Climate change is rapidly altering aquatic ecosystems through rising temperatures, ocean acidification, hypoxia, ultraviolet radiation, salinity fluctuations, and interacting environmental stressors. These changes impose substantial physiological challenges on aquatic organisms, with oxidative stress representing an important mechanistic pathway linking environmental disturbances to biological responses across multiple levels of organization. This review synthesizes current evidence on oxidative stress responses associated with climate change-related environmental stressors across aquatic taxa, including fish, aquatic invertebrates, corals, phytoplankton, macroalgae, amphibians, and polar and deep-sea organisms. We examine the mechanisms underlying reactive oxygen species production, disruption of antioxidant defenses, and oxidative damage, while critically evaluating biochemical, molecular, and omics-based biomarkers for environmental stress assessment. Particular emphasis is placed on how oxidative stress may translate from cellular and organismal responses into changes in growth, reproduction, behavior, survival, species distributions, population dynamics, community structure, biodiversity, and ecosystem resilience. We also highlight limitations of current biomarker approaches, including species-specific variability, methodological inconsistencies, and difficulties in extrapolating laboratory findings to natural ecosystems. Future research should prioritize integrated multi-biomarker and multi-stressor approaches, long-term ecological monitoring, standardized protocols, and the integration of omics, environmental DNA, remote sensing, and artificial intelligence. Overall, oxidative stress biomarkers provide complementary tools for assessing climate-change impacts on aquatic biodiversity and ecosystem resilience.
Continue reading ‘Oxidative stress as a potential mechanistic link between climate change and aquatic biodiversity loss’Posts Tagged 'photosynthesis'
Oxidative stress as a potential mechanistic link between climate change and aquatic biodiversity loss
Published 4 November 2026 Science Leave a CommentTags: abundance, adaptation, algae, biological response, calcification, community composition, corals, echinoderms, fish, light, mollusks, mortality, multiple factors, nutrients, otherprocess, oxygen, performance, photosynthesis, physiology, phytoplankton, plastics, protists, reproduction, review, temperature, zooplankton
Kinetics of dissolved inorganic carbon acquisition by red seaweeds (Rhodophyta) with and without carbon-dioxide concentrating mechanisms
Published 4 November 2026 Science Leave a CommentTags: algae, biological response, laboratory, photosynthesis, physiology, South Pacific
Seaweed responses to ocean acidification (OA) may depend on whether they possess a carbon dioxide (CO2) concentrating mechanism (CCM). Using photosynthesis versus dissolved inorganic carbon (DIC) experiments, we determined the photosynthetic affinity (K0.5(CO2)) for CO2 for the red algae Pollexfenia lobata (CCM), and Callophyllis rangiferina, Delisea pulchra and Plocamium cirrhosum (non-CCM). K0.5(CO2) was statistically similar for CCM and non-CCM species, but P. lobata had values lower than those published for isolated red algal Rubiscos. Maximum photosynthetic rates (Pmax) were 2.5 times higher for Pl. cirrhosum and D. pulchra. Non-CCM species may benefit from future OA because photosynthesis would be less limited by DIC.
Continue reading ‘Kinetics of dissolved inorganic carbon acquisition by red seaweeds (Rhodophyta) with and without carbon-dioxide concentrating mechanisms’Community metabolism generates chemical legacies that alter coral physiology
Published 3 November 2026 Science Leave a CommentTags: biogeochemistry, biological response, communityMF, corals, field, mesocosms, multiple factors, photosynthesis, physiology, primary production, respiration, South Pacific
Coral reefs are among the world’s most diverse ecosystems and contribute substantially to ocean productivity and the carbon budget. Disturbances are shifting reefs to altered community states, yet how these new communities indirectly alter organismal physiology by modifying the local biogeochemical environment remains largely unknown. We investigated this biogeochemical feedback in a 25-d mesocosm experiment in Mo’orea, French Polynesia. We exposed the common coral Porites rus to the biogeochemical environments generated by three distinct communities representative of recent benthic states in this system: coral-, macroalgae-, and crustose coralline algae-enriched relative to a seawater-only control. While net community production was similar among communities, net community calcification was lowest in the macroalgae-enriched state. Across treatments, community metabolism drove changes in the organic and inorganic carbon pool, with net community production increasing both pH and dissolved organic carbon. Using structural equation modeling, we tested how these community-generated chemical legacies propagated through coral physiology. Elevated pH increased chlorophyll a content, which increased endosymbiont density, tissue biomass, gross photosynthesis, and respiration through a series of indirect pathways. Dissolved organic carbon had no detectable effect on downstream corals at 25 d. These results reveal a mechanistic pathway linking disturbance-driven shifts in benthic communities to coral performance. Altered community metabolism modifies local carbon chemistry, which reshapes symbiont physiology and ultimately influences host metabolic function. By identifying the pathways through which community states engineer their chemical environment, this study provides a framework for predicting coral performance and ecosystem trajectories as reefs transition away from coral-enriched states.
