Posts Tagged 'laboratory'

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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.

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
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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.

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

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.

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

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.

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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.

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The effects of high carbonate alkalinity under low salinity on the survival, physiological metabolism, and redox homeostasis of Crassostrea hongkongensis

Published 28 July 2026 Science Closed
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High carbonate alkalinity can impose composite hydrochemical stress on bivalves by altering inorganic carbon speciation, buffering capacity and ion-exchange conditions. The Hong Kong oyster (Crassostrea hongkongensis) naturally inhabits estuarine areas where low salinity can occur together with carbonate-system disturbance, yet its physiological response to high carbonate alkalinity under a low-salinity background remains unclear. In this study, oysters were exposed at salinity 5 to a Control treatment, A10 (carbonate alkalinity 10 mmol L⁻¹) and A20 (carbonate alkalinity 20 mmol L⁻¹). Salinity was treated as a controlled background condition, whereas the alkalinity treatments represented a composite carbonate-alkalinity perturbation involving alkalinity, pH and carbonate chemistry. Survival, feeding rate, oxygen consumption, ammonia excretion and hemolymph ammonia were measured across Control, A10 and A20. Hemolymph catalase (CAT), glutathione peroxidase (GSH-Px), glucose and ATP were analyzed as A10 and A20 time-course endpoints because a parallel Control was not included for these assays. A 24-h mantle transcriptome was used to screen candidate transcripts associated with innate defense and glutathione metabolism. Oysters under A10 retained partial compensatory capacity, whereas A20 significantly reduced survival. A10 and A20 suppressed early oxygen consumption and ammonia excretion, and altered feeding allocation among microalgae. Within the A10 and A20 biochemical time-course dataset, CAT, GSH-Px, glucose and ATP showed stage-specific variation, suggesting redox and energy-metabolism adjustment under alkalinity stress. Overall, high carbonate alkalinity reduced survival and was associated with metabolic depression, feeding compensation and hemolymph redox-energy remodeling in C. hongkongensis. This study will provide a theoretical basis for water quality regulation in saline-alkaline water aquaculture and the sustainable development of aquaculture.

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Warming and acidification alter essential fatty acid profiles in marine diatom Skeletonema marinoi

Published 28 July 2026 Science Closed
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Marine diatoms are key components of the planetary ocean, playing crucial roles in trophic networks: fixing carbon, producing fatty acids (FA) that cannot be synthesized de novo by higher trophic organisms. To better comprehend how the combined action of climatic change influences the dietary value and the impacts on the upper trophic levels, we used a 2 × 2 factorial experiment to investigate how the FA profiles of Skeletonema marinoi changed in response to the individual and combined effects of warming (7, 19°C) and acidification (400, 1 000 ppm CO2). Three S. marinoi strains were exposed for ~ 40 weeks to ambient conditions, warming, acidification and their combination and analyzed for FA profiles, focusing on polyunsaturated (PUFA), omega-3 and omega-6 FA. We found that omega-3 FA increased under warming exposure, while acidification alone led to lower omega-3/omega-6 ratios. In contrast, the ratios increased under warming, alone or coupled with acidification, in all three strains, indicating better food quality for higher trophic levels. Our results suggest the long-term exposure to both drivers will help the marine diatoms to acclimatize to their combined effects, allowing them to buffer the changes brought by warming and ocean acidification.

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pH–salinity-driven regulation in carbon utilization kinetics of the intertidal seagrass Zostera japonica along China’s coastline

Published 27 July 2026 Science Closed
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Highlights

  • We innovatively define two biophysical parameters (pH change rate and acceleration) of Zostera japonica photosynthesis.
  • pH change acceleration is sensitive to the regulation of carbon utilization pathways during Z. japonica photosynthesis.
  • A progressive pH–salinity-driven regulation mode of carbon utilization pathways in Z. japonica photosynthesis is summarized.
  • The impact of ocean acidification and alkalization on seagrass is characterized from a new biophysical standpoint.

