Posts Tagged 'North Atlantic'

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How oysters are impacted by environmental conditions and farming practices

Published 29 January 2026 Web sites and blogs Closed
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The Rhode Island aquaculture industry is more robust than ever. The value of aquaculture products was $8,795,493 in 2024 and 89 active aquaculture farms covered 392.5 acres, according to a report by the Rhode Island Coastal Resources Management Council.

Eastern oysters account for approximately 99% of the state’s aquaculture production, the report noted. Jacqueline Rosa, who is pursuing her master’s degree in oceanography from GSO, spent 18 months conducting field work on how water quality and farming practices impact these mollusks.

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Jacqueline Rosa (center) uses a water quality sensor to measure key parameters, including temperature, salinity, and pH during weekly sampling at Wickford Oyster Company in 2024. Rosa is accompanied by oyster farmers John McKillop (left) and Kevin Tuttle. (Photo courtesy of Gage Whilden)

To examine the environmental conditions, Rosa deployed two sensors at Wickford Oyster Company’s 4-acre farm in May 2024, one at the surface of the water and one at the bottom of the water column.

Rosa revisited the farm each week to collect water samples from the surface and the bottom. She brought the samples to the Ocean Carbon Laboratory at the Graduate School of Oceanography for analysis.

“I tested the samples for pH, salinity, alkalinity, and dissolved inorganic carbon,” said Rosa, who is from Newtown, Connecticut. “These carbonate chemistry parameters help us understand trends in ocean acidification and how changing conditions may impact calcifying organisms. Shifts in carbonate chemistry can influence shell formation, growth rates, and survival, particularly during early-life stages, making these measurements critical for understanding potential stressors for farmed oysters.”

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Persistence of extreme low pH in a coralline algae habitat

Published 27 January 2026 Science Closed
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Abstract

The extent of projected ocean acidification is partly dependent on the natural variability of marine carbonate chemistry—which is higher in coastal systems than in the open ocean. However, there are limited empirical studies quantifying the rate, magnitude and drivers of coastal environmental variability, preventing accurate assessments for how species and their associated communities may respond to projected climate change. Here, we quantified the annual variability of pH, temperature and dissolved oxygen in a coralline algae reef, a globally distributed biodiverse habitat that may be one of the most sensitive to projected climate change. We found that coralline algae and their communities are exposed to pH values as low as those projected for 2100 (even under a low emission scenario) for 63% of the year, including most of autumn and all of winter. Annual fluctuations in pH ranged by 0.46 units, with identifiable patterns at diel to seasonal timescales driven by various biogeochemical factors. Biologically driven patterns in dissolved oxygen and pH were coupled at multiple periodicities, and temperature was coupled to pH during the winter. Tidal cycling additionally modulated biological forcing of pH, increasing the complexity of intra-seasonal pH variability. Forecasting this environmental variability to the future led to projections of new pH extremes well beyond all IPCC emission scenarios. However, persistent long-term exposure to low pH may increase the acclimation and adaptation potential of coralline algae and their associated communities, providing a level of optimism for the continued survival of this habitat despite sensitivity to projected climate change.

Plain Language Summary

Here, we studied how the underwater environment naturally changes during the year on a coastal reef made of coralline algae, a type of red seaweed that builds reef habitats and supports diverse marine life. These reefs are thought to be especially vulnerable to climate change, particularly ocean acidification, which lowers the pH of seawater. Unlike the open ocean, coastal areas naturally experience more variability in pH, temperature, and oxygen. Monitoring these throughout the year, we found that the coralline algae reef already experiences pH levels as low as those expected for the year 2100. In fact, for about two-thirds of the year, including all of winter, the reef was exposed to these low pH conditions. We found that pH levels also varied a lot throughout the day and between seasons, influenced by biological activity of the algae and animals living in the reef, the ebb and flow of the tide, and water temperature. With some optimism, since long-term exposure to low pH is already experienced, these algae and their ecosystems may already be somewhat adapted to future conditions. This gives hope that they will be more resilient to future climate change than previously thought.

Key Points

  • Coralline algae are naturally exposed to pH at or below future climate projections, especially during autumn and winter
  • This is driven by an interaction between physical factors (temperature, tidal cycling) and biological processes (community metabolism)
  • Given future climate projections, these pH lows may become more extreme, but prolonged exposure may increase coralline algae resilience
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Coastal eutrophication and freshwater inputs drive acidification in the Indian River Lagoon, Florida

Published 22 January 2026 Science Closed
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Highlights

  • First quantification of acidification throughout the IRL using Ωarag.
  • A positive relationship was found between Ωarag and salinity.
  • Ωarag had a negative relationship with dissolved nutrients.
  • Nutrients, algal blooms, and freshwater are drivers of acidification in the IRL.
  • Ωarag is important to understand eutrophication in estuaries.

