Posts Tagged 'laboratory'

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Ocean acidification exacerbates UVR-induced inhibition of photosystem II and I in Corallina officinalis

Published 16 July 2026 Science Closed
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Highlights

  • OA reduces calcification, compromising the UV shield and exacerbating photoinhibition in C. officinalis.
  • OA amplifies PSII donor-side damage, disrupts electron flow to PSI, and suppresses PSI function.
  • OA shifts PSII damage-repair balance toward irreversible photoinhibition by increasing damage and suppressing repair.

Abstract

Ocean acidification (OA) exerts diverse effects on marine macroalgae, with calcified species being particularly vulnerable. Due to calcified skeletons can contribute to physical screening against solar ultraviolet radiation (UVR), OA-driven calcification loss may increase exposure of the photosynthetic apparatus to UVR. Here, we cultured Corallina officinalis under ambient CO₂ (∼420 μatm) or elevated CO₂ (∼1000 μatm), with or without UVR, under natural solar radiation. Our results confirmed that OA reduced calcification and, under UVR, enhanced donor-side impairment of photosystem II (PSII), as evidenced by an increase in the relative K-step (Wk, an indicator of OEC damage) and a decrease in the maximum quantum yield of PSII (Fᵥ/Fₘ). This donor-side injury was accompanied by a reconfiguration of energy fluxes per PSII reaction center, particularly under combined OA and UVR. These impairments further extended to intersystem electron transport and limited the linear electron flow from PSII to the intersystem chain. Photosystem I (PSI) related electron transport was also functionally constrained, as evidenced by the reduced electron transfer probability and terminal reduction yield. This, together with the reduction of cyclic electron transport around PSI, resulted in over-reduction of the intersystem chain and making PSI the limiting photosystem. Together, these results indicate that OA amplified UVR-induced net photodamage and weakened PSII repair capacity in C. officinalis, while also constraining PSI-related electron transport. These findings highlight the potential vulnerability of calcified red algae under future high-CO₂, high-UVR coastal oceans.

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Multigenerational physiological plasticity of the marine copepod Acartia tonsa in response to ocean acidification

Published 16 July 2026 Science Closed
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Ocean acidification (OA) refers to the increase in the partial pressure of CO2 and decrease in the pH of seawater resulting from the absorption of atmospheric CO2 by the ocean. This study investigated OA impacts across multiple generations (F0-F3) of the copepod Acartia tonsa which were exposed to four pH conditions (8.1, 7.8, 7.6 and 7.1). Key reproductive and developmental traits were evaluated, including egg production, hatchability, development time, fecal pellet production, and sex ratio. Results showed that pH 7.1 significantly reduced egg production, hatchability and fecal pellet production, while prolonging the N–C time; N-A time remained unaffected by pH across all groups. For sex ratio, a downward trend was observed with increasing generations and decreasing pH: in F3, female proportion in pH 7.8, 7.6 and 7.1 groups was significantly lower than in the control group, and pH 7.1 and 7.6 groups had lower F3 female proportion than in the F1 generation. A. tonsa showed some tolerance under short-term acidification conditions at pH 7.1, but its physiological functions were further reduced after long-term exposure, suggesting a limited adaptive capacity. Ecologically, A. tonsa is a dominant coastal zooplankton species that links phytoplankton to higher trophic levels (e.g., fish larvae) and mediates energy flow and biogeochemical cycling. These results highlight the risks to key zooplankton populations and associated ecosystem functioning. Future studies should focus on the long-term effects of acidification on A. tonsa and combine multi-species experiments with field surveys to assess the ecological risks of OA.

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Climate change and ocean acidification outweigh local stressors in Mediterranean mussels: a multi-method convergence analysis

Published 15 July 2026 Science Closed
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Highlights

  • Climate change explains ∼40% of biological stress variance in Mediterranean mussels.
  • Ocean acidification drives 67% of metal bioavailability changes via pH-metal speciation.
  • 64% of climate effects on biomarkers operate indirectly through metal bioaccumulation.
  • Multi-method convergence (LMG, GAM, SEM, Bayesian Networks) confirms stressor ranking.
  • Only SSP1-2.6 keeps biological stress below the chronic-stress threshold through 2050.

Abstract

Marine coastal ecosystems face concurrent pressure from climate change and anthropogenic contamination, yet their relative contributions to biological stress remain poorly quantified. Here we present a decade-long (2014–2023) biomonitoring study on Mytilus galloprovincialis in the Ligurian Sea (NW Mediterranean), integrating quarterly biomarker measurements, heavy metal bioaccumulation data (12 metals), and high-resolution oceanographic records at a control site (Gorgona Island Marine Protected Area) and an offshore regasification terminal.

