Discarded plastics are accumulating in the global ocean and posing threat to marine life. The plastisphere – the community colonizing plastic surfaces – profoundly influences plastic’s environmental behavior, affecting its degradation and entry into marine food webs. Ocean acidification (OA) resulted from anthropogenic CO2 emissions, is also threatening marine ecosystems, but the effect of OA on the structure and ecological function of the plastisphere community remains poorly understood. Here, using a mesocosm experiment, we investigated the effects of OA on the plastisphere colonizing floating PET plastic bottles. The study was conducted using subtropical eutrophic coastal water from Southern China under two CO2 conditions: increased CO2 to 1000 μatm (HC) and ambient CO2 410 μatm (LC). Metagenomic sequencing of the plastic samples, after exposure for 32 days, showed striking changes in relative abundance of eukaryotes and bacteria caused by HC. There was a 75.3 % decrease in eukaryote read abundances at high CO2, most strikingly a 95.6% decrease in the relative abundance of diatoms. In addition, the relative abundance of genes involved in photosystem II light reactions and pigment synthesis decreased under high CO2 conditions. This suggests that OA could reduce the photosynthetic potential within the plastisphere. Shifts in plastisphere community structure and potentially diminished photosynthesis under OA could influence the food chains within plastisphere, plastic degradation, transportation, and carbon cycle involving plastics. Overall, our results suggest that OA can alter the functional ecology of the plastisphere, with potential implications for marine biogeochemical processes and food web dynamics in subtropical eutrophic coastal water.
Continue reading ‘Ocean acidification reduces diatom and photosynthetic gene abundance on plastic in an coastal bay mesocosm experiment’Posts Tagged 'phytoplankton'
Ocean acidification reduces diatom and photosynthetic gene abundance on plastic in an coastal bay mesocosm experiment
Published 25 February 2026 Science ClosedTags: abundance, biological response, BRcommunity, community composition, laboratory, mesocosms, molecular biology, North Pacific, otherprocess, phytoplankton, prokaryotes
Acute microbial and nutrient responses to elevated temperature and pCO2: a coastal UK microcosm study
Published 13 February 2026 Science ClosedTags: abundance, biogeochemistry, community composition, laboratory, multiple factors, North Atlantic, nutrients, otherprocess, phytoplankton, temperature
The coastal ocean’s ecosystem resilience is consistently hampered by the compounding impacts of projected climate change and anthropogenic perturbation. In this microcosm study, we investigated how elevated temperature and pCO2, together with episodic nutrient pollution and a short-term marine heatwave, affect the nano- and picoplanktonic community of primary producers and subsequent changes in coastal biogeochemistry. Our study demonstrates that future elevated temperature and pCO2 conditions impact the planktonic community, first by a ∼ 50 % decreased autotrophic abundance, and second by a shift from larger eukaryotic to smaller cells. When combined with a heatwave, total primary producers experienced an additional 37–38 % decrease, indicative of a negative synergistic effect beyond either stressor alone. Picoeukaryotes were particularly sensitive, declining by 44–50 %. Short-term nutrient pollution under ambient conditions induced a 41 % increase in cell abundance, but failed to stimulate biomass under elevated temperature and pCO2, and instead led to altered organic matter dynamics, including significantly lower carbon fixation. These findings emphasize the need for further evaluation of multi-stressor interactions to better understand biogeochemical vulnerability, nutrient retention, and ecological functioning in coastal ecosystems undergoing rapid climatic and anthropogenic change.
Continue reading ‘Acute microbial and nutrient responses to elevated temperature and pCO2: a coastal UK microcosm study’Prolonged low pH reprograms carbon and nitrogen metabolism and micronutrient use in Symbiodinium kawagutii and reveals indicators for reef water quality management
Published 23 January 2026 Science ClosedTags: biological response, growth, laboratory, molecular biology, photosynthesis, physiology, phytoplankton
Highlights
- Low- pH stress suppresses S. kawagutii growth by ∼50%
- Enhanced NPQ and reduced chlorophyll indicate increased photoprotection
- Lipid pools increase as proteins and carbohydrates are diverted to fatty acids
- Elevated C:N ratios and Fe/Mn loss reveal nutrient limitation under acid stress
- Multi-omics uncover upregulated CA, antioxidant enzymes, and proton pumps
Abstract
Ocean acidification is a pervasive driver of coastal and reef water-quality change. We investigated how chronic low-pH exposure representative of extreme reef scenarios (pH 7.4-7.5) reshapes the physiology and metabolism of the coral symbiont Symbiodinium kawagutii. Integrating growth assays, photophysiology, ultrastructural imaging, biochemical profiling, transcriptomics, and metabolomics, we show that low pH suppresses growth and redirects resources from biosynthesis to stress mitigation. Non-photochemical quenching increased while chlorophyll content declined, indicating photoprotective energy reallocation. Ultrastructural deterioration coincided with losses of protein and carbohydrate pools, whereas fatty-acid stores expanded, evidencing a shift in carbon storage. Elemental and trace-metal measurements revealed higher cellular C:N and significant Fe/Mn depletion, indicating micronutrient constraints under acid stress. Multi-omics analyses identified coordinated upregulation of carbonic anhydrases, vacuolar H+-ATPases, and antioxidant defenses with downregulation of nitrogen and phosphorus assimilation, forming a plastic network that maintains pH and redox homeostasis at the expense of growth. These cellular trade-offs clarify how symbiont plasticity can buffer acidified conditions while altering the quality and quantity of photosynthate available to hosts. By linking mechanistic responses to potential monitoring indicators, this study provides actionable targets to anticipate and manage acidification impacts on reef water quality and to guide restoration strategies that prioritize acid-tolerant symbiont strains and relief of micronutrient stress.