Continue reading ‘Community metabolism generates chemical legacies that alter coral physiology’Abrupt pH changes overestimate the responses of Chaetoceros muelleri to ocean acidification
Published 30 October 2026 Science Leave a CommentTags: adaptation, biogeochemistry, biological response, globalmodeling, growth, laboratory, modeling, molecular biology, otherprocess, photosynthesis, physiology, phytoplankton, primary production, protists
Ocean acidification, characterized by a gradual seawater pH decline, influences marine primary producers such as diatoms, which contribute substantially to oceanic carbon fixation. Experimental studies aiming to project climate change impacts often simulate acidification via abrupt pH shifts, potentially misrepresenting ecological and evolutionary responses. Here we conduct a long-term evolution experiment with the marine diatom Chaetoceros muelleri, comparing abrupt and gradual CO2 increases from 440 to 1000 ppm over 1100 generations. Integrating evolutionary genomics, physiological assays, elemental stoichiometry, and Earth System Modeling, we find that abrupt acidification exaggerates diatom growth and carbon fixation responses by up to 15%, driven by enhanced divergent genomic signals and persistent gene expression changes. Gradual acidification elicits weaker phenotypic and genomic shifts, aligning more closely with natural ocean conditions. These findings suggest that models based on abrupt CO2 increases may overestimate the contribution of Chaetoceros muelleri and maybe also other diatoms to productivity and biogeochemical cycling under ocean acidification, highlighting the importance of gradual pH decline in experimental designs to accurately predict marine ecosystem responses.
Continue reading ‘Abrupt pH changes overestimate the responses of Chaetoceros muelleri to ocean acidification’Elevated pCO2 promotes growth but compromises PSII repair and antioxidant balance in the bloom-forming diatom Skeletonema costatum under ultraviolet radiation
Published 28 October 2026 Science Leave a CommentTags: biological response, growth, laboratory, light, multiple factors, photosynthesis, physiology, phytoplankton, protists
Highlights
- Elevated pCO2 stimulates growth but not UV photoprotection in Skeletonema costatum.
- Ocean acidification constrains PSII repair and PsbA turnover under UVR.
- Trade-off between carbon-sequestration capacity and antioxidant defense raises UV sensitivity.
Abstract
Diatoms serve as key marine primary producers, driving global biogeochemical cycles, but their physiological performance is increasingly challenged by ocean acidification (OA) and enhanced ultraviolet radiation (UVR). This study investigated how OA caused by elevated pCO2 (1000μatm) modulates the UVR sensitivity of the bloom-forming diatom Skeletonema costatum. Elevated pCO2 significantly enhanced the specific growth rate by ~11.6%; it did not significantly aggravate the UVR-induced decline in Fv/Fm, but it constrained PSII repair and PsbA turnover, as indicated by lower rate constants for PSII repair (Krec, s−1) and PsbA removal (KPsbA, s−1), and was associated with a greater net decline in total PsbA content under PAR + UVR. Although elevated pCO2 upregulated the relative maximal electron transport rate (rETRmax) and light-saturation parameter (Ik), and maintained a higher RbcL/PsbA ratio consistent with a possible role of carbon assimilation as a downstream sink, it did not enhance the sustained non-photochemical quenching (NPQs). Furthermore, under elevated pCO2, CAT activity had a lower baseline; although CAT increased under UVR relative to PAR, its absolute activity remained lower, indicating an imbalanced antioxidant response. Collectively, these findings reveal a physiological trade-off: elevated pCO2 promotes growth and carbon-sequestration capacity but simultaneously compromises photoprotective mechanisms. Consequently, S. costatum grown under elevated pCO2 becomes more susceptible to UVR-induced photoinhibition, potentially suppressing photosynthetic production during surface blooms and influencing bloom persistence and carbon export.
Continue reading ‘Elevated pCO2 promotes growth but compromises PSII repair and antioxidant balance in the bloom-forming diatom Skeletonema costatum under ultraviolet radiation’Surviving together: evolutionary dependency, community dynamics, and mortality in marine microbial communities
Published 26 October 2026 Science Leave a CommentTags: abundance, adaptation, biological response, community composition, growth, laboratory, light, molecular biology, mortality, multiple factors, nutrients, otherprocess, photosynthesis, physiology, phytoplankton, primary production, prokaryotes, reproduction, respiration, temperature
Oligotrophic regions of the world ocean sustain vast phytoplankton populations despite extremely low nutrient levels. However, the mechanisms governing their coexistence, interdependence, and mortality are poorly understood. This dissertation investigates how evolutionary dependency, community feedback, and regulated cell death (RCD) jointly shape the stability of marine microbial communities using the Prochlorococcus/Parasynechococcus/Alteromonas model system.
