Under realistic climate change scenarios, marine bivalves face compounding stressors from concurrent ocean warming and acidification. Research has established the separate effects of these factors; however, the synergy driving physiological adaptation in mollusks has yet to be fully elucidated. We assessed the physiological responses of an ecologically significant mussel, Mytilus coruscus, to 2 mo exposure under varying environmental conditions (25°C/28°C and pH 7.7/8.1). Key metrics included shell properties, flesh weight, antioxidant defenses, bioenergetics, and gene expression. Compared to control groups, experimental groups showed reductions in shell hardness and compressive strength, >10% decrease in flesh weight, and 40-52% suppression of carbonic anhydrase and Ca2+-ATPase activities. Molecular analyses of the mantle tissue demonstrated compromised mitochondrial energy transduction (>40% reduction in ATP6 expression) alongside upregulated stress response markers (>2.1-fold COX3 increase). Notably, cellular energy allocation declined, accompanied by depletion of energy reserves (proteins, lipids, carbohydrates), indicating metabolic prioritization toward stress compensation. These findings elucidate how coupled stressors disrupt homeostasis through multilevel interactions, forcing energy trade-offs between defense mechanisms and growth processes, and confirm the tissue-specific vulnerability of the mantle and individual resilience of bivalves under multifactorial climate change.
Continue reading ‘Coupled ocean warming and acidification reduce shell integrity and bioenergetics in juvenile Mytilus coruscus’Posts Tagged 'laboratory'
Coupled ocean warming and acidification reduce shell integrity and bioenergetics in juvenile Mytilus coruscus
Published 7 May 2026 Science Leave a CommentTags: biological response, laboratory, molecular biology, mollusks, morphology, multiple factors, physiology, temperature
Effects of ocean acidification on radular tooth material properties in Littorina littorea (Gastropoda, Mollusca)
Published 6 May 2026 Science Leave a CommentTags: biological response, laboratory, mollusks, mortality, philosophy
Ocean acidification is known to affect calcified structures in marine organisms, yet its impact on non-calcified but functionally essential feeding tools remains poorly understood. The radula is a defining molluscan apomorphy, whose mechanical performance is critical for feeding and survival. Here we investigated the effects of reduced seawater pH on the radular teeth of the intertidal gastropod Littorina littorea. Individuals were maintained for seven weeks under acidified conditions (pH 7.5) or near-present-day conditions (pH 8.1) and compared with a field-collected control group. Radulae were analysed using scanning electron microscopy, confocal laser scanning microscopy, energy-dispersive X-ray spectroscopy, and nanoindentation.
Radulae from acid-treated individuals exhibited markedly increased tooth wear in the working zone despite largely preserved gross morphology. Wear was most pronounced at the cusps of central and lateral teeth and showed rounded profiles indicative of progressive abrasive wear. Acidic conditions caused pronounced changes in the outer tooth coating, including reduced silicon enrichment and substantial decreases in stiffness and hardness, while the inner tooth structure was only weakly affected. Confocal microscopy revealed treatment-specific autofluorescence patterns, suggesting pH-dependent alterations of the organic matrix. Differences between laboratory-maintained and field-collected individuals further indicate that feeding conditions influence radular tooth properties.
These results demonstrate that ocean acidification can impair radular function through material-level degradation of composite feeding structures, potentially reducing grazing efficiency and imposing sublethal fitness costs.
Continue reading ‘Effects of ocean acidification on radular tooth material properties in Littorina littorea (Gastropoda, Mollusca)’The influence of localized water quality on Eastern oysters (Crassostrea virginica) and their internal microbiome under changing environmental conditions
Published 5 May 2026 Science Leave a CommentTags: biological response, laboratory, mollusks, morphology, North Atlantic, physiology, prokaryotes
Oysters are found ubiquitously in estuaries along the Georgia coast, where marsh morphology and large daily tidal fluctuations create dynamic and stressful conditions to which oysters may be locally adapted. Based on water quality data from the Sapelo Island National Estuarine Research Reserve, it is evident that changing climatic conditions are rapidly causing shifts in water quality that may be adversely affecting oyster health, especially as ocean acidification alters the carbonate buffering capacity, increasing the amplitude of daily pH variations. Importantly, the rate of change of conditions are not uniform within estuaries, varying on spatial and temporal scales. The symbiotic relationship between oysters and their internal microbiome has been increasingly analyzed as a metric for oyster health. As filter feeders, oysters continuously introduce microorganisms into their hemolymph. Core families of bacteria, including Mycoplasmataceae, have been identified to be associated with healthy oysters. The abundance of core groups, or of pathogenic genera like Vibrio, can be used as an indicator of oyster condition. Utilizing reciprocal transplant and common garden tank designs, we examined how changing variability in localized water quality conditions drive oyster health using physical and microbial indicators, including oyster growth, condition index, and shifts in microbial community dynamics. Our results suggest that low pH conditions are detrimental to oyster physiology, inducing stress, leading to a reduction in overall health and growth. Low pH causes a shift within the microbial composition, altering community dynamics, and increasing the abundance of stress-related bacteria, including Arcobacteraceae and Vibrionaceae. Drivers of oyster health and host-associated microbial dynamics are site- and scale-dependent and will need further research to fully understand which biotic or abiotic factors are most influential in oyster conditions amidst low pH conditions. Oysters are increasingly used in nature-based restoration efforts to support reef recovery and salt marsh expansion, making it critical to understand how relocation influences oyster health. Our results indicate that oyster condition is driven by destination rather than origin, with relocation success dependent on water quality at the transplant site.
