Elevated CO2 and diverse nitrogen inputs interactively modulate nitrogen uptake rates.
Ammonium-induced suppression of nitrate and subsequent co-dominance maximize nitrogen uptake.
Efficient biological pump as the regenerated and new production coexist.
West coast of India serves as a model system for rapidly developing tropical basins.
Abstract
The interaction between CO2 enrichment and nitrogen uptake under anthropogenic nitrogen inputs in the tropical coastal seas remains poorly understood. In this experimental study, we investigate the effects of elevated CO2 and impacts of various nitrogen sources such as river runoff, submarine groundwater discharge, industrial effluents, and atmospheric deposition, adding on NH4+ and NO3−uptake in tropical coastal waters. Using microcosm experiments along the west coast of India, a representative model system for tropical coastal ecosystems experiencing rapid anthropogenic development, we show that CO2 enrichment enhances nitrogen uptake, under intense anthropogenic nutrient enrichment. Our observations revealed a distinct uptake pattern of initial preference for NH4+ actively suppressed NO3− assimilation, subsequently leading to the co-dominance of NO3− and NH4+ uptake rates. The correlation between regenerated and new production acts as an efficient coastal biological pump in the coastal waters. These findings suggest that rising anthropogenic CO2, alongside nutrient inputs, may intensify nitrogen cycling in tropical coastal oceans, with implications for primary production and ecosystem dynamics under changing environmental conditions.
We tested OceanSpeak, a novel approach to marine environmental education that integrates an AI wildlife agent with VR.
All participants experienced a significant increase in ocean connectedness and nature connectedness.
Adjusting for covariates, AI-powered conversation with a virtual harbor seal led to greater empathy for seals.
AI-powered conversation increased pro-environmental engagement among participants with prior experiences with seals.
AI-powered conversation improved knowledge of seals for some participants but reduced knowledge of environmental actions.
Abstract
This study presents an empirical investigation of OceanSpeak—a unique combination of virtual reality (VR) scuba diving and conversational artificial intelligence (AI) designed to educate about how ocean acidification and overfishing impact marine life. This pre-registered study examined the effect of interacting with an AI-powered harbor seal on ocean connectedness, empathy with seals, pro-ocean behaviors, and knowledge. The participants were 106 adults affiliated with a university in California, the United States. Participants in the experimental group (N = 53) engaged with the complete version of OceanSpeak, including AI-powered conversation with a virtual harbor seal. We implemented a yoked control design such that participants in the control group (N = 53) were exposed to identical content but experienced another participant’s AI-enabled conversation. In addition, we measured a number of individual differences related to their views on the environment and specific experience with seals. All participants experienced a significant increase in ocean connectedness as a result of the intervention. The control condition outperformed the AI condition regarding knowledge of pro-environmental actions, whereas a small subset of AI participants demonstrated better understanding of seal-specific issues. Without accounting for individual differences, there were no significant differences between conditions in terms of ocean connectedness, empathy, and protective behaviors. However, post hoc analyses indicated that after accounting for baseline ocean connectedness and nature connectedness and their interactions with condition, AI-powered conversation led to significantly more empathy with seals. Moreover, AI-powered conversation with a virtual seal increased protective ocean behaviors among participants with prior seal exposure, suggesting previous experiences with the actor who is speaking in conversational AI may improve the outcome of those interactions.
Our oceans are in trouble and new research from Flinders University shows how changes in diatoms (microalgae) could further undermine the foundation of aquatic life’s food webs – as well as vital deep-sea carbon capture or sequestration.
A new study published in Marine Ecology used high-tech methods to test common microalgal species to assess how various stressors, including acidification from excessive carbon dioxide (CO₂) levels, affect absorption of trace metals and therefore undermine their overall health and role in Earth’s carbon cycling.
Although microscopic, the single-celled algae diatoms that live in oceans, lakes, rivers and even damp soil are among the most important organisms on Earth as they produce a significant portion of oxygen in the atmosphere.
Diatoms account for 40%-50% of primary production in oceans, and they contribute to organic carbon being exported to the deep ocean by fixing CO₂ from near-surface waters, says senior author Professor Sophie Leterme, director of the ARC Industry Transformation Training Centre for Biofilm Research and Innovation at Flinders University’s College of Science and Engineering.
