Posts Tagged 'nutrients'

Physiological and transcriptomic responses of a harmful algal bloom-causing dinoflagellate Karenia mikimotoi to multiple environmental factors

Published 12 January 2026 Science Leave a Comment
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Highlights

  • Elevated temperature was the primary factor significantly reducing K. mikimotoi growth and photosynthesis.
  • Increased pCO₂ and high N: P ratios partially mitigated thermal stress induced by elevated temperature.
  • K. mikimotoi consistently up-regulated energy and lipid metabolism to cope with environmental stressors irrespective of treatment.
  • K. mikimotoi may persist and even thrive under multiple stressors, subsequently influencing productivity and biogeochemical cycles.

Abstract

Dinoflagellates play a crucial role in marine food webs and biogeochemical cycles, yet they are increasingly affected by global environmental changes. While there is limited understanding of their response to individual stressors projected under future oceanic conditions, their response to multiple concurrent environmental stressors remains inadequately explored. This study investigated the singular and interactive effects of elevated temperature (26 °C vs. 22 °C), increased pCO2 (1000 μatm vs. 400 μatm), and a high nitrogen-to-phosphorus ratio (N:P = 180:1 vs. 40:1) on the harmful algal bloom-forming dinoflagellate Karenia mikimotoi over a 40-day exposure period. Among these factors, elevated temperature exerted the most pronounced influence, markedly reducing the cell growth rate and photosynthesis while simultaneously increasing the particulate organic matter content and antioxidant level. Transcriptomic analyses indicated that elevated temperature enhanced the expression of genes associated with oxidative stress, suggesting a potential defense mechanism against thermal stress. Notably, increased pCO2 and a high N:P ratio appeared to mitigate thermal stress to some extent. Irrespective of the treatment, K. mikimotoi demonstrated a consistent response strategy characterized by the synergistic upregulation of energy metabolism and lipid biosynthesis pathways, coordinated by the modulation of both upstream and downstream genes in the tricarboxylic acid cycle. This metabolic reprogramming likely facilitates a more efficient allocation of energy, thereby enhancing the resilience of K. mikimotoi to environmental stress. This study underscores the interactive effects of multiple stressors on marine dinoflagellates, highlighting that elevated temperature is the most critical factor affecting dinoflagellates in future oceanic environments.

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Physiological and transcriptomic responses of Sargassum hemiphyllum var. chinense to ocean acidification and nitrogen enrichment

Published 21 November 2025 Science Closed
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Sargassum hemiphyllum var. chinense is a major brown macroalga and has important ecological and economic significance. Ocean acidification and nitrogen enrichment are serious threats to marine ecosystems primarily by altering the physiology of organisms. However, the response of S. hemiphyllum var. chinense to the combined effects of ocean acidification and elevated nitrogen levels remains unclear. This study conducted a 7-day dual-factor experiment to investigate the physiological and transcriptional responses of S. hemiphyllum var. chinense under two CO2 levels (400 μatm and 1000 μatm) and two NO3⁻ levels (50 μmol/L and 300 μmol/L). The results showed that high CO2 and NO3− concentrations promoted the synthesis of photosynthetic pigments including qN and NPQ. Physiological results showed that high CO2 and the combined high NO3− and CO2 treatments enhanced growth rate and NO3− uptake rate, but NR activity was significantly decreased. Transcriptome analysis identified differentially expressed genes involved in oxidative phosphorylation, carbon metabolism, the TCA cycle, and nitrogen metabolic pathways. Notably, genes related to oxidative phosphorylation and TCA cycle were significantly up-regulated under high NO3− and dual-factor treatments, suggesting that carbohydrate metabolism and energy metabolism of S. hemiphyllum var. chinense were significantly enhanced. The qRT-PCR analysis revealed that the expression levels of key genes involved in carbon fixation and nitrogen metabolism, including PFK, PRK, GAPDH, Rubisco, NR, and MDH, were significantly downregulated. These findings elucidate the molecular mechanisms by which S. hemiphyllum var. chinense adapts to ocean acidification and nitrogen enrichment, offering valuable insights for understanding its capacity to withstand changing marine environments.

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Can ocean acidification alleviate carbon deficiency in eelgrass Zostera marina clonal ramets under conditions of nutrients, sulfate and ocean acidification?

