oxygen Archives - Ocean Acidification

Posts Tagged 'oxygen'

Invasive macroalgae exert stronger effects than elevated CO₂ on seagrass (Posidonia oceanica) seedling performance and associated microbiomes

Published 11 August 2026 Science Closed
Tags: algae, biological response, laboratory, Mediterranean, mesocosms, multiple factors, oxygen, phanerogams, physiology, primary production, reproduction, respiration

Highlights

Invasive macroalgae reduced P. oceanica seedling biomass and leaf development.
Macroalgal invasion depleted carbohydrate reserves in seedling roots and rhizomes.
Elevated CO₂ increased rhizome starch but did not mitigate invasion impacts.
Root microbiome diversity declined markedly under macroalgal invasion.
Future CO₂ enrichment unlikely to buffer invasion stress at recruitment stage.

Abstract

Seagrass seedlings are key to meadow recovery under global change, as they enable recolonization of degraded areas and provide genetic variability needed for adaptation. While invasive macroalgae increasingly threaten seagrass communities, elevated CO₂ has been proposed to enhance seagrass performance and potentially buffer other stressors. Here, we conducted a mesocosm experiment to test the combined effects of two invasive macroalgae (Lophocladia trichoclados and Caulerpa cylindracea) and elevated CO₂ on Posidonia oceanica seedlings. CO₂ enrichment increased carbohydrate reserves in rhizomes and induced subtle shifts in root-associated microbiomes. In contrast, invasive macroalgae had consistently negative effects on seedling development and physiology and strongly altered both above- and belowground microbial communities. Despite its potential to stimulate seagrass productivity, elevated CO₂ did not mitigate the detrimental impacts of invasive macroalgae. These findings indicate that future CO₂ conditions may not offset invasion-driven stress at the recruitment stage, highlighting the need for targeted management efforts to limit macroalgal proliferation and support seagrass meadow regeneration.

Continue reading ‘Invasive macroalgae exert stronger effects than elevated CO₂ on seagrass (Posidonia oceanica) seedling performance and associated microbiomes’

The effects of high carbonate alkalinity under low salinity on the survival, physiological metabolism, and redox homeostasis of Crassostrea hongkongensis

Published 28 July 2026 Science Closed
Tags: biological response, laboratory, mollusks, mortality, multiple factors, oxygen, performance, physiology, salinity

High carbonate alkalinity can impose composite hydrochemical stress on bivalves by altering inorganic carbon speciation, buffering capacity and ion-exchange conditions. The Hong Kong oyster (Crassostrea hongkongensis) naturally inhabits estuarine areas where low salinity can occur together with carbonate-system disturbance, yet its physiological response to high carbonate alkalinity under a low-salinity background remains unclear. In this study, oysters were exposed at salinity 5 to a Control treatment, A10 (carbonate alkalinity 10 mmol L⁻¹) and A20 (carbonate alkalinity 20 mmol L⁻¹). Salinity was treated as a controlled background condition, whereas the alkalinity treatments represented a composite carbonate-alkalinity perturbation involving alkalinity, pH and carbonate chemistry. Survival, feeding rate, oxygen consumption, ammonia excretion and hemolymph ammonia were measured across Control, A10 and A20. Hemolymph catalase (CAT), glutathione peroxidase (GSH-Px), glucose and ATP were analyzed as A10 and A20 time-course endpoints because a parallel Control was not included for these assays. A 24-h mantle transcriptome was used to screen candidate transcripts associated with innate defense and glutathione metabolism. Oysters under A10 retained partial compensatory capacity, whereas A20 significantly reduced survival. A10 and A20 suppressed early oxygen consumption and ammonia excretion, and altered feeding allocation among microalgae. Within the A10 and A20 biochemical time-course dataset, CAT, GSH-Px, glucose and ATP showed stage-specific variation, suggesting redox and energy-metabolism adjustment under alkalinity stress. Overall, high carbonate alkalinity reduced survival and was associated with metabolic depression, feeding compensation and hemolymph redox-energy remodeling in C. hongkongensis. This study will provide a theoretical basis for water quality regulation in saline-alkaline water aquaculture and the sustainable development of aquaculture.