Continue reading ‘The influence of localized water quality on Eastern oysters (Crassostrea virginica) and their internal microbiome under changing environmental conditions’Combined effects of ammonium and pH on sea urchin embryogenesis: insights for sediment quality assessment
Published 30 April 2026 Science Leave a CommentTags: biological response, echinoderms, laboratory, Mediterranean, multiple factors, physiology, reproduction, sediment, toxicants
Highlights
- Reduced pH enhances ammonium toxicity on sea urchin embryos in filtered seawater.
- In elutriates ammonium is a major driver of P. lividus embryotoxicity.
- Data support setting ammonium thresholds in sediment quality frameworks.
- Ocean acidification potentially increases ammonium toxicity for sea urchin larvae.
Abstract
Ammonium is a key component of coastal marine systems, originating from both natural and anthropogenic sources, with possible toxic effects on marine organisms depending on the concentration and pH. This study evaluates, for the first time, the combined effects of ammonium and seawater acidification on early development of the sea urchin Paracentrotus lividus under both laboratory conditions and exposure to environmental matrices derived by dredged sediments from harbor area. Embryos were incubated with increasing concentrations of ammonium in filtered seawater at pH 8.1 and 7.6, as well as in sediment elutriates from the Pescara harbor (Adriatic Sea, Italy), selected as a case study with relevant concentrations of ammonium (0.1–3.5 mg/L). A combined effect between ammonium and pH was observed, with increasing ammonium toxicity by ∼20% at pH 7. Moreover, in sediment elutriates, ammonium affect sea urchin embryo development, with EC50 ranging between 1.388 and 1.538 mg/L NH4+ at pH 8.1 and 7.6, respectively, without significant differences due to pH. Chemical analyses of sediments confirmed low levels of trace metals and organic pollutants, indicating that ammonium is the primary driver of embryotoxicity without a direct toxic effect of other contaminants. The results further underscore the need to integrate ammonium assessment into sediment quality frameworks and for management strategies, particularly in the context of future ocean acidification, to safeguard the early life stages of sensitive marine invertebrates.
Continue reading ‘Combined effects of ammonium and pH on sea urchin embryogenesis: insights for sediment quality assessment’Ocean acidification and harmful algal blooms combine to suppress the growth and survival of North Atlantic bivalve larvae
Published 29 April 2026 Science Leave a CommentTags: algae, biological response, community composition, laboratory, mollusks, mortality, North Atlantic, otherprocess, reproduction
While harmful algal blooms (HABs) and ocean acidification (OA) are environmental factors that can impair bivalves, the manner in which these two stressors may act and interact to impact bivalve larvae is poorly understood. This study exposed larvae of hard clams (Mercenaria mercenaria) and Eastern oysters (Crassostrea virginica) to a range of pCO2 levels found in estuaries (400–3,000 µatm) and three harmful algae, Alexandrium catenella, Dinophysis acuminata, and Margalefidinium polykrikoides, at densities found during HABs (500–7,000 cells mL-1), with one HAB species exposure per experiment. The combined OA and HAB treatment significantly reduced larval survival in all 21 experiments by 91 ± 4.6% (SE) compared to controls and reduced larval sizes in 92% of experiments by 40 ± 3.5%. Cultured M. polykrikoides had a stronger negative effect on larvae than cellular equivalent bloom populations. Densities of D. acuminata >750 cells mL-1 reduced larval survival and size (p < 0.01), but the addition of OA to D. acuminata did not suppress survival further. While the combined A. catenella and OA treatment reduced larval growth and survival at all densities (p < 0.01), A. catenella alone did not impact M. mercenaria survival or size at or below 1,000 cells mL-1 and did not impact C. virginica at any density. Oyster larvae were less impacted than hard clams by OA (33 vs. 67% of experiments) and by HABs (67 vs. 100% of experiments). Given the very low survival of bivalve larvae when exposed to combined HABs and OA in all experiments (<0.1–5%), bivalve restoration and conservation efforts should seek to avoid regions that experience these co-stressors.
