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

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

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

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

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Impacts of ocean acidification on reproduction and early life development in marine teleost fish—a synthesis

Published 17 July 2026 Science Closed
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Ocean acidification (OA) remains a major and underexplored threat to marine fishes, particularly regarding reproductive physiology and early life stages (ELS). Although research over the past 15 years has documented diverse OA effects, substantial knowledge gaps persist. Most studies focussed on a limited set of species from North America and Europe, leaving broad uncertainty across phylogenetic groups, geographic regions and multi-stressor conditions. In adult fish, especially females, elevated pCO2 can shift energy allocation to prioritise reproductive output at the expense of egg or clutch size. While adult and juvenile fish have well-developed acid–base balancing systems, embryos and larvae possess only rudimentary mechanisms, making them more vulnerable to OA. This article stresses the importance of understanding these physiological and mechanistic responses to predict the future of fish stocks and ecosystem health as OA intensifies due to ongoing CO2 emissions. Our results highlight that OA responses in fish are highly variable and often specific to life stage and species, with acute and sometimes stage-specific effects not fully documented. Lastly, our recommendations on targeted research and funding are necessary to address the remaining knowledge gaps, including broadening taxonomic and geographic sampling, exploring multi-stressor scenarios and improving understanding of the downstream effects of OA on fish reproduction and development. Maintaining robust fish populations is vital for food security, employment and ecosystem functioning, making continued investigation into OA’s impacts a scientific and societal priority.

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Distinct polar carbon regimes reveal hemispheric asymmetry in surface ocean pCO₂ regulation

Published 17 July 2026 Science Closed
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Polar oceans play a major role in the global carbon cycle, absorbing a substantial fraction of human-emitted carbon dioxide and helping regulate Earth’s climate. Extreme conditions and seasonal sea-ice limit in situ observations, leaving major uncertainties in how carbon exchange varies across these regions. Consequently, the processes controlling surface ocean carbon at high latitudes remain poorly understood. Here we demonstrate that polar oceans exhibit a pronounced hemispheric asymmetry in the drivers of surface carbon variability. By combining machine learning with a data-driven regionalization of biogeochemical provinces, we reconstruct surface carbon patterns across both polar oceans over the period 1998-2022 and identify their dominant controls. Variability in the Southern Ocean is primarily governed by non-thermal processes linked to biological activity and wind-driven mixing, whereas in the Arctic Ocean thermodynamic forcing dominates in open waters and freshwater-driven stratification shapes the central basin. Polar oceans therefore do not operate as a single carbon regime. Instead, distinct mechanisms governing carbon cycling in each hemisphere are associated with opposing long-term pCO₂ trajectories, with weak or negative trends across much of the Southern Ocean but widespread increases throughout the Arctic.

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Lessons learned report — GOOD-OARS Summer School 2025

Published 17 July 2026 Courses and training , Newsletters and reports , Science Closed

The GOOD-OARS International Summer School 2025 aimed to equip the next generation of ocean scientists with the multidisciplinary research skills to enhance our understanding of how marine ecosystems will respond over the coming decades and support efforts to address harmful impacts on the ocean.

The Global Ocean Oxygen Decade (GOOD) and the Ocean Acidification Research for Sustainability (OARS) programmes are endorsed under the United Nations Decade of Ocean Science for Sustainable Development (2021-2030) and led by the Global Ocean Oxygen Network (GO2NE) and the Global Ocean Acidification Observing Network (GOA-ON) of IOC-UNESCO.

This Lessons Learned Report provides a summary and key insights on the training from the organisers and participants.

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

Published 16 July 2026 Science Closed
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Highlights

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

Abstract

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

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

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

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Ocean acidification, a silent threat to life on earth

Published 16 July 2026 Science Closed
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Did you know that the ocean plays a vital role in controlling the planet’s temperature, as well as providing food, minerals, and half of the oxygen we breathe? Another important role is balancing the amount of carbon dioxide gas in the atmosphere. Unfortunately, due to large emissions of carbon dioxide over the past few centuries, the ocean is becoming acidic. This process is called ocean acidification. Ocean acidification affects many sea organisms, especially those with shells, like mussels and corals, but it can also affect other animals’ sense of orientation, like fish. Scientists are discovering more about the potential impacts of ocean acidification on the marine system and, consequently, on humans and other life forms who depend on or explore the ocean. In this article, we explain why ocean acidification started, where it has been detected, its present and future impacts on marine life, and how we can help correct it.

