Applications open: training course on ocean alkalinity enhancement – assessing the impact on marine organisms

Published 2 April 2026 Events Leave a Comment

The IAEA Ocean Acidification International Coordination Centre is hosting a second Training Course on Ocean Alkalinity Enhancement – Assessing the Impact on Marine Organisms. The deadline to apply is Thursday April 30th (extended from what is indicated in the linked announcement). To apply, applicants will need to submit their application through their national authority to the IAEA – in most cases, this will be your country’s permanent mission to the IAEA. Travel and lodging for all scientists accepted to the course will be covered. Priority will be given to early-career scientists with experience in marine environmental changes who have already received training on ocean acidification and seawater carbonate chemistry. Preference will be given to applicants with experience in biological response research and who are interested in conducting studies on the ecological impact of OAE. If you have questions on the application procedure, please contact Ms Lina Hansson (L.Hansson(at)iaea.org) or Ms Carolina Galdino (C.Galdino(at)iaea.org).

Dates: 15 – 19 June 2026

Location: IAEA Marine Environment Laboratories, Monaco.

Application Forms

Introduction
The Training Course on Ocean Alkalinity Enhancement — Assessing the Impact on Marine Organisms is part of the capacity building program of the IAEA Ocean Acidification International Coordination Centre (OA-ICC). The program aims to support IAEA Member States to minimize and address the impacts of ocean acidification (Sustainable Development Goal 14.3) and study the impacts of ocean-based solutions.

The course 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).

Objectives
The ocean is under pressure from warming, acidification and oxygen loss, adversely impacting marine ecosystems and the communities and societies who depend on them. But the ocean, covering 70% of Earth’s surface, can also be a vital part of the solution and our ally to mitigate and adapt to climate change. Meeting the objectives of the Paris Agreement to limit warming to well below 2º C would not only require drastic cuts in carbon dioxide (CO2) emissions, but also the active removal of carbon CO2 on the order of 100–1000 Gt CO2 over the 21st century (IPCC, 2018). Ocean alkalinity enhancement (OAE) is a marine Carbon Dioxide Removal (mCDR) approach which is receiving growing interest from scientists, policy makers and industry. It entails the addition of alkaline materials to the sea with the goal of increasing the ocean’s potential to absorb CO2. There is limited scientific information to date about the impact that OAE might have on marine organisms and ecosystems. Building technical expertise to assess ecological impacts of OAE is critically needed to allow for informed policy decisions about this approach.

The aim of this course is to train scientists on how to perform laboratory experiments on the potential impact of OAE on marine organisms. The course includes both theoretical and practical exercises with the goals of designing purposeful experiments, analyzing complex datasets, avoiding typical pitfalls, and ensuring data comparability with other studies. Lectures on the broader context and implications of OAE will also be provided (e.g., societal and governance aspects). The course will be largely based on the 2023 Guide to Best Practices for Ocean Alkalinity Enhancement Research, especially the chapters on experimental design.

Target Audience
The course is open to 10-12 trainees. Priority will be given to early-career scientists with experience in marine environmental changes who have already received training on ocean acidification and seawater carbonate chemistry. Preference will be given to applicants with experience in biological response research and who are interested in conducting studies on the ecological impact of OAE. At least one publication in the field of marine environmental changes is required.

Working Language
English

…

Participation and Registration
Scientists wishing to participate in the event must 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, participants are requested to send the Participation Form (Form A) to their competent national authority (e.g. Ministry of Foreign Affairs, Permanent Mission to the IAEA, or National Atomic Energy Authority) for onward transmission to the IAEA by 17 April 2026. Participants who are members of an organization invited to attend are requested to send the Participation Form (Form A) through their organization to the IAEA by the above deadline.
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.

