Posts Tagged 'physiology'

Seawater acidification accelerates growth but hastens decline in batch cultures of the marine diatom Thalassiosira pseudonana

Published 22 April 2026 Science Leave a Comment
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Diatoms are characterized by rapid cell division and a high capacity to adapt to environmental variability, and some species can form blooms when environmental conditions are favorable. Previous studies have largely focused on the bloom development phase, during which biomass accumulates rapidly, whereas the decline phase-despite its critical role in carbon export and microbial loop dynamics-has received far less attention. Here, we tracked changes in cell density and inorganic carbon utilization characteristics throughout the entire course of a simulated Thalassiosira pseudonana bloom under ambient (420 μatm) and elevated pCO2 (1000 μatm) conditions. Inhibitors of carbonic anhydrase and direct bicarbonate transporters were applied to investigate the characteristics of inorganic carbon utilization. The relationship between photosynthetic rate and inorganic carbon concentration was measured to assess inorganic carbon affinity. The simulated T. pseudonana bloom was characterized by rapid cell density accumulation, reaching a peak within 10 days, followed by a rapid decline without a distinct stationary phase. As the bloom progressed, photosynthetic rate and the maximum quantum yield of photosystem II declined, whereas the inorganic carbon affinity increased. Elevated CO2 enhanced growth and maximum quantum yield during the acceleration phase but resulted in an 86% higher fitted death rate during the decline phase. Regarding the relationship between photosynthetic rate and dissolved inorganic carbon concentration, elevated CO2 increased the maximum photosynthetic rate and half-saturation constant only during the acceleration phase. Collectively, these results indicate that seawater acidification can influence both biomass accumulation and decline intensity in diatom blooms, with potential consequences for carbon sequestration and its redistribution among biogeochemical pools.

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Ocean acidification induces neuronal hyperexcitation and anxiety-like behaviour in marine medaka via ASIC activation

Published 21 April 2026 Science Leave a Comment
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Ocean acidification presents a significant threat to marine life, yet its neurobiological mechanisms remain poorly understood. This study examined how acid-sensing ion channels (ASICs) mediate neuronal excitability and anxiety-like behaviour in marine medaka (Oryzias melastigma) under elevated CO2 concentrations (1000 and 1900 ppm). Transcriptomics revealed early upregulation of asic1a (4 days), while RT-qPCR demonstrated increased asic1a, asic1b, asic2 and asic4a (7 days), with only asic1a sustained at 30 days. Immunofluorescence confirmed heightened Asic2 in emotion-processing brain regions following acidification. Transmission electron microscopy unveiled distinct ultrastructural alterations: widened synaptic clefts, thinned postsynaptic densities, and decreased mitochondrial aspect ratios. Mitochondrial membrane potential assays revealed a reduction in membrane potential in response to acidification. Electrophysiological recordings showed increased neuronal firing count in the dorsolateral telencephalon under acidification, behavioural assessments revealed significant anxiety-like phenotypes, effects that were fully rescued by ASIC inhibition. These results indicated that temporal specificity in ASIC subtype expression in acidification response. The interplay of synaptic and mitochondrial dysfunction, neuronal hyperexcitability, and behavioural alterations suggested acidification impaired both synaptic transmission efficiency and mitochondrial function, destabilizing neural circuits. This study systematically elucidates the neurotoxic effects of ocean acidification on marine fish, providing critical scientific evidence for predicting the ecological impacts of climate change on marine organisms.

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Nonlinear responses of phytoplankton size, diversity, and chlorophyll a to environmental forcing along the Yellow Sea

Published 20 April 2026 Science Leave a Comment
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Highlights

  • Miniaturization coincides with reduced species diversity and elevated chlorophyll a.
  • Declining pH and reduced dissolved inorganic nitrogen are key drivers for smaller cells.
  • Salinity, dissolved oxygen and cooling jointly reshape phytoplankton community structure.

Abstract

Phytoplankton are tiny drifting photosynthetic organisms that support marine food webs and help control the global carbon cycle. However, it remains unclear how ongoing environmental changes are altering their cell size, species diversity, and chlorophyll a concentration in coastal seas. In this study, we investigated changes in phytoplankton cell size, species diversity, and chlorophyll a concentration along the Yellow Sea coast of China from 2021 to 2024, based on fourteen research cruises conducted at twenty-six coastal stations. We then employed statistical models to explore how individual and combined environmental factors were related to those biological features. We observed a clear shift to predominance of smaller cells, a reduction in species diversity, and an increase in chlorophyll a concentration. pH and reduced dissolved inorganic nitrogen were strongly associated with smaller cell size, while higher salinity and higher oxygen were associated with lower diversity. Lower surface water temperature and higher dissolved oxygen were associated with higher chlorophyll a concentrations. Overall, our findings suggest that interacting changes in pH, nutrient supply, temperature, salinity, and oxygen are associated with a simpler phytoplankton community structure, smaller mean cell size, and higher biomass levels in the Yellow Sea coastal region, with potential consequences for local food webs and carbon cycling.