Continue reading ‘The effects of high carbonate alkalinity under low salinity on the survival, physiological metabolism, and redox homeostasis of Crassostrea hongkongensis’

Water mass-driven variations in primary production and bacterial respiration during the spring bloom in the Fram Strait

Published 23 July 2026 Science Closed
Tags: Arctic, biological response, community composition, field, laboratory, modeling, multiple factors, otherprocess, oxygen, photosynthesis, primary production, prokaryotes, regionalmodeling, respiration

Highlights

Remote sensing indicates declining bloom in cold and developing bloom in warm water
Primary production peaks in polar and arctic surface water masses
Bacterial production is coupled to primary production despite thermal sensitivity
Oxygen-based community respiration is highest in warmer water masses
Oxygen-based and INT-based respiration estimates differ by an order of magnitude

Abstract

The Fram Strait is the primary oceanic gateway to the Arctic Ocean and has highly dynamic oceanographic conditions. Oceanographic conditions can shape community compositions, which is increasingly shown using molecular studies, but rate measurements remain scarce, especially for respiration in the Arctic Ocean. Here, we assessed primary production (PP), bacterial production (BP), bacterial abundances (BA), and community respiration (CR) using Winkler titrations and in vivo Iodo-Nitro-Tetrazolium (INT) reduction within the upper 50 m across water masses of the Fram Strait that had varying bloom conditions in spring 2021. We complemented in situ observations with remote sensing of sea surface temperature (SST) and chlorophyll-a (SSC) to infer bloom phenology in warm (θ>2°C), intermediate (2>θ>0°C), and cold (θ<0°C) waters using remote sensing machine-learning. In the cold, nutrient-rich surface waters, a subsiding spring bloom was associated with elevated PP, BP, and BA alongside a high temperature sensitivity (Q₁₀) that indicates active microbial turnover. In contrast, the warm Atlantic-influenced waters exhibit a relatively lower PP but moderate cell-specific BP, suggesting bacterial maintenance metabolism under pre-bloom conditions. Notably, bacterial respiration (BR) estimates differed by 5- to 80-fold between the Winkler and in vivo INT methods. Although the true BR likely lies between these estimates, our results highlight the substantial microbial activity and underscore the need for more accurate BR measurements in Arctic studies.

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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
Tags: biological response, fish, laboratory, mortality, multiple factors, oxygen, physiology, reproduction, temperature

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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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 Closed
Tags: biological response, corals, dissolution, growth, laboratory, morphology, mortality, multiple factors, North Atlantic, oxygen, physiology, respiration, temperature

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.

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

Published 25 March 2026 Science Closed
Tags: biological response, chemistry, crustaceans, laboratory, multiple factors, oxygen, physiology, respiration, South Pacific

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’

Acidification stimulates N2O production by oceanic nitrifying bacteria

Published 9 March 2026 Science Closed
Tags: biological response, laboratory, multiple factors, otherprocess, oxygen, physiology, prokaryotes

Recent studies have shown changes in the production rates of nitrous oxide (N2O) in aerobic seawater in response to ocean acidification (OA). Understanding how N2O production responds to OA is crucial because N2O is a strong greenhouse gas and stratospheric ozone‐depleting substance emitted from the ocean. The pH dependence of N2O production rates on marine bacteria Nitrosococcus oceani strain NS58, one of the ammonia oxidizing bacteria that are relevant to nitrification occurring in eutrophic seawater, was investigated under several dissolved oxygen (DO) conditions. We also measured abundance ratios of N2O molecules substituted with rare stable isotopes (isotopocules) to distinguish the two major pathways of N2O production by nitrifiers: NH2OH oxidation and NO2⁻ reduction. The ammonium oxidation rate (VNO2 $V {NO}_{2}$ ) and N2O production rate (VN2O $V_{N_{2} O}$ ) calculated respectively from the temporal change of the product concentrations were 4–34 × 10⁻¹⁵ mol h⁻¹ cell⁻¹ and 1–15 × 10⁻¹⁷ mol h⁻¹ cell⁻¹. When compared in the stable phase (t = 44–76 hr), VNO2 $V {NO}_{2}$ decreased concomitantly with decreasing DO, also exhibiting a slight increase in acidified water. In contrast, VN2O $V_{N_{2} O}$ was highest at 35% DO (air saturation), showing a 5%–60% increase by acidification (pH 7.7 vs. 8.0) depending on DO. Isotopocule ratios showed an increased contribution from NO2⁻ reduction over NH2OH oxidation under 35% and 3% DO, but its pH dependence was negligible except under 3% DO. These results suggest that OA increases N2O emission in particular from eutrophic seawater and that both N2O production pathways can be stimulated to the same degree.