Continue reading ‘Ocean acidification and harmful algal blooms combine to suppress the growth and survival of North Atlantic bivalve larvae’Light and tidal inundation and exposure regulate the sensitivity of estuarine benthic greenhouse gas fluxes to warming and ocean acidification
Published 28 April 2026 Science Leave a CommentTags: biogeochemistry, biological response, Indian, laboratory, light, multiple factors, physiology, primary production, respiration, sediment
Coastal sediments are globally significant sources and sinks of greenhouse gases (GHGs), yet their contributions to climate feedbacks of warming and ocean acidification remain uncertain, in part due to limited understanding of short-term variability. Here, we use a fully factorial laboratory experiment to disentangle how diel light–dark and tidal inundation and exposure interact with warming and elevated pCO2 to regulate benthic fluxes of CO2, CH4, and N2O in estuarine sediments, alongside concurrent changes in benthic oxygen exchange. While warming and pCO2 exerted strong independent effects, their influence was shaped by diel and tidal fluctuations in redox conditions and oxygen availability, reflecting shifts in metabolic balance between primary production and respiration. Light consistently limited CO2, CH4, and N2O emissions through enhanced autotrophic uptake and oxygenation, while dark promoted anaerobic production pathways. N2O showed the greatest sensitivity to the combined effects of climate forcing and redox dynamics. Despite warming-driven stimulation of benthic heterotrophy and the production of all GHGs, CO2 remained the dominant greenhouse gas, with minimal CH4 and N2O fluxes due to the limited organic matter availability within the sediment. This reflects the strong redox controls on CH4 and N2O production, which relies on both oxygen depletion and organic substrate supply. Our findings emphasize that fine-scale temporal variability can significantly shape both the magnitude and climate sensitivity of benthic GHG emissions. Capturing these fine-scale controls is essential for accurately modeling the contributions of estuarine sediments to global GHG budgets and their feedbacks.
Continue reading ‘Light and tidal inundation and exposure regulate the sensitivity of estuarine benthic greenhouse gas fluxes to warming and ocean acidification’Climate change resilience and positive Scope for Growth in wild adult Sydney rock oysters, Saccostrea glomerata (Gould 1850)
Published 27 April 2026 Science Leave a CommentTags: biological response, growth, laboratory, mollusks, multiple factors, physiology, temperature
Climate change resilience and positive Scope for Growth in wild adult Sydney rock oysters, Saccostrea glomerata (Gould 1850)
Oysters have ecological and economic importance worldwide as they provide ecosystem services and sustain profitable aquaculture industries. Calcifying bivalves including oysters have been found to be sensitive to ocean warming and acidification caused by anthropogenic climate change. This study tested whether adult wild Sydney rock oyster, Saccostrea glomerata, exposed to elevated pCO2 (331 μatm and 867 μatm) and temperature (24°C and 28°C) in an orthogonal design for five weeks, have resilience and can maintain sufficient scope for growth or are pushed into a suboptimal state. At the end of the exposure growth, condition index, clearance, ingestion and absorption efficiency and rates were measured and scope for growth calculated. Sydney rock oysters responded to elevated pCO2 and temperature with no change in overall growth or condition index, but significantly increased metabolic, clearance, ingestion, and absorption rates and positive Scope for Growth. Our results indicate that adult S. glomerata can cope with the moderate level of climate change stress predicted for 2100 through increased standard metabolic rate and increased energetic processes. If, however, food availability becomes limiting, and other environmental stressors interact with climate change stressors then resilience thresholds maybe breached for this economically, ecologically and indigenous significant and iconic oyster species.