Published 16 October 2025 Science Closed
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Highlights

  • The ratio of Chl a/b is reduced by the interaction between CO2 and NO3-N.
  • The interaction between CO2 and NO3-N reduces the soluble sugar contents in leaves.
  • CO2 promotes the content of soluble protein in leaves while reduces that in roots.
  • CO2 reduces both the SOD activities of the rhizomes and the eelgrass mortality rate.
  • Eelgrass has complex carbon supply and conversion mechanisms to ensure its survival.

Abstract

Carbon deficiency in the eelgrass caused by nutrient eutrophication and high concentrations of sulfate causes eelgrass mortality; however, ocean acidification provides sufficient carbon. Thus, it is inferred that ocean acidification might reduce the carbon deficiency. To verify this hypothesis, eelgrass clonal ramets were exposed to 72—h combined conditions of ocean acidification (CO2), nitrate (NO3-N), ammonia (NH4-N), phosphate (PO4-P) and sulfate (SO4-S). The pigment contents were affected by nutrients; however, the Chl a/b ratio was inhibited by the interaction between CO2 and NO3-N and was promoted by interaction between NO3-N and NH4-N. The soluble protein contents in leaves were increased by CO2; however, the soluble protein contents in roots were reduced by CO2. The soluble sugar contents in the leaves had negatively correlation with the interaction between NO3-N and CO2. Moreover, the SOD activities of the rhizomes were inhibited by CO2. All these findings suggest that ocean acidification does not seem to effectively alleviate the deficiency of soluble carbon in eelgrass under eutrophication and high concentrations of sulfate; however, the eelgrass mortality rate was inhibited by CO2 and the interaction between PO4-P and SO4-S. Thus, eelgrass has extremely complex carbon supply and conversion mechanisms to ensure its survival under composite conditions or eelgrass has another mechanism of death in eutrophication.

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Ocean acidification and nitrate enrichment can mitigate negative effects of soft coral (Xenia) competition on hard coral (Stylophora pistillata) endosymbionts

Published 21 August 2025 Science Closed
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The combination of ocean acidification (OA) and eutrophication can undermine the physiological performance of reef-building corals during competition for benthic space, leading to shifts towards non-accreting organisms like soft corals. We conducted a 28-day laboratory orthogonal experiment to test if acidification (950 µatm pCO2) and moderate to high nitrate enrichment (4 and 8 µmolL−1) negatively affect the hard coral Stylophora pistillata while physically competing with the soft coral Xenia spp. We measured photosynthetic efficiency (PE) in hard corals and growth rate, Symbiodiniaceae density, and chlorophyll-a concentration in both hard and soft corals as proxies for their condition and responses to competition. Competition with the soft coral reduced PE, Symbiodiniaceae and chlorophyll-a contents of S. pistillata, while acidification alone and coupled with nitrate enrichment mitigated endosymbiont responses. The growth and chlorophyll-a concentrations of Xenia spp. were decreased by competition, but the soft coral was consistently benefited under nitrate enrichment. These results highlight that competition alone has a stronger negative impact on hard corals than on soft corals. Our study provides experimental evidence on how OA and eutrophication interact and shape coral dynamics, an overlooked but urgent topic in predicting reef futures under environmental 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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Acidification, warming, and nutrient management are projected to cause reductions in shell and tissue weights of oysters in a coastal plain estuary

Published 16 July 2025 Science Closed
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Coastal acidification, warming, and nutrient management actions all alter water quality conditions that marine species experience, with potential impacts to their physiological processes. Decreases in calcite saturation state (ΩCa) and food availability, combined with warming water temperatures, pose a threat to calcifying organisms; however, the magnitude of future changes in estuarine systems is challenging to predict and is not well known. This study aims to determine how and where oysters will be affected by future acidification, warming, and nutrient reductions, and the relative effects of these stressors. To address these goals, an oyster growth model for Eastern oysters (Crassostrea virginica) was embedded in a 3-D coupled hydrodynamic-biogeochemistry model implemented for two tributaries in the lower Chesapeake Bay. Model simulations were forced with projected future conditions (mid-21st century atmospheric CO2 and atmospheric temperature under Representative Concentration Pathway (RCP) 8.5, as well as managed nutrient reductions) and compared with a realistic present-day reference run. Together, all three stressors are projected to reduce ΩCa and growth of oyster shell and tissue. Increased atmospheric CO2 is projected to cause widespread reductions in ΩCa. The resulting reductions in oyster shell and tissue growth will be most severe along the tributary shoals. Future warming during peak oyster growing seasons is projected to have the strongest negative influence on tissue and shell growth, due to summer water temperatures reducing filtration rates, enhancing shell dissolution and oyster respiration rates, and increasing organic matter remineralization rates, thus reducing food availability. Nutrient reductions will exacerbate deficits in oyster food availability, contributing to further reductions in growth. Quantifying the effects of these stressors provides insight on the areas in the lower bay where oysters will be most vulnerable to mid 21st-century conditions.