“We showed that changes in the ocean pH can affect the growth, abundance and elemental composition of these diatoms,” says Professor Leterme. “We need to investigate how these changes interplay between various trace elements and can lead to broader ecological impacts, such as disruption to marine food webs, reduced carbon and silicon export, and increased microbial and nutrient activity.”
Rising carbon emissions affect pH levels in seawater, which can alter planktonic algae’s absorption of trace elements including iron, zinc and cadmium, which are essential for inorganic carbon acquisition.
The dissolution of CO₂ into the ocean has already induced a global drop in pH of 0.1 units since the end of the Industrial Revolution, and values are expected to drop another 0.3–to-0.6 units by the end of this century.
Diatom species are great bio-indicators, often used to assess water quality and boost understanding of how ongoing ocean acidification and rising water temperatures downgrade their physiology and functioning – which have important consequences for the future of oceans.
The Flinders researchers say a better understanding how these complex processes work in seawater will help find solutions, including the development of novel biofilms to reduce shipping pollution in harbours.
Using seawater samples collected in South Australia’s Gulf St Vincent and from the CSIRO algae collection, the researchers’ highly sensitive neutron activation analysis was used in experimental setups on the species Thalassiosira pseudonana and Nitzschia navis-varingica.
The experiments, supported by ANSTO expertise, showed how trace metal uptake by marine diatoms could be applied to other marine organisms’ absorption to a wide range of a wide range of other elements in the environment.
“While a higher abundance and growth of diatoms might be beneficial to reduce carbon dioxide levels, the impact of lower concentrations of major and trace elements in the environment is not well understood.
The research article – ‘The impact of ocean acidification on the sorption of trace metals by diatoms’ (2026) by Sophie C Leterme, Tamar Jamieson, Alessandra Mazzoli, Angus Hambrook, Rachel S Popelka-Filcoff, John Bennett and Attila Stopic – has been published in Marine Ecology (Wiley). DOI: 10.1111/maec.70112.
River-dominated ocean margins (RiOMar) and their benthic compartments play a key role in coastal carbon cycling due to the combined effect of high inputs of particulate organic carbon (POC), benthic mineralization and burial processes. This study quantified benthic fluxes of DIC, TA, and oxygen along a transect influenced by riverine POC inputs, providing new insights in diagenetic processes when switching from anaerobic to aerobic dominated sediment form the river mouth to the adjacent shelf. Fluxes at the sediment-water interface were measured ex-situ with sediment cores incubation during two cruises at the end of spring 2018 and 2022. Stations closest to the river mouth exhibit high benthic fluxes averaging 54 ± 20, 30 ± 21 and −27 ± 14 mmol m−2 d−1 for DICflux, TAflux and TOU, respectively, reflecting intense anaerobic remineralization and a strong decoupling between oxygen consumption and DIC production (DICflux:TOU ratio of 1.5 to 3.5). These large TA fluxes further support that FeS burial limits the reoxidation of reduced compounds in these sediments, allowing the upward diffusion of TA produced at depth towards bottom waters. Offshore, In contrast, shelf stations show lower flux intensities, 8 ± 3 mmol m−2 d−1 for DICflux, −1 ± 2 mmol m−2 d−1 for TAflux and −9 ± 2 mmol m−2 d−1 for TOU, suggesting a greater influence of aerobic mineralization, reoxidation processes and nitrification. Stations located in the Rhône prodelta show intermediate benthic fluxes of 24 ± 11, 6 ± 4 and −17 ± 7 mmol m−2 d−1 for DICflux, TAflux and TOU, respectively. By substantially expanding the spatial and temporal resolution of benthic DICflux, TAflux and TOU in this system, this study provides a robust quantitative framework for assessing the contribution of RiOMar sediments to coastal alkalinity budgets and emphasizes the important role of TA fluxes released from the sediment in increasing the buffering capacity bottom waters.
Coastal-estuarine habitats are rapidly changing with respect to ocean acidification (OA). Along the West Coast of the United States, coastal upwelling regions are high in productivity and rich in nutrients, making them key areas for aquaculture oyster production. The native Olympia oyster Ostrea lurida has experienced population collapse due increased commercial harvest, habitat loss, and the introduction of the non-native Pacific oyster Magallana gigas. Despite intense focus on physiological responses of oysters to OA stress, molecular underpinnings of have yet to be fully described, particularly in niche species. Juvenile oysters of both M. gigas and O. lurida were exposed to a range of experimental OA conditions for six weeks to investigate transcriptomic and biomineralization responses under fluctuating and chronic low pH. Low pH had a significant effect on shell dissolution for both Pacific and Olympia oysters, with no statistical difference observed between the two species. Differential gene expression revealed distinct differences in responses of the Pacific and Olympia oysters to OA on the transcriptomic level, with M. gigas showing elevated molecular responses to OA stress. Our findings suggest that the two species may employ distinct adaptive strategies to mitigate low pH that are informative for species-specific management strategies.