Biological stress variance was partitioned using five complementary analytical frameworks — Lindeman–Merenda–Gold (LMG) variance decomposition, Hierarchical and Generalised Additive Models (HGAM/GAM), Structural Equation Modelling (SEM), and Bayesian Networks — applied to four biomarkers: DNA damage, lysosomal membrane stability, gill tissue integrity, and immune response. A campaign-specific T0 baseline normalisation isolated environmental signals from initial population variability.

Climate change emerged as the dominant driver, consistently explaining ∼40% of variance across all methods, significantly exceeding metal bioaccumulation (∼30%), terminal influence (∼13%), and seasonal effects (∼2%). Ocean acidification was the primary climate mechanism, influencing 67% of analysed metals. Causal mediation analysis revealed that 64% of the climate effect operates indirectly through enhanced metal bioaccumulation (Climate→Metals→Biomarkers), while 36% acts directly. Climate and biological stress indices co-varied strongly (ρ = 0.78, p < 0.001), with marine heatwaves coinciding with peak biomarker responses.

Under IPCC Shared Socioeconomic Pathway (SSP) scenarios, the Biological Stress Index is projected to cross chronic-stress thresholds by 2035–2040 under the high-emission scenario (SSP5-8.5) and the intermediate-emission scenario (SSP2-4.5), with only the low-emission scenario (SSP1-2.6) maintaining stress below critical levels through 2050.

These findings challenge pollution-centric monitoring paradigms and demonstrate that CO2 mitigation now constitutes the highest-leverage intervention for marine invertebrate health in the Mediterranean.

Graphical abstract

This graphical abstract illustrates the main findings of a decade-long field study (2014–2023) on the effects of climate change and metal contamination on Mytilus galloprovincialis in the Ligurian Sea (NW Mediterranean). Three panels summarise the causal chain from environmental drivers to biological outcomes. The first panel depicts the key oceanographic trends recorded at the study site: ocean warming (+0.41°C/decade), acidification (−0.020 pH units/decade), deoxygenation, and a doubling of marine heatwave frequency after 2018. The second panel shows how pH decline enhances the bioavailability of 67% of the metals analysed, driving a predominantly indirect pathway (64%) from climate stressors to biological stress, mediated by metal bioaccumulation, as revealed by structural equation modelling and Bayesian network analysis. The final panel presents the four biomarkers used to compute the Biological Stress Index (BSI), its strong temporal correlation with the Climate Change Index (ρ = 0.78), and BSI projections to 2050 under three IPCC emission scenarios, showing that only SSP1-2.6 keeps BSI below the chronic-stress threshold throughout the projection period.

Continue reading ‘Climate change and ocean acidification outweigh local stressors in Mediterranean mussels: a multi-method convergence analysis’

Anthropogenic stressors and amphipod size influence herbivory on eelgrass in San Francisco Bay

Published 15 July 2026 Science Closed
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Seagrasses provide valuable ecosystem functions, yet they are declining globally due to anthropogenic stressors. Understanding how global climate stressors like ocean acidification interact with local environmental conditions (e.g., increased nutrient pollution) to affect ecosystem dynamics can be used to inform management of these habitats. In San Francisco Bay, it is unknown how stressor interactions will affect herbivory by Ampithoe valida, an invasive amphipod that exhibits novel feeding behavior by directly consuming the tissue of Zostera marina (eelgrass), which has been linked to negative impacts on local meadows. The goal of this study was to determine how anthropogenic stressors and amphipod size influence A. valida herbivory on eelgrass in San Francisco Bay to evaluate the ecological implications for eelgrass habitats. To further understand this relationship, feeding assays first examined food preferences of A. valida of three sizes on eelgrass of two ages and epiphytic algae. Secondly, a mesocosm experiment exposed A. valida of medium and large sizes to levels of ocean acidification expected with accelerating climate change and eelgrass to levels of nutrient pollution possible from point sources along shorelines, to test if these combined stressors affect A. valida direct herbivory of eelgrass. Additionally, A. valida were collected in the field during peak eelgrass growing season in summer and early fall to determine their size distributions and provide context to the experiments. Results found that A. valida largely prefer epiphytic algae over eelgrass regardless of their size. When offered only eelgrass, medium to large individuals consumed the tissue, whereas small individuals exhibited near-zero consumption. Although small A. valida were most abundant in field collections, medium-sized individuals were also present in moderate numbers, suggesting amphipods of this size may be the primary contributors to direct eelgrass consumption in San Francisco Bay, with high-consuming large individuals less common. Mesocosm results indicated that increased nutrients reduced eelgrass aboveground morphology (leaf size) and biomass, while tissue nutrient content increased, suggesting that although nutrients were taken up, they were not used for growth. Finally, feeding assays revealed that the effects of reduced pH and nutrient additions on A. valida eelgrass herbivory varied with grazer size and experimental context. In the no-choice assay, medium-sized individuals increased consumption under reduced pH relative to ambient pH, while large individuals consumed more of the highest nutrient-enriched eelgrass tissue. In contrast, the choice assay showed higher eelgrass consumption under ambient pH relative to reduced pH, and no effect of nutrient additions. This suggests that under reduced pH A. valida may shift their feeding behavior depending on environmental context, potentially increasing consumption through compensatory feeding on lower-quality tissue when food options are limited or reducing consumption when alternative refugia and higher-quality resources are available. This also indicates that ocean acidification may primarily alter eelgrass grazing behavior among mid sized A. valida, while nutrient enrichment may increase grazing pressure from larger individuals, potentially exacerbating eelgrass vulnerability in San Francisco Bay given reduced plant performance under high-nutrient conditions.

