Dinoflagellates, particularly harmful algal bloom (HAB)-forming species, exhibit remarkable resilience to climate change stressors, including ocean warming and acidification. However, their specific acclimation strategies compared to other phytoplankton groups remain poorly understood. This study investigates the multi-generational acclimation mechanisms of Scrippsiella trochoidea under simulated future ocean conditions (25°C, 1000 ppm pCO₂; HTHC) compared to present-day conditions (21°C, 400 ppm pCO₂; LTLC). Over 10 generations, S. trochoidea demonstrated significant physiological and biochemical adjustments, including a 79% increase in growth rate, a 73% rise in cell volume, and notable elevations in macromolecular components such as carbohydrates (38%), lipids (48%), proteins (90%), and chlorophyll (158%). These changes were accompanied by enhanced carbon fixation and nutrient acquisition. During the compensation phase (fifth generation), S. trochoidea exhibited a unique nitrate-phosphate trade-off, redirecting nitrates to nucleic acid biosynthesis and chlorophyll production while utilizing phosphorus storage for phospholipid synthesis. This strategy resulted in increased residual phosphorus and alternative lipid sources, highlighting a distinct acclimation mechanism compared to other phytoplankton groups. These findings underscore the ecological importance of dinoflagellates in shaping biogeochemical cycles under future ocean scenarios. By revealing their unique adaptive strategies, this study provides essential insights into predicting HAB dynamics and mitigating their ecological and economic impacts. Incorporating these results into predictive models will enhance our ability to forecast bloom events and guide effective marine management strategies, such as nutrient runoff control and habitat restoration, in the context of climate change.
Continue reading ‘Multi generational acclimation of Scrippsiella trochoidea to ocean warming and acidification’Posts Tagged 'phytoplankton'
Multi generational acclimation of Scrippsiella trochoidea to ocean warming and acidification
Published 4 August 2025 Science ClosedTags: adaptation, biological response, growth, laboratory, multiple factors, otherprocess, physiology, phytoplankton, temperature
Effect of acidification on the chronic toxicity of diclofenac to Daphnia magna
Published 28 July 2025 Science ClosedTags: biological response, laboratory, multiple factors, phytoplankton, reproduction, toxicants
Highlights
- Chronic diclofenac (DCF) exposure was tested in Daphnia magna at pH 7.0 and 8.7.
- An unexpected pH increase in M4 medium was observed during the experiment.
- The NOEC (no observed effect concentration) of DCF was 5 mg l-1 at pH 8.7.
- Initial pH 7.0 prolonged the time to release of the first hatchlings.
- At 1.3 mg l-1 DCF, fewer neonates were observed at pH 7.0 than at pH 8.7.
Abstract
Pharmaceuticals, as ionizable compounds, are a challenging group of pollutants to analyze because the pH of the environment can alter its ecotoxicological features. However, changes in the toxicity of pharmaceuticals toward aquatic organisms were observed even when there was no change in the ionization of the molecules with a pH shift. Therefore, we conducted a study that aimed to check how pH influences the chronic toxicity of diclofenac (DCF, pKa ≈ 4.0) toward Daphnia magna at two pH levels, 7.0 and 8.7, where DCF is obtained as relatively polar anion. The performance of the experiment with OECD 211 was found to be challenging because of the medium pH shift during the exposure test. Acidification increased the toxicity of DCF, reducing the number of neonates (at a concentration of 1.3 mg l-1) and showing a tendency towards delayed hatching and reduced number of hatchings. In addition, the acidification itself also changes D. magna reproduction, affecting the number of hatchings and the first day of hatching. We conclude that the pH, as a factor of toxicity modulation for ionizable compounds, needs to be evaluated and presented in scientific protocols.