Continue reading ‘Prolonged low pH reprograms carbon and nitrogen metabolism and micronutrient use in Symbiodinium kawagutii and reveals indicators for reef water quality management’Transcriptomic responses of the marine diatom Phaeodactylum tricornutum to high carbon and low nitrogen stress
Published 23 January 2026 Science ClosedTags: adaptation, biological response, laboratory, molecular biology, multiple factors, nutrients, otherprocess, phytoplankton
Diatoms play a pivotal role in global biogeochemical cycling and marine primary productivity, making them ideal model organisms for understanding how phytoplankton respond to environmental fluctuations associated with global climate change. In natural marine systems, diatoms frequently encounter simultaneous variations in carbon and nitrogen availability, yet most previous studies have examined the effects of these factors in isolation. To elucidate the integrated transcriptional mechanisms underlying diatom acclimation to coupled carbon–nitrogen (C—N) imbalance, we employed RNA sequencing (RNA‐Seq) to characterize the global transcriptional response of the model diatom Phaeodactylum tricornutum to high CO2 (~2000 μatm) and low nitrogen (10% of nitrogen concentration in f/2 medium) under parallel culture conditions. The results revealed both shared and distinct transcriptional responses between the two treatments. Key genes involved in carbon metabolism, such as phosphoglycerate mutase (PGAM_7) and dihydrolipoamide succinyltransferase (PHATRDRAFT_40430), were significantly upregulated, indicating enhanced glycolytic and TCA cycle activity. In contrast, the Calvin‐cycle enzyme fructose‐1,6‐bisphosphatase (FBPC4) was downregulated. Genes associated with nitrogen assimilation‐including nitrate reductase (PHATRDRAFT_54983), nitrite reductases (PHATRDRAFT_13154, PHATRDRAFT_8155), and ferredoxin–nitrite reductase (PHATRDRAFT_27757)‐were strongly induced under both conditions. Pathway enrichment analysis further indicated the activation of lactic acid fermentation and nitrogen salvage pathways, suggesting a metabolic shift toward energy conservation and nutrient recycling. Collectively, these findings provide an overview of the transcriptional adjustments that enable P. tricornutum to maintain C—N homeostasis under high CO2 and low nitrogen stress, offering new insights into diatom metabolic plasticity under changing ocean conditions.
Continue reading ‘Transcriptomic responses of the marine diatom Phaeodactylum tricornutum to high carbon and low nitrogen stress’Ocean acidification and anthropogenic carbon in the Eastern Mediterranean Sea and the effects of acidification on marine organisms
Published 15 January 2026 Science ClosedTags: biological response, chemistry, field, fisheries, growth, laboratory, Mediterranean, mollusks, mortality, photosynthesis, physiology, phytoplankton, respiration
Ocean acidification (OA), driven by rising atmospheric carbon dioxide (CO2) levels, is a critical issue affecting our oceans. The Eastern Mediterranean Sea (EMS) remains poorly understood in terms of the carbonate system and the impact of OA, despite its key role in Levantine Intermediate Water (LIW) formation and its peculiar characteristics in buffering capacity and ongoing OA. This study provides the first comprehensive spatial and temporal assessment of carbonate system in the North-Eastern Levantine Basin, in EMS, providing essential reference data for Total Alkalinity (TA), Dissolved Inorganic Carbon (DIC), and Anthropogenic Carbon (CANT). The mean TA of the measurements was 2622.11 μmol/kg, with higher surface values in summer, reflected also in the surface salinity (S) maximum caused by strong evaporation. A clear vertical gradient was observed, with TA decreasing with depth. Hot and dry meteorological conditions contribute to increased S and TA, resulting in seasonal and vertical variations in the water column. The mean DIC of the measurements was 2291.23 μmol/kg. In contrast to the observations for TA, surface DIC values were higher in winter than in summer. The higher DIC values in winter are attributed to thermodynamic equilibrium and vertical mixing in the surface waters. This study has also investigates the presence of CANT, has infiltrated deep layers, with a mean concentration of 52.07 μmol/kg, decreasing significantly throughout the water column. These findings confirms the ongoing influence of human activities on intermediate and deep layers in EMS. To reconstruct past carbonate system dynamics, the relationships of TA and DIC were determined with salinity (S) and temperature (T) data. Long-term data from METU-IMS Erdemli Time Series (ETS) stations, collected monthly for a decade, provided valuable findings into seasonal patterns and temporal shifts in TA, DIC, and pH. The coastal station displayed clear trends in the carbonate system over time, reflecting its sensitivity to local environmental changes. In contrast, the offshore station exhibited minimal variability, indicating greater stability against seasonal and long-term fluctuations. These results highlight the heightened vulnerability of coastal waters to carbonate system changes, while offshore waters remain more stable. Understanding carbonate chemistry and acidification levels is crucial for assessing impacts on marine life. In addition to the characterization of carbonate chemistry, this study also explores OA’s biological impacts on two key organisms of the Mediterranean ecosystem: phytoplankton and mussels. Firstly, effects of elevated CO₂ on phytoplankton, an essential primary producer in aquatic food webs and global biogeochemical cycles are