Applications open: fourth winter school on ocean acidification and multiple stressors

Published 20 October 2026 Events Leave a Comment

Dates: 30 November – 11 December 2026

Location: IAEA Marine Environment Laboratories, Monaco.

Deadline for application through InTouch+ platform: 6 November 2026

The Winter School is organized by the IAEA OA-ICC in partnership with the Prince Albert II of Monaco Foundation through the OACIS Initiative (Ocean Acidification and other ocean Changes – Impacts and Solutions) and the Laboratoire d’Océanographie de Villefranche (LOV).

Introduction

Ocean acidification is a global environmental stressor that threatens marine life and the livelihoods of coastal communities. Ocean acidification is caused by increasing atmospheric carbon dioxide being absorbed by the ocean, resulting in changes to seawater carbonate chemistry, including a drop in pH. Due to global concerns about its consequences, ocean acidification is included in international policies such as Target 3 of UN Sustainable Development Goal (SDG) 14 and Target 8 of the Global Biodiversity Framework (GBF).

The IAEA’s Ocean Acidification International Coordination Centre (OA-ICC) supports IAEA Member States to minimize and adapt to OA and report towards SDG 14.3 and the GBF, with a strong focus on building capacity to study ocean acidification and related stressors and promoting international collaboration and coordination.

Ocean acidification is not happening in isolation, but in combination with other human-driven pressures, including pollution, warming, and oxygen loss. The impact of multiple ocean stressors on marine life and ecosystem function is not well understood, yet this information is crucial to inform adaptation strategies that might minimize negative effects on organisms, ecosystems, and associated socioeconomic benefits.

The Fourth Winter School on Ocean Acidification and Multiple Stressors is part of the capacity building program of the OA-ICC.  This two-week training course will provide participating scientists with a thorough understanding about key concepts and experimental design used to study the impacts of ocean acidification in the context of additional stressors.

Objectives

The aim of the Winter School is to train early-career scientists who already have experience researching ocean acidification on how to study acidification in the context of other co-occurring stressors. Through lectures and practical exercises in the laboratory, the students will gain understanding of key concepts in multiple-stressor research (e.g., What is a stressor? What is a mode of action? What is an interaction?), purposeful experimental design, and analysis of complex datasets. During the course, participants will collaborate on a joint laboratory experiment to elucidate the effects of three simultaneous drivers on marine organisms.

Target Audience

The course is open to 10-12 trainees. Priority will be given to early-career scientists with experience in marine environmental change with a focus on ocean acidification; a background in biological sciences is preferred. At least one publication in the field of marine environmental change is required.

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Participation and Registration

All persons wishing to participate in the event have to be designated by an IAEA Member State or should be members of organizations that have been invited to attend.

In order to be designated by an IAEA Member State or invited organization, participants are requested to submit their application via the InTouch+ platform (https://intouchplus.iaea.org) to the competent national authority (Ministry of Foreign Affairs, Permanent Mission to the IAEA or National Atomic Energy Authority) or organization for onward transmission to the IAEA by 6 November 2026, following the registration procedure in InTouch+:

1. Access the InTouch+ platform (https://intouchplus.iaea.org):

  • Persons with an existing NUCLEUS account can sign in to the platform with their username and password;
  • Persons without an existing NUCLEUS account can register here.

2. Once signed in, prospective participants can use the InTouch+ platform to:

  • Complete or update their personal details under ‘Complete Profile’ and upload the relevant supporting documents;
  • Search for the relevant event under the ‘My Eligible Events’ tab;
  • Select the Member State or invited organization they want to represent from the drop-down menu entitled ‘Designating Authority’ (if an invited organization is not listed, please contact InTouchPlus.Contact-Point@iaea.org);
  • If applicable, indicate whether a paper is being submitted and complete the relevant information;
  • If applicable, indicate whether financial support is requested and complete the relevant information (this is not applicable to participants from invited organizations);
  • Based on the data input, the InTouch+ platform will automatically generate the Participation Form (Form A) and/or the Grant Application Form (Form C);
  • Submit their application.

Once submitted through the InTouch+ platform, the application, together with the auto-generated form(s), will be transmitted automatically to the required authority for approval. If approved, the application, together with the applicable form(s), will automatically be sent to the IAEA through the online platform.

NOTE: The application for financial support should be made, together with the submission of the application, by 6 November 2026.

For additional information on how to apply for an event, please refer to the InTouch+ Help page. Any other issues or queries related to InTouch+ can be sent to InTouchPlus.Contact-Point@iaea.org.

Selected participants will be informed in due course on the procedures to be followed with regard to administrative and financial matters.

Participants are hereby informed that the personal data they submit will be processed in line with the Agency’s Personal Data and Privacy Policy and is collected solely for the purpose(s) of reviewing and assessing the application and to complete logistical arrangements where required. The IAEA may also use the contact details of Applicants to inform them of the IAEA’s scientific and technical publications, or the latest employment opportunities and current open vacancies at the IAEA. These secondary purposes are consistent with the IAEA’s mandate.

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Additional Requirements

Participants should have a university degree in marine chemistry, biology, oceanography or a related scientific field, and should be currently involved in or planning to study the ecological impact of multiple stressors, including ocean acidification. Experience with the R software is strongly encouraged.

