Posts Tagged 'photosynthesis'

Impact of acidification and ultraviolet radiation on the physiology of Ulva fasciata

Published 19 December 2025 Science Leave a Comment
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Ocean acidification and increased UVR exposure driven by factors such as global warming, ozone layer depletion and anthropogenic activities are impacting the physiology and ecology of macroalgae in species-specific, diverse and complex ways. This study aims to investigate the individual and combined effects of ocean acidification and ultraviolet radiation (UVR) on the physiological responses of the cosmopolitan macroalgae species Ulva fasciata. The algae samples were cultured under laboratory conditions at two different pH levels (8.2 and 7.7) and under either the presence or absence of UVR. In U. fasciata, the maximum quantum efficiency of photosystem II (Fv/Fm) decreased with low pH and UVR, and a synergistic stress response was observed when these two stressors were applied together. The relative electron transport rate (rETRmax) varied depending on pH, while UVR increased this rate. These findings indicated that U. fasciata samples were under physiological stress. The incubation period significantly affected rETRmax and showed that the organism developed time-dependent adaptation responses. Alpha, a photosynthetic efficiency indicator, was negatively affected by UVR, whereas the light saturation point (Ik) varied as a result of the interaction between incubation time, pH, and UVR. The findings suggest that UVR exerted a more pronounced inhibitory effect on the photosynthetic system and growth of U. fasciata than low pH. Furthermore, combined exposure to UVR and low pH resulted in stronger growth inhibition, and a significant interaction between the two stressors was observed. Low pH and UVR exposure caused increased carbonic anhydrase activity (CA), while high CO2 led to a decrease in nitrate reductase activity (NR). UV-absorbing compounds (UVACs) were significantly affected by low pH and culture duration, whereas the effect of UVR on these compounds became significant only through its interaction with the incubation period. This suggests that the effect of UVR emerges through temporal accumulation. The findings reveal that this species is capable of developing late-phase acclimation strategies in response to environmental stress factors and possesses a potential adaptive capacity to cope with future marine change scenarios.

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Asymmetric effects of acidification and warming on foundation species and their predators in the California rocky intertidal zone

Published 11 December 2025 Science Leave a Comment
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The effects of climate change on marine organisms act through multiple pathways, as ocean warming and acidification can affect both their physiology and interspecies interactions. Asymmetries in species-specific physiological responses to climate change may alter the strength of interactions, such as those between predator and prey, which will have cascading effects on ecosystem structure. How foundation species and their interactions are affected by climate change will profoundly affect their community due to their dominance. I assessed the physiological responses of two common California rocky intertidal consumer–resource pairs across multiple trophic levels. I measured metabolic rates after four weeks of exposure to a range of nine pH levels (7.2–8.0) at two temperature levels (ambient, +4°C). At the lowest trophic level, I examined the effects of climate change on a primary producer foundation species, Silvetia compressa (golden rockweed), and its herbivore, Tegula eiseni, under differing upwelling regimes in early and late spring. Rockweed responded more to acidification than warming, decreasing photosynthetic rates in early spring and increasing rates during late spring. Their snail consumer, however, responded most strongly to temperature—increasing both respiration rates and calcification under warm conditions in late spring. In addition to species specific responses to climate stressors, the rockweed–snail pair had context-dependent responses based on background environmental conditions. Greater upwelling during late spring, combined with a younger snail population could explain differences in responses between early and late spring. Next, I examined asymmetries between a calcifying foundation species, Mytilus californianus, and its whelk predator, Nucella emarginata. Specifically, mussels were generally resistant to acute exposure to ocean warming and acidification, while whelks were highly sensitive to temperature. Whelks decreased their calcification, respiration, shell extension, and probability of drilling a mussel under warmer conditions. Across both experiments, I observed asymmetries in response to changes in pH and temperature between consumer and resource, which can shift ecosystems between bottom-up and top-down processes. Overall, I showed that mesopredators, such as herbivorous and carnivorous snails, appeared to be the most sensitive to changes in temperature relative to their foundation species prey. Climate change may reshape rocky intertidal communities by altering predation patterns on foundation species, which could either facilitate or threaten the survival of other associated species in a changing environment.