explored. Specifically, the study explores the impacts on phytoplankton physiology, focusing on growth rates, respiration, and photopigment content in selected species from the coccolithophores, dinoflagellates, and diatoms groups. While growth rates and respiration remained relatively stable under reduced pH conditions, photopigment content was significantly influenced by changes in seawater pH, highlighting the importance of considering environmental influences on photopigment composition. The study further investigated the effects of acidification on calcifying organisms through a global program aimed at understanding the long-term effects of acidification on key seafood species and exploring adaptation strategies with a collaborative approach. This study focused on the long-term (6 months long experiment) physiological impacts of OA on marine calcifiers, specifically Mediterranean mussel, Mytilus galloprovincialis, an abundant species and one of the most consumed non-fish marine species in Türkiye. Results indicate that OA poses a substantial threat to mussel health and survival. Reduced pH levels negatively impacted survival rates, while other physiological parameters like clearance rate, condition index, respiration, and the distribution of a radionuclide, 210Po, did not significantly change. However, lipid content and immune response were affected. Oxygen consumption decreased over time, especially at lower pH. This study underscores the potential risks of OA to the fitness of the commercially important mussel species, indicating that future OA may impact both this key seafood species and its associated ecosystems. The established baseline data are crucial for future monitoring and provide valuable insights into the vulnerability of marine organisms and ecosystems to ongoing OA. By integrating chemical, biological, and ecological perspectives, this dissertation offers a comprehensive assessment of OA in EMS. It establishes baseline data for carbonate system variables, revealing distinct spatial and temporal variations influenced by S, T, and mixing processes. By linking changes in carbonate chemistry to physiological responses in primary producers and a commercially vital shellfish species, this study highlights the ecological and economic impacts of OA in EMS. The findings emphasize the need for continued research and mitigation efforts to protect marine ecosystems and commercially important species. This integrated approach provides valuable insights into the vulnerability of marine organisms and ecosystems to ongoing OA, underscoring the significance of this research for the Mediterranean Sea.
Continue reading ‘Ocean acidification and anthropogenic carbon in the Eastern Mediterranean Sea and the effects of acidification on marine organisms’Physiological and transcriptomic responses of a harmful algal bloom-causing dinoflagellate Karenia mikimotoi to multiple environmental factors
Published 12 January 2026 Science ClosedTags: biological response, growth, laboratory, molecular biology, multiple factors, North Pacific, nutrients, photosynthesis, physiology, phytoplankton, temperature
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.
Continue reading ‘Physiological and transcriptomic responses of a harmful algal bloom-causing dinoflagellate Karenia mikimotoi to multiple environmental factors’The role of heterotrophy in the response of Oculina arbuscula to ocean acidification
Published 31 December 2025 Science ClosedTags: biological response, BRcommunity, calcification, corals, laboratory, multiple factors, North Atlantic, physiology, phytoplankton
On both tropical and temperate reefs, the calcium carbonate skeletons produced by scleractinian corals provide habitat that supports a high biodiversity of fishes and invertebrates. Ocean acidification (OA), driven by excess anthropogenic CO2 uptake, causes declines in seawater pH and carbonate ion concentration and can compromise coral calcification by causing increased energetic demands. Deciphering how corals meet this increased energetic demand is critical to predicting their future persistence. Oculina arbuscula is a facultatively symbiotic temperate coral common on subtropical reefs of the South Atlantic Bight. This coral has demonstrated calcification resilience to reduced pH conditions in both symbiotic and aposymbiotic forms, despite aposymbiotic colonies lacking access to photosynthetically-derived energy. I hypothesized that energy acquired through heterotrophy is a mechanism by which O. arbuscula obtains the resources necessary to overcome the heightened energy demand created by ocean acidification. To investigate the role of heterotrophy, a 90-day laboratory experiment was conducted exposing aposymbiotic O. arbuscula fragments to a pH of either 7.7 or 8.0 under three different feeding levels of Artemia spp. nauplii. Although fragments with greater food consumption showed significantly higher calcification rates, this effect was independent of pH. Similarly, biochemical analyses indicated that total protein and total carbohydrate stores increased with higher food consumption but were unaffected by pH exposure. In contrast, total lipid stores decreased during the experiment, regardless of pH exposure or food level, suggesting the heterotrophic contribution to lipid stores was deficient. Together, these results indicate that while heterotrophically-derived energy may not be a primary mechanism underlying the ability of O. arbuscula to sustain calcification rates under OA stress, this coral species should continue to thrive in an increasingly acidifying ocean as long as heterotrophic food resources are in abundance.