Selection will be based on merit and interest. Applications should include:

 * A motivation letter with a short description of the candidate’s research interests and how the course would benefit the applicant’s current or future research on ocean acidification and multiple stressors (max one A4 page)

  * CV with publication list

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Connecting international ocean, climate and biodiversity governance to protect deep-sea life

Published 29 October 2026 Science Leave a Comment
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Deep-ocean biodiversity plays a fundamental role in the global carbon cycle and Earth’s climate system. Despite this critical function, international biodiversity and climate change governance frameworks have rarely considered deep-sea life to any considerable extent historically. Recent developments create opportunities to close this gap, including through the Agreement under the United Nations Convention on the Law of the Sea on the Conservation and Sustainable Use of Marine Biological Diversity of Areas beyond National Jurisdiction (BBNJ Agreement), the Paris Agreement under the UN Framework Convention on Climate Change (UNFCCC), and the Kunming-Montreal Global Biodiversity Framework under the Convention on Biological Diversity (CBD). We review the history and developments of these conventions to date regarding how they address the interface between climate, biodiversity, and the deep ocean, and use this historical overview to identify specific opportunities and mechanisms that can be used to sustain and protect life in the deep ocean more effectively and coherently going forward. Practical suggestions include incorporating climate and carbon considerations in the creation of marine protected areas and other area-based management tools under the BBNJ Agreement, establishing cross-cutting mechanisms that can align efforts under the UNFCCC, CBD, and the BBNJ Agreement, and, under the Paris Agreement, incorporating deep-ocean actions in nationally determined contributions, reconsidering what counts as mitigation or adaptation to encourage consideration of carbon conservation actions, and ensuring that climate change mitigation efforts do not harm deep-ocean biodiversity.

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Monsoon-linked gut microbiome variation in a tropical sea urchin: a single-reef case study from the Arabian Sea

Published 29 October 2026 Science Leave a Comment
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Highlights

  • Stomopneustes variolaris gut microbiota shows clear seasonal structuring in response to monsoon-driven biogeochemical variability.
  • The gut microbiota of Stomopneustes variolaris is dominated by Bacteroidota, and most diverse during winter and spring inter-monsoon.
  • Gut microbial composition covaries with seasonal oxygen, pH, temperature, and nutrient gradients.
  • The sea urchin gut microbiome shows seasonal plasticity under monsoon-linked stress.

Abstract

Tropical coastal ecosystems of the Eastern Arabian Sea (EAS) experience pronounced monsoon-driven shifts in water-column biogeochemistry, yet their influence on the gut-associated microbiomes of benthic invertebrates remains poorly understood. Sea urchins are ecologically important grazers in reef-associated habitats, and their gut microbiota may reflect both environmental and dietary variability. Here, we provide an exploratory characterisation of the gut-associated microbiome of the sea urchin Stomopneustes variolaris from the Grande Island archipelago (Goa, India) across four monsoon-associated periods: Winter monsoon (WM), Spring-inter monsoon (SIM), Summer monsoon (SM), and Fall-inter monsoon (FIM). Using 16S rRNA gene sequencing, we analysed gut tissue and gut digesta from S. variolaris alongside environmental samples (seawater, sediment, and seaweed). Bacteroidota dominated the urchin gut microbiome, whereas Proteobacteria were more abundant in environmental samples. Gut microbial diversity was highest in WM and SIM and lowest during SM and FIM. Exploratory analyses indicated that gut microbial composition varied temporally, with taxa affiliated with sulphur-cycling lineages more prevalent during sampling points associated with low-oxygen monsoon phases (SM and FIM) and Firmicutes and organic matter-associated taxa more prominent during comparatively oxygenated periods (WM and SIM). Ordination analyses suggested an association between gut and environmental microbial assemblages and gradients in dissolved oxygen, temperature, pH, nutrients, and pCO2. This study provides baseline insights into the gut microbiome of a tropical echinoid from an understudied region and highlights monsoon-associated patterns in microbial community composition, forming a foundation for future functional and experimental investigations.

Graphical abstract

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Unlocking spatial ecological assessment for tropical seagrass habitats using a new rapid assessment method (SEARAM)

Published 29 October 2026 Science Leave a Comment
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Highlights

  • Rapid and standardized assessment of tropical seagrass ecological state.
  • Multimetric index combining structure and vitality indicators.
  • Spatial mapping of seagrass fragmentation and degradation.
  • Links between habitat condition, environment, and megafauna.
  • A practical tool for coastal monitoring and impact mitigation.

