Posts Tagged 'prokaryotes'

Assessing sponge resilience to ocean acidification in natural reef environments

Published 28 January 2026 Science Leave a Comment
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Highlights

  • Sponges are key components of coral reefs globally providing a range of important functional roles.
  • We used in situ incubation chambers to measure chlorophyll concentrations, oxygen fluxes and microbial communities for two common Indo-Pacific sponge species (Melophlus sarasinorum and Neopetrosia chaliniformis) at a natural CO2 vent (pHT 7.6–7.7) and control site in Papua New Guinea.
  • We found little evidence for any physiological differences between vent and control sponges, and no differences in the overall microbial communities
  • Overall, our results support the emerging evidence that heterotrophic sponges will likely be resilient to future ocean acidification.

Abstract

Sponges are key components of coral reefs globally providing a range of important functional roles. While sponges are under threat from the impacts of global climate change, there is an emerging picture of sponge tolerance to ocean acidification (OA). However, to date all physiological studies on sponge tolerance to OA have been under ex-situ experimental conditions and only for a limited number of sponge species. Instead, here we used in situ incubation chambers to measure chlorophyll concentrations and oxygen fluxes for two common Indo-Pacific sponge species (Melophlus sarasinorum and Neopetrosia chaliniformis) at a natural CO2 vent (pHT 7.6–7.7) and control site in Papua New Guinea. We also explored differences between the sponge microbial community composition between control and vent locations for N. chaliniformis. We found very low concentrations of chlorophyll in both species, compared to other sponges, suggesting these species are largely heterotrophic. We also found little evidence for any physiological differences between vent and control sponges, and no differences in the overall microbial communities, except some specific microbes. Overall, our results support the emerging evidence that heterotrophic sponges will likely be resilient to future ocean acidification.

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Insight into the multifactorial effect of climate change on marine bacteria: resilience mechanisms and mitigation strategies

Published 10 December 2025 Science Closed
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Industrialization marked a significant turning point that impacted the global climate at an unprecedented scale. Oceans, covering 71% of the surface of Earth, play a pivotal role in regulating climate change factors, serving as essential components of planetary processes. In these oceanic ecosystems, marine bacteria are intricately involved in regulating various biogeochemical cycles that are crucial to climate regulation and ecosystem functioning. However, the ongoing climatic changes pose significant challenges to marine bacteria and their associated processes. In the Anthropocene epoch, the interaction between anthropogenic pollutants and climatic stressors further amplifies their impact on marine bacteria across diverse ecological niches and their resilience mechanisms. It delves into the interactive effects of anthropogenic pollutants with climatic stressors on bacteria, particularly emphasizing on organic pollutants, heavy metals, and microplastics. The review entails the impact and resilience mechanisms of marine bacteria in response to climatic stressors. The current trajectory of climatic changes highlights the urgent need for concerted global action to mitigate greenhouse gas emissions and adapt to the inevitable impacts of climate change. In this context, various strategies employing marine bacteria in mitigating climate change for a sustainable future have also been discussed.

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Impact of ocean acidification on the intestinal microflora of Sinonovacula constricta

Published 20 November 2025 Science Closed
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The intestinal microflora, which is vital for nutrient absorption and immune regulation, can experience dysbiosis under environmental stress, potentially enhancing host susceptibility to pathogenic invasion. The impact of ocean acidification on bivalves is substantial, but its effects on their intestinal microflora remain poorly understood. To explore the impact of ocean acidification on the intestinal microflora of Sinonovacula constricta, this study used high-throughput 16S rRNA sequencing technology to investigate the variations in the intestinal microflora communities of S. constricta during ocean acidification across different time points. After exposure to ocean acidification, changes in the composition of the intestinal microflora of S. constricta were observed, with no significant difference in α-diversity between the acidified and control groups. The abundance of Proteobacteria in the acidification group increased, whereas that of Cyanobacteria decreased. The abundance of Firmicutes initially decreased and then increased. At the genus level, the relative abundance of Pseudomonas was lower than that in the control group, whereas the relative abundance of Photobacterium, Acinetobacter, and Enterobacter gradually increased. LEfSe analysis identified Serpens as the discriminative biomarker at 7 days of acidification, Enterobacteriales, Rhodobacteraceae, and Martvita at 14 days of acidification, and Serpens, Acidibacteria, and Aeromonadaceae at 35 days of acidification. Functional prediction analysis indicated significant stimulation in various metabolic pathways at different time points following acidification stress. Specifically, pathways involved in biosynthesis were significantly stimulated at 14 days of acidification, while those related to sucrose degradation were disrupted at 35 days. The results further indicated that ocean acidification stress can influence the intestinal microflora of S. constricta, but no severe dysbiosis or digestive system impairment was observed at the microbial level. This study provides new insights into the effects of ocean acidification on the intestinal microflora of marine bivalves.