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Ocean acidification changes diet effects and differentially impacts two populations of red abalone (Haliotis rufescens)

Published 14 July 2026 Science Closed
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Absorption of CO2 by global oceans is decreasing pH resulting in ocean acidification (OA). Impacts on shellfish have been documented in ecologically and commercially important species. We examined the influence of diet and OA between two populations of red abalone (Haliotis rufescens) a species of aquaculture importance and declining wild populations. Populations experience different exposure histories: strong upwelling (Van Damme, California [VD]) historically exposed to low-pH conditions and weak-intermittent upwelling (Santa Barbara, California [SB]). Abalone were cultured under control-pH or OA-conditions and fed crustose coralline algae (CCA) or diatoms used in aquaculture. We tested treatment effects of population, settlement diet, and OA-exposure on survival as influenced by larval-energy stores. Survival in both populations was enhanced by CCA when cultured under both treatment conditions; however, by later stages, this effect remained only for SB. SB had reduced post-settlement survival when cultured under OA-conditions, whereas post-settlement survival of VD was not. Diet affected the relationship between larval-energy and post-settlement survival; a positive relationship when fed diatoms and a negative relationship with CCA. The relationship between larval energy and post-settlement survival was stronger in VD. CCA enhanced juvenile growth in SB cultured abalone at both three-months and one-year post-settlement. Settlement diets can reduce the impacts of OA on early-life stages of abalone, but population differences driven by underlying energetics affect the consistency of this outcome. These findings illuminate the impacts from OA, suggesting populations may be at risk, and inform strategies for developing and sustaining shellfish aquaculture in the face of changing ocean conditions.

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Brown algae as winners: divergent resilience to high light under acidified conditions shapes macroalgal communities around a carbon dioxide vent

Published 14 July 2026 Science Closed
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To investigate the effects of ocean acidification (OA) on macroalgae, we conducted in situ surveys along a natural CO2 vent gradient in Shikine Island, Japan, together with complementary laboratory culture experiments. The in-situ surveys revealed that near the CO2 vent (where pH dropped by 0.37), macroalgal diversity and species-richness were less than half those at the reference sites under ambient pH conditions. Nevertheless, the rates of CO2 assimilation of several common macroalgae increased from the reference site to the areas near the CO2 vent. This enhancement coincided with decreased photosynthetic CO2 affinity, reflecting that the acidified area down-regulated CO2-concentrating mechanisms in the algae. Measured photosystem II activity revealed that macroalgae at reference sites had lower electron transport rate and light utilization efficiency. The laboratory culture experiments, in which the dominant species (Gelidium elegans and Dictyopteris undulata), were cross-exposed to ambient and elevated CO2 conditions, further demonstrated that the stress near the CO2 vent significantly exacerbated photoinhibition under high light stress. Our results demonstrate that reduced pH and high sunlight act synergistically to impair macroalgal photosynthesis through exacerbated photoinhibition. This effect was more pronounced in red algae (e.g., G. elegans) than in brown algae (e.g., D. undulata). These different physiological responses provide a mechanistic explanation for an observed community shift, from red algal dominance in ambient pCO2 areas to brown algal dominance near the vent. Our findings imply that future OA, when combined with high-light stress, may selectively disadvantage high-light-sensitive species, thereby altering macroalgal community structure in coastal waters.

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Strong effects of sun exposure on oyster shell corrosion and compensatory calcification: a factor confounding coastal acidification responses

Published 13 July 2026 Science Closed
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The dynamics of calcium carbonate structures in marine organisms (skeletons and shells) has become increasingly important due to heightened interest in marine environmental acidification. Research into molluscan shell corrosion and calcification in response to acidification is typically carried out in laboratory-controlled settings, which often overlooks the intricate interactions found in natural environments. Mollusks inhabiting intertidal zones are especially susceptible to intense shell weathering caused by tidal cycles of heating, cooling, wetting, and drying, exacerbated by solar radiation during periods of air exposure. We investigated the effect of sun exposure (solar radiative heating) on both outer shell corrosion and inner shell compensatory calcification in the tropical oyster, Saccostrea scyphophilla. Shell properties were compared between oysters from neighboring populations in sun-exposed and shaded habitats. Habitat temperatures were measured using iButtons, and right shell valve corrosion was quantified. Compensatory calcification was assessed through measurements of shell thickness, shell density, shell compression strength, and mineralogical properties. Our results revealed that oysters in the sun that experience global irradiance, higher temperature peaks and broader daily temperature ranges (averaging an increase of 10 °C) show considerably greater outer shell surface corrosion (87%) compared to shaded oysters (31%) that experience only diffuse irradiance. Sun-exposed shells also become thickened in the midsection and around the adductor muscle, and they are slightly stronger, indicating compensation for the outer shell loss. These findings highlight the need for caution when interpreting molluscan shell dynamics based on laboratory marine acidification protocols that fail to account for the many natural environmental factors influencing shell formation and dissolution.