Continue reading ‘Effect of acidification on the chronic toxicity of diclofenac to Daphnia magna’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’Chapter 6 – Effects of ocean acidification and molecular mechanisms
Published 17 July 2025 Science ClosedTags: biological response, growth, physiology, phytoplankton, review
This chapter reviews the literature on the impacts of elevated CO2 and acidification conditions on algal growth rates and toxin productivity. It then investigates why increases in CO2 and decreases in pH cause different outcomes in different phytoplankton species. The chapter concludes by discussing the effects of ocean acidification (OA) on HABs and toxin production.
Continue reading ‘Chapter 6 – Effects of ocean acidification and molecular mechanisms’Shifts in coral reef holobiont communities in the high-CO2 marine environment of Iōtorishima Island
Published 15 July 2025 Science ClosedTags: adaptation, biological response, BRcommunity, community composition, corals, field, molecular biology, North Pacific, otherprocess, phytoplankton, prokaryotes, vents
Ocean acidification (OA), driven by rising atmospheric CO2, presents a serious threat to marine biodiversity, especially within coral reef ecosystems. Natural analogue sites, such as the high-pCO2 seep at Iōtorishima Island in Japan, offer insights into future conditions. This study investigated the holobiont communities of Symbiodiniaceae and bacteria in the zoantharian Palythoa tuberculosa at Iōtorishima and compared them to specimens from control sites in Okinawa and Hawaiʻi. Using amplicon sequencing of the dinoflagellate internal transcribed spacer 2 (ITS2) region of ribosomal DNA and microbial 16S rRNA gene, we detected significant shifts in both Symbiodiniaceae and bacterial communities under high-pCO2 conditions at Iōtorishima. Specifically, P. tuberculosa at the seep site had reduced Symbiodiniaceae diversity, predominatly featuring Cladocopium C1 and C3 types. Additionally, its bacterial communities showed lower richness with distinct taxonomic profiles, including increased levels of Mollicutes and Vibrio spp. These results highlight the potentially adverse effects of OA on hexacoral holobionts and emphasize the need for detailed, high-resolution studies across various holobiont species and geographic locations. The shifts observed specifically in Symbiodiniaceae and bacterial communities at the Iōtorishima seep suggest that holobionts may exhibit plasticity in response to environmental stress, which has implications for resilience and adaptation of zoantharians and other reef organisms amid climate change. This research provides crucial baseline data for predicting future coral reef compositions in an OA-affected world.
Continue reading ‘Shifts in coral reef holobiont communities in the high-CO2 marine environment of Iōtorishima Island’Impact of ocean acidification on fish health and marine ecosystem dynamics
Published 11 July 2025 Science ClosedTags: algae, biological response, corals, fish, mollusks, phanerogams, phytoplankton, review, zooplankton
Ocean acidification (OA) causes an increase in carbon dioxide (CO2) and a reduction in the pH of ocean waters. This chapter reviews the current literature to investigate the adverse effects of OA on fish health and marine ecosystem dynamics. OA poses serious threats to marine biodiversity and ecosystem dynamics. Fish experience severe physiological problems such as impaired growth, development, tissue damage, Impaired behavioral changes, sensory and brain functions, and disruption in predator-prey interactions due to acidification with a 74% decline in survival rates of egg and larval stages. Besides affecting fish, OA also affects marine ecosystem dynamics: reducing calcification rates in calcifying species, increasing seagrass production, causing effects on habitat-forming species, and disrupting the food web. Vulnerable species, such as coral reef fish, show high sensitivity, risking the stability of their habitats. The United Nations recognized the OA as a threat to marine biodiversity through the Convention on Biodiversity. The future research needs to focus on understanding fish and marine animals’ adaptive mechanisms to OA, its interaction with other stressors, and global collaboration to address the underlying causes of OA.
Continue reading ‘Impact of ocean acidification on fish health and marine ecosystem dynamics’Responses of the natural phytoplankton assemblage to Patagonian dust input and anthropogenic changes in the Southern Ocean
Published 10 July 2025 Science ClosedTags: Antarctic, biological response, community composition, growth, laboratory, morphology, multiple factors, nutrients, otherprocess, physiology, phytoplankton, temperature
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.