Abstract

Seagrass meadows are key coastal ecosystems supporting biodiversity, carbon storage, and essential trophic functions, yet they are increasingly threatened by anthropogenic and climatic pressures. Based on the Seagrass Meadows Rapid Assessment Method (SEARAM), a standardized protocol grounded in seagrass biodiversity indicators (SBIs), we developed a reliable and operational index to assess seagrass ecological state at high spatial resolution. Using 536 circular plots and 144 faunal stations across three intertidal reef habitats in Mayotte (Western Indian Ocean), SEARAM integrates structural and vitality sub-indices into a composite seagrass ecological state index (SESI), spatialized by geostatistical interpolation and analyzed using ANOVA, PCA, and multiple regression models. Results revealed highly fragmented meadows dominated by Halodule uninervis and Halophila ovalis, with low canopy height (5 ± 2 cm) and substantial epiphyte loads (37 ± 17%). The inner fringing reef flat showed the poorest ecological state (SESI = 4.8 ± 0.7/10), whereas the barrier reef (5.4 ± 0.8/10) and exposed fringing reef flat (5.6 ± 0.8/10) exhibited moderate scores. Key environmental drivers (turbidity, grain size, pH), significantly explained spatial patterns of seagrass structure and vitality, confirming the influence of sediment and light regimes. Functional relationships were also demonstrated between seagrass condition and associated fauna, particularly green turtle density and dugong feeding traces. SEARAM proved to be a rapid and robust tool for diagnosing tropical seagrass states. Its multimetric framework connects benthic condition to habitat suitability for megafauna, offering an operational foundation for ecological monitoring, management, and impact mitigation within the Avoid–Reduce–Offset (ARO) doctrine.

Graphical abstract

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Closer to danger: southern Ocean pteropods build their shells deeper in the water column during winter-spring

Published 29 October 2026 Science Leave a Comment
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Shelled pteropods are at risk from ocean acidification, with known effects on their shell durability and calcification. Pteropods typically form their aragonitic shells over specific depth ranges known as the “calcification depth,” which varies depending on species and habitats. Some Southern Ocean waters are already undersaturated with respect to aragonite and this could negatively affect shelled pteropods. However, the calcification depths of pteropods have not been determined nor used to infer consequences of changing seawater carbonate chemistry in the Southern Ocean. In this study, we analyzed the stable oxygen isotopic composition of Limacina rangii shells, collected by sediment traps in the sub-Antarctic zone, to estimate their calcification depth. Shallow calcification depths (13–126 m) were detected in summer–autumn, while L. rangii calcified their shells deeper in the water column during winter–spring (302–525 m). Recent shoaling of the aragonite saturation horizon is likely to negatively affect pteropods that calcify their shells in deep water. Such shoaling could affect pteropod calcification, shell integrity and threaten population viability.

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How ocean acidification makes marine fish reproduction vulnerable: physiological mechanisms and ecosystem consequences

Published 29 October 2026 Science Leave a Comment
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Highlights

What are the main findings?

  • Ocean Acidification (OA) disrupts the HPG axis, reducing sex steroids and vitellogenesis.
  • OA impairs gamete quality, sperm motility, egg integrity, and Ca²⁺ signaling.
  • pH decline may weaken Dax1 repression of P450arom, but this remains unvalidated.
  • OA plus warming often worsens reproductive dysfunction; multigenerational recruitment effects are still unknown.

What is the implication of the main finding?

  • OA threatens fish recruitment, community structure, and fishery productivity/food security.
  • Long-term, multigenerational, multi-stressor field studies are needed for effective management.

Abstract

Ocean acidification, driven by the absorption of anthropogenic carbon dioxide into seawater, poses a significant threat to marine environments and biodiversity. This comprehensive review examines the specific impacts of acidification on the reproductive physiology of fish, integrating recent advances in our understanding of gonadal development, gametogenesis, and early embryonic development. We synthesize current findings on how altered carbonate chemistry disturbs the reproductive system from gametogenesis and fertilization to larval development and beyond. Our analysis reveals that ocean acidification affects multiple physiological pathways, including disruption of the hypothalamic–pituitary–gonadal (HPG) axis, impairment of calcium signaling, and alterations in sex hormone synthesis. We propose a mechanistic model in which pH reduction may weaken Dax1-mediated repression of P450arom transcription, thereby dysregulating aromatase activity and leading to sex hormone imbalance that impairs gonadal development; however, this proposed mechanism requires direct experimental validation under ocean acidification, as the net outcome may be modulated by additional regulatory layers such as epigenetic modifications and other transcription factors. Furthermore, we discuss the synergistic effects of ocean acidification with temperature elevation and other stressors, which often exacerbate reproductive dysfunction. This review concludes that no multi-generational study has yet evaluated HPG axis disruption to population-level recruitment failure, a critical gap for fishery resource assessment. We emphasize the critical importance of multi-generational and field-based studies to fully understand these impacts, which is essential for forecasting consequences for global marine biodiversity and the long-term sustainability of fisheries.

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Coastal benthic ecosystems in a changing ocean: a mini review

Published 29 October 2026 Science Leave a Comment
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Coastal benthic ecosystems are shaped by the combined effects of climate change and anthropogenic pressures. Ocean warming, acidification, and deoxygenation interact with eutrophication, pollution, bottom trawling, and coastal development, altering biodiversity, habitat structure, and functioning from shallow coasts to continental margins. Benthic communities, comprising infaunal and epifaunal taxa, regulate key processes including nutrient cycling, sediment dynamics, and carbon burial, thereby underpinning benthic-pelagic coupling and biogeochemical dynamics. Rising temperatures and marine heatwaves drive widespread losses of habitat-forming species, while ocean acidification constrains calcification. Warming, acidification, hypoxia, eutrophication, and pollution increasingly simplify assemblages, and alter trophic pathways and performance. Interactions among stressors can amplify organismal sensitivity and push ecosystems towards ecological thresholds. However, many knowledge gaps remain. Recent methodological advances, including environmental DNA metabarcoding, automated imaging, trait-based analyses, and multi-stressor experiments, are improving the detection of ecosystem changes at large and our mechanistic understanding of ecosystem responses to ongoing change. By summarizing the various stressors that benthic habitats and taxa face, their interactions and potential outlooks, this review provides a concise synthesis of current understanding and identifies key knowledge gaps for future research and management under accelerating climate change.