Abstract

Seagrass carbon concentration mechanisms are modulated by seawater pH and salinity, yet their progressive regulation in photosynthetic inorganic carbon utilization pathways remain poorly characterized. This study novelly mathematically characterized first-order (pH change rate) and second-order (pH change acceleration) derivatives from pH-drift experiments in the intertidal seagrass Zostera japonica along China’s coastline. The pH change-based method effectively highlights the dissolved inorganic carbon (DIC) utilization and biomass accumulation of seagrass, while pH change acceleration is sensitive to the progressive switch of DIC utilization pathways during Z. japonica photosynthesis. As pH increases, six significant regulations emerge that have ecophysiological significance: a. primary regulation via reaching the CO2 compensation point; b. extracellular carbonic anhydrase (exCA) activity dropping to negligible levels; c. diminished efficiency of proton pump-mediated extracellular acidification in supplying CO2; d. regulation via reaching the bicarbonate saturation point; e. regulation via reaching the bicarbonate compensation point; and f. regulation via enhanced respiratory CO2 into seawater temporarily stimulating photosynthesis as a feedback. We summarize a progressive and universal pH–salinity-driven regulation mode reflecting different combinations of DIC utilization pathways and their respective intensities. Specifically, seawater pH modulates the mode’s fluctuating thresholds, while salinity governs the amplitude. Unexpectedly, elevated salinity serves as an effective stimulant for Z. japonica to maintain strong DIC utilization intensity in high pH (> 9.1) environments. Ocean acidification could increase pH change acceleration by 166%, enhancing carbon fixation, whereas artificial ocean alkalinity enhancement (Ca(OH)2 supplementation and olivine-seawater weathering) could reduce it by 165% and 105%, respectively, risking mortality of Z. japonica. Additionally, the salinity-dependent braking point (where acceleration drops to zero) serves as a critical threshold for seagrass photosynthesis and a new factor for transplantation-based restoration.

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Response of Zostera japonica rhizosphere bacteria to ocean acidification

Published 24 July 2026 Science Closed
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Abstract

Amidst global climate change, the escalating atmospheric CO2 levels have intensified ocean acidification (OA), significantly impacting the structure and function of marine ecosystems. Seagrass beds, representative nearshore ecosystems, play a pivotal role in carbon sequestration, biodiversity preservation, and nearshore environmental equilibrium. Rhizosphere microorganisms within seagrass beds, essential components of the ecosystem, drive material cycling and energy flow. Their community structure and functions demonstrate heightened sensitivity to environmental variations. While previous studies have primarily focused on the effects of ocean acidification on seagrass hosts, limited attention has been given to the rhizosphere. Therefore, this study selected Zostera japonica as the focal species and systematically evaluated changes in the structure and function of the rhizosphere bacterial community across varying acidification levels (400 ppm, 1,000 ppm, 2,000 ppm CO2) within an ocean acidification context. The results revealed a significant decline in the richness and diversity of the rhizosphere bacterial community under acidification, accompanied by shifts in community composition characterized by an increase in the relative abundance of Bacteroidota and Tenacibaculum with escalating acidification levels. In high acidification conditions, bacterial network interactions exhibited a trend toward simplification; yet the number of key taxonomic units increases, and there was a shift in community assembly from stochastic to deterministic processes. Functional predictions indicated the enhancement of microbial carbon sequestration and nitrogen fixation under acidification, while denitrification and specific sulfur metabolism pathways were inhibited. This implies that in acidified environments, the rhizosphere bacterial community may enhance carbon and nitrogen fixation to uphold nutrient supply.

Importance

Against the background of escalating global climate change and ocean acidification, seagrass beds, as crucial blue carbon sink ecosystems, face formidable challenges to their ecological functions and stability. Rhizosphere microorganisms of seagrasses, serving as the “second genome” of the seagrass host, play a central role in material cycling, nutrient supply, and system stability within seagrass beds. They are a key biological component that supports seagrass adaptation to environmental changes. Therefore, investigating the response and adaptation mechanisms of seagrass rhizosphere bacterial communities under ocean acidification is essential for deepening our understanding of the stability and resilience of seagrass bed ecosystems.

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Water mass-driven variations in primary production and bacterial respiration during the spring bloom in the Fram Strait

Published 23 July 2026 Science Closed
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Highlights

  • Remote sensing indicates declining bloom in cold and developing bloom in warm water
  • Primary production peaks in polar and arctic surface water masses
  • Bacterial production is coupled to primary production despite thermal sensitivity
  • Oxygen-based community respiration is highest in warmer water masses
  • Oxygen-based and INT-based respiration estimates differ by an order of magnitude