Additional Requirements
The participants should have a university degree in marine chemistry, biology, oceanography, or a related scientific field, and must have already received training on ocean acidification and seawater carbonate chemistry or performed ocean acidification biological response experiments. Selection will be based on merit and interest. Your applications should include:

  • A motivation letter with a short description of your research interests, why you would like to
    participate, and your plans regarding present and future research on OAE (max one A4 page)
  • CV with publication list
Continue reading ‘Applications open: training course on ocean alkalinity enhancement – assessing the impact on marine organisms’

OA-ICC bibliographic database updated

Published 3 April 2026 Science Leave a Comment

An updated version of the OA-ICC bibliographic database is available online.

The database currently contains 9,798 references and includes citations, abstracts and assigned keywords. Updates are made every month.

The database is available as a group on Zotero. Subscribe online or, for a better user experience, download the Zotero desktop application and sync with the group OA-ICC in Zotero. Please see the “User instructions” for further details.

OA-ICC, 3 April 2026.

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

Published 3 April 2026 Science Leave a Comment
Tags: , , , , , , , , ,

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

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

Ocean acidification affects the timing of puberty and the reproductive output in a marine temperate fish

Published 2 April 2026 Science Leave a Comment
Tags: , , , , , , , ,

Ocean acidification (OA) is a major climate-related threat to fish that can disrupt the regulation of the reproductive axis of fish, impacting reproductive success. However, previous studies have only focused on a single reproductive cycle and reported increased fecundity in some species exposed to OA. Since acclimation over several reproductive cycles can occur, it is necessary to evaluate successive reproductive cycles for predicting the actual resilience of species to OA. In this study we assessed the impact of lifetime exposure to different ocean pH/pCO2 levels (Current condition, Moderate OA and High OA) on the sexual maturation and spawning phenology of the European sea bass, over its two first reproductive periods. We tested the hypothesis that OA would exert its greatest impact at the onset of puberty (first reproduction). Accordingly, High OA exposure induced an earlier onset of puberty in both sexes, resulting in a longer spawning period and an increased fecundity. These effects were reduced during the second reproductive season. However, OA affected egg quality and sperm motility profile during the second reproductive season, leading to a total mortality at hatching of embryos spontaneously produced. This mortality was not observed in embryos produced through hormone-induced oocyte maturation and in vitro fertilisation. These results suggest that OA affects the regulation of oocyte maturation and/or the synchronisation of eggs and sperm release. The OA-driven shift in spawning may misalign with optimal environmental conditions for offspring survival. This increases the population’s vulnerability and could favour species whose reproduction is more resilient to OA.

Continue reading ‘Ocean acidification affects the timing of puberty and the reproductive output in a marine temperate fish’

California’s 2026 Coast and Ocean Assessment

Published 1 April 2026 Science Leave a Comment
Tags: , ,

Key Messages

  1. California’s coastal ocean moderates our climate, holds potential solutions to climate change, and is directly impacted by a changing climate. California’s coast and ocean are also critical natural resources and economic assets, generating $51.3 billion in gross domestic product and supporting more than 500,000 jobs.
  2. The public and policymakers can get a broad, state-level understanding of the overall status of the coast and ocean through this synthesis of complex data into single statewide metrics and subsequent aggregation of those evaluations in this report. At the same time, some categories are better understood through downscaled or local evaluations.
  3. This coast and ocean assessment is the result of the work of more than 120 scientific experts from academic institutions, state and federal agencies, NGOs, and Tribes. The widespread support that it has garnered exemplifies the value of leveraging buy-in from a broad scientific community that stands poised to continue to support in delivering the best available science to policymakers.
  4. State-federal partnerships provide essential infrastructure: evaluations for 13 of the 19 categories leveraged federal data, and the evaluations of five categories were fully reliant on the specialized expertise and in-kind time of federal scientists.
  5. Distilling data into single metrics for each category enabled us to flexibly incorporate multiple data types, retain geographic information while providing statewide coverage, and present findings that are both accurate and easily understood. This approach also ensures forward compatibility to incorporate new data as they become available and repeat this
    analysis in the future.
  6. The 2014-2015 marine heatwave was a seminal event that disrupted California’s ocean ecosystems, including loss of species and ecosystem services, declining populations, and geographic range shifts. We can expect more warm years like this in the future.
  7. The state has a valuable role to play in strengthening the ocean monitoring and evaluation enterprise, such as expanding monitoring in Northern California, coordinating networks and standardizing methods, supporting innovative monitoring technologies to better track cryptic species, and identifying where strategic investments can fill data gaps.