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When oceans acidify: metal toxicity, uptake–depuration, and ion homeostasis in the copepod Nitokra sp.

Published 28 October 2026 Science Leave a Comment
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Highlights

  • Seawater pH affected metal toxicokinetics, but not toxicity in Nitokra sp.
  • Seawater pH affected Cu, Zn and Cd toxicokinetics, but not toxicity in Nitokra sp.
  • The highest bioconcentration factor was observed for Cu at pH 8.1.
  • Acute Cu, Cd, and Zn exposure did not reduce significantly copepod Ca or Na at pH 8.1 and 7.6.
  • Copepod Ca declined 48 h after Cd exposure ended, indicating Cd-induced ionic imbalance.

Abstract

Mechanisms governing metal kinetics help maintain trace element levels required for physiological functions and ion regulation in aquatic organisms. However, both essential and non-essential metals can become toxic at excessive concentrations. Water physicochemical properties, including pH and dissolved anions, influence metal speciation, bioavailability, and toxicity. Under acidic conditions, bioavailability may increase as H+ competes with metal cations for binding sites, increasing free metal ions. Greater bioavailability may also disrupt uptake of essential macronutrients such as calcium (Ca) and sodium (Na) through competition at biotic binding sites. In the present study, we assessed the toxicity (half maximal lethal concentration [LC50]), toxicokinetics (bioaccumulation at the 10% lethal concentration [LC10] followed by depuration), and the impacts on Ca and Na levels of cadmium (Cd), copper (Cu), and zinc (Zn) in the estuarine copepod Nitokra sp. at pH 8.1 (natural) and pH 7.6 (acidified, as projected by the Intergovernmental Panel on Climate Change). All tested metals followed typical dose–response toxicity curves, with Cu being the most toxic, followed by Cd and Zn, with no significant differences between pH 8.1 and 7.6. Contrary to our hypothesis, bioconcentration factors were higher at pH 8.1 than at pH 7.6. Metal exposure did not significantly affect Ca and Na, but trends suggest early physiological disturbance, with Ca decreasing with exposure to Cd or Zn and increasing with exposure to Cu. During elimination, Ca levels were higher in Cu-exposed copepods than in Cd-exposed ones and similar to controls, suggesting that Cd competes with Ca at the cellular level.

Graphical abstract

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Ocean acidification: historical progression, feedbacks, and future projections

Published 28 October 2026 Science Leave a Comment
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Ocean acidification is increasingly recognized as a dynamic driver of Earth system change, rather than a passive chemical response to anthropogenic CO₂ uptake. Over the past decade, key research discoveries—including perturbations to surface ocean seasonal cycles, accelerated subsurface trends, and growing relevance of the biological carbon pump—have fundamentally reshaped our understanding of ocean acidification. They have also revealed critical deficiencies in how Earth System Models represent seasonality, vertical carbon distributions, and the calcium carbonate cycle. Leveraging observational advances to address model deficiencies is essential for improving future carbon cycle projections and the understanding of associated ecological impacts.

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The climate observing system – ocean acidification

Published 28 October 2026 Science Leave a Comment
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The ocean has absorbed approximately one-quarter of anthropogenic carbon dioxide (CO2) emissions since the industrial era, moderating atmospheric warming while driving significant changes in marine carbonate chemistry. Collectively referred to as ocean acidification (OA), these changes include declining seawater pH, reduced carbonate ion availability, and decreasing calcium carbonate saturation states, with consequences for marine ecosystems, biogeochemical cycles, and ocean services. Detecting and quantifying OA is challenging because anthropogenic trends are superimposed on substantial natural variability across a wide range of spatial and temporal scales. Consequently, no single variable, platform, or observing approach can adequately characterize OA.

This chapter reviews the principal components of the contemporary OA observing system and the methodologies used to quantify changes in marine carbonate chemistry. It introduces the marine carbonate system and the analytical methods used to measure key OA variables, including pH, dissolved inorganic carbon (DIC), total alkalinity (TA), and partial pressure of CO2 (pCO2). The chapter examines the role of sustained time-series stations in detecting long-term trends and distinguishing anthropogenic change from natural variability, highlighting evidence for widespread acidification across open-ocean, coastal, polar, and marginal seas. The complementary contributions of surface underway observations, repeat hydrography programs, and autonomous observing platforms are reviewed, including major international initiatives such as SOCONET, SOCAT, GO-SHIP, GLODAP, and Biogeochemical-Argo (BGC-Argo). Particular emphasis is placed on how these observing elements provide complementary information across spatial and temporal scales and together form an integrated OA observing system.

