Diatoms are a major phytoplankton group that plays a critical role in aquatic biogeochemical processes. Their metabolism relies on trace metals as cofactors for numerous enzymes, and changes in seawater pH may therefore influence metal sorption. Here, we investigated the effects of pH variability on diatom growth and trace-metal sorption using neutron activation analysis (NAA). Although NAA has rarely been applied to phytoplankton, we demonstrate its suitability for marine diatom samples. Overall, diatoms exposed to CO2 treatment exhibited higher cell abundance but lower intracellular elemental concentrations. In particular, Nitzschia navis-varingica showed significantly lower concentrations of Al, Ce, Co, Cr, Fe, Mg, Mn and Zn under the CO2 treatment. These trends are consistent with previous studies. For example, Zinc, which is a cofactor in many enzymes, plays a role in inorganic carbon acquisition; under lower pH, reduced enzymatic metal requirements likely explain the lower Zn concentrations observed. Nitzschia navis-varingica also had significantly lower levels of Co under lower pH. Both Thalassiosira pseudonana and Nitzschia navis-varingica showed lower Fe concentrations under CO2 treatment. As Iron is required for photosynthetic and respiratory processes that support the carbon-concentrating mechanism (CCM), reduced CCM activity at lower pH may decrease Fe demand. Overall, this study highlights NAA as a robust approach for quantifying metal sorption in marine organisms and provides new insight into the effects of ocean acidification on the growth and elemental composition of diatoms.
Continue reading ‘The impact of ocean acidification on the sorption of trace metals by diatoms’Posts Tagged 'phytoplankton'
Ocean acidification drives species-specific and time-dependent pigment responses in three phytoplankton taxa
Published 9 September 2026 Science ClosedTags: biological response, BRcommunity, growth, laboratory, light, multiple factors, photosynthesis, physiology, phytoplankton, respiration
Phytoplankton are primary producers in marine ecosystems and play a central role in biogeochemical cycles, yet their physiological responses to altered seawater pH vary among taxa and over time. Here, we examined the effects of sustained pH manipulation on pigment composition, growth, and dark respiration in three ecologically important phytoplankton taxa – a diatom (Pseudo-nitzschia spp.), a dinoflagellate (Heterocapsa pygmaea), and a haptophyte (Emiliania huxleyi) – during a 15-day controlled laboratory experiment. Cultures were maintained at pH 8.1, 7.8, and 7.5, representing present-day and enhanced acidification conditions. Responses to pH were species-specific and strongly time-dependent. Growth and cell-specific respiration rates showed relatively small and often transient differences among pH treatments, suggesting short-term metabolic adjustment under altered pH. In contrast, pigment composition exhibited clearer and more consistent pH-related responses, primarily expressed as shifts in temporal patterns rather than uniform directional changes. In Pseudo-nitzschia spp. and H. pygmaea, several key pigments displayed pronounced pH-dependent trajectories, whereas E. huxleyi showed greater temporal variability and weaker separation among pH treatments. Overall, these results demonstrate that photophysiological traits respond sensitively to sustained pH changes even when population-level growth and respiration remain comparatively stable, highlighting pigment composition as a potentially sensitive indicator of short-term phytoplankton acclimation to ocean acidification.
Continue reading ‘Ocean acidification drives species-specific and time-dependent pigment responses in three phytoplankton taxa’A hidden driver of the greenhouse effect: production mechanisms and climate implications of N2O derived from marine planktonic ammonia-oxidizing archaea
Published 18 August 2026 Science ClosedTags: biogeochemistry, phytoplankton, review
Nitrous oxide (N2O) is a potent and long-lived greenhouse gas, and the ocean represents its primary natural source. An accurate understanding of the emission intensity and driving mechanisms of oceanic N2O directly affects the estimation of atmospheric N2O budget and the projection of climate change. Recent studies have demonstrated that ammonia-oxidizing archaea (AOA) dominate nitrification in marine environments and are thus recognized as an important biological source of marine N2O production. However, their specific metabolic pathways, regulatory mechanisms, and environmental response patterns remain poorly understood. This paper systematically reviews the spatial distribution characteristics of marine N2O and its major biogeochemical sources, with a particular focus on the potential metabolic pathways and key intermediates involved in AOA-derived N2O production. We further synthesize the current understanding of how environmental factors—including dissolved oxygen, pH, temperature, substrate availability, and organic carbon—regulate AOA nitrogen metabolism and N2O generation. In addition, we discuss the potential mechanisms underlying the shift in AOA metabolic strategies and variations in N2O yield under multifactorial coupling scenarios the scenario of multifactorial coupling. On this basis, we identify the major knowledge gaps in existing research, particularly regarding culture systems, mechanistic elucidation, in situ validation, and global-scale quantification. Finally, we proposed future research directions for AOA-derived N2O emissions under ongoing oceanic changes. This review aims to advance the understanding of the biogeochemical mechanisms governing marine N2O production and to provide a theoretical basis for improving the parameterization of marine nitrogen cycle and climate models.