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An indoor mesocosm system for cost-effective simulation of multiple ocean stressors affecting marine organisms

Published 16 January 2026 Science Closed
Tags: laboratory, methods, multiple factors, oxygen, temperature

Global climate change is exacerbating multiple ocean stressors, including ocean acidification (OA), ocean warming (OW), and deoxygenation (deOxy), which collectively threaten marine ecosystems and fisheries. Understanding how these stressors interact to shape organismal and ecosystem responses is increasingly critical, yet it remains technically challenging and expensive to simulate them concurrently under controlled indoor conditions. To address this limitation, we developed a closed indoor mesocosm system that enables stable and long-term simulation of these three stressors for biological and aquaculture research. The system maintains consistent levels of CO₂, temperature, and dissolved oxygen (DO) over multi-month experiments without automated control units, relying instead on robust initial settings. High-purity CO₂ and N₂ gases are blended with ambient air in controlled ratios to regulate carbonate chemistry and oxygen levels, while chillers and heaters ensure precise temperature control. Validation experiments demonstrated that the system can (1) increase pCO₂ to approximately twice the present-day level with a pH reduction of ~ 0.22 units, (2) elevate temperature by + 3 °C above ambient temperature, and (3) reduce DO by up to 40% relative to ambient concentration, reflecting projected climate scenarios. This simple and versatile mesocosm provides a practical platform for investigating the ecophysiological responses of marine organisms under multi-stressor environments, supporting research on climate adaptation and aquaculture resilience.

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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
Tags: biological response, growth, laboratory, mollusks, mortality, multiple factors, North Atlantic, oxygen, physiology, reproduction, respiration

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)’

Effect of experimental seawater acidification on the prooxidant-antioxidant system of the Pacific oyster Magallana gigas (Thunberg, 1793) under normoxic and hypoxic conditions

Published 8 January 2026 Science Closed
Tags: biological response, Black Sea, fisheries, laboratory, mollusks, mortality, multiple factors, oxygen, physiology

Highlights

Lipid peroxidation in oyster gills was enhanced during exposure to acidification + hypoxia.
SOD and GPx activities changed in gills and hepatopancreas, while CAT activity unchanged in both.
Water acidification does not promote DNA strand breaks in hemocytes of M. gigas.
Acidification + hypoxia more severe damaging than acidification under normoxia.

Abstract

Bivalve mollusks, particularly the Pacific oyster (Magallana gigas), are both environmentally and commercially significant species that live in coastal waters and may be affected by global climate change factors including hypoxia and acidification. In this study, we investigated the impact of acidification in combination with normoxia and hypoxia on oxidative stress markers in the gills and hepatopancreas of M. gigas oysters. Oysters were collected from a shellfish farm and subjected to acidified conditions (pH 7.3 ± 0.05) in combination with either normoxic (8.0 ± 0.3 mg/L O₂) or hypoxic (2.0 ± 0.3 mg/L O₂) conditions for an 8-day period. Changes of DNA damage levels, reactive oxygen species (ROS) production in hemocytes, as well as antioxidant enzyme activities (catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx)) and lipid peroxidation in the gills and hepatopancreas were evaluated. Additionally, the mortality rate in experimental groups was monitored throughout the experiment. Our results showed that lipid peroxidation in gills was enhanced during prolonged acidification in combination with hypoxia (6–8 days). We observed rapid and consistent changes in SOD and GPx activity in gills and hepatopancreas. CAT activity remained stable in both tissues. The results of the study indicate that acidification was shown to induce oxidative stress in oysters. Combination of acidic environment to hypoxia had a more severe effect on oysters compared to acidification under normal oxygen conditions, leading to their death after 8 days of exposure.