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Coexpression among eastern oyster host and microbiome genes suggests coordinated regulation of calcifying fluid chemistry

Published 13 April 2026 Science Leave a Comment
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Significance

Oysters and many marine animals build shells by controlling the chemistry of extracellular fluids where minerals form, yet whether microbes in these fluids influence calcification remains unclear. We show that oysters maintain favorable conditions for mineral formation by regulating the carbonate chemistry of the shell-forming fluid, and that resident microbes respond to these changes by expressing nitrogen- and sulfur-cycling genes capable of altering pH, alkalinity, and carbonate availability. Many of these microbial transcripts were tightly correlated with oyster immune and signaling genes, suggesting that host and microbiome processes may be linked within the calcifying environment. These findings point to a host–microbiome interaction in the regulation of calcifying-fluid chemistry that directly links microbial activity to the carbonate chemistry underlying biomineralization.

Abstract

Marine animals that build shells, such as oysters, carefully regulate the chemistry of their internal calcifying fluids, but the molecular mechanisms behind this control, as well as whether microbes play a role in calcification, are poorly understood. To better understand oysters’ molecular mechanisms and the role of their calcifying-fluid microbes, we conducted experiments that simulated a tidal cycle, measured calcifying fluid pH and total dissolved inorganic carbon, and characterized host and microbial gene expression via transcriptomics. These experiments showed that calcifying fluid pH remained relatively stable throughout tidal pH fluctuations, with corresponding increases in oyster transcripts for ion transport and acid–base regulation. These data provide direct evidence that tidal fluctuations drive rapid changes in oyster calcifying fluid chemistry. Most surprisingly, increases in microbial transcripts related to nitrogen and sulfur cycling correlated to higher calcifying fluid DIC, and coexpression network analysis revealed patterns of gene expression that linked oyster immune and neural pathways to microbial redox processes, providing molecular evidence of potential host modulation of microbial metabolism. Together, these results reveal that oysters actively regulate their calcifying fluid pH over short timescales, and the endemic microbiome metabolic responses can yield metabolites that influence calcifying fluid pH, alkalinity, and ultimately calcification. These data offer a perspective on oyster physiological capacity and, most importantly, the potential role of microbes in oyster calcification. In light of ongoing changes in ocean pH and temperature, oysters provide a model for studying animal–microbial responses to environmental acidification and how their interactions may shape biomineralization.

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Unravelling marine benthic functioning shifts under ocean acidification

Published 10 April 2026 Science Leave a Comment
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Ocean acidification (OA) driven by increasing atmospheric CO2 is altering marine biodiversity. However, impacts of OA on ecosystem functioning at the community level, including calcification, primary production and nutrient uptake, remain largely unknown. Here, we conducted community transplant experiments at natural CO2 vents to assess how declining pH affects marine community species composition, biomass, and key ecosystem processes over time. Our results indicate that community shifts caused by declining pH lead to decreased biomass and calcification rates, while photosynthesis and nutrient uptake rates increased. By leveraging OA field model systems and in situ measurements of ecosystem functioning, this study provides critical insights into how OA-induced biodiversity loss reshapes the structure and functioning of temperate marine coastal ecosystems.

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Intracellular acid-base regulation mediates a trade-off between shell and somatic growth in a clam under ocean acidification

Published 9 April 2026 Science Closed
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Highlights

  • Clams actively regulate intracellular pH against ocean acidification via CAc
  • RNAi confirms CAc’s essential role in H+ efflux, measured by in vivo SIET.
  • A CAc-sAC-NKA network forms a conserved regulatory pathway for acid-base balance.
  • DEB model shows this pH defense sustains shell linear growth despite metabolic costs.

SUMMARY

Ocean acidification (OA) is predicted to threaten marine bivalves, casting them as passive victims of changing carbonate chemistry. Contributing to a revised understanding, we identified a conserved mechanism for acid-base regulation that supports intracellular resilience. Using the Manila clam Ruditapes philippinarum as a model, this study demonstrated that intracellular pH (pHi) homeostasis under elevated pCO2 was maintained through cytosolic carbonic anhydrase (CAc)-mediated H+ efflux. A causal link was established by combining in vivo scanning ion-selective electrode technique (SIET) with RNA interference (RNAi), where RpCAc knockdown suppressed H+ efflux and compromised pHi. A coordinated regulatory network involving CAc, soluble adenylyl cyclase (sAC), and Na+/K+-ATPase (NKA) was synergistically upregulated, suggesting an evolved adaptive pathway. Dynamic Energy Budget (DEB) modeling, calibrated with experimental data, revealed that this cellular compensation carries a high energetic cost, leading to a significant reallocation of resources: shell growth was maintained, but somatic growth was severely suppressed. These results elucidate a conserved cytoprotective mechanism that enables short-term tolerance of OA at a substantial somatic cost, redefining resilience to include energetic trade-offs.