Continue reading ‘Responses of the natural phytoplankton assemblage to Patagonian dust input and anthropogenic changes in the Southern Ocean’CO2 enrichment enhances biomass density and C:N:P ratios in phytoplankton assemblage in the coastal water of the Taiwan Strait
Published 3 July 2025 Science ClosedTags: abundance, biogeochemistry, biological response, community composition, laboratory, North Pacific, otherprocess, phytoplankton
Seawater CO2 concentrations are steadily increasing in the Taiwan Strait of the Southeast China, while the effects of rising CO2 on carbon fixation and elemental composition of phytoplankton assemblages in this area are still poorly understood. Here, we enriched the seawater CO2 concentrations to 808 μatm and above to simulate the CO2–induced ocean acidification, and investigated the effects of CO2 enrichment on concentrations of chlorophyll (Chl) a, particulate organic carbon (POC), nitrogen (PON) and phosphorus (POP), the C:N:P ratio, and phytoplankton community composition in the coastal surface seawaters of the northwest Taiwan Strait in autumn 2023 and spring 2024 through an outdoor incubation experiment. After three days of incubation, CO2 enrichment increased the concentrations of Chl a by 1–14%, POC by 21–32% and PON by 21–56%, whereas reduced the POP concentrations by 1–37%, leading to elevated ratios of POC:POP and PON:POP. Furthermore, elevated CO2 level enhanced cell abundances of the dominant diatom genera at three stations. These results suggest that phytoplankton has the potential to buffer against rising atmospheric CO2 level and can help us to understand the elemental biogeochemistry in the Taiwan Strait under future ocean acidification scenarios.
Continue reading ‘CO2 enrichment enhances biomass density and C:N:P ratios in phytoplankton assemblage in the coastal water of the Taiwan Strait’Decreased dimethylsulfide and increased polybrominated methanes: potential climate effects of microplastic pollution in acidified ocean
Published 3 July 2025 Science ClosedTags: biogeochemistry, biological response, community composition, laboratory, multiple factors, otherprocess, phytoplankton, plastics
Microplastic (MP) pollution and ocean acidification (OA) are pressing marine environmental concerns, but their combined impacts on short-lived biogenic climate-active gases and the resulting climate effects remain unclear. To address this gap, a ship-based microcosm experiment was conducted, where OA and MP pollution were simulated under in situ conditions to explore their effects on the production of dimethylsulfide (DMS), bromoform (CHBr3), and dibromomethane (CH2Br2). The results indicated that both MP and OA inhibited phytoplankton growth and DMS concentration, with OA inducing further reductions in the production rate and yield of DMS. MP addition led to extra dissolved organic matter, and the acidified condition enhanced bromoperoxidase activity, both of which promoted the production of CHBr3 and CH2Br2. When OA and MP addition were combined, DMS concentrations decreased by 61%, whereas CHBr3 and CH2Br2 concentrations increased by 132% and 45%, respectively. Based on the results, MP pollution under OA conditions might directly reduce DMS accumulation or decrease the formation of DMS-derived sulfate aerosols by increasing CHBr3 and CH2Br2 levels, which finally weaken DMS’s climate-cooling capabilities. This study underscores the potential for MP pollution in future acidified oceans to exacerbate global warming by disrupting the cycle of marine biogenic climate-active gases.