Finally, the chapter discusses uncertainty assessment, trend attribution, data integration, and the role of international coordination mechanisms, including GOOS, GCOS, IOCCP, and GOA-ON. It further examines how OA observations support climate assessments, model evaluation, ecosystem-risk assessments, Sustainable Development Goal (SDG) 14.3.1 reporting, and emerging monitoring, reporting, and verification needs associated with marine carbon dioxide removal.

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Elevated pCO2 promotes growth but compromises PSII repair and antioxidant balance in the bloom-forming diatom Skeletonema costatum under ultraviolet radiation

Published 28 October 2026 Science Leave a Comment
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Highlights

  • Elevated pCO2 stimulates growth but not UV photoprotection in Skeletonema costatum.
  • Ocean acidification constrains PSII repair and PsbA turnover under UVR.
  • Trade-off between carbon-sequestration capacity and antioxidant defense raises UV sensitivity.

Abstract

Diatoms serve as key marine primary producers, driving global biogeochemical cycles, but their physiological performance is increasingly challenged by ocean acidification (OA) and enhanced ultraviolet radiation (UVR). This study investigated how OA caused by elevated pCO2 (1000μatm) modulates the UVR sensitivity of the bloom-forming diatom Skeletonema costatum. Elevated pCO2 significantly enhanced the specific growth rate by ~11.6%; it did not significantly aggravate the UVR-induced decline in Fv/Fm, but it constrained PSII repair and PsbA turnover, as indicated by lower rate constants for PSII repair (Krec, s−1) and PsbA removal (KPsbA, s−1), and was associated with a greater net decline in total PsbA content under PAR + UVR. Although elevated pCO2 upregulated the relative maximal electron transport rate (rETRmax) and light-saturation parameter (Ik), and maintained a higher RbcL/PsbA ratio consistent with a possible role of carbon assimilation as a downstream sink, it did not enhance the sustained non-photochemical quenching (NPQs). Furthermore, under elevated pCO2, CAT activity had a lower baseline; although CAT increased under UVR relative to PAR, its absolute activity remained lower, indicating an imbalanced antioxidant response. Collectively, these findings reveal a physiological trade-off: elevated pCO2 promotes growth and carbon-sequestration capacity but simultaneously compromises photoprotective mechanisms. Consequently, S. costatum grown under elevated pCO2 becomes more susceptible to UVR-induced photoinhibition, potentially suppressing photosynthetic production during surface blooms and influencing bloom persistence and carbon export.

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OA pumpkin stencils

Published 28 October 2026 Art , Web sites and blogs Leave a Comment

Looking for last-minute pumpkin carving ideas? Get creative with the OA pumpkin stencils! Download our designs and bring a touch of ocean science to your pumpkin creations.

Click the images below to download the stencils.

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The data diaries: MAPCO2 buoys (video)

Published 28 October 2026 Art , Web sites and blogs Leave a Comment

In this episode, we follow carbon data points as they are collected by a buoy at the surface of the ocean and transmitted to scientists. Not only do these global measurements of carbon dioxide help us understand the rate of exchange between our ocean and atmosphere, but they also inform the health of ecosystems that communities around the world rely on.

With support from NOAA’s Global Ocean Monitoring and Observations Program and Ocean Acidification Program, scientists at NOAA’s Atlantic Oceanographic and Meteorological Laboratory, Pacific Marine Environmental Laboratory and other labs and programs aid international efforts to monitor the global ocean’s accumulation of atmospheric carbon as part of the carbon cycle.

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From response to resilience: celebrating 15 years of NOAA’s Ocean Acidification Program

Published 27 October 2026 Web sites and blogs Leave a Comment

Fifteen years ago, oyster hatcheries on the West Coast faced an invisible crisis. Oyster larvae were dying by the billions from an unknown culprit, threatening a multi-million dollar industry and families’ livelihoods. Oyster growers turned to scientists to uncover the hidden threat – changing ocean chemistry that brought more corrosive waters to western shores.

Now, our nation is no longer flying blind. Congressional action empowered NOAA’s Ocean Acidification Program (OAP) to better understand ocean and coastal acidification (OA) and its ecological and economic impacts.

Highlights include:

  • OAP’s work helps harvesters of the nation’s most valuable shellfish fisheries understand a changing ocean and how they can adapt to keep up production.
  • OAP established the first-ever dedicated national ocean acidification observing network
  • Our science has advanced from from collecting observations to putting them to use in models and forecasts that enable community and industry planning.
  • OAP leads interagency coordination and outreach to on-the-ground communities most impacted by a ocean acidification.

Key Insight: Hatcheries on the West Coast were pumping in local water during upwelling, a natural process that has been delivering more corrosive waters to the surface due to OA. Technological advances allow hatcheries to measure acidity in real-time, and adjust the acidity of the water to protect oysters as they grow. Today, OAP helps growers prepare for continued OA from investigating practices from seawater to genes.

Recognizing the severe ecological and economic threats posed by OA, Congress passed the Federal Ocean Acidification Research and Monitoring Act (FOARAM) of 2009, officially establishing NOAA’s Ocean Acidification Program. Recently reauthorized under the CHIPS and Science Act of 2022, this mandate charged OAP with the critical mission to monitor ocean chemistry, understand its impacts on marine life, and give communities the information and tools they need to adapt.