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Responses of the natural phytoplankton assemblage to Patagonian dust input and anthropogenic changes in the Southern Ocean

Published 10 July 2025 Science Closed
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Abstract

The cumulative effects of multi‐faceted changes on the phytoplankton community of the Southern Ocean (SO) are not yet known, which is a major limitation to predicting the future direction of the biological carbon pump. Thus, our study aimed to estimate the effects of intensified Patagonian dust inputs, warming and acidification on the growth, composition and production of phytoplankton assemblages in the Polar Frontal Zone (PFZ) and the High‐Nutrient Low‐Chlorophyll (HNLC) region of the Indian sector of the SO during the austral summer 2022. Natural phytoplankton communities were incubated for 5‐day under 4 scenarios (present and future conditions, and 2 intermediate scenarios). In the PFZ, +3°C and acidification stimulated the growth of phytoplankton, mainly cyanobacteria, while intensified dust inputs alone did not have notable impact. Conversely, in HNLC waters, the addition of Fe‐dust alone increased the total chlorophyll a of diatoms (mainly F. kerguelensis), whereas the negative effect of acidification and +3°C counteracted the positive impact of dust input on the diatoms. In these waters, future conditions benefited smaller species (haptophytes and cyanobacteria). The net particulate organic carbon production (POC) was also unaltered by future conditions, suggesting that primary production may not change in the future SO. However the increase in the length and number of long‐chain diatoms under future HNLC conditions may indicate that POC export could intensify in the future.

Plain Language Summary

Phytoplankton in the Southern Ocean (SO) play a critical role in absorbing atmospheric carbon dioxide and supporting marine ecosystems, however their response to future environmental changes remains unclear. This study examined how increased dust inputs, warming, and acidification affect the phytoplankton community in two contrasted biogeochemical domains of the SO, the Polar Frontal Zone (PFZ) and the High‐Nutrient Low‐Chlorophyll (HNLC) region. In the PFZ, warming and acidification favored the smaller phytoplankton species, while in the HNLC region, iron‐rich dust stimulated diatom species, though this effect was attenuated by warming and acidification. While overall the production of organic carbon by phytoplankton remained unchanged, diatoms may enhance carbon export to deeper waters under future conditions due to increased number and length of chain‐forming species. These findings highlighted the complexity of phytoplankton responses, which vary across regions and are influenced by interactive environmental factors. Understanding the impact of these environmental factors on phytoplankton is critical to predicting how future changes will shape the role of the SO in the global carbon cycle.

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Physiological and transcriptomic responses of Sargassum hemiphyllum to ocean acidification and nitrogen enrichment

Published 18 June 2025 Science Closed
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Sargassum hemiphyllum is a major brown macroalga and has important ecological and economic significance. Ocean acidification and nitrogen enrichment are serious threats to marine ecosystems primarily by altering the physiology of organisms. However, the response of S. hemiphyllum to the combined effects of ocean acidification and elevated nitrogen levels remains unclear. This study conducted a 7-day dual-factor experiment to investigate the physiological and transcriptional responses of S. hemiphyllum under two CO2 levels (400 μatm and 1000 μatm) and two NO3⁻ levels (50 μmol/L and 300 μmol/L). The results showed that high CO2 and NO3- concentrations promoted the synthesis of photosynthetic pigments including qN and NPQ. Physiological results showed that high CO2 and the combined high NO3- and CO2 treatments enhanced growth rate and NO3- uptake rate, but NR activity was significantly decreased. Transcriptome analysis identified differentially expressed genes involved in oxidative phosphorylation, carbon metabolism, the TCA cycle, and nitrogen metabolic pathways. Notably, genes related to oxidative phosphorylation and TCA cycle were significantly up-regulated under high NO3- and dual-factor treatments, suggesting that carbohydrate metabolism and energy metabolism of S. hemiphyllum were significantly enhanced. The qRT-PCR analysis revealed that the expression levels of key genes involved in carbon fixation and nitrogen metabolism, including PFK, PRK, GAPDH, Rubisco, NR, and MDH, were significantly downregulated. These findings elucidate the molecular mechanisms by which S. hemiphyllum adapts to ocean acidification and nitrogen enrichment, offering valuable insights for understanding its capacity to withstand changing marine environments.