Abstract

The additive effects of eutrophication and acidification in coastal environments have a wide range of implications for the health of organisms and ecosystems. In the eutrophic waters of the Indian River Lagoon (IRL), FL, USA, decreases in overall shellfish size have been reported, which may be related to coastal acidification. To better understand the relationship between acidification and eutrophication in the IRL, environmental parameters, dissolved nutrients, and aragonite saturation state (Ωarag) were monitored along the entire IRL in the 2016–2017 wet and dry seasons. Additionally, three sites in the central IRL were sampled approximately weekly from June 2016–June 2017 to observe temporal variability. For the IRL-wide survey, northern sites with higher dissolved nutrient concentrations had lower Ωarag due to nutrient pollution and harmful algal blooms, while southern sites with lower salinity had lower Ωarag related to freshwater inputs (i.e., discharges and rainfall). In the time series sampling, there was a positive correlation between Ωarag with salinity and negative correlations with dissolved nutrient concentrations. This work suggests that freshwater inputs and associated dissolved nutrients and organics have implications for acidification in the IRL, which will be important considerations for restoration efforts in the IRL and beyond.

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Chronic exposure to low pH negatively impacts blue mussels (Mytilus edulis) from an intertidal zone

Published 20 January 2026 Science Closed
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In intertidal ecosystems, mussels experience daily fluctuations in pH due to the biological activity, intertidal currents, freshwater inflow and anthropogenic influences. This study aimed to determine whether these short-term fluctuations enable blue mussels (Mytilus edulis) to endure long-term exposure to low pH using biological indicators (mortality rates, oxidative stress and enzyme activities). Mussels were collected from an intertidal zone in the western coast of Morocco and exposed for 6 months to seawater pH ranging from 6.6 to 8.0. Our results showed that mortality rates increased exponentially with decreasing pH, while growth rates declined linearly. At pH 6.6, mortality was observed after approximately 15 days and reached 22% at 6 months. Low pH negatively impacted the function of metabolic enzymes (glyceraldehyde-3-phosphate dehydrogenase and succinate dehydrogenase), and caused oxidative stress (elevated lipid peroxidation and protein oxidation) in the mantle, digestive gland, and whole tissues. Additionally, the activity of antioxidant enzymes catalase and superoxide dismutase increased in response to higher levels of reactive oxygen species at low pH. These findings suggest that, although mussels can inhabit intertidal zones with short-term pH fluctuations, this does not equip them with the ability to deal with chronic exposure to low pH (6.6), significantly impairing their fitness.

Continue reading ‘Chronic exposure to low pH negatively impacts blue mussels (Mytilus edulis) from an intertidal zone’

Northern shrimp exhibit origin-specific proteomic remodelling under ocean acidification, with limited response to ocean warming

Published 19 January 2026 Science Closed
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Highlights

  • Ocean acidification, but not warming, drives proteomic response in Northern Shrimp.
  • Shrimp from different origins show distinct molecular responses to ocean acidification.
  • St. Lawrence shrimp display the strongest protein changes to ocean acidification.
  • Local conditions shape how shrimp cope with global change drivers.
  • Conservation plans must consider regional differences in shrimp responses.

Abstract

The Northern shrimp (Pandalus borealis) is an ecologically important species and the target of one of the world’Canas largest shellfish fisheries. Yet, its habitats are rapidly changing due to human-driven climate change, with temperatures projected to increase by ∼4 °C and seawater pH to decline by 0.3 pH units the end of the century. These stressors may cause interactive effects, with responses differing among origins due to local adaptation or long-term acclimatisation. We investigated the impacts of ocean warming and acidification (individually and combined) on the proteome of female P. borealis from four geographic origins. Shrimp proteomes responded to ocean acidification, but not to warming, with marked origin-specific differences. Comparing the most favourable condition (2 °C, pH 7.75) to low pH (7.35) across tested temperatures, we detected 109 differentially abundant proteins (DAPs) in shrimp from the Saint Lawrence Estuary (SLE), six in those from the Northeast Newfoundland Coast (NNC) and Eastern Scotian Shelf (ESS), and three in the Esquiman Channel (EC). SLE shrimp showed widespread downregulation across metabolic, genetic information processing, and signalling pathways, suggesting higher sensitivity to acidification relative to other origins, where responses were muted. These findings highlight intraspecific variation in proteomic responses to ocean acidification in this commercially valuable crustacean. They confirm ocean acidification as a major concern in the context of rapid environmental change and suggest that uniform conservation strategies may be ineffective. Instead, management efforts should account for origin-specific sensitivities, reflecting the complex adaptive landscape shaping the resilience of P. borealis and other exploited marine species.