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Climate-driven restructuring of phytoplankton productivity and community composition in the south-eastern Black Sea: insights from seasonal CO2-temperature manipulation experiments

Published 9 April 2026 Science Closed
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Semi-enclosed marine systems with low buffering capacity, such as the Black Sea, are expected to experience amplified impacts of ocean acidification and warming, yet experimental evidence on their combined short-term effects on natural phytoplankton assemblages remains limited. Here, we present a seasonally resolved one-year study (four experiments conducted between 2022 and 2023) based on 48 h short-term microcosm incubation experiments using natural phytoplankton communities collected from coastal and offshore stations in the south-eastern Black Sea. CO2 concentrations (360, 600, and 760 ppm) and temperature (ambient and +3 °C) were manipulated to examine short-term physiological and compositional responses under projected climate scenarios. We hypothesised that CO2 and warming would exert both independent and interactive effects on short-term particulate organic carbon production (14C uptake rates) and relative community composition, with responses varying seasonally and being most pronounced during summer stratification.

Short-term particulate primary production increased by ∼22% and ∼36% at 600 and 760 ppm CO2, respectively (p<0.05), while warming provided an additional 14–22% enhancement depending on season, with significant CO2 × temperature interaction terms detected for total production (two-way ANOVA, p<0.05), indicating synergistic CO2–temperature effects. Warming and moderate CO2 enrichment were associated with increased relative contributions of nano- and picophytoplankton (by ∼6–10%), whereas high CO2 reduced the warming-driven shift toward smaller cells by maintaining microphytoplankton contributions ∼10–15% higher than in the warming-only treatment. Carbonate chemistry responded strongly to CO2 manipulation, with pH declining from in-situ values of 8.09–8.21 to 7.06–7.52 during incubations and minor reductions in total alkalinity, reflecting the weak buffering capacity of the system. Pigment composition and microscopy indicated short-term increases in dinoflagellate relative abundance (∼12–18%) and concurrent declines in diatom markers, accompanied by accelerated nitrate depletion and reduced nitrogen-to-phosphorus (N:P) ratios, consistent with enhanced nitrogen limitation.

Overall, these findings demonstrate pronounced short-term sensitivity of natural phytoplankton assemblages in the south-eastern Black Sea to combined CO2 and warming under controlled incubation conditions. Because these results derive from 48 h microcosm experiments, they represent short-term physiological and compositional responses rather than direct evidence of long-term ecosystem restructuring, yet the observed patterns suggest potential implications for trophic efficiency, harmful algal bloom development, and carbon cycling in this low-buffer, stratified basin under future climate forcing.

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Investigation of the adaptive mechanisms to ocean acidification in Patella species from CO2 vent systems of the Mediterranean Sea