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Carbon dioxide–induced acidification enhances short-lived brominated hydrocarbons production in oligotrophic oceans

Published 18 February 2025 Science Closed
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Oceanic emission is a primary source of brominated very short-lived substances (BrVSLs) to the atmosphere, which have important effects on stratospheric ozone chemistry. Marine biogeochemical processes regulating BrVSLs are often sensitive to ocean acidification. Yet, the response of BrVSLs production to acidification remains poorly understood. Herein, the effects of acidification on the production of two main BrVSLs, dibromomethane (CH2Br2) and tribromomethane (CHBr3), were studied by ship-based incubation experiments at three stations in the South Atlantic and Indian Oceans. The average CH2Br2 and CHBr3 concentrations increased by 17.2–58.7% and 14.3–80.3% due to acidification under the in situ nutrient conditions with nutrient and/or iron limitation at the three stations, but the mechanisms driving these increases varied among different regions. The increased bromoperoxidase (BrPO) activity caused by acidification facilitated BrVSLs release in the Eastern Tropical Indian Ocean, where diatoms were dominant. CHBr3 increased due to acidification as a result of enhanced reactivity of dissolved organic matter (DOM) in the Eastern Tropical Atlantic, where dinoflagellates were dominant. Brominated very short-lived substances increased due to acidification as a result of a combined effect of the above two mechanisms in the Benguela Current Coastal with high phytoplankton abundance. Under the nutrient and/or iron addition conditions with nutrient and iron sufficiency, however, acidification did not promote BrVSLs production due to its only minor effect on the BrPO activity and reactivity of DOM, partly because the effect of increased oxidative stress was offset by that of changed phytoplankton composition. Our study provided a basis for future modeling on the impact of acidification on global BrVSLs emissions.

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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 Closed
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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.

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Iron and phosphorus limitations modulate the effects of carbon dioxide enrichment on a unicellular nitrogen-fixing cyanobacterium

Published 21 January 2025 Science Closed
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Iron (Fe) and phosphorus (P) availability constrain the growth and N2 fixation of diazotrophic cyanobacteria in the global ocean. However, how Fe and P limitation may modulate the effects of ocean acidification on the unicellular diazotrophic cyanobacterium Crocosphaera remains largely unknown. Here, we examined the physiological responses of Crocosphaera watsonii WH8501 to CO2 enrichment under both nutrient-replete and steadily Fe- or P-limited conditions. Increased CO2 (750 μatm vs. 400 μatm) reduced the growth and N2 fixation rates of Crocosphaera, with Fe limitation intensifying the negative effect, whereas CO2 enrichment had a minimal impact under P limitation. Mechanistically, the high CO2 treatment may have led to a reallocation of limited Fe to nitrogenase synthesis to compensate for the reduction in nitrogenase efficiency caused by low pH; consequently, other Fe-requiring metabolic pathways, such as respiration and photosynthesis, were impaired, which in turn amplified the negative effects of acidification. Conversely, under P limitation, CO2 enrichment had little or no effect on cellular P allocation among major P-containing molecules (polyphosphate, phospholipids, DNA, and RNA). Cell volumes were significantly reduced in P-limited and high CO2 cultures, which increased the surface : volume ratio and could facilitate nutrient uptake, thereby alleviating some of the negative effect of acidification on N2 fixation. These findings highlight the distinct responses of Crocosphaera to high CO2 under different nutrient conditions, improving a predictive understanding of global N2 fixation in future acidified oceans.