Continue reading ‘The role of heterotrophy in the response of Oculina arbuscula to ocean acidification’Compound hypoxia with heat or acidification stress induces synergistic and additive effects on coral physiology
Published 26 December 2025 Science ClosedTags: biological response, BRcommunity, corals, laboratory, morphology, multiple factors, North Atlantic, oxygen, photosynthesis, physiology, phytoplankton, respiration
As climate change accelerates, coastal marine ecosystems are increasingly exposed to co-occurring stressors whose combined effects are nonlinear and difficult to predict. Deoxygenation is a rapidly intensifying yet underrecognized threat to coral reefs that interacts with heat and acidification to alter coral physiology and stress resilience. However, the effects of hypoxia-related compound events on corals are largely unknown, underscoring the need for multi-stressor studies. Here, we conducted two extended-exposure experiments (12–17 days) across the coral species Porites furcata, Porites astreoides and Siderastrea siderea, to disentangle the individual and combined effects of low dissolved oxygen (hypoxia) with either heat or acidification. We measured eight phenotypic traits related to growth, metabolism, and symbiosis health to test whether hypoxia imposes energetic constraints or other physiological stress that amplify the effects of heat or acidification. Standardized effect size analysis across 24 stressor–trait combinations revealed 13 additive, 10 synergistic, and only one antagonistic response. Hypoxia consistently suppressed dark respiration by 37–49% across species and altered photophysiology in the two Porites species, whereas acidification alone had minimal effects, particularly in S. siderea. Heat stress caused the most pronounced declines across nearly all traits, and when combined with hypoxia, it produced the highest number of synergistic interactions. In contrast, the combination of hypoxia and acidification largely resulted in additive responses, suggesting that independent physiological mechanisms underlie these effects. All corals showed strong metabolic depression under hypoxia which is likely beneficial as a short-term adaptive response but may impose energetic constraints in the long-term. These findings highlight deoxygenation as critical yet often overlooked drivers of coral reef vulnerability. More multi-stressor experiments across a range of species are urgently needed to improve predictions of reef resilience under future ocean conditions, where compound stress events are expected to become more frequent and severe.
Continue reading ‘Compound hypoxia with heat or acidification stress induces synergistic and additive effects on coral physiology’Interactive effects of ocean acidification and benthic biofilm composition on the early development of the European abalone Haliotis tuberculata
Published 23 December 2025 Science ClosedTags: biological response, communityMF, laboratory, mollusks, morphology, multiple factors, North Atlantic, performance, phytoplankton, reproduction, respiration
Ocean acidification (OA) and associated shifts in carbonate chemistry represent major threats to marine organisms, particularly calcifiers. OA effects can be influenced by other environmental variables, including the biotic environment. This study investigated the individual and interactive effects of OA and algal density, acting through biofilm composition, on post-larval and juvenile abalone (Haliotis tuberculata). In a three-month factorial experiment, abalone were exposed from metamorphosis onward to two pH conditions (ambient 8.0 and reduced 7.7) and two initial densities of the green alga Ulvella lens on settlement plates. Biofilm biomass and composition were characterised using spectral reflectance and HPLC pigment analysis. Biological (density, length), physiological (respiration rate), behavioural (hiding response) and shell parameters (colour, surface corrosion, strength) of abalone were measured throughout the experiment. Biofilm biomass and composition remained relatively stable under both pH conditions, though greater variability in algal biomass occurred at low initial Ulvella density. Post-larval density and total length decreased significantly under low pH, while high Ulvella density reduced juvenile length at 80 days, likely due to competition between algal groups. A pH × Ulvella interaction affected shell fracture resistance and colouration, but not metabolism or behaviour, indicating that juvenile abalone maintained vital functions. Overall, the results confirm the sensitivity of early H. tuberculata stages to moderate OA (−0.3 pH units) and highlight indirect macroalgal effects through changes in diatom communities. In natural environments, the capacity of abalone to cope with future OA will depend on complex trade-offs between direct acidification effects and food-related biotic interactions.