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Colony formation sustains the global competitiveness of N2-fixing Trichodesmium under ocean acidification

Published 10 November 2025 Science Closed
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Anthropogenic CO2 emissions drive ocean acidification (OA). Trichodesmium, a key marine N2 fixer, displays contrasting growth responses to OA across morphotypes, with negative responses in free trichomes but neutral or positive in colonies. However, the lack of mechanistic understanding for these discrepancies has impaired our ability to predict the ecophysiological response of Trichodesmium in the changing ocean. Here, we developed ecophysiological models of Trichodesmium and underpin mechanisms behind contrasting responses to OA by distinct morphological adaptations. For free trichomes, our diurnal model corroborated previous findings that OA impairs nitrogenase efficiency and photosynthetic energy production. In colonies, however, OA alleviated copper and ammonia toxicity within the microenvironment, potentially with increased iron acquisition synergies, outweighing the minor effects of inorganic carbon limitation relief in the colony center. Projections suggest that globally, OA will reduce N2 fixation of trichomes by 16±6% but increase that of colonies by 19±24% within this century. By resolving morphotype-specific mechanisms, our study clarifies Trichodesmium’s adaptive strategies, which may enable it to sustain its competitiveness and biogeochemical impacts in the changing ocean.

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Gut microbial community plasticity as a climate shield mediating sea cucumber resilience to ocean acidification and warming

Published 28 October 2025 Science Closed
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Ocean acidification (OA) and ocean warming (OW) pose escalating threats to marine ecosystems, particularly to benthic organisms, such as sea cucumbers, that play pivotal roles in nutrient cycling and sediment health. Existing studies have mostly focused on the physiological responses of sea cucumbers, yet overlooked the critical roles of both gut microbial communities and metabolites in the host’s responses under environmental stress. Herein, a mesocosm experiment was constructed and analyzed by using integrated gut microbiome and metabolomics approaches to investigate the responses of sea cucumbers Apostichopus japonicus to OA and OW. Results revealed that microbial community plasticity underpins holobiont adaptation, with warming restructuring gut microbiota toward thermotolerant taxa, whereas acidification enriches alkalinity-modulating Rhodobacteraceae and Halioglobus sp.. Metabolomic profiling identified 43 amino acid derivatives that exhibit significantly increased concentrations in the OA and OW groups. These derivatives include upregulated N-methyl-aspartic acid and γ-glutamyl peptides, which stabilize macromolecules and enhance redox homeostasis. Conversely, antioxidative metabolites, such as ergothioneine and L-homocystine, are suppressed, reflecting trade-offs between energy allocation and stress protection. In OW group, the antioxidant synthesis pathway is shifted to energy metabolism related to heat tolerance, whereas in OA group, energy is preferentially used for alkalinity regulation pathways rather than oxidative stress defense. Changes in microbial community structure mechanistically explain the trends in metabolite concentrations, as the proliferation of Vibrio spp. in the OW group drives lysine catabolism, leading to a significant increase in L-saccharopine levels. The reduction of Bacteroidetes in the OA group is correlated with the downregulation of L-homocystine, suggesting that pH-driven microbial interactions are disrupted. These findings demonstrate that gut microbiota reconfigure community structure and metabolic landscapes to buffer hosts against climate stress synergies, highlighting the importance of microbiome-mediated resilience in marine ecosystems under global climate change.

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Coupled acidification-nitrification dynamics in eutrophic estuarine waters

Published 20 October 2025 Science Closed
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Highlights

  • Mid-estuary emerges as a hotspot for coupled acidification-nitrification, intensified by hydrology.
  • Nitrifier community structure adapts to acidification stress, while responds differently.
  • AOB is more sensitive to acidification in estuarine water compared to AOA.
  • Future climate change scenarios project intensified acidification and nitrification coupling in mid-estuary.