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The impact of climate change stressors on microbial respiration and community structure: ocean acidification and artificial upwellling

Published 14 January 2025 Science Closed
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Microbial community respiration significantly influences the oceans capacity to sequester CO2 in marine ecosystems. Despite its pivotal role, there remains limited understanding of the variability and magnitude of community respiration in marine ecosystems, especially regarding its sensitivity to climate change stressors. This knowledge gap hinders a comprehensive grasp of its contribution to the global carbon cycle. Traditional in situ approaches for measuring community respiration are subject to several methodological limitations, particularly that of sensitivity in oligotrophic ecosystems, which cover more than 40% of the Earth’s ocean surface. These limitations thus contribute significantly to the uncertainty in global estimates of carbon budgets. To address these challenges, enzymatic techniques such as ETSvitro offer a fast and sensitive method to assess respiratory activity rates at spatial scales that are difficult to cover using conventional approaches. The method involves reducing the tetrazolium salt, INT, within the respiratory chain under substrate saturation levels (i.e., NADH, NADPH, and succinate). However, the reliability of the ETSvitro method has been questioned because it measures potential respiratory activity rather than actual respiration. In response to these concerns, another enzymatic technique, ETSvivo, emerged presumably as a more realistic estimate of actual respiration. Unlike ETSvitro, ETSvivo measures INT under in vivo conditions, utilizing substrates naturally available inside the cell. Nevertheless, before these methods can be considered feasible proxies for community respiration, further evaluation is needed to determine their universal applicability in marine ecosystems. In this thesis, our objective was to improve our understanding of community respiration by addressing its methodological limitations and investigating the drivers responsible for its variability. We paid particular attention to planktonic community structure and the impact of two climate change stressors: ocean acidification and changes in nutrient fertilization. Simulating a typical ETSvivo assay in eight independent experiments using surface coastal and open ocean waters from the Canary region, we observed that INT alone significantly influences the physiological status of bacteria. Bacteria are considered the primary contributors to respiration in oligotrophic environments, but their physiological status is largely affected by the inherent toxicity of INT. Consequently, we question the applicability of the ETSvivo method as a proxy for community respiration in oligotrophic regions. On the other hand, we explore the temporal variability of respiratory metabolism through two mesocosm experiments conducted in the oligotrophic waters of the subtropical Eastern North Atlantic. In the first mesocosms experiment, we investigated the impact of changing community structure and biomass on the temporal variability of community respiration measured through the Winkler method (R), ETS activity, and their ratio (R/ETS) in response to increasing CO2 concentrations and nutrient fertilization (e.g., due to local upwelling events). Our results suggest that community respiration and ETS activity do not respond to CO2 during oligotrophic conditions. However, following fertilization, community respiration increased in the two high CO2 mesocosms coinciding with an increase in microplankton, primarily diatoms. Simultaneously, the R/ETS ratio showed no correlation with community structure or biomass, indicating its variability makes it unsuitable for application with communities undergoing abrupt changes in trophic conditions. In light of these findings, the second mesocosm experiment explored the influence of different upwelling intensities and frequencies (singular pulse versus recurring upwelling) on community respiration. Our results demonstrate that community respiration is sensitive to changes in upwelling intensities but more significantly to the mode in which nutrients are supplied to oligotrophic waters. The planktonic community structure significantly influenced the observed variability in community respiration, revealing notable differences under varying upwelling intensities.The results of this thesis underscore the significance of mitigating methodological uncertainties to achieve precise measurements of respiration rates. It is crucial to adequately assess the impact of climate change-induced stressors, especially ocean acidification and changes in nutrient fertilization, along with planktonic community structure, as drivers of temporal variability. This thorough examination is essential for gaining a deeper understanding and, consequently, making more accurate predictions of community respiration in marine ecosystems.

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Interactive effects of CO2, temperature, and nitrate limitation on the growth and physiology of strain CCMP 1334 of the marine cyanobacterium Synechococcus (Cyanophyceae)