See summary of ocean acidification findings.

Continue reading ‘California’s 2026 Coast and Ocean Assessment’

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

Published 31 March 2026 Science Leave a Comment
Tags: , , , , , ,

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

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

Millennial-scale changes in marine lithofacies during the Paleocene-Eocene Thermal Maximum: a deep-time analog for Anthropocene hydrologic and acidification impacts

Published 30 March 2026 Science Leave a Comment
Tags: , ,

Highlights

  • Global marine sediment changes during the PETM were quantitatively reconstructed.
  • Sediment changes controlled by sea level and latitudinal hydrology.
  • Acidification influenced pelagic sediment composition, especially in the Atlantic.
  • Carbonate “overshoot” occurred during the PETM recovery.

Abstract

Extreme climatic events can significantly alter marine lithofacies. However, global oceanic sediment patterns during deep-time hyperthermal events, which are potential analogues for the hydrologic and climatic impacts of modern anthropogenic warming, remain poorly constrained. Here, we compile 162 marine stratigraphic records to track millennial-scale sediment dynamics during the Paleocene–Eocene Thermal Maximum (PETM). We find that sedimentation was primarily controlled by hydrologic intensification (resulting in ∼36% carbonate platform demise), eustatic fluctuations (resulting in ∼52% siliciclastic shelf retrogradation), and ocean acidification (resulting in ∼41% deep-sea calcareous sediment replacement). Lithofacies changes along continental margins show distinct latitudinal zonation, reflecting variations in hydrologic intensity and carbonate productivity. The impact of eustatic sea-level change is strongest in region where hydrologic effects are muted. Deep-sea acidification was widespread, with the strongest expression in the Atlantic, and weaker effects in the Pacific and Indian oceans. Widespread carbonate “overshoot” following PETM recovery suggests enhanced continental weathering. This study implies that ongoing anthropogenic warming could rapidly reorganize marine sedimentation through intensified hydrological cycle, accelerated sea-level rise, and ocean acidification on centennial timescales, much faster than during the PETM and potentially with greater magnitude.

Continue reading ‘Millennial-scale changes in marine lithofacies during the Paleocene-Eocene Thermal Maximum: a deep-time analog for Anthropocene hydrologic and acidification impacts’

State of the global climate 2025

Published 30 March 2026 Newsletters and reports Leave a Comment
Tags: , ,

The temperature of the Earth changes in response to the rate at which energy enters and leaves the Earth system. Increasing concentrations of greenhouse gases in the atmosphere such as carbon dioxide, methane and nitrous oxide, all of which reached their highest level in 800 000 years in 2024 (the last year for which we have consolidated global figures), reduce the rate at which energy leaves the Earth system. This imbalance – the Earth’s energy imbalance, a new indicator in this year’s report – leads to an accumulation of excess energy.

One of the longest observational records of climate change is that of global mean near-surface temperature. The past three years are the three warmest years in the 176-year combined land and ocean observational record. The year 2025 is the second or third warmest year, depending on the dataset used, slightly cooler than the record warmth of 2024, due in part to the transition from El Niño at the start of 2024 to La Niña in 2025. The warming seen at the surface and throughout the troposphere represents just 1% of the excess energy trapped by greenhouse gases.

The vast majority of the excess energy – around 91% – has been absorbed by the ocean in the form of heat. Ocean heat content reached a new record high in 2025, reflecting the continued increase in energy.