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Impacts of warming, acidification, and deoxygenation on embryos and larvae of gilthead seabream (Sparus aurata)

Published 13 July 2026 Science Closed
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Simple Summary

This study evaluated how the combination of ocean warming, acidification, and deoxygenation (“deadly trio”) affects the early development of the fish Sparus aurata. Embryos and recently hatched larvae were exposed to increased temperature (Δ + 4 °C; 22 °C), elevated CO2 levels (pCO2 ~1000 μatm, Δ − 0.4 units; pH 7.7), and reduced oxygen (Δ − 60% O2 saturation; 3 mg O2 L −1). Deoxygenation emerged as the primary stressor, significantly reducing hatching rates, larval survival, and heart rates. These effects were further intensified when combined with warming and acidification. Acidification alone also reduced larval phototactic behavior by 50%, while exposure to all three stressors eliminated phototactic responses entirely. Overall, the results demonstrate that multiple climate-related stressors together severely harm fish early life stages, emphasizing the need to study combined environmental changes to better predict future impacts of climate change on marine fish populations and ecosystem functioning.

Abstract

The interaction between increased dissolved carbon dioxide, rising temperatures, and oxygen loss—the so-called “deadly trio”—is expected to strongly affect marine biota over the coming years, undermining ocean services and uses. Nonetheless, no study has so far scrutinized the cumulative impact of these three stressors on fish embryos and larvae. To fill this knowledge gap, we conducted a fully multi-factorial experiment to investigate the effects of warming (+4 °C: 22 °C), acidification (Δ − 0.4 pH units: 7.7 pH, pCO2 ~1000 μatm), and deoxygenation (Δ − 60% O2 saturation: 3 mg O2 L−1) on physiological and behavioral responses of the commercially important species Sparus aurata. Deoxygenation was the primary factor reducing hatching rates (64.25%), survival (46.71%), and heart rates (31.99%) of recently hatched larvae, being generally further exacerbated when combined with warming and acidification. No larvae exposed to the interaction of the three treatments reacted to the phototactic behavior test. However, acidification alone caused a 50% reduction in phototactic behavior. Our findings demonstrate that the deadly trio is detrimental to early fish development, impacting several key features at this critical life stage, and the need to assess the impacts of stressors’ interaction on marine taxa to better predict future ecosystem responses to ocean changes.

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The fate of macroalgal carbon under microbial anaerobic respiration: a critical factor in macroalgae cultivation for climate change mitigation

Published 8 July 2026 Science Closed
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Highlights

  • Anoxic remineralization rates were not consistently lower than oxic rates.
  • Macroalgal degradation modulates the DIC pool, crucial for carbon sequestration.
  • Alkalinity generated by anaerobic respiration stabilizes the DIC pool.

Abstract

Macroalgae play a significant role in global carbon sequestration. Substantial macroalgal organic carbon inputs and subsequent degradation can cause deoxygenation; however, the impact of oxygen deficiency on carbon fate remains understudied, which is critical for assessing the climate mitigation role of macroalgae. Here, we investigated changes in the carbon pool and non-CO2 greenhouse gases (N2O and CH4) to assess the influence of oxygen levels on the carbon sink capacity of macroalgae. The microbial remineralization rate of macroalgal organic matter was not consistently slower under anoxic conditions (AK) compared to oxic conditions (OK). Total organic carbon (TOC) concentrations in the water column were 530 ± 94 (OK) and 282 ± 38 (AK) μmol kg−1. For dissolved inorganic carbon (DIC), concentrations on day 30 were 4585 ± 197 (OK) and 5200 ± 492 (AK) μmol kg−1, while those for total alkalinity (TA) were 2684 ± 18 (OK) and 4523 ± 671 (AK) μmol kg−1. Following a 30-day sealed incubation, the bags were opened to reach atmospheric equilibrium. Subsequently, DIC dropped to 1837 ± 79 (OK) and 3744 ± 354 (AK) μmol kg−1, and TA fell to 2059 ± 14 (OK) and 4431 ± 657 (AK) μmol kg−1. Ultimately, relative to the control group (seawater only, OS) under air-sea equilibrium, the ΔDIC values were −22 ± 76 and 1885 ± 351 μmol kg−1 in the OK and AK treatments, respectively, while ΔTA values were −57 ± 11 and 2315 ± 655 μmol kg−1. The emissions of N2O and CH4 did not substantially offset the climate effect of carbon sequestration. These results suggest that, beyond the traditional focus on organic carbon preservation, anaerobic respiration under anoxic conditions may also contribute to macroalgal carbon sequestration by generating alkalinity that enhances the retention and stabilization of DIC.