Continue reading ‘Interactive effects of ocean acidification and benthic biofilm composition on the early development of the European abalone Haliotis tuberculata’Genotype and symbiont composition rather than environment influence susceptibility to stony coral tissue loss disease in coral restoration broodstock
Published 19 December 2025 Science ClosedTags: biological response, BRcommunity, corals, multiple factors, North Atlantic, performance, phytoplankton, temperature
Over the last several decades, Florida’s Coral Reef has been impacted by global and local stressors causing significant declines in living coral with no signs of natural recovery. Ocean warming, ocean acidification, and infectious diseases are major contributors to the precipitous loss of corals within this region. Since 2014, the stony coral tissue loss disease (SCTLD) outbreak has been particularly devastating, causing unprecedented mortality in over 20 massive coral species. As SCTLD is now endemic in the region, and threats from climate change are likely to persist, studying the disease susceptibility of different coral genotypes under future environmental scenarios is vital for effective restoration. Here, we exposed Orbicella faveolata and Pseudodiploria clivosa genotypes to wild colonies showing signs consistent with SCTLD immediately following a 2-month long exposure to ocean warming (OW) and ocean acidification (OA) scenarios. Corals were exposed to SCTLD for 3 weeks while maintaining the environmental treatments. For both species, pre-exposure to OW and OA scenarios did not make corals more susceptible to SCTLD. However, three genotypes hosting higher levels of Breviolum were at increased risk for showing SCTLD signs under these conditions. One O. faveolata genotype was consistently resistant to SCTLD under the different scenarios, suggesting that natural levels of resistance exist in coral restoration broodstock. Understanding why this genotype could withstand exposure to these stressors may be critical for ensuring survival of restored populations into the future.
Continue reading ‘Genotype and symbiont composition rather than environment influence susceptibility to stony coral tissue loss disease in coral restoration broodstock’Seasonal variations of physico-chemical variables interaction and their influence on phytoplankton and pCO2 dynamics in the Southwest Bay of Bengal
Published 12 December 2025 Science ClosedTags: abundance, biogeochemistry, biological response, chemistry, community composition, field, Indian, otherprocess, phytoplankton
The carbonate system and nutrient dynamics play a crucial role in regulating phytoplankton productivity and carbon cycling in tropical coastal ecosystems, which are highly sensitive to climate change and anthropogenic activities. The present study investigates the spatio-temporal variability of physico-chemical parameters, nutrient dynamics and their influence on phytoplankton community structure along the southwest coast of Bay of Bengal (SWBoB), with particular focus on their relationship with partial pressure of carbon di-oxide (pCO₂). Seasonal sampling was carried out entirely with onboard cruise programs, with each cruise representing different season such as pre-monsoon, monsoon, post-monsoon and summer. The study covered SWBoB among six stations namely Tuticorin, Nagapattinam, Poombuhar, Pondicherry, Mahabalipuram and Chennai during 2022–2023. A total of 77 phytoplankton species representing five taxonomic classes were identified and quantified, where minimum and maximum phytoplankton density were observed during summer (7.498 × 103 cells. L-1) and pre-monsoon (7.0014 × 104 cells. L-1) respectively. A pronounced spatio-temporal variations were observed in physico-chemical parameters and nutrients with peak phytoplankton density and pCO₂ value (487.47 µatm) during pre-monsoon period were attributed to enhanced microbial respiration, riverine input and upwelling of CO₂-rich subsurface waters. In contrast, reduced pCO₂ level (274.27 µatm) observed during summer coincided with water column stratification, nutrient limitation and elevated photosynthetic uptake by phytoplankton. Canonical Correspondence Analysis (CCA) indicated a strong association were attributed nutrient availability and phytoplankton assemblages, with diatoms prevailing under nutrient-rich and moderate pCO₂ conditions, simultaneously dinoflagellate dominated at high pCO₂ conditions. A significant positive relationship between pCO₂ and phytoplankton species with canonical score (0.91) of Noctiluca scintillans highlights the sensitivity of SwBoB productivity to carbon system variability. During pre-monsoon, high pCO₂ (487.47 µatm), chlorophyll-a (3.10 µg L-1) and phytoplankton density (7.0014 × 104 cells. L-1) at station T2, co-dominated by both diatom (46 %) and dinoflagellates (40 %), specifically Noctiluca scintillans (6.32 %). This indicated that nutrient enrichment and CO₂-rich upwelling enhanced phytoplankton productivity and carbon dynamics. These findings imply that pCO₂ variations, determined by temperature, salinity and nutrient inputs which influence the phytoplankton structure and productivity, impacts carbon cycling and ecosystem dynamics in the SWBoB region. This study provides valuable insights into carbon cycling and ecosystem functioning, crucial for sustaining regional fisheries and anticipating monsoon-driven changes in coastal productivity.