Another 3% of the excess energy warms and melts ice. In a global set of reference glaciers with long-term measurements, eight of the ten most negative annual glacier mass balances since 1950 have occurred since 2016. The ice sheets on Antarctica and Greenland have both lost significant mass since satellite records began.

The extent of sea ice in the Arctic has decreased in all seasons since satellite measurements began in 1979, and the annual maximum extent in 2025 was the lowest or second lowest in the observed records. Sea-ice extent around Antarctica showed a small long-term increase until 2015, but since then, extents throughout the annual cycle have dropped considerably, and the past four years have seen the four lowest Antarctic sea-ice minima on record.

The warming ocean and melting of ice on land from glaciers and ice sheets have both contributed to the long-term rise in global mean sea level. The rate of global sea-level rise has increased since satellite measurements began in 1993.

The remaining ~5% of the excess energy is stored in the continents, increasing the temperature of the land mass and thereby affecting terrestrial processes.

As well as absorbing the majority of the energy trapped by increasing concentrations of greenhouse gases, the ocean has also absorbed around 29% of the anthropogenic emissions of carbon dioxide in the past decade. While this helps to buffer the effects of climate change, it also alters the chemical composition of the ocean water, reducing the pH in a process known as ocean acidification.

These rapid large-scale changes in the Earth system have cascading impacts on human and natural systems, contributing to food insecurity and displacement where hazards intersect with high vulnerability and limited adaptive capacity.

Continue reading ‘State of the global climate 2025’

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

Published 30 March 2026 Science Leave a Comment
Tags: , , , , , ,

Highlights

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

Abstract

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

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

Metabolic rate measurements of two benthic invertebrates under simulated climate change conditions

Published 30 March 2026 Science Leave a Comment
Tags: , , , , , , , , , ,

Background

Climate change is profoundly altering marine ecosystems through ocean warming and acidification. These stressors are especially pronounced in the Mediterranean Sea, a climate change hotspot projected to warm faster than the global average. Increased temperatures and reduced pH directly affect metabolic processes in marine invertebrates by elevating respiration rates up to species-specific thermal limits, beyond which physiological performance declines. Ocean acidification further disrupts metabolic processes by increasing energetic maintenance costs. Sessile and sedentary marine invertebrates, such as sponges and benthic gastropods, are particularly exposed to such environmental shifts due to their limited ability to escape unfavorable conditions, making physiological plasticity and local adaptation crucial for persistence.

New information

This manuscript presents a dataset of oxygen consumption rates and wet weight measurements for two low-mobility marine species, the gastropod Hexaplex trunculus and the sponge Chondrilla nucula. Using a common garden experiment, individuals from North and South Aegean populations were exposed for three months to simulated climate change conditions combining increased temperature and reduced pH. The dataset documents respiration measurements obtained using metabolic chambers after three months of exposure, allowing comparisons across species, geographic origin, and experimental treatments.The dataset accounts for intraspecific variation in these responses, providing insight into potential adaptive differences among geographically distinct populations. These data provide a resource for future analyses of metabolic responses of marine invertebrates to combined warming and acidification conditions.

Continue reading ‘Metabolic rate measurements of two benthic invertebrates under simulated climate change conditions’

Ocean acidification and blue food security: mapping two overlapping regime complexes