In Chapter 1, I argue that the Black Queen (BQ) hypothesis—which posits that microbes lose costly metabolic functions supplied by community partners—provides a unifying framework for understanding phytoplankton ecology. This framework helps resolve longstanding puzzles, including the paradox of the plankton and the evolutionary maintenance of RCD in unicellular organisms. Building on this framework, Chapter 2 uses transcriptomic analysis of Alteromonas in co-culture with picocyanobacteria to demonstrate that community composition induces greater changes in gene expression than pCO₂ alone. Reduced 2-phosphoglycolate/glycolate exudation by Prochlorococcus under elevated pCO₂ may disrupt the helper heterotroph effect underlying this cyanobacterium’s BQ dependency.
Chapter 3 integrates co-culture experiments, RNA-seq, metabolomics, and mathematical modeling to demonstrate that the stable coexistence of Prochlorococcus and Parasynechococcus is maintained by an “Ouroboros network” of feedback loops. In this network, resource competition, carbon exudation, BQ dependency, and possibly RCD collectively stabilize the community across environmental gradients and during adaptation to changing conditions.
Chapter 4 resolves the cellular mechanisms underlying RCD in these cyanobacteria, showing that differences in cell death modes and the number of checkpoint-linked mortality events between taxa are associated with divergent life-history strategies. These findings suggest that carbon released at these checkpoints may shape interactions with helper Alteromonas, linking individual cell death to community-level interdependencies.
In conclusion, these findings converge on a new resolution to the paradox of the plankton: coexistence in resource-limited environments emerges from interdependent metabolic exchanges, feedback, and regulated cell death shaped by multilevel selection. I propose that together, these processes form an “altruistic bargain” in which stability arises from self-constraint rather than competition alone. Because these interactions are environmentally sensitive, climate change, including warming and acidification, may disrupt the dependencies that sustain microbial diversity and ecosystem function in the world ocean.
Continue reading ‘Surviving together: evolutionary dependency, community dynamics, and mortality in marine microbial communities’The impact of the CO2 fertilization effect in seagrasses: a comparative perspective with terrestrial plants
Published 20 October 2026 Science ClosedTags: biological response, communityMF, morphology, multiple factors, nutrients, phanerogams, photosynthesis, physiology, reproduction, review, temperature
This article comments on:
Pazzaglia J, Marín-Guirao L, Ambrosino L, Pes K, Costa M, Barrote I, Silva J, Procaccini G. 2025. Handling the heat: ocean acidification mitigates the effects of marine heatwaves on Posidonia oceanica seedlings. Journal of Experimental Botany 76, 6958–6973. https://doi.org/10.1093/jxb/eraf276.
Seagrass meadows are among the world’s most ecologically and economically important marine ecosystems. Although they cover only 0.1% of the seafloor, they sequester carbon at rates rivalling tropical rainforests, protect coastlines, and support marine biodiversity (do Amaral Camara Lima et al., 2023). Yet they are declining globally due to anthropogenic pressures including coastal development, pollution, and climate change (Waycott et al., 2009; Dunic et al., 2021). While ocean acidification and ocean warming are pervasive stressors under accelerating global change, Pazzaglia et al. (2025) have demonstrated that elevated dissolved CO2 may enhance seagrass resilience by increasing thermal tolerance in Posidonia oceanica seedlings through the CO2 fertilization effect.
Continue reading ‘The impact of the CO2 fertilization effect in seagrasses: a comparative perspective with terrestrial plants’Asymmetric metabolic responses of rockweed and herbivores reveal seasonal vulnerabilities to warming and acidification
Published 22 September 2026 Science ClosedTags: algae, biological response, BRcommunity, calcification, mollusks, multiple factors, photosynthesis, respiration, temperature
Macroalgal-herbivore interactions are fundamental to the stability of coastal ecosystems and their vulnerability to climate-driven shifts will affect biodiversity and ecosystem functioning. However, the effects of climate change on species interactions may be context dependent and vary by seasonal oceanographic processes. We examined the effects of warming and acidification on an intertidal primary producer foundation species, Silvetia compressa, and its herbivore, Agathistoma eiseni, under differing upwelling regimes in early (low upwelling) and late spring (high upwelling). We measured metabolic rates including photosynthesis, respiration, and calcification after four weeks of exposure to a range of nine pH levels (7.2–8.0) at two temperature levels (16°C, 20°C). Rockweed responded more to acidification than to warming, but showed different seasonal responses, decreasing photosynthetic rates in early spring and increasing rates during late spring. Their snail consumer, however, responded most strongly to temperature, increasing both respiration and calcification rates under warm conditions in late spring. Our findings demonstrate that seasonal differences can modulate responses of macroalgae and herbivores to changing environmental conditions. Warming may increase top-down effects through increased snail metabolism, while acidification affects rockweed production to affect bottom-up forcing. By assessing physiological responses across different ecological regimes, our study advances understanding of how top-down and bottom-up processes interact in intertidal ecosystems under global change.