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Warming coupled with elevated pCO2 modulates microplastic inhibition in a commercial red alga Pyropia haitanensis

Published 5 December 2025 Science Closed
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Highlights

  • Microplastics exert concentration-dependent negative effects on Pyropia haitanensis.
  • Warming (24 °C) exacerbated microplastic-induced growth inhibition at ambient CO₂ level.
  • High CO₂ inhibited growth at 20 °C but enhanced it at 24 °C under high microplastic stress.

Abstract

Ocean acidification, warming, and microplastics are pervasive stressors in coastal ocean, yet their combined effects on economically important seaweed Pyropia haitanensis remain unclear. To investigate how elevated pCO2, warming, and microplastics interact to affect physiology of P. haitanensis, we cultured thalli at ambient (418 μatm, AC) and elevated (1000 μatm, HC) CO2 levels with two temperatures (20 and 24 °C), and a gradient of microplastics (0.025, 2.5, 25, 50, 100 mg L−1) in a controlled indoor experiment. Our results indicate that microplastics imposed a strong, concentration-dependent stress on P. haitanensis, consistently reducing relative growth rate (RGR), Fv/Fm, photosynthetic pigments (chlorophyll a, carotenoids, and phycobiliproteins), and cellular reserves (soluble protein and carbohydrates), with the strongest inhibition observed at concentration of 100 mg L−1. However, while the increased temperature (24 °C) promoted the content of pigments and soluble protein of the thalli, it decreased the content of soluble carbohydrate among the microplastic concentrations regardless of pCO2 levels. It is noteworthy that under ambient pCO2 level, elevated temperature exacerbated the growth inhibition caused by microplastics, resulting in the highest inhibition rate of 57 % occurring at 100 mg L−1. In contrast, this temperature-aggravated microplastic toxicity was mitigated by high pCO2 levels, with the inhibition rate of 32 % at the highest microplastic concentration. These findings reveal that while elevated pCO2 and warming can modulate microplastic stress via physiological reallocation, persistent declines in photochemical efficiency and light-harvesting pigments may constrain yield and nutritional quality of P. haitanensis where microplastics are high in coastal aquaculture area.

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

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

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Elevated carbon dioxide does not increase macroalgal community photosynthesis

Published 4 November 2025 Science Closed
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Ocean acidification, driven by rising atmospheric carbon dioxide levels, has impacts on marine ecosystems. While elevated carbon dioxide concentrations have the potential to enhance Blue Carbon fixation and storage, the response of community photosynthesis in macroalgal-dominated ecosystems remains poorly understood. Here, we investigated the effects of elevated carbon dioxide on macroalgal communities using volcanic carbon dioxide vents as a natural analogue of ocean acidification. Net community photosynthesis was assessed using chambers positioned on the seafloor as well as water mass dynamics monitoring. Despite a shift in algal community composition, only minimal differences in net community photosynthesis were observed between reference and high carbon dioxide sites. The high carbon dioxide site had a lower abundance of algal species with carbon dioxide concentrating mechanisms, based on δ13C isotope measurements. Carbon dioxide concentrating mechanisms facilitate photosynthesis under present-day levels of carbon dioxide in seawater, resulting in a negligible effect of elevated carbon dioxide on macroalgal community photosynthesis. These results challenge the assumption that ocean acidification will enhance Blue Carbon uptake and storage, necessitating a reevaluation of this perspective.

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The negative responses and acclimation mechanisms of Neopyropia yezoensis conchocelis filaments to short- and long-term ocean acidification

Published 30 October 2025 Science Closed
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Background

Ocean acidification (OA) significantly alters the carbonate chemistry of seawater, leading to a decrease of seawater pH to impact the physiological and biochemical processes of those intertidal macroalgae. Previous studies have focused on the response of macroalgae to OA at thallus stage, while the effects at filamentous stage remain insufficiently explored.