Continue reading ‘Decreased dimethylsulfide and increased polybrominated methanes: potential climate effects of microplastic pollution in acidified ocean’Effects of different environmental stressors on marine biogenic sulfur compounds in the Northwest Pacific and Eastern Indian Oceans
Published 2 July 2025 Science ClosedTags: abundance, biogeochemistry, biological response, community composition, growth, Indian, laboratory, multiple factors, North Pacific, otherprocess, physiology, phytoplankton
Abstract
Key roles of marine dimethyl sulfoniopropionate (DMSP), dimethyl sulfide (DMS), methyl mercaptan (MeSH), and carbon disulfide (CS2) in the sulfur cycle and/or atmospheric chemistry, alongside the rapid environmental changes in marine ecosystems, underscore the need to understand their responses to dynamic ecosystem shifts. We conducted two ship-based incubation experiments in the Northwest Pacific and Eastern Indian Oceans to explore how dust deposition, ocean acidification, and microplastic exposure impact these compounds. Our results demonstrate that these stressors not only alter phytoplankton community but also modify per-cell DMSP production capacity and DMSP degradation pathways, subsequently influencing DMSP, DMS, and MeSH concentrations. CS2‘s response closely mirrors phytoplankton abundance and species. Initial physical-chemical conditions, such as carbonate system and nutrient availability, may mediate the sensitivity of phytoplankton and sulfur compounds to environmental shifts. This study enhances our understanding of biogenic sulfur responses in dynamic marine ecosystems and provides essential basis for future climate modeling.
Key Points
- External stressors alter algal communities and production and degradation of dimethyl sulfoniopropionate, thus affecting biogenic sulfides
- Response of carbon disulfide to different environmental stressors is closely linked to algal abundance
- Initial physical-chemical conditions of seawater mediate algae and biogenic sulfides’ sensitivity to environmental stressors
Plain Language Summary
Biogenic sulfur-containing compounds in the ocean, such as dimethyl sulfoniopropionate (DMSP), dimethyl sulfide (DMS), methyl mercaptan (MeSH), and carbon disulfide (CS2), play critical roles in the global sulfur cycle and have the potential to influence the Earth’s climate. For instance, DMS released from the ocean into the atmosphere contributes to cloud formation, which in turn affects weather patterns. Over recent decades, rapid environmental changes in marine ecosystems may have significantly impacted marine biogeochemical processes. To investigate how these compounds respond to such changes, we conducted two ship-based incubation experiments in the Northwest Pacific and Eastern Indian Oceans. We assessed the effects of dust deposition, ocean acidification (due to increased carbon dioxide), and microplastic pollution on the production of DMSP, DMS, MeSH, and CS2 by marine organisms. Our results demonstrate that these stressors alter phytoplankton growth and community composition and impact the pathways through which DMSP is degraded. Consequently, the concentrations of sulfur compounds in seawater are affected. Notably, changes in CS2 levels were more closely related to shifts in phytoplankton abundance. These findings enhance our understanding of how marine sulfur compounds may respond to future oceanic changes and offer valuable data for improving climate models.
Continue reading ‘Effects of different environmental stressors on marine biogenic sulfur compounds in the Northwest Pacific and Eastern Indian Oceans’Novel sequential modeling framework improves phytoplankton biomass predictions in response to multiple environmental stressors
Published 1 July 2025 Science ClosedTags: biological response, modeling, North Pacific, phytoplankton, regionalmodeling
Understanding the impacts of multiple environmental stressors on phytoplankton biomass is crucial for predicting marine ecosystem responses under global climate change. This study employed a sequential modeling framework integrating principal component analysis, generalized additive models, and artificial neural networks to improve predictions of phytoplankton chlorophyll a concentrations in the Taiwan Strait. Analyzing a decadal dataset, we found that a 2C rise in sea surface temperature and a 0.2 pH decline will each lead to an 11.3% reduction in chlorophyll a biomass, whereas nitrogen enrichment is expected to increase it by only 2.8%. The combined effects of these stressors will result in an 18.3% reduction, with the most significant declines occurring in high-chlorophyll areas during algal blooms. Compared to simpler models, our approach improved accuracy by reducing overestimation biases, particularly under acidification scenarios, highlighting the need for advanced, multivariate models in forecasting phytoplankton dynamics under global changes.