Continue reading ‘Northern shrimp exhibit origin-specific proteomic remodelling under ocean acidification, with limited response to ocean warming’

Explainable machine learning models for coastal pH forecasting at aquaculture-relevant thresholds in Eastern Canada

Published 19 January 2026 Science Closed
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Highlights

  • Benchmark of ML models for coastal pHSWS forecasting.
  • Models trained on rare high-frequency data from Eastern Canada.
  • XGBoost balances sensitivity and precision at pHSWS < 7.75
  • SHAP shows Julian day dominance as composite environmental driver.
  • Promising low-cost framework for aquaculture acidification early warning.

Abstract

Ocean acidification poses a growing threat to marine ecosystems and aquaculture productivity, particularly in under-monitored coastal regions such as Eastern Canada. Existing pH prediction frameworks typically rely on multi-year records combining extensive carbonate chemistry, physical, and biological parameters. While these models can achieve high accuracy, their data requirements make them costly, complex, and challenging to implement for local, site-specific acidification forecasting in aquaculture contexts. To address this limitation, this study benchmarks several machine learning models for coastal pHSWS prediction using only three routinely measured environmental variables (temperature, salinity, sea level), from which we derived moving-average descriptors, local gradients, and two temporal indicators, resulting in a compact set of 11 input features. Six different models and a multivariate linear regression baseline were trained on one of the most complete and extended high-frequency datasets available (BSSS2018) and evaluated across four independent datasets: one from the same site but six months earlier (BSSS2017), and three from nearby bays in northeastern New Brunswick collected between 2017 and 2019. Among all tested models, XGBoost emerged as the most reliable and interpretable, achieving the best trade-off between sensitivity and precision at the operational acidification threshold (pHSWS < 7.75). Its performance remained acceptable within-site but declined across bays due to environmental and seasonal discrepancies, underscoring the importance of training data representativeness. SHAP-based explainability confirmed that Julian day was the dominant predictor, integrating the composite effects of seasonal environmental variability. Overall, this study demonstrates that using only low-cost, routinely measured features provides a promising foundation for short-term coastal pH forecasting, particularly for aquaculture monitoring needs. Despite limited inter-bay generalization, the proposed framework shows that interpretable machine learning models can deliver actionable early-warning insights under realistic data constraints. It constitutes one of the first data-driven benchmarks explicitly tested at aquaculture-relevant thresholds, highlighting a scalable and transparent approach toward operational acidification forecasting.

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Developing indicators of risk to environmental variability based on species dependency in U.S. fishing communities in the Northeast and Southeast Regions

Published 13 January 2026 Science Closed
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Fishing communities worldwide have or are likely to experience social, economic, and cultural impacts from environmental variability. Changes in marine fisheries will require adaptation by fishing communities and fisheries managers alike. Here, Community Environmental Variability Risk Indicators (CEVRI) were developed to assess risk to environmental change for fishing communities in the U.S. Northeast and Southeast Regions based on spatial and temporal trends between 2000 and 2022. To accomplish this, we analyzed commercial landings value as it relates to species level Climate Vulnerability Assessment (CVA) scores for species considered commercially, recreationally, and ecologically important. The CVA considers the vulnerability of species to 12 sensitivity and 12 exposure factors relating to important environmental factors within the regional context. Here, we used three sensitivity factors: Stock Size/Status, Ocean Acidification, and Temperature, as well as Total Sensitivity and Total Vulnerability. Community level scores were used to analyze intra and inter region variation, and to understand trends in community risk as revenue dependence on different species changes through time. In general, communities in the Gulf of America/Florida Keys sub-region presented lower risk to the factors analyzed than the South Atlantic sub-region and the Northeast. Ocean Acidification was the sensitivity factor with the highest levels of risk for communities. The findings of this study have important applications to inform decision-making and to help communicate environmental variability associated risks to broader audiences, thus further developing the ability of stakeholders to understand and assess cumulative impacts and complex trade-offs affecting the sustainability of marine ecosystems and resources.

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Strength and duration of diel pH and dissolved oxygen cycles control the survival and performance of early life stage North Atlantic bivalves (Mercenaria mercenaria, Crassostrea virginica, Argopecten irradians and Mytilus edulis)

Published 9 January 2026 Science Closed
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Highlights

  • Cycling from nocturnal hypoxia – acidification to mild hyperoxia- hypocapnia reduced larval survival in all experiments.
  • Cycling from nocturnal hypoxia – acidification to normoxia- normocapnia reduced survival of larvae in 50 % of experiments.
  • Nocturnal hypoxia and acidification caused increased clearance and respiration rates in juvenile mussels.
  • The impacts of diel DO and pH cycles on early life stage bivalves depend on cycle duration, cycle intensity, and species.