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Evaluating the combined effects of ocean acidification and harmful algal blooms on the fitness of Artemia salina

Published 6 July 2026 Science Closed
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This study assessed the potential synergistic effects of harmful algal blooms (HABs) and ocean acidification (OA) on the survival and grazing potential on HABs by brine shrimp (Artemia salina). The effects on the fitness of three life stages (i.e. newly hatched, 1-week old, and 2-week old post hatch) of A. salina was evaluated over a 24-hour period. Using well plates, A. salina were individually exposed to toxin producing HABs (i.e. Alexandrium catenella or Margalefidinium polykrikoides), a non-toxin producing HAB (i.e. Gymnodinium aureolum), and fed or unfed non-HAB controls. pH conditions administered were ambient (pH ~ 8) or acidified (pH ~ 7.2). Survival analysis revealed a significant effect of treatment on mortality across life stages. Hazard ratios showed elevated mortality in HAB treatments relative to controls, while OA alone did not. HAB exposure or ontogeny are more important for survival of A. salina than short-term OA exposure. Regarding grazing potential, significant reductions in HAB cell density were more commonly found in treatments with older individuals than younger conspecifics. Cell density of A. catenella was never significantly reduced as compared with other HAB treatments. Overall, exposure to OA conditions did not affect the survival or grazing potential of A. salina, but the species of HAB did.

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Interactive effects of triclosan, microplastic vectors, and ocean warming–acidification on sea urchin embryo development

Published 6 July 2026 Science Closed
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Highlights

  • Microplastics modulate triclosan toxicity in a concentration-dependent manner.
  • Microplastic loads reverse triclosan attenuation affecting larval development.
  • Acidification amplifies triclosan–microplastic toxicity in sea urchin embryos.
  • Ocean Warming modulates toxicity; degree-day normalization reveals hidden stress.

Abstract

Understanding how emerging contaminants interact with climate-driven stressors is essential for accurate ecological risk assessment in coastal ecosystems. This study evaluates the individual and combined effects of triclosan (TC), polyethylene microplastics (MP), ocean warming (OW), and ocean acidification (OA) on the early development of Paracentrotus lividus embryos. A tiered experimental design was implemented to: (i) characterize TC dose–response curves alone and in combination with increasing concentrations of MP (300–3000 particles mL−1), and (ii) assess how OW (24 °C) and OA (pH 7.6) modulate contaminant toxicity. TC showed concentration-dependent growth inhibition, while MP exhibited a biphasic interaction with TC: at moderate concentrations, MP increased EC10 values and steepened dose–response slopes, consistent with contaminant sorption reducing freely dissolved TC. At 3000 particles mL−1, this trend reversed, lowering EC50 values and enhancing toxicity. Morphometric analyses revealed that co-exposure to TC alone and with MP loads impaired arm elongation, increased body-width ratios, and reduced stomach volume, indicating compromised feeding and skeletal development. Climate stressors significantly altered toxicological outcomes. OA strongly amplified the combined toxicity of TC + MP, reducing larval growth to near-zero levels, whereas OW alone did not exacerbate toxicity and partially mitigated OA-driven effects in MP-TC treated groups. Degree-day normalization demonstrated that warming accelerates development but reduces growth efficiency across treatments. Overall, these results reveal threshold-dependent MP–TC interactions and highlight acidification as a critical amplifier of contaminant effects. Incorporating realistic MP–pollutant interactions and climate variables is crucial for improving hazard assessments under future ocean scenarios.

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Study on the mechanical characteristics of the stress relaxation in the carbonate rock after high-temperature acidification

Published 3 July 2026 Science Closed
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To elucidate the mechanism by which acidification influences wellbore stability in deep reservoir formations, this study investigates the rheological and mechanical behaviors of the carbonate rock subjected to high-temperature acid etching. A novel experimental system was developed to characterize the stress relaxation behavior of the acid-etched carbonate rock, and the characteristics of the stress relaxation curves under various acid etching conditions and strain levels were systematically analyzed. Combined with Burgers model and the Levenberg–Marquardt algorithm, the evolution of rheological parameters of the carbonate rock under different acid etching regimes was quantitatively evaluated. The results indicate that the acid-etched carbonate rock exhibit significant rheological mechanical properties due to the presence of developed microcracks and complex pore structures. Under the identical acid etching duration and temperature, the initial stress, residual stress, and time required for stress relaxation stabilization all increase with increasing the strain level. Overall, the stress relaxation magnitude prior to the core fracture ranges from 15 to 25 MPa, and the stabilization time for the core stress relaxation falls between 5 and 7 h. The stress relaxation behavior of the acid-etched carbonate core is well described by the Burgers model. At fixed strain levels and temperatures, the instantaneous shear modulus  decreases linearly with extended acid etching time, whereas the instantaneous shear modulus  and the viscosity coefficients  and  exhibit exponential degradation. The final variation ranges of the key rheological parameters are determined as follows: instantaneous shear modulus  ranges from 5 × 103 to 2 × 104 MPa, instantaneous shear modulus  ranges from 6 × 105 to 2 × 106 MPa, viscosity coefficient  ranges from 2 × 107 to 8 × 107 MPa h, and viscosity coefficient  ranges from 1 × 105 to 1.2 × 106 MPa h. Furthermore, the evolutionary equations correlating the global model fitting parameters with the porosity of acid-etched samples are established, using acid etching time as an intermediate variable. The results of this study provide a theoretical basis for the analysis of wellbore stability after acidification and the selection of acid fracturing completion methods of deep reservoirs.