From water chemistry to resilience

This year marks OAP’s fifteenth year on the frontlines of ocean acidification. Our understanding has evolved far beyond the initial identification of this ocean crisis. A robust observing network that powers modern forecasts now stands. This set the foundation to then unravel the complex sensitivities of many marine species, and deliver essential tools that communities rely on to secure their livelihoods and futures.

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Response of volatile halocarbons release to atmospheric deposition and ocean acidification in the tropical eastern Indian Ocean

Published 27 October 2026 Science Leave a Comment
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Highlights

  • Fe(III) inputs increased CH3I emission by photochemical and biogenic processes.
  • Nutrient inputs enhanced volatile halocarbons by boosting biogenic processes.
  • Ocean acidification enhanced CH2Br2/CHBr3 emissions by BrPO-mediated halogenation.

Abstract

Short-lived volatile halocarbons (SLVHCs) are important trace greenhouse gases and ozone-depleting substances influencing global climate. Anthropogenic activities have accelerated ocean acidification (OA) and enhanced atmospheric deposition, yet how these perturbations regulate SLVHCs production in open ocean remains unclear. Herein, we investigated the effects of OA and atmospheric deposition derived Fe(III) and nutrient input on SLVHCs production through ship-based incubation experiments at two stations in the tropical eastern Indian Ocean (10°N-10°S) from March to May 2022. Our findings revealed that nutrient addition promoted phytoplankton growth with the maximum Chlorophyll a (Chl a) increasing to 6.17 μg L−1, enhanced bromoperoxidase (BrPO) activity (by 108.3 % compared to the control group), and stimulated release of dissolved organic carbon (DOC), ultimately driving the production of CH3I, CH2Br2, and CHBr3 (by 152.0 %, 200.2 %, and 141.8 % increases, respectively). OA and Fe(III) additions promoted phytoplankton growth (Chl a up to 1.85 μg L⁻1), thereby enhancing SLVHCs production through biological and photochemical processes, whereas they exhibited no significant effects on SLVHCs production in relatively oligotrophic regions. Mechanistically, CH3I release was regulated by phytoplankton-mediated biogenic processes and photochemical processes. In contrast, CH2Br2 and CHBr3 production was predominantly associated with phytoplankton-mediated biogenic processes (BrPO-mediated halogenation). These results demonstrating that OA, Fe(III), and nutrient inputs regulate marine SLVHC production by altering phytoplankton-mediated biogenic processes and photochemical reactivity. Our study offers a novel perspective and direct evidence for quantifying the production of SLVHCs under climate change scenarios, thereby underscoring the need to reassess oceanic climate feedbacks in the context of anthropogenic forcing.

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Interactive effects of ocean acidification and benzophenone-3 on mussel physiology: a biomarker-based approach

Published 27 October 2026 Science Leave a Comment
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Highlights

  • Ocean acidification was the primary driver of biomarker responses.
  • Low pH enhanced BP3-induced cytotoxicity in hemocytes.
  • BP3 detoxification mainly involved the GST/GSH pathway.
  • Lipid peroxidation occurred in gills and digestive gland despite antioxidant response.
  • Acidification impacts biomineralization enzymes more strongly than BP3.

Abstract

Benzophenone-3 (BP3), a widely used ultraviolet (UV) filter in personal care products and industrial applications, is an emerging concern in aquatic ecosystems due to its lipophilicity, bioaccumulation potential, and toxicity to marine biota. Its occurrence in marine environments coincides with ocean acidification driven by rising atmospheric CO2 emissions, which disrupts the bicarbonate buffer system and reduces pH. This study investigated the acute effects (96 h exposure) of BP3 (at realistic concentrations of 0.2 and 2 μg/L) under 3 pH conditions (8.1- the current South Atlantic condition- and 7.6 and 7.3 as projected acidification scenarios for 2100 and 2300, respectively) in the brown mussel Perna perna. The effects were investigated through analysis of hemocyte viability and biomarkers related to detoxification (glutathione S-transferase, glutathione, glutamate cysteine ligase, and reduced glutathione), oxidative stress (antioxidant capacity against peroxyl radicals and lipid peroxidation), and biomineralization (carbonic anhydrase and Ca2+ATPase), measured in the gills, digestive gland, and mantle. Despite BP3-induced activation of glutathione-related detoxification pathways, as evidenced by increased GSH levels and GST activity, particularly in the gills, hemocyte viability decreased after BP3 exposure, with the greatest reduction at pH 7.3. Lipid peroxidation (LPO) also increased in the gills and digestive gland under acidified conditions, with the magnitude of the response varying according to BP3 concentration. CA and Ca2+ATPase activities were more strongly influenced by acidification than by BP3 exposure, although their responses were tissue-specific and, in some cases, modulated by BP3 exposure. Multivariate analyses identified pH as the primary driver of biomarker responses.

