Ocean Acidification

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.

Highlights

• 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 Ω_arag. 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 Ω_arag 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.

Highlights

• 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.

Coastal ocean acidification in river-dominated marginal seas exhibits distinct evolutionary trajectories from the open ocean. However, quantitatively decoupling its multi-stressor drivers remains challenging due to historical data scarcity and the confounding effects of shifting hydrology and localized human activities. We established a robust calibration framework using sedimentary 3‑hydroxy fatty acids to reconstruct a 60-year pH history in the Changjiang Estuary and the adjacent East China Sea shelf. Our reconstruction reveals that the shelf water pH declined at a rate of −0.00093 units yr^-1 over the past six decades, closely tracking the invasion of atmospheric CO₂, whereas the estuarine zone was governed by regional biogeochemical processes. Variation partitioning analysis and generalized additive models quantify that hydrological forcing, anthropogenic forcing and hydro-biological fluctuations accounted for independent variance contributions of 41.3%, 24.8% and 16.3% of the pH variability in the estuary. These findings suggest that the sensitivity of coastal carbonate chemistry to climate-related environmental change depends not merely on atmospheric CO₂ forcing, but also on the balance between regional hydrological regimes and ecosystem state. Scenario-based perturbation analyses further suggest that variations in freshwater discharge, warming, and oxygen dynamics will either amplify or partially buffer coastal acidification signals, depending on the dynamic competition between physical dilution and biologically mediated carbonate processes. This underscores the critical necessity of conducting integrated, multi-stressor assessments to guide adaptive watershed coastal management, rather than treating river-dominated marginal seas as a single homogeneous domain.

Summary

• Ceratostigma willmottianum, which can mineralize atmospheric CO₂ directly into CaCO₃ for long-lasting C sequestration, has both organic and inorganic C sequestration functions. However, how elevated CO₂ affects CaCO₃ mineralization and the allocation of C between the two C sequestration remains unclear.
• Therefore, C. willmottianum was exposed to five CO₂ concentrations (400, 550, 700, 850, and 1000 ppm) in combination with ¹³C isotope labeling, carbonic anhydrase (CA) inhibitor treatments, and transient overexpression assays to systematically investigate these effects.
• Results showed that 700 ppm CO₂ was the most effective in promoting plant growth, photosynthesis, and CaCO₃ accumulation, whereas 1000 ppm CO₂ exerted an inhibitory effect. ¹³C tracing revealed that elevated CO₂ increased C allocation to CaCO₃ mineralization from 3.03% (400 ppm) to 4.62% (700 ppm), while decreasing that to net organic C fixation from 63.40 to 60.51%. CA inhibitor experiments further indicated that extracellular CA plays a key role in promoting more C allocation to CaCO₃ mineralization. Gene expression and functional validation identified CwβCA2 as a key gene responding to elevated CO₂ and promoting CaCO₃ mineralization.
• This study provides a theoretical basis and candidate gene resources for developing biomineralization-based C capture and storage technologies to cope with rising CO₂ in the future.

Highlights

• Ocean acidification causes pH- and time-dependent disruption of nacreous and prismatic microstructures.
• Shell compressive strength declines progressively with decreasing pH and exposure duration.
• Quantitative mantle phosphoproteomics identified 3720 phosphoproteins and 10,780 phosphosites.
• Differential phosphorylation is associated with signaling, vesicular trafficking, autophagy, and metabolic pathways.
• Molecular and shell-level responses support a proof-of-concept dual-indicator framework.

Abstract

Ocean acidification (OA), driven by rising atmospheric CO₂, threatens