Abstract

Many economically important bivalves spawn during the summer months when diel cycles of dissolved oxygen (DO) and pH occur in estuaries. Little is known, however, regarding how cycles of differing durations and magnitudes affect these organisms. Here, larval bivalves (Mercenaria mercenaria, Crassostrea virginica, Argopecten irradians) and juvenile mussels (Mytilus edulis) were exposed to cycles of low DO and pH of varying duration (4-, 6-, 8-, and 12-h) and strength (moderate: DO range ∼ 6 mg L−1, pH range ∼ 0.6 and severe: DO range ∼ 10 mg L−1, pH range ∼ 0.9) compared to positive (normoxic and normocapnic) and negative (hypoxic and acidified) static controls. Growth, survival, respiration and clearance rates were measured. During experiments, 12 h of nocturnal hypoxia and acidification coupled with mildly hyperoxic (∼11.3 mg L−1 DO) and hypocapnic (∼8.13 pH) conditions by day significantly reduced survival in larval C. virginica, M. mercenaria, and A. irradians in all experiments (p < 0.05), while 12 h of nocturnal hypoxia and acidification without hyperoxic and hypocapnic conditions did so in only half of experiments indicating that hyperoxia and hypocapnia were additional and significant stressors. Six hours of low DO/pH significantly reduced survival in only 16 % of experiments, indicating that larval bivalves are more impacted by longer duration and greater magnitude cycles of DO and pH compared to cycles of shorter duration or lower magnitude. Across species, M. mercenaria larvae were more resilient to nocturnal hypoxia and acidification than A. irradians and C. virginica. The growth and survival of juvenile M. edulis were unaffected by nocturnal hypoxia and acidification but mussels experienced significantly increased clearance and respiration rates under these conditions (p < 0.01) evidencing physiological mechanisms for coping with these stressors. Collectively, this study demonstrates that the impacts of diel DO and pH cycles on early life stage bivalves are dependent upon cycle duration, cycle intensity, bivalve life stage, and bivalve species.

Continue reading ‘Strength and duration of diel pH and dissolved oxygen cycles control the survival and performance of early life stage North Atlantic bivalves (Mercenaria mercenaria, Crassostrea virginica, Argopecten irradians and Mytilus edulis)’

Ocean acidification in Massachusetts bay and Boston harbor: insights from a 1-D modeling approach

Published 8 January 2026 Science Closed
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Highlights

  • NeBEM, an ERSEM-based biogeochemical and ecosystem model, is established for the U.S. Northeast.
  • NeBEM provides process-based insights into carbonate system variability beyond the capability of empirical data-fitting methods.
  • Biological processes strongly influence TA and DIC variability in outer Massachusetts Bay.

Abstract

Massachusetts Bay (MB)/Boston Harbor (BH) in the northeastern United States has reduced buffering capability, making it highly vulnerable to ocean acidification (OA). We applied the U.S. Northeast Biogeochemistry and Ecosystem Model (NeBEM), integrating the unstructured grid, Finite Volume Community Ocean Model with a modified European Regional Seas Ecosystem Model (ERSEM), to investigate seasonal and interannual OA variability through one-dimensional (1-D) experiments. Objectives were to (a) evaluate model skill in reproducing observed seasonal cycles of OA-related variables, particularly pCO2 and pH, in shallow and deep regions, and (b) assess sensitivity to parameterizations and algorithms for calculating dissolved inorganic carbon (DIC), total alkalinity (TA), pCO2, and pH. The 1-D NeBEM reproduced variability of nutrients, dissolved oxygen, chlorophyll-a, pCO2, and pH at the deep outer bay site, where air-sea interactions dominate, but failed at the shallow inner bay site due to the absence of river discharge-driven advection. Of TA algorithms tested, the semi-diagnostic method best captured observed seasonal pCO2 variation, achieving the highest correlation and lowest root mean square error, although all methods performed similarly for pH. Comparisons with multi-linear regression methods showed that empirical models are highly sensitive to calibration set. Mechanistic analysis indicated that TA variability is mainly regulated by nitrification and net community production (NCP), while DIC variability is driven primarily by NCP. Atmospheric CO₂ loading was the first-order contributor to DIC change in magnitude. However, it has decreased in MB over the past two decades, in contrast to regional and global trends. Therefore, it is not a major driver of OA progression in this system.

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Modeling the spatiotemporal effects of ocean acidification and warming on Atlantic sea scallop growth to guide adaptive fisheries management

Published 7 January 2026 Science Closed
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Highlights

  • We spatially couple a scallop bioenergetic model to a regional oceanographic model.
  • Our model reproduces observed growth patterns using temperature, food, and pCO2.
  • Mid-century warming enhances scallop growth except in the south.
  • By 2100, scallops grow faster but reach smaller sizes under warming and acidification.
  • This tool can inform adaptive fisheries management under climate change.