Abstract

The interplay between acidification and nitrification in estuarine systems could have profound effects on coastal biogeochemistry and ecosystem health. However, the lack of integrated field research risks oversimplifying their relationships in complex ecosystem dynamics. This study investigates the spatiotemporal covariations of acidification sensitivity and nitrification rates derived from observed inorganic carbon and nutrients data along a land-sea continuum. In the middle estuary, estuarine pH exhibited the highest sensitivity to ammonium concentration, coinciding with maximum nitrification rates. The coupling effect intensified by 40% during the transition from dry to wet hydrological conditions. Despite that microbial network complexity generally decreased with increased acidification sensitivity, ammonia-oxidizing bacterial communities are more sensitive to acidification in estuarine water compared to ammonia-oxidizing archaea. Conversely, in the lower estuary, acidification was associated with a decline in nitrification activities. Machine learning-based models suggest that climate change scenarios could exacerbate acidification and nitrification in the Pearl River Estuary, potentially amplifying their coupling effect in the middle estuary. This holistic approach not only advances our fundamental understanding of estuarine processes, also provides critical insights for policymakers and coastal managers striving to maintain the ecological integrity of these vital ecosystems in an era of rapid global change.

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The bacterial community composition of American lobster (Homarus americanus) embryos and recently hatched larvae held under different temperature and acidification conditions

Published 16 October 2025 Science Closed
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Previous research investigating the microbial community of American lobster embryos has long led researchers to believe this habitat comprised only a select few bacterial taxa. However, using 16S rRNA gene sequencing, we show this community to be more diverse than previously thought. We investigated how the bacterial communities of American lobster embryos and larvae change over embryogenesis and hatching in response to two environmental variables. Ovigerous female lobsters caught from Maine and Massachusetts were held under varying temperature and pH regimes that approximated observed and predicted warming and ocean acidification conditions in the Gulf of Maine (GoM) and Southern New England (SNE). The bacterial microbiome associated with the lobster embryos was quantified from two-time points during the experiment, and larvae were collected within 12 hours of hatching. Alpha diversity increased with each life history stage, and embryo and larvae microbiomes shared little community overlap with that in the surrounding tank water. Neither environmental conditions nor lobster origin significantly altered bacterial communities, with life history stage driving alpha and beta diversity. Embryos and larvae shared three core bacterial members identified as members of the genera Rubritalea, Delftia, and Stenotrophomonas. American lobster embryos and larvae appear to have a highly selective microhabitat for bacteria that is not altered by environmental conditions. This leads us to wonder what role the microbiome may have on a developing lobster, and where the microbiome is originating if not from the surrounding seawater.

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Research progress on responses of upper-ocean nitrogen uptake and nitrification to ocean acidification and warming (in Chinese)

Published 10 October 2025 Science Closed
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Nitrogen uptake by phytoplankton and nitrification mediated by nitrifying microorganisms in the upper ocean are key processes affecting marine productivity and carbon sequestration. How these two critical nitrogen cycle processes respond to the dual stressors of ocean acidification and warming represents a pressing research frontier in marine biogeochemical cycles and global change. Elucidating this issue will provide a theoretical foundation for accurately assessing future changes in ocean productivity and the efficiency of the biological pump. However, most existing studies rely on laboratory pure culture experiments, which may fail to adequately reflect the complex interactions between phytoplankton and nitrifying microorganisms in natural marine ecosystems and their responses to changes in environmental factors. The impacts and mechanisms of ocean acidification and warming on nitrogen uptake and nitrification are systematically summarized. In addition, more attention needs to be paid to other factors, such as strengthened ocean stratification and decreased dissolved oxygen contents, induced by ocean acidification and warming, which could indirectly affect nitrogen uptake and nitrification. Existing problems, such as insufficient in-situ monitoring of ecosystems, limited synergistic studies on multiple processes and stresses, and inadequate understanding of long-term adaptation processes, are highlighted. Finally, three key areas of research that need to be focused on in the future were prospected: ① to conduct the synchronous coupling analysis of nitrogen uptake and nitrification processes and clarify the interactive effects of acidification and warming, ② to explore the vertical differentiation response mechanisms of the above processes in the upper ocean, particularly in oligotrophic oceans, where critical knowledge gaps exist, and ③ to elucidate the long-term adaptation processes and nonlinear response laws of phytoplankton and nitrifying microorganisms. A three-in-one research framework is constructed in the spatial dimension, temporal scale and the experimental system to provide a scientific basis for evaluating the evolution of key nitrogen processes and marine productivity under global change.