Continue reading ‘A hidden driver of the greenhouse effect: production mechanisms and climate implications of N2O derived from marine planktonic ammonia-oxidizing archaea’Short-term pH variability reshapes phytoplankton and microzooplankton communities in the northern Indian Ocean
Published 17 August 2026 Science ClosedTags: biological response, community composition, Indian, laboratory, otherprocess, photosynthesis, physiology, phytoplankton
Phytoplankton and microzooplankton (MZP) are key components of marine food webs, driving carbon transfer through the microbial loop. Short-term laboratory microcosm bottle incubations using seawater from the Bay of Bengal (BoB) and Arabian Sea (AS) in 2022 examined the effects of reduced pH. Phytoplankton biomass (Chl-a) remained stable or increased by up to 12% under low pH, suggesting reduced grazing or improved prey quality. MZP diversity (Shannon index, H′) showed basin-specific responses. In the BoB (Exps. 1–2), H′ ranged 2.00–3.70 with high evenness (J′ = 0.93–1.00) and slight declines under medium acidification (ΔpH = 0.2). In contrast, the AS (Exps. 3–4) showed wider variability (H′ = 0.00–3.63) and greater sensitivity, with sharp diversity losses under stronger acidification (ΔpH = 0.4). AS assemblages showed pronounced richness declines (D′ = 2.85–0.00), whereas BoB communities remained stable. Regional and pH-related differences were linked to shifts in ciliates and dinoflagellates. Autotrophic bacteria sustained under low pH, while heterotrophic bacteria increased later, indicating altered microbial-loop functioning. Overall, pH, chlorophyll-a, and heterotrophic bacteria structured the community, accounting for > 65% of the variation. Thus, short-term acidification reshapes MZP assemblages and may modify trophic interactions across the northern Indian Ocean.
Continue reading ‘Short-term pH variability reshapes phytoplankton and microzooplankton communities in the northern Indian Ocean’Ocean acidification alters phytoplankton diversity and community structure in the coastal water of the East China Sea
Published 4 August 2026 Science ClosedTags: biological response, community composition, field, laboratory, mesocosms, North Pacific, otherprocess, physiology, phytoplankton, primary production, respiration
Anthropogenic CO2 emissions and their continuous dissolution into seawater lead to seawater pCO2 rise and ocean acidification (OA). Phytoplankton groups are known to be differentially affected by carbonate chemistry changes associated with OA in different regions of contrasting physical and chemical features. To explore responses of phytoplankton to OA in the Chinese coastal waters, we conducted a mesocosm experiment in a eutrophic bay of the southern East China Sea under ambient (410 µatm, AC) and elevated (1000 µatm, HC) pCO2 levels. The HC condition stimulated phytoplankton growth and primary production during the initial nutrient-replete stage, while the community diversity and evenness in both pCO2 treatments were reduced during this stage due to the rapid nutrient consumption and diatom blooms, and the subsequent shift from diatoms to hetero-dinoflagellates led to a decline in primary production during the mid and later phases under nutrient depletion. HC treatment suppressed the diatom-to-dinoflagellate succession and enhanced the subsequent remineralization of organic matter, thereby facilitating smaller phytoplankton to dominant and sustaining primary production. Our findings indicate that, the impacts of OA on phytoplankton diversity in the coastal water of the southern East China Sea depend on availability of nutrients, with primary productivity and biodiversity of phytoplankton reduced in the eutrophicated coastal water.