Published 13 December 2024 Science Closed
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The marine cyanobacterium Synecococcus sp. (CCMP 1334) was grown in a continuous culture system on a 12:12 h light:dark cycle at all combinations of low and high pCO2 (400 and 1000 ppmv, respectively), nutrient availability (nitrate-limited and nutrient-replete conditions), and temperatures of 21, 24, 28, 32, and 35°C. The maximum nutrient-replete growth rate was ~1.15 day−1 at 32–35°C. Median nutrient-replete growth rates were higher at 1000 ppmv than at 400 ppmv pCO2 at all temperatures. Carbon:nitrogen ratios were independent of pCO2 at a fixed relative growth rate (i.e., growth rate ÷ nutrient-replete growth rate) but decreased with increasing temperature. Carbon:chlorophyll a ratios were decreased monotonically with increasing temperature and were higher under nitrate-limited than nutrient-replete conditions. Ratios of phycoerythrin to chlorophyll a were independent of growth conditions. Productivity indices were independent of temperature and nutrient limitation but were consistently higher at 1000 ppmv than 400 ppmv pCO2. Both growth rates and dark respiration rates were positively correlated with temperature, and the associated Q10 values were 2.2 and 2.3, respectively. A model of phytoplankton growth in which cellular carbon is allocated to structure, storage, or the light or dark reactions of photosynthesis accounted for the general patterns of cell composition and growth rate. This strain of Synechococcus appears well suited to changes in environmental conditions that are expected as the climate warms in response to anthropogenic emissions of CO2.

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The important role of the antioxidant stress capacity in the response of Prochlorococcus to increased CO2 under varying iron and light conditions

Published 9 December 2024 Science Closed
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Highlights

  • Low-light-adapted Prochlorococcus ecotypes have stronger low-iron adaptation capacity
  • Fe limitation in Prochlorococcus is enhanced under both low growth-limiting light and high photo-inhibitory light
  • High CO2 promotes the growth of low-light-adapted Prochlorococcus ecotypes due to a reduction in cellular oxidation stress

Abstract

Ocean acidification caused by the ongoing increase in atmospheric carbon dioxide (CO2) is expected to impact the growth of marine phytoplankton. Additionally, CO2-driven climate change influences light intensity and iron (Fe) availability in surface seawaters, two critical factors for marine phytoplankton carbon fixation and growth due to their central role in regulating photosynthesis. The cyanobacterium Prochlorococcus often dominates marine productivity in oligotrophic oceans with low but variable Fe concentrations and light intensities. However, the combined effects of light intensity, Fe availability and CO2 concentration on the growth and photosynthesis of Prochlorococcus remain unclear. In this study, we found that the high-light-adapted Prochlorococcus strain MED4, isolated from shallower depths, required much higher Fe concentrations and light intensities to grow than the low-light-adapted strain NATL1A, isolated from deeper depths. Increased CO2 had no effect on the growth of strain MED4 under any light or Fe conditions. In contrast, increased CO2 caused a 29% increase in the growth of strain NATL1A under low Fe coupled with high photo-inhibitory light condition, owing to a reduction in cellular oxidative stress. The varying antioxidant stress capacities of different Prochlorococcus strains appeared to influence their responses to increased CO2. These results indicate complex interactions among light intensity, Fe limitation, and CO2 concentration, which may affect the species distributions and productivities of marine phytoplankton, including Prochlorococcus, in a future high-CO2 ocean.

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Phytoplankton responses to changing irradiance and carbon fertilization

Published 25 November 2024 Science Closed
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Phytoplankton play a crucial role in marine ecosystems due to their innate ability to fix carbon. As atmospheric CO2 levels continue to rise from fossil fuel combustion, the resulting increase in dissolved CO2 and the concurrent decrease in ocean pH are likely to impact the phytoplankton community. The response of phytoplankton to elevated CO2 can vary significantly among species and environmental conditions (e.g. light, temperature, nutrient availability). To address these variations, an experiment was conducted using a controlled photobioreactor system, maintaining high and low light, constant temperature, nutrient levels, and two pCO2 concentrations. This study focused on two regionally relevant phytoplankton in the northern Gulf of Mexico. Skeletonema (a diatom) increased growth rates with the combination of high light and high carbon, but this was not accompanied by increases in particulate organic carbon and nitrogen (POC/N). In contrast, Micromonas commoda (a green alga) did not show changes in growth rate or POC/PON but allocated more energy towards photosynthesis. Additionally, Skeletonema displayed a decoupling between growth rate and silicification, leading to higher biogenic silica content per cell in elevated pCO2 environments. These results highlight the necessity for genera specific and regionally focused research, as the physiological plasticity among phytoplankton can vary.

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Regulation of seawater dissolved carbon pools by environmental changes in Ulva prolifera originating sites: a new perspective on the contribution of U. prolifera to the seawater carbon sink function

Published 21 October 2024 Science Closed
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Highlights

  • Moderate light, temperature and nitrate addition boost U. prolifera DIC absorption.
  • U. prolifera adapts carbon fixation modes to environmental changes.
  • Origin environmental conditions determine U. prolifera’s carbon sink contribution.

