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.
Continue reading ‘Shifts in coral reef holobiont communities in the high-CO2 marine environment of Iōtorishima Island’Posts Tagged 'prokaryotes'
Shifts in coral reef holobiont communities in the high-CO2 marine environment of Iōtorishima Island
Published 15 July 2025 Science ClosedTags: adaptation, biological response, BRcommunity, community composition, corals, field, molecular biology, North Pacific, otherprocess, phytoplankton, prokaryotes, vents
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 ClosedTags: algae, biological response, BRcommunity, corals, laboratory, Mediterranean, molecular biology, multiple factors, physiology, prokaryotes, reproduction, temperature
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.
Continue reading ‘Positive interactions in a warmer and more acidic ocean: crustose coralline algae holobionts enhance gorgonian larval settlement under climate change’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 ClosedTags: biogeochemistry, BRcommunity, chemistry, community composition, field, molecular biology, North Atlantic, otherprocess, prokaryotes
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.
Continue reading ‘Exploring the land-ocean biogeochemical and microbial connectivity in the Ría de Vigo (NW Iberian Peninsula) through submarine groundwater discharge’Microzooplankton community dynamics under ocean acidification: key observations and insights
Published 30 April 2025 Science ClosedTags: abundance, biological response, BRcommunity, community composition, Indian, laboratory, otherprocess, phytoplankton, prokaryotes, zooplankton
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.
Continue reading ‘Microzooplankton community dynamics under ocean acidification: key observations and insights’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 ClosedTags: biological response, BRcommunity, community composition, laboratory, molecular biology, mollusks, morphology, North Pacific, otherprocess, prokaryotes
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 ClosedTags: biological response, BRcommunity, community composition, laboratory, mollusks, North Pacific, otherprocess, performance, physiology, prokaryotes, respiration
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 ClosedTags: biological response, BRcommunity, community composition, laboratory, mollusks, North Pacific, otherprocess, performance, physiology, phytoplankton, prokaryotes
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 ClosedTags: adaptation, biological response, growth, laboratory, otherprocess, performance, physiology, prokaryotes
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’The nasal microbiota of two marine fish species: diversity, community structure, variability and first insights into the impacts of climate change-related stressors
Published 25 February 2025 Science ClosedTags: biological response, BRcommunity, community composition, fish, laboratory, molecular biology, multiple factors, otherprocess, prokaryotes, temperature
Vertebrate nasal microbiota (NM) plays a key role regulating host olfaction, immunity, neuronal differentiation, and structuring the epithelium. However, little is known in fish. This study provides the first comprehensive analysis of the NM in two marine fish species, the European seabass and the Atlantic cod. Given its direct environmental exposure, fish NM is likely influenced by seawater fluctuations. We analysed the community structure, specificity regarding seawater, and interindividual variability of 32 to 38 fish reared under ambient conditions. Additionally, we conducted an experiment to investigate the influence of acidification and a simplified heatwave on cod NM (3 fish per replicate). High-throughput 16S rRNA sequencing revealed species-specific NM communities at the genus-level with Stenotrophomonas and Ralstonia dominating seabass and cod NM, respectively. This suggests potential habitat- or physiology-related adaptations. The most abundant bacterial genera in seabass NM were also present in seawater, suggesting environmental acquisition. Alpha diversity was highest in Brest seabass NM and variability greatest in Tromsø cod NM. Simulated climate change-related scenarios did not significantly alter cod NM structure. We propose a minimum of 13 cod rosettes per replicate for future studies. This research establishes a foundation for understanding marine fish NM and its response to environmental changes.
Continue reading ‘The nasal microbiota of two marine fish species: diversity, community structure, variability and first insights into the impacts of climate change-related stressors’Short-term negative effects of seawater acidification on the rhodolith holobionts metatranscriptome
Published 7 February 2025 Science ClosedTags: algae, biological response, BRcommunity, community composition, laboratory, molecular biology, otherprocess, prokaryotes, South Atlantic
Highlights
- Cyanobacteria dominate the microbial community in living rhodoliths.
- Vibrionales dominate dead rhodolith skeletons.
- Short-term (1 h) acidification affects the microbial community structure.
- Diverse functional genes modulate microbe-host interactions.