Continue reading ‘Ocean acidification alters phytoplankton diversity and community structure in the coastal water of the East China Sea’Freshwater forcing along the Indian Coastal Seas: impacts on productivity and acidification
Published 31 July 2026 Science ClosedTags: biological response, Indian, phytoplankton
Freshwater fluxes from precipitation and river runoff play a critical role in modulating upper-ocean stratification, nutrient availability, and biogeochemical processes in the coastal waters of the Indian subcontinent. The formation of the barrier layer thickness (BLT) links freshwater input to vertical mixing, influencing both productivity and carbonate chemistry. High-resolution (5 km) MITgcm-BLINGv2 simulations are conducted for the Arabian Sea (AS) and the Bay of Bengal (BoB), and sensitivity experiments are performed to represent reduced and increased freshwater perturbations. We analyzed seasonal variability of buoyancy frequency (N2), mixed layer depth (MLD), net primary productivity (NPP), pH, and phytoplankton biomass across five coastal regions. Reduced freshwater scenarios weakened or eliminated BLT, leading to deeper MLD and N2 maxima, with subsurface nutrient-rich waters entrained upward. This enhanced nutrient availability increased NPP in the coastal regions. However, the upward transport of subsurface carbon also lowered surface pH by 0.03, indicating a trade-off between biological enhancement and increased surface acidification. In the increased freshwater scenario, the BLT strengthened, the MLD shoaled, and NPP decreased, while surface pH increased due to reduced vertical carbon exchange. Interestingly, stratification deepening under reduced freshwater input is more pronounced in the southeastern AS than in the BoB, contrasting conventional understanding. Vertical phytoplankton responses are consistent with these trends, with small and large phytoplankton biomass increasing under weaker BLT and decreasing under enhanced BLT. Freshwater-driven BLT modulation drives a complex interplay between carbon uptake and export along Indian coastal waters. These findings emphasize the importance of accurately representing freshwater fluxes in biogeochemical models to capture regional ecosystem responses.
Continue reading ‘Freshwater forcing along the Indian Coastal Seas: impacts on productivity and acidification’Interplay between nutrient limitation and ocean acidification: plankton community shifts in the oligotrophic western Bay of Bengal
Published 30 July 2026 Science ClosedTags: biological response, community composition, Indian, morphology, multiple factors, nutrients, otherprocess, phytoplankton
Highlights
- Nutrient limits the phytoplankton growth in the Bay of Bengal due to stratification.
- Picoplankton dominated the phytoplankton community in the Bay.
- An increase in phytoplankton biomass was observed in response to ocean acidification (OA) in nutrient-rich regions.
- Decrease in phytoplankton biomass, bacteria and microzooplankton abundance was found in the nutrient-poor regions.
- Nutrient limitation overshadow the ocean acidification impact in the Bay of Bengal.
Abstract
The perennial rise in atmospheric carbon dioxide (CO2) from anthropogenic activities increased oceanic carbon uptake, thereby lowering seawater pH. Rapid ocean acidification (OA) by 2 to 3 times than other regions of the same latitudinal belts was reported in the Bay of Bengal (BoB) due to the deposition of atmospheric pollutants, in addition to the dissolution of atmospheric CO2. Therefore, the impact of OA on phytoplankton composition is hypothesized to be greater in the BoB than elsewhere in the globe. On the other hand, the BoB experiences intense oligotrophic conditions due to strong stratification driven by nutrient-poor freshwater discharge from major rivers, which is the primary bottleneck for phytoplankton growth, rather than carbon. It is hypothesized that nutrient limitation may overshadow OA’s impact on plankton in the BoB. To test this hypothesis, six microcosm experiments were conducted in the western BoB between 13 and 20°N with different nutrient levels in the surface waters. The pH of the surface water was adjusted by 0.2 units below the ambient pH using CO2 gas bubbling to simulate the projected OA scenario for the year 2100. Following pH adjustment, incubations were carried out for three days. Picoplankton dominated the phytoplankton community (∼96%) at all stations, with prochlorophytes as the dominant group. Among the phytoplankton, procholorophytes, diatoms, and prymeniophytes increased due to OA across all stations, while other groups of phytoplankton were declined. The increase in phytoplankton biomass was observed in the nutrient-rich stations, while a decrease in phytoplankton biomass, bacteria and microzooplankton abundance was found in the nutrient-poor stations, suggesting that nutrient availability dominated over the OA. Under a business-as-usual scenario, an increase in stratification due to melting Himalayan glaciers is projected, leading to strong stratification and reduced nutrient inputs through vertical mixing in the future in the BoB. Under such a scenario, nutrient limitation may possibly overshadow the OA impact in the future, despite a rapid decline in pH driven by increased CO2 dissolution and deposition of atmospheric pollutants.