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Mapping the knowledge domain of ocean acidification impacts on marine microbial communities: visual exploration based on citespace

Published 29 September 2025 Science Closed
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Ocean acidification (OA) threatens marine microbial communities that underpin global biogeochemical cycles and marine food webs, however, a systematic synthesis of research progress in this area remains limited. This study presents the first comprehensive bibliometric analysis of ocean acidification impacts on microbial ecology, analyzing 495 Web of Science publications (2005-2025) using CiteSpace to characterize the field’s evolution and identify emerging frontiers. Global collaboration spans 53 countries, led primarily by China, the United States, and Germany, with the GEOMAR Helmholtz Centre for Ocean Research prominent within institutional networks. The research focus has shifted from basic chemical parameters to complex ecosystem processes, with “responses” identified as the most active contemporary research frontier. Overall, the field has matured into a highly internationalized, interdisciplinary domain. We outline four strategic directions for future work: (1) integrating advanceds molecular technologies, including multi-omics and single-cell approaches, to resolve mechanisms; (2) expanding temporal and spatial scales through global observatory networks; (3) quantifying multiple-stressor interactions, particularly with warming and deoxygenation; and (4) connecting molecular processes to biogeochemical cycles at the ecosystem level. These findings provide a data-driven roadmap for next-generation on OA–microbe interactions, essential for predicting marine ecosystem responses to accelerating environmental change and for informing evidence-based ocean conservation policy.

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Effects of ocean acidification on intestinal homeostasis and organismal performance in a marine bivalve: from microbial shifts to physiological suppression

Published 18 September 2025 Science Closed
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Highlights

  • OA stimulates the colonization of the pathogenic bacterium Mycoplasma.
  • Microbiota dysbiosis and oxidative damage trigger intestinal inflammation.
  • OA causes significant epithelial damage to the intestines of C. nobilis.
  • Physiological suppression of C. nobilis is decreased in a pH-dependent manner.

Abstract

Ocean acidification (OA) poses significant threats to marine calcifiers through multifaceted physiological disruptions. While bivalve mollusks are particularly vulnerable, the intestinal defense mechanisms against OA-induced stress remain poorly characterized. This study systematically investigated the intimate associations between the organismal physiological toxicity responses and intestinal homeostasis of Chlamys nobilis (C. nobilis) under simulated OA situations (pH 7.3–8.0) to reveal the potential physiological and biochemical damage. The results revealed that acidification stimulated pathogenic bacteria(Mycoplasma)colonization, disrupted microbiota homeostasis, and induced oxidative responses, thereby triggering intestinal inflammation and epithelial damage. Furthermore, the filtration rates and oxygen consumption rates of C. nobilis were significantly decreased in a pH-dependent manner across all the treatments, which might result from the intestinal dysfunction and the inhibition of acetylcholinesterase activities. These findings establish a link between OA-induced intestinal dysbiosis and organismal physiology, providing novel insights into the interplay between physiological performance and intestinal homeostasis under OA scenarios. The results advance our understanding of bivalve mollusk adaptation strategies and inform predictive models for its sustainability in acidifying marine ecosystems.

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The effects of ocean acidification on the epiphytic bacterial community of Sargassum thunbergii via high-throughput sequencing

Published 11 September 2025 Science Closed
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Marine macroalgae and their epiphytic bacteria have established a symbiotic relationship. Although the effects of ocean acidification (OA) on macroalgae have been extensively studied, its impact on these epiphytic bacteria remains unclear. This study investigated the OA-induced shifts in the epiphytic bacterial community of Sargassum thunbergii from Qingdao’s intertidal zone using 16S rDNA sequencing. The results indicated that elevated CO2 altered bacterial community structure and function, reducing diversity while maintaining dominant taxa but significantly changing their relative abundances. The abundances of Proteobacteria, Firmicutes, and Verrucomicrobiota declined, whereas Campylobacterota, Desulfobacterota, and Spirochaetota increased. The specific phyla like Cloacimonadota, Calditrichota and Entotheonellaeota also emerged. These shifts were linked to the environmental adaptability and stress resistance of epiphytic bacteria as well as the metabolic activities of the host algae, particularly in protein and fatty acid degradation.