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Thermal regulation of benthic fluxes in temperate estuaries

Published 2 July 2026 Science Closed
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The effects of short-term heatwave extremes on biogeochemical cycling and fluxes in a temperate estuary of a semi-dry climate were studied using an experimental setup of temperature-controlled benthic incubations. The results demonstrated a strong thermal effect, notably under extreme warming events, for shifts in exchanges across the sediment-water interface. Extreme heatwave conditions (+5 °C of the seasonal mean) boosted acidification, hypoxia, and ammonification, due to accelerated remineralization rates, resulting in strong effluxes of NH4, Si(OH)4, and PO4 to the overlying water. These excessive nutrient loads may increase eutrophication risk via runoff or tidal action, specifically in adjacent oligotrophic coastal waters. CO2 production rates reached ~4000 µatm under extreme hypoxia and acidification, 2.3-fold higher than the ambient rate, with a maximal flux of ~27.0 mmol m-2 d-1. Hence, our experiments show that marine heatwaves amplify CO2 emissions while reducing the CO2 buffering capacity of temperate estuaries. It emphasizes temperate estuaries as highly sensitive ecosystems to climate change.

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Short-term plasticity and long-term transcriptomic rewiring under natural ocean acidification in an ecosystem-relevant sea urchin

Published 1 July 2026 Science Closed
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Highlights

  • Natural CO2 vents reveal transcriptomic responses to chronic ocean acidification.
  • Acute low-pH exposure triggers rapid but limited plastic responses in Arbacia lixula.
  • Vent-origin Arbacia lixula exhibit extensive metabolic reprogramming and antioxidant activation.
  • Low pH supresses biomineralization genes and up-regulates collagen and extracellular matrix pathways.
  • Persistence under ocean acidification is associated with energetic trade-offs and skeletal homeostasis.

Abstract

Ocean acidification is reshaping coastal ecosystems as a consequence of anthropogenic CO2 emissions. Natural CO2 vent systems provide valuable analogues for investigating organismal responses to long-term acidified conditions under ecologically realistic scenarios. Here, we examined genome-wide transcriptomic responses of the sea urchin Arbacia lixula, an ecosystem-relevant grazer inhabiting a natural CO2 vent system in La Palma (Canary Islands, Spain). Using RNA sequencing of 24 adults (n = 8 per treatment), we compared: (i) acute experimental exposure of ambient-origin individuals to low pH, (ii) chronic exposure by comparing ambient and vent-origin populations in their native pH conditions, and (iii) a genotype-of-origin comparison under shared low pH. Acute exposure triggered a limited transcriptional response (116 differentially expressed genes, DEG), characterized by activation of ion transport, redox regulation, and NAD-associated metabolism. In contrast, chronically exposed vent-origin urchins showed a tenfold increase in transcriptional changes (1053 DEG), reflecting metabolic reprogramming involving lipid, carbohydrate and amino acid pathways, and strengthened antioxidant capacity. Chronic low-pH exposure was also associated with suppression of biomineralization and developmental genes, alongside strong upregulation of collagen and extracellular matrix–associated genes that may help maintain skeletal performance under reduced carbonate availability. Genotype-of-origin effects (131 DEGs) revealed constitutive differences in metabolic, redox, extracellular matrix, and biomineralization pathways in vent populations. Together, these findings indicate that persistence under natural acidification involves both rapid plastic responses and sustained physiological reorganization, providing mechanistic insight into how calcifying species maintain functional performance under ongoing ocean acidification.