Continue reading ‘Asymmetric metabolic responses of rockweed and herbivores reveal seasonal vulnerabilities to warming and acidification’Physiological responses of coralline algae to climate change
Published 18 September 2026 Science ClosedTags: adaptation, algae, biological response, calcification, community composition, field, laboratory, molecular biology, morphology, mortality, multiple factors, North Pacific, otherprocess, photosynthesis, reproduction, South Pacific, temperature, vents
Ocean acidification and ocean warming are among the most pressing threats to marine ecosystems, with significant implications for calcifying organisms such as crustose coralline algae (CCA). These habitat-forming species play critical ecological roles in reef systems, yet they are particularly vulnerable to ocean acidification and ocean warming. While laboratory studies have documented declines in coralline algal growth and calcification under elevated CO₂ and temperature, less is known about their responses in natural settings where environmental variability and potential acclimatization may modulate stress impacts. Furthermore, the interactive effects of multiple stressors across generations remain poorly understood, limiting our ability to predict ecosystem-level consequences of climate change. This thesis explores the physiological responses of coralline algae to ocean acidification, ocean warming, and marine heatwaves through complementary field and laboratory approaches. Using natural climate analogues, I investigated how CCA communities respond to chronic exposure to low pH and elevated temperatures in situ (Chapters 2 and 3). These natural systems provide unique opportunities to assess long-term acclimatization and identify potentially resilient populations. To disentangle the mechanisms underlying stress responses and examine multi-generational effects, I conducted a multigenerational, multi-stressor laboratory experiment exposing coralline algae to factorial combinations of elevated pCO₂ and temperature over successive generations (Chapter 4). Together, these approaches enabled assessment of single-driver impacts, stressor interactions, and the capacity for phenotypic plasticity and acclimatization under both fluctuating natural conditions and controlled experimental regimes. Results from natural analogues revealed species-specific variation in stress tolerance, with some CCA populations maintaining growth and calcification despite chronic exposure to conditions projected for year 2100. The laboratory experiment revealed that growth significantly declined when exposed to ocean acidification and the combined effect of ocean acidification and ocean warming over multiple generations. This research advances our understanding of how marine calcifiers respond to climate change across ecological and temporal scales. The findings have important implications for predicting ecosystem trajectories and identifying potential climate refugia in an increasingly acidic and warming ocean.
Continue reading ‘Physiological responses of coralline algae to climate change’Coral acclimatization to novel, co-varying stressors is associated with fitness trade-offs
Published 18 September 2026 Science ClosedTags: adaptation, biological response, calcification, corals, field, morphology, mortality, multiple factors, North Atlantic, oxygen, photosynthesis, physiology, respiration, temperature
Reef-building corals are under pressure to acclimatize and/or adapt to multiple co-occurring stressors, including climate change and declines in water quality. However, their capacity to do so is largely unknown. Yet, some corals naturally persist in habitats with multi-stressor conditions which can provide crucial insight into coral adaptive capacity under future ocean conditions. To assess the role of phenotypic plasticity and local adaptation in coral acclimatory responses to novel conditions, we reciprocally transplanted two coral species (Siderastrea siderea, branching Porites) between an inland bay characterized by multiple, co-varying stressors, including warmer seawater temperatures, higher pollution and more variable temperatures, pH and dissolved oxygen concentrations, and an environmentally less extreme, more stable fringing reef. We measured key phenotypic traits (e.g., calcification, tissue biomass, metabolic rates, chlorophyll concentrations) of all transplant groups after 0, 4 and 12 months. Reef-origin corals demonstrated high plasticity when transplanted to the bay, as both species maintained high survival and calcification, and matched bay natives’ other phenotypic traits. Yet, reef-to-bay transplants of both species had reduced photosynthesis-to-respiration ratios in the bay, highlighting the risk of metabolic trade-offs unless compensated for through increased heterotrophy. Conversely, bay-origin corals had enhanced photosynthetic performance but lower calcification on the reef. Reaction norms provided stronger evidence for environmental specialization in bay-origin than reef-origin corals, which could limit their use as stress-tolerant source corals for reef restoration. Overall, our findings suggest multi-stressor variability may promote specialized genotypes, rather than increased phenotypic plasticity, though this may also depend on predictability of environmental variability.