Scientific Significance Statement
Phytoplankton are critical to marine ecosystems and global biogeochemical cycles, yet predicting their responses to the combined stressors of warming, acidification, and eutrophication remains a major challenge. Traditional models struggle with multicollinearity and nonlinear interactions among environmental variables. This study introduces an innovative sequential modeling framework that integrates principal component analysis, generalized additive models, and artificial neural networks, addressing these challenges by combining the strengths of each method in a series. This approach not only improves predictive accuracy, particularly during algal blooms, but also reveals that combined stressors lead to an 18.3% decline in phytoplankton biomass, underscoring their vulnerability under future climate scenarios. By bridging methodological advancements with ecological discovery, this work provides a powerful tool for understanding and forecasting marine ecosystem responses to global change.
Continue reading ‘Novel sequential modeling framework improves phytoplankton biomass predictions in response to multiple environmental stressors’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’Surface seawater chlorophyll-a variability in the South China Sea: influence of pCO2 and co-varying environmental factors
Published 26 May 2025 Science ClosedTags: biological response, chemistry, field, North Pacific, phytoplankton
Highlights
- Surface seawater Chl-a shows a generally stable trend with slight decline over 20 years.
- Limited CO2-driven Chl-a response detected over two decades.
- Light–nutrient–temperature co-limitation dominates phytoplankton growth in the SCS.
Abstract
The partial pressure of CO2 (pCO2) in surface seawater continues to increase with the rising atmospheric carbon dioxide (CO2). However, whether elevated pCO2 enhances marine primary productivity and its actual impact on Chl-a shows distinct regional variability. Using chlorophyll-a (Chl-a, from Ocean Colour Climate Change Initiative satellite data), combined with high-resolution pCO2 dataset, we analyzed the spatiotemporal variations of surface seawater Chl-a and their response to pCO2 in the South China Sea (SCS) from August 2002 to December 2022. We demonstrate that Chl-a concentrations are higher in coastal regions, lower in the central basin, peak in winter, and are lowest in spring. Over the past two decades, surface seawater Chl-a has exhibited a generally stable pattern with a slight declining tendency, with a faster decrease in nearshore waters (−0.00693 mg m−3·yr−1, −0.27 %) than in central open waters (−0.00123 mg m−3·yr−1, −0.60 %). In contrast, surface seawater pCO2 has increased steadily, with a more rapid rise in central open waters (1.44 μatm yr−1) compared to nearshore areas (0.496 μatm yr−1), accompanied by a concurrent warming trend, where sea surface temperature increased at rates of 0.0346 °C·yr−1 and 0.0408 °C·yr−1 in nearshore and central open waters, respectively. Partial correlation analysis indicates that light inhibition is the main factor constraining phytoplankton growth in the SCS, while carbon availability is not a key influencing factor for phytoplankton in this region. Rising pCO2, accompanied by climate change effects such as rising sea surface temperatures and enhanced water column stratification, may contribute to a weakening of surface seawater Chl-a in the SCS. Further studies are needed to evaluate its future under climate change.
Continue reading ‘Surface seawater chlorophyll-a variability in the South China Sea: influence of pCO2 and co-varying environmental factors’Microzooplankton community dynamics under ocean acidification: key observations and insights
Published 30 April 2025 Science ClosedTags: abundance, biological response, BRcommunity, community composition, Indian, laboratory, otherprocess, phytoplankton, prokaryotes, zooplankton
