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.
Continue reading ‘Coping with ocean acidification: metabolic shifts in Porites corals from the Palau Archipelago’Posts Tagged 'photosynthesis'
Coping with ocean acidification: metabolic shifts in Porites corals from the Palau Archipelago
Published 9 September 2025 Science ClosedTags: adaptation, biological response, calcification, corals, field, growth, North Pacific, otherprocess, photosynthesis, physiology, respiration
Influence of intensified upwelling on two different Corallina officinalis Linneo 1758 populations by exploring direct and indirect effects
Published 26 August 2025 Science ClosedTags: adaptation, algae, biological response, laboratory, otherprocess, photosynthesis, physiology, South Pacific
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.
Continue reading ‘Influence of intensified upwelling on two different Corallina officinalis Linneo 1758 populations by exploring direct and indirect effects’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 ClosedTags: adaptation, biological response, growth, laboratory, mesocosms, multiple factors, otherprocess, photosynthesis, physiology, phytoplankton, temperature
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.
Continue reading ‘Adaptive phenotypic evolution of Skeletonema costatum to ocean acidification and warming with trade-offs from a multi-year outdoor experiment’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 ClosedTags: algae, biological response, fisheries, growth, laboratory, multiple factors, nutrients, photosynthesis, physiology, salinity
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.
Continue reading ‘Ocean acidification interacts with low salinity and phosphorus limitation to modulate growth, photosynthesis, and physiology of mass-cultivated Gracilariopsis lemaneiformis’Species-specific mechanisms of benthic foraminifera in response to shell dissolution
Published 31 July 2025 Science ClosedTags: biological response, dissolution, laboratory, light, mortality, multiple factors, North Atlantic, performance, photosynthesis, protists, respiration
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.
Continue reading ‘Species-specific mechanisms of benthic foraminifera in response to shell dissolution’Ocean acidification impairs growth and induces oxidative stress in the macroalgae Ulva fasciata and Petalonia fascia
Published 22 July 2025 Science ClosedTags: algae, biological response, growth, laboratory, photosynthesis, physiology, South Atlantic
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.
Continue reading ‘Ocean acidification impairs growth and induces oxidative stress in the macroalgae Ulva fasciata and Petalonia fascia’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 ClosedTags: biological response, community composition, laboratory, mesocosms, molecular biology, multiple factors, North Pacific, otherprocess, photosynthesis, physiology, phytoplankton, temperature
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.
Continue reading ‘Combined effects of ocean acidification and warming on phytoplankton productivity and community structure in the coastal water of Southern East’Handling the heat: ocean acidification mitigates the effects of marine heatwaves on Posidonia oceanica seedlings
Published 8 July 2025 Science ClosedTags: biological response, laboratory, Mediterranean, mitigation, molecular biology, multiple factors, phanerogams, photosynthesis, physiology, reproduction, respiration, temperature
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.
Continue reading ‘Handling the heat: ocean acidification mitigates the effects of marine heatwaves on Posidonia oceanica seedlings ‘Variable responses to ocean acidification among mixotrophic protists with different lifestyles
Published 13 June 2025 Science ClosedTags: biological response, growth, laboratory, performance, photosynthesis, protists
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.
Continue reading ‘Variable responses to ocean acidification among mixotrophic protists with different lifestyles’Alleviation of competitive constraints through long-term adaptation to high CO2 in mixed cultures of two diatom species
Published 27 May 2025 Science ClosedTags: adaptation, biological response, BRcommunity, community composition, growth, North Pacific, otherprocess, photosynthesis, physiology, phytoplankton, respiration
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 ClosedTags: algae, biological response, growth, laboratory, photosynthesis, physiology
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 ClosedTags: adaptation, biological response, growth, laboratory, morphology, multiple factors, photosynthesis, physiology, phytoplankton, temperature
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’Effects of pH/pCO2 fluctuations on photosynthesis and fatty acid composition of two marine diatoms, with reference to consequences of coastal acidification (update)
Published 10 March 2025 Science ClosedTags: biological response, growth, laboratory, North Pacific, photosynthesis, physiology, phytoplankton
Coastal waters are impacted by a range of natural and anthropogenic factors, which superimpose on effects of increasing atmospheric CO2, resulting in dynamically changing seawater carbonate chemistry. Research on the influences of dynamic pH/pCO2 on marine ecosystems is still in its infancy, although effects of ocean acidification have been extensively studied. In the present study, we manipulated the culturing pH to investigate physiological performance and fatty acid (FA) composition of two coastal diatoms, Skeletonema costatum and Thalassiosira weissflogii, in both steady and fluctuating pH regimes. Generally, seawater acidification and pH variability showed neutral or positive effects on the specific growth rate, chlorophyll a, and biogenic silica contents of the two species. Decreased pH inhibited the net photosynthetic rate by 27 % and enhanced the mitochondrial respiration rate of S. costatum by 36 % in the steady pH regime, while these rates were unaltered by decreased pH in the fluctuating regime. Acidification conditions led to lower saturated FA and higher polyunsaturated FA proportions in both species, regardless of steady or fluctuating regimes. Our results indicate that coastal acidification could affect primary production in a different way from ocean acidification. Together with the altered nutritional quality of prey for higher trophic levels, coastal acidification might have far-reaching consequences for marine ecosystem functioning.