Continue reading ‘Seasonal variations of physico-chemical variables interaction and their influence on phytoplankton and pCO2 dynamics in the Southwest Bay of Bengal’Ocean acidification alters phytoplankton diversity and community structure in the coastal water of the East China Sea
Published 5 December 2025 Science ClosedTags: biogeochemistry, biological response, community composition, laboratory, mesocosms, North Pacific, otherprocess, 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 stimulated phytoplankton growth and primary production during the initial nutrient-replete stage, while the community diversity and evenness 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. Such suppression of diatom-to-dinoflagellate succession occurred with enhanced remineralization of organic matter under the HC conditions, with smaller phytoplankton becoming dominant for the sustained 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’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 2 December 2025 Science ClosedTags: biological response, physiology, 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, which serve as critical interfaces between terrestrial and marine ecosystems, are regarded as metabolic hotspots in the oceans, due to their intense biological and biogeochemical activities. Additionally, they are particularly sensitive to the impacts of global climate change. In this regard, 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. Many experiments confirmed theoretical predictions, notably regarding the predicted positive effects of increased temperature and nutrient concentrations on metabolism, but more complex responses, often linked to trophic cascade mechanisms and thresholds between positive and negative feedbacks were also often reported. Overall, this review, the first comprehensive synthesis of experimental evidence on PCR in European coastal waters, highlights critical knowledge gaps, notably regarding non- and understudied areas and understudied interactions between stressors that occurs jointly in natural ecosystems. Future research should aim to integrate controlled experiments, long-term monitoring, and modeling approaches to deepen our understanding of PCR dynamics under changing environmental conditions and to predict potential feedbacks to global climate processes.
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’The larva-Symbiodiniaceae association at risk: putative impacts of climate change on reproduction, dispersal, and recruitment in coral reefs
Published 24 November 2025 Science ClosedTags: biological response, BRcommunity, cnidaria, corals, mollusks, physiology, phytoplankton, porifera, reproduction, review
The relationship between invertebrates and Symbiodiniaceae dinoflagellates is the ecological foundation of diverse and productive coral reef ecosystems. Climate change-induced breakdown of this partnership, i.e., bleaching, is repeatedly driving widespread reef degradation. Thus, the future trajectory of this ecosystem depends on the reproduction and dispersal capacity of invertebrate-Symbiodiniaceae symbiosis. This review examines how climate change affects the biology of larvae from three invertebrate phyla—Porifera, Cnidaria, and Mollusca—that host Symbiodiniaceae, focusing on differences in symbiont transmission mode, symbiont location, and the larvae´s reliance on these associations. Due to limited research on Porifera and Mollusca hosts, most knowledge of larvae-Symbiodiniaceae associations stems from coral larvae patterns. The myriads of combinations of genetic and ecophysiologically distinct hosts and symbionts result in highly context-dependent responses to warming, but symbiotic larvae tend to be more susceptible to oxidative stress and show higher mortality than aposymbiotic larvae. While ocean acidification has little direct effect on the algal symbionts, it impacts larvae variably, especially calcifying larvae (e.g., mollusks), which suffer from impaired calcification and higher mortality. Climate change also impairs the reproductive processes of Symbiodiniaceae-bearing invertebrates, reducing gamete output, causing asynchronous spawning, and lowering larval survival. These effects will result in a persistent decline in recruitment with increased larval retention, consequently reducing reef connectivity and genetic diversity, thus weakening ecosystem resilience. This underscores the urgent need to hasten knowledge on larval ecology under climate change and the functional role of symbionts to better inform marine conservation planning and to incorporate larval ecology in the future predictions.
Continue reading ‘The larva-Symbiodiniaceae association at risk: putative impacts of climate change on reproduction, dispersal, and recruitment in coral reefs’Calcifying plankton: from biomineralization to global change
Published 28 October 2025 Science ClosedTags: biological response, mollusks, physiology, phytoplankton, protists, review, zooplankton
BACKGROUND
The production and dissolution of calcium carbonate (CaCO3) is a key component of the ocean carbon cycle. In the open ocean, nearly all CaCO3 is produced by three groups of calcifying plankton: coccolithophores, foraminifers, and pteropods. These taxonomically and functionally diverse organisms play a major role in ocean biogeochemistry by modulating air-sea CO2 exchange, and facilitating the export of carbon and alkalinity to depth.
Despite their biogeochemical importance, these groups are typically considered separately, precluding an integrated understanding. Yet the pathways by which CaCO3 is produced and cycled through the ocean have important consequences for the carbon cycle and ecosystem functioning. Notably, none of the Earth system models included in the current Coupled Model Intercomparison Project (CMIP6) explicitly represents these groups of organisms. Here, we review the distinct functional traits of coccolithophores, foraminifers, and pteropods to elucidate how these traits shape their global distributions, vulnerabilities to climate change and acidification, and their role in modulating ocean chemistry and the Earth system.
ADVANCES
Recent advances in data compilation at multiple levels offer a comprehensive but still incomplete view of the CaCO3 cycle, from biomineralization up to the global ocean, with different traits leading to differing vulnerabilities to environmental change. For example, coccolithophores, as primary producers, are relatively less affected by changes in oxygen concentration compared with heterotrophs, but are particularly sensitive to ocean acidification because of the proton load generated during intracellular calcification, which requires effective pH regulation and proton expulsion. Differing resource requirements contribute to the geographic distributions of each group, while traits such as body size and turnover rate are fundamentally linked to global production, export, dissolution, and burial. Compiling these data allows us to compare the markedly different fates of the CaCO3 produced by each group, from surface production through export to eventual sediment burial. A major imbalance exists in the global CaCO3 cycling related to each calcifying plankton group, with key uncertainties, especially in rates of group-specific production and shallow biologically mediated dissolution. Current best estimates indicate that a large fraction of coccolithophore-derived CaCO3—the dominant source of CaCO3 in the ocean—is dissolved and recycled in the upper ocean. This underscores the central role of ecological processes such as predation, particle aggregation, and microbial respiration in shaping ocean carbonate chemistry.