Abstract

Climate-ready fisheries management requires reliable predictions of species responses to changing conditions across large-scale environmental gradients. Bioenergetic frameworks, such as Dynamic Energy Budget (DEB) models, relate physiological processes to environmental conditions, enabling predictions of organismal growth under projected climate change conditions. Here, we provide the first large-scale coupling of a DEB model to downscaled regional oceanographic simulations to resolve spatiotemporal changes and reveal how climate stressors emerge at relevant biogeographic, economic, and oceanographic scales. We calibrated our DEB model for the Atlantic sea scallop (Placopecten magellanicus) with forcing from a realistic oceanographic and biogeochemical model for the Northeast U.S. continental shelf to predict the effects of ocean acidification (OA) and warming on individual growth historically and over the next century. Our model reproduced observed historical patterns in scallop age at harvest size and maximum size. At mid-century (2035–2050), scallop growth was projected to increase in most areas except the southern Mid-Atlantic, and OA effects were limited to the deep Gulf of Maine. By the end of the century (2080–2095) under a high emissions scenario, scallops were predicted to grow faster but attain smaller maximum sizes. Our results highlight that warming stress is more acute than previously accounted for, particularly in the southern Mid-Atlantic. While warming stress emerges in the south first, OA stress emerges before warming in the north. Together, these emerging stressors compress the spatial range for optimal growth. Altogether, our findings demonstrate the utility of the spatially coupled DEB model as a tool to inform adaptive fisheries management.

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The role of heterotrophy in the response of Oculina arbuscula to ocean acidification

Published 31 December 2025 Science Closed
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On both tropical and temperate reefs, the calcium carbonate skeletons produced by scleractinian corals provide habitat that supports a high biodiversity of fishes and invertebrates. Ocean acidification (OA), driven by excess anthropogenic CO2 uptake, causes declines in seawater pH and carbonate ion concentration and can compromise coral calcification by causing increased energetic demands. Deciphering how corals meet this increased energetic demand is critical to predicting their future persistence. Oculina arbuscula is a facultatively symbiotic temperate coral common on subtropical reefs of the South Atlantic Bight. This coral has demonstrated calcification resilience to reduced pH conditions in both symbiotic and aposymbiotic forms, despite aposymbiotic colonies lacking access to photosynthetically-derived energy. I hypothesized that energy acquired through heterotrophy is a mechanism by which O. arbuscula obtains the resources necessary to overcome the heightened energy demand created by ocean acidification. To investigate the role of heterotrophy, a 90-day laboratory experiment was conducted exposing aposymbiotic O. arbuscula fragments to a pH of either 7.7 or 8.0 under three different feeding levels of Artemia spp. nauplii. Although fragments with greater food consumption showed significantly higher calcification rates, this effect was independent of pH. Similarly, biochemical analyses indicated that total protein and total carbohydrate stores increased with higher food consumption but were unaffected by pH exposure. In contrast, total lipid stores decreased during the experiment, regardless of pH exposure or food level, suggesting the heterotrophic contribution to lipid stores was deficient. Together, these results indicate that while heterotrophically-derived energy may not be a primary mechanism underlying the ability of O. arbuscula to sustain calcification rates under OA stress, this coral species should continue to thrive in an increasingly acidifying ocean as long as heterotrophic food resources are in abundance.

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Aquaculture of seaweeds (Saccharina latissima, Ulva spp., Gracilaria spp.) significantly improves the growth of co-cultivated bivalves in mesotrophic, but not eutrophic, estuaries

Published 29 December 2025 Science Closed
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The co-cultivation of seaweeds with bivalve shellfish is a potential strategy for protecting bivalve crops against anthropogenic coastal acidification and hypoxia. We co-cultivated seaweeds and bivalves using a succession of seaweed species according to season (winter, Saccharina latissima → spring, Ulva spp. → summer, Gracilaria spp.) together with eastern oysters (Crassostrea virginica) and blue mussels (Mytilus edulis). Bivalves and seaweeds were deployed in two estuaries that contrasted in trophic state, one mesotrophic and one eutrophic. In all five experiments in the mesotrophic system, cocultivation with seaweeds significantly increased weight- and/or shell-based growth of bivalves (p < 0.05). Growth rate increases for C. virginica were modest, with weight-based growth improving by 17–21% and shell-based growth improving by 3–27% with seaweed co-culture of all macroalgal species. For M. edulis, the effect was large; co-culture with S. latissima caused 47% and 114% increases in shell- and weight-based growth rates, respectively. In the four experiments in the eutrophic estuary, co-culture with seaweeds did not significantly improve bivalve growth. Seaweed cultivation significantly improved water quality metrics (increased pH and dissolved oxygen (DO); p < 0.05 in all cases) in and around the seaweed sites at both locations, although increases in pH and DO were modest, and even in control treatments, there were no prolonged periods of harmful pH or DO levels. An abundance of macroalgal detritus may have bolstered the diets of co-cultivated bivalves in the mesotrophic estuary, a hypothesis supported by lower chlorophyll a concentration, and therefore lower planktonic food levels, at that site. Given that seaweeds display species-specific allelopathic effects against phytoplankton, it is also possible that the presence of seaweeds altered the phytoplankton community to the benefit of the bivalves. Regardless, the findings here demonstrate that co-cultivation with seaweeds can accelerate the growth of bivalves.