Continue reading ‘Effect of experimental seawater acidification on the prooxidant-antioxidant system of the Pacific oyster Magallana gigas (Thunberg, 1793) under normoxic and hypoxic conditions’

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

Published 26 December 2025 Science Closed
Tags: biological response, BRcommunity, corals, laboratory, morphology, multiple factors, North Atlantic, oxygen, photosynthesis, physiology, phytoplankton, respiration

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

Published 28 November 2025 Science Closed
Tags: biological response, corals, growth, laboratory, morphology, mortality, multiple factors, North Atlantic, oxygen, respiration, temperature

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 pH_T) 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.

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The multiple responses of Mytilus galloprovincialis in the multi-stressor scenario: impacts of low pH, low dissolved oxygen, and microplastics

Published 18 November 2025 Science Closed
Tags: biological response, laboratory, Mediterranean, mollusks, multiple factors, oxygen, physiology, plastics, respiration

Highlights

Low pH, low dissolved oxygen (DO), and microplastics (MPs) did not notably affect organismal parameters or ETS activity.
Stressors significantly affected hemocytes, genotoxicity, and gill metabolites individually and interactively.
Hemolymph phagocytic activity, granulocyte/hyalinocyte ratio, and mantle lipid peroxidation were partly affected.
Metabolomic analyses showed that mussel gills are valuable indicators of metabolic status under stress.

Abstract

Along with high temperatures, acidification, deoxygenation, and microplastics (MPs) pollution represent key drivers in coastal marine ecosystems. Sessile invertebrates living in coastal habitats are primarily exposed to the combination of these drivers, often at severe levels. Here, we investigated the individual and combined impacts of low pH (pH_T: 7.35), low dissolved oxygen (DO) (1.91 mg L⁻¹), and MP (26 μg L⁻¹) in the Mediterranean mussel Mytilus galloprovincialis by measuring organismal and cellular parameters after a 15-day exposure period. Organismal parameters (respiration rate, ammonia excretion rate, absorption efficiency) as well as electron transport system (ETS) activity were not impacted by the stressors, either individually or combined. At the cellular level, however, we observed significant effects of these stressors individually and interactively on the hemocyte count, hemocyte viability, genotoxicity (comet assay), and gill metabolite profiles. In addition, we observed partial effects on the hemolymph phagocytic activity (PA) and granulocyte/hyalinocyte (G/H) ratio, and mantle lipid peroxidation (LPO). Metabolomics results manifested that the gill of mussels can serve as a valuable indicator of metabolic status under the stress of low pH, low DO and MP. Metabolites involved in osmoregulation, membrane stability, oxidative stress, energy, amino acid and nitrogen metabolism were significantly affected by the stressors, with low DO being the main driver of metabolic changes. We suggest that the individual and variable interactions of these stressors negatively impact M. galloprovincialis, except for the organismal and, to some extent, biochemical parameters.

Continue reading ‘The multiple responses of Mytilus galloprovincialis in the multi-stressor scenario: impacts of low pH, low dissolved oxygen, and microplastics’

The influence of maternal size/age effects on the physiological responses of adult female gopher rockfish (Sebastes carnatus) to ocean acidification and hypoxia

Published 13 August 2025 Science Closed
Tags: biological response, fish, laboratory, multiple factors, North Pacific, oxygen, physiology, reproduction

Climate change is rapidly reshaping the chemistry of the ocean. Fishes living in California coastal waters are experiencing increased ocean acidification and hypoxia (OAH) due to more frequent and intense upwelling. Nearshore rockfish may be particularly threatened by these conditions due to their long generational times. However, it is unknown how OAH may impact maternal physiology and reproduction in these viviparous fish. To understand the physiological effects of OAH during gestation, adult female gopher rockfish, Sebastes carnatus, were exposed to a variety of combined OAH stress treatments during different gestational stages. Routine metabolic rate (RMR), maximum metabolic rate (MMR), blood hematocrit (Hct), hemoglobin (tHb), pCO₂, HCO₃^–, Na⁺, K⁺, Cl^–, and metabolites, were measured to assess physiological responses to OAH stress. Ovarian oxygen was measured to examine the ability to buffer embryos against low oxygen. Fish exposed to higher OAH stress displayed elevated blood Hct, tHb, pCO₂ and HCO₃^–, and decreased MMR, indicating attempted compensation for low pH and hypoxia (with varying levels of success), at increased physiological costs. Fish showed signs of buffering their ovaries against hypoxia. Lastly, pregnancy altered Hct and RMR under OAH exposure and size/age did not have a consistent effect on maternal physiology. By evaluating responses of maternal physiology to OAH stress, we can better understand how climate change affects fecundity, larval condition, and survival, influencing nearshore fisheries in an ever-changing climate.