Abstract
Rhodolith holobionts are formed by calcareous coralline algae (e.g., Corallinales) and associated microbiomes. The largest rhodolith bank in the South Atlantic is located in the Abrolhos Bank, in southwestern Brazil, covering an area of 22,000 km2. Rhodoliths serve as nurseries for marine life. However, ocean acidification threatens them with extinction. The acute effects of high pCO₂ levels on rhodolith metatranscriptomes remain unknown. This study investigates the transcriptomic profiles of rhodoliths exposed to short-term (96-h) high pCO₂ levels (up to 1638 ppm). Metatranscriptomes were generated for both dead and alive rhodoliths (15.48 million Illumina reads in total). Alive rhodoliths showed an enrichment of gene transcripts related to environmental stress responses and photosynthesis (Cyanobacteria). In contrast, the metatranscriptomes of dead rhodoliths were dominated by heterotrophic (Proteobacteria and Bacteroidetes) metabolism and virulence factors. The rhodolith holobiont metatranscriptomes respond rapidly to short-term acidification (within 1 h), suggesting that these holobionts may have some capacity to cope with acute acidification effects. However, the negative impacts of prolonged ocean acidification on rhodolith health cannot be overlooked. Rhodoliths exposed to low pH (7.5) for 96 h exhibited a completely altered transcriptomic profile compared to controls. This study highlights the plasticity of rhodolith transcriptomes in the face of ocean acidification and climate change.
Continue reading ‘Short-term negative effects of seawater acidification on the rhodolith holobionts metatranscriptome’Iron and phosphorus limitations modulate the effects of carbon dioxide enrichment on a unicellular nitrogen-fixing cyanobacterium
Published 21 January 2025 Science ClosedTags: biological response, growth, laboratory, multiple factors, nitrogen fixation, nutrients, physiology, prokaryotes
Iron (Fe) and phosphorus (P) availability constrain the growth and N2 fixation of diazotrophic cyanobacteria in the global ocean. However, how Fe and P limitation may modulate the effects of ocean acidification on the unicellular diazotrophic cyanobacterium Crocosphaera remains largely unknown. Here, we examined the physiological responses of Crocosphaera watsonii WH8501 to CO2 enrichment under both nutrient-replete and steadily Fe- or P-limited conditions. Increased CO2 (750 μatm vs. 400 μatm) reduced the growth and N2 fixation rates of Crocosphaera, with Fe limitation intensifying the negative effect, whereas CO2 enrichment had a minimal impact under P limitation. Mechanistically, the high CO2 treatment may have led to a reallocation of limited Fe to nitrogenase synthesis to compensate for the reduction in nitrogenase efficiency caused by low pH; consequently, other Fe-requiring metabolic pathways, such as respiration and photosynthesis, were impaired, which in turn amplified the negative effects of acidification. Conversely, under P limitation, CO2 enrichment had little or no effect on cellular P allocation among major P-containing molecules (polyphosphate, phospholipids, DNA, and RNA). Cell volumes were significantly reduced in P-limited and high CO2 cultures, which increased the surface : volume ratio and could facilitate nutrient uptake, thereby alleviating some of the negative effect of acidification on N2 fixation. These findings highlight the distinct responses of Crocosphaera to high CO2 under different nutrient conditions, improving a predictive understanding of global N2 fixation in future acidified oceans.
Continue reading ‘Iron and phosphorus limitations modulate the effects of carbon dioxide enrichment on a unicellular nitrogen-fixing cyanobacterium’The response mechanisms of kelp Macrocystis pyrifera holobiont to elevated temperature and CO2 concentration
Published 17 January 2025 Science ClosedTags: algae, biological response, BRcommunity, community composition, laboratory, multiple factors, otherprocess, physiology, prokaryotes, temperature
The kelp Macrocystis pyrifera, a crucial component of marine ecosystems, is significantly impacted by climate change and environmental stresses. Macrocystis pyrifera and its associated bacteria form a holistic functional unit (holobiont), yet the regulatory roles of bacteria in stress responses and acclimation are often overlooked. This study investigates the diversity of M. pyrifera associated bacteria and their chemical interactions under high temperature and elevated CO2 conditions. Our findings indicate that high temperatures significantly reduce associated bacterial diversity, while elevated CO2 does not alter community structure. Key microbial biomarkers identified include Pseudomonas, Sulfitobacter, and Olleya. However, it is unknown how they function in M. pyrifera. In metabolite analysis, we identified 18 metabolites with significant differences. These metabolites included phospholipids, antibacterial compounds, signaling molecules, and various compounds of unclear function. The changes in these compounds are probably connected to how M. pyrifera respond to climate change. These results will enrich the baseline data related to the chemical interactions between the microbiota and M. pyrifera and provide clues for predicting the resilience of M. pyrifera to future climate change.