Results

This study investigated the physiological-biochemical and molecular mechanisms of the filamentous conchocelis stage (the diploid sporophyte) of Neopyropia yezoensis responding to short- (5 days) and long-term (20 days) OA (2000 ppm CO2, pH 7.53). The results showed that short-term OA rapidly inhibited the growth and photosynthesis, suppressed chlorophyll synthesis and nitrogen assimilation, and down-regulated genes associated with photosynthesis, Calvin cycle, and carbohydrate metabolism of N. yezoensis conchocelis filaments. However, N. yezoensis conchocelis filaments showed acclimation strategies under long-term OA, in terms of metabolic reorganization, prioritizing stress tolerance over growth. Further weighted gene co-expression network analysis (WGCNA) based on the metabolomic and transcriptomic results under long-term OA showed that the strategy was manifested by the accumulation of soluble sugars as osmolytes, lipid β-oxidation compensating for energy deficits, and H+ extrusion mediated via ABC transporters.

Conclusions

This study suggested time-depended responses of N. yezoensis conchocelis filaments to OA, proving the pronounced negative effects of OA on N. yezoensis conchocelis filaments, revealing N. yezoensis conchocelis filaments could acclimate to long-term OA by resource reallocation. These findings provide new insight into the survival of N. yezoensis conchocelis filaments under OA, and facilitate the development of technologies and breeding strategies for improved acidification tolerance in N. yezoensis.

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Elevated pCO2 and temperature levels modulate the ratios of the photosynthetic methane production to CO2 fixation in the coccolithophorid Emiliania huxleyi

Published 6 October 2025 Science Closed
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Most phytoplankton species have been shown to release methane (CH4) during photosynthesis; however, little has been documented on how changed levels of CO2 at different temperatures affect their CH4 production along with photosynthetic C fixation. Here, we examined CH4 production and photosynthetic performance in the most cosmopolitan coccolithophorid, Emiliania huxleyi, grown under high (1000 μatm, HC) and ambient (415 μatm, LC) pCO2 levels at five temperatures (16, 20, 22, 24 and 27°C). The HC treatment slightly lowered the optimal temperature for growth and CH4 production, and temperature changes significantly affected both carbon fixation and CH4 production. Under suboptimal temperatures, increasing temperature from 16 to 20°C led to about 96% increase in CH4 production per POC and HC treatment further enhanced this increase by an additional 9%. In contrast, under super-optimal temperatures, a temperature rise by 4°C reduced the microalgal CH4 production per POC under HC treatment by about 24% compared to the control. The calculated CH4 production quotient (MPQ, CH4 released vs. CO2 fixed) ranged between 2 × 10−5−6 × 10−5, and showed a decreasing trend with increasing temperature under both pCO2 levels, implying that the CH4 production by this microalga is being affected by global ocean changes, and the CH4 produced by phytoplankton should be quantified and included in assessing the feedback of marine phytoplankton to climate change.

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Microplastic exposure under future oceanic conditions further threatens an endangered coral, Acropora cervicornis

Published 22 September 2025 Science Closed
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Microplastic pollution is ubiquitous in the oceans. However, little is known about the physiological impact of microplastics on corals, particularly under predicted future ocean conditions. This study investigated the individual impacts of microplastic exposure (MP) and predicted future ocean conditions [ocean acidification and warming (OAW)] as well as the combination of these stressors (OAW+MP) on the growth and physiology of Acropora cervicornis, a threatened Caribbean coral and its associated symbiont, Symbiodiniaceae. After 22 days, the OAW+MP treatment resulted in more pronounced physiological changes than either stressor individually or the control. OAW conditions alone had minimal impacts, despite A. cervicornis generally being sensitive to thermal stress. The OAW+MP treatment and the MP treatment also disrupted the host-symbiont relationship evidenced by the higher symbiont densities relative to the control and the OAW treatments. Additionally, the OAW+MP treatment resulted in lower chlorophyll a per symbiont cell. Microplastic handling is energetically costly, possibly leading to changes in host-symbiont signaling. Photosynthetic efficiency was only marginally lower in the OAW+MP treatment, and values did not indicate photosystem damage. Negative host health impacts were found with the OAW+MP treatment exhibiting lower skeletal growth compared to the control and lower host protein concentrations compared to the OAW treatment. These results indicate that although short term microplastic exposure alone may not pose a significant threat to coral health, when adding additional stressors, it can further threaten the health and recovery of this already vulnerable species.