Abstract

The Ulva prolifera bloom is considered one of the most serious ecological disasters in the Yellow Sea in the past decade, forming a carbon sink in its source area within a short period but becoming a carbon source at its destination. To explore the effects of different environmental changes on seawater dissolved carbon pools faced by living U. prolifera in its originating area, U. prolifera were cultured in three sets with different light intensity (54, 108, and 162 μmol m−2 s−1), temperature (12, 20, and 28 °C) and nitrate concentration gradients (25, 50, and 100 μmol L−1). The results showed that moderate light (108 μmol m−2 s−1), temperature (20 °C), and continuous addition of exogenous nitrate significantly enhanced the absorption of dissolved inorganic carbon (DIC) in seawater by U. prolifera and most promoted its growth. Under the most suitable environment, the changes in the seawater carbonate system were mainly dominated by biological production and denitrification, with less influence from aerobic respiration. Facing different environmental changes, U. prolifera continuously changed its carbon fixation mode according to tissue δ13C results, with the changes in the concentrations of various components of DIC in seawater, especially the fluctuation of HCO3− and CO2 concentrations. Enhanced light intensity of 108 μmol m−2 s−1 could shift the carbon fixation pathway of U. prolifera towards the C4 pathway compared to temperature and nitrate stimulation. Environmental conditions at the origin determined the amount of dissolved carbon fixed by U. prolifera. Therefore, more attention should be paid to the changes in marine environmental conditions at the origin of U. prolifera, providing a basis for scientific management of U. prolifera.

Continue reading ‘Regulation of seawater dissolved carbon pools by environmental changes in Ulva prolifera originating sites: a new perspective on the contribution of U. prolifera to the seawater carbon sink function’

Elevated pCO2 may increase the edible safety risk of clams exposed to toxic Alexandrium spp.

Published 2 October 2024 Science Closed
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Highlights

  • High pCO2 diversely affects PSTs production of various Alexandrium spp.
  • Elevated pCO2 alters PSTs composition and toxicity in clams than in algae.
  • High pCO2 is beneficial to bioaccumulation of highly toxic PST in clams.
  • Elevated pCO2 inhibits elimination of highly toxic PST components in clams.
  • High pCO2 enhances PSTs toxicity in clams exposed to different Alexandrium spp.

Abstract

Toxic harmful algal blooms (HABs) have received increasing attention owing to their threat to the health of aquatic life and seafood consumers. This study evaluated the impacts of elevated atmospheric partial pressure of CO2 (pCO2) on the production of paralytic shellfish toxins (PSTs) in different Alexandrium spp. strains, together with its further effects on the bioaccumulation/elimination dynamics of PSTs in bivalves contaminated with PSTs from toxic dinoflagellates. Our results showed that elevated pCO2 stimulated the growth of the two Alexandrium spp. (A. catenella and A. pacificum) isolated from the northern and southern coastal areas of China, respectively, and affected PST production including content and toxicity of the two strains differently. Further PSTs bioaccumulation/elimination in PSTs-contaminated Manila clam, Ruditapes philippinarum under high pCO2 also occurred. It is worth noting the biotransformation of neosaxitoxin (NEO) with high toxicity through trophic transfer with effect of elevated pCO2. When in microalgae cultured under the control (410 ppm) and elevated pCO2 conditions (495 and 850 ppm), the proportion of NEO in the PST content produced by A. catenella was reduced from 11.1 to 6.4 and 2.6 %, while the proportion of NEO in A. pacificum was increased from 3.1 to 3.6 and 4.7 %, respectively. NEO accounted for >50 % of total PST contents in clams, which were biotransformed via transfer from dinoflagellates and higher pCO2 enhanced this biotransformation leading to increased NEO accumulation. The negatively affected elimination of PSTs, especially NEO, in clams fed with A. catenella or A. pacificum, indicates that the detoxification of PSTs-contaminated clams may be more difficult under elevated pCO2. This study provides reference for developing models to assess the safety of bivalves under the co-stress of environmental change and toxic HABs, suggesting that ocean acidification may lead to the higher safety risk of Manila clams exposed to toxic HAB dinoflagellates.