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

Published 15 July 2026 Science Closed
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Highlights

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

Abstract

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

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

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

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

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

Graphical abstract

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

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

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

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Policy brief: ocean acidification & food security

Published 15 July 2026 Science Closed
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Key insights

Policymakers and researchers can better understand, mitigate, and adapt to the impact of ocean acidification on food security, ensuring a more sustainable future for blue foods and the communities that depend on them if they:

  1. Ensure baseline measurements of acidification are taken across different ocean basins.
  2. Research the impact of ocean acidification on fisheries, shellfish, coral and plankton and priortize seafood
    species of local importance.
  3. Explore knowledge gaps in ocean acidification science and research through a food security lens.
  4. Align and integrate ocean acidification and food security research with regional and national policy objectives.
  5. Leverage international frameworks to direct research, policy and financing support to more adequately assist
    nations in prolonged responses to the impacts of ocean acidification on food security

Key takeaways:

By implementing these recommendations, policymakers and researchers can better understand, mitigate, and adapt to the impact of ocean acidification on food security, ensuring a more sustainable future for blue foods and the communities that depend on them:

  • Ensure baseline measurements of acidification are taken across different ocean basins.
  • Research the impact of ocean acidification on fisheries, shellfish, coral and plankton and prioritize seafood species of local importance.
  • Explore knowledge gaps in ocean acidification science and research through a food security lens.
  • Align and integrate ocean acidification and food security research with regional and national policy objectives.
  • Leverage international frameworks to direct research, policy and financing support to more adequately assist nations in prolonged responses to the impacts of ocean acidification on food security.

…

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MACAN coastal acidification in the classroom curriculum- grades 9-12

Published 15 July 2026 Educational Materials , Resources , Science , Web sites and blogs Closed
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This curriculum developed by the Mid-Atlantic Coastal Acidification Network (MACAN) brings coastal and ocean acidification into the classroom in clear, practical ways. It provides complete lesson plans, hands-on activities, and data-driven investigations that support student inquiry while aligning with Next Generation Science Standards (NGSS).

Designed for high school classrooms, the lessons can be taught as a full unit or selected individually to fit existing course needs.

Lesson 1: This section introduces the curriculum and key concepts in ocean acidification through background reading and short videos. It includes NGSS-aligned questions and transcripts that can be used in class or for flipped learning.
Lesson 2: Students learn how carbon moves through Earth’s systems and how emissions affect atmospheric CO₂. An interactive game helps reinforce sources and sinks through hands-on participation.
Lesson 3: Students explore how increased atmospheric CO₂ changes ocean pH and water chemistry. Demonstrations and guided activities help introduce the foundational processes behind ocean acidification.
Lesson 4: Through hands-on lab activities, students investigate the chemical reactions that drive ocean acidification. These labs also introduce how changes in chemistry affect shell formation in marine organisms.
Lesson 5: Students compare ocean and coastal acidification using data and infographics. The lesson emphasizes how estuaries and coastal waters experience different conditions than the open ocean.
Lesson 6: Students examine data on Mid-Atlantic species to understand how decreasing pH affects growth, reproduction, and survival. They connect changes in chemistry to impacts on living organisms.
Lesson 7: Students work individually and in groups to analyze data related to bivalve health. The lesson focuses on interpreting evidence and drawing conclusions about the effects of dissolved CO₂.
Lesson 8 Part 1: This lesson engages students in investigating declining bay scallop populations while exploring the scientific method and experimental design. Students analyze data, build critical thinking skills, and examine coastal acidification’s impacts on biological species.
Lesson 8 Part 2: In Part 2, students apply the scientific method to investigate the bay scallop mystery by reviewing key steps, conducting research, developing hypotheses, and designing experiments to guide their inquiry.
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Ocean acidification education toolkit – Pacific Northwest

Published 15 July 2026 Educational Materials , Resources , Science , Web sites and blogs Closed
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Bring your students into the Pacific Northwest to discover how the ocean acts like a carbon sponge and its effects on salmon and plankton that fuel the ecosystem. This toolkit utilizes effective communication strategies to convey the significance of ocean acidification effects and empower mitigation actions within communities. Tested in classrooms, this toolkit increased ocean acidification literacy for ages 9 and older. Students can become OA Ambassadors as they apply what they know toward ocean acidification solutions.