Continue reading ‘Aquaculture of seaweeds (Saccharina latissima, Ulva spp., Gracilaria spp.) significantly improves the growth of co-cultivated bivalves in mesotrophic, but not eutrophic, estuaries’

Ecological stability of late Maastrichtian benthic foraminifera amidst Deccan volcanism

Published 29 December 2025 Science Closed
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Highlights

  • Benthic foraminifera assemblage at Bidart reveal a stable, mesotrophic late Maastrichtian seafloor.
  • K/Pg boundary at Bidart shows signs of ecological stress and taphonomic dissolution.
  • Deccan-induced calcification stress was restricted to surface ocean and had minimal impact on benthic foraminifera.
  • Robust test ratio and fragmentation index together serve as effective taphonomic proxies.

Abstract

The late Maastrichtian witnessed profound disruptions in biogeochemical cycles, leading to the fifth mass extinction at the Cretaceous–Paleogene (K/Pg) boundary. At Bidart section (France), the final ∼60 kyr of the Maastrichtian coincide with mercury (Hg) peaks, low magnetic susceptibility, evidence of biological stress and taphonomic alteration in planktic foraminifera, indicative of an ocean acidification event. While this event primarily appears to be a surface-ocean phenomenon, previous studies also documented a minor rise in benthic foraminiferal test fragmentation beginning 0.5 m below the K/Pg boundary, with a pronounced spike at the boundary itself.

A detailed investigation of benthic foraminifera in biozone CF1 at Bidart section (France) reveals a diverse and balanced assemblage preceding the K/Pg boundary, with minimal taphonomic alterations. At the K/Pg boundary, infaunal populations diminished, diversity declined sharply, test fragmentation intensified, yet paradoxically, the absolute abundance of genera rose markedly. Preferential preservation is evident in the dominance of robust taxa (Cibicidoides spp., Coryphostoma spp.), while a high fragmentation index reflects strong taphonomic dissolution and time-averaging. A plausible explanation for this could be CO2-rich waters mixing into the ocean interior over 100–1,000 years, driving dissolution during the ∼10,000-year deposition of the K/Pg boundary red clay. The stark contrast between the planktic and benthic census and morphometric data at Bidart section clearly constrains any Deccan-related calcification stress to the surface mixed layer. Lastly, the integrated planktic and benthic considerations re-emphasize a need to carefully separate taphonomic signals from true ecological stress.

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Compound hypoxia with heat or acidification stress induces synergistic and additive effects on coral physiology

Published 26 December 2025 Science Closed
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As climate change accelerates, coastal marine ecosystems are increasingly exposed to co-occurring stressors whose combined effects are nonlinear and difficult to predict. Deoxygenation is a rapidly intensifying yet underrecognized threat to coral reefs that interacts with heat and acidification to alter coral physiology and stress resilience. However, the effects of hypoxia-related compound events on corals are largely unknown, underscoring the need for multi-stressor studies. Here, we conducted two extended-exposure experiments (12–17 days) across the coral species Porites furcata, Porites astreoides and Siderastrea siderea, to disentangle the individual and combined effects of low dissolved oxygen (hypoxia) with either heat or acidification. We measured eight phenotypic traits related to growth, metabolism, and symbiosis health to test whether hypoxia imposes energetic constraints or other physiological stress that amplify the effects of heat or acidification. Standardized effect size analysis across 24 stressor–trait combinations revealed 13 additive, 10 synergistic, and only one antagonistic response. Hypoxia consistently suppressed dark respiration by 37–49% across species and altered photophysiology in the two Porites species, whereas acidification alone had minimal effects, particularly in S. siderea. Heat stress caused the most pronounced declines across nearly all traits, and when combined with hypoxia, it produced the highest number of synergistic interactions. In contrast, the combination of hypoxia and acidification largely resulted in additive responses, suggesting that independent physiological mechanisms underlie these effects. All corals showed strong metabolic depression under hypoxia which is likely beneficial as a short-term adaptive response but may impose energetic constraints in the long-term. These findings highlight deoxygenation as critical yet often overlooked drivers of coral reef vulnerability. More multi-stressor experiments across a range of species are urgently needed to improve predictions of reef resilience under future ocean conditions, where compound stress events are expected to become more frequent and severe.