Continue reading ‘Effects of pH/pCO2 fluctuations on photosynthesis and fatty acid composition of two marine diatoms, with reference to consequences of coastal acidification (update)’Interactive effects of elevated atmospheric CO2 and UV-B radiation: a multi-level study on marine diatom Skeletonema pseudocostatum
Published 24 February 2025 Science ClosedTags: biological response, growth, laboratory, light, multiple factors, photosynthesis, physiology, phytoplankton
Highlights
- Combined effects of UVB radiation and increased atmospheric CO2 was assessed on Skeletonema pseudocostatum.
- Additive, synergistic and antagonistic effects were characterized based on modified independent action (IA) model.
- The combined effects on S. pseudocostatum were dose-dependent and target-specific.
- Additivity was most common, synergy occurred in ROS and growth, while carotenoids content reduced antagonistically.
- An effect pathway was developed to characterize the propagation of combined effects across t biological levels.
Abstract
Climate change as a result of increases in greenhouse gas emissions, such as CO2, is causing significant alteration in global environmental conditions, including ocean acidification (OA). Although the depletion of the ozone layer has reduced, the penetration of ultraviolet-B (UVB) radiation into the oceans still remains an environmental factor that may potentially enhance the effects of OA on biota. Improved understanding of the complex interactions between multiple stressors, such as UV-B radiation and increased CO2 levels, is thus important for safeguarding ecosystems and developing effective conservation and management strategies. A 72 h experiment was carried out to investigate the combined effects of UVB irradiance (0.5 W m−2) and varying CO2 levels (350, 500, 1000 ppm) on the diatom Skeletonema pseudocostatum. The study aimed to characterize the potential combined effects at different levels of biological organization, including ROS formation, lipid peroxidation (LPO), photosynthesis, pigments, oxidative phosphorylation (OXPHOS) and growth. The findings indicate that exposure to elevated CO2 (500 ppm) alone resulted in increased total carotenoid content and growth of S. pseudocostatum, but did not significantly impact photosystem efficiency, oxidative stress, and OXPHOS. Sole UVB exposure induced oxidative stress, inhibited photosynthesis and OXPHOS processes, and suppressed growth in S. pseudocostatum. However, when co-exposed with CO2, synergistic impacts were observed for reactive oxygen species (ROS), lipid peroxidation (LPO), and growth, while carotenoids were reduced in an antagonistic manner. A putative impact pathway was proposed as an initial effort to characterize the combined effects of these stressors under proposed future marine OA scenarios involving elevated CO2.
Continue reading ‘Interactive effects of elevated atmospheric CO2 and UV-B radiation: a multi-level study on marine diatom Skeletonema pseudocostatum’Contrasting species-specific stress response to environmental pH determines the fate of coccolithophores in future oceans
Published 14 February 2025 Science ClosedTags: adaptation, biological response, BRcommunity, growth, laboratory, otherprocess, photosynthesis, physiology, phytoplankton, respiration
Highlights
- Molecular mechanisms dictating sensitivity of coccolithophores to pH remain elusive.
- Coastal species was resilient to pH changes, but ancient open-ocean species was not.
- Bloom-forming species showed unique molecular changes under stress.
- Cellular carbon fixation will be higher under future acidification.