Continue reading ‘Coral acclimatization to novel, co-varying stressors is associated with fitness trade-offs’Ocean acidification drives species-specific and time-dependent pigment responses in three phytoplankton taxa
Published 9 September 2026 Science ClosedTags: biological response, BRcommunity, growth, laboratory, light, multiple factors, photosynthesis, physiology, phytoplankton, respiration
Phytoplankton are primary producers in marine ecosystems and play a central role in biogeochemical cycles, yet their physiological responses to altered seawater pH vary among taxa and over time. Here, we examined the effects of sustained pH manipulation on pigment composition, growth, and dark respiration in three ecologically important phytoplankton taxa – a diatom (Pseudo-nitzschia spp.), a dinoflagellate (Heterocapsa pygmaea), and a haptophyte (Emiliania huxleyi) – during a 15-day controlled laboratory experiment. Cultures were maintained at pH 8.1, 7.8, and 7.5, representing present-day and enhanced acidification conditions. Responses to pH were species-specific and strongly time-dependent. Growth and cell-specific respiration rates showed relatively small and often transient differences among pH treatments, suggesting short-term metabolic adjustment under altered pH. In contrast, pigment composition exhibited clearer and more consistent pH-related responses, primarily expressed as shifts in temporal patterns rather than uniform directional changes. In Pseudo-nitzschia spp. and H. pygmaea, several key pigments displayed pronounced pH-dependent trajectories, whereas E. huxleyi showed greater temporal variability and weaker separation among pH treatments. Overall, these results demonstrate that photophysiological traits respond sensitively to sustained pH changes even when population-level growth and respiration remain comparatively stable, highlighting pigment composition as a potentially sensitive indicator of short-term phytoplankton acclimation to ocean acidification.
Continue reading ‘Ocean acidification drives species-specific and time-dependent pigment responses in three phytoplankton taxa’Coral reef community structure and photophysiology differ between upwelling and non-upwelling locations on the Pacific Coast of Costa Rica
Published 28 August 2026 Science ClosedTags: biological response, community composition, corals, echinoderms, field, North Pacific, otherprocess, photosynthesis, physiology
Reef-building corals and coralline algae form the calcium carbonate frameworks that underpin tropical coral reefs, yet in some locations, coral cover has declined by ~50% in recent decades due to marine heatwaves and other stressors. Identifying refugia environments, such as upwelling systems, that may buffer stress, promote recovery, and could enhance resilience by promoting physiological plasticity that supports thermotolerance is therefore critical. Here, we compared benthic community composition, coral percent cover, and photophysiology between an upwelling location in the Gulf of Papagayo and a non-upwelling location in Sámara on the Pacific coast of Costa Rica. Waters in Papagayo were cooler, more acidic, and had higher chlorophyll-a concentrations. Reefs at this location exhibited higher crustose coralline algae, higher sea urchin abundance, and lower macroalgae cover, compared to Sámara. Papagayo also showed higher stony coral cover, driven by Pocillopora spp., while Sámara was dominated by massive, heat-tolerant Porites spp. Photophysiological parameters were significantly different between locations. Specifically, photosynthetic efficiency (Fv′/Fm′) was 10–45% higher, and maximum photosynthetic rate (Pmax) was 20–40% lower in corals from Papagayo than in those from Sámara. These results reveal that two locations differing in environmental regime within a relatively small geographic area also differ in coral community composition and photophysiological features. Although further research is needed to resolve whether these environmental contrasts shape the observed biological differences, the observed patterns are consistent with the hypothesis that such regimes may support reef persistence or refugia, providing a basis for future work to test this hypothesis directly.
Continue reading ‘Coral reef community structure and photophysiology differ between upwelling and non-upwelling locations on the Pacific Coast of Costa Rica’Calcium carbonate formation in coastal macroalgal ecosystems via multiple pathways
Published 24 August 2026 Science ClosedTags: algae, biological response, BRcommunity, community composition, otherprocess, photosynthesis, physiology, review
Calcium carbonate formation in coastal macroalgal ecosystems via multiple pathways
Highlights
- Focused on a novel inorganic carbon sequestration pathway of non-calcifying macroalgae.
- Clarified algae-bacteria synergistic driving mechanism for calcium carbonate precipitation.
- Systematically sorted out potential mineralizing microbial taxa within the phycosphere and their core metabolic pathways.