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Impact of water quality and gear type on Eastern oyster (Crassostrea virginica) growth in Narragansett Bay, RI

Published 1 July 2026 Science Closed
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Oyster aquaculture is expanding in Rhode Island, yet key farming regions in the lower West Passage of Narragansett Bay (WPNB) lack the in-situ, high-temporal resolution monitoring needed to evaluate emerging stressors and support production. At the same time, the industry is undergoing rapid technological development aimed at improving production while reducing labor and overall costs. In recent years, a low maintenance, alternative surface gear was introduced in WPNB; however, its impact on oyster performance relative to traditional cultivation methods has not been quantified. This study established a 1.5-year continuous water quality time series in WPNB and paired these observations with physiological assessments of Crassostrea virginica grown in three cultivation methods (i.e., traditional surface, alternative surface, and bottom gear). This work aimed to better understand the impact of environmental variability and gear type on oyster health, growth, and survival. Multiparameter sondes and discrete bottle samples were used to monitor water quality and calculate carbonate saturation state (Ω) at a 4-acre oyster farm. Nine mesh bags containing early-life stage C. virginica (16 ± 0.4 mm; n = 300 per bag) were deployed in July 2025, with three replicate bags in each gear type. Subsamples (n = 15) from each gear type were collected over a 6-month period for morphometric measurements and scope for growth (SFG) determinations. Minimal differences in carbonate chemistry were observed among sampling sites and Ω remained supersaturated (Ω >1) for the majority of the study period, indicating that ocean acidification was not a major stressor for farmed oysters. Survival was highest (82 ± 4.5%) in surface gear types compared to bottom gear (27 ± 0.58%), while physical growth (shell and tissue) and SFG were largely similar among all gear types. These results suggest that the alternative surface gear may support comparable production and product quality to traditional gear types, while also reducing maintenance and labor demands. Overall, this study provides important physiological and biological context for oyster aquaculture while informing gear selection and farm management strategies.

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Skeletal porosity of a cold-water coral increases with decreasing aragonite saturation state along a depth gradient in the Mediterranean Sea

Published 29 June 2026 Science Closed
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Background

Cold-water corals (CWCs) are key ecosystem engineers that create complex three-dimensional habitats much like tropical reefs, but in deep, cold seas. However, like other reef-building systems, they are increasingly threatened by climate change and ocean acidification. CWC communities in the Mediterranean Sea may be especially vulnerable because these waters absorb more atmospheric CO2 than the global ocean, making it a mesocosm that mirrors broader global trends affecting marine life. Since calcification is energetically costly and likely becomes even more demanding as pH and carbonate ion availability decline, understanding how the decrease in aragonite saturation state (Ωarag) affects biomineralization is essential for predicting the future of these corals.

Results

Here, we investigated skeletal structural and compositional changes of the scleractinian CWC Desmophyllum dianthus along an Ωarag gradient in the Mediterranean Sea using specimens collected between 400 and 1200 m depth. Our findings indicate that skeletal porosity increases at the macro-scale with decreasing Ωarag, while micro- and nano-scale structural and compositional features remained unaffected.

Conclusions

The persistence of micro- and nano-scale skeletal features across an 800 m depth gradient suggests that D. dianthus maintains tight biological control over mineralization at these scales, even as Ωarag declines. This control does not extend to the macro-scale, where increasing porosity alters the skeleton’s overall architecture under lower Ωarag. D. dianthus thus appears to preserve the fundamental “building blocks” of its skeleton while changing its larger-scale structure, a decoupling that may make macro-scale porosity an early marker of acidification stress in CWCs.

Continue reading ‘Skeletal porosity of a cold-water coral increases with decreasing aragonite saturation state along a depth gradient in the Mediterranean Sea’

Acute low pH associated with coastal acidification is detrimental to larval development of the Cape urchin Parechinus angulosus

Published 26 June 2026 Science Closed
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Acidification in coastal habitats is increasing in duration and amplitude under the continued influence of ocean acidification and contributing coastal processes. The impacts of low pH conditions on calcifying organisms, especially echinoderms, is well established, with the early developmental stages being especially vulnerable. This is the first study to assess the impact of locally relevant coastal acidification scenarios on the early development of the Cape urchin Parechinus angulosus. Our findings suggest that the early larval stages of this species are unlikely to survive when exposed to low pH conditions, specifically during the onset of skeletogenesis. In our laboratory experiments, larvae that were exposed to the low pH treatment (pH 7.32) showed significantly reduced growth (GLMM, Time × Treatment interaction: β = −0.361 ± 0.019, z = −19.06, p < 0.001) and developmental regression compared with those from the control treatment (pH 7.95). Substantially slower growth rates were observed in the low pH treatment (length = 72.3 hpf0.18) compared with in the control treatment (length = 24.24 hpf0.54). There was also evidence of abnormal and delayed development and potential dissolution of skeletal structures under the low pH condition. However, fertilisation success and larval survival did not differ significantly between the experimental treatments, suggesting that developmental impacts of low pH over short durations, even though substantial, may be sublethal. The developmental impacts are likely to impair the transition of larvae to the adult stages, which may ultimately affect populations of this ecologically important species under future coastal acidification scenarios.