Continue reading ‘The response mechanisms of kelp Macrocystis pyrifera holobiont to elevated temperature and CO2 concentration’The impact of climate change stressors on microbial respiration and community structure: ocean acidification and artificial upwellling
Published 14 January 2025 Science ClosedTags: biological response, BRcommunity, community composition, field, mesocosms, multiple factors, North Atlantic, nutrients, otherprocess, physiology, phytoplankton, prokaryotes, respiration
Microbial community respiration significantly influences the oceans capacity to sequester CO2 in marine ecosystems. Despite its pivotal role, there remains limited understanding of the variability and magnitude of community respiration in marine ecosystems, especially regarding its sensitivity to climate change stressors. This knowledge gap hinders a comprehensive grasp of its contribution to the global carbon cycle. Traditional in situ approaches for measuring community respiration are subject to several methodological limitations, particularly that of sensitivity in oligotrophic ecosystems, which cover more than 40% of the Earth’s ocean surface. These limitations thus contribute significantly to the uncertainty in global estimates of carbon budgets. To address these challenges, enzymatic techniques such as ETSvitro offer a fast and sensitive method to assess respiratory activity rates at spatial scales that are difficult to cover using conventional approaches. The method involves reducing the tetrazolium salt, INT, within the respiratory chain under substrate saturation levels (i.e., NADH, NADPH, and succinate). However, the reliability of the ETSvitro method has been questioned because it measures potential respiratory activity rather than actual respiration. In response to these concerns, another enzymatic technique, ETSvivo, emerged presumably as a more realistic estimate of actual respiration. Unlike ETSvitro, ETSvivo measures INT under in vivo conditions, utilizing substrates naturally available inside the cell. Nevertheless, before these methods can be considered feasible proxies for community respiration, further evaluation is needed to determine their universal applicability in marine ecosystems. In this thesis, our objective was to improve our understanding of community respiration by addressing its methodological limitations and investigating the drivers responsible for its variability. We paid particular attention to planktonic community structure and the impact of two climate change stressors: ocean acidification and changes in nutrient fertilization. Simulating a typical ETSvivo assay in eight independent experiments using surface coastal and open ocean waters from the Canary region, we observed that INT alone significantly influences the physiological status of bacteria. Bacteria are considered the primary contributors to respiration in oligotrophic environments, but their physiological status is largely affected by the inherent toxicity of INT. Consequently, we question the applicability of the ETSvivo method as a proxy for community respiration in oligotrophic regions. On the other hand, we explore the temporal variability of respiratory metabolism through two mesocosm experiments conducted in the oligotrophic waters of the subtropical Eastern North Atlantic. In the first mesocosms experiment, we investigated the impact of changing community structure and biomass on the temporal variability of community respiration measured through the Winkler method (R), ETS activity, and their ratio (R/ETS) in response to increasing CO2 concentrations and nutrient fertilization (e.g., due to local upwelling events). Our results suggest that community respiration and ETS activity do not respond to CO2 during oligotrophic conditions. However, following fertilization, community respiration increased in the two high CO2 mesocosms coinciding with an increase in microplankton, primarily diatoms. Simultaneously, the R/ETS ratio showed no correlation with community structure or biomass, indicating its variability makes it unsuitable for application with communities undergoing abrupt changes in trophic conditions. In light of these findings, the second mesocosm experiment explored the influence of different upwelling intensities and frequencies (singular pulse versus recurring upwelling) on community respiration. Our results demonstrate that community respiration is sensitive to changes in upwelling intensities but more significantly to the mode in which nutrients are supplied to oligotrophic waters. The planktonic community structure significantly influenced the observed variability in community respiration, revealing notable differences under varying upwelling intensities.The results of this thesis underscore the significance of mitigating methodological uncertainties to achieve precise measurements of respiration rates. It is crucial to adequately assess the impact of climate change-induced stressors, especially ocean acidification and changes in nutrient fertilization, along with planktonic community structure, as drivers of temporal variability. This thorough examination is essential for gaining a deeper understanding and, consequently, making more accurate predictions of community respiration in marine ecosystems.