Microzooplankton (MZP) community dynamics under ocean acidification were studied through pH manipulated microcosm experiments conducted in the coastal waters of the Bay of Bengal (off Vishakhapatnam) during the months of July and October 2022 (Experiment 1 and Experiment 2). The total abundance of phytoplankton and microzooplankton (MZP) communities was varied from 3.66 × 104 to 5.27 × 105 Cells. L−1 and 0.06 × 103 to 1.53 × 103 Cells. L−1, respectively, and a significant difference in phytoplankton and MZP abundance was found between the initial and final day of the entire experimental samples (control and acidified). The initial seawater samples were dominated with centric diatom species Dactyliosolen fragilissimus (Experiment 1 and Experiment 2: 72–82%) and shifted to pennate diatoms such as Pseudo-nitzschia sp. (Experiment 1: 60–68%) and Amphora sp. (Experiment 2: 80–94%) at the end of the experiments (all acidified and control samples). The initial MZP community composition consisted of four different groups LC: loricate ciliates, ALC: aloricate ciliates (heterotrophy and mixotrophy), HDS: heterotrophic dinoflagellates and copepod nauplii, and at the end of the experiments, it was shifted entirely to the dominance of aloricate ciliates (16–73%) and heterotrophic dinoflagellates (67–100%) in all the samples (control and acidified) in Experiments 1 and 2, respectively. Statistical analysis (Spearman’s rank correlation) results showed a relative and significant inverse relation of MZP with phytoplankton biomass and abundance and heterotrophic bacterial counts in all the samples (control and acidified). Besides, the LC showed a weak correlation with Chl-a, and the HDS showed a significant correlation with LC, phytoplankton biomass and abundance, and bacterial counts (picocyanobacteria and heterotrophic bacteria). These results indicate that the MZP may graze on both picocyanobacteria and heterotrophic bacteria, and also, HDS may graze on their relative community like LC. Canonical correlation analysis (CCA) revealed that prey abundance such as phytoplankton biomass (Chl-a), picocyanobacteria, and heterotrophic bacterial communities are most influencing variables on the MZP assemblages than other environmental variables such as pH, temperature, and salinity. Thus, these findings show that the MZP community dynamics under ocean acidification may vary with different species and groups due to their food availability (indirect effect) and individual competence (direct effect) to different environmental conditions, such as pH variations.
Continue reading ‘Microzooplankton community dynamics under ocean acidification: key observations and insights’A simple CO2 enrichment incubator for investigating physiological responses of harmful algae to ocean acidification
Published 23 April 2025 Science ClosedTags: biological response, growth, methods, morphology, phytoplankton
A CO2 manipulation incubation system using off-the-shelf components was developed to study the effects of ocean acidification (OA) on marine microalgae. The system successfully monitored CO2 concentrations in real time at the desired levels. The incubation experiment was based on the IPCC’s CMIP6 worst-case scenario (SSP5-8.5), with elevated CO2 concentrations of up to 1000 ppm. Under these conditions, exposure to 1000 ppm CO2 significantly increased growth rate, cell diameter, and biovolume of harmful microalgae, Alexandrium tamiyavanichii. These effects were more pronounced, highlighting the potential for ocean acidification to exacerbate harmful algal blooms. The study also emphasized the importance of accounting for light attenuation in the incubation setup, revealing a 20% loss in light within culture bottles due to uneven light distribution. Correcting light intensity variations caused by the materials of the culture vessels was essential for unbiased growth assessments.
Continue reading ‘A simple CO2 enrichment incubator for investigating physiological responses of harmful algae to ocean acidification’Long-term successional dynamics and response strategies of harmful algal blooms to environmental changes in Tolo Harbour
Published 18 April 2025 Science ClosedTags: biogeochemistry, biological response, BRcommunity, chemistry, community composition, communitymodeling, field, mitigation, modeling, North Pacific, otherprocess, physiology, phytoplankton, policy
Highlights
- Long-term monitoring reveals significant shifts in harmful algal bloom species and toxin dynamics in Tolo Harbour.
- Government actions reduced nutrient levels, but climate change and organic nutrients influenced HABs’ species succession.
- Number of HABs decreased, meanwhile frequency and types of new toxin species emerged, highlighting complex ecological changes.
- Balanced dual nutrient reduction strategies are essential for controlling HABs and restoring coastal ecosystem health.