Continue reading ‘Elevated pCO2 may increase the edible safety risk of clams exposed to toxic Alexandrium spp.’

Ocean acidification does not prolong recovery of coral holobionts from natural thermal stress in two consecutive years

Published 24 September 2024 Science Closed
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Under predicted future ocean conditions, corals will experience frequent and intense thermal stress events while simultaneously being exposed to chronic ocean acidification. Yet, some corals will likely be more resistant and/or resilient to these predicted conditions than others and may be critical to reef persistence in the future. Following natural thermal stress in two consecutive years (2014 and 2015), we evaluated the effects of feeding and simulated ocean acidification on the physiological recovery of Montipora capitata and Porites compressa sourced from Kāneʻohe Bay and Waimānalo Bay, Hawaiʻi. Following the 2014 thermal stress event, simulated ocean acidification did not slow recovery of the holobiont and feeding enhanced recovery. However, feeding did not decrease susceptibility to the 2015 thermal stress event, and simulated ocean acidification did not increase susceptibility. Recovery strategies employed between species and between sites clearly differed, highlighting that coral reef restoration and management should consider species-level and site-specific vulnerabilities. Overall, our findings call attention to the immediate threat which ocean warming presents, the lack of additional stress to the holobiont from ocean acidification, the importance of heterotrophy in coral resilience, and the potential significance of additional local biotic stressors (i.e., predator outbreaks) for coral resiliency under annual thermal stress.

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Lactiplantibacillus plantarum I induces gonad growth in the queen scallop Aequipecten opercularis (Linnaeus, 1758) under conditions of climate change

Published 19 September 2024 Science Closed
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Climate change has presented a serious problem in recent times, which is why a new approach is being sought in terms of aquacultural food quality. In this study, the influence of temperature increase (by 2 °C) and pH decrease (by 0.2) was investigated on the queen scallop, Aequipecten opercularis (Linnaeus, 1758). Furthermore, the effect of a food-enriched diet with the probiotic culture Lactiplantibacillus plantarum I was assessed in climate-changed conditions. Scallops’ morphometric parameters were measured before the experimental setup and after one month of being kept in controlled conditions. Morphometric parameters included the elongation index, compactness index, convexity index, density index, condition index, meat yield, gonadosomatic index, adductor muscle index, and hepatosomatic index. Climate-changed conditions had no effect on the scallop condition index, meat yield, or hepatosomatic index. Nevertheless, the addition of probiotics to their diet had a positive effect on the queen scallops cultivated under conditions of climate change, influencing positive allometry and the increase of the gonadosomatic indices. On the other hand, the same conditions negatively affected the adductor muscle index of the scallops. To conclude, in the context of climate change conditions, queen scallops could be a good organism of choice that can be very well adapted to the changed environmental conditions, especially with the addition of the lactic acid bacteria culture Lpb. plantarum I.

Continue reading ‘Lactiplantibacillus plantarum I induces gonad growth in the queen scallop Aequipecten opercularis (Linnaeus, 1758) under conditions of climate change’

Interactive effects of ocean acidification and nitrate on Ulva lactuca

Published 2 July 2024 Science Closed
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The global ocean is undergoing gradual acidification and eutrophication which may have significant impacts on macroalgal communities. However, little is known regarding the interactive effects of ocean acidification (OA) and nitrate on Ulva lactuca, a primary producer widely distributed in coastal waters. This study focuses on the possible interactive effects of OA and elevated nitrate levels on physiological parameters of U. lactuca. Higher nitrate levels may increase growth, photosynthesis, respiration, pigment synthesis, Fv/Fm and Effective Quantum Yield, whereas CO2 enrichment may result in a reduction in photosynthesis, pigment content, Fv/Fm and Effective Quantum Yield. Higher nitrate levels increase NO3– uptake rate and nitrate reductase activity, which are further amplified by elevated CO2 levels. However, the stimulation of high nitrate towards pigment synthesis and photosynthesis is negatively affected by elevated CO2 levels. Our results suggest that U. lactuca could potentially increase its biomass in coastal eutrophic waters, and OA in the future is not expected to promote the growth of U. lactuca, but it can enhance its potential biofiltration to remove nitrate from coastal ecosystems.

Continue reading ‘Interactive effects of ocean acidification and nitrate on Ulva lactuca’

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