Graphical abstract

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From population to individual: bulk and single-cell analysis reveal Fe bioavailability, limitation thresholds, and biological responses for marine diatom Chaetoceros debilis

Published 27 October 2026 Science Leave a Comment
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Highlights

  • Fe speciation and pH jointly regulated Fe bioavailability.
  • A critical bioavailable Fe limitation threshold (∼10 nM) was identified for the marine algae.
  • Single-cell analysis revealed previously hidden heterogenous Fe accumulation.
  • Fe stress induced adaptive responses including metallome remodeling.

Abstract

In marine ecosystems, Fe fundamentally regulates algal productivity and drives biogeochemical cycling in the hydrosphere, yet its environmental controls and cellular responses remain insufficiently resolved, particularly at the single-cell level. Herein, we combined bulk and single-cell analysis to systematically investigate Fe bioaccumulation process in the marine diatom Chaetoceros debilis under varying Fe species, initial pH, and concentration conditions. Fe bioavailability followed the order Fe-ethylenediaminetetraacetate > Fe-deferoxamine B > Ferrihydrite and decreased with declining initial pH, highlighting the combined control of chemical speciation and ocean acidification. A critical bioavailable Fe limitation threshold of ∼10 nM was identified, below which algal growth, pigmentation, and cell size were significantly suppressed. Under Fe limitation, cells exhibited compensatory accumulation of other metals (e.g., Zn, Mn, Cu, and Ni), indicating metallome remodeling as an adaptive strategy. Notably, single-cell analysis revealed pronounced heterogeneity in Fe accumulation within populations, with heterogeneity positively related to bioavailable Fe levels. These findings demonstrate that algal Fe accumulation is governed by coupled environmental and physiological processes and that population-level averages mask critical cell-to-cell variability and their adaptive strategies under environmental stress. This work provides mechanistic insights into how environmental chemistry regulates metal bioavailability and biological responses, offering a broadly applicable framework for understanding the environmental behavior and ecological effects of trace metals and other contaminants in aquatic ecosystems.

Graphical abstract

Continue reading ‘From population to individual: bulk and single-cell analysis reveal Fe bioavailability, limitation thresholds, and biological responses for marine diatom Chaetoceros debilis’

Surviving together: evolutionary dependency, community dynamics, and mortality in marine microbial communities

Published 26 October 2026 Science Leave a Comment
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Oligotrophic regions of the world ocean sustain vast phytoplankton populations despite extremely low nutrient levels. However, the mechanisms governing their coexistence, interdependence, and mortality are poorly understood. This dissertation investigates how evolutionary dependency, community feedback, and regulated cell death (RCD) jointly shape the stability of marine microbial communities using the Prochlorococcus/Parasynechococcus/Alteromonas model system.

In Chapter 1, I argue that the Black Queen (BQ) hypothesis—which posits that microbes lose costly metabolic functions supplied by community partners—provides a unifying framework for understanding phytoplankton ecology. This framework helps resolve longstanding puzzles, including the paradox of the plankton and the evolutionary maintenance of RCD in unicellular organisms. Building on this framework, Chapter 2 uses transcriptomic analysis of Alteromonas in co-culture with picocyanobacteria to demonstrate that community composition induces greater changes in gene expression than pCO₂ alone. Reduced 2-phosphoglycolate/glycolate exudation by Prochlorococcus under elevated pCO₂ may disrupt the helper heterotroph effect underlying this cyanobacterium’s BQ dependency.

Chapter 3 integrates co-culture experiments, RNA-seq, metabolomics, and mathematical modeling to demonstrate that the stable coexistence of Prochlorococcus and Parasynechococcus is maintained by an “Ouroboros network” of feedback loops. In this network, resource competition, carbon exudation, BQ dependency, and possibly RCD collectively stabilize the community across environmental gradients and during adaptation to changing conditions.

Chapter 4 resolves the cellular mechanisms underlying RCD in these cyanobacteria, showing that differences in cell death modes and the number of checkpoint-linked mortality events between taxa are associated with divergent life-history strategies. These findings suggest that carbon released at these checkpoints may shape interactions with helper Alteromonas, linking individual cell death to community-level interdependencies.

In conclusion, these findings converge on a new resolution to the paradox of the plankton: coexistence in resource-limited environments emerges from interdependent metabolic exchanges, feedback, and regulated cell death shaped by multilevel selection. I propose that together, these processes form an “altruistic bargain” in which stability arises from self-constraint rather than competition alone. Because these interactions are environmentally sensitive, climate change, including warming and acidification, may disrupt the dependencies that sustain microbial diversity and ecosystem function in the world ocean.

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Large-scale water-sediment regulation (Yellow River) substantially reshapes organic carbon mineralization pathways and benthic fluxes in sediment of a river-dominated sea (Bohai Sea)

