Global warming and ocean acidification are having an unprecedented impact on marine ecosystems, yet we do not yet know how phytoplankton will respond to simultaneous changes in multiple drivers. To better comprehend the combined impact of oceanic warming and acidification, we experimentally estimated how evolution shifted the temperature-CO2 growth response surfaces of two strains of Skeletonema marinoi that were each previously adapted to four different temperature × CO2 combinations. These adapted strains were then grown under a factorial combination of five temperatures and five CO2 concentrations to capture the temperature-CO2 response surfaces for their unacclimated growth rates. The development of the first complete temperature-CO2 response surfaces showed the optimal CO2 concentration for growth to be substantially higher than expected future CO2 levels (~6000 ppm). There was minimal variation in the optimal CO2 concentration across the tested temperatures, suggesting that temperature will have a greater influence on growth rates compared to enhanced CO2. Optimal temperature did not show a unimodal response to CO2, either due to the lack of acclimation or the highly efficient CO2 concentrating mechanisms, which diatoms (e.g. Skeletonema) can up-/downregulate depending on the CO2 conditions. We also found that both strains showed evidence of evolutionary shifts as a result of adaptation to temperature and CO2. The evolutionary response differed between strains, underscoring how genetic differences (perhaps related to historical regimes) can impact phytoplankton performance. Understanding how a dominant algal species responds to multiple drivers provides insight into real-world scenarios and helps construct theoretical predictions of environmental change.
Continue reading ‘Quantifying evolutionary changes to temperature-CO2 growth response surfaces in Skeletonema marinoi after adaptation to extreme conditions ‘Posts Tagged 'growth'
Quantifying evolutionary changes to temperature-CO2 growth response surfaces in Skeletonema marinoi after adaptation to extreme conditions
Published 19 August 2025 Science ClosedTags: adaptation, biological response, growth, laboratory, multiple factors, otherprocess, phytoplankton, temperature
When time reveals the cost: effects of long-term exposure to low pH on a predatory gastropod
Published 13 August 2025 Science ClosedTags: biological response, calcification, growth, laboratory, Mediterranean, mollusks, morphology
Ocean acidification, a direct consequence of anthropogenic carbon dioxide emissions, is among the major challenges for marine organisms. While an increased body of evidence is documenting the negative effects of ocean acidification, most of these studies are still based on short-term exposure. Long-term experiments, studying multiple traits simultaneously, and accounting for short-term local pH variability in the species’ habitat are needed. This study investigated the impact of a 310-day exposure to low pH on the banded-dye murex, Hexaplex trunculus (Linnaeus, 1758), a predatory Mediterranean gastropod. Temperature strongly influences the behavior and activity of the banded-dye murex, so we allowed it to vary naturally in this experiment. Our results showed that the net calcification rate was negatively affected by low pH throughout the duration of the experiment. While the banded-dye murexes were able to maintain their total body weight at the beginning of the experiment, it decreased under chronic exposure to low pH. Soft tissue body weight remained unaffected for more than 200days, followed by a pronounced decrease when exposed to lower pH. No sex-specific differences in response to low pH were observed, but females generally exhibited higher rates of calcification and growth during the winter period, likely due to energy allocation strategies associated with the reproductive cycle. These results suggest that while the banded-dye murex can temporarily reallocate energy to maintain essential physiological functions under low pH, this capacity diminishes over time, revealing physiological limits to long-term stress tolerance. This finding highlights the importance of incorporating long-term, multi-trait experiments in ocean acidification research to better predict species vulnerability, ecosystem-level impacts, and the resilience of coastal marine communities under future climate change scenarios.