We suggest that the overlooked process of shallow dissolution, mainly of coccolithophores, is also likely at play within the geological record of this group.
OUTLOOK
The three major groups of calcifying plankton play essential but distinct roles within ocean ecosystems and the marine carbon cycle. Their diverse traits govern global distributions, production, export, and their differing response to environmental change. The magnitude of biologically mediated CaCO3 dissolution in the upper ocean remains broadly unrecognized, with implications for both the global alkalinity budget and interpretations of the fossil record. Sediment cores provide a fossil record going back 65 million years, revealing large variation in organism size and diversity likely linked to changes in seawater carbonate chemistry (acidification) and warming. The extent to which shallow, selective dissolution has biased this record remains an important unresolved question. Addressing discrepancies between CaCO3 production and export from the upper ocean will require renewed focus on both quantifying and understanding the individual and combined contribution of these groups, as well as the biological processes driving shallow dissolution. These efforts are also critical for incorporating a mechanistically resolved CaCO3 cycle into future climate models, thereby supporting a more integrated view of ocean biogeochemistry under climate change.
Continue reading ‘Calcifying plankton: from biomineralization to global change’Oxidative stress and histological alterations in coral Briareum violacea co-exposed to ocean acidification and microplastic stressors
Published 17 October 2025 Science ClosedTags: biological response, BRcommunity, corals, laboratory, morphology, multiple factors, North Pacific, performance, physiology, phytoplankton, plastics
Ocean acidification and microplastic pollution are two major stressors threatening coral health, yet their combined impacts and underlying mechanisms remain poorly understood. This study investigated the combined effects of ocean acidification and microplastics exposure to coral health. Briareum violacea was exposed to pH at 7.7, 7.5, and 7.3 combined with polyethylene microplastic (PE-MP; 50 mg/L) for 21 days. Polyp length and behavioral adaptability were monitored daily, while coral was collected on days 14 and 21 to assess Symbiodiniaceae density, antioxidant enzyme activity, and histopathological alterations. Results showed that combined exposure to different pH (7.7, 7.5, and 7.3) and PE-MP significantly impaired coral condition, reduced polyp length and Symbiodiniaceae density, along with intensified oxidative stress and tissue damage compared to single stressors. These findings underscore coral vulnerability under combined stressors, emphasizing the necessity for future research to address long-term ecological consequences and resilience mechanisms in coral reef ecosystems.
Continue reading ‘Oxidative stress and histological alterations in coral Briareum violacea co-exposed to ocean acidification and microplastic stressors’Research progress on responses of upper-ocean nitrogen uptake and nitrification to ocean acidification and warming (in Chinese)
Published 10 October 2025 Science ClosedTags: biogeochemistry, biological response, multiple factors, otherprocess, phytoplankton, prokaryotes, review, temperature
Nitrogen uptake by phytoplankton and nitrification mediated by nitrifying microorganisms in the upper ocean are key processes affecting marine productivity and carbon sequestration. How these two critical nitrogen cycle processes respond to the dual stressors of ocean acidification and warming represents a pressing research frontier in marine biogeochemical cycles and global change. Elucidating this issue will provide a theoretical foundation for accurately assessing future changes in ocean productivity and the efficiency of the biological pump. However, most existing studies rely on laboratory pure culture experiments, which may fail to adequately reflect the complex interactions between phytoplankton and nitrifying microorganisms in natural marine ecosystems and their responses to changes in environmental factors. The impacts and mechanisms of ocean acidification and warming on nitrogen uptake and nitrification are systematically summarized. In addition, more attention needs to be paid to other factors, such as strengthened ocean stratification and decreased dissolved oxygen contents, induced by ocean acidification and warming, which could indirectly affect nitrogen uptake and nitrification. Existing problems, such as insufficient in-situ monitoring of ecosystems, limited synergistic studies on multiple processes and stresses, and inadequate understanding of long-term adaptation processes, are highlighted. Finally, three key areas of research that need to be focused on in the future were prospected: ① to conduct the synchronous coupling analysis of nitrogen uptake and nitrification processes and clarify the interactive effects of acidification and warming, ② to explore the vertical differentiation response mechanisms of the above processes in the upper ocean, particularly in oligotrophic oceans, where critical knowledge gaps exist, and ③ to elucidate the long-term adaptation processes and nonlinear response laws of phytoplankton and nitrifying microorganisms. A three-in-one research framework is constructed in the spatial dimension, temporal scale and the experimental system to provide a scientific basis for evaluating the evolution of key nitrogen processes and marine productivity under global change.