The toolkit includes four NGSS aligned modules that can be used independently or together. Each module includes the ocean acidification literacy goal, a value that can be used to better engage or connect with students, discussion guide, and solutions students can take part. In addition, an optional script that uses specific language will guide the instructor in successful and effective ocean acidification dialogue.

ModuleDescription
I. Our Ocean: The Giant SpongeStudents learn how the ocean absorbs carbon dioxide and the difference between regular and uncontrolled amounts through a guided demonstration.
II. Our Changing OceanStudents make the connection between carbon dioxide in the ocean and increased acidity. With a simple experiment, they compare ocean acidity now with the past.
III. Swim, Snack, SinkStudents learn about the impacts of increased acidity on the plankton that feed the food web through an interactive activity.
IV. Senseless Salmon!Students understand the impacts of ocean acidification on a salmon’s ability to smell to migrate and avoid predators through a game.
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Development of hypoxia and acidification during harmful algal blooms: dynamic multi-stressor conditions in NY, USA, estuaries

Published 14 July 2026 Science Closed
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Highlights

  • Alexandrium blooms occurred with normoxic conditions and moderate pH (7.5-8.0).
  • Alexandrium blooms occurred with moderate pCO2 (400 – 1,000 µatm) and saturating conditions for aragonite.
  • Dinophysis blooms co-occurred nocturnal acidification (8.71 to 13.6 hr d−1) and hypoxia (0.52 to 3.88 hr d−1).
  • Dinophysis blooms co-occurred with high pCO2 (1,000 – 3,500 µatm) and undersaturated aragonite (Ωar < 1).
  • The co-occurrence of nocturnal hypoxia, acidification, Ωar undersaturation, and HABs coupled is a significant threat for marine life.

Abstract

While harmful algal blooms (HABs), hypoxia, and ocean acidification are common occurrences in coastal zones, research investigating the co-occurrence and interactions between these processes has been lacking. Here, we documented the initiation, peak, and demise of eight distinct HAB events caused by Alexandrium catenella and Dinophysis acuminata over a two-year period in two estuaries (Northport Harbor and Cold Spring Harbor, NY, USA). We concurrently characterized the dynamics of carbonate chemistry, including pCO2 and the saturation state of aragonite (Ωar), pH, dissolved oxygen (DO), and general environmental conditions in space and time. HABs occurred in succession and reached high densities with A. catenella blooms exceeding 104 cells L−1 being succeeded by D. acuminata blooms exceeding 106 cells L−1. A. catenella blooms occurred during spring months under generally normoxic conditions with moderate levels of pCO2 (400 – 1,000 µatm), only brief periods of acidification (pH < 7.5), mostly saturating conditions for aragonite, and an absence of hypoxia. In contrast, D. acuminata blooms, which occurred in summer, consistently co-occurred with bouts of extended nocturnal acidification (8.71 to 13.6 hr d−1) and hypoxia (0.52 to 3.88 hr d−1) coupled with higher levels of pCO2 (1,000 – 3,500 µatm), and undersaturating conditions for aragonite (Ωar < 1). During both blooms, nearshore locations hosted higher cell densities, lower pH and DO, and higher pCO2 compared to open water regions. The co-occurrence of multiple stressors including nocturnal hypoxia, acidification, Ωar undersaturation, and HABs, coupled with strong diel cycling of DO, pH, and pCO2, especially during D. acuminata blooms, represents a significant and previously unrecognized threat for marine life.