Continue reading ‘When time reveals the cost: effects of long-term exposure to low pH on a predatory gastropod’Adaptive phenotypic evolution of Skeletonema costatum to ocean acidification and warming with trade-offs from a multi-year outdoor experiment
Published 11 August 2025 Science ClosedTags: adaptation, biological response, growth, laboratory, mesocosms, multiple factors, otherprocess, photosynthesis, physiology, phytoplankton, temperature
Human-induced climate change is increasing variability in marine environments, significantly affecting marine organisms and ecosystems. While marine diatoms can adapt to ocean acidification and warming in stable laboratory settings, their responses to long-term environmental changes under natural variability remain unclear. To investigate this, we cultivated Skeletonema costatum in outdoor semi-continuous cultures for over 3 years, exposing them to fluctuating natural light and temperature that tracked the in situ sea surface temperatures. We simulated current and future ocean conditions through four treatments: ambient CO2 and temperature (LTLC), elevated CO2 (LTHC), elevated temperature (+4°C, HTLC) and combined increases (HTHC). After 1396 days, we assessed populations in two assay environments (20°C, 400 ppm CO2 and 24°C, 1000 ppm CO2) for adaptations in growth rate, pigment composition and photosynthesis. The HTLC-selected group showed the highest growth rates in the HTHC assay environment, while the LTLC-selected group grew fastest in the LTLC assay environment, indicating adaptive evolution. Furthermore, populations selected under elevated conditions exhibited lower fitness in LTLC environments, highlighting a trade-off and underscoring the complexity of evolutionary adaptation in marine diatoms. Understanding these mechanisms is crucial for predicting phytoplankton dynamics and their role in marine ecosystems, especially in response to climate change.
Continue reading ‘Adaptive phenotypic evolution of Skeletonema costatum to ocean acidification and warming with trade-offs from a multi-year outdoor experiment’Ocean acidification interacts with low salinity and phosphorus limitation to modulate growth, photosynthesis, and physiology of mass-cultivated Gracilariopsis lemaneiformis
Published 4 August 2025 Science ClosedTags: algae, biological response, fisheries, growth, laboratory, multiple factors, nutrients, photosynthesis, physiology, salinity
Due to the effective removal of phosphorus during eutrophication control and intensive macroalgal cultivation, phosphorus limitation in coastal waters is normalized. As an economic macroalga cultivated on a large scale in production, Gracilariopsis lemaneiformis is also inevitably influenced by the combination of phosphorus limitation, ocean acidification caused by the increase of dissolved CO2 concentration and salinity decrease as a consequence of rainfall. In this study, G. lemaneiformis was cultured for 15 days under two pCO2 levels (LC: 400 μatm, HC: 1000 μatm), two salinities (LS: 22, HS: 30) and two phosphorus concentrations (LP: 0.1 μmol L−1, HP: 10.1 μmol L−1) to study the growth and photophysiology responses of this macroalga to the coupling of phosphorus limitation, ocean acidification and low salinity. Lower phosphorus (LP) treatment substantially reduced multiple parameters compared to higher phosphorus (HP) condition, including relative growth rate (RGR), photosynthetic rate, chlorophyll fluorescence parameters, and the contents of pigments, soluble protein, and soluble carbohydrate. Elevated CO₂ (HC) exposure induced a significant reduction in algal RGR under LP condition, while demonstrating no statistically significant impact on RGR under HP condition. Furthermore, HC treatment significantly inhibited carotenoid biosynthesis under LP condition. Notably, lower salinity (LS) stimulation significantly enhanced RGR in the ambient CO₂ (LC) group, but this promotive effect was completely negated under HC condition. These findings demonstrated that phosphorus limitation had an adverse outcome on algal growth, and phosphorus limitation exacerbated the adverse effect of ocean acidification on its growth. Moreover, the promotion effect of low salinity on algal growth could be neutralized by ocean acidification. This study provided important information about the influence of environmental changes on the photophysiological characteristics of G. lemaneiformis and new breeding directions for large-scale cultivation of coastal economic macroalgae.
Continue reading ‘Ocean acidification interacts with low salinity and phosphorus limitation to modulate growth, photosynthesis, and physiology of mass-cultivated Gracilariopsis lemaneiformis’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
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’Mid-Miocene warmth pushed fossil coral calcification to physiological limits in high-latitude reefs
Published 28 July 2025 Science ClosedTags: biological response, calcification, corals, field, growth, morphology, paleo
The history of resilience of organisms over geologic timescales serves as a reference for predicting their response to future conditions. Here we use fossil Porites coral records of skeletal growth and environmental variability from the subtropical Central Paratethys Sea to assess coral resilience to past ocean warming and acidification. These records offer a unique perspective on the calcification performance and environmental tolerances of a major present-day reef builder during the globally warm mid-Miocene CO2 maximum and subsequent climate transition (16 to 13 Ma). We found evidence for up-regulation of the pH and saturation state of the corals’ calcifying fluid as a mechanism underlying past resilience. However, this physiological control on the internal carbonate chemistry was insufficient to counteract the sub-optimal environment, resulting in an extremely low calcification rate that likely affected reef framework accretion. Our findings emphasize the influence of latitudinal seasonality on the sensitivity of coral calcification to climate change.