Continue reading ‘Climate change resilience and positive Scope for Growth in wild adult Sydney rock oysters, Saccostrea glomerata (Gould 1850)’Seawater acidification accelerates growth but hastens decline in batch cultures of the marine diatom Thalassiosira pseudonana
Published 22 April 2026 Science ClosedTags: biological response, growth, laboratory, photosynthesis, physiology, phytoplankton
Diatoms are characterized by rapid cell division and a high capacity to adapt to environmental variability, and some species can form blooms when environmental conditions are favorable. Previous studies have largely focused on the bloom development phase, during which biomass accumulates rapidly, whereas the decline phase-despite its critical role in carbon export and microbial loop dynamics-has received far less attention. Here, we tracked changes in cell density and inorganic carbon utilization characteristics throughout the entire course of a simulated Thalassiosira pseudonana bloom under ambient (420 μatm) and elevated pCO2 (1000 μatm) conditions. Inhibitors of carbonic anhydrase and direct bicarbonate transporters were applied to investigate the characteristics of inorganic carbon utilization. The relationship between photosynthetic rate and inorganic carbon concentration was measured to assess inorganic carbon affinity. The simulated T. pseudonana bloom was characterized by rapid cell density accumulation, reaching a peak within 10 days, followed by a rapid decline without a distinct stationary phase. As the bloom progressed, photosynthetic rate and the maximum quantum yield of photosystem II declined, whereas the inorganic carbon affinity increased. Elevated CO2 enhanced growth and maximum quantum yield during the acceleration phase but resulted in an 86% higher fitted death rate during the decline phase. Regarding the relationship between photosynthetic rate and dissolved inorganic carbon concentration, elevated CO2 increased the maximum photosynthetic rate and half-saturation constant only during the acceleration phase. Collectively, these results indicate that seawater acidification can influence both biomass accumulation and decline intensity in diatom blooms, with potential consequences for carbon sequestration and its redistribution among biogeochemical pools.
Continue reading ‘Seawater acidification accelerates growth but hastens decline in batch cultures of the marine diatom Thalassiosira pseudonana’Ocean acidification induces neuronal hyperexcitation and anxiety-like behaviour in marine medaka via ASIC activation
Published 21 April 2026 Science ClosedTags: biological response, fish, laboratory, molecular biology, performance, physiology
Ocean acidification presents a significant threat to marine life, yet its neurobiological mechanisms remain poorly understood. This study examined how acid-sensing ion channels (ASICs) mediate neuronal excitability and anxiety-like behaviour in marine medaka (Oryzias melastigma) under elevated CO2 concentrations (1000 and 1900 ppm). Transcriptomics revealed early upregulation of asic1a (4 days), while RT-qPCR demonstrated increased asic1a, asic1b, asic2 and asic4a (7 days), with only asic1a sustained at 30 days. Immunofluorescence confirmed heightened Asic2 in emotion-processing brain regions following acidification. Transmission electron microscopy unveiled distinct ultrastructural alterations: widened synaptic clefts, thinned postsynaptic densities, and decreased mitochondrial aspect ratios. Mitochondrial membrane potential assays revealed a reduction in membrane potential in response to acidification. Electrophysiological recordings showed increased neuronal firing count in the dorsolateral telencephalon under acidification, behavioural assessments revealed significant anxiety-like phenotypes, effects that were fully rescued by ASIC inhibition. These results indicated that temporal specificity in ASIC subtype expression in acidification response. The interplay of synaptic and mitochondrial dysfunction, neuronal hyperexcitability, and behavioural alterations suggested acidification impaired both synaptic transmission efficiency and mitochondrial function, destabilizing neural circuits. This study systematically elucidates the neurotoxic effects of ocean acidification on marine fish, providing critical scientific evidence for predicting the ecological impacts of climate change on marine organisms.
Continue reading ‘Ocean acidification induces neuronal hyperexcitation and anxiety-like behaviour in marine medaka via ASIC activation’Effects of ocean acidification on the growth, shell integrity, and vulnerability to thermal stress and predation in Pacific oysters (Magallana gigas), and bay mussels (Mytilus spp.)
