Posts Tagged 'biological response'

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Effects of ocean acidification on radular tooth material properties in Littorina littorea (Gastropoda, Mollusca)

Published 6 May 2026 Science Closed
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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.

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The influence of localized water quality on Eastern oysters (Crassostrea virginica) and their internal microbiome under changing environmental conditions

Published 5 May 2026 Science Closed
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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.

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Evaluating the role of seaweed farming in ocean acidification mitigation: insights from high-frequency observations

Published 5 May 2026 Science Closed
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The oceanic uptake of anthropogenic CO2 has resulted in ocean acidification (OA). Macroalgae farming has the potential to mitigate OA by removing CO2 from the surface water via photosynthesis. However, continuous in-situ observations of marine carbonate chemistry related to macroalgae farming remain limited, leaving its effectiveness in addressing OA uncertain. To address these knowledge gaps, this study examined a 2-acre Saccharina latissima, sugar kelp, farm located at Point Judith, Rhode Island, as a case study to assess the potential of sugar kelp aquaculture in mitigating local OA. Over the full growing season from December 2022 to May 2023, high-temporal-resolution (every 30–60 minutes) measurements of surface temperature, salinity, dissolved oxygen and pH were taken inside and outside the kelp farm. The results demonstrate that sugar kelp farming does not significantly impact the carbonate system, thus providing negligible OA mitigation locally. Specifically, a temporary, local-scale CO2 reduction and higher pH occurred during very early kelp growth in early February, but was reversed by a higher surface CO2, exaggerating OA, starting in mid-February. Over the entire observation period, kelp growth resulted in a 5.1 ± 11.6 μatm increase of pCO2 per week compared to the control site in the surface, a signal which is small compared to the substantial natural variability. However, the minimal pCO2 difference at the kelp farm may be reflective of the relatively small cultivation area (2 acres) or depressed growth of phytoplankton, resulting from nutrient competition between the kelp and in-situ phytoplankton. This study underscores the need for future sustained observations to evaluate the impact of seaweed cultivation on OA mitigation and the carbon cycle at the ecosystem scale.

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Combined effects of ammonium and pH on sea urchin embryogenesis: insights for sediment quality assessment

Published 30 April 2026 Science Closed
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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.

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Ocean acidification and harmful algal blooms combine to suppress the growth and survival of North Atlantic bivalve larvae

Published 29 April 2026 Science Closed
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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.

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Research progress on the comprehensive response mechanisms of marine organisms to multiple environmental stressors

Published 28 April 2026 Science Closed
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The ocean constitutes a vital component of the Earth’s ecosystem, serving as the breeding and habitat ground for marine organisms. Currently, the global marine ecosystem is confronting combined threats from multiple environmental stressors, such as seawater warming, acidification, hypoxia, and microplastic pollution. Research focusing solely on individual stressors can hardly reveal the authentic response patterns of marine organisms accurately. This paper presents a comprehensive review. It systematically integrates cutting-edge research findings from recent years. The review centers on two core themes. These themes are the interactive effects of multiple environmental stressors and the response mechanisms of marine organisms. Studies indicate significant species-specific differences in organism responses to combined stress. These differences exist across various organism groups. Additionally, the interactive effects of multiple environmental stressors often induce biological responses. These responses deviate from the predictions derived from single-factor studies. The research results presented herein can provide crucial theoretical support for the conservation of marine biological resources, the restoration of biodiversity, and the protection of the marine ecological environment. Meanwhile, they lay a foundation for the establishment of predictable marine stress-response relationship models.

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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 Closed
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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.

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Climate change resilience and positive scope for growth in wild adult Sydney rock oysters, Saccostrea glomerata (Gould 1850)

Published 27 April 2026 Science Closed
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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.

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Coccolithophore genetic diversity, morphology, and contribution to particulate inorganic carbon production in Western North American coastal waters

Published 27 April 2026 Science Closed
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Coccolithophores, as calcifying phytoplankton, play a critical role in the global carbon cycle by producing calcium carbonate (CaCO3) in the ocean through their calcitic coccoliths. Here we examine Gephyrocapsa huxleyi (formerly Emiliania huxleyi) and related species abundance and genetic diversity along the West Coast of North America from samples taken on the 2021 NOAA West Coast Ocean Acidification (WCOA21) cruise, along the margin from British Columbia, Canada, to San Diego, California, USA. Significant carbonate chemistry gradients were observed across 17 transects, mostly in the onshore-offshore and north-to-south direction. Abundance and morphometrics of Gephyrocapsa spp. was evaluated using real-time PCR of mitochondrial cytochrome c oxidase subunit 3 ( cox3 ) gene and by microscopy. Variation in PIC concentrations, G. huxleyi and related species abundance, and coccosphere thickness were found to be associated with the gradients in carbonate chemistry and nutrient concentrations (phosphate, nitrate, nitrite, ammonium) across stations sampled during the cruise. We identified 5 unique amplicon sequence variants (ASVs) of Gephyrocapsa spp. cox3 that systematically varied in relative abundance across the California Current System. Southern California locations had greater diversity in cox3 sequences than northerly locations. These analyses represent baselines for evaluation of the impacts of future environmental changes in coastal waters along this productive upwelling regime.

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Seawater acidification accelerates growth but hastens decline in batch cultures of the marine diatom Thalassiosira pseudonana

Published 22 April 2026 Science Closed
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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 Closed
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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.