Climate driven processes intensify microplastic fragmentation and redistribution.
Microplastics disrupt carbon cycling and climate sensitive ocean processes.
Warming acidification and ice melt amplify microplastic impacts on marine biota.
Polar ice acts as a major reservoir and emerging source of legacy microplastics.
Integrating microplastics into climate policy is critical for ocean resilience.
Abstract
Microplastics (MPs) pollution and climate change are now recognized as two pervasive and interacting stressors reshaping marine ecosystems, yet their combined effects remain insufficiently integrated within marine pollution research. This review synthesizes current global evidence on how climate-driven processes modulate the sources, transport, fate, and ecological impacts of MPs, and how MPs in turn influence climate-linked ocean processes. A systematic literature review was conducted following PRISMA principles, drawing on peer-reviewed studies retrieved from major scientific databases without temporal restriction. A total of 205 publications included for qualitative synthesis. The results demonstrate that ocean warming, acidification, sea-ice melt, extreme weather events, and altered circulation patterns intensify MP fragmentation, redistribution, and bioavailability across marine environments. Warming accelerates polymer degradation and enhances biological interactions, acidification alters surface chemistry and toxicity, and polar ice melt releases large reservoirs of legacy MPs into vulnerable ecosystems. Evidence further shows that MPs disrupt key climate-related processes, including primary productivity, nutrient cycling, and the biological carbon pump, thereby creating feedbacks that may weaken oceanic climate regulation. Combined exposure to MPs and climate stressors amplifies physiological stress, reduces growth and reproductive performance, and compromises resilience across multiple trophic levels. These findings highlight that MPs are not passive contaminants but active modifiers of climate-sensitive marine systems. Integrating MP dynamics into climate research, monitoring frameworks, and policy instruments is therefore essential. Addressing plastic pollution alongside climate mitigation and adaptation strategies will be critical to safeguarding marine ecosystem functioning under future global change.
Comparative review of behavioural responses to major abiotic stressors
Conserved physiological mechanisms underlie diverse behavioural responses
Cross-stressor synthesis identifies common and stressor-specific effects
Ecological consequences extend from individuals to populations
Research priorities for predicting fish responses to global environmental change
Abstract
Anthropogenic activities, including global warming, deforestation, urbanization, intensive agriculture, and aquaculture, are accelerating environmental change with consequences for aquatic ecosystems. As ectothermic vertebrates, fishes are sensitive to alterations in abiotic conditions, responding through behavioural changes that influence survival, reproduction, and species interactions. Although several studies have investigated the effects of abiotic stressors, comparative syntheses across stressors remain limited, constraining our understanding of how environmental drivers influence fish behaviour. In this review, we synthesize evidence on the impacts of six abiotic stressors, including temperature, hypoxia, acidification, turbidity, salinity, and ammonia, and examine the processes underlying responses. Across these stressors, behavioural alterations affect swimming performance, feeding, predator avoidance, social interactions, habitat selection, exploration, courtship, and anxiety-like behaviours. Despite differences in their primary modes of action, these stressors frequently converge on physiological disturbances involving oxidative stress, neurotransmitter regulation, sensory impairment, ion homeostasis, and energy metabolism, ultimately producing behavioural outcomes with ecological consequences. Most studies have been conducted under controlled laboratory settings, limiting ecological relevance. Furthermore, the combined effects of multiple abiotic stressors, together with long-term, multigenerational, and transgenerational responses, remain poorly understood despite their potential consequences for fish growth, reproduction, recruitment, and community structure. This review highlights the urgent need for integrative, multi-stressor, and multigenerational studies spanning diverse species, developmental stages, and ecosystems to improve predictions of fish responses under environmental change. By identifying shared and stressor-specific responses, this synthesis provides a conceptual framework for understanding how abiotic stressors affect fish through physiological pathways that ultimately converge on common behavioural outcomes with important ecological implications.