Published 17 April 2026 Science ClosedTags: biological response, laboratory, mesocosms, mollusks, morphology, mortality, multiple factors, North Pacific, predation, temperature
The ocean is absorbing approximately one third of the anthropogenic carbon dioxide (CO₂) emissions to the atmosphere. As a result, the pH of the ocean is declining steadily, a phenomenon known as ocean acidification (OA). This decline in pH and the associated reductions in calcium carbonate saturation states of the water can have widespread consequences for marine life, particularly to calcifying organisms. In this thesis, I aim to understand the effects of OA on the growth, shell integrity, and susceptibility to secondary stressors like heatwaves or predation, of two important shellfish species in British Columbia, Pacific oysters (Magallana gigas) and bay mussels (Mytilus spp.). I also aim to identify potential tipping points beyond which the biological responses of these shellfish to OA rapidly become more pronounced. I reared oysters and mussels in experimental mesocosms, in four pCO₂ treatments for eight-weeks to determine growth. I subsequently exposed these OA-acclimated animals to a secondary stressor by simulating heatwave conditions to assess thermal tolerance, and by introducing a predatory sea star to assess vulnerability to predation. Finally, shell condition was visually assessed, and shells were mechanically crushed to determine integrity. I found that OA decreased the growth of both oysters and mussels. No tipping point was observed for oyster growth, but reduced growth only emerged at the highest levels of OA in mussels. Sensitivity to atmospheric warming was not increased after exposure to acidic conditions for either species, although oysters had a considerably higher thermal tolerance than mussels. Mussel vulnerability to predation did increase, although the relationship was complex and depended on predator size. OA negatively affected shell strength, and possible tipping points emerged for this response metric in both species. Overall, OA was shown to negatively affect both species, but patterns of effect and the presence of potential tipping points depended on the species and the response metric. Understanding how these ecologically and commercially important bivalves are responding to OA is important for understanding how changing ocean chemistry will affect marine ecosystems, and to inform aquaculture managers on mitigation strategies.
Continue reading ‘Effects of ocean acidification on the growth, shell integrity, and vulnerability to thermal stress and predation in Pacific oysters (Magallana gigas), and bay mussels (Mytilus spp.)’Effects of pH on phytoplankton growth and diversity in a tropical coastal ay: an experimental study
Published 14 April 2026 Science ClosedTags: biological response, BRcommunity, community composition, growth, Indian, laboratory, otherprocess, phytoplankton
This research was intended to investigate the effects of reduced pH on the growth rates and diversity of phytoplankton in the coastal waters of Visakhapatnam in the Bay of Bengal. A short-term (six days) microcosm experiment was conducted with different pH conditions such as ambient (control-in situ pH), pH 8.0 (0.2 pH units drop from in situ pH) and pH 7.8 (0.4 pH units drop from in situ pH) corresponding to low, medium, and high future pH decline scenarios, respectively, to study the direct acidification impact on phytoplankton. The results revealed that the phytoplankton communities exhibit a wide range of responses including changes in growth rate during incubation. From the two treatments, a more pronounced response was observed in pH 7.8 conditions compared to the present pH scenario. Some phytoplankton communities exhibited positive growth responses to acidification, while others showed negative reactions in terms of biodiversity. Notably, Pseudo-nitzschia sp. became dominant during acidification, whereas larger centric diatoms such as Skeletonema spp., Chaetoceros spp., Rhizosolenia sp., Dactyliosolen fragilissimus, and Ditylum brightwellii showed no significant growth response to upcoming acidified conditions. This indicates a diverse array of physiological tolerance among the plankton species to environmental shifts. This study recommends further research to explore the impact of ocean acidification on other planktonic species in the coastal waters of Bay of Bengal.
Continue reading ‘Effects of pH on phytoplankton growth and diversity in a tropical coastal ay: an experimental study’Coexpression among eastern oyster host and microbiome genes suggests coordinated regulation of calcifying fluid chemistry
Published 13 April 2026 Science ClosedTags: biological response, BRcommunity, laboratory, molecular biology, mollusks, North Atlantic, physiology, prokaryotes
Significance
Oysters and many marine animals build shells by controlling the chemistry of extracellular fluids where minerals form, yet whether microbes in these fluids influence calcification remains unclear. We show that oysters maintain favorable conditions for mineral formation by regulating the carbonate chemistry of the shell-forming fluid, and that resident microbes respond to these changes by expressing nitrogen- and sulfur-cycling genes capable of altering pH, alkalinity, and carbonate availability. Many of these microbial transcripts were tightly correlated with oyster immune and signaling genes, suggesting that host and microbiome processes may be linked within the calcifying environment. These findings point to a host–microbiome interaction in the regulation of calcifying-fluid chemistry that directly links microbial activity to the carbonate chemistry underlying biomineralization.