Functional predictions revealed that OA primarily affected nitrogen and sulfur metabolism in the epiphytic bacterial community, with effects intensifying over time. Specifically, nitrogen fixation increased, while dark oxidation of sulfur compounds, dark sulfite oxidation, and dark sulfur oxidation decreased. In conclusion, ocean acidification directly induced changes in the abundance of epiphytic bacterial taxa with varying stress resistance and adaptability. Simultaneously, it promoted shifts in bacterial taxa closely associated with the host algal metabolic activities, ultimately reshaping the epiphytic bacterial community on S. thunbergii. These findings provided new insights into the macroalgae-epiphytic bacteria interactions under ocean acidification and provided important guidance for macroalgal cultivation.

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Interactive effects of ocean acidification and warming disrupt calcification and microbiome composition in bryozoans

Published 12 August 2025 Science Closed
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Marine habitat-forming species provide crucial ecosystem functions and services worldwide. Still, the individual and combined long-term effects of ocean acidification and warming on bryozoan populations, structures, and microbiomes remain unexplored. Here, we investigate the skeletal properties, microbiome shifts, and population trends of two bryozoan species living inside and outside a volcanic CO2 vent, a natural analog to future ocean acidification conditions. We show that bryozoans can acclimatize to acidification by adjusting skeletal properties and maintaining stable microbiomes. However, we document a decrease in microbial genera playing essential functions under acidified conditions. Moreover, we show that ocean acidification exacerbates bryozoan cover loss and mortality caused by ocean warming. The observed shifts in the microbiome and cover suggest that, despite their morphological plasticity, bryozoan species will be heavily impacted by future ocean conditions, posing a threat to many benthic ecosystems in which they play a pivotal role.

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Shifts in coral reef holobiont communities in the high-CO2 marine environment of Iōtorishima Island

Published 15 July 2025 Science Closed
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Ocean acidification (OA), driven by rising atmospheric CO2, presents a serious threat to marine biodiversity, especially within coral reef ecosystems. Natural analogue sites, such as the high-pCO2 seep at Iōtorishima Island in Japan, offer insights into future conditions. This study investigated the holobiont communities of Symbiodiniaceae and bacteria in the zoantharian Palythoa tuberculosa at Iōtorishima and compared them to specimens from control sites in Okinawa and Hawaiʻi. Using amplicon sequencing of the dinoflagellate internal transcribed spacer 2 (ITS2) region of ribosomal DNA and microbial 16S rRNA gene, we detected significant shifts in both Symbiodiniaceae and bacterial communities under high-pCO2 conditions at Iōtorishima. Specifically, P. tuberculosa at the seep site had reduced Symbiodiniaceae diversity, predominatly featuring Cladocopium C1 and C3 types. Additionally, its bacterial communities showed lower richness with distinct taxonomic profiles, including increased levels of Mollicutes and Vibrio spp. These results highlight the potentially adverse effects of OA on hexacoral holobionts and emphasize the need for detailed, high-resolution studies across various holobiont species and geographic locations. The shifts observed specifically in Symbiodiniaceae and bacterial communities at the Iōtorishima seep suggest that holobionts may exhibit plasticity in response to environmental stress, which has implications for resilience and adaptation of zoantharians and other reef organisms amid climate change. This research provides crucial baseline data for predicting future coral reef compositions in an OA-affected world.

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Positive interactions in a warmer and more acidic ocean: crustose coralline algae holobionts enhance gorgonian larval settlement under climate change

Published 21 May 2025 Science Closed
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Background: The increasing frequency of marine heatwaves is leading to mass mortality of gorgonians in the Mediterranean Sea, threatening some populations with local extinction. A better understanding of the dynamics of gorgonians’ early life stages under climate change is urgent to ensure their conservation. Crustose coralline algae (CCAs) and their associated bacteria are known to induce the larval settlement of several coral species through the production of chemical cues. The larvae of the white gorgonian Eunicella singularis have been observed to preferentially settle and metamorphose on CCAs. Here, we investigated this positive interaction, and explored how it might be altered by climate change. Specifically, we tested the capacity of two Mediterranean CCA holobionts, Macroblastum dendrospermum and Lithophyllum stictiforme, to foster E. singularis larval settlement after exposure to SSP5-8.5 projected conditions for 2100 (warming and acidification), combined or not with a simulated marine heatwave event.