Published 27 March 2026 Science Leave a Comment
Tags: , ,

The dual challenges of blue food security and ocean acidification (OA) have become increasingly urgent concerns for global sustainability. Blue foods, which provide key nutrients, are threatened by OA, posing risks to biodiversity, fisheries, and the livelihoods of communities that depend on them. The pressure of OA highlights the urgency of addressing blue food security through the lens of OA. Understanding the governance landscape that shapes responses is crucial, yet existing literature has largely considered the OA and blue food security regimes separately. This paper analyzes whether and how the international governance of OA and blue food security intersect by mapping their regime complexes. The central research question investigates how international regimes interact in governing this nexus. The analysis finds that the two regime complexes overlap in many areas, including fisheries/marine resources and climate change. Although many actors and instruments mention both topics, significant governance fragmentation persists. Case studies on the Food and Agriculture Organization (FAO) and the United Nations Framework Convention on Climate Change (UNFCCC) reveal that neither institution provides a comprehensive framework for governing the nexus of OA and blue food security resilience. The FAO lacks an explicit mandate for OA governance. If mentioned, OA is relegated to a list of stressors. The UNFCCC addresses OA only indirectly through CO2 mitigation efforts, and its instruments, while referencing food production, generally do not link it explicitly to OA. This results in fragmented authority, unclear responsibility, and limited integration across policy domains. Furthermore, a discrepancy exists where blue food security is recognized as a topic of legal and political urgency, while OA often only gains scientific attention. We conclude that further joint integration of OA and blue food security in legal and policy frameworks is necessary to enhance coherence and coordination across these regimes.

Continue reading ‘Ocean acidification and blue food security: mapping two overlapping regime complexes’

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

Published 27 March 2026 Science Leave a Comment
Tags: , , , , , , , , , , , ,

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

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

Individual foraminiferal analysis: a promising tool for high-resolution temperature and pH reconstruction

Published 27 March 2026 Science Leave a Comment
Tags: , , , , , ,

Compared with traditional bulk foraminiferal analysis methods, in situ analysis of individual foraminiferal tests (individual foraminiferal analysis or IFA) offers several advantages over traditional bulk methods, including enhanced temporal resolution where fossiliferous sample material is limited as well as potentially resolving seasonal-scale climate variability in deep time. Despite these advantages, applications of element-to‑calcium (El/Ca) ratios and δ11B in benthic foraminifera using IFA remain limited, and the biogeochemical drivers of intra-test and inter-test geochemical variability are poorly constrained. In this study, we systematically evaluate El/Ca ratios and δ11B in individual benthic foraminifera. By analysing Holocene epifaunal benthic foraminiferal species Cibicidoides wuellerstorfi from a deep ocean core site (ODP Site 999), we conclude that intra- and inter-test variabilities are regulated by ontogenetic effects resulting in inter-test variabilities of ±0.14 mmol/mol Mg/Ca, ± 14 μmol/mol B/Ca, and ± 0.18 ‰ δ11B. Application of the IFA method to epifaunal benthic foraminifera species Cibicides lobatulus from a box core in the English Channel, UK reveals ~0.1 pH units acidification and ~ 1 °C warming since the mid-19th century. By demonstrating that individual-level variability in reconstructed temperature and pH tracks seasonal trends in the available contemporaneous water-column instrumental measurements at the same site, we provide a ground-truthing to our multi-proxy IFA methodology, and also demonstrate the potential for benthic IFA to provide seasonal-scale reconstructions of ocean climate over hundreds to millions of years.

Continue reading ‘Individual foraminiferal analysis: a promising tool for high-resolution temperature and pH reconstruction’

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

Published 26 March 2026 Science Leave a Comment
Tags: , , , , , ,

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

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

Resilient adults but vulnerable larvae: demographic pathways of chiton decline under ocean acidification

Published 26 March 2026 Science Leave a Comment
Tags: , , , , , , , , , , , , , ,

Highlights

  • Natural CO₂ seep systems showed reduced intertidal chiton abundance.
  • Adult chitons showed resilience to acidification in field and lab experiments.
  • Larval survival and recruitment were strongly impaired under acidified seawater.
  • Population declines are linked to early life-stage vulnerability.
  • Loss of chitons may reduce grazing and bulldozing, reshaping intertidal communities.