ABSTRACT
The production and succession of harmful algae blooms (HABs) are attributed more to excessive nutrient concentrations and unbalanced nutrient stoichiometry than to other environmental drivers as the absence of long-term monitoring data. This study analyzed HABs succession patterns and key drivers in Tolo Harbour from 1986 to 2023, leveraging nearly 40 years of data. Effective governmental measures significantly improved water quality, with dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), 5-day biochemical oxygen demand (BOD5), and Escherichia coli (E. coli) concentrations decreasing by 53%, 80%, 45%, and 59%, respectively. Annual HABs events dropped from 28 to 3, and species diversity declined from 6 to 2. However, toxic species frequency rose from 21% to 46%. Dinoflagellates emerged as dominant initial species, with a shift in secondary dominance from diatoms to ochrophytes and toxin types from diarrhetic shellfish poisoning (DSP) to hemolytic toxins (HT). These shifts likely result from combined human and natural influences. Model simulations confirmed that red tide outbreaks, species succession, and shifts in toxin types were driven by declining pH, rising temperatures, unbalanced nitrogen-phosphorus ratios, organic nutrient increases, and algal antagonism. The study emphasizes the importance of the dual reduction of both DIN and DIP, meanwhile inorganic and organic nutrients, suggesting that overly focusing on or distract from one nutrient (e.g., DIP or DON) could lead to unintended ecological consequences, like the proliferation of rare and toxic species. We highlight the combined impacts of climate change (warming and ocean acidification) and anthropogenic activities (nutrient pollution and eutrophication) on HABs, particularly the number and toxin production. This research links policy changes to HAB dynamics, offering strategic recommendations for managing red tides and contribute novel perspectives on the impact of nutrient reduction in comparable bay ecosystems.
Continue reading ‘Long-term successional dynamics and response strategies of harmful algal blooms to environmental changes in Tolo Harbour’Variations of coccolith morphology and their influencing factors in the northeastern South China Sea since the last glacial maximum
Published 15 April 2025 Science ClosedTags: biological response, chemistry, field, morphology, North Pacific, paleo, phytoplankton, sediment
Coccoliths are widely present in marine sediments of the South China Sea and closely associated with paleoenvironmental changes. This study investigates the morphological variations and driving factors of coccoliths since the Last Glacial Maximum(LGM) by analyzing the morphology and related indicators of Noelaerhabdaceae coccoliths in sediment samples from core MD18-3569 (0.01~12.41 m; 0.69~26.58 ka) in the northeastern South China Sea(22°09.30’N, 119°49.24’E at water depth 1320 m), and a total of 155 samples were collected, with a sampling resolution of approximately 167 years. Morphological attributes such as coccolith length, thickness, area, and mass were obtained through microscopic measurements and computational formulas. Coccolith morphological constants were used to evaluate preservation conditions. Based on these data, morphological divergence index and calcification index were calculated. Using the PyCO2SYS model, ocean carbonate system parameters were reconstructed to explore their impact on coccolith morphology.
The results show that coccolith length ranged from 2.69 μm to 3.86 μm(mean: 3.20 μm) since the LGM, with significant variability but no clear trend. Thickness ranged from 0.07 μm to 0.17 μm(mean: 0.13 μm) and exhibited a decreasing trend since the LGM. Coccolith mass varied between 2.31 pg and 9.02 pg(mean: 5.61 pg), also showing a decreasing trend since the LGM. Coccolith morphological constants indicate good preservation and high data reliability. Morphological divergence index results suggest a decline in coccolith size diversity, reflecting reduced seasonal variation and regional productivity. Calcification intensity metrics indicate a weakening of calcification since the LGM.
By comparing temperature, salinity, and ocean carbonate system parameters, the study identifies rising atmospheric CO2 concentrations and resultant ocean acidification as the primary factors contributing to reduced coccolith calcification. The impacts of temperature and salinity were relatively minor. These findings demonstrate the complex response of Noelaerhabdaceae coccoliths to environmental changes and highlight the significant roles of regional climate variations and carbonate system evolution in shaping coccolith morphology.
Continue reading ‘Variations of coccolith morphology and their influencing factors in the northeastern South China Sea since the last glacial maximum’Ocean acidification disrupts the energy balance and impairs the health of mussels (Mytilus coruscus) by weakening their trophic interactions with microalgae and intestinal microbiome
Published 4 April 2025 Science ClosedTags: biological response, BRcommunity, community composition, laboratory, mollusks, North Pacific, otherprocess, performance, physiology, phytoplankton, prokaryotes
Highlights
- Ocean acidification disrupts mussel energy balance by weakening trophic interactions.