Abstract
Marine animals that build shells, such as oysters, carefully regulate the chemistry of their internal calcifying fluids, but the molecular mechanisms behind this control, as well as whether microbes play a role in calcification, are poorly understood. To better understand oysters’ molecular mechanisms and the role of their calcifying-fluid microbes, we conducted experiments that simulated a tidal cycle, measured calcifying fluid pH and total dissolved inorganic carbon, and characterized host and microbial gene expression via transcriptomics. These experiments showed that calcifying fluid pH remained relatively stable throughout tidal pH fluctuations, with corresponding increases in oyster transcripts for ion transport and acid–base regulation. These data provide direct evidence that tidal fluctuations drive rapid changes in oyster calcifying fluid chemistry. Most surprisingly, increases in microbial transcripts related to nitrogen and sulfur cycling correlated to higher calcifying fluid DIC, and coexpression network analysis revealed patterns of gene expression that linked oyster immune and neural pathways to microbial redox processes, providing molecular evidence of potential host modulation of microbial metabolism. Together, these results reveal that oysters actively regulate their calcifying fluid pH over short timescales, and the endemic microbiome metabolic responses can yield metabolites that influence calcifying fluid pH, alkalinity, and ultimately calcification. These data offer a perspective on oyster physiological capacity and, most importantly, the potential role of microbes in oyster calcification. In light of ongoing changes in ocean pH and temperature, oysters provide a model for studying animal–microbial responses to environmental acidification and how their interactions may shape biomineralization.
Continue reading ‘Coexpression among eastern oyster host and microbiome genes suggests coordinated regulation of calcifying fluid chemistry’Intracellular acid-base regulation mediates a trade-off between shell and somatic growth in a clam under ocean acidification
Published 9 April 2026 Science ClosedTags: biological response, growth, individualmodeling, laboratory, mesocosms, modeling, molecular biology, mollusks, North Pacific, physiology
Highlights
- Clams actively regulate intracellular pH against ocean acidification via CAc
- RNAi confirms CAc’s essential role in H+ efflux, measured by in vivo SIET.
- A CAc-sAC-NKA network forms a conserved regulatory pathway for acid-base balance.
- DEB model shows this pH defense sustains shell linear growth despite metabolic costs.
SUMMARY
Ocean acidification (OA) is predicted to threaten marine bivalves, casting them as passive victims of changing carbonate chemistry. Contributing to a revised understanding, we identified a conserved mechanism for acid-base regulation that supports intracellular resilience. Using the Manila clam Ruditapes philippinarum as a model, this study demonstrated that intracellular pH (pHi) homeostasis under elevated pCO2 was maintained through cytosolic carbonic anhydrase (CAc)-mediated H+ efflux. A causal link was established by combining in vivo scanning ion-selective electrode technique (SIET) with RNA interference (RNAi), where RpCAc knockdown suppressed H+ efflux and compromised pHi. A coordinated regulatory network involving CAc, soluble adenylyl cyclase (sAC), and Na+/K+-ATPase (NKA) was synergistically upregulated, suggesting an evolved adaptive pathway. Dynamic Energy Budget (DEB) modeling, calibrated with experimental data, revealed that this cellular compensation carries a high energetic cost, leading to a significant reallocation of resources: shell growth was maintained, but somatic growth was severely suppressed. These results elucidate a conserved cytoprotective mechanism that enables short-term tolerance of OA at a substantial somatic cost, redefining resilience to include energetic trade-offs.
Continue reading ‘Intracellular acid-base regulation mediates a trade-off between shell and somatic growth in a clam under ocean acidification’Climate-driven restructuring of phytoplankton productivity and community composition in the south-eastern Black Sea: insights from seasonal CO2-temperature manipulation experiments
Published 9 April 2026 Science ClosedTags: biological response, Black Sea, community composition, laboratory, multiple factors, otherprocess, physiology, phytoplankton, temperature
Semi-enclosed marine systems with low buffering capacity, such as the Black Sea, are expected to experience amplified impacts of ocean acidification and warming, yet experimental evidence on their combined short-term effects on natural phytoplankton assemblages remains limited. Here, we present a seasonally resolved one-year study (four experiments conducted between 2022 and 2023) based on 48 h short-term microcosm incubation experiments using natural phytoplankton communities collected from coastal and offshore stations in the south-eastern Black Sea. CO2 concentrations (360, 600, and 760 ppm) and temperature (ambient and +3 °C) were manipulated to examine short-term physiological and compositional responses under projected climate scenarios. We hypothesised that CO2 and warming would exert both independent and interactive effects on short-term particulate organic carbon production (14C uptake rates) and relative community composition, with responses varying seasonally and being most pronounced during summer stratification.
Short-term particulate primary production increased by ∼22% and ∼36% at 600 and 760 ppm CO2, respectively (p<0.05), while warming provided an additional 14–22% enhancement depending on season, with significant CO2 × temperature interaction terms detected for total production (two-way ANOVA, p<0.05), indicating synergistic CO2–temperature effects. Warming and moderate CO2 enrichment were associated with increased relative contributions of nano- and picophytoplankton (by ∼6–10%), whereas high CO2 reduced the warming-driven shift toward smaller cells by maintaining microphytoplankton contributions ∼10–15% higher than in the warming-only treatment. Carbonate chemistry responded strongly to CO2 manipulation, with pH declining from in-situ values of 8.09–8.21 to 7.06–7.52 during incubations and minor reductions in total alkalinity, reflecting the weak buffering capacity of the system. Pigment composition and microscopy indicated short-term increases in dinoflagellate relative abundance (∼12–18%) and concurrent declines in diatom markers, accompanied by accelerated nitrate depletion and reduced nitrogen-to-phosphorus (N:P) ratios, consistent with enhanced nitrogen limitation.