Results: Our results showed a threefold increase of larval settlement in presence of the CCAs previously exposed to acidification and warming treatments. After these treatments, both CCAs hosted a consistently high abundance of bacteria belonging to the Pirellulaceae family, and exhibited a higher abundance of monosaccharides in their exudates. We hypothesize that the enhanced larval settlement was driven by the bacterial breakdown and utilization of CCA polysaccharides, in combination with their release through the CCA cell walls. This release may have been enhanced by a decalcification process induced by climate change conditions. Furthermore, we showed that CCAs act as sources of bacterial taxa that can establish and persist in adult E. singularis holobiont, independently of climate change effects.

Conclusions: Our results highlight that CCA-larvae interaction is critical for E. singularis recruitment success, especially under future climatic conditions, and influences the development of its microbiome. This research underscores the importance of studying positive interspecific interactions across biological levels (from microorganisms to macroorganisms) under climate change scenarios, and provides valuable insights that inform the conservation and restoration of the Mediterranean white gorgonian.

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Exploring the land-ocean biogeochemical and microbial connectivity in the Ría de Vigo (NW Iberian Peninsula) through submarine groundwater discharge

Published 20 May 2025 Science Closed
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Highlights

  • SGD affects the carbonate system, methane and nitrous oxide content of the embayment
  • Solute composition of SGD largely impacted by subterranean estuary reactivity
  • Contrasting poor microbial connectivity across the different aquatic environments
  • Subterranean estuaries may act as microbial boundaries in the aquatic continuum

Abstract

Increasing evidence demonstrates the widespread occurrence of submarine groundwater discharge (SGD) in coastal zones, where it may influence biogeochemistry and microbial ecology. Here, we analyze the biogeochemical composition and microbial communities across diverse aquatic environments in a highly productive coastal system (Ría de Vigo, NW Iberian Peninsula), influenced by significant fresh SGD, to assess the extent of microbial and biogeochemical connectivity—i.e., mass transfer—among them. Samples were collected from surface and deep porewaters from two subterranean estuaries (STEs), surface seawater, riverine water, and continental groundwater. These samples were analyzed for a comprehensive set of microbial and biogeochemical variables, including radioisotopes used as SGD tracers. A significant correlation between SGD tracers and carbonate system parameters, N2O, and CH4 concentrations in surface seawater indicates SGD influences biogeochemistry of the embayment. However, some of these solutes do not originate from continental groundwater but are produced in the local STEs, which act as biogeochemical reactors modifying fresh SGD. The findings also reveal highly diverse microbial communities, with higher diversity in STEs due to the variety of niches present. Indicator taxa included the phyla Euryarchaeota, Chloroflexi, Omnitrophicaeota, and the family Nitrosopumilaceae in STEs; the phylum Cyanobacteria and the family Burkholderiaceae in freshwater endmembers; and the Flavobacteriaceae and Cryomorphaceae families in seawater. Most operational taxonomic units (∼87%) were unique to a single environment (river, continental groundwater, coastal water, or STE), showing STEs limit subterranean microbial transfer between groundwater and marine ecosystems. Our results highlight STEs as reservoirs of diversity and zones of intense biogeochemical reactivity.

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Microzooplankton community dynamics under ocean acidification: key observations and insights