Extreme abiotics drive sediment biocomplexity along pH gradients in a shallow submarine volcanic vent
Published 3 January 2025 Science ClosedTags: biogeochemistry, biological response, BRcommunity, community composition, field, Mediterranean, otherprocess, phanerogams, prokaryotes, sediment, vents
Highlights
- Shallow CO2 vents generate pH gradients that influence sediment biogeochemistry
- Sedimentary organic matter (SOM) and prokaryotic community were analysed along a pH gradient
- Environmental gradients drive distribution and abundance of benthic prokaryotic communities and origin of SOM
- Vent-derived sources contributed largely to SOM up to 350 m from the vent
- CO2-driven benthic community shifts affect spatial dynamics of SOM origin and composition with expected rebounds on biota
Abstract
Volcanic emissions in shallow vents influence the biogeochemistry of the sedimentary compartment, creating marked abiotic gradients. We assessed the spatial dynamics of the sediment compartment, as for the composition and origin of organic matter and associated prokaryotic community, in a volcanic shallow CO2 vent (Vulcano Island, Italy). Based on elemental (carbon, nitrogen content and their ratio) and isotopic composition (δ13C, δ15N and δ34S), the contribution of vent-derived organic matter (microbial mats) to sedimentary organic matter was high close to the vent, while the marine-derived end-members (seagrasses) contributed highly at increasing distance. Chemoautotrophic Campylobacterota and hyperthermophilic Achaea prevailed close to the vent, whilst phototrophic and chemoheterotrophic members dominated at increasing distance. Abiotic gradients generated by the volcanic CO2 vent drive relevant changes in the composition, origin and nutritional quality of sedimentary organic matter, and influence the structure and complexity of associated prokaryotic communities, with expected relevant impact on the entire food-web.
Continue reading ‘Extreme abiotics drive sediment biocomplexity along pH gradients in a shallow submarine volcanic vent’Resource homogenisation drives niche convergence between generalists and specialists in a future ocean
Published 13 December 2024 Science ClosedTags: algae, biological response, community composition, laboratory, mesocosms, multiple factors, otherprocess, prokaryotes, temperature
Highlights
- Do marine herbivores adjust their trophic niches under climate change?.
- Specialist and generalist herbivore niches and their food were tested using stable isotopes.
- Food resources were dominated by turf algae and SOM under climate change.
- Niche breath of generalists narrowed under climate stress but widened in specialists.
- Generalists and specialists appear to converge their trophic niches under climate change.
Abstract
When humans drive rapid environmental change, is it favourable to be a generalist or specialist? To address this question, we compare how specialist and generalist marine herbivores adjust their isotopic niches (used as proxy for trophic niche) in response to predicted resource alterations under the simulated effects of ocean warming and acidification (based on a 6-month mesocosm experiment). Here, we show that when exposed to multiple climate stressors, food resources homogenized towards dominance of turf algae and suspended organic matter, with generalists and specialists adjusting their trophic niches in opposing ways. Whilst the niche breath of most generalists narrowed under climate stressors, those of specialists generally broadened, causing increasing overlap between their niches. The magnitude of this change was such that some generalists turned into specialists, and vice versa. Under ocean acidification, there was a greater probability of generalists increasing and specialists maintaining their biomass, respectively, but under warming the biomass of both specialists and generalists had a greater probability of collapse. For specialists, this collapse occurred even though they had adequate thermal tolerance and the capacity to expand their trophic niche. Climate change constrains or liberates resources, but where they are homogenized, generalists and specialists are likely to converge their trophic niches so they can exploit transforming environments for their survival or adaptive advantage.
Continue reading ‘Resource homogenisation drives niche convergence between generalists and specialists in a future ocean’The important role of the antioxidant stress capacity in the response of Prochlorococcus to increased CO2 under varying iron and light conditions
Published 9 December 2024 Science ClosedTags: biological response, growth, light, multiple factors, nutrients, physiology, prokaryotes
Highlights
- Low-light-adapted Prochlorococcus ecotypes have stronger low-iron adaptation capacity
- Fe limitation in Prochlorococcus is enhanced under both low growth-limiting light and high photo-inhibitory light
- High CO2 promotes the growth of low-light-adapted Prochlorococcus ecotypes due to a reduction in cellular oxidation stress
Abstract
Ocean acidification caused by the ongoing increase in atmospheric carbon dioxide (CO2) is expected to impact the growth of marine phytoplankton. Additionally, CO2-driven climate change influences light intensity and iron (Fe) availability in surface seawaters, two critical factors for marine phytoplankton carbon fixation and growth due to their central role in regulating photosynthesis. The cyanobacterium Prochlorococcus often dominates marine productivity in oligotrophic oceans with low but variable Fe concentrations and light intensities. However, the combined effects of light intensity, Fe availability and CO2 concentration on the growth and photosynthesis of Prochlorococcus remain unclear. In this study, we found that the high-light-adapted Prochlorococcus strain MED4, isolated from shallower depths, required much higher Fe concentrations and light intensities to grow than the low-light-adapted strain NATL1A, isolated from deeper depths. Increased CO2 had no effect on the growth of strain MED4 under any light or Fe conditions. In contrast, increased CO2 caused a 29% increase in the growth of strain NATL1A under low Fe coupled with high photo-inhibitory light condition, owing to a reduction in cellular oxidative stress. The varying antioxidant stress capacities of different Prochlorococcus strains appeared to influence their responses to increased CO2. These results indicate complex interactions among light intensity, Fe limitation, and CO2 concentration, which may affect the species distributions and productivities of marine phytoplankton, including Prochlorococcus, in a future high-CO2 ocean.