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

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

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

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

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

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

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

Published 13 July 2026 Science Closed
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Simple Summary

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

Abstract

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

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The effects of single and multiple climate-driven stressors exposures on the seagrass Posidonia oceanica: phenological, cellular, and genetic adaptations

Published 10 July 2026 Science Closed
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Posidonia oceanica is a foundation seagrass species endemic to the Mediterranean Sea, where it forms highly productive meadows that support biodiversity, coastal protection and long-term blue carbon storage. However, these ecosystems are increasingly threatened by the combined effects of climate change and local anthropogenic pressures, including ocean warming, marine heatwaves, ocean acidification, hypersalinity and thermal pollution. Despite growing evidence of the vulnerability of P. oceanica to environmental change, the mechanisms underlying its acclimation capacity, resilience and potential vulnerability thresholds remain only partially understood, particularly under multiple-stressor scenarios.This study investigates the responses of P. oceanica to climate change-related stressors across multiple levels of biological organization, integrating evidence from meta-analysis, controlled mesocosm experiments, molecular analyses and field observations. Special attention is given to the role of environmental history in shaping population-specific responses, comparing plants exposed to contrasting environmental conditions and assessing their phenological, physiological, metabolic and molecular performance under single and combined stressors.By linking organismal, molecular and meadow-scale responses, this work provides new insights into the capacity of P. oceanica to cope with future climate scenarios and local anthropogenic disturbances. The findings contribute to identifying resilience mechanisms and vulnerability patterns in Mediterranean seagrass ecosystems, supporting the development of more effective monitoring, management and conservation strategies under ongoing global change.

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Coastal Ocean Data Analysis Product in North America (CODAP-NA, Version 2026) from 1981-08-23 to 2024-11-23 (NCEI Accession 0315529)

Published 10 July 2026 Science Closed
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The coastal Ocean Data Analysis Product in North America (CODAP-NA) Version 2026 represents a major expansion of coastal ocean carbonate chemistry synthesis for North American continental margins. Compared to CODAP-NA Version 2021 (61 cruises, 3,391 profiles, and 28,206 data rows), the updated product integrates newly available cruise observations spanning more than four decades, substantially increasing both the spatial and temporal coverage of coastal biogeochemical measurements across all North American continental shelves. This version of the CODAP-NA is composed of 32,250 oceanographic profiles from 446 research cruises covering all continental shelves in North America (U.S. west coast, U.S. east coast, Gulf of Mexico, and Alaska coast). Data for 14 variables (temperature; salinity; dissolved oxygen concentration; dissolved inorganic carbon concentration; total alkalinity; pH on the Total Scale; carbonate ion concentration; fugacity of carbon dioxide; and concentrations of silicate, phosphate, nitrate, nitrite, nitrate plus nitrite, and ammonium) have been subjected to extensive quality control. Funding for this work comes from the National Oceanic and Atmospheric Administration (NOAA) Ocean Acidification Program.

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Impact of climate change on Portuguese marine coastal environments

Published 9 July 2026 Science Closed
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The potential impacts of climate change on marine habitats were assessed using RCP4.5 and RCP8.5 projections of environmental parameters that included sea surface temperature (SST), pH, salinity, planktonic productivity (PP) and current strength (CS). The analysis was conducted separately for three distinct oceanographic regions of the Portuguese coastline (North, Centre and South) up to the middle of the century. Temporal trends in environmental variables were assessed using time series analyses. Overall, changes expected up to the middle of the century include increasing SST and PP, decreasing pH and salinity, and slight increases in CS. Spatial–temporal analyses revealed high present–future environmental overlay for most environmental variables. However, changes in individual environmental variables cumulatively resulted in statistically significant changes in environmental similarity. Still, the projected changes are not expected to exceed ecological thresholds, above which they would be likely to alter species’ habitat suitability or to result in species distribution shifts. Anomaly analyses suggest that present–future shifts do not surpass 1/5 (pH, PP, CS) or 2/3 (salinity) of the unit, regardless of projection and area, while SST anomalies ranged from −1.1 °C to 1.1 °C. Compared to IPCC large-scale predictions for Atlantic/Mediterranean regions, the intensity of shifts on the Portuguese coast may be lower.

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