Published 30 April 2025 Science Closed
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Microzooplankton (MZP) community dynamics under ocean acidification were studied through pH manipulated microcosm experiments conducted in the coastal waters of the Bay of Bengal (off Vishakhapatnam) during the months of July and October 2022 (Experiment 1 and Experiment 2). The total abundance of phytoplankton and microzooplankton (MZP) communities was varied from 3.66 × 104 to 5.27 × 105 Cells. L−1 and 0.06 × 103 to 1.53 × 103 Cells. L−1, respectively, and a significant difference in phytoplankton and MZP abundance was found between the initial and final day of the entire experimental samples (control and acidified). The initial seawater samples were dominated with centric diatom species Dactyliosolen fragilissimus (Experiment 1 and Experiment 2: 72–82%) and shifted to pennate diatoms such as Pseudo-nitzschia sp. (Experiment 1: 60–68%) and Amphora sp. (Experiment 2: 80–94%) at the end of the experiments (all acidified and control samples). The initial MZP community composition consisted of four different groups LC: loricate ciliates, ALC: aloricate ciliates (heterotrophy and mixotrophy), HDS: heterotrophic dinoflagellates and copepod nauplii, and at the end of the experiments, it was shifted entirely to the dominance of aloricate ciliates (16–73%) and heterotrophic dinoflagellates (67–100%) in all the samples (control and acidified) in Experiments 1 and 2, respectively. Statistical analysis (Spearman’s rank correlation) results showed a relative and significant inverse relation of MZP with phytoplankton biomass and abundance and heterotrophic bacterial counts in all the samples (control and acidified). Besides, the LC showed a weak correlation with Chl-a, and the HDS showed a significant correlation with LC, phytoplankton biomass and abundance, and bacterial counts (picocyanobacteria and heterotrophic bacteria). These results indicate that the MZP may graze on both picocyanobacteria and heterotrophic bacteria, and also, HDS may graze on their relative community like LC. Canonical correlation analysis (CCA) revealed that prey abundance such as phytoplankton biomass (Chl-a), picocyanobacteria, and heterotrophic bacterial communities are most influencing variables on the MZP assemblages than other environmental variables such as pH, temperature, and salinity. Thus, these findings show that the MZP community dynamics under ocean acidification may vary with different species and groups due to their food availability (indirect effect) and individual competence (direct effect) to different environmental conditions, such as pH variations.

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Low-pH conditions drive transient changes in shell calcification and the microbiome in a pH-resistant strain of the the Pacific oyster Magallana gigas

Published 29 April 2025 Science Closed
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The study explores the effects of elevated pCO2 on shell calcification, microbiome composition, and gene expression in a strain of Pacific oyster (Magallana gigas) selectively bred for low-pH resistance. Juvenile oysters reared under low-pH conditions exhibited increased shell mass compared to the control population by 51 days post-fertilization, despite high variance in shell size at earlier stages. Microbiome analyses revealed significant shifts in community composition under low-pH conditions, particularly in bacterial taxa involved in CO2 production and biogeochemical cycling, which could influence carbonate chemistry within oyster tissues. Gene expression profiling demonstrates differential regulation of genes related to biomineralization, immunity, and microbial interactions under low-pH conditions. For example, multiple carbonic anhydrases exhibited treatment-specific expression patterns, suggesting a role in adapting to low-pH environments. Observed changes in immune-related genes imply a relaxation of immune responses, potentially reflecting resource reallocation toward calcification processes. These results collectively support the “dysbiosis hypothesis,” where oysters adapt to environmental stress by modulating their microbiomes and gene expression. Future studies should investigate whether these responses are consistent across oyster strains and environmental conditions, providing insights into the resilience of aquaculture species to ocean acidification.

Continue reading ‘Low-pH conditions drive transient changes in shell calcification and the microbiome in a pH-resistant strain of the the Pacific oyster Magallana gigas’

Effects of ocean acidification on intestinal homeostasis and organismal performance in a marine bivalve: from microbial shifts to physiological suppression

Published 25 April 2025 Science Closed
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Ocean acidification (OA) poses significant threats to marine calcifiers through multifaceted physiological disruptions. While bivalve mollusks are particularly vulnerable, the intestinal defense mechanisms against OA-induced stress remain poorly characterized. This study systematically investigated the intimate associations between the organismal physiological toxicity responses and intestinal homeostasis of Chlamys nobilis (C. nobilis) under simulated OA situations (pH 7.3-8.0) to reveal the potential physiological and biochemical damage. The results revealed that acidification stimulated pathogenic bacteria（Mycoplasma）colonization, disrupted microbiota homeostasis, and induced oxidative responses, thereby triggering intestinal inflammation and epithelial damage. Furthermore, the filtration rates and oxygen consumption rates of C. nobilis were significantly decreased in a pH-dependent manner across all the treatments, which might result from the intestinal dysfunction and the inhibition of acetylcholinesterase activities. These findings establish a link between OA-induced intestinal dysbiosis and organismal physiology, providing novel insights into the interplay between physiological performance and intestinal homeostasis under OA scenarios. The results advance our understanding of bivalve mollusk adaptation strategies and inform predictive models for its sustainability in acidifying marine ecosystems.