Continue reading ‘The important role of the antioxidant stress capacity in the response of Prochlorococcus to increased CO2 under varying iron and light conditions’Seawater warming rather than acidification profoundly affects coastal geochemical cycling mediated by marine microbiome
Published 28 November 2024 Science ClosedTags: BRcommunity, community composition, laboratory, mesocosms, molecular biology, multiple factors, otherprocess, prokaryotes, sediment, temperature
Highlights
- The structure and function of coastal microbial communities are influenced by ocean warming and acidification.
- Elevated temperature more profoundly impacts microbial communities than does acidification.
- Warming promotes denitrification that may increase nitrogen loss.
- The nitrogen, sulfur cycles, and carbon-fixation pathways exhibit distinct variation patterns under warming.
Abstract
The most concerning consequences of climate change include ocean acidification and warming, which can affect microbial communities and thus the biogeochemical cycling they mediate. Therefore, it is urgent to study the impact of ocean acidification and warming on microbial communities. In the current study, metagenomics was utilized to reveal how the structure and function of marine microorganisms respond to ocean warming and acidification. In terms of community structure, Non-metric Multidimensional Scaling analysis visualized the similarity or difference between the control and the warming or acidification treatments, but the inter-group differences were not significant. In terms of gene functionality, warming treatments showed greater effects on microbial communities than acidification. After treatment with warming, the relative abundance of genes associated with denitrification increased, suggesting that ocean nitrogen loss can increase with increased temperature. Conversely, acidification treatments apparently inhibited denitrification. Warming treatment also greatly affected sulfur-related microorganisms, increasing the relative abundance of certain sulfate-reducing prokaryote, and enriched microbial carbon-fixation pathways. These results provide information on the response strategies of coastal microorganisms in the changing marine environments.
Continue reading ‘Seawater warming rather than acidification profoundly affects coastal geochemical cycling mediated by marine microbiome’Chemical interactions between kelp Macrocystis pyrifera and symbiotic bacteria under elevated CO2 condition
Published 26 November 2024 Science ClosedTags: algae, biological response, community composition, molecular biology, otherprocess, physiology, prokaryotes, protists, reproduction
Kelps are pivotal to temperate coastal ecosystems, providing essential habitat and nutrients for diverse marine life, and significantly enhancing local biodiversity. The impacts of elevated CO2 levels on kelps may induce far-reaching effects throughout the marine food web, with potential consequences for biodiversity and ecosystem functions. This study considers the kelp Macrocystis pyrifera and its symbiotic microorganisms as a holistic functional unit (holobiont) to examine their collective response to heightened CO2 levels. Over a 4 month cultivation from the fertilization of M. pyrifera gametes to the development of juvenile sporophytes, our findings reveal that elevated CO2 levels influence the structure of the M. pyrifera symbiotic microbiome, alter metabolic profiles, and reshape microbe-metabolite interactions using 16S rRNA amplicon sequencing and liquid chromatography coupled to mass spectrometry analysis. Notably, Dinoroseobacter, Sulfitobacter, Methylotenera, Hyphomonas, Milano-WF1B-44 and Methylophaga were selected as microbiome biomarkers, which showed significant increases in comparative abundance with elevated CO2 levels. Stress-response molecules including fatty-acid metabolites, oxylipins, and hormone-like compounds such as methyl jasmonate and prostaglandin F2a emerged as critical metabolomic indicators. We propose that elevated CO2 puts certain stress on the M. pyrifera holobiont, prompting the release of these stress-response molecules. Moreover, these molecules may aid the kelp’s adaptation by modulating the microbial community structure, particularly influencing potential pathogenic bacteria, to cope with environmental change. These results will enrich the baseline data related to the chemical interactions between the microbiota and M. pyrifera and provide clues for predicting the resilience of kelps to future climate change.