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Coping with ocean acidification: metabolic shifts in Porites corals from the Palau Archipelago

Published 9 September 2025 Science Closed
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Increased atmospheric CO2 levels lead to ocean acidification, threatening coral reefs. However, certain coral species thrive in naturally acidified environments, offering unique opportunities to explore potential acclimatization or adaptation strategies. We assessed the physiological and biochemical parameters of Porites cf. lobata. colonies from control and acidified sites in the Palau Archipelago. Using a holistic approach, we compared markers related to trophic state, symbiotic state, physiology, energy storage, and redox status, along with calcification and oxidative metabolism. Our findings indicate that these colonies can acclimatize to low-pH conditions by utilizing CO2 more effectively. The increased passive diffusion of CO2 through their tissues enables them to maintain photosynthesis and calcification rates by reallocating energy that would typically go toward bicarbonate uptake. However, this energy reallocation cannot maintain skeleton density. Corals expend energy to elevate pH in the extracellular calcifying fluid, which is highly energy-demanding and reduces lipid reserves, potentially compromising long-term resilience. Despite the heightened energy production requirements, oxidative stress does not appear to worsen; the colonies exhibited lower antioxidant defenses and protein damage under low-pH conditions. The absence of metabolic suppression due to stable respiration rates and increased biomass suggests modifications in metabolic pathways, likely shifting toward a Warburg-like effect. These findings highlight the potential for some corals to tolerate near-future ocean acidification, the trade-offs associated with this resilience, and the potential for cascading effects on reef ecosystems. Further research should explore corals metabolic pathways as potential coping mechanisms.

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Influence of intensified upwelling on two different Corallina officinalis Linneo 1758 populations by exploring direct and indirect effects

Published 26 August 2025 Science Closed
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In the perspective of a future ocean, climate change can alter upwelling systems globally. Along the Chilean coast, upwelling becomes intensified, leading to cool temperatures and low pH, which can affect common and widespread calcifying seaweed species such as Corallina officinalis. We measured physiological, biomineralogical, and palatability responses in two distinct populations originating from contrasting upwelling regimes, one from an upwelling area and the other from an upwelling shadow, by exposing them to current and future upwelling conditions. After 20 days of experimentation, photosynthetic responses such as maximum quantum yield (Fv/Fm) remained high (> 0.5) across populations. In contrast, maximal photosynthetic efficiency (rETRmax), light saturation point (Ek) and pigment content were higher in individuals exposed to future conditions, while alpha (electron transport efficiency) decreased over time. The carbonate content was higher in individuals exposed to future conditions, while the organic matter content differed between populations, with lower contents in the population originating from the site with higher environmental variability (-1.1%). Individuals exposed to future upwelling conditions presented higher soluble protein contents (2-3 mg/g wet weight) and were also more consumed by sea urchins (+162.7%). Our results indicate that the two C. officinalis populations possess strategies that confer tolerance to projected increases in upwelling, demonstrating their capacity to adapt to changing environmental conditions. However, rising herbivory pressure associated with intensified upwelling may exert a stronger influence on ecosystem dynamics, potentially altering future community composition.

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Adaptive phenotypic evolution of Skeletonema costatum to ocean acidification and warming with trade-offs from a multi-year outdoor experiment

Published 11 August 2025 Science Closed
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Human-induced climate change is increasing variability in marine environments, significantly affecting marine organisms and ecosystems. While marine diatoms can adapt to ocean acidification and warming in stable laboratory settings, their responses to long-term environmental changes under natural variability remain unclear. To investigate this, we cultivated Skeletonema costatum in outdoor semi-continuous cultures for over 3 years, exposing them to fluctuating natural light and temperature that tracked the in situ sea surface temperatures. We simulated current and future ocean conditions through four treatments: ambient CO2 and temperature (LTLC), elevated CO2 (LTHC), elevated temperature (+4°C, HTLC) and combined increases (HTHC). After 1396 days, we assessed populations in two assay environments (20°C, 400 ppm CO2 and 24°C, 1000 ppm CO2) for adaptations in growth rate, pigment composition and photosynthesis. The HTLC-selected group showed the highest growth rates in the HTHC assay environment, while the LTLC-selected group grew fastest in the LTLC assay environment, indicating adaptive evolution. Furthermore, populations selected under elevated conditions exhibited lower fitness in LTLC environments, highlighting a trade-off and underscoring the complexity of evolutionary adaptation in marine diatoms. Understanding these mechanisms is crucial for predicting phytoplankton dynamics and their role in marine ecosystems, especially in response to climate change.