Continue reading ‘Effects of ocean acidification on intestinal homeostasis and organismal performance in a marine bivalve: from microbial shifts to physiological suppression’

Ocean acidification disrupts the energy balance and impairs the health of mussels (Mytilus coruscus) by weakening their trophic interactions with microalgae and intestinal microbiome

Published 4 April 2025 Science Closed
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Highlights

  • Ocean acidification disrupts mussel energy balance by weakening trophic interactions.
  • Mussels exposed to acidified conditions show reduced energy gain from microalgae.
  • Energy imbalance caused by acidification impairs mussel health and fitness.
  • Ocean acidification can threaten mussel farming and marine ecosystem stability.

Abstract

Despite extensive research in the last two decades, exploring the potential mechanisms underlying the sensitivity and resistance of marine organisms to ocean acidification is still imperative. Species interactions can play a role in these mechanisms, but the extent to which they modulate organismal responses to ocean acidification remains largely unknown. Here, we investigated how ocean acidification (pH 7.7) affects energy homeostasis and fitness of mussels (Mytilus coruscus) by assessing their physiological responses, intestinal microbiome and nutritional quality of their food (microalgae). Under ocean acidification, the mussels had reduced feeding rates by 34 % and reduced activities of digestive enzymes (pepsin by 39 %, trypsin by 28 % and lipase by 53 %) due to direct exposure to acidified seawater and increased phenol content of microalgae. Richness and diversity of intestinal microbiome (OTU, Chao1 index and Shannon index) were also lowered by ocean acidification, which can undermine nutrient absorption. On the other hand, energy expenditure of mussels increased by 53 % under ocean acidification, which was associated with the upregulation of antioxidant defence (SOD, CAT and GPx activities). Consequently, energy reserves in mussels decreased by 28 %, which were underpinned by the reduction in protein, carbohydrate and lipid contents. Overall, we demonstrate that ocean acidification could disrupt herbivore-algae and host-microbe interactions, thereby lowering the energy balance and impairing the health of marine organisms. This can have ramifications on the population and energy dynamics of marine communities in the acidifying ocean.

Continue reading ‘Ocean acidification disrupts the energy balance and impairs the health of mussels (Mytilus coruscus) by weakening their trophic interactions with microalgae and intestinal microbiome’

Impact of simulated pH conditions on phenotypic expression in shrimp pathogenic and non-pathogenic Vibrio campbellii strains

Published 13 March 2025 Science Closed
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Environmental pH fluctuation in oceanic and marine ecosystems can significantly impact the distribution and behavior of pathogenic Vibrio species, including their interactions with marine invertebrates such as crustaceans. This study focused on Vibrio campbellii, a common shrimp pathogen, and its phenotypic responses to varying pH conditions. Both pathogenic strain HY01 and non-pathogenic strain ATCC BAA-1116 were cultured in 30 pL/L Luria-Bertani Sea Salt under 3 pH conditions, including pH 6 (slightly acidic), pH 8 (representing the oceanic pH), and pH 9 (alkaline). Growth patterns and phenotypic traits were evaluated. Results revealed no significant growth difference between the 2 strains under the different pH conditions, although the non-pathogenic strain showed a slight growth reduction at pH 9 during the exponential phase. Both strains were able to buffer environmental pH shifts, adjusting to near-oceanic pH levels (around pH 8). At pH 9, a stressor level for V. campbellii, delays were observed in bioluminescence, biofilm formation, exopolysaccharide production, shrimp surface colonization, motility, and caseinase production, affecting both strains. In contrast, mildly acidic conditions (pH 6) induced the highest expression of several phenotype traits. Statistical analyses indicated significant interactions between strain type and pH levels in influencing phenotypic expression. In conclusion, the pathogenic V. campbellii strain HY01 exhibited greater adaptability and virulence across various pH conditions compared to the non-pathogenic ATCC BAA-1116, emphasizing pH as a critical environmental factor in shaping the growth and pathogenic potential of V. campbellii. Our studies provide valuable insights into managing pH conditions in aquaculture environments to optimize proper shrimp cultivation and prevent cross-contamination of V. campbellii from seawater habitats to farms. These findings provide a physiological profile of Vibrio under pH stress, which can support the development of predictive outbreak models to assess the risk of luminous vibriosis, especially in to seasonal changes and ocean acidification.

Continue reading ‘Impact of simulated pH conditions on phenotypic expression in shrimp pathogenic and non-pathogenic Vibrio campbellii strains’

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