Continue reading ‘Mid-Miocene warmth pushed fossil coral calcification to physiological limits in high-latitude reefs’Ocean acidification impairs growth and induces oxidative stress in the macroalgae Ulva fasciata and Petalonia fascia
Published 22 July 2025 Science ClosedTags: algae, biological response, growth, laboratory, photosynthesis, physiology, South Atlantic
Ocean acidification (OA), driven by increasing anthropogenic CO2 uptake, poses a significant threat to marine ecosystems; understanding the physiological responses of key primary producers like macroalgae is crucial for predicting ecological consequences. This study investigated the impacts of OA on two common intertidal macroalgae, the green alga Ulva fasciata and the brown alga Petalonia fascia, aiming to determine the effects of decreased seawater pH on their relative growth, photosynthetic performance, biochemical composition, and oxidative stress responses. Algae were exposed for 15 days to three pH levels (8.2, 7.4, and 6.5), and measurements included relative growth rate, membrane damage, total chlorophyll, soluble protein and sugar content, chlorophyll a fluorescence parameters, H2O2 content, lipid peroxidation, and activities of superoxide dismutase and catalase. Results showed that decreasing pH significantly reduced RGR in both species, particularly at pH 6.5, with U. fasciata generally exhibiting higher growth. Photosynthetic efficiency and total chlorophyll content declined under lower pH, while non-photochemical quenching generally increased. Both species exhibited increased membrane damage, H2O2 content, and TBARS levels at lower pH, indicative of oxidative stress. Antioxidant enzyme activities were significantly modulated by pH and showed species-specific patterns, with significant interactions between pH and species observed for most parameters. For instance, U. fasciata maintained higher Fv/Fm at pH 6.5, whereas P. fasciata often showed higher antioxidant enzyme activity; soluble protein and sugar contents were also significantly altered. These findings indicate that both Ulva fasciata and Petalonia fascia are susceptible to detrimental effects from simulated OA, suggesting potential shifts in the competitive balance and structure of intertidal macroalgal communities.
Continue reading ‘Ocean acidification impairs growth and induces oxidative stress in the macroalgae Ulva fasciata and Petalonia fascia’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’Physiological and growth responses of Black Sea salmon (Salmo labrax) to long-term salinity and high carbon dioxide stress
Published 16 July 2025 Science ClosedTags: biological response, Black Sea, fish, fisheries, growth, laboratory, molecular biology, morphology, multiple factors, physiology, salinity
Black Sea salmon (Salmo labrax), an anadromous salmonid species of regional importance, is increasingly considered for aquaculture in the Black Sea. This study investigates the physiological and growth responses of Black Sea salmon to seawater transfer, with a particular focus on carbon dioxide (CO₂) stress. The experiment began on 5 July 2022 with 720 fish (76.68±15.34 g) reared under semi-controlled conditions using a freshwater recirculating aquaculture system (RAS). On 12 October 2022, a group of fish was transferred to Black Sea water (18 ppt), and a subgroup was exposed to elevated CO₂ (1000 µatm pCO₂) until the end of the trial on 7 March 2023. Exposure to carbon dioxide showed negligible or minimal effects on seawater adaptation and growth. In contrast, physiological markers such as gill Na⁺/K⁺-ATPase (NKA) activity and the expression of nkaα1a, nkaα1b, and nkcc1a genes, along with growth metrics—including specific growth rate (SGR), condition factor (K value), and liver gene expression of igf-I, igfbp1b, ghr1, and ctsl—indicated that the fish were not physiologically prepared for seawater transfer in autumn. These findings suggest that the commonly practiced autumn sea transfer in the region may lead to suppressed growth and suboptimal performance. The results emphasize the importance of aligning seawater transfer with the smoltification window to support fish health and optimize aquaculture outcomes in Black Sea salmon farming.
Continue reading ‘Physiological and growth responses of Black Sea salmon (Salmo labrax) to long-term salinity and high carbon dioxide stress’Impact of ocean acidification on skeletal structures in gilthead sea bream (Sparus aurata): in vitro and in vivo studies
Published 15 July 2025 Science ClosedTags: biological response, fish, growth, laboratory, Mediterranean, molecular biology, morphology, physiology
Highlights
- Ocean acidification affects bone mineralization.