Abstract

The Fram Strait is the primary oceanic gateway to the Arctic Ocean and has highly dynamic oceanographic conditions. Oceanographic conditions can shape community compositions, which is increasingly shown using molecular studies, but rate measurements remain scarce, especially for respiration in the Arctic Ocean. Here, we assessed primary production (PP), bacterial production (BP), bacterial abundances (BA), and community respiration (CR) using Winkler titrations and in vivo Iodo-Nitro-Tetrazolium (INT) reduction within the upper 50 m across water masses of the Fram Strait that had varying bloom conditions in spring 2021. We complemented in situ observations with remote sensing of sea surface temperature (SST) and chlorophyll-a (SSC) to infer bloom phenology in warm (θ>2°C), intermediate (2>θ>0°C), and cold (θ<0°C) waters using remote sensing machine-learning. In the cold, nutrient-rich surface waters, a subsiding spring bloom was associated with elevated PP, BP, and BA alongside a high temperature sensitivity (Q10) that indicates active microbial turnover. In contrast, the warm Atlantic-influenced waters exhibit a relatively lower PP but moderate cell-specific BP, suggesting bacterial maintenance metabolism under pre-bloom conditions. Notably, bacterial respiration (BR) estimates differed by 5- to 80-fold between the Winkler and in vivo INT methods. Although the true BR likely lies between these estimates, our results highlight the substantial microbial activity and underscore the need for more accurate BR measurements in Arctic studies.

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Changes in photosynthesis and grazing facilitate growth of a mixotrophic protist under ocean acidification and warming

Published 22 July 2026 Science Closed
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Summary

  • Mixotrophic protists capable of both photosynthesis and phagotrophy are key members of marine plankton communities. Yet, little is known about their responses to the combination of ocean acidification and warming.
  • A marine mixotrophic chrysophyte, Ochromonas CCMP2951, was subjected to two levels of pCO2 (300 and 800 ppm, resulting in pH of 8.2 and 7.8) and temperature (21°C and 26°C) in a factorial design.
  • Enhanced growth rates were observed in both the high CO2 and high temperature treatments, while cell size significantly decreased with temperature. Strongly decreased cellular phosphorus content led to increased N : P and C : P ratios of Ochromonas with temperature. Furthermore, warming increased grazing rates, while elevated CO2 reduced the Chl content but increased photosynthetic carbon acquisition, albeit only at low temperature. The combination of warming and elevated CO2 had antagonistic effects on the balance between autotrophic and heterotrophic carbon acquisition, keeping the net role of this mixotroph in the marine carbon cycle stable.
  • Altogether, both the direct stimulation of growth and the indirect effects of altered stoichiometry may favor mixotrophs under future ocean conditions. However, their contribution to future carbon cycling in complex natural communities will need further study.

Graphical Abstract

Grazing rates of Ochromonas CCMP2951 expressed as carbon obtained per mean cell volume (a) and Caut/het-photosynthetically fixed carbon divided by carbon obtained through grazing (b) in the four experimental treatments.

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Fish trait-based indicators of mercury bioaccumulation under natural ocean acidification: insights from a mediterranean CO₂ vent system

Published 22 July 2026 Science Closed
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Highlights

  • Low pH conditions at CO₂ vents increase THg bioavailability and fish exposure.
  • Functional traits explain THg patterns better than species identity.
  • Under low pH, less-mobile benthic fish accumulate more THg than highly-mobile fish.
  • Trophic position drives stronger THg biomagnification at low pH sites.

Abstract

Ocean acidification is not an isolated climate-related threat to marine organisms, as it may act in combination with other stressors such as trace element contamination. Here, we took advantage of naturally acidified conditions and mercury spill-out from the shallow CO2 vent of Vulcano Island (Italy) to test whether fish functional traits explain contaminant dynamics better than species identity under ocean acidification scenarios. Specifically, we investigated if trophic group and mobility influence total mercury (THg) bioaccumulation and trophic transfer in fish inhabiting Cymodocea nodosa seagrass meadows under low and ambient pH conditions. Low-mobility benthic fish, mainly represented by invertebrate feeders and small piscivores, exhibited higher THg concentration at the vent site than at reference sites, while highly mobile zooplanktivorous fish showed no significant differences, highlighting the importance of fish mobility and local trophic benthic pathways in shaping contaminant exposure and bioaccumulation. Moreover, the relationship between trophic position and THg concentration in fish was stronger in the low pH site, indicating enhanced trophic transfer and biomagnification when Hg availability is higher. In contrast, weak or absent biomagnification in the reference sites suggests that Hg transfer depends more on contaminant availability and food web structure than trophic position alone. Overall, these findings indicate that functional traits better predict Hg bioaccumulation patterns than species identity, supporting trait-based approach to assess contaminant dynamics in future ocean acidification scenarios.