Published 7 April 2026 Science Closed
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The continuous increase in anthropogenic carbon dioxide (CO2) emissions into the atmosphere is one of the main factors contributing to ocean acidification (OA). In fact, CO2 is partially absorbed by the oceans, where it alters carbonate chemistry and seawater pH, which is expected to decrease from the current level of 8.1 to 7.7 by 2100. OA exerts harmful impacts primarily on calcifying organisms, as it affects the availability of carbonates, which makes their calcareous structures thinner and more fragile. Moreover, several studies have described the detrimental effects of OA across many marine taxa, affecting important physiological and metabolic mechanisms. On the other hand, research conducted at CO2 vent systems, which are volcanic naturally acidified sites, showed that several organisms can survive under acidified conditions through specific tolerance and/or adaptive strategies. Among these organisms, the gastropod Patella spp. is one of the few calcifiers capable of inhabiting naturally acidified sites, such as the Castello Aragonese vent systems at Ischia Island and the San Giorgio vent systems at Sicily Island. Nonetheless, the complex mechanisms that allow survival and potential adaptation of these organisms to natural OA conditions need to be understood. Therefore, this PhD study aimed at investigating the potential molecular, physiological, metabolic, genetic, and epigenetic mechanisms that enable these organisms to tolerate and survive under OA conditions through a stepwise approach. Specifically, this PhD research attempted to answer the following questions: • Does OA entail a stressful condition in resident populations of Patella spp. living at reduced pH conditions, thereby affecting their overall well-being and health status? • Are there specific physiological, metabolic, and biochemical mechanisms that contribute in defining tolerance to OA? • Are limpets genetically adapted to OA? • Is DNA methylation contributing to promote tolerance to OA in limpets? • What is the role of environmental conditions in shaping the response to OA? The first chapter of this thesis considered three Patella species (P. caerulea, P. rustica, and P. ulyssiponensis) collected from the CO2 vent systems of the Castello Aragonese (Ischia Island). This vent system exhibits a natural acidification gradient ranging from ambient pH (N1: pH = 8.1), to intermediate pH (N2: pH = 7.7), and to extremely low pH (N3: pH < 7.4). Resident populations were collected along the gradient and at San Pietro, an additional ambient pH site (pH = 8.1), located at a distance of 4 km from the Castello vent. In addition, a 30-day in situ transplant experiment was conducted using P. caerulea, in order to evaluate the short-term responses induced by OA. Morphometric traits, such as shell length, height, width, and soft-tissue weight, were measured, and a set of biomarkers related to antioxidant system, energy metabolism, neurotoxicity, and biomineralization was applied. For resident populations, P. caerulea showed increased size and energy reserves at the extremely acidified site, likely related to a shift from erect calcified algae to biofilm, or to reduced competition and/or predatory pressure under acidified conditions. Biochemical endpoints measured in both P. caerulea and P. ulyssiponensis were not modified by OA. Conversely, P. rustica exhibited significant modulation of nearly all biochemical parameters, likely due to its different position on the rocky shore, which makes this species more exposed to tidal fluctuations and therefore to an additional source of disturbance, besides OA. Short-term exposure of P. caerulea to OA resulted in a decrease in protein content and an increase in glycogen content at the extremely acidified site, with the induction of superoxide dismutase and glutathione-S-transferase activities at intermediate pH, suggesting the activation of compensatory mechanisms to cope with reduced pH conditions. Overall, results revealed a distinct response to OA of the three species of Patella. Moreover, the increased size and energy-related endpoints observed in P. caerulea and P. rustica highlighted the need to further investigate energy metabolism aspects, in order to better understand the trade-offs between compensatory mechanisms and the energetic cost underlying tolerance to OA. Based on these evidences, the second chapter focused exclusively on P. caerulea, with the aim of deeply investigating metabolic and physiological stress-responses, comparing resident populations of the Castello Aragonese vent systems and transplanted organisms, similarly to the first chapter. Respiration and ammonia excretion rates were measured four times across the year. Additionally, untargeted metabolomics analyses were performed to investigate metabolic pathways potentially involved in response to OA. Only during summer, OA increased respiration rate in limpets from the most acidified site, while simultaneously reduced excretion rates, likely to allocate more energy resources to face the increasing temperature, besides OA. Furthermore, both resident and transplanted populations up-regulated carnitine metabolism, suggesting that OA induced an increase of energy production through β-oxidation and subsequent Krebs cycles. Moreover, several metabolites involved in osmoregulation, oxidative stress, and nucleic acid mechanisms were increased. Overall, results seem to confirm the presence of negative effects and of an energetic cost underpinning tolerance to OA. The third and final chapter investigated the potential influence of phenotypic plasticity, genetic adaptation, and DNA methylation in tolerance to OA in adult and juvenile populations of P. caerulea collected from two CO2 vent systems of the Mediterranean Sea. Adult and juvenile specimens were sampled along the acidification gradient of the Castello Aragonese vent systems of Ischia Island (San Pietro/N1: pH = 8.1; N2: pH = 7.7; N3: pH < 7.4) and from the San Giorgio vent systems of Sicily Island (Patti: pH = 8.1; San Giorgio: pH = 7.8). Following genomic DNA extractions from foot tissue and individual libraries preparation with the NEB Next® Enzymatic Methyl-seq Kit, samples were sequenced on the Illumina NovaSeq 6000 sequencer. Data processing and analyses were conducted on Euler platform mainly using biscuit tool, which enabled to simultaneously extract genomic and epigenomic information from DNA methylation sequencing. Population genomics and epigenomics analyses revealed divergent patterns between the Ischia and Sicily populations. Populations from the Ischia vent revealed marked signs of genomic differentiation, particularly in adults from the intermediate and extremely low pH sites, while reduced differences in DNA methylation levels were detected, especially in adults. These findings suggest a strong signature of purifying selection acting on standing genetic variation, through a within-generation response, likely driven by the more pronounced pH fluctuations occurring at these sites. Conversely, no genomic differentiation was observed between the Sicily populations, but greater differences in DNA methylation were detected between acidified and non-acidified sites at both adult and juvenile stages. These results revealed that this epigenetic mechanism, rather than genomic changes, may play a key role in the response to the milder pH variations of this vent and potentially enhance organisms’ tolerance to OA. In conclusion, this PhD project investigated tolerance to OA in limpets through a holistic approach that, for the first time, integrated morphological, physiological, metabolic, biochemical, genetic, and epigenetic analyses. Overall, findings revealed that Patella spp. has the ability to survive under acidified conditions even though with a physiological and metabolic cost, which could be partially compensated by more favorable environmental conditions. This study further highlights the importance of conducting research in naturally acidified environments, since it allows to formulate more realistic hypotheses about the ability of marine organisms to persist in future changing oceans.

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The impact of climate change on lobster production: a systematic synthesis of literature

Published 6 April 2026 Science Closed
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Climatic impact-drivers are projected to change in coastal and marine regions globally, especially towards the fisheries production of the commercially important global shellfish, such as lobster species. Thus, there is an immediate need for ongoing, rigorous systematic review that continuously assesses and analyzes the risk of climatic factors towards lobsters’ production (i.e., growth, reproduction, etc.). A global relevant literature was analyzed from the inception to 31st December 2024. The review targets commercially important lobster, across various life history stages. The current study presents a systematic analysis of the research articles on lobster growth, reproduction, and development from relevant literature through two main academic databases, Scopus (n = 284) and Web of Science (n = 310). During literature search, duplicate articles were removed manually (n = 177). A total of 46 research articles were generated from the strict systematic selection process at various life history stages of lobsters. Climate change elements such as temperature, salinity, carbon dioxide, pH, and hypoxia significantly impact ovigerous females, reproduction, hatching success, larval stages, and juvenile development of lobsters. As global climate change intensifies, the reproductive and developmental capacity of lobster populations may be increasingly compromised, particularly in early life history stages. To date, a comprehensive synthesis of reproductive and biological impacts across taxa and regions has been lacking. This review provides a foundational reference for future assessments and adaptation strategies for sustainable management of lobsters under climate change.