Marine sponges are key benthic organisms whose ecological success is closely linked to their associated microbial communities. This thesis investigated the microbiome responses of three Mediterranean HMA demosponges, Chondrosia reniformis, Petrosia ficiformis, and Chondrilla nucula, inhabiting natural CO₂ vents off Ischia Island. By comparing wild populations under ambient and reduced pH with in situ transplants, this work explored long-term acclimatization and short-term responses. Species-specific transplantation protocols were optimized to ensure survival of the three sponges and experimental reliability. Then, 16S rRNA gene metabarcoding was used to characterize sponge-associated and seawater microbial communities. Results showed that sponge microbiomes were distinct from seawater and structured by host identity but each species displayed different degrees of stability and plasticity under acidified conditions. Chondrosia reniformis exhibited a highly stable microbiome, with acidification inducing only fine-scale shifts within a conserved core. Petrosia ficiformis showed greater flexibility, but short-term responses were strongly constrained by donor identity and source-associated signatures. In C. nucula, light availability emerged as the main driver of microbiome reorganization, while low pH modulated this response, promoting shifts from photosymbiosis-related taxa toward lineages potentially linked to nitrification and chemoautotrophy. Overall, sponge holobiont resilience appears to rely not on extensive microbial replacement, but on species-specific rearrangements of resident symbionts within persistent host-associated frameworks.
Clam addition rapidly altered nitrogen, oxygen and dissolved-carbon dynamics.
All chamber treatments maintained negative CO₂ fluxes during incubation.
Algal monoculture showed stronger 6-h CO₂ uptake than co-culture.
Hydrochemical variables and cardiac activity were recorded concurrently.
Abstract
Global warming and ocean acidification threaten marine aquaculture. Bivalve-microalgae co-culture is considered a promising approach for low-carbon aquaculture, but its effects on water quality, carbon dynamics and bivalve physiology are not fully understood. This study tested Ruditapes philippinarum and Chlorella vulgaris in sealed static chambers with three treatments: sterile seawater (NP-C), Chlorella monoculture (WP-C) and clam-Chlorella co-culture (WP). Water-quality variables, dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), air-water CO₂ flux and clam heart rate were measured in separate 3-h and 6-h incubations. At the end of incubation, WP had higher ammonium concentrations and lower dissolved oxygen than WP-C, indicating that clam addition changed nitrogen and oxygen conditions. DOC and DIC also changed differently in the two biological treatments. All treatments showed negative air-water CO₂ fluxes. In the 6-h experiment, CO₂ uptake was strongest in WP-C and intermediate in WP. Heartbeats were recorded continuously in four clams for 7.07 h. Overall, the co-culture rapidly altered water-quality and dissolved-carbon dynamics but did not result in greater short-term CO₂ uptake than the algal monoculture under the present chamber conditions.
Are you attending the ASLO 2027 Aquatic Sciences Meeting? Do you want to share your work ocean acidification in the Caribbean and Latin America with a broader audience? Consider submitting your abstract by the September 15 deadline to the session below and contact the organizers below directly with any questions about the session.
The meeting will take place February 28 – March 5, 2027 in San Juan, Puerto Rico. You must register for the meeting and pay the abstract submission fee prior to submitting. After registering, you’ll receive a link to the submission site. Be sure to review the Session List to ensure your abstract is in the right session. There are limited student and early career travel grants, as well as caregiver grants, available for ASLO members.
SS15 Ocean Acidification in the Caribbean and Latin America: Monitoring High-Risk Areas
Organizers Jose Martinez, Caribbean Coastal Acidification Network Debbie-Ann Gordon-Smith, Global Ocean Acidification Observing Network (GOA-ON) Caribbean Hub Cecilia Chapa-Balcorta, Global Ocean Acidification Observing Network (GOA-ON) Latin American and Caribbean Network (LAOCA) Jessie Turner, OA Alliance
Session Description The Caribbean and Latin America are home to diverse landscapes and vital marine ecosystems that form the bedrock of the region’s economy, supporting over 700 million people. Unfortunately, decades of urbanization, continuous monoculture, and global climate change threaten to destabilize these ecosystems. One of these destabilizing forces is ocean acidification (OA), caused by excess atmospheric CO2 entering ocean basins resulting in shifting ocean chemistry in the direction of lower pH. This stresses marine organisms, especially calcifiers like corals, making it harder to grow and maintain their shells and skeletons, risking key economic sectors like fisheries and tourism. While OA is a global phenomenon, there is significant variation in regional severity and impact, especially in coastal zones where local stressors, marine organisms, and hydrodynamics play a strong role in regulating carbonate chemistry.