- Mussels exposed to acidified conditions show reduced energy gain from microalgae.
- Energy imbalance caused by acidification impairs mussel health and fitness.
- Ocean acidification can threaten mussel farming and marine ecosystem stability.
Abstract
Despite extensive research in the last two decades, exploring the potential mechanisms underlying the sensitivity and resistance of marine organisms to ocean acidification is still imperative. Species interactions can play a role in these mechanisms, but the extent to which they modulate organismal responses to ocean acidification remains largely unknown. Here, we investigated how ocean acidification (pH 7.7) affects energy homeostasis and fitness of mussels (Mytilus coruscus) by assessing their physiological responses, intestinal microbiome and nutritional quality of their food (microalgae). Under ocean acidification, the mussels had reduced feeding rates by 34 % and reduced activities of digestive enzymes (pepsin by 39 %, trypsin by 28 % and lipase by 53 %) due to direct exposure to acidified seawater and increased phenol content of microalgae. Richness and diversity of intestinal microbiome (OTU, Chao1 index and Shannon index) were also lowered by ocean acidification, which can undermine nutrient absorption. On the other hand, energy expenditure of mussels increased by 53 % under ocean acidification, which was associated with the upregulation of antioxidant defence (SOD, CAT and GPx activities). Consequently, energy reserves in mussels decreased by 28 %, which were underpinned by the reduction in protein, carbohydrate and lipid contents. Overall, we demonstrate that ocean acidification could disrupt herbivore-algae and host-microbe interactions, thereby lowering the energy balance and impairing the health of marine organisms. This can have ramifications on the population and energy dynamics of marine communities in the acidifying ocean.
Continue reading ‘Ocean acidification disrupts the energy balance and impairs the health of mussels (Mytilus coruscus) by weakening their trophic interactions with microalgae and intestinal microbiome’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’Eukaryotic phytoplankton drive a decrease in primary production in response to elevated CO2 in the tropical and subtropical oceans
Published 14 March 2025 Science ClosedTags: biological response, BRcommunity, community composition, field, North Pacific, phytoplankton, primary production
Significance
Marine phytoplankton, which contribute ~45% of global net primary production, are projected to be affected by ongoing ocean acidification (OA). However, the response of phytoplankton to acidification is not well constrained in ultraoligotrophic tropical and subtropical oceans where small (<20 µm) phytoplankton dominate. By conducting onboard microcosm experiments, we found community-level primary production decreased consistently following CO2 enrichment in the North Pacific Subtropical Gyre and northern South China Sea, while no significant changes were observed at the northernmost boundary of the subtropical gyre. Eukaryotic phytoplankton but not cyanobacteria were key drivers of these responses which occur primarily under nitrogen limitation. These findings enhance our understanding of OA impacts on phytoplankton and marine productivity in a changing climate.
Abstract
Ocean acidification caused by increasing anthropogenic CO2 is expected to impact marine phytoplankton productivity, yet the extent and even direction of these changes are not well constrained. Here, we investigate the responses of phytoplankton community composition and productivity to acidification across the western North Pacific. Consistent reductions in primary production were observed under acidified conditions in the North Pacific Subtropical Gyre and the northern South China Sea, whereas no significant changes were found at the northern boundary of the subtropical gyre. While prokaryotic phytoplankton showed little or positive responses to high CO2, small (<20 µm) eukaryotic phytoplankton which are primarily limited by low ambient nitrogen drove the observed decrease in community primary production. Extrapolating these results to global tropical and subtropical oceans predicts a potential decrease of about 5 Pg C y−1 in primary production in low Chl-a oligotrophic regions, which are anticipated to experience both acidification and stratification in the future.
Continue reading ‘Eukaryotic phytoplankton drive a decrease in primary production in response to elevated CO2 in the tropical and subtropical oceans’