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Combined ecotoxicity of microplastics and crude oil co-pollutants: occurrence, distribution and its synergistic impact with ocean acidification on Artemia franciscana

Published 3 April 2026 Science Closed
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Microplastics (MPs) are recognized as a global concern, with specific attention shifted towards marine MPs pollution. This particular study investigates the abundance and distribution of crude oil-loaded microplastics (COMPs) along the Chennai coastline, Tamil Nadu, India and evaluates their combined toxicological effects with ocean acidification on Artemia franciscana. Spatial analysis revealed that Ennore Creek exhibited the highest MP concentration (10.82 ± 0.2 items/L). Polypropylene was recorded as the predominant polymer type followed by low density polyethylene and polyethylene terephthalate, with particle size ranging from 250 to 500 µm. COMPs were detected across all sampling sites, with concentrations declining from Ennore Creek (0.21 ± 0.03 items/L) to Kasimedu Beach (0.10 ± 0.02 items/L). The adsorption of crude oil on MPs is primarily mediated by physical interaction with multi-layer adsorption behaviour. The results highlighted that increase in MP concentration and decrease in seawater pH significantly induced acute toxicity and oxidative stress responses in A. franciscana. At pH 7.8, experimental groups exposed to 0.5 mg/mL of COMPs developed higher ROS, SOD and catalase activity (p<0.001). Whereas control groups alone showed significant increase in oxidative stress responses at lower pH level such as pH 7.8 and 8.0. Combined exposure of COMPs and low pH conditions significantly increased oxidative damages in A. franciscana and affected its hatching ability. The observations from this study emphasize the urgent need for integrated monitoring and further research to explore combined toxicological effects of MPs and ocean acidification to other marine organisms as well.

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Impacts of ocean acidification on marine zooplankton: a review of physiological, developmental, and reproductive responses

Published 31 March 2026 Science Closed
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Acidification. The increasing levels of carbon dioxide CO₂ in the atmosphere are leading to ocean acidification, and this is altering the chemical content of marine water and is endangering life in the oceans. The examples of marine zooplankton, including Copepods, Pteropods, krill, and larvae of invertebrates are essential to the pelagic food webs and carbon cycles, even though they differ in their tolerance to low PH concentration and high pCO₂ levels. Early developmental phases are particularly vulnerable, with them showing retardation in developmental stages, reduced hatch rates, physical deformities as well as a lack of calcification. Higher carbon dioxide CO₂ levels interfere with the acid-base balance, increase oxidative stress and alter the allocation of metabolism, leading to trade-offs that lower growth, reproduction and survival rates. Calcifying organisms such as the pteropods are highly susceptible whereas some of the non-calcifying copepods exhibit a level of physiological resilience. Negative effects of other stressors may be affected by increased temperature, oxygen depletion, and nutrient enrichment which may further compound negative effects. There is some evidence that there is some possible acclimation in the short term and that there might be transgenerational plasticity but we do not understand adaptive capacity in the long term. Knowledge gaps exist in regard to multigenerational response, non-calcifying and gelatinous species and how physiological plasticity occurs. Species-specific responses are an important aspect of predictive models to estimate the impact of the ecosystem and guide conservation efforts. To ensure marine ecosystems remain stable as ocean acidification continues, vulnerable zooplankton should be safeguarded to preserve tropic structure, nutrient cycling, and nutrient stability.

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pCO2-induced seawater acidification influencing cadmium toxicity on antioxidant defenses responses in juvenile Manila clam Ruditapes philippinarum

Published 30 March 2026 Science Closed
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Highlights

  • GSH system and SOD-CAT act as complementary lines of antioxidant defense
  • SA alters Cd effects on antioxidants depending on metal concentration
  • High SA overrides Cd effects on antioxidant defenses in Manila clams
  • Combined high SA and Cd exposure overwhelms antioxidant capacity
  • Candidate biomarkers for monitoring SA or Cd stress are proposed

Abstract

Ocean acidification is known to interact with heavy metals, impacting physiological processes of marine organisms. This study investigated antioxidant defenses of juvenile Manila clam Ruditapes philippinarum exposed to cadmium (Cd) across ambient-relevant to high concentrations, under pCO2-induced seawater acidification (SA) scenarios corresponding to IPCC ocean pH projections. Results revealed that clam’s antioxidant system, encompassing GSH defense system and SOD-CAT defense lines, collectively combated oxidative stress dependent on specific stressors and their stress levels. GSH system is vital for detoxification and maintaining redox balance, while SOD and CAT are essential for scavenging ROS. Cd exposure notably activated GSH redox cycle, and SA markedly inhibited the antioxidants associated with this cycle. SOD and CAT exhibited distinct regulatory pathways with asynchronous responses to SA and Cd co-exposure. SA conditions modulate Cd-induced antioxidant response dependent on metal concentrations. Antioxidant biomarkers responded more prominently to SA and Cd interactions than to individual exposure, particularly, high SA effects could override Cd effects on antioxidant responses. Although SA effects did not directly induce lipid peroxidation, elevated MDA levels under Cd exposure occurred only under SA conditions, indicating insufficient antioxidant defense against lipid peroxidation under excess co-exposure. GSH and SOD were more sensitive to SA exposure, whereas MDA and GST were sensitive to Cd exposure, suggesting their potential as biomarkers for assessing SA or Cd-induced oxidative stress, respectively. These findings provide insights into interplay between metal toxicity and ocean acidification on antioxidant defenses in bivalves, shedding light on their strategies to combat metal pollution amidst global ocean change.