This session will bring together presentations that highlight ocean and coastal acidification work in the Caribbean and Latin America, with particular emphasis on monitoring in high-risk areas. We define “high-risk” as locations where OA intersects with other stressors such as nutrient runoff, warming, deoxygenation and activities like coral restoration and shellfish aquaculture. Along the Latin American Pacific, upwelling of low-pH water creates chronic stress similar to recurrent Sargassum inundation events on Caribbean coasts, both of which can acutely exacerbate global OA. This emphasizes the importance of OA regional studies, as they create a scientific baseline to inform locally appropriate OA mitigation and adaptation strategies.
However, long-term monitoring and research in the Caribbean and Latin America have lagged behind those of other stressors. For example, only 34% of ocean professionals engaged in OA monitoring in the Caribbean measure two of the four OA parameters required to characterize a carbonate chemistry system (Grabb et al. 2025). A lack of low-cost sensors and/or complex laboratory methods that require specific training and expensive instruments likely drives this gap, meaning that the very studies we need are not occurring at the pace OA demands of us. All of this results in a disparity in how governments and coastal communities respond to OA’s local and regional impacts. Fortunately, many across the region have recognized this and moved beyond isolated efforts to establish regional networks driven by international frameworks dedicated to overcoming challenges like limited resources and technical capacity. These networks include the Global Ocean Acidification Observing Network (GOA-ON), that has a Latin American (LAOCA) and Caribbean Hub, IAEA Ocean Acidification International Coordination Centre (OA-ICC), the Caribbean Coastal Ocean Observing Systems (CARICOOS), and the Caribbean Coastal Acidification Network (Cari-CAN).
These networks have achieved success, including LAOCA’s recent session for young scientists on understanding the impacts of OA, CARICOOS’s MapCO2 buoy (which has been gathering OA data since 2009), and the OA-ICC’s recent training course on monitoring OA in Jamaica. We must further leverage these networks to foment the creation of low-cost OA monitoring methods and strengthen the technical capacity of the region’s researchers. This would bridge the gap that governments and coastal communities need to manage, adapt, and mitigate the impacts of OA.
Ocean acidification is accelerating – yet most people have never heard of it.
Changing Waters: Time for Action on Ocean Acidification aims to change that.
In just 15 minutes, this character-led short film brings science to life. Following real individuals from government, indigenous communities, the seafood industry, and scientists, this film showcases their response to the accelerating impacts of ocean acidification and their calls for action.
Filmed by LUMA Storytelling in Washington State, Colombia, and Fiji Changing Waters features OA Alliance members’ stories and experiences tackling ocean acidification and climate-ocean change in North America, Latin America, and the Pacific Island Region.
This is not a story of doom. On the contrary, it’s about all that we can still save by taking ambitious climate action and the leadership shown by those who refuse to give up.
Progressive ocean acidification and deoxygenation are expected to threaten many marine zooplankton, but their combined effects across life stages remain poorly understood. We investigated stage-specific responses of the egg-carrying copepod Pseudodiaptomus annandalei to changes in pHT (5.97–8.05) and dissolved oxygen (DO; 0.90–8.20 mg L−1). Nauplii were the most sensitive stage in 24-h exposures, with survival dropping below 40% at pHT 6.1 and declining to 55–70% when DO fell below 1 mg O2 L−1. Under combined stress, naupliar survival declined to about 65% in the most severe treatment (pHT 7.11, DO 1.74 mg O2 L−1), whereas copepodites and adults showed no significant short-term survival response. In contrast, moderate combined stress (pHT 7.62, DO 4.11 mg O2 L−1) produced sublethal effects, increasing development time by approximately 70%, reducing development success from 86% to 28%, and decreasing nauplii production by approximately one-third. Thus, nauplii form a critical bottleneck for recruitment under combined stress.
Scientific Significance Statement
Coastal marine ecosystems are increasingly exposed to concurrent acidification and deoxygenation, yet the combined effects of these stressors across zooplankton life stages remain poorly resolved. Using the egg-carrying copepod Pseudodiaptomus annandalei, we show that short-term adult survival was relatively insensitive to combined low pH and low oxygen, whereas naupliar development and reproductive output were strongly reduced. These results identify the naupliar stage as a critical bottleneck under combined acidification and hypoxia. This stage-specific vulnerability implies that adult survival alone can underestimate recruitment impacts of changing coastal carbonate and oxygen conditions.