Abstract
Molecular mechanisms driving species-specific environmental sensitivity in coccolithophores are unclear but crucial in understanding species selection and adaptation to environmental change. This study examined proteomic and physiological changes in three species under varying pH conditions. We showed that changing pH drives intracellular oxidative stress and changes membrane potential. Upregulation in antioxidant, DNA repair and cell cycle-related protein-groups indicated oxidative damage across high (pH 8.8) and low pH (pH 7.6) compared to control pH (pH 8.2), and correlated with reduced growth rates. Upregulation of mitochondrial proteins suggested higher metabolite demand for restoring cellular homeostasis under pH-induced stress. Photosynthetic rates generally correlated with CO2 availability, driving higher net carbon fixation rates at low pH. The intracellular pH-buffering capacity of the coastal Chrysotila carterae and high metabolic adaptability in the bloom-forming Gephyrocapsa huxleyi will likely facilitate their adaptation to ocean acidification or artificial ocean alkalinisation. However, the pH sensitivity of the ancient open-ocean Coccolithus braarudii will possibly result in reduced growth and shrinking of its ecological niche.
Continue reading ‘Contrasting species-specific stress response to environmental pH determines the fate of coccolithophores in future oceans’Thalassia hemprichii may benefit from ocean acidification and slightly increased salinity in the future
Published 13 February 2025 Science ClosedTags: biological response, growth, laboratory, multiple factors, phanerogams, photosynthesis, physiology, salinity
Highlights
- Thalassia hemprichii highly adapted to acidified environments.
- The effect of elevated salinity on the physiology and growth of Thalassia hemprichii is not linearly.
- Ocean acidification could further enhance the resilience of Thalassia hemprichii to high salinity.
- Both acidification and slight salinity increased the photosynthetic activity of Thalassia hemprichii.
Abstract
Since the industrial revolution, the direct impacts of elevated CO2 concentrations, such as ocean acidification, and indirect impacts, such as extreme drought events, have synergistically influenced coastal ecosystems, including seagrass meadow. Consequently, investigating the individual and combined effects of ocean acidification and extreme drought-induced increased salinity on seagrasses is crucial for enhancing the management and monitoring of these ecosystems. This study used a two-factor crossover indoor simulation experiment to thoroughly examine the effects of seawater acidification at pH 7.7 and elevated salinity levels at 43‰ and 51‰ on the physiological responses and growth status of the dominant tropical seagrass species Thalassia hemprichii. The results indicated that seawater acidification at pH 7.7 significantly enhanced the growth rate and photosynthetic activity of T. hemprichii across all salinity levels. A salinity of 43‰ activated certain antioxidant enzymes without inducing severe osmotic stress in T. hemprichii and positively influenced leaf photosynthetic activity, with a 15.6% increase in growth rate compared to the CK group. The extreme salinity of 51‰ imposed osmotic stress, leading to increase in reactive oxygen species and decreased photosynthetic activity and a 52% decrease in growth rate compared to seagrasses in the CK group. Under future scenarios of ocean acidification and frequent extreme droughts, T. hemprichii inhabiting enclosed marine environments may exhibit greater adaptability and secure an ecologically competitive edge. Our findings underscore the importance of conserving declining meadows, forecasting the ecological trajectory of these ecosystems, and managing salinity in lagoons for the well-being of seagrass ecosystems.
Continue reading ‘Thalassia hemprichii may benefit from ocean acidification and slightly increased salinity in the future’CO2 fertilisation counteracts the negative effect of poor water quality on the growth and photosynthesis of a Great Barrier Reef coralline alga
Published 10 February 2025 Science ClosedTags: algae, biological response, growth, laboratory, light, multiple factors, nutrients, photosynthesis, physiology
The global problem of ocean acidification and localised decline in water quality are major threats to coral reefs worldwide. This study examined the individual and interactive impacts of global and local stressors by investigating the effects of increased seawater pCO2, elevated nutrient concentrations and reduced light levels on linear growth and metabolic rates of the common branching crustose coralline alga Lithophyllum cf. pygmaeum. We found complex interactions between factors on algal growth and photosynthetic rates, but overall, growth was significantly enhanced by pCO2 enrichment under all light and nutrient combinations. This is the first study to report a positive growth response in coralline algae to elevated pCO2 using linear extension methods. In contrast, the combination of reduced light levels and high nutrient concentrations simulating poor water quality conditions reduced algal growth rates by up to 67% (compared to individuals exposed to high light, low nutrients and elevated pCO2). Decreased light levels reduced linear growth, Pgross and Pnet rates by 33%, 18% and 24%, respectively, highlighting the critical role of light in coralline algal physiology. We suggest that poor water quality may counteract any CO2 fertilisation effect under ocean acidification conditions on the growth of coralline algae, and this has implications for coral reef conservation as it emphasises the importance of improving water quality to maintaining coral reef functions. These results further highlight the need for multifactorial experiments to better understand the interplay between global and local processes on coralline algae growth.