- Ocean acidification modifies otolith size.
- Low extracellular pH increases the viability and mineralization of osteoblasts.
- Changes in cell culture pH modify the gene expression of osteoblasts.
Abstract
Ocean acidification is considered a significant risk to aquaculture, as it may adversely affect the growth and development of aquatic organisms. The effect of ocean acidification has been shown to impair the growth and survival of fish and to increase otoliths calcification in certain species; however, its effects on bone mineralization remain not well studied. The objective of the present study was to examine the effects of seawater acidification on the skeletal mineralization of gilthead sea bream juveniles, and to assess the direct impact of distinct pH levels on bone-derived cells development. After 68 days of exposure to low pH, fish exhibited a significantly reduced specific growth rate and elevated plasma pH levels, which influenced electrolyte concentrations such as potassium. Moreover, fish exposed to low pH showed increased otoliths size but no differences in shape. In bone, a higher vertebral length/height ratio was also observed, accompanied by significantly reduced opacity and increased expression of the osteoblast and osteoclast markers, alkaline phosphatase (alp) and matrix metalloproteinase 9 (mmp9), respectively, suggesting an elevated rate of bone turnover although reduced mineralization. In vitro, osteoblasts exposed to a low extracellular pH for 30 days exhibited increased viability and mineralization compared to cells maintained at a plasma pH or an alkaline pH. Additionally, the pH level significantly influenced the expression of several extracellular matrix components and osteoblast markers supporting those observations. Overall, these findings underscore the threat that ocean acidification poses to aquaculture, particularly through its impact on skeletal mineralization in gilthead sea bream, and highlight the importance of identifying approaches to farming resilient fish.
Continue reading ‘Impact of ocean acidification on skeletal structures in gilthead sea bream (Sparus aurata): in vitro and in vivo studies’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’Larval Arctic cod (Boreogadus saida) exhibit stronger developmental and physiological responses to temperature than to elevated pCO2
Published 10 July 2025 Science ClosedTags: Arctic, biological response, fish, growth, laboratory, morphology, mortality, multiple factors, physiology, reproduction, temperature
High-latitude ecosystems are simultaneously warming and acidifying under ongoing climate change. Arctic cod (Boreogadus saida) are a key species in the Arctic Ocean and have demonstrated sensitivity to ocean warming and acidification as adults and embryos, but their larval sensitivity to the combined stressors is unknown. In a laboratory multistressor experiment, larval Arctic cod were exposed to a combination of three temperatures (1.8, 5 and 7.3°C) and two carbon dioxide (pCO2) levels (ambient: 330 μatm, high: 1470 μatm) from hatching to 6-weeks of growth. Mortality rates were highest at 7.3°C (5% day°1); however, both growth and morphometric-based condition were also highest at this temperature. When these metrics were assessed via a mortality: growth (M:G) ratio, 5°C appeared to be an optimal temperature for net population biomass, as faster growth at 7.3°C did not fully compensate for higher mortality. In contrast, although morphometric-based condition was lowest at 1.8°C, lipid-based condition was highest, which may reflect prioritization of lipid storage at cold temperatures. The capacity of larval Arctic cod to acclimate to a range of temperatures was exhibited by two lipid-based indicators of membrane fluidity, including a ratio of unsaturated to saturated fatty acids and a ratio of polar lipids to sterols. The effects of elevated pCO2 were subtle, as well as temperature- and metric dependent. When exposed to elevated pCO2 levels, Arctic cod at 1.8°C exhibited signs of lipid dysregulation, suggesting potential interference with membrane acclimation; larvae at 5°C were in lower morphometric-based condition; and larvae at 7.3°C had higher activity eicosanoid substrates, indicating possible physiological stress. Overall, Arctic cod physiological response to temperature variation was more pronounced than their response to elevated pCO2. Future projections of pCO2 effects on Arctic cod health in a warming ecosystem will need to consider the complexity of temperature-dependence and the specificity of multiple physiological responses.