Continue reading ‘Interplay between nutrient limitation and ocean acidification: plankton community shifts in the oligotrophic western Bay of Bengal’Experimental evidence of climate change effects on plankton community respiration in European coastal waters: current insights and knowledge gaps in tested disturbances and studied areas
Published 29 July 2026 Science ClosedTags: biological response, community composition, otherprocess, phytoplankton, respiration, review
Plankton community respiration (PCR) plays a central role in aquatic ecosystems, driving the breakdown of organic matter and influencing global carbon cycling through its contribution to the production and consumption of carbon and oxygen. Coastal areas are regarded as metabolic hotspots in the oceans, due to their intense biological and biogeochemical activities. This review synthesizes experimental evidence to explore how environmental constraints and climate drivers affect PCR in European coastal waters. In total, 46 studies were found in which PCR was measured during experiments testing the effects of one or multiple global climate change drivers in European coastal waters. Among them, the majority of experiments focused on changes in temperature, nutrient concentrations and stoichiometry, and/or pH, while other stressors were less studied. In addition to this qualitative synthesis, a quantitative meta-analysis was conducted on warming and acidification experiments, the only drivers for which comparable experimental designs were available. This analysis, based on 19 warming and 6 acidification studies, was used to perform a standardized comparison of effect sizes across studied areas and experimental set-ups. This review highlights critical knowledge gaps, notably regarding non- and understudied areas and understudied interactions between stressors that occurs jointly in ecosystems.
Continue reading ‘Experimental evidence of climate change effects on plankton community respiration in European coastal waters: current insights and knowledge gaps in tested disturbances and studied areas’Warming and acidification alter essential fatty acid profiles in marine diatom Skeletonema marinoi
Published 28 July 2026 Science ClosedTags: biological response, BRcommunity, laboratory, molecular biology, North Atlantic, physiology, phytoplankton
Marine diatoms are key components of the planetary ocean, playing crucial roles in trophic networks: fixing carbon, producing fatty acids (FA) that cannot be synthesized de novo by higher trophic organisms. To better comprehend how the combined action of climatic change influences the dietary value and the impacts on the upper trophic levels, we used a 2 × 2 factorial experiment to investigate how the FA profiles of Skeletonema marinoi changed in response to the individual and combined effects of warming (7, 19°C) and acidification (400, 1 000 ppm CO2). Three S. marinoi strains were exposed for ~ 40 weeks to ambient conditions, warming, acidification and their combination and analyzed for FA profiles, focusing on polyunsaturated (PUFA), omega-3 and omega-6 FA. We found that omega-3 FA increased under warming exposure, while acidification alone led to lower omega-3/omega-6 ratios. In contrast, the ratios increased under warming, alone or coupled with acidification, in all three strains, indicating better food quality for higher trophic levels. Our results suggest the long-term exposure to both drivers will help the marine diatoms to acclimatize to their combined effects, allowing them to buffer the changes brought by warming and ocean acidification.
Continue reading ‘Warming and acidification alter essential fatty acid profiles in marine diatom Skeletonema marinoi’Climate change and aquatic ecosystems: impacts on salinity, species survival, and ecological resilience
Published 29 June 2026 Science ClosedTags: biological response, fisheries, mesocosms, mortality, phytoplankton, reproduction, review, salinity
Highlights
- Unveils Climate-Driven Disease Mechanisms Across Aquatic Systems.
- Integrates Multistressor Impacts Including Pollution, Eutrophication, and Salinity Fluctuations.
- Explores Shifts in Species Distribution, Reproduction, and Food Web Dynamics.
- Highlights Adaptive Traits and Resilience Mechanisms in Aquatic Organisms.
- Provides Science-Based Recommendations for Climate-Responsive Management.
Abstract
Climate change is rapidly transforming aquatic ecosystems, posing complex environmental challenges with far-reaching ecological and socio-economic implications. Rising temperatures, sea-level rise, altered precipitation patterns, shifting hydrological regimes, and sea-ice loss are intensifying pressures on coastal, estuarine, freshwater, and polar systems. These stressors contribute to habitat degradation, increased frequency of hypoxic events, and altered species distributions. Crucially, while some dual stressors, such as warming and acidification, can paradoxically increase primary producer biomass, our findings reveal that this resultant biomass often accumulates as detritus rather than being efficiently transferred to higher trophic levels. This observation directly challenges the simplistic assumption that “more growth” is invariably beneficial, highlighting complex indirect effects on food web dynamics and ecosystem function. Ecological perturbations propagate through trophic networks, resulting in biodiversity loss, reduced ecosystem resilience, and declining fisheries productivity, thereby threatening food security and coastal livelihoods. Marine and freshwater organisms are increasingly exposed to multiple, interacting stressors, including warming, acidification, salinity fluctuations (requiring distinct osmoregulatory strategies, e.g., heterosmotic regulation in teleosts vs. isosmotic intracellular regulation in crustaceans), pollution, and overexploitation. These cumulative pressures can exacerbate disease outbreaks, modify host–pathogen dynamics, and facilitate the emergence and spread of aquatic pathogens, with consequences for ecosystem stability and human health. In aquaculture systems, climate-driven stress often acts synergistically with anthropogenic disturbances, amplifying production risks and economic vulnerability. Furthermore, anthropogenic infrastructure like reservoirs can act as unintended hubs facilitating species dispersal following extreme events like floods, altering community structures. At the biogeochemical scale, climate-induced alterations in nutrient cycling, primary productivity, and carbon sequestration are reshaping ecosystem functioning, particularly in high-latitude and freshwater environments where adaptive capacity is comparatively constrained. Changes in food web architecture and energy transfer efficiency further compromise ecosystem services. This review specifically centers on the biological and ecological mechanisms underlying these climate-driven changes, including organism-level stress responses, shifts in species interactions, and alterations in pathogen dynamics. Recognizing the societal implications and public discourse surrounding climate change underscores the urgency of examining its tangible impacts on sensitive environments, such as estuarine ecosystems, which serve as critical interfaces between terrestrial and marine realms and are thus highly susceptible to both climatic shifts and human influence.