Continue reading ‘Chemical interactions between kelp Macrocystis pyrifera and symbiotic bacteria under elevated CO2 condition’Effects of CO2 on the nitrogen isotopic composition of marine diazotrophic cyanobacteria
Published 13 November 2024 Science ClosedTags: biological response, BRcommunity, growth, laboratory, photosynthesis, physiology, phytoplankton, prokaryotes
Biological N2 fixation has been crucial for sustaining early life on Earth. Very negative δ15N values detected in Archean sediments, which are not observed in present-day environments, have been attributed to the low efficiency of proto-nitrogenases. Alternatively, variations in early atmospheric CO2 may also play a role. Here we examine the effects of CO2 concentrations on the biomass δ15N signatures of the diazotrophs Trichodesmium erythraeum and Crocosphaera watsonii, which utilize Mo-Fe nitrogenase (the most common form of the enzyme). Our results show that these organisms produce biomass with δ15N values up to ∼3‰ lower under both decreased and elevated CO2 concentrations compared to modern levels (∼380 μatm). These deviations from modern CO2 levels reduce nitrogenase enzyme efficiency, leading to increased organismal isotopic fractionation during N2 fixation. This study offers an alternative explanation for the observed fluctuations in geological δ15N records and provides new insights into the past nitrogen cycle on Earth.
Key Points
- The effects of CO2 on the biomass δ15N signatures of the diazotrophs Trichodesmium erythraeum and Crocosphaera watsonii are examined
- Both species produce biomass with δ15N values lower under both decreased and elevated CO2 concentrations compared to modern CO2 levels
- CO2-controlled nitrogenase efficiency significantly influences organismal isotopic fractionation during N2 fixation
Plain Language Summary
The isotope effect of biological N2 fixation is crucial for understanding the nitrogen cycle, but its regulation under different atmospheric CO2 levels as appeared in Earth’s history is not well understood. Our research shows that CO2 levels significantly influence the nitrogen isotope composition in the biomass of the diazotrophic cyanobacteria Trichodesmium and Crocosphaera by affecting the nitrogenase efficiency and thus the growth rate. This study sheds light on the geological changes in the δ15N records and provides new insights into the historical nitrogen cycle on Earth.
Continue reading ‘Effects of CO2 on the nitrogen isotopic composition of marine diazotrophic cyanobacteria’Combined effects of low pH stress and bacterial infection on the transcriptional changes of hemocytes in Chinese mitten crab Eriocheir sinensis
Published 6 November 2024 Science ClosedTags: biological response, BRcommunity, crustaceans, laboratory, performance, physiology, prokaryotes
Highlights
- Low pH stress might disturb the maintaining of protein homeostasis in hemocytes.
- Combination of low pH stress and bacterial infection cause disruption of TLR pathway.
- Low pH stress and bacterial infection inhibit the TCA cycle in hemocytes.
Abstract
Water pH is a critical environmental factor for aquaculture. Acidification is a pressing environmental issue that poses significant threats to the aquaculture industry. Since the outbreaks of disease generally accompany with environmental stress, comparative transcriptome analyses were performed to investigate the combined effects of low pH stress and bacterial infection on the transcriptional changes of hemocytes in the economically important crab Eriocheir sinensis. The results revealed that the immune deficiency (IMD) pathway and prophenoloxidase (proPO) system was activated to defense against Vibro parahaemolyticus even when crabs were subjected to low pH stress, whereas low pH stress resulted in the disorder of Toll-like receptor (TLR) pathway upon V. parahaemolyticus infection. Moreover, low pH stress might weaken crabs′ defense against V. parahaemolyticus by inhibiting the up-regulation of crustin and suppressing the expression of lysozyme, and disturb the maintaining of protein homeostasis through the transcriptional decrement of a batch of heat shock proteins (HSPs). It is worth noting that both V. parahaemolyticus infection and low pH stress might suppress the energy metabolism in the hemocytes via inhibiting the expression of critical enzymes, dihydrolipoyllysine-residue acetyltransferase component of pyruvate dehydrogenase complex and fumarase, in the tricarboxylic acid (TCA) cycle. This study provides novel understandings concerning the transcriptional changes of hemocyte in E. sinensis subjected to a combination of low pH stress and V. parahaemolyticus infection as well as contribute to optimize the management strategies for the prevention and control of diseases in E. sinensis farming.
Continue reading ‘Combined effects of low pH stress and bacterial infection on the transcriptional changes of hemocytes in Chinese mitten crab Eriocheir sinensis’