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Skeletal growth and loss of the cold-water coral Lophelia pertusa from multiple environmental drivers in a year-long experiment

Published 27 March 2026 Science Closed
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Colony-forming scleractinian cold-water corals (CWCs) are important ecosystem engineers, forming complex 3-dimensional habitats in the deep sea, which in turn sustain high biodiversity. They are threatened by future environmental changes such as ocean acidification, warming, deoxygenation, and food limitation, but little is known about the effect of these drivers in combination or on the long-term. We conducted a year-long aquarium experiment with Lophelia pertusa (syn. Desmophyllum pertusum) under projected end-of-century conditions, investigating the combined effect of differences in pH (8.1 and 7.7), temperature (9°C and 12°C), oxygen concentration (100% and 90%) and food supply (100% and 60%) on coral survival, growth, respiration rates, skeletal dissolution and energetic reserves. Growth rates of L. pertusa decreased significantly in both multiple driver treatments, resulting in negative and more variable growth rates. However, growth rates only started to decrease after 4.5 months, clearly showing a delayed response. In addition, survival rates and energetic reserves were slightly lower in multiple driver treatments, whereas L. pertusa was not affected by reduced oxygen concentration examined as a single factor. Negative growth rates in multiple driver treatments were driven by dissolution of bare skeletal parts due to reduced seawater pH and temporary aragonite undersaturation, visualised here through micro-computed tomography images. While live CWCs may be able to cope with projected future environmental changes over the timescale of 1 year, ocean acidification will lead to dissolution of the dead skeletal framework of CWC reefs and net loss, reducing the complexity and associated biodiversity of these reefs. However, the challenge remains in closing the gap between long-term experiments and the much longer-term chronic exposure of CWCs to projected environmental changes.

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Tolerance to future elevated CO2 conditions in sablefish (Anoplopoma fimbria), a deep-water benthic dwelling fish species

Published 26 March 2026 Science Closed
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Numerous studies have found that elevated CO2 levels in marine waters induced significant physiological and behavioral effects in fish. In an earlier study of coho salmon (Oncorhynchus kisutch), we observed that elevated CO2 exposure impaired signaling in the olfactory bulb, through a mechanism likely involving interference of gamma-aminobutyric acid (GABA) signaling. However, the effects of elevated CO2 may be species-specific, and there have been few studies addressing the effects of elevated CO2 on benthic fish. In the current study, we investigated the effects of elevated CO2 exposures on the deep-water benthic species, sablefish (Anoplopoma fimbria). Sablefish were exposed to three different levels of CO2 (700, 1600 and 2700 µatm) for two weeks, followed by behavioral, neurophysiological and gene expression analysis of the olfactory system. Analysis of behaviors mediated by food odors, including swimming activity and food strikes did not differ between fish maintained under elevated or control CO2 conditions. Similarly, electro-olfactogram recordings of odorant signaling did not differ among treatment and controls. mRNA expression patterns of olfactory bulb genes that were altered in coho salmon exposed to elevated CO2 levels, were similarly examined in sablefish. Sablefish mRNAs encoding genes involved in GABA-mediated olfactory bulb signaling were generally unaffected by high CO2, but aldh9a1, an enzyme involved in the synthesis of GABA, was elevated by high CO2. The results of our study contrast other studies demonstrating adverse effects of elevated CO2 in pelagic fish, but support differences among fish species to susceptibility to elevated CO2, potentially associated with life history traits.

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CO2 rise modulates the physiological performance of the diatoms Thalassiosira pseudonana and Thalassiosira weissflogii to light challenge

Published 25 March 2026 Science Closed
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Highlights

  • Ocean acidification boosts diatom growth independent of CO2 ramping speed.
  • Acidification changed PSII repair and photoprotection strategies under high light.
  • Species-specific adaptive advantages altered in acidified, light-variable oceans.

Abstract

Diatoms are major contributors to marine primary productivity and typically dominate well-mixed coastal environments characterized by rapidly fluctuating light levels. Yet, how the ongoing ocean acidification (OA) caused by rising CO2 affects their capacity to exploit such variable light is not well known. In this study, the diatoms Thalassiosira pseudonana and Thalassiosira weissflogii were cultured under two CO2 acidification regimes (gradual increase from ambient 400 to 1000 ppmV in ∼200 ppmV increments vs. direct elevation from 400 to 1000 ppmV) and exposed to high light stress to assess comparative physiological responses. Both diatoms showed significant increases in maximum electron transfer rate and saturation light intensity, with T. weissflogii additionally exhibiting elevated PsbA and Rubisco content. Growth rates increased by 15 % and 27 % for T. pseudonana and T. weissflogii respectively, with no significant difference between direct versus gradual CO2 elevation treatments. T. pseudonana demonstrated higher intrinsic susceptibility to PSII photoinhibition than T. weissflogii, OA didn’t significantly alter the functional absorption cross-section for PSII photoinactivation in either species. Notably, OA decreased PSII repair rates in T. pseudonana, while T. weissflogii maintained repair capacity through increased PsbA content and sustained non-photochemical quenching. These findings suggest T. weissflogii may gain a competitive advantage in future acidified, light-variable oceans due to its enhanced photoprotection and PSII repair capacity, highlighting species-specific resilience to combined environmental stresses.