Continue reading ‘The influence of maternal size/age effects on the physiological responses of adult female gopher rockfish (Sebastes carnatus) to ocean acidification and hypoxia’

Impacts of multiple coastal stressors across life-history stages in the eastern oyster

Published 31 July 2025 Science Closed
Tags: adaptation, biological response, laboratory, molecular biology, mollusks, multiple factors, otherprocess, oxygen, reproduction

Urbanized estuaries are characterized as a complex of biotic and abiotic stressors, which currently challenge marine life and are expected to intensify and become increasingly unpredictable under the ongoing impacts of climate change. The persistence of coastal species that inhabit these stressful environments will ultimately depend on their ability to adapt. Many of these species have complex life cycles, featuring distinct morphological and physiological developmental stages that can exhibit unique responses to environmental pressures. However, since all stages share the same genome, selective pressures acting on one stage can have cascading effects throughout the life cycle. The larval stage, being particularly sensitive to environmental stressors and often the only free-moving stage, plays a crucial role in gene flow across populations. Consequently, selection during this stage can set the trajectory for the entire life cycle and significantly influence the adaptive structure of populations. This dissertation explores the impacts of multiple environmental stressors across the life-history stages of the eastern oyster (Crassostrea virginica). In Chapter 1, we integrated genomic information about larval stressor response into a seascape genomics framework, using adult oysters sampled from various localities with differing environmental profiles in Narragansett Bay, Rhode Island. We identified environmentally driven signatures of local adaptation corresponding to different genomic regions, even amidst high gene flow. In loci putatively under selection in larvae exposed to coastal stressors, we found stressor-specific associations with environmental conditions that aligned with adult candidate loci, highlighting the critical role of the larval stage in shaping population adaptive divergence. In Chapter 2, we exposed genetically diverse pools of larval oysters to diurnal fluctuating acidification and hypoxia for most of their development. Genomic analysis of samples taken before and after exposure revealed substantial shifts in allele frequencies at loci putatively under selection, suggesting a potential for rapid adaptation to future environmental conditions. Chapter 3 extended this work by exposing oysters to these stressors from the pediveliger stage, through settlement, and into early juvenile development. Genomic analysis from the larval and settlement exposure periods revealed both unique and shared signatures of selection across the early developmental stages. While the juvenile stage was more tolerant to the stressor conditions, we found that stressor exposure through the pediveliger larval and settlement stages had short-term carryover effects on juvenile performance. These findings demonstrate the complex connection of evolutionary responses across the full life cycle. While early developmental stages are sensitive to coastal stressors, our analysis reveals adaptive responses that highlight the resilience of this species. Specifically, these early life-stage responses can influence later developmental stages, shaping the species’ overall adaptive capacity and impacting population structure dynamics. Consequently, understanding these dynamics is crucial for predicting how population structure and adaptive divergence will evolve in response to intensifying coastal stressors.

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Metabolic responses of the European flat oyster (Ostrea edulis) to combined ocean acidification and hypoxia

Published 18 July 2025 Science Closed
Tags: biological response, laboratory, Mediterranean, mollusks, multiple factors, oxygen, performance, physiology, respiration

Ocean acidification and the accompanying hypoxia, which have become increasingly important environmental stress factors, can have varying effects on marine organisms, such as impaired physiological metabolism and immune function. Here, I studied the effects of high pCO2 and low dissolved oxygen (DO) in European flat oyster Ostrea edulis. Changes in physiological and immunological parameters were investigated in oysters during 18 days of exposure at two different pH (7.90 and 7.30) and DO levels (7.5 and 2 mg L-1). Low pH and low DO reduced haemocye count and viability, both individually and in combination. Low pH and combined exposure decreased feeding and respiration, which exacerbated by duration. Low pH and low dissolved oxygen increased ammonia excretion rate, which exacerbated by time. I suggest that the low pH and low DO lead metabolic depression, impaired immune function, and alteration in energy allocation in oysters, which further collectively negatively affect fitness of the oyster.