Overall, these findings demonstrate pronounced short-term sensitivity of natural phytoplankton assemblages in the south-eastern Black Sea to combined CO2 and warming under controlled incubation conditions. Because these results derive from 48 h microcosm experiments, they represent short-term physiological and compositional responses rather than direct evidence of long-term ecosystem restructuring, yet the observed patterns suggest potential implications for trophic efficiency, harmful algal bloom development, and carbon cycling in this low-buffer, stratified basin under future climate forcing.
Continue reading ‘Climate-driven restructuring of phytoplankton productivity and community composition in the south-eastern Black Sea: insights from seasonal CO2-temperature manipulation experiments’Combined ecotoxicity of microplastics and crude oil co-pollutants: occurrence, distribution and its synergistic impact with ocean acidification on Artemia franciscana
Published 3 April 2026 Science ClosedTags: biological response, crustaceans, Indian, laboratory, multiple factors, physiology, plastics, reproduction, toxicants, zooplankton
Microplastics (MPs) are recognized as a global concern, with specific attention shifted towards marine MPs pollution. This particular study investigates the abundance and distribution of crude oil-loaded microplastics (COMPs) along the Chennai coastline, Tamil Nadu, India and evaluates their combined toxicological effects with ocean acidification on Artemia franciscana. Spatial analysis revealed that Ennore Creek exhibited the highest MP concentration (10.82 ± 0.2 items/L). Polypropylene was recorded as the predominant polymer type followed by low density polyethylene and polyethylene terephthalate, with particle size ranging from 250 to 500 µm. COMPs were detected across all sampling sites, with concentrations declining from Ennore Creek (0.21 ± 0.03 items/L) to Kasimedu Beach (0.10 ± 0.02 items/L). The adsorption of crude oil on MPs is primarily mediated by physical interaction with multi-layer adsorption behaviour. The results highlighted that increase in MP concentration and decrease in seawater pH significantly induced acute toxicity and oxidative stress responses in A. franciscana. At pH 7.8, experimental groups exposed to 0.5 mg/mL of COMPs developed higher ROS, SOD and catalase activity (p<0.001). Whereas control groups alone showed significant increase in oxidative stress responses at lower pH level such as pH 7.8 and 8.0. Combined exposure of COMPs and low pH conditions significantly increased oxidative damages in A. franciscana and affected its hatching ability. The observations from this study emphasize the urgent need for integrated monitoring and further research to explore combined toxicological effects of MPs and ocean acidification to other marine organisms as well.
Continue reading ‘Combined ecotoxicity of microplastics and crude oil co-pollutants: occurrence, distribution and its synergistic impact with ocean acidification on Artemia franciscana’Ocean acidification affects the timing of puberty and the reproductive output in a marine temperate fish
Published 2 April 2026 Science ClosedTags: adaptation, biological response, fish, laboratory, morphology, mortality, North Atlantic, otherprocess, reproduction
Ocean acidification (OA) is a major climate-related threat to fish that can disrupt the regulation of the reproductive axis of fish, impacting reproductive success. However, previous studies have only focused on a single reproductive cycle and reported increased fecundity in some species exposed to OA. Since acclimation over several reproductive cycles can occur, it is necessary to evaluate successive reproductive cycles for predicting the actual resilience of species to OA. In this study we assessed the impact of lifetime exposure to different ocean pH/pCO2 levels (Current condition, Moderate OA and High OA) on the sexual maturation and spawning phenology of the European sea bass, over its two first reproductive periods. We tested the hypothesis that OA would exert its greatest impact at the onset of puberty (first reproduction). Accordingly, High OA exposure induced an earlier onset of puberty in both sexes, resulting in a longer spawning period and an increased fecundity. These effects were reduced during the second reproductive season. However, OA affected egg quality and sperm motility profile during the second reproductive season, leading to a total mortality at hatching of embryos spontaneously produced. This mortality was not observed in embryos produced through hormone-induced oocyte maturation and in vitro fertilisation. These results suggest that OA affects the regulation of oocyte maturation and/or the synchronisation of eggs and sperm release. The OA-driven shift in spawning may misalign with optimal environmental conditions for offspring survival. This increases the population’s vulnerability and could favour species whose reproduction is more resilient to OA.