Published 26 October 2026 Science Leave a Comment
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Large-scale hydrological engineering has fundamentally altered the rhythm of land-to-ocean material transport globally, yet the mechanistic response of coastal benthic biogeochemistry to these “pulse” events remains poorly quantified. Here, we investigated the transient impacts of the annual Yellow River Water-Sediment Regulation (WSR), a massive anthropogenic flood, on sediment organic carbon (OC) mineralization and benthic fluxes in the Bohai Sea (BHS) by combining geochemical analyses with sediment incubations. Results indicated that the WSR enhanced sediment OC mineralization rates by an average factor of 1.65, driven primarily by pulsed input of labile OC and probably also reflecting a priming effect. This stimulation reconfigured dominant diagenetic pathways: significantly elevating the role of dissimilatory iron reduction at the expense of both aerobic respiration and sulfate reduction. In addition, pulsed nitrate inputs promoted denitrification, establishing it as an important OC mineralization pathway. Concurrently, diffusive nutrient fluxes increased by a factor of 1.9–5.1 following the WSR, and the mean ratio of total alkalinity to dissolved inorganic carbon fluxes decreased from 1.34 to 0.96. This shift in the ratio signifies a reduced capacity for carbonate buffering in the bottom waters, which could exacerbate seasonal bottom-water acidification. Collectively, our findings demonstrate that short-term anthropogenic perturbations can rapidly reprogram sediment diagenesis and benthic fluxes, thereby perturbing carbon and nutrient cycling as well as benthic-pelagic coupling in river-dominated coastal systems.

Plain Language Summary

The annual Water-Sediment Regulation of the Yellow River is one of the world’s largest engineered flow manipulations, rapidly delivering huge amounts of freshwater and sediment into the Bohai Sea (BHS). While much is known about its effects on the water column ecochemistry, how such a large-scale human intervention alters organic carbon degradation and chemical exchange in seafloor sediments has remained unclear. By combining field measurements and laboratory experiments, we show that this event strongly enhances sediment carbon degradation rates and shifts the dominant pathways, favoring iron reduction and nitrate reduction processes. These changes drive substantial increases in benthic fluxes of dissolved inorganic carbon and nutrients (ammonium, silicate, and phosphate) into overlying waters. Notably, the regulation reduces the ratio of alkalinity to inorganic carbon flux, implying a temporary decline in the capacity of the sea to absorb atmospheric CO2. Our findings provide critical insights by revealing that large-scale human-regulated river discharges can rapidly reshape coastal sediment biogeochemistry. These results have important implications for carbon and nutrient cycling, offering valuable references for understanding not only the BHS but also other river-dominated coastal systems worldwide.

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Hypoxia and acidification antagonistically suppress nitrification but enhance its N2O production in coastal waters

Published 26 October 2026 Science Leave a Comment
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The concurrent intensification of hypoxia and acidification poses a growing threat to estuarine-coastal ecosystems globally, yet their interactive impacts on nitrification, a key process in the nitrogen (N) cycle and a substantial source of nitrous oxide (N2O), remain poorly understood. This knowledge gap hinders reliable projections of future N cycling and climate feedbacks in these critical ecosystems. Here, we demonstrate that along the estuarine-coastal continuum, the co-occurrence of hypoxia and acidification suppresses nitrification rates but stimulates nitrification-derived N2O emissions—although their combined effect is lesser than the sum of their individual effects. Metatranscriptomic analysis provided molecular evidence for these isotopically traced responses and uncovered critical microbial coping strategies through transcriptional adjustments in metabolic pathways for energy conservation and stress tolerance. This previously overlooked interaction disrupts microbial N cycling with potential impacts on N2O emissions and climate feedbacks, highlighting the necessity to revise predictive models by incorporating such multistressor dynamics.

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Physiological responses of Atlantic surfclams (Spisula solidissima) to moderate ocean acidification across thermal regimes

Published 23 October 2026 Science Leave a Comment
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Highlights

  • Interactive effects of warming and acidification tested in surfclams.
  • Growth, feeding, and metabolic rates measured after 6-week exposure.
  • Moderate acidification had limited effects under warming conditions.
  • Surfclams showed resilience to near-future ocean acidification.
  • Multi-stressor design improves ecological relevance of lab studies.

Abstract

Understanding marine organismal responses to co-occurring climate stressors is critical for predicting changes in ecosystems and commercial fisheries. The Atlantic surfclam supports a major commercial fishery in the Northeastern United States, where ocean warming and acidification are rapidly altering marine habitats. To evaluate how changing ocean conditions may affect bivalve physiology, surfclams were exposed to conditions reflective of ocean warming and acidification, respectively. One-year-old surfclams were exposed to nine conditions in a fully crossed design of temperature (ambient, +2 °C, and + 5 °C) and pH (7.88 ± 0.05, 7.76 ± 0.05, and 7.51 ± 0.07) for six weeks in a flow-through laboratory experiment using natural seawater. We quantified several physiological responses including growth, feeding, digestion, respiration rates, and shell weight and thickness to assess organismal performance across treatments.

Surfclams generally exhibited resistance to moderate ocean acidification across warming, but non-thermally stressful, temperatures. No effects of ocean acidification were observed on surfclam growth or respiration, although other physiological metrics (shell thickness and absorption rate) decreased with decreasing pH at some temperatures. These findings provide experimentally-derived insight into species-specific responses to interacting climate stressors. Further, the experimental design highlights the importance of integrating natural environmental variability into laboratory studies and studying multiple environmental stressors concurrently. This study contributes a basis for refining models of surfclam growth and distribution in potential future climate scenarios, with implications for sustainable fisheries management.

Continue reading ‘Physiological responses of Atlantic surfclams (Spisula solidissima) to moderate ocean acidification across thermal regimes’

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