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The molecular footprint of global change in Antarctic coral

Published 21 July 2026 Science Closed
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Anthropogenic CO2 emissions are altering marine ecosystems through two interconnected processes: climate change and ocean acidification, both of which are particularly affecting the Southern Ocean. However, the molecular responses of cold-water corals to these stressors remain poorly understood. In this study, we investigated the transcriptomic response of the Antarctic coral Malacobelemnon daytoni exposed to ocean acidification (pH ~7.7; LpH) and elevated temperatures (+2°C and +4°C above ambient; T1 and T2, respectively) under controlled laboratory conditions. Using high-throughput RNA sequencing (RNA-Seq), we compared gene expression profiles across six treatments, including a control (pH ~8.1, CpH; 0–1°C; CT), acidification, warming, and their combinations. Principal component analysis revealed treatment-specific clustering and greater transcriptomic dispersion under LpH conditions. Differential expression analysis identified between 475 and 767 differentially expressed genes (DEGs), with the strongest transcriptional responses observed under combined stress conditions (LpH + T1 and LpH + T2). Combined exposure to ocean acidification and warming elicited the largest gene expression response, suggesting enhanced, potentially non-additive effects of multiple stressors. Functional enrichment analyses revealed differential regulation of genes associated with protein folding, signal transduction, energy metabolism, oxidative stress, and regulation of cell death. Our findings demonstrate that Malacobelemnon daytoni exhibits complex, treatment-dependent gene expression responses to environmental stressors. These results highlight the capacity of this Antarctic octocoral to mount molecular responses to projected future ocean conditions while also emphasizing its potential vulnerability to the interacting effects of ocean warming and acidification.

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Coral carbonate pH records show localized stability within Philippine waters

Published 20 July 2026 Science Closed
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The process of decreasing seawater pH due to increasing atmospheric carbon dioxide known as ocean acidification is a global phenomenon with very strong regional effects. We report the first seasonal and interannual carbonate chemistry variabilities in the Philippines determined using carbonate boron systematics. Coral δ11B-pHsw from two contrasting site conditions showed more positive trends than basin-wide averages, suggesting that reef waters around the Philippines represented by these sites may be offsetting the general pH decline in global seawater. This pattern is consistent with δ11B-pHsw studies in neighboring Palau and Taiwan and can be explained by decreases in net ecosystem calcification and/or increases in net ecosystem productivity. Other potential site-specific local drivers of δ11B-pHsw changes include vent-driven input of nutrient- and CO2-rich groundwater that alters seawater dissolved inorganic carbon (DIC). The El Niño Southern Oscillation that influences water mass movement along the Philippine Pacific seaboard, and seasonal zonal current reversal in the Verde Island Passage (VIP) that switches source waters within the VIP, may also contribute to the recorded changes in δ11B-pHsw. Differences between the coral internal fluid chemistry and modelled regional seawater pH trends highlight the importance of localized monitoring of acidification for accurate management strategies of reef habitats.

Continue reading ‘Coral carbonate pH records show localized stability within Philippine waters’

The effects of decreased pH and increased temperature on survival and shell development of the larvae of the endemic Hawaiian oyster Dendostrea sandvichensis

Published 17 July 2026 Science Closed
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Climate change models predict future ocean-wide decreases in pH and increases in temperature, posing a serious threat to calcifying marine invertebrates. In Hawaiʻi, local seawater temperature and pH are predicted to change even more rapidly. The Hawaiian oyster Dendostrea sandvichensis, an endemic species, remains understudied despite its ecological roles in reef- building, biofiltration, and as a food source. While previous studies have revealed the alarming impacts of ocean acidification and warming on bivalves, little is known about how the planktonic larvae of D. sandvichensis will respond to projected climate conditions.

To investigate these effects, the larvae of D. Sandvichensis were reared under present-day conditions in Pearl Harbor, HI (pH 8.1, 26.5 °C) and projected future conditions (pH 7.7, 30.0°C) for one week. Shell growth, density, and degradation were then measured using micro-CT, confocal, and scanning electron microscopy. Additionally, two larval husbandry methods were evaluated, with a static-flow system paired with UV water treatment yielding approximately 11- fold higher survival than an open-flow system. Elevated temperature reduced larval survival (~67%) compared to ambient conditions. Reduced pH significantly decreased shell length (~11.8μm), while both stressors reduced shell density in Experiment 3. Shell density decreased by ~12% under elevated temperature, ~18% under reduced pH, and ~43% under the combined stressors, and was accompanied by increased shell degradation and abnormalities.

These findings indicate that elevated temperature and reduced pH impact larval oysters through multiple pathways, including reduced survival and compromised shell integrity. This study provides new insights into the vulnerability of an endemic Hawaiian species and essential data for predicting its resilience under future climate change scenarios.

Continue reading ‘The effects of decreased pH and increased temperature on survival and shell development of the larvae of the endemic Hawaiian oyster Dendostrea sandvichensis’

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