Continue reading ‘Climate change and aquatic ecosystems: impacts on salinity, species survival, and ecological resilience’Response of HAB-forming microalgae competition to ocean acidification, warming, and changing light fields
Published 17 June 2026 Science ClosedTags: algae, biological response, BRcommunity, community composition, growth, laboratory, light, multiple factors, otherprocess, phytoplankton, temperature
In recent years, the East China Sea (ECS) has experienced frequent harmful algal blooms (HABs), driven by the complex interplay of climate change—specifically ocean warming and acidification—and eutrophication-induced light attenuation. Despite their ecological significance, the interactive effects of these environmental stressors on the competitive dynamics between bloom-forming microalgae remain poorly understood. This study aimed to elucidate how warming, reduced light, and elevated CO2 influence the competition between two dominant diatoms. We conducted controlled monoculture and mixed-culture experiments using two key species: Skeletonema costatum and Chaetoceros curvisetus. The experimental design incorporated varying levels of CO2, temperature, and light intensity to simulate future coastal scenarios. Growth rates, peak cell densities, and successional patterns were monitored to assess competitive outcomes under multiple stressors. Monoculture results indicated that high temperature and low light intensity promoted the growth of both species. However, in mixed cultures, these conditions significantly accelerated the time to reach peak density and induced a definitive successional shift from S. costatum to C. curvisetus. Notably, while the general successional pattern was consistent, elevated CO2 further enhanced the competitive advantage of C. curvisetus, particularly when combined with high-temperature and low-light scenarios. These findings suggest that the synergy of future warming, declining light availability, and intensified ocean acidification in the ECS will likely favor C. curvisetus over S. costatum. This shift may increase the frequency of HAB events dominated by C. curvisetus, driving significant climate-related restructuring of phytoplankton communities in coastal ecosystems.
Continue reading ‘Response of HAB-forming microalgae competition to ocean acidification, warming, and changing light fields’Coastal phytoplankton response to acidification and warming under differing levels of nutrient availability
Published 12 June 2026 Science ClosedTags: biological response, community composition, mesocosms, multiple factors, nutrients, otherprocess, photosynthesis, phytoplankton, South Pacific
Ocean acidification and warming will alter phytoplankton biomass and composition, yet despite numerous studies, there are few consistent responses on which to base predictions. To determine the responses of chlorophyll-a and phytoplankton size and composition to predicted lower pH (−0.33 to −0.5) alone, and also combined with elevated temperature (+2.5–3.5 °C), two mesocosm experiments were carried out in austral spring and autumn in temperate New Zealand coastal waters. Lower pH alone had no effect on chlorophyll-a in either experiment and, as the treatment pH was lower than the pH minimum recorded in a parallel four-year time series, this lack of response in chlorophyll-a was not attributable to prior in situ exposure. Conversely, chlorophyll-a increased under lower pH and warming in both experiments, with the large (>20 µm) phytoplankton size fraction showing opposing responses under nutrient deplete and replete conditions. Diatom biomass also increased in both treatments when nutrient availability was maintained, with a dominant pennate species Cylindrotheca clostridium emerging. The results highlight the value of contextual time series for experimental interpretation, and also the importance of assessing warming and acidification together using regionally representative nutrient concentrations, for prediction of coastal phytoplankton response to climate change.