Abstract
Macroalgae are dominant primary producers that drive carbon sequestration in coastal ecosystems. Macroalgal carbon sequestration primarily refers to the long-term storage of macroalgae-derived organic carbon in the ocean. However, calcium carbonate (CaCO3) formation is frequently observed in non-calcifying macroalgal environments, suggesting the existence of an overlooked inorganic carbon process in macroalgal ecosystems. Here, we introduce multiple pathways that may drive CaCO3 formation in macroalgal ecosystems. These include the effects of macroalgal photosynthesis and carbon-concentrating mechanisms on the seawater carbonate system, the role of phycosphere interfacial properties in facilitating CaCO3 nucleation, and the macroalgae-bacteria synergy that promotes CaCO3 formation. We identified several current knowledge gaps—the unclear carbon sequestration or source effect of CaCO3 formation in macroalgal ecosystems and the stability of CaCO3 minerals in macroalgal ecosystems—that require further investigation. This review advances the understanding of macroalgal carbon cycling beyond organic pathways and emphasizes the importance of a comprehensive assessment of macroalgal carbon sequestration, including that of inorganic carbon.
Short-term pH variability reshapes phytoplankton and microzooplankton communities in the northern Indian Ocean
Published 17 August 2026 Science ClosedTags: biological response, community composition, Indian, laboratory, otherprocess, photosynthesis, physiology, phytoplankton
Phytoplankton and microzooplankton (MZP) are key components of marine food webs, driving carbon transfer through the microbial loop. Short-term laboratory microcosm bottle incubations using seawater from the Bay of Bengal (BoB) and Arabian Sea (AS) in 2022 examined the effects of reduced pH. Phytoplankton biomass (Chl-a) remained stable or increased by up to 12% under low pH, suggesting reduced grazing or improved prey quality. MZP diversity (Shannon index, H′) showed basin-specific responses. In the BoB (Exps. 1–2), H′ ranged 2.00–3.70 with high evenness (J′ = 0.93–1.00) and slight declines under medium acidification (ΔpH = 0.2). In contrast, the AS (Exps. 3–4) showed wider variability (H′ = 0.00–3.63) and greater sensitivity, with sharp diversity losses under stronger acidification (ΔpH = 0.4). AS assemblages showed pronounced richness declines (D′ = 2.85–0.00), whereas BoB communities remained stable. Regional and pH-related differences were linked to shifts in ciliates and dinoflagellates. Autotrophic bacteria sustained under low pH, while heterotrophic bacteria increased later, indicating altered microbial-loop functioning. Overall, pH, chlorophyll-a, and heterotrophic bacteria structured the community, accounting for > 65% of the variation. Thus, short-term acidification reshapes MZP assemblages and may modify trophic interactions across the northern Indian Ocean.
Continue reading ‘Short-term pH variability reshapes phytoplankton and microzooplankton communities in the northern Indian Ocean’The responding mechanisms of Nannochloropsis oceanica to high CO2 and the regulating functions of H+-PPase
Published 31 July 2026 Science ClosedTags: algae, biological response, laboratory, molecular biology, photosynthesis, physiology
Highlights
- Cytoplasmic pH homeostasis was critical for N. oceanica to tolerate 5% CO2.
- The tolerant mechanisms involved multiple physiological-biochemical processes.
- H+-PPase was the central regulator for alleviating cytoplasmic acidification.
- avp1 overexpression improved cytoplasmic pH regulation by raising H+-PPase activity.
Abstract
High CO2 tolerance microalgae screen/breeding shows the urgent research priority when applying microalgae for flue gas CO2 sequestration. In this study, we chose the important resource microalgae Nannochloropsis oceanica as the target organism, the regulatory mechanisms of N. oceanica were elucidated under 5% and 20% high CO2 conditions, and the function of key regulating gene avp1 encoding H+-PPase was further explored. The results showed N. oceanica was tolerant to the 5% CO2 that maintained intracellular pH homeostasis, while severe cytoplasmic acidification was occurred under the 20% CO2 condition. Integrated physiological, biochemical, and transcriptomic analysis revealed that P-ATPase and H+-PPase activities were enhanced at 4 h and 4 d under the 5% CO2 condition, respectively. Concurrently, the reprogramming of organic acid metabolism and maintenance cellular energy supply additionally mitigated intracellular acidification. Further functional validation showed that overexpression of avp1 enhanced H+-PPase activity, increased cytoplasmic pH values, promoted pigments accumulation and growth of N. oceanica under the high CO2 condition. Therefore, this study clarified the working mode of N. oceanica to tolerant high CO2 and cytoplasmic acidification, and firstly timely proved the function of avp1, provided important data basis and gene candidates for the research of applying microalgae to CO2 sequestration.