Sporophytes and gametophytes differed in germ cell release.
Sporophytes and gametophytes differed in physiological responses.
The different responses lead to Ulva sp. green tide outbreak.
Abstract
The Ulva sp. green tide is one global marine ecological disaster, and its prevention and control have drawn global attention. However, existing control strategies based on ecological mechanisms of Ulva sp. green tide without distinguishing sporophytes from gametophytes have yielded limited success, suggesting that the green tide outbreaks are driven by intrinsic biological mechanisms. Ulva australis Areschoug gametophytes and sporophytes differ in chromosome number; hence, it is inferred that their reproductive strategies respond differentially to environment factors, which explains the biological mechanism of Ulva sp. green tides from the perspective of the origin of germ cells. To verify this hypothesis and for effective control of green tides, the sporophytes and gametophytes of U. australis Areschoug were respectively cultivated and exposed to the conditions of nutrient salts, salinity and carbon dioxide (CO2) superimposed in a uniform design experiment for 48 h to observe the release of germ cells (spores or gametes). The spore release rate of sporophytes was positively correlated with salinity (p<0.05). The gamete release rate of gametophytes had a positive correlation with the interaction between NH4-N and PO4-P (p<0.05), and a negative correlation with CO2 concentration (p<0.05). The difference in responses of sporophytes and gametophytes to environmental factors ensures the availability of germ cells of U. australis Areschoug, which facilitates the green tide outbreak. Thus, the sporophyte and gametophyte respond differently to environmental factors, suggesting that they can adapt to different habitats, which implies that the green tide outbreak of the Ulva sp. has an inherent biological promoting mechanism. Moreover, it is understandable that the effect of a single control strategy in dealing with Ulva sp. green tides is not satisfactory.
The scallop Zygochlamys patagonica is an ecologically and economically important seafood species in the Southwest Atlantic Ocean that has been shown to be sensitive to ocean acidification (OA), a global process caused by anthropogenic carbon dioxide emissions. This study experimentally evaluated the effects of a long-term exposure to low pH, including an OA scenario on the scallop adductor muscle— the commercially valuable tissue. We tested three levels of pH, two pH values within the present range of natural variability (high pHT= 8.00 and medium pHT= 7.80) and a lower pH level representing a true OA scenario (low pHT: 7.52). We examined biochemical alterations induced by low pH and assessed the potential for reversibility following a depuration period. No significant effects were observed for medium pH exposure. However, after 14 and 28 weeks of exposure to low pH (OA), significant reductions in protein and total lipid content were observed, resulting in decreased overall energy reserves, while glycogen levels remained unchanged. The fatty acid profile shifted under OA with an increased PUFA/ SFA ratio and higher sums of EPA and DHA. No signs of recovery were detected after the 2-month depuration period. These results indicate that OA-driven changes in biochemical composition may reflect altered physiological status, with potential socio-ecological implications for the sustainable exploitation of this valuable resource.
Elevated CO₂ is a common water-quality challenge in recirculating aquaculture systems. Although its effects are often accompanied by environmental acidification, the direct impact of elevated CO₂ under stable-pH conditions on fish olfactory function remains poorly understood. This study investigated the effects of elevated CO₂ on olfactory function and olfactory epithelial homeostasis in juvenile largemouth bass (Micropterus salmoides). Fish were exposed to approximately 5 mg L−1 (control), 10 mg L−1, and 15 mg L−1 CO₂ for 4 days while maintaining stable pH. Olfactory function and olfactory epithelial responses were evaluated using behavioral assays, calcium imaging, histological analyses, Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining, immunofluorescence, and gene-expression analyses. Exposure to 10 and 15 mg L−1 CO₂ significantly reduced attraction to food odor without affecting swimming activity, indicating impaired olfactory sensitivity. Calcium imaging revealed attenuated olfactory responses to L-alanine, accompanied by altered expression of genes involved in olfactory signal transduction. Elevated CO₂ also increased the number and area of acidic mucous cells, reduced the abundance of mature olfactory sensory neurons, increased apoptosis in the olfactory epithelium, and altered the expression of genes associated with apoptosis, cell proliferation, and neurogenesis. These findings indicate that elevated CO₂ under stable-pH conditions impairs olfactory function and disrupts olfactory epithelial homeostasis in juvenile largemouth bass. The present study demonstrates that dissolved CO₂, independent of environmental acidification, adversely affects the fish olfactory system and highlights the importance of monitoring CO₂ as a key water-quality parameter in recirculating aquaculture systems.