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Lithium isotopes reveal impaired ion transport in tropical corals exposed to high pCO2

Published 26 June 2026 Science Closed
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Ocean acidification, driven by rising atmospheric CO₂, threatens the ability of corals to build their skeletons by reducing their capacity to maintain an elevated pH at the calcification site (pHcf), a process essential for calcium carbonate precipitation. Boron isotopes have commonly been used to show that the response of pHcf to ocean acidification is highly species-specific. However, the physiological mechanisms underlying this variability remain poorly understood. Recently, lithium (Li) isotopes have been used to trace the activity of ionic transport involved in cellular pH regulation and calcification (e.g. H+, Na+ and Ca2+), and may therefore help resolve these mechanisms. Here, we investigate multiple coral species from Tutum Bay (Papua New Guinea), a natural CO₂ seep system creating pH gradients (mean pHT = 7.66 at seeps vs. 8.01 at control sites) analogous to future ocean acidification scenarios. Our results show a relationship between seawater pH, calcifying fluid chemistry, and lithium isotopic composition. Corals exposed to low seawater pH exhibit significantly altered δ⁷Li values relative to colonies from the control site, with some species becoming enriched in ⁷Li (up to 2‰) as pHcf declines. This isotopic shift is consistent with reduced efficiency of Na⁺/H⁺ exchangers (NHEs), active transporters that preferentially incorporate the lighter ⁶Li isotope under optimal conditions but may become less effective under elevated proton concentrations. By linking Li isotopes to calcifying-fluid chemistry, these results provide geochemical evidence that ocean acidification may disrupt ionic regulation in corals and that Li isotopes can help to resolve biogeochemical controls of carbonate-systems.  

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Marine invertebrates and fishes exhibit inconsistent body size responses to ocean acidification

Published 18 June 2026 Science Closed
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Body size is a fundamental characteristic of all living organisms that determines physiological functions and life-history traits. Ecological theory predicts that ocean acidification can cause body size reductions, confirmed by several studies reporting miniaturization in ectotherms. Based on this prediction, we would expect a broad suite of species to show similar plastic body-size responses to elevated CO2. Using four natural climate change analogues of ocean acidification across the northern and southern hemispheres, we quantified body size alterations across 18 marine invertebrate and fish taxa to test for climate-driven miniaturization. Only three species consistently showed body-size reductions under ocean acidification: one urchin and two fish species. In contrast, 15 other species, ranging from highly calcified to non-calcified, displayed unchanged or increased body sizes or inconsistent miniaturization. If body-size miniaturization responses were consistently reproducible across taxa we would have observed it more frequently, suggesting that species responses to ocean acidification are more variable than previously thought and likely vary depending on a species’ physiology and life history. Thus, rather than entire communities undergoing miniaturization, species are likely to display a spectrum of responses, with some exhibiting size reductions, others demonstrating physiological resistance to elevated CO2, and others potentially benefiting from the indirect effects of ocean acidification.

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Pteropod vulnerability to ocean acidification in the eastern Arabian Sea

Published 18 June 2026 Science Closed
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Highlights

  • First study on pteropod response to ocean acidification in the eastern Arabian Sea.
  • High pteropod abundance during fall inter monsoon season due to food availability.
  • pH in the Arabian Sea was low during south west monsoon with pHT upto 7.75
  • Pteropod shell dissolution was observed under acidified conditions
  • Protrusions through the pteropod shell were observed under acidified conditions

Abstract

The rapid rise in atmospheric CO2 and its subsequent uptake by the oceans has led to ocean acidification and other associated changes in the marine ecosystem. The recent reports of the shoaling of the aragonite saturation horizon in the northern Indian Ocean are particularly alarming, as they pose a serious threat to the survival of calcareous organisms. Pteropods, also known as sea-butterflies, are believed to be highly susceptible to ocean acidification due to their thin aragonite shell. In our study in the eastern Arabian Sea, we found low pH conditions with surface pHT as low as 7.751 during late South-west monsoon (SWM). The pteropod abundance is high during the fall inter-monsoon (FIM), suggesting that the system continues to sustain productivity even after the cessation of peak monsoon activity. This also implies that the food availability regulates pteropod abundance in the eastern Arabian Sea. As pteropods are key components of food sources for many marine species, such as fish, any changes in their abundance can have cascading effects on the marine food web. To show how pteropods will be affected in futuristic elevated CO2 conditions, a CO2 manipulation experiment was conducted in the eastern Arabian Sea during December 2024. Pteropods belonging to Creseis acicula from the eastern Arabian Sea were subjected to pHT = 7.470, and pCO2 = 1734 μatm under controlled conditions. Our findings suggest that acidification led to the dissolution of pteropod shells. Acidification also led to protrusion through the shells, and these protrusions varied in length up to 88 μm. These structural alterations represent an acute response of pteropod shells to reduced pH, highlighting their rapid vulnerability to acidification stress. These observed protrusions need to be assessed further to determine if they provide any competitive advantage in combating or minimizing the impact of ocean acidification.

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