Abstract

Ocean acidification (OA) is a major threat to marine calcifiers; however, the sensitivity across taxa and life stages remains elusive. In this study, we combined field surveys of natural CO₂ seeps with laboratory exposure, transplantation, and larval settlement experiments to assess the effect of OA on chitons, a group of calcifying grazers and bulldozers that play critical roles in the structure of rocky intertidal ecosystems. Field surveys revealed approximately 98.6% reduction in chiton (Acanthopleura loochooana, Liolophura japonica, and Acanthochitona rubrolineata) abundance at acidified habitats (pH 7.6), despite greater microalgal food availability and no detectable increase in predator abundance. Laboratory CO₂-exposure experiments showed no direct effect of OA on adult A. loochooana survival, which is consistent with the presence of protective structural features in the valves that confer resistance to dissolution. Transplant experiments revealed no evidence of increased adult A. loochooana mortality in the acidified habitats (pH 7.6). In contrast, larvae showed pronounced sensitivity to OA, with acidified seawater (pH 7.6) reducing larval settlement by approximately 81.5% compared to control conditions (pH 8.1); early life stages were the most vulnerable. These findings suggest that OA-associated decline in chiton abundance is mainly mediated by impaired recruitment rather than by direct adult mortality, predation, or food limitation. Given the role of chitons as grazers and bulldozers, their loss could substantially change intertidal community dynamics by decreasing grazing pressure and disturbing algal and microbial assemblages. Our findings underscore the criticality of considering life-stage vulnerability and ecological function when evaluating the ecosystem-level consequences of OA.

Continue reading ‘Resilient adults but vulnerable larvae: demographic pathways of chiton decline under ocean acidification’

The role of seagrass in modifying dissolved oxygen and pH in coastal systems: a meta-analysis

Published 26 March 2026 Science Leave a Comment
Tags: , , , ,

Highlights

  • Seagrass productivity drives diel pH–DO variation, enhancing local buffering capacity
  • Oxygen–pH coupling highlights seagrass role in mitigating acidification during photosynthesis
  • Studies should integrate temperature, salinity, and light to parse biological drivers
  • Expanded geographic scope, especially tropics and Global South, is urgently needed
  • Standardized pH scales and advanced sensors to improve comparability and monitoring

Abstract

Seagrass meadows, highly productive ecosystems, can influence local water chemistry by increasing dissolved oxygen in the water column and removing dissolved CO2 thus raising pH. This study provides the first quantitative synthesis of literature comparing pH and dissolved oxygen (DO) between systems with and without seagrasses. Through a systematic literature review and meta-analysis, we collated and analysed data from 63 studies reporting pH values and 70 studies reporting DO. Across studies, seagrass habitats were associated with slightly higher mean pH relative to non-seagrass habitats. Seagrass habitats showed the highest mean pH (8.11 ± 0.30) and the greatest diel variability (0.47 ± 0.65) of all habitats investigated with unvegetated areas exhibiting lower mean pH and reduced variability. The diel pH range was also significantly higher in seagrass habitats (p = 0.024). The pooled standardized mean difference was small (0.15), indicating a modest overall effect of seagrass presence on pH across studies. Although mean DO concentrations were slightly lower in seagrass habitats compared to other vegetated systems, they experienced fewer hypoxic events (12% of values < 2 mg/L) compared to other vegetated systems (55%). Generalized additive models identified DO as the strongest predictor of pH, with minor contributions from temperature and salinity. Overall, seagrass habitats are associated with increasing average pH and reducing hypoxia across multiple sites and regions. However, the magnitude and direction of effects vary widely among studies (I2 = 97%). These findings indicate that seagrass influences on water chemistry are context-dependent and likely driven by interactions among biological processes and local environmental conditions. Key knowledge gaps were identified; including the need for a greater focus on H+ concentration and the need for more research on seagrass ecosystems in underrepresented geographical regions.