Continue reading ‘The responding mechanisms of Nannochloropsis oceanica to high CO2 and the regulating functions of H+-PPase’pH–salinity-driven regulation in carbon utilization kinetics of the intertidal seagrass Zostera japonica along China’s coastline
Published 27 July 2026 Science ClosedTags: biological response, BRcommunity, field, laboratory, methods, morphology, North Pacific, phanerogams, photosynthesis, physiology
Highlights
- We innovatively define two biophysical parameters (pH change rate and acceleration) of Zostera japonica photosynthesis.
- pH change acceleration is sensitive to the regulation of carbon utilization pathways during Z. japonica photosynthesis.
- A progressive pH–salinity-driven regulation mode of carbon utilization pathways in Z. japonica photosynthesis is summarized.
- The impact of ocean acidification and alkalization on seagrass is characterized from a new biophysical standpoint.
Abstract
Seagrass carbon concentration mechanisms are modulated by seawater pH and salinity, yet their progressive regulation in photosynthetic inorganic carbon utilization pathways remain poorly characterized. This study novelly mathematically characterized first-order (pH change rate) and second-order (pH change acceleration) derivatives from pH-drift experiments in the intertidal seagrass Zostera japonica along China’s coastline. The pH change-based method effectively highlights the dissolved inorganic carbon (DIC) utilization and biomass accumulation of seagrass, while pH change acceleration is sensitive to the progressive switch of DIC utilization pathways during Z. japonica photosynthesis. As pH increases, six significant regulations emerge that have ecophysiological significance: a. primary regulation via reaching the CO2 compensation point; b. extracellular carbonic anhydrase (exCA) activity dropping to negligible levels; c. diminished efficiency of proton pump-mediated extracellular acidification in supplying CO2; d. regulation via reaching the bicarbonate saturation point; e. regulation via reaching the bicarbonate compensation point; and f. regulation via enhanced respiratory CO2 into seawater temporarily stimulating photosynthesis as a feedback. We summarize a progressive and universal pH–salinity-driven regulation mode reflecting different combinations of DIC utilization pathways and their respective intensities. Specifically, seawater pH modulates the mode’s fluctuating thresholds, while salinity governs the amplitude. Unexpectedly, elevated salinity serves as an effective stimulant for Z. japonica to maintain strong DIC utilization intensity in high pH (> 9.1) environments. Ocean acidification could increase pH change acceleration by 166%, enhancing carbon fixation, whereas artificial ocean alkalinity enhancement (Ca(OH)2 supplementation and olivine-seawater weathering) could reduce it by 165% and 105%, respectively, risking mortality of Z. japonica. Additionally, the salinity-dependent braking point (where acceleration drops to zero) serves as a critical threshold for seagrass photosynthesis and a new factor for transplantation-based restoration.
Continue reading ‘pH–salinity-driven regulation in carbon utilization kinetics of the intertidal seagrass Zostera japonica along China’s coastline’Response of Zostera japonica rhizosphere bacteria to ocean acidification
Published 24 July 2026 Science ClosedTags: biological response, community composition, laboratory, molecular biology, North Pacific, otherprocess, phanerogams, photosynthesis, prokaryotes
Abstract
Amidst global climate change, the escalating atmospheric CO2 levels have intensified ocean acidification (OA), significantly impacting the structure and function of marine ecosystems. Seagrass beds, representative nearshore ecosystems, play a pivotal role in carbon sequestration, biodiversity preservation, and nearshore environmental equilibrium. Rhizosphere microorganisms within seagrass beds, essential components of the ecosystem, drive material cycling and energy flow. Their community structure and functions demonstrate heightened sensitivity to environmental variations. While previous studies have primarily focused on the effects of ocean acidification on seagrass hosts, limited attention has been given to the rhizosphere. Therefore, this study selected Zostera japonica as the focal species and systematically evaluated changes in the structure and function of the rhizosphere bacterial community across varying acidification levels (400 ppm, 1,000 ppm, 2,000 ppm CO2) within an ocean acidification context. The results revealed a significant decline in the richness and diversity of the rhizosphere bacterial community under acidification, accompanied by shifts in community composition characterized by an increase in the relative abundance of Bacteroidota and Tenacibaculum with escalating acidification levels. In high acidification conditions, bacterial network interactions exhibited a trend toward simplification; yet the number of key taxonomic units increases, and there was a shift in community assembly from stochastic to deterministic processes. Functional predictions indicated the enhancement of microbial carbon sequestration and nitrogen fixation under acidification, while denitrification and specific sulfur metabolism pathways were inhibited. This implies that in acidified environments, the rhizosphere bacterial community may enhance carbon and nitrogen fixation to uphold nutrient supply.