Continue reading ‘CO2 fertilisation counteracts the negative effect of poor water quality on the growth and photosynthesis of a Great Barrier Reef coralline alga’Conspecific interactions between corals mediate the effect of submarine groundwater discharge on coral physiology
Published 30 January 2025 Science ClosedTags: biological response, BRcommunity, chemistry, corals, field, photosynthesis, physiology, respiration, South Pacific
Land-based inputs, such as runoff, rivers, and submarine groundwater, can alter biologic processes on coral reefs. While the abiotic factors associated with land-based inputs have strong effects on corals, corals are also affected by biotic interactions, including other neighboring corals. The biologic responses of corals to changing environmental conditions and their neighbors are likely interactive; however, few studies address both biotic and abiotic interactions in concert. In a manipulative field experiment, we tested how the natural environmental gradient created by submarine groundwater discharge (SGD) affected holobiont and symbiont metabolic rates and endosymbiont physiology of Porites rus. We further tested how the effect of SGD on the coral was mediated by intra and interspecific interactions. SGD is a natural land-sea connection that delivers nutrients, inorganic carbon, and other solutes to coastal ecosystems worldwide. Our results show that a natural gradient of nutrient enrichment and pH variability as a result of acute SGD exposure generally benefited P. rus, increasing gross photosynthesis, respiration, endosymbiont densities, and chlorophyll a content. Conspecifics in direct contact with the a neighboring coral, however, altered the relationship between coral physiology and SGD, lowering the photosynthetic and respiration rates from expected values when the coral had no neighbor. We show that the response of corals to environmental change is dependent on the types of nearby neighbor corals and how neighbors alter the chemical or physical environment around the coral. Our study underscores the importance of considering biotic interactions when predicting the physiologic responses of corals to the environment.
Continue reading ‘Conspecific interactions between corals mediate the effect of submarine groundwater discharge on coral physiology’Multi-interacting global-change drivers reduce photosynthetic and resource use efficiencies and prompt a microzooplankton-phytoplankton uncoupling in estuarine communities
Published 10 January 2025 Science ClosedTags: biological response, BRcommunity, community composition, laboratory, otherprocess, photosynthesis, phytoplankton, protists, South Atlantic, zooplankton
Highlights
- Multi-interacting driver effects were evaluated on South Atlantic estuarine plankton
- Warming×pH×nutrients×UVR reduced the photosynthetic and resource use efficiencies
- A multi-driver change condition prompted a microzooplankton-phytoplankton uncoupling
- Altered trophic interactions could reduce the energy transfer efficiency in food webs
Abstract
Plankton communities are subjected to multiple global change drivers; however, it is unknown how the interplay between them deviates from predictions based on single-driver studies, in particular when trophic interactions are explicitly considered. We investigated how simultaneous manipulation of temperature, pH, nutrient availability and solar radiation quality affects the carbon transfer from phytoplankton to herbivorous protists and their potential consequences for ecosystem functioning. Our results showed that multiple interacting global-change drivers reduced the photosynthetic (gross primary production-to-electron transport rates ratios, from 0.2 to 0.6-0.8) and resource use efficiencies (from 9 to 1 μg chlorophyll a (Chl a) μmol nitrogen-1) and prompted uncoupling between microzooplankton grazing (m) and phytoplankton growth (μ) rates (μ > m). The altered trophic interaction could be due to enhanced intra-guild predation or to microzooplankton growing at suboptimal temperatures compared to their prey. Because phytoplankton-specific loss rates to consumers grazing are the most significant uncertainty in marine biogeochemical models, we stress the need for experimental approaches quantifying it accurately to avoid bias in predicting the impacts of global change on marine ecosystems.
Continue reading ‘Multi-interacting global-change drivers reduce photosynthetic and resource use efficiencies and prompt a microzooplankton-phytoplankton uncoupling in estuarine communities’