Continue reading ‘Larval Arctic cod (Boreogadus saida) exhibit stronger developmental and physiological responses to temperature than to elevated pCO2’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’Variable responses to ocean acidification among mixotrophic protists with different lifestyles
Published 13 June 2025 Science ClosedTags: biological response, growth, laboratory, performance, photosynthesis, protists
Marine phytoplankton are facing increasing dissolved CO2 concentrations and ocean acidification caused by anthropogenic CO2 emissions. Mixotrophic organisms are capable of both photosynthesis and phagotrophy of prey and are found across almost all phytoplankton taxa and diverse environments. Yet, we know very little about how mixotrophs respond to ocean acidification. Therefore, we studied responses to simulated ocean acidification in three strains of the mixotrophic chrysophyte Ochromonas (CCMP1391, CCMP2951, and CCMP1393). After acclimatization of the strains to treatment with high-CO2 (1000 ppm, pH 7.9) and low-CO2 concentrations (350 ppm, pH 8.3), strains CCMP1393 and CCMP2951 both exhibited higher growth rates in response to the high-CO2 treatment. In terms of the balance between phototrophic and heterotrophic metabolism, diverse responses were observed. In response to the high-CO2 treatment, strain CCMP1393 showed increased photosynthetic carbon fixation rates, while CCMP1391 exhibited higher grazing rates, and CCMP2951 did not show significant alteration of either rate. Hence, all three Ochromonas strains responded to ocean acidification, but in different ways. The variability in their responses highlights the need for better understanding of the functional diversity among mixotrophs in order to enhance predictive understanding of their contributions to global carbon cycling in the future.
Continue reading ‘Variable responses to ocean acidification among mixotrophic protists with different lifestyles’Alleviation of competitive constraints through long-term adaptation to high CO2 in mixed cultures of two diatom species
Published 27 May 2025 Science ClosedTags: adaptation, biological response, BRcommunity, community composition, growth, North Pacific, otherprocess, photosynthesis, physiology, phytoplankton, respiration
Highlights
- The resources competition of two diatoms reduced most performance parameters.
- High CO₂ adaptation partially alleviates the detrimental effects of competition.
- Resource competition changes phytoplankton’s adaptation strategy to high CO2.
Abstract
Diatoms play a pivotal role in marine ecosystems, contributing significantly to global primary production and carbon cycling. Understanding their responses to high CO₂ is critical for predicting oceanic changes under future climate scenarios. This study investigates the long-term adaptation of two diatom species, Thalassiosira weissflogii and Phaeodactylum tricornutum, to high CO₂ (1000 µatm) over 3.5–4 years and the consequences of their interactions in mixed cultures. Mono- and mixed-species cultures were maintained under both ambient (400 µatm) and high CO₂ conditions to assess various physiological performances. Our results revealed that most measured parameters (growth rate, photosynthesis and respiration rate, chlorophyll fluorescence parameters, and pigment concentration) were significantly reduced in mixed cultures compared to mono-cultures under both CO₂ conditions, underscoring the detrimental effects of interspecific competition. However, long-term adaptation to high CO₂ partially alleviated these reductions, particularly in photosynthesis, respiration, and chlorophyll-a content. These findings highlight the complex interplay between physiological adaptation and interspecific competition in shaping diatom responses to high CO₂. This study advances our understanding of the ecological and evolutionary implications of ocean acidification and underscores the importance of long-term experimental approaches for assessing the impacts of climate change on marine phytoplankton.
Continue reading ‘Alleviation of competitive constraints through long-term adaptation to high CO2 in mixed cultures of two diatom species’Evaluating the impact of ocean acidification on seafood – a global approach
Published 23 April 2025 Science ClosedTags: biological response, crustaceans, echinoderms, fish, fisheries, growth, mitigation, mollusks, mortality, review
The quality of human life and food security are closely linked to the health of the ocean and the many goods and services it provides. However, the ocean is under cumulative stress from various human-driven pressures, leading to eutrophication, deoxygenation, loss of genetic biodiversity, contamination with emerging pollutants (e.g., microplastics and pesticides), and climate change (warming and ocean acidification). The effects of multiple ocean stressors and their interplay on marine life and ecosystems remain poorly understood. This underscores the urgent need for innovative science to resolve the complexity of the interplay of stressors and the resulting impacts. This paper reports findings from the Coordinated Research Project CRP K41018, a five-year program framed by the IAEA. The project was explicitly designed to advance Member States’ understanding of both quantitative and qualitative impacts of ocean acidification on key economically relevant seafood species across different world regions. Furthermore, based on different sensitivity baselines across species, it aimed at exploring adaptation pathways for aquaculture and food industries. As a result, Member States would have improved their comprehension of resilience building in specific local contexts (e.g., types of environments, geographical parameters, human dimension). In this context, it is essential to look for ocean solutions to mitigate adverse impacts on seafood and support adaptation strategies based on nature that can counteract stressors. It is concluded that there is great synergy in planning integrated mitigation and adaptation strategies to multiple stressors in marine ecosystems.