Continue reading ‘Research progress on responses of upper-ocean nitrogen uptake and nitrification to ocean acidification and warming (in Chinese)’Coral calcification resistance to acidification is physiologically linked with complex intracellular calcium ion dynamics between host and symbiont cells
Published 8 October 2025 Science ClosedTags: biological response, BRcommunity, calcification, corals, laboratory, molecular biology, North Pacific, phytoplankton
Coral calcification is a highly complex process with numerous caveats regarding the mechanisms that dictate productivity and function. Ion homeostasis, however, is the foremost physiological process unanimously shared among Scleractinia and essential for calcification. Consequently, changes to the seawater environment may elicit adverse effects on ion homeostasis. With increasing climate shifts, the physicochemical regime of our global ocean is changing rapidly. Responses of coral calcification to physicochemical change prevail in having little uniformity on an unambiguous mechanism of resistance. Therefore, this study chose a relatively tolerant Hawaiian coral, Montipora capitata to focus efforts on understanding ion homeostasis under chemical seawater manipulation designed to limit calcification. Results indicate a physiological hormesis (two-phase adaptive response) of overall coral host gene expression that was not shared with algal symbionts and decoupled from calcification rates. The sole ion homeostatic mechanism shown was calcium ion regulation by both the host and symbiont cells. Calcium ion homeostasis was also found to be mechanistically different between winter and summer seasons. Thus, potentially indicating complex interactions between host and symbiont cells, as well as the ability for M. capitata to promote calcification under stress. Putatively synthesized here are the physiological cascades and mechanisms of resistance to environmental triggers of acidosis and seasonal change. This work provides insight into linking calcium ion homeostasis with coral resistance and aims to suggest this mechanism as biomolecular indicator used in future assessments to compare tolerance.
Continue reading ‘Coral calcification resistance to acidification is physiologically linked with complex intracellular calcium ion dynamics between host and symbiont cells’Relative enrichment of ammonium and its impacts on open-ocean phytoplankton community composition under a high-emissions scenario
Published 7 October 2025 Science ClosedTags: biogeochemistry, biological response, community composition, field, globalmodeling, modeling, otherprocess, phytoplankton
Ammonium (NH4+) is an important component of the ocean’s dissolved inorganic nitrogen (DIN) pool, especially in stratified marine environments where intense recycling of organic matter elevates its supply over other forms. Using a global-ocean biogeochemical model with good fidelity to the sparse NH4+ data that are available, we project increases in the NH4+: DIN ratio in over 98 % of the ocean by the end of the 21st century under a high-emission scenario. This relative enrichment of NH4+ is driven largely by circulation changes and secondarily by warming-induced increases in microbial metabolism, as well as reduced nitrification rates due to pH decreases. Supplementing our model projections with geochemical measurements and phytoplankton abundance data from Tara Oceans, we demonstrate that shifts in the form of DIN to NH4+ may impact phytoplankton communities by disadvantaging nitrate-dependent taxa like diatoms while promoting taxa better adapted to NH4+. This could have cascading effects on marine food webs, carbon cycling and fishery productivity. Overall, the form of bioavailable nitrogen emerges as a potentially underappreciated driver of ecosystem structure and function in the changing ocean.
Continue reading ‘Relative enrichment of ammonium and its impacts on open-ocean phytoplankton community composition under a high-emissions scenario’Elevated pCO2 and temperature levels modulate the ratios of the photosynthetic methane production to CO2 fixation in the coccolithophorid Emiliania huxleyi
Published 6 October 2025 Science ClosedTags: biological response, laboratory, multiple factors, North Atlantic, photosynthesis, physiology, phytoplankton, temperature
Most phytoplankton species have been shown to release methane (CH4) during photosynthesis; however, little has been documented on how changed levels of CO2 at different temperatures affect their CH4 production along with photosynthetic C fixation. Here, we examined CH4 production and photosynthetic performance in the most cosmopolitan coccolithophorid, Emiliania huxleyi, grown under high (1000 μatm, HC) and ambient (415 μatm, LC) pCO2 levels at five temperatures (16, 20, 22, 24 and 27°C). The HC treatment slightly lowered the optimal temperature for growth and CH4 production, and temperature changes significantly affected both carbon fixation and CH4 production. Under suboptimal temperatures, increasing temperature from 16 to 20°C led to about 96% increase in CH4 production per POC and HC treatment further enhanced this increase by an additional 9%. In contrast, under super-optimal temperatures, a temperature rise by 4°C reduced the microalgal CH4 production per POC under HC treatment by about 24% compared to the control. The calculated CH4 production quotient (MPQ, CH4 released vs. CO2 fixed) ranged between 2 × 10−5−6 × 10−5, and showed a decreasing trend with increasing temperature under both pCO2 levels, implying that the CH4 production by this microalga is being affected by global ocean changes, and the CH4 produced by phytoplankton should be quantified and included in assessing the feedback of marine phytoplankton to climate change.
Continue reading ‘Elevated pCO2 and temperature levels modulate the ratios of the photosynthetic methane production to CO2 fixation in the coccolithophorid Emiliania huxleyi’