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Cross-generational plasticity in Atlantic silversides (Menidia menidia) under the combined effects of hypoxia and acidification

Published 17 July 2025 Science Closed
Tags: biological response, fish, laboratory, molecular biology, mortality, multiple factors, North Atlantic, oxygen, physiology, reproduction

We investigated the potential for cross-generational plasticity to influence how offspring respond to hypoxia and ocean acidification (hereafter HypOA) in the coastal forage fish Atlantic silverside (Menidia menidia). Mature wild silversides were treated with a control (dissolved oxygen (DO):100% air saturation (a.s.) / pCO₂: 650 µatm) or HypOA conditions (DO: 40% a.s. / pCO₂: 2300 µatm) for 10 days prior to spawning. Their offspring were reared under both treatments in factorial experimental design. Parental environment had minimal effects on offspring phenotype: exposure to HypOA reduced survival and developmental rates regardless of parental treatment. However, RNAseq analysis revealed that direct offspring exposure to HypOA induced substantial transcriptional changes, with 1,606 differentially expressed transcripts (DETs) in larvae from control parents. These changes affected neural development, synaptic signaling, oxygen acquisition, and extracellular matrix organization. In contrast, larvae from HypOA-exposed parents exhibited a muted transcriptional response to HypOA, with only 4 DETs. Although we did not detect a statistically significant interaction between parental and offspring environments at the gene-wise level, a gene set test supported a consistent attenuation of expression changes in offspring from HypOA-treated parents. This pattern may be consistent with transcriptional frontloading, when stress-induced changes are retained and may modify future responses. However, because this effect did not improve offspring performance under HypOA, they are unlikely to represent an adaptive response. Instead, they may reflect non-adaptive carryover effects of parental exposure. Our findings highlight the potential for cross-generational effects to shape transcriptional plasticity, even in the absence of benefits to offspring.

Continue reading ‘Cross-generational plasticity in Atlantic silversides (Menidia menidia) under the combined effects of hypoxia and acidification’

Nutritional status and shell properties of the scallop Argopecten purpuratus are sensitive to intense upwelling events

Published 8 July 2025 Science Closed
Tags: adaptation, biological response, field, mollusks, morphology, multiple factors, otherprocess, oxygen, physiology, South Pacific, temperature

Highlights

The scallop Argopecten purpuratus cope with permanent environmental fluctuations.
Upwelling intensity and duration affect its physiological perfomance.
Shell organic matrix was adversely affected by intense upwelling events.
The nutritional status of the A. purpuratus is modulated by upwelling intensity.
A. purpuratus seems to be partially adapted to colder, low pH and hypoxic conditions.

Abstract

Changes in environmental conditions can be particularly stressful for marine biota. However, marine organisms possess a variety of biological mechanisms (e.g., expression of stress proteins, down or up metabolic regulation, among others) that enable them to adapt to such conditions. This will ultimately determine their resilience and adaptive capacity to the natural environmental fluctuations occurring in their habitats, but also to future climate-driven shifts. In Chile, the scallop Argopecten purpuratus inhabits regions under permanent upwelling conditions causing, at different temporal and spatial scales, cooling, low pH and hypoxic conditions of diverse magnitude. In one-year field experiment, we observed that A. purpuratus was, in some occasions, adversely affected by intense upwelling events during the spring season, when the most intense upwelling events were observed, and thus the lowest temperatures, pH and oxygen levels were registered. These effects were more evident in some shell properties, such as the shell organic matrix, a key component of the biomineralization process. Also, no impacts or positive responses (i.e., up-regulation) were observed on parameters associated to their nutritional status (i.e., carbohydrate and protein muscle content), and periostracum thickness suggesting the presence of physiological trade-offs, but also adaptive mechanisms serving to cope with stressful environmental conditions. Ultimately, our findings also raise concerns about the potential consequences of intensified upwelling due to climate change, particularly for the aquaculture sector that relies on this species, since the majority of impacts were observed in individuals of sizes considered attractive to the market.