Continue reading ‘Evaluating the impact of ocean acidification on seafood – a global approach’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’Metabolomic profiling of a red alga, Gracilaria changii, under current ambient and elevated pCO2 levels using an untargeted gas chromatography-mass spectrometry (GC–MS) approach
Published 14 April 2025 Science ClosedTags: algae, biological response, growth, laboratory, photosynthesis, physiology
Metabolomics offers valuable insights into the final stages of biological processes within organisms and holds promise for environmental monitoring. The escalating levels of anthropogenic CO2 due to industrialization are projected to raise atmospheric pCO2 to levels exceeding 1000 ppm by 2100. The ocean absorbs approximately 30% of this increase in CO2, altering seawater chemistry and decreasing pH levels. In this study, untargeted gas chromatography-mass spectrometry (GC–MS) complemented by physio-biochemical analyses, was utilized to explore the impact of elevated pCO2 on the growth, photosynthesis, agar yield and quality, and metabolite composition of the red alga Gracilaria changii. Although elevated pCO2 did not increase the growth rate of G. changii, an increase in the photosynthetic electron transport rate suggests that photosynthetic carbon assimilation was enhanced. The extra photosynthate was used for other cellular processes including proton export to regulate cellular pH homeostasis given the excess H+ in the environment, rather than being invested in new tissue growth. Thymine emerged as a key metabolite influenced by elevated pCO2 in G. changii. Pathway analysis unveiled significant impacts on amino acid synthesis pathways in G. changii at high pCO2. The concentration of compounds such as dopamine and glutamic acid, which are known to be triggered during stress response and provide antipathogenic bioactivity, increased in thalli cultured at higher pCO2. Heatmap analysis indicates d-3 as the turning point for G. changii cultivated at higher pCO2, where the macroalgae begin to regulate their metabolites to alleviate abiotic stresses from higher pCO2 and to maintain essential metabolic functions.
Continue reading ‘Metabolomic profiling of a red alga, Gracilaria changii, under current ambient and elevated pCO2 levels using an untargeted gas chromatography-mass spectrometry (GC–MS) approach’The impact of ocean acidification on gastropod shell dissolution and microstructure
Published 11 April 2025 Science ClosedTags: biological response, dissolution, growth, laboratory, mollusks, morphology, North Pacific
Highlights
- Ocean acidification causes gastropod shell dissolution and microstructural change.
- Shell growth is inhibited below pH 7.5, with dissolution pits in the inner surface.
- At pH 7.1, shell surface erosion intensifies, with extensive periostracum peeling.
- Shell dissolution negatively correlates with pH, offering a new bio-proxy.
- Shell structural changes can assess past ocean acidification events.
Abstract
Global seawater pH is projected to decrease by 0.3–0.5 units on average by the end of this century, which is considered detrimental to the shells of marine calcareous organisms. However, there is limited understanding of how ocean acidification affects the morphology and structure of these shells, as well as the underlying mechanisms. This study examines the shell growth, surface erosion, and microstructural changes of the marine gastropod Lunella coronata granulata after 85 days of exposure to varying pH (8.1–7.1). The results reveal that at pH ≤ 7.5, shell growth is notably inhibited, with pronounced dissolution hole formation on the inner surface. At pH 7.1, shell surface erosion becomes more pronounced, accompanied by extensive peeling of the shell periostracum. These changes—dissolution hole formation and periostracum peeling—are critical indicators of gastropod shell response to ocean acidification and can serve as biological indicators reflecting current and past ocean acidification. Additionally, our study shows a clear negative correlation between shell dissolution and pH, providing new bio-proxy for indicating the pH changes.
Continue reading ‘The impact of ocean acidification on gastropod shell dissolution and microstructure’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’