Biogenic acidification increases with stocking density in sea urchin culture.
Total alkalinity mitigates acidification and promotes growth and gonadal development.
Higher alkalinity shifts metabolism toward biosynthesis and energy storage.
Abstract
Among cultured sea urchins in China, Strongylocentrotus intermedius has the highest annual production, with seed production and grow-out primarily conducted under high-density intensive conditions where biogenic acidification readily develops. To investigate its development, effects, and mitigation, we conducted a short-term incubation experiment (1 d) and a 20-day cultivation experiment. In the short-term incubation experiment, a control group with initial pH ≈ 8.1 and TA ≈ 2300 μmol/kg and a TA-elevated group with initial pH ≈ 8.1 and TA ≈ 3600 μmol/kg were established, and sea urchins were cultured across a density gradient of 20–80 g/3 L. In the 20-d experiment, stocking density was 88 g/3 L with the same initial pH and TA settings. The short-term experiment showed that seawater acidification occurred in the control group, and stocking density was significantly correlated to pCO2, ΔpH (pH reduction), TA–DIC, and Ωarag. With increasing stocking density, pCO2 increased significantly, whereas ΔpH and TA–DIC significantly decreased simultaneously. In the TA-elevated group, all parameters except pCO2 were higher than those in the control group across all stocking densities. At the lowest stocking density, ΔpH, TA–DIC, and Ωarag in the control group were −0.09 ± 0.01, 111.48 ± 1.73 μmol/kg, and 1.43 ± 0.00, respectively, whereas the corresponding values in the TA-elevated group were 0.11 ± 0.01, 252.26 ± 6.98 μmol/kg, and 3.23 ± 0.08. These results indicate that increasing TA mitigates biogenic acidification and works to strengthen the buffering capacity of the carbonate system. At the end of the 20-day cultivation experiment, urchins from the TA-elevated group showed significantly higher specific growth rate (1.60 ± 0.08% vs. 1.27 ± 0.06%), weight gain rate (37.72 ± 2.25% vs. 29.04 ± 1.48%), and gonad index (6.09 ± 1.58% vs. 3.54 ± 0.49%) than those from the control group. Metabolomics analysis revealed that TA elevation enriched pathways related to protein biosynthesis, glycerophospholipid metabolism, and sphingolipid signaling, with higher abundances of essential amino acids (L-methionine, DL-isoleucine), sphingomyelins, and the antioxidant indole-3-pyruvic acid. In contrast, the oxidative stress marker DL-2-aminoadipic acid was upregulated in the control group. Overall, increasing seawater TA mitigates biogenic acidification in high-density sea urchin culture, shifting metabolism from stress defense toward biosynthesis and reserve accumulation, thereby supporting growth and gonadal development in juvenile sea urchins.
Global challenges such as ocean acidification can be understood as complex systems involving interconnected causes, effects and relationships. To navigate this complexity, systems thinking (ST) is considered an essential competency that can be fostered through science education. However, empirically tested teaching materials for fostering ST in chemistry education remain scarce. We developed and evaluated a task on ocean acidification based on the ChEMIST table. The task includes subtasks on observation, explanation, modelling, prediction and reflection, including the construction and revision of causal maps on coral decline. The task was piloted with upper secondary students (n = 10) and implemented in a main study (n = 16) using semi-structured interviews. Responses were analysed by subtask, with focus on assessing granularity, complexity and causality of the causal maps. The findings are presented along five ChEMIST characteristics. Findings show that students demonstrated more analytical aspects of ST when identifying elements and direct causal links. More holistic aspects of ST emerged in prediction and reflection subtasks, where students connected ecological, societal and human dimensions of ocean acidification and considered future developments and their own role within the system. Implications include the need for explicit representational scaffolds and prompts that target feedback and cross-level integration.
This chapter examines the role of the oceans as the largest active surface reservoir of carbon in the Earth system and the chemical and physical processes that regulate the storage and redistribution of carbon in seawater. The oceans contain roughly 38,700 Gt of carbon, about fifty times more than the atmosphere, mostly in the form of dissolved inorganic carbon distributed among carbonic acid, bicarbonate, and carbonate species, whose proportions are largely controlled by seawater pH and alkalinity. The chapter introduces the fundamental equilibria of the marine carbonate system, including gas exchange with the atmosphere governed by Henry’s law, and explains how dissolved inorganic carbon and alkalinity determine the ocean’s capacity to absorb atmospheric CO2. It also reviews the origin and composition of seawater and the geochemical processes responsible for ocean salinity. Finally, the chapter describes the major mechanisms transferring carbon from the surface ocean to deeper waters, by the solubility, biological, and carbonate pumps, and examines how the depth of the saturation state of calcium carbonate, the lysocline, and the carbonate compensation depth regulate carbonate sedimentation and provide long-term negative feedback on atmospheric CO2.
Bivalve larvae are highly sensitive to ocean acidification (OA) conditions, a global climate shift that applies selective pressure on calcareous marine organisms. Although a growing body of work exists on the effects of OA on bivalve larvae, most studies rely on pooled-larval sampling, which may obscure gene expression patterns by including larvae with severely underdeveloped or deformed phenotypes, which are common in OA conditions but are unlikely to survive to metamorphosis. Here, we tested a combination of single-larva transcriptomic techniques to investigate the expression of a candidate gene previously shown to be upregulated in OA conditions, Na+K+ATPase (NKA), in Pacific oyster larvae of known phenotypes. We found that upregulation of the NKA gene is detected primarily in larvae with a developed first shell (prodissoconch I), and was not pronounced in underdeveloped or deformed larvae, suggesting its expression reflects active shell formation under OA conditions, rather than a generalized stress response. Further, NKA mRNA was primarily localized along the dorsal shell hinge, the site of CaCO3 deposition, substantiating its role in early shell development. This study provides a methodological framework for phenotype-anchored sampling to investigate the expressional signatures underpinning successful shell development in OA conditions.
CgPGC-1α with classical RRM domain was identified from Crassostrea gigas.
CgPGC-1α mRNA was ubiquitously expressed with the highest level in gill.
CgPGC-1α could respond to acidification treatment, promote mitochondrial biogenesis.
Acidification enhanced mitochondrial biogenesis and ATP via AMPKα/PGC-1α.
Abstract
Ocean acidification poses a significant threat to calcifying marine organisms. The Pacific oyster Crassostrea gigas is an economically and ecologically important bivalve species. Understanding the molecular mechanisms underlying its physiological adaptation to acidification stress is therefore of great ecological and aquaculture relevance. Peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) is a central regulator of mitochondrial biogenesis and cellular energy metabolism, which plays important roles in response to various stressors. In this study, a PGC-1α homolog was identified from Crassostrea gigas (CgPGC-1α), which harbors an evolutionarily conserved RRM domain. The phylogenetic tree indicated that CgPGC-1α first clustered with PGC-1α from molluscs, then grouped with vertebrate PGC-1α, and finally joined with the PGC-1α of arthropods. During larval development, expression level of CgPGC-1α increased from the early embryonic stages, reached its highest level at blastula stage, and subsequently decreased during later development stages. In adult oysters, expression level of CgPGC-1α were detected in haemocytes and all examined tissues, with the highest level in gills. When the oysters were exposed to acidified seawater at pH 7.4, the expression level of CgPGC-1α in gonad was significantly upregulated at 7 and 21 days. Furthermore, at 7 days after acidification treatment, the mtDNA copy number, the expression level of CgMFN mRNA transcripts, the CgPGC-1α protein levels and the pAMPKα (Thr172) phosphorylation levels all significantly increased (p < 0.05), while the relative mRNA expression level of CgDRP1 significantly decreased (p < 0.05). Moreover, a significant increase in the number of mitochondria with morphology changing from elliptical to irregular and cristae becoming swollen was observed, and the ATP content was significantly elevated. After 28d days of acidification, mtDNA copy number and the expression level of CgMFN and CgNRF2 were significantly decreased, whereas the expression level of CgDRP1 was significantly increased. Collectively, these findings reveal a temporal response to acidification, characterized by an early compensatory activation of the AMPKα/PGC-1α axis and enhanced mitochondrial biogenesis, followed by impaired mitochondrial homeostasis under prolonged acidification stress. This study provides new insights into the molecular mechanisms underlying oyster resilience to ocean acidification and highlights the potential importance of mitochondrial adaptation in coping with future environmental changes.