Continue reading ‘Nutritional status and shell properties of the scallop Argopecten purpuratus are sensitive to intense upwelling events’

Developmental and transgenerational effects of climate change on inorganic mercury toxicity in a marine copepod

Published 25 June 2025 Science Closed
Tags: biological response, crustaceans, laboratory, molecular biology, multiple factors, North Pacific, oxygen, physiology, reproduction, zooplankton

Highlights

Offspring/persistent OA plus OW aggravated IHg toxicity in T. japonicus.
Persistent OA had stronger mitigating effect on IHg toxicity than offspring OA.
OA plus OW intensified IHg toxicity in copepods mainly via lysosome dysfunction.
Persistent OA enhanced energy metabolism and Hg efflux, decreasing IHg toxicity.
Different scenarios of climate change can variably affect IHg toxicity in copepods.

Abstract

Dynamic shifts in multiple stressors are frequent in the marine environment. Here, we conducted a multigenerational experiment (F1-F4) to explore how different temporal scenarios of climate change, i.e., offspring/persistent ocean acidification (OA), warming (OW), and their combination (AW), could affect inorganic mercury (IHg) toxicity in the marine copepod Tigriopus japonicus. We found that persistent OA exhibited stronger mitigating effect on IHg toxicity in copepods than offspring OA, while offspring/persistent OW and AW aggravated its toxicity effects. We specifically performed transcriptomic analysis for the copepods of F4. Our transcriptomic result showed energy metabolism and detoxification were activated by persistent OA, enabling the copepods to resist IHg exposure. Instead, detoxification- and reproduction-related processes were inhibited in IHg-treated copepods under offspring/persistent OW and AW scenarios. Although apoptosis was suppressed to probably protect IHg-treated copepods under persistent AW, oxidative stress and lysosomal dysfunction ultimately caused reproductive impairment. Our study highlights that offspring/persistent (i.e., developmental/transgenerational) OA and OW could differentially modulate Hg toxicity in marine copepods, and more studies should focus on the temporal variation and complex interaction of multiple stressors, helping accurately project marine biota’s response in the future ocean.

Continue reading ‘Developmental and transgenerational effects of climate change on inorganic mercury toxicity in a marine copepod’

Multiple-stressor effects of ocean warming, acidification and hypoxia on the locomotor behavior of sea cucumber Apostichopus japonicus

Published 6 March 2025 Science Closed
Tags: biological response, echinoderms, laboratory, multiple factors, North Pacific, oxygen, performance, temperature

Highlights

Ocean warming, acidification, and hypoxia simultaneously affect marine organisms.
The combined stress significantly affects the locomotor behavior of A. japonicus.
The movement intensity of A. japonicus was increased under combined stressors.
The erratic movement patterns indicates a stress-induced escape response.

Abstract

Driven by human activities, global climate change is causing unprecedented changes in marine ecosystems, such as ocean warming, ocean acidification and hypoxia. These stressors, which often occur simultaneously and interact with each other, have significant negative impacts on marine organisms and ecosystems, and are referred to as the “deadly trio”. Understanding how these environmental stressors affect marine organisms is critical, particularly concerning their behavior and survival. Locomotion behavior, an essential aspect of an organism’s ability to find food, evade predators, and reproduce, can be significantly disrupted by environmental changes. The sea cucumber (Apostichopus japonicus), an IUCN-listed endangered species further threatened by climate change, serves as a crucial model organism for studying these effects. This study investigates the impact of combined stressors—ocean warming, acidification and hypoxia on the locomotion behavior of A. japonicus under future ocean scenarios. Cumulative movement distance, cumulative movement time, mean velocity, and maximum velocity of sea cucumbers were measured. The results show that the synergetic interaction of environmental stressors alters locomotor behavior of A. japonicus, increasing movement activity with more erratic patterns. Specifically, compared to the control group (NC), the combined stress group (WAH) showed an increase in cumulative movement time from 79.06 % to 93.40 % (P < 0.05), an increase in cumulative movement distance from 2722.11 cm to 5700.09 cm (P < 0.01), and an increase in mean velocity from 4.63 cm/s to 9.50 cm/s (P < 0.05). These findings indicate that combined stressors significantly affect the locomotion behavior of A. japonicus, providing new insights into its behavioral phenotypic adjustments or responses to environmental stress. This study emphasizes the importance of understanding the impacts of multiple-factor stressors on marine organisms to better predict and mitigate the effects of global climate change.

Continue reading ‘Multiple-stressor effects of ocean warming, acidification and hypoxia on the locomotor behavior of sea cucumber Apostichopus japonicus’

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