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Interactive effects of ocean acidification and benthic biofilm composition on the early development of the European abalone Haliotis tuberculata

Published 23 December 2025 Science Closed
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Ocean acidification (OA) and associated shifts in carbonate chemistry represent major threats to marine organisms, particularly calcifiers. OA effects can be influenced by other environmental variables, including the biotic environment. This study investigated the individual and interactive effects of OA and algal density, acting through biofilm composition, on post-larval and juvenile abalone (Haliotis tuberculata). In a three-month factorial experiment, abalone were exposed from metamorphosis onward to two pH conditions (ambient 8.0 and reduced 7.7) and two initial densities of the green alga Ulvella lens on settlement plates. Biofilm biomass and composition were characterised using spectral reflectance and HPLC pigment analysis. Biological (density, length), physiological (respiration rate), behavioural (hiding response) and shell parameters (colour, surface corrosion, strength) of abalone were measured throughout the experiment. Biofilm biomass and composition remained relatively stable under both pH conditions, though greater variability in algal biomass occurred at low initial Ulvella density. Post-larval density and total length decreased significantly under low pH, while high Ulvella density reduced juvenile length at 80 days, likely due to competition between algal groups. A pH × Ulvella interaction affected shell fracture resistance and colouration, but not metabolism or behaviour, indicating that juvenile abalone maintained vital functions. Overall, the results confirm the sensitivity of early H. tuberculata stages to moderate OA (−0.3 pH units) and highlight indirect macroalgal effects through changes in diatom communities. In natural environments, the capacity of abalone to cope with future OA will depend on complex trade-offs between direct acidification effects and food-related biotic interactions.

Continue reading ‘Interactive effects of ocean acidification and benthic biofilm composition on the early development of the European abalone Haliotis tuberculata’

Genotype and symbiont composition rather than environment influence susceptibility to stony coral tissue loss disease in coral restoration broodstock

Published 19 December 2025 Science Closed
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Over the last several decades, Florida’s Coral Reef has been impacted by global and local stressors causing significant declines in living coral with no signs of natural recovery. Ocean warming, ocean acidification, and infectious diseases are major contributors to the precipitous loss of corals within this region. Since 2014, the stony coral tissue loss disease (SCTLD) outbreak has been particularly devastating, causing unprecedented mortality in over 20 massive coral species. As SCTLD is now endemic in the region, and threats from climate change are likely to persist, studying the disease susceptibility of different coral genotypes under future environmental scenarios is vital for effective restoration. Here, we exposed Orbicella faveolata and Pseudodiploria clivosa genotypes to wild colonies showing signs consistent with SCTLD immediately following a 2-month long exposure to ocean warming (OW) and ocean acidification (OA) scenarios. Corals were exposed to SCTLD for 3 weeks while maintaining the environmental treatments. For both species, pre-exposure to OW and OA scenarios did not make corals more susceptible to SCTLD. However, three genotypes hosting higher levels of Breviolum were at increased risk for showing SCTLD signs under these conditions. One O. faveolata genotype was consistently resistant to SCTLD under the different scenarios, suggesting that natural levels of resistance exist in coral restoration broodstock. Understanding why this genotype could withstand exposure to these stressors may be critical for ensuring survival of restored populations into the future.

Continue reading ‘Genotype and symbiont composition rather than environment influence susceptibility to stony coral tissue loss disease in coral restoration broodstock’

Multifactorial neural disruption in the brain of the Senegalese Sole (Solea senegalensis) under ocean acidification

Published 9 December 2025 Science Closed
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Global ocean acidification, driven by rising atmospheric CO2, is threatening marine ecosystems and biodiversity, with increasing evidence of its disruptive effects on fish neurobiology and behaviour, yet the mechanisms underpinning its impact on fish neurobiology remain unresolved. Here, we reveal how chronic exposure to future-predicted CO2 levels disrupts brain function in the marine teleost Solea senegalensis, a species with functionally distinct olfactory organs. Using an integrative approach combining electrophysiology, immunohistochemistry, and transcriptomics, we demonstrate that elevated CO2 conditions induce a complex multifaceted disruption in brain physiology. Notably, our findings conflict with the widely held GABAA receptor reversal hypothesis; we observed increased Cl- and CO2 in cerebrospinal fluid and suppressed neural excitability, rather than the predicted loss of Cl- and heightened excitatory signalling. Immunohistochemistry further revealed reduced expression of glial fibrillary acidic protein across multiple brain regions, suggesting glial impairment. Furthermore, transcriptomic profiling of the olfactory bulb uncovered immune modulation, downregulation of neural excitability genes, and upregulation of neuroplasticity, ciliary, and anti-inflammatory pathways, hallmarks of cellular stress adaptation. Notably, genes involved in circadian regulation and thyroid signalling were also dysregulated, pointing to broader neuroendocrine disruption. These findings challenge current relatively simple models of ocean acidification impact and unveil a complex cascade of central and peripheral alterations, including enhanced GABAergic inhibition, immune shifts, glial dysfunction, and disrupted timekeeping mechanisms, likely contributing to the behavioural impairments observed under high CO₂. Challenging current models, our work highlights the need for integrative neurophysiological frameworks to predict marine fish resilience and vulnerability in a changing ocean.

