency of the carbonate-based biological carbon pump. This study provides quantitative field-based evidence linking seasonal carbonate chemistry to shell density variability in open-ocean calcifiers.

Continue reading ‘Seasonal variations in the bulk density of planktic foraminiferal tests in response to oceanographic changes in the western North Pacific’

Effect of warming and acidification on polar lipid fatty acid composition in juvenile European sea bass (Dicentrarchus labrax)

Published 31 July 2026 Science Closed
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The present study experimentally investigates how temperature and acidification affect the polar lipid fatty acid (FA) composition of European sea bass (Dicentrarchus labrax) juveniles. Fish were reared for 92 days and fed ad libitum under four conditions: a control (CT; with natural fluctuating temperature and pH); a warming (WT, +4°C above control, and control pH), an acidification (AT, control temperature and −0.4 pH units below the control), and a combined warming and acidification treatment (WAT, +4°C and −0.4 pH units relative to the control). Results showed that warm treatments (WT and WAT) increased final weight and length similarly, whether or not combined with acidification, and that acidification alone (AT) had no effect on these variables. Polar lipid FA profiles of muscle and brain were only mildly impacted by temperature and not by acidification. Overall, the results suggest that European sea bass, under unrestricted quantity of food is able to maintain a very stable polar lipid FA composition. However, complementary studies with individuals under different feeding regimes or from wild populations subject to natural dietary variability are needed.

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The responding mechanisms of Nannochloropsis oceanica to high CO2 and the regulating functions of H+-PPase

Published 31 July 2026 Science Closed
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Highlights

  • Cytoplasmic pH homeostasis was critical for N. oceanica to tolerate 5% CO2.
  • The tolerant mechanisms involved multiple physiological-biochemical processes.
  • H+-PPase was the central regulator for alleviating cytoplasmic acidification.
  • avp1 overexpression improved cytoplasmic pH regulation by raising H+-PPase activity.

Abstract

High CO2 tolerance microalgae screen/breeding shows the urgent research priority when applying microalgae for flue gas CO2 sequestration. In this study, we chose the important resource microalgae Nannochloropsis oceanica as the target organism, the regulatory mechanisms of N. oceanica were elucidated under 5% and 20% high CO2 conditions, and the function of key regulating gene avp1 encoding H+-PPase was further explored. The results showed N. oceanica was tolerant to the 5% CO2 that maintained intracellular pH homeostasis, while severe cytoplasmic acidification was occurred under the 20% CO2 condition. Integrated physiological, biochemical, and transcriptomic analysis revealed that P-ATPase and H+-PPase activities were enhanced at 4 h and 4 d under the 5% CO2 condition, respectively. Concurrently, the reprogramming of organic acid metabolism and maintenance cellular energy supply additionally mitigated intracellular acidification. Further functional validation showed that overexpression of avp1 enhanced H+-PPase activity, increased cytoplasmic pH values, promoted pigments accumulation and growth of N. oceanica under the high CO2 condition. Therefore, this study clarified the working mode of N. oceanica to tolerant high CO2 and cytoplasmic acidification, and firstly timely proved the function of avp1, provided important data basis and gene candidates for the research of applying microalgae to CO2 sequestration.

Continue reading ‘The responding mechanisms of Nannochloropsis oceanica to high CO2 and the regulating functions of H+-PPase’

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