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Ocean acidification interacts with low salinity and phosphorus limitation to modulate growth, photosynthesis, and physiology of mass-cultivated Gracilariopsis lemaneiformis

Published 4 August 2025 Science Closed
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Due to the effective removal of phosphorus during eutrophication control and intensive macroalgal cultivation, phosphorus limitation in coastal waters is normalized. As an economic macroalga cultivated on a large scale in production, Gracilariopsis lemaneiformis is also inevitably influenced by the combination of phosphorus limitation, ocean acidification caused by the increase of dissolved CO2 concentration and salinity decrease as a consequence of rainfall. In this study, G. lemaneiformis was cultured for 15 days under two pCO2 levels (LC: 400 μatm, HC: 1000 μatm), two salinities (LS: 22, HS: 30) and two phosphorus concentrations (LP: 0.1 μmol L−1, HP: 10.1 μmol L−1) to study the growth and photophysiology responses of this macroalga to the coupling of phosphorus limitation, ocean acidification and low salinity. Lower phosphorus (LP) treatment substantially reduced multiple parameters compared to higher phosphorus (HP) condition, including relative growth rate (RGR), photosynthetic rate, chlorophyll fluorescence parameters, and the contents of pigments, soluble protein, and soluble carbohydrate. Elevated CO₂ (HC) exposure induced a significant reduction in algal RGR under LP condition, while demonstrating no statistically significant impact on RGR under HP condition. Furthermore, HC treatment significantly inhibited carotenoid biosynthesis under LP condition. Notably, lower salinity (LS) stimulation significantly enhanced RGR in the ambient CO₂ (LC) group, but this promotive effect was completely negated under HC condition. These findings demonstrated that phosphorus limitation had an adverse outcome on algal growth, and phosphorus limitation exacerbated the adverse effect of ocean acidification on its growth. Moreover, the promotion effect of low salinity on algal growth could be neutralized by ocean acidification. This study provided important information about the influence of environmental changes on the photophysiological characteristics of G. lemaneiformis and new breeding directions for large-scale cultivation of coastal economic macroalgae.

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Species-specific mechanisms of benthic foraminifera in response to shell dissolution

Published 31 July 2025 Science Closed
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Highlights

  • Living specimens and empty tests of two benthic foraminifera species were cultured in different pH and light conditions.
  • In acidic conditions, greater dissolution of empty tests compared to living specimens was observed.
  • No differences in the degrees of dissolution between the two species were observed.
  • Living foraminifera have active mechanism(s) to tolerate acidification.

Abstract

Ammonia confertitesta and Haynesina germanica are two common estuarine benthic foraminifera subject to sediment acidification. Nevertheless, mechanisms involved in their response to acidification are still poorly understood. Since H. germanica is kleptoplastic and photosynthetically active, unlike A. confertitesta, these species were cultured in controlled experiments to determine whether these mechanisms could mitigate acidification-induced shell dissolution. Both living and dead specimens were incubated at two pH (8.0 and 6.8) and two light conditions (0 and 24 μmol photon m-2.s-1) for 18 days. For each species, respiration and photosynthesis rates were calculated based on oxygen measurements. At the end of incubation, foraminiferal viability was assessed with CellTracker Green™ biomarker, and each test was categorised according to a dissolution scale (DS) using SEM. For both species, in acidic conditions, the tests of dead specimens were significantly more dissolved than the tests of living specimens, suggesting active mechanisms providing tolerance to acidification. For the living specimens, no significant difference in the DS distribution was observed between the two species at both conditions, suggesting that kleptoplast photosynthetic activity in H. germanica does not provide additional resistance to acidification. Until at least day 12, respiration data revealed a different biological activity for the two species, and we observed distinct behaviours (e.g., encystment and pseudopod emission). These suggest each species exhibits species-specific responses to cope with acidification. On day 18, respiration rates and binocular observations showed low biological activity, suggesting dormancy or death. Further investigation is required to identify the cellular mechanisms involved to counter acidification stress.