Continue reading ‘Coastal phytoplankton response to acidification and warming under differing levels of nutrient availability’Darkness and body size shaped end-Cretaceous marine extinction patterns
Published 29 May 2026 Science ClosedTags: communitymodeling, modeling, paleo, phytoplankton
The Chicxulub asteroid impact at the Cretaceous–Paleogene (K–Pg) boundary (66 Ma) is thought to have caused the extinction of around 75% of species in the fossil record by triggering catastrophic environmental changes1. However, despite decades of research, the mechanisms linking the environmental changes to the selective extinction patterns observed in the marine fossil record remain unresolved. Here we use a global trait-based ecosystem model2,3 to establish this causality for the marine plankton community beyond the fossilized groups. Our model simulates diversity dynamics during the initial 100 years after the K–Pg boundary and represents explicitly extinction based on biomass thresholds that scales with body size. Under K–Pg climatic forcings, the model reproduces successfully key observed extinction patterns, including the high vulnerability of planktic foraminifera and other zooplankton, the survival of small mixotrophs4 and phytoplankton5,6, and potential for reduced diversity loss in high-latitude settings7. Our analysis suggests that impact-driven darkness and body-size-dependent extinction thresholds drove most of the observed extinction patterns. These results suggest that plankton ecologies enhance survival through differences in energy demand and acquisition. Our study bridges the gap between fossil evidence of extinction patterns and the K–Pg impact winter hypothesis, highlighting the value of trait-based models for understanding past biodiversity crises.
Continue reading ‘Darkness and body size shaped end-Cretaceous marine extinction patterns’Carbon allocation strategy of Thalassiosira weissflogii in response to elevated pCO2
Published 25 May 2026 Science ClosedTags: adaptation, biological response, laboratory, molecular biology, otherprocess, photosynthesis, physiology, phytoplankton
Diatoms are of significance in the marine ecosystem, playing a pivotal role in the sustenance of marine life and the transfer of carbon from the surface ocean to deeper waters. Although numerous studies have investigated the effects of elevated carbon dioxide (CO2) on marine diatoms across both short- and long-term adaptation scales, the molecular mechanisms governing chitin metabolism in response to ocean acidification remain poorly understood. In this study, we employed an integrated approach combining transcriptomic, metabolomic, and physiological analyses to examine the marine diatom Thalassiosira weissflogii following 40-day acclimation to high-CO2 conditions. Physiological studies have demonstrated that ocean acidification has the capacity to result in an augmentation of the C/N ratio, chitin content, maximum PSII quantum yield (Fv/Fm), and photosynthetic pigment content of T. weissflogii. Analysis of chlorophyll fluorescence dynamics further demonstrated enhanced primary photochemical efficiency of PSII in the acidified treatment group. Consistent with this, the transcriptome results also showed that the photosynthesis-related pathways were upregulated to meet the increased material and energy requirements after adaptation to elevated CO2 levels. More importantly, it was determined that acidification treatment resulted in the upregulation of chitin synthesis and the downregulation of chitin degradation in T. weissflogii, consequently leading to an augmentation in chitin content. These findings indicate that ocean acidification (high CO2, low pH) prompts T. weissflogii to prioritize the allocation of carbon resources to the synthesis of chitin. The synthesis of chitin may reinforce cell wall formation as an adaptive response to ocean acidification. Our research provides new insights into the marine acidification adaptation strategies of T. weissflogii.
Continue reading ‘Carbon allocation strategy of Thalassiosira weissflogii in response to elevated pCO2’Divergent responses of the diatom Thalassiosira weissflogii to ocean acidification during light and dark periods
Published 11 May 2026 Science ClosedTags: biological response, laboratory, light, multiple factors, physiology, phytoplankton, temperature
Given the limited understanding of discrepancies in responses of diatoms to ocean acidification (OA), we comparatively investigated the physiological and transcriptional performances of a diatom Thalassiosira weissflogii acclimated to OA (pHt drop of 0.35–0.41) between day and night periods. We found that OA enhanced its specific growth rate (up to 10%) in the light period by upregulating light reaction, Calvin cycle and H+ pumps to cope with the decreased pH. On the other hand, OA reduced its apparent specific growth rate (14%) in the dark period due to additive pH drop caused by OA-enhanced respiratory CO2 release. In the dark period, the cells could not effectively cope with the decreased pH since H+ pumps were downregulated. Consequently, OA did not affect cell growth during a 24 h diel cycle. These findings suggest that daytime positive and night negative effects of OA on diatoms could be responsible for differential results observed under different conditions, with implications for possible seasonal and latitudinal effects of OA.