Continue reading ‘Multifactorial neural disruption in the brain of the Senegalese Sole (Solea senegalensis) under ocean acidification’

Resistance of the cold-water coral Dendrophyllia cornigera to single and combined global change stressors

Published 28 November 2025 Science Closed
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Current knowledge of the consequences on global change in deep marine ecosystems is still limited, especially since environmental pressures do not act separately, and their potential interactions are mostly unknown. Cold-water corals (CWC) play a significant role in the deep sea, being ecosystem engineers supporting high biodiversity. However, global change may impact CWCs, compromising their integrity and survival. In this study, a nine-month aquaria experiment was conducted on the CWC Dendrophyllia cornigera from the NW Iberian Shelf (NE Atlantic Ocean). The aim was to assess the individual and combined effects of elevated temperature (12 vs. 15 °C), low pH (~ 7.99 vs. 7.69 pHT) and low oxygen (~ 6.4 vs. 4.7 mL L−1), based on the IPCC RCP 8.5 scenario. During the experiment, coral survival, skeletal growth, tissue cover and respiration were monitored as response variables. No significant effects were found on any of the response variables for either individual or combined stressors, pointing to the resistance of D. cornigera to different global change scenarios. Such a physiological resistance may support D. cornigera persistence under future conditions where other CWCs with narrower tolerance ranges may face greater limitations. However, further research is needed to assess potential trade-offs to cope with environmental change, which might impact the long-term survival capacity of this species.

Continue reading ‘Resistance of the cold-water coral Dendrophyllia cornigera to single and combined global change stressors’

Ocean acidification in the Bay of Biscay: two decades of data reveal a silent shift

Published 26 November 2025 Press releases Closed
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The sea along the Basque coast is changing quietly. An analysis of more than 21,700 measurements collected between 2002 and 2022 shows that the pH of seawater is steadily decreasing—clear evidence of ocean acidification driven by rising atmospheric carbon dioxide.

According to the study, published in Continental Shelf Research, the pH of waters from the surface down to 100 meters is declining by 0.022 to 0.041 units per decade. “If this trend continues at the same pace, the impacts on the health of marine ecosystems could be significant,” explains Ernesto Villarino, AZTI researcher and lead author of the study.

Conducted by AZTI with the support of the Naturklima Foundation, as part of the Gipuzkoa Marine Climate Change Observatory, and in collaboration with the Institute of Marine Sciences of Andalusia (ICMAN-CSIC), this research analyzes the longest continuous pH monitoring series ever recorded along the Basque coast. The data, provided by the Basque Water Agency (URA), confirm that the Bay of Biscay is also affected by ocean acidification, underlining the need to strengthen mitigation and climate-adaptation strategies.

Continue reading ‘Ocean acidification in the Bay of Biscay: two decades of data reveal a silent shift’

A synthesis of Eastern oyster (Crassostrea virginica) growth and calcification responses under changing environmental conditions

Published 21 November 2025 Science Closed
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Eastern oysters (Crassostrea virginica) are foundational reef builders and ecosystem engineers that provide habitat complexity, enhance biodiversity, and influence biogeochemical cycles by shifting local carbonate chemistry in estuaries along the U.S. Atlantic coast and Gulf of Mexico. However, the environmental ranges governing oyster shell growth and calcification rates remain poorly constrained because available studies vary in the metrics quantified, experimental settings, and spatial coverage. We synthesized existing literature on C. virginica growth and calcification, assessing directional responses to changing environmental conditions. Variability in ecological, spatial, and temporal scales among studies and disparities between laboratory and field-based measurements complicate direct comparisons. Despite heterogeneity in the synthesized data, consistent patterns emerged; shell growth limitations were common at salinities below ~ 12 in U.S. Gulf of Mexico populations, and calcification declines were frequently observed under acidified conditions (pH < 7.7) in U.S. Atlantic populations. By summarizing patterns across life stages, regions, and study types, we highlight environmental stressors likely to impair oyster reef resilience and function. A more integrative research approach, incorporating both individual- and reef-scale processes across experimental and natural settings, is critical for refining predictions of oyster reef resilience. Standardized methodologies and interdisciplinary frameworks will enhance our ability to quantify the role of oyster reefs in carbon cycling and assess their response to future environmental stressors.

Continue reading ‘A synthesis of Eastern oyster (Crassostrea virginica) growth and calcification responses under changing environmental conditions’

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