Continue reading ‘Ocean acidification affects the timing of puberty and the reproductive output in a marine temperate fish’pCO2-induced seawater acidification influencing cadmium toxicity on antioxidant defenses responses in juvenile Manila clam Ruditapes philippinarum
Published 30 March 2026 Science ClosedTags: biological response, laboratory, metals, mollusks, multiple factors, North Pacific, physiology
Highlights
- GSH system and SOD-CAT act as complementary lines of antioxidant defense
- SA alters Cd effects on antioxidants depending on metal concentration
- High SA overrides Cd effects on antioxidant defenses in Manila clams
- Combined high SA and Cd exposure overwhelms antioxidant capacity
- Candidate biomarkers for monitoring SA or Cd stress are proposed
Abstract
Ocean acidification is known to interact with heavy metals, impacting physiological processes of marine organisms. This study investigated antioxidant defenses of juvenile Manila clam Ruditapes philippinarum exposed to cadmium (Cd) across ambient-relevant to high concentrations, under pCO2-induced seawater acidification (SA) scenarios corresponding to IPCC ocean pH projections. Results revealed that clam’s antioxidant system, encompassing GSH defense system and SOD-CAT defense lines, collectively combated oxidative stress dependent on specific stressors and their stress levels. GSH system is vital for detoxification and maintaining redox balance, while SOD and CAT are essential for scavenging ROS. Cd exposure notably activated GSH redox cycle, and SA markedly inhibited the antioxidants associated with this cycle. SOD and CAT exhibited distinct regulatory pathways with asynchronous responses to SA and Cd co-exposure. SA conditions modulate Cd-induced antioxidant response dependent on metal concentrations. Antioxidant biomarkers responded more prominently to SA and Cd interactions than to individual exposure, particularly, high SA effects could override Cd effects on antioxidant responses. Although SA effects did not directly induce lipid peroxidation, elevated MDA levels under Cd exposure occurred only under SA conditions, indicating insufficient antioxidant defense against lipid peroxidation under excess co-exposure. GSH and SOD were more sensitive to SA exposure, whereas MDA and GST were sensitive to Cd exposure, suggesting their potential as biomarkers for assessing SA or Cd-induced oxidative stress, respectively. These findings provide insights into interplay between metal toxicity and ocean acidification on antioxidant defenses in bivalves, shedding light on their strategies to combat metal pollution amidst global ocean change.
Continue reading ‘pCO2-induced seawater acidification influencing cadmium toxicity on antioxidant defenses responses in juvenile Manila clam Ruditapes philippinarum’Metabolic rate measurements of two benthic invertebrates under simulated climate change conditions
Published 30 March 2026 Science ClosedTags: adaptation, biological response, laboratory, Mediterranean, mollusks, morphology, multiple factors, otherprocess, porifera, respiration, temperature
Background
Climate change is profoundly altering marine ecosystems through ocean warming and acidification. These stressors are especially pronounced in the Mediterranean Sea, a climate change hotspot projected to warm faster than the global average. Increased temperatures and reduced pH directly affect metabolic processes in marine invertebrates by elevating respiration rates up to species-specific thermal limits, beyond which physiological performance declines. Ocean acidification further disrupts metabolic processes by increasing energetic maintenance costs. Sessile and sedentary marine invertebrates, such as sponges and benthic gastropods, are particularly exposed to such environmental shifts due to their limited ability to escape unfavorable conditions, making physiological plasticity and local adaptation crucial for persistence.
New information
This manuscript presents a dataset of oxygen consumption rates and wet weight measurements for two low-mobility marine species, the gastropod Hexaplex trunculus and the sponge Chondrilla nucula. Using a common garden experiment, individuals from North and South Aegean populations were exposed for three months to simulated climate change conditions combining increased temperature and reduced pH. The dataset documents respiration measurements obtained using metabolic chambers after three months of exposure, allowing comparisons across species, geographic origin, and experimental treatments.The dataset accounts for intraspecific variation in these responses, providing insight into potential adaptive differences among geographically distinct populations. These data provide a resource for future analyses of metabolic responses of marine invertebrates to combined warming and acidification conditions.
Continue reading ‘Metabolic rate measurements of two benthic invertebrates under simulated climate change conditions’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 ClosedTags: 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.
Continue reading ‘Skeletal growth and loss of the cold-water coral Lophelia pertusa from multiple environmental drivers in a year-long experiment’