Continue reading ‘The role of seagrass in modifying dissolved oxygen and pH in coastal systems: a meta-analysis’

Characteristics of meiofaunal community in the subtidal zone near Hupo, anticipating ocean acidification on the coast of Korea

Published 25 March 2026 Science Leave a Comment
Tags: , , , , , , , , ,

This study aimed to investigate the meiofauna community characteristics in coastal waters affected by ocean acidification. Therefore, the meiofauna communities in the coastal waters of Hupo in Uljin-gun, which showed a high ocean acidification trend in the integrated data on the coastal areas of South Korea for the previous ten years, were monitored over five years. During the study period, the mean abundance of total meiofauna communities expressed in population density was 614 individuals (Inds.)/10 cm2. The most dominant taxa were nematodes (65–70%) and harpacticoids (7–20%); these two taxa accounted for approximately 80% of the total meiofauna abundance. Station (St.) 5 and 10, which had the lowest seawater pH values, showed the lowest average abundance values for harpacticoids (average 46 Inds./10 cm2) and nauplius (average 4 Inds./10 cm2) among the major meiofaunal groups over the 5-year period. In addition, St. 5 indicated the lowest meiofaunal diversity index of 0.54. To examine the effect of ocean acidification on meiofauna communities at the species level, species of nematodes, the most dominant taxon, were analyzed. The results indicated that the number of nematode species at St. 10, one of the two stations with the lowest pH, was the lowest compared to those at other stations. Analysis of c-p values for nematode species ​​showed that both species sensitive to environmental disturbance and species resistant to environmental pollution appeared at high rates. According to the feeding type of nematodes, epistrate feeders accounted for a remarkably high proportion at St. 10. This study provides various data on meiofauna community characteristics to understand the effects of ocean acidification on coastal ecosystems.

Continue reading ‘Characteristics of meiofaunal community in the subtidal zone near Hupo, anticipating ocean acidification on the coast of Korea’

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

Published 25 March 2026 Science Leave a Comment
Tags: , , , ,

Highlights

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

Abstract

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

Continue reading ‘CO2 rise modulates the physiological performance of the diatoms Thalassiosira pseudonana and Thalassiosira weissflogii to light challenge’

Analysing the distribution and variability of dissolved inorganic carbon and alkalinity over the Bay of Bengal region using the coupled ocean biogeochemical modeling

Published 25 March 2026 Science Leave a Comment
Tags: , , ,

Highlights

  • High-resolution regional coupled ocean biogeochemical modeling in the Bay of Bengal.
  • Spatio-temporal variability of Dissolved Inorganic Carbon and Alkalinity is studied.
  • Aragonite (calcite) saturation depth in the Bay of Bengal is estimated.
  • ENSO and IOD events significantly influence surface DIC of the BoB region.

Abstract

A prototype high-resolution regional coupled ocean biogeochemical modeling experiment is carried out in the Bay of Bengal (BoB) region to study the distribution and spatio-temporal variability of Dissolved Inorganic Carbon (DIC) and Alkalinity (Alk) during the period 2000-2021. It is found that in the eastern as well as head BoB, the DIC concentration remains less (1.6-1.7 mol/m3) as compared to the south-west and west-central BoB, where the DIC concentration remains particularly high (>1.9 mol/m3). The highest (lowest) DIC concentration in the BoB remains in the Mar-April (Oct) months. The seasonal variability of the DIC and Alk is studied vis-à-vis seasonal changes in the currents and freshwater flux. The depth profiles of DIC, Alk, and DIC/Alk ratio are also investigated across different sections in the BoB. The DIC remains stratified in the BoB, and the stratification becomes much more pronounced on moving from south to north (and west to east) part of the model domain. The aragonite (calcite) saturation depth ranges between approx. 100-400 m (500-4000 m) in the BoB. The particularly high (>8.1) and low (∼8) pH values are found in the head BoB and southwest BoB, respectively. It is shown that the influence of El Nino – Southern Oscillation (ENSO) event on the surface DIC concentration over the BoB region is much stronger as compared to the Indian Ocean Dipole (IOD) event.

Continue reading ‘Analysing the distribution and variability of dissolved inorganic carbon and alkalinity over the Bay of Bengal region using the coupled ocean biogeochemical modeling’

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

Published 25 March 2026 Science Leave a Comment
Tags: , , , , , , , ,

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

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

Subscribe

Search

  • Reset

OA-ICC Highlights

Resources