Scientific Significance Statement
Progressive ocean acidification (OA) due to continuous dissolution of anthropogenic CO2 into seawater is known to affect diatoms that contribute to approximately 20% of the Earth’s primary production. However, impacts of OA on diatoms through a daily cycle remain poorly understood. Our data provide compelling evidence from both physiological and molecular aspects that OA enhances growth of a diatom during the light period by upregulating its photosynthetic CO2 fixation against the stress of decreased pH, but decreases its apparent specific growth rate during the night period due to the aggravated stress of pH drop from respiratory CO2 release overlaid with OA. These findings align well with transcriptional imprints, suggesting the essential role of light in modulating the effects of OA on diatoms, with implications for possible seasonal and latitudinal effects of OA given the changing lengths of daytime.
Continue reading ‘Divergent responses of the diatom Thalassiosira weissflogii to ocean acidification during light and dark periods’Projected future of African marine ecosystems under climate change and stratospheric aerosol injection
Published 8 May 2026 Science ClosedTags: biological response, modeling, multiple factors, North Atlantic, phytoplankton, regionalmodeling, salinity, temperature
Stratospheric Aerosol Injection (SAI) has been proposed as a potential strategy to cool the planet. The ARISE-SAI-1.5 approach, which employes a moderate emission scenario, is simulated to limit future global warming to 1.5°C by injecting aerosols into the stratosphere in the year 2035. However, the climate response to this SAI scenario, particularly along the African coast, remains unclear. In this study, we investigate the potential impacts of climate change under the SSP2-4.5 scenario and ARISE-SAI-1.5 on regional African marine ecosystems through key biological (chlorophyll), physical (salinity, temperature), and chemical (nitrate, acidification, and dissolved oxygen) parameters. Our results indicate that climate change may reduce productivity in African coastal ecosystems, with chlorophyll concentrations decreasing between 10% and 62%. Sea surface temperatures are projected to rise by 1.5°C along the entire coast by 2069, while surface salinity increases up to 0.3 g/kg, except for a slight decrease of up to 0.1 g/kg along the Congolese-Angolan coast. This salinity dipole in the Gulf of Guinea results from enhanced precipitation and river discharge, reinforced by stratification that traps freshwater at the surface. Additionally, climate change drives ocean acidification and may expand the oxygen minimum zone in the Gulf of Guinea, with oxygen levels decreasing by 10%–30% at depths of 100–200 m. Although ARISE-SAI-1.5 may help reduce surface oxygen depletion, it may not significantly mitigate subsurface oxygen loss or continued acidification. Nevertheless, it may reduce some negative climate change impacts on marine ecosystems by stabilizing chlorophyll levels, sea surface temperatures, and salinity.
Plain Language Summary
Stratospheric Aerosol Injection is being explored as a way to cool the planet and limit future global warming, for instance, to 1.5°C in the scenario we explore here (ARISE-SAI-1.5). However, its effects on the ocean, especially along the African coast, are not fully understood. This study examines key factors such as chlorophyll, water temperature, salinity, and oxygen levels to assess changes in marine ecosystems. Our findings show that climate change could reduce productivity, with chlorophyll levels dropping by 10%–62%. Sea surface temperatures are expected to rise by 1.5°C by 2069, and salinity will increase along most coastal areas. The low-oxygen zone in the Gulf of Guinea may expand, making deep waters less habitable for marine life. While the SAI we study here helps slow oxygen loss near the surface, it does not prevent deeper waters from losing oxygen or the ocean from becoming more acidic. However, it can still reduce some harmful effects of climate change by stabilizing chlorophyll levels, temperatures, and salinity.
Continue reading ‘Projected future of African marine ecosystems under climate change and stratospheric aerosol injection’Evaluating the role of seaweed farming in ocean acidification mitigation: insights from high-frequency observations
Published 5 May 2026 Science ClosedTags: algae, biological response, field, mitigation, North Atlantic, phytoplankton
The oceanic uptake of anthropogenic CO2 has resulted in ocean acidification (OA). Macroalgae farming has the potential to mitigate OA by removing CO2 from the surface water via photosynthesis. However, continuous in-situ observations of marine carbonate chemistry related to macroalgae farming remain limited, leaving its effectiveness in addressing OA uncertain. To address these knowledge gaps, this study examined a 2-acre Saccharina latissima, sugar kelp, farm located at Point Judith, Rhode Island, as a case study to assess the potential of sugar kelp aquaculture in mitigating local OA. Over the full growing season from December 2022 to May 2023, high-temporal-resolution (every 30–60 minutes) measurements of surface temperature, salinity, dissolved oxygen and pH were taken inside and outside the kelp farm. The results demonstrate that sugar kelp farming does not significantly impact the carbonate system, thus providing negligible OA mitigation locally. Specifically, a temporary, local-scale CO2 reduction and higher pH occurred during very early kelp growth in early February, but was reversed by a higher surface CO2, exaggerating OA, starting in mid-February. Over the entire observation period, kelp growth resulted in a 5.1 ± 11.6 μatm increase of pCO2 per week compared to the control site in the surface, a signal which is small compared to the substantial natural variability. However, the minimal pCO2 difference at the kelp farm may be reflective of the relatively small cultivation area (2 acres) or depressed growth of phytoplankton, resulting from nutrient competition between the kelp and in-situ phytoplankton. This study underscores the need for future sustained observations to evaluate the impact of seaweed cultivation on OA mitigation and the carbon cycle at the ecosystem scale.