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Nonlinear responses of phytoplankton size, diversity, and chlorophyll a to environmental forcing along the Yellow Sea

Published 20 April 2026 Science Closed
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Highlights

  • Miniaturization coincides with reduced species diversity and elevated chlorophyll a.
  • Declining pH and reduced dissolved inorganic nitrogen are key drivers for smaller cells.
  • Salinity, dissolved oxygen and cooling jointly reshape phytoplankton community structure.

Abstract

Phytoplankton are tiny drifting photosynthetic organisms that support marine food webs and help control the global carbon cycle. However, it remains unclear how ongoing environmental changes are altering their cell size, species diversity, and chlorophyll a concentration in coastal seas. In this study, we investigated changes in phytoplankton cell size, species diversity, and chlorophyll a concentration along the Yellow Sea coast of China from 2021 to 2024, based on fourteen research cruises conducted at twenty-six coastal stations. We then employed statistical models to explore how individual and combined environmental factors were related to those biological features. We observed a clear shift to predominance of smaller cells, a reduction in species diversity, and an increase in chlorophyll a concentration. pH and reduced dissolved inorganic nitrogen were strongly associated with smaller cell size, while higher salinity and higher oxygen were associated with lower diversity. Lower surface water temperature and higher dissolved oxygen were associated with higher chlorophyll a concentrations. Overall, our findings suggest that interacting changes in pH, nutrient supply, temperature, salinity, and oxygen are associated with a simpler phytoplankton community structure, smaller mean cell size, and higher biomass levels in the Yellow Sea coastal region, with potential consequences for local food webs and carbon cycling.

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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 Closed
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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.)’

Synergistic effects of ocean acidification and thermal stress on shell biomineralization and parasitism in the white clam Leukoma asperrima (Bivalvia: Veneridae)

Published 17 April 2026 Science Closed
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Ocean acidification (OA) and global warming are fundamentally altering the biomineralization processes of calcifying marine organisms. This study evaluates shell malformations and parasitism in the white clam Leukoma asperrima at Bique Beach, Panama, from December 2024 to November 2025. Environmental parameters (pH, temperature) were monitored monthly across two sampling stations (n=1100). Results indicate that 13.6% of the population exhibited shell malformations, and 6.3% were parasitized by the pea crab Pinnotheres pisum. A strong positive correlation was found between pH and healthy individuals (r=0.97, p<0.001), whereas critical pH levels (min. 5.75) were associated with increased shell fragility and dissolution. Despite thermal tolerance observed up to 35.7°C, the synergistic effect of OA and local stressors compromises the structural integrity of L. asperrima, threatening the sustainability of this socio-economic resource in the Tropical Eastern Pacific.

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Effects of pH on phytoplankton growth and diversity in a tropical coastal ay: an experimental study

Published 14 April 2026 Science Closed
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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.

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Coexpression among eastern oyster host and microbiome genes suggests coordinated regulation of calcifying fluid chemistry

Published 13 April 2026 Science Closed
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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.

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Unravelling marine benthic functioning shifts under ocean acidification

Published 10 April 2026 Science Closed
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Ocean acidification (OA) driven by increasing atmospheric CO2 is altering marine biodiversity. However, impacts of OA on ecosystem functioning at the community level, including calcification, primary production and nutrient uptake, remain largely unknown. Here, we conducted community transplant experiments at natural CO2 vents to assess how declining pH affects marine community species composition, biomass, and key ecosystem processes over time. Our results indicate that community shifts caused by declining pH lead to decreased biomass and calcification rates, while photosynthesis and nutrient uptake rates increased. By leveraging OA field model systems and in situ measurements of ecosystem functioning, this study provides critical insights into how OA-induced biodiversity loss reshapes the structure and functioning of temperate marine coastal ecosystems.

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Intracellular acid-base regulation mediates a trade-off between shell and somatic growth in a clam under ocean acidification

Published 9 April 2026 Science Closed
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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.

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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 Closed
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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’

Responses of reef fish populations to similar environmental changes across distant oceanic islands

Published 9 April 2026 Science Closed
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Oceanic islands are among the most remote and understudied regions of the planet, yet they harbour unique reef fish communities that are increasingly vulnerable to global environmental change. Because these islands are geographically isolated, their populations are often assumed to respond mainly to local environmental conditions. However, by analysing temporal patterns in oceanographic variables across two distant systems (3204 km apart) in the South Mid-Atlantic Ridge (both encompassed by marine protected areas—MPAs), we found that temporal alignment in environmental conditions was associated with coordinated shifts in counts of nine reef fish populations in each study area. Among the evaluated variables, pH emerged as the most influential factor. Despite the divergent responses among reef fishes, possibly reflecting differences in physiological plasticity, shared temporal patterns in pH appeared central to parallel population patterns observed across assemblages. Increases in sea surface height and chlorophyll-a played secondary roles, potentially benefiting some populations, although such effects may be transient. These results suggest that climate-driven convergence in environmental conditions can override geographic isolation, promoting similar biological responses that may reduce resilience and increase extinction risk. Given that both islands are legally protected, our findings highlight that even MPAs are not insulated from large-scale oceanographic stressors, underscoring the need for long-term monitoring and adaptative conservation strategies for remote reef systems.

Continue reading ‘Responses of reef fish populations to similar environmental changes across distant oceanic islands’

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