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Diel variability and decoupled pH-oxygen dynamics drive metabolic plasticity in kelp crabs from an upwelling seascape

Published 25 March 2026 Science Closed
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Coastal upwelling zones, shaped by global change and human impacts, naturally impose hypoxia and acidification on marine species, creating selective pressures that influence physiological responses and drive phenotypic variability. Understanding these responses is crucial for predicting marine biodiversity dynamics in heterogeneous seascapes. We explored diel cycles of pH and dissolved oxygen (DO) and their influence on the metabolic performance of the kelp crab Taliepus dentatus, a species with limited larval dispersal. Kelp crabs from two environmentally contrasting sites along an upwelling seascape in central Chile—an upwelling shadow and an active upwelling zone—were studied using field sensor data and laboratory experiments. Active upwelling disrupted the regular diel pH cycle, resulting in persistently low pH (pHT ≈ 7.5) decoupled from oxygen dynamics. Experimental simulations of diel pH–DO fluctuations revealed that nocturnal low DO/low pH conditions (DO = 1 and 5 mg l⁻¹; pH = 7.5 and 7.8 for ‘upwelling’ and ‘downwelling’ conditions, respectively) reduced metabolic rates and respiratory quotient in crabs. Individuals from the active upwelling zone exhibited elevated metabolic rates, haemolymph pH and lactate accumulation under extremely low pH/low DO conditions compared with those from the upwelling shadow, suggesting site-specific physiological adjustments. These findings underscore the importance of incorporating natural variability into experimental designs and management frameworks aimed at predicting species resilience under climate change.

Continue reading ‘Diel variability and decoupled pH-oxygen dynamics drive metabolic plasticity in kelp crabs from an upwelling seascape’

Tolerance of egg and yolk-sac larval yellowfin sole (Limanda aspera) to ocean warming and acidification

Published 23 March 2026 Science Closed
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Yellowfin sole (Limanda aspera) support the largest flatfish fishery in the world and contribute substantially to the eastern Bering Sea (EBS) flatfish catch. The EBS has been warming and acidifying, trends that are expected to intensify into the future. Sustainable management of yellowfin sole requires an understanding of how yellowfin sole respond to environmental change, which can be assessed through controlled laboratory investigations. Across four independent trials, yellowfin sole embryos and larvae were incubated at one of six experimental treatments spanning three temperatures (9°C, 12°C, and 15°C) and two pCO2 target levels (low and high), and a range of organismal and physiological responses were measured. Embryonic daily mortality rates and metabolic rates increased with increasing temperature but were not affected by ocean acidification. At- hatch and at- yolk absorption, morphometric measurements (length, dry weight, myotome height, and yolk area) were temperature- sensitive, but the response differed across the four trials. There was a consistent increase in length- based growth and yolk absorption rates with increasing temperature across trials. All morphometric and rate- based measurements were not affected by ocean acidification. Yellowfin sole metabolic enzyme activities were measured at- yolk absorption. Lactate dehydrogenase (anaerobic metabolism) and β- hydroxyacyl CoA dehydrogenase (fatty acid metabolism) both increased with increasing temperature, indicating elevated energy demand. Citrate synthase (aerobic metabolism) declined with increasing pCO2 levels, indicating potential metabolic suppression. Overall, embryonic and larval yellowfin sole demonstrated relatively high tolerance to ocean warming and acidification. We hypothesize the variation in temperature responses across the trials may be driven by maternal effects, which could support tolerance to future ocean conditions.

Continue reading ‘Tolerance of egg and yolk-sac larval yellowfin sole (Limanda aspera) to ocean warming and acidification’

Ocean acidification disrupts the biomineralization process in the oyster Crassostrea virginica via intracellular calcium signaling dysregulation

Published 20 March 2026 Science Closed
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Calcium is a key component in the shell and skeleton structure, serving as a second messenger for regulating biomineralization across many species. Ocean acidification (OA) is well-studied for causing shell dissolution in marine bivalve species by disordering calcium deposition. However, the regulatory pathway of calcification affected by OA remains unclear. This study assessed eastern oyster (Crassostrea virginica) to determine how calcium signaling responds to elevated pCO2 and influences shell formation. Under elevated pCO2, increased calcium influx was found in mantle epithelial cells, followed by the upregulation of calmodulin, a primary sensor of intracellular calcium. Expression levels of shell matrix proteins (SMPs), representing shell construction conditions, were significantly upregulated in the CO2-induced mantle cells. Larval C. virginica exhibited developmental stage-dependent alterations in calcium signaling and SMPs disarrangement stimulated by pCO2. Pharmaceutical blockage of the calcium binding on calmodulin induced abnormal expression of downstream genes and shell matrix changes consistent with those caused by elevated pCO2. Restored SMPs expressions in CO2-treated mantle cells were achieved by rescuing the level of calcineurin, a downstream effector of calmodulin. These findings suggest that shell deformities under OA are primarily caused by the disruption of the calcium-calmodulin signaling pathway in mantle epithelial cells.