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Ocean acidification impairs growth and induces oxidative stress in the macroalgae Ulva fasciata and Petalonia fascia

Published 22 July 2025 Science Closed
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Ocean acidification (OA), driven by increasing anthropogenic CO2 uptake, poses a significant threat to marine ecosystems; understanding the physiological responses of key primary producers like macroalgae is crucial for predicting ecological consequences. This study investigated the impacts of OA on two common intertidal macroalgae, the green alga Ulva fasciata and the brown alga Petalonia fascia, aiming to determine the effects of decreased seawater pH on their relative growth, photosynthetic performance, biochemical composition, and oxidative stress responses. Algae were exposed for 15 days to three pH levels (8.2, 7.4, and 6.5), and measurements included relative growth rate, membrane damage, total chlorophyll, soluble protein and sugar content, chlorophyll a fluorescence parameters, H2O2 content, lipid peroxidation, and activities of superoxide dismutase and catalase. Results showed that decreasing pH significantly reduced RGR in both species, particularly at pH 6.5, with U. fasciata generally exhibiting higher growth. Photosynthetic efficiency and total chlorophyll content declined under lower pH, while non-photochemical quenching generally increased. Both species exhibited increased membrane damage, H2O2 content, and TBARS levels at lower pH, indicative of oxidative stress. Antioxidant enzyme activities were significantly modulated by pH and showed species-specific patterns, with significant interactions between pH and species observed for most parameters. For instance, U. fasciata maintained higher Fv/Fm at pH 6.5, whereas P. fasciata often showed higher antioxidant enzyme activity; soluble protein and sugar contents were also significantly altered. These findings indicate that both Ulva fasciata and Petalonia fascia are susceptible to detrimental effects from simulated OA, suggesting potential shifts in the competitive balance and structure of intertidal macroalgal communities.

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Combined effects of ocean acidification and warming on phytoplankton productivity and community structure in the coastal water of Southern East

Published 17 July 2025 Science Closed
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Highlights

  • Ocean warming partly offsets acidification-driven impacts on primary productivity in a southern coastal water of China.
  • Acidification alters phytoplankton communities with increased proportions of dinoflagellates and reduced that of diatoms.
  • Combination of warming and acidification reduced overall microbial diversity in the coastal water.

Abstract

Progressive global ocean changes, including ocean acidification and warming, are expected to impact ecosystems differentially due to regional environmental differences that govern biogeochemical and ecological processes. In this study, we investigated the impacts of ocean acidification and warming on the phytoplankton community and primary productivity in the southern coastal water of the East China Sea by running land-based mesocosms controlled under current atmospheric pCO2 (∼430 μatm) and projected levels for the year 2100 (∼1000 μatm, HC, High CO2) at 27°C (ambient) and 30°C (warming, HT, High Temperature). Our results indicate that warming, acidification, and their combined effects (HCHT) initially enhanced community biomass as determined by chl a concentration; however, this effect diminished over time, ultimately resulting in lower biomass density compared to the control in later stages. Primary productivity per volume of seawater in the HT and HCHT treatments was initially suppressed but increased in the later stages compared to the control group, whereas the HC treatment appeared to suppress it consistently. While higher effective photochemical efficiency and non-photochemical quenching coincided with higher photosynthetic carbon fixation per chlorophyll an under the HT and HCHT treatments, their decline under the HC after the acclimation was concurrent with decreased photosynthetic carbon fixation. Analysis of 18S rDNA revealed that diatoms and dinoflagellates dominated under the treatments of HC, HT, and HCHT, but compared to the control, the proportion of diatoms decreased by 23%, 14%, and6 %, while that of dinoflagellates increased by 19%, 9%, and 11%, respectively, under the corresponding treatments. Plankton richness increased under warming, while diversity declined, particularly with combined warming and acidification, highlighting community sensitivity to the stressors. With reference to heterotrophic microbes, the relative abundance of Basidiomycota increased by 16%–18% under HT or HCHT, along with insignificant impacts on prokaryotic communities based on 16S rDNA analysis. In conclusion, the combination of ocean acidification and warming treatment during the experimental period ultimately reduced the phytoplankton biomass density and altered the microbial community structure.