Importance
Against the background of escalating global climate change and ocean acidification, seagrass beds, as crucial blue carbon sink ecosystems, face formidable challenges to their ecological functions and stability. Rhizosphere microorganisms of seagrasses, serving as the “second genome” of the seagrass host, play a central role in material cycling, nutrient supply, and system stability within seagrass beds. They are a key biological component that supports seagrass adaptation to environmental changes. Therefore, investigating the response and adaptation mechanisms of seagrass rhizosphere bacterial communities under ocean acidification is essential for deepening our understanding of the stability and resilience of seagrass bed ecosystems.
Continue reading ‘Response of Zostera japonica rhizosphere bacteria to ocean acidification’Water mass-driven variations in primary production and bacterial respiration during the spring bloom in the Fram Strait
Published 23 July 2026 Science ClosedTags: Arctic, biological response, community composition, field, laboratory, modeling, multiple factors, otherprocess, oxygen, photosynthesis, primary production, prokaryotes, regionalmodeling, respiration
Highlights
- Remote sensing indicates declining bloom in cold and developing bloom in warm water
- Primary production peaks in polar and arctic surface water masses
- Bacterial production is coupled to primary production despite thermal sensitivity
- Oxygen-based community respiration is highest in warmer water masses
- Oxygen-based and INT-based respiration estimates differ by an order of magnitude
Abstract
The Fram Strait is the primary oceanic gateway to the Arctic Ocean and has highly dynamic oceanographic conditions. Oceanographic conditions can shape community compositions, which is increasingly shown using molecular studies, but rate measurements remain scarce, especially for respiration in the Arctic Ocean. Here, we assessed primary production (PP), bacterial production (BP), bacterial abundances (BA), and community respiration (CR) using Winkler titrations and in vivo Iodo-Nitro-Tetrazolium (INT) reduction within the upper 50 m across water masses of the Fram Strait that had varying bloom conditions in spring 2021. We complemented in situ observations with remote sensing of sea surface temperature (SST) and chlorophyll-a (SSC) to infer bloom phenology in warm (θ>2°C), intermediate (2>θ>0°C), and cold (θ<0°C) waters using remote sensing machine-learning. In the cold, nutrient-rich surface waters, a subsiding spring bloom was associated with elevated PP, BP, and BA alongside a high temperature sensitivity (Q10) that indicates active microbial turnover. In contrast, the warm Atlantic-influenced waters exhibit a relatively lower PP but moderate cell-specific BP, suggesting bacterial maintenance metabolism under pre-bloom conditions. Notably, bacterial respiration (BR) estimates differed by 5- to 80-fold between the Winkler and in vivo INT methods. Although the true BR likely lies between these estimates, our results highlight the substantial microbial activity and underscore the need for more accurate BR measurements in Arctic studies.
Continue reading ‘Water mass-driven variations in primary production and bacterial respiration during the spring bloom in the Fram Strait’Changes in photosynthesis and grazing facilitate growth of a mixotrophic protist under ocean acidification and warming
Published 22 July 2026 Science ClosedTags: algae, biological response, BRcommunity, growth, laboratory, multiple factors, photosynthesis, physiology, protists, temperature
Summary
- Mixotrophic protists capable of both photosynthesis and phagotrophy are key members of marine plankton communities. Yet, little is known about their responses to the combination of ocean acidification and warming.
- A marine mixotrophic chrysophyte, Ochromonas CCMP2951, was subjected to two levels of pCO2 (300 and 800 ppm, resulting in pH of 8.2 and 7.8) and temperature (21°C and 26°C) in a factorial design.
- Enhanced growth rates were observed in both the high CO2 and high temperature treatments, while cell size significantly decreased with temperature. Strongly decreased cellular phosphorus content led to increased N : P and C : P ratios of Ochromonas with temperature. Furthermore, warming increased grazing rates, while elevated CO2 reduced the Chl content but increased photosynthetic carbon acquisition, albeit only at low temperature. The combination of warming and elevated CO2 had antagonistic effects on the balance between autotrophic and heterotrophic carbon acquisition, keeping the net role of this mixotroph in the marine carbon cycle stable.
- Altogether, both the direct stimulation of growth and the indirect effects of altered stoichiometry may favor mixotrophs under future ocean conditions. However, their contribution to future carbon cycling in complex natural communities will need further study.
Graphical Abstract
Grazing rates of Ochromonas CCMP2951 expressed as carbon obtained per mean cell volume (a) and Caut/het-photosynthetically fixed carbon divided by carbon obtained through grazing (b) in the four experimental treatments.