Continue reading ‘Ocean acidification disrupts the biomineralization process in the oyster Crassostrea virginica via intracellular calcium signaling dysregulation’

Multi-level holobiont dysregulation increases the ecological risk of combined ocean acidification and benzo[a]pyrene pollution to the reef-building coral Porites lutea

Published 17 March 2026 Science Closed
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Highlights

  • Combined ocean acidification and BaP induce holobiont dysregulation, evidencing by a decoupled Symbiodiniaceae proliferation and a collapse of the archaeal Nanoarchaeota-Halobacterota symbiosis.
  • The coral host shifts its defense strategy from antioxidant capacity to cellular homeostasis, while the bacterial community increases functional redundancy, revealing a costly acclimation mechanism.
  • The multi-level dysregulation demonstrates an underestimated ecological risk, highlighting that current single-stressor risk assessments are inadequate for protecting corals under complex pollution scenarios.

Abstract

Reef-building corals are increasingly threatened by the combined effects of global climate change and localized organic pollutants. However, the holistic impacts of co-exposure to ocean acidification (OA) and benzo[a]pyrene (BaP) on coral holobionts remain poorly understood. Here, we investigated the multi-level responses of the reef-building coral Porites lutea to short-term (7-day) exposure to OA (pH 7.80), BaP (10 µg/L), and their combination, by integrating physiological measurements with microbiome profiling (ITS2 and 16S rRNA). We found that combined stress was associated with a dysregulated response in Symbiodiniaceae, characterized by a significant increase in cell density without a parallel rise in chlorophyll content, suggesting a possible compensatory but inefficient proliferation response. Despite this, the dominant symbiont Cladocopium C15 remained stable. The bacterial diversity increased (e.g., enrichment of Ruegeria and Acanthopleuribacter, decline of Endozoicomonas), which may suggest enhanced functional redundancy, while the archaeal community was significantly restructured, most notably a marked decline of the putative obligate Nanoarchaeota–Halobacterota symbiosis. At the host level, combined stress was associated with suppressed antioxidant enzyme activities (SOD/POD) but upregulated genes related to protein folding (Hsp90) and calcium homeostasis (NCX1, VAMP4). These findings suggest a complex holobiont reconfiguration under combined stress, involving a stabilized core symbiont, altered microbiomes, and a shifted host defense strategy. Our study suggests that the ecological risk of combined OA and organic pollution may not be extrapolated from single-stressor responses, indicating the need to incorporate multi-stressor frameworks into coral reef risk assessments.

Continue reading ‘Multi-level holobiont dysregulation increases the ecological risk of combined ocean acidification and benzo[a]pyrene pollution to the reef-building coral Porites lutea’

Effects of rapid acidification in marine seawater: focus on Actinopterygii

Published 17 March 2026 Science Closed
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Highlights

  • The review reports physiological, behavioural, developmental and reproductive effects.
  • Studies on Actinopterygii exposure to various pCO₂ levels are integrated.
  • Fishes show strong species- and life-stagesingle bondspecific vulnerability to high pCO2.
  • Most experiments with extreme CO₂ levels are short-term, limiting current knowledge.

Abstract

The progressive acidification of the world’s oceans has led to widespread concern regarding the potential consequences for marine biosphere. As a result, most research has been focused on the steady increase of dissolved CO₂ and consequent acidification thus on calcifying species while less attention has been paid to the physiological and developmental impacts of teleost fish. However, rapid and massive release of carbon dioxide (CO₂) into the marine environment may occur due to both natural and anthropogenic causes. This review specifically examines the outcomes of rapid but confined CO₂ emissions, with a focus on their role in accelerating the local acidification of seawater and on the related effects on Actinopterygii. It examines the impacts of elevated CO₂ levels on marine fishes, also emphasizing the lack of experimental evidence on embryonic larval and larval phases, which are highly vulnerable to acid-base imbalances and related physiological disruptions. A broad review of literature published between 1963 and 2025, on fishes’ exposure to varying CO₂ conditions, highlights pronounced variability in responses across species and developmental stages. Early life phases frequently exhibit reduced survival, skeletal and sensory anomalies, and shifts in metabolic demand. Although some taxa demonstrate compensatory adjustments, the resulting energetic costs and physiological trade-offs can limit growth, reproduction, and long-term resilience. Advancing our understanding of fish vulnerability and adaptive potential under seawater acidification of marine fishes in an acidifying environment requires long-term, ecologically relevant designs and integrated approaches that link multiple life stages and biological scales.

Continue reading ‘Effects of rapid acidification in marine seawater: focus on Actinopterygii’

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