Continue reading ‘Evaluating the role of seaweed farming in ocean acidification mitigation: insights from high-frequency observations’Coccolithophore genetic diversity, morphology, and contribution to particulate inorganic carbon production in Western North American coastal waters
Published 27 April 2026 Science ClosedTags: abundance, biogeochemistry, biological response, chemistry, field, molecular biology, morphology, North Pacific, phytoplankton
Coccolithophores, as calcifying phytoplankton, play a critical role in the global carbon cycle by producing calcium carbonate (CaCO3) in the ocean through their calcitic coccoliths. Here we examine Gephyrocapsa huxleyi (formerly Emiliania huxleyi) and related species abundance and genetic diversity along the West Coast of North America from samples taken on the 2021 NOAA West Coast Ocean Acidification (WCOA21) cruise, along the margin from British Columbia, Canada, to San Diego, California, USA. Significant carbonate chemistry gradients were observed across 17 transects, mostly in the onshore-offshore and north-to-south direction. Abundance and morphometrics of Gephyrocapsa spp. was evaluated using real-time PCR of mitochondrial cytochrome c oxidase subunit 3 ( cox3 ) gene and by microscopy. Variation in PIC concentrations, G. huxleyi and related species abundance, and coccosphere thickness were found to be associated with the gradients in carbonate chemistry and nutrient concentrations (phosphate, nitrate, nitrite, ammonium) across stations sampled during the cruise. We identified 5 unique amplicon sequence variants (ASVs) of Gephyrocapsa spp. cox3 that systematically varied in relative abundance across the California Current System. Southern California locations had greater diversity in cox3 sequences than northerly locations. These analyses represent baselines for evaluation of the impacts of future environmental changes in coastal waters along this productive upwelling regime.
Continue reading ‘Coccolithophore genetic diversity, morphology, and contribution to particulate inorganic carbon production in Western North American coastal waters’Seawater acidification accelerates growth but hastens decline in batch cultures of the marine diatom Thalassiosira pseudonana
Published 22 April 2026 Science ClosedTags: biological response, growth, laboratory, photosynthesis, physiology, phytoplankton
Diatoms are characterized by rapid cell division and a high capacity to adapt to environmental variability, and some species can form blooms when environmental conditions are favorable. Previous studies have largely focused on the bloom development phase, during which biomass accumulates rapidly, whereas the decline phase-despite its critical role in carbon export and microbial loop dynamics-has received far less attention. Here, we tracked changes in cell density and inorganic carbon utilization characteristics throughout the entire course of a simulated Thalassiosira pseudonana bloom under ambient (420 μatm) and elevated pCO2 (1000 μatm) conditions. Inhibitors of carbonic anhydrase and direct bicarbonate transporters were applied to investigate the characteristics of inorganic carbon utilization. The relationship between photosynthetic rate and inorganic carbon concentration was measured to assess inorganic carbon affinity. The simulated T. pseudonana bloom was characterized by rapid cell density accumulation, reaching a peak within 10 days, followed by a rapid decline without a distinct stationary phase. As the bloom progressed, photosynthetic rate and the maximum quantum yield of photosystem II declined, whereas the inorganic carbon affinity increased. Elevated CO2 enhanced growth and maximum quantum yield during the acceleration phase but resulted in an 86% higher fitted death rate during the decline phase. Regarding the relationship between photosynthetic rate and dissolved inorganic carbon concentration, elevated CO2 increased the maximum photosynthetic rate and half-saturation constant only during the acceleration phase. Collectively, these results indicate that seawater acidification can influence both biomass accumulation and decline intensity in diatom blooms, with potential consequences for carbon sequestration and its redistribution among biogeochemical pools.
Continue reading ‘Seawater acidification accelerates growth but hastens decline in batch cultures of the marine diatom Thalassiosira pseudonana’