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Handling the heat: ocean acidification mitigates the effects of marine heatwaves on Posidonia oceanica seedlings 

Published 8 July 2025 Science Closed
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Ocean acidification (OA) and marine heatwaves (MHWs) are key drivers of marine ecosystem changes that can interact and influence marine organisms. Seagrasses, including the long-lived Posidonia oceanica endemic to the Mediterranean Sea, are widely distributed along coastal habitats, forming highly valuable underwater meadows. The germination and survival of the early life stages of P. oceanica are strongly affected by environmental changes. To assess the impact of warming and acidification on its future, we conducted a multifactorial experiment where P. oceanica seedlings were grown under OA conditions for six months and then exposed to a seawater warming event. Seedlings’ performance was investigated by analyzing photo-physiology, antioxidant capacity, energetic metabolism and transcriptomic profiles. The Weighted Gene Correlation Network Analysis (WGCNA) was used to integrate phenotypic plant traits with transcriptomic results to identify central genes involved in plant responses to OA and temperature exposure. Results demonstrated that prolonged OA exposure enhances P. oceanica seedling resilience to MHW. Specifically, seedlings regulated their antioxidant systems and transcriptomic machinery to better cope with thermal stress. Under current CO2 concentrations, elevated temperatures induced stress in P. oceanica seedlings, impacting photosynthesis and respiration. However, OA could mitigate the impact of warming in the future, enhancing P. oceanica‘s resilience to global stressors.

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Variable responses to ocean acidification among mixotrophic protists with different lifestyles

Published 13 June 2025 Science Closed
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Marine phytoplankton are facing increasing dissolved CO2 concentrations and ocean acidification caused by anthropogenic CO2 emissions. Mixotrophic organisms are capable of both photosynthesis and phagotrophy of prey and are found across almost all phytoplankton taxa and diverse environments. Yet, we know very little about how mixotrophs respond to ocean acidification. Therefore, we studied responses to simulated ocean acidification in three strains of the mixotrophic chrysophyte Ochromonas (CCMP1391, CCMP2951, and CCMP1393). After acclimatization of the strains to treatment with high-CO2 (1000 ppm, pH 7.9) and low-CO2 concentrations (350 ppm, pH 8.3), strains CCMP1393 and CCMP2951 both exhibited higher growth rates in response to the high-CO2 treatment. In terms of the balance between phototrophic and heterotrophic metabolism, diverse responses were observed. In response to the high-CO2 treatment, strain CCMP1393 showed increased photosynthetic carbon fixation rates, while CCMP1391 exhibited higher grazing rates, and CCMP2951 did not show significant alteration of either rate. Hence, all three Ochromonas strains responded to ocean acidification, but in different ways. The variability in their responses highlights the need for better understanding of the functional diversity among mixotrophs in order to enhance predictive understanding of their contributions to global carbon cycling in the future.

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Alleviation of competitive constraints through long-term adaptation to high CO2 in mixed cultures of two diatom species

Published 27 May 2025 Science Closed
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Highlights

  • The resources competition of two diatoms reduced most performance parameters.
  • High CO₂ adaptation partially alleviates the detrimental effects of competition.
  • Resource competition changes phytoplankton’s adaptation strategy to high CO2.

Abstract

Diatoms play a pivotal role in marine ecosystems, contributing significantly to global primary production and carbon cycling. Understanding their responses to high CO₂ is critical for predicting oceanic changes under future climate scenarios. This study investigates the long-term adaptation of two diatom species, Thalassiosira weissflogii and Phaeodactylum tricornutum, to high CO₂ (1000 µatm) over 3.5–4 years and the consequences of their interactions in mixed cultures. Mono- and mixed-species cultures were maintained under both ambient (400 µatm) and high CO₂ conditions to assess various physiological performances. Our results revealed that most measured parameters (growth rate, photosynthesis and respiration rate, chlorophyll fluorescence parameters, and pigment concentration) were significantly reduced in mixed cultures compared to mono-cultures under both CO₂ conditions, underscoring the detrimental effects of interspecific competition. However, long-term adaptation to high CO₂ partially alleviated these reductions, particularly in photosynthesis, respiration, and chlorophyll-a content. These findings highlight the complex interplay between physiological adaptation and interspecific competition in shaping diatom responses to high CO₂. This study advances our understanding of the ecological and evolutionary implications of ocean acidification and underscores the importance of long-term experimental approaches for assessing the impacts of climate change on marine phytoplankton.

Continue reading ‘Alleviation of competitive constraints through long-term adaptation to high CO2 in mixed cultures of two diatom species’

Metabolomic profiling of a red alga, Gracilaria changii, under current ambient and elevated pCO2 levels using an untargeted gas chromatography-mass spectrometry (GC–MS) approach

Published 14 April 2025 Science Closed
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Metabolomics offers valuable insights into the final stages of biological processes within organisms and holds promise for environmental monitoring. The escalating levels of anthropogenic CO2 due to industrialization are projected to raise atmospheric pCO2 to levels exceeding 1000 ppm by 2100. The ocean absorbs approximately 30% of this increase in CO2, altering seawater chemistry and decreasing pH levels. In this study, untargeted gas chromatography-mass spectrometry (GC–MS) complemented by physio-biochemical analyses, was utilized to explore the impact of elevated pCO2 on the growth, photosynthesis, agar yield and quality, and metabolite composition of the red alga Gracilaria changii. Although elevated pCO2 did not increase the growth rate of G. changii, an increase in the photosynthetic electron transport rate suggests that photosynthetic carbon assimilation was enhanced. The extra photosynthate was used for other cellular processes including proton export to regulate cellular pH homeostasis given the excess H+ in the environment, rather than being invested in new tissue growth. Thymine emerged as a key metabolite influenced by elevated pCO2 in G. changii. Pathway analysis unveiled significant impacts on amino acid synthesis pathways in G. changii at high pCO2. The concentration of compounds such as dopamine and glutamic acid, which are known to be triggered during stress response and provide antipathogenic bioactivity, increased in thalli cultured at higher pCO2. Heatmap analysis indicates d-3 as the turning point for G. changii cultivated at higher pCO2, where the macroalgae begin to regulate their metabolites to alleviate abiotic stresses from higher pCO2 and to maintain essential metabolic functions.

Continue reading ‘Metabolomic profiling of a red alga, Gracilaria changii, under current ambient and elevated pCO2 levels using an untargeted gas chromatography-mass spectrometry (GC–MS) approach’

Metabolomic and physiological analyses of two picochlorophytes from distinct oceanic latitudes under future ocean acidification and warming

Published 28 March 2025 Science Closed
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Highlights

  • Ocean acidification and warming impacted picochlorophytes’ metabolome and physiology
  • High CO2 significantly altered Chlorella‘s metabolome, with fewer changes in Parachlorella.
  • High temperature enhanced Chlorella photosynthesis, while high CO2 benefited Parachlorella.

Abstract

Phytoplankton are cosmopolitan marine photosynthetic organisms that are vital to biogeochemical cycles and marine ecosystems. The current rise in atmospheric CO2 and surface ocean temperatures are poised to disrupt the ecological niches of phytoplankton. Picochlorophytes, a broad taxon of small green eukaryotic phytoplankton, have been shown to perform well under future rising oceanic CO2 and temperature scenarios. This study investigates the acclimation responses of cosmopolitan picochlorophytes from the Chlorella-lineage under high CO2 (1000 p.p.m.) and a rise of 4˚C (8˚C – polar picochlorophyte; 32 ˚C, tropical picochlorophyte). In order to determine how the future ocean warming and acidification might affect picochlorophytes, a polar strain of Chlorella and a tropical Parachlorella were selected, and their physiology and GCMS-based metabolomics were investigated. Growth rate and cellular dimensions (diameter, volume, and surface area) of Chlorella significantly increased in all environmental future scenarios compared to Parachlorella. Photosynthetic parameters of the picochlorophytes studied showed acclimation, with high temperature and high CO2 triggering the adaptation of Fv/Fm , NPQmax, and Ek of Chlorella and Parachlorella, respectively. High CO2 induced the most changes in the Chlorella metabolome, altering the levels of metabolites related to amino acids and their derivatives, glutathione production, carbohydrates, and photochemical quenching. Combined high CO2/temperature altered Parachlorella’s metabolome, though with a small number of biomarkers detected. This study provided evidence to support the hypothesis that picochlorophytes could thrive in a more acidified and warmer ocean.

Continue reading ‘Metabolomic and physiological analyses of two picochlorophytes from distinct oceanic latitudes under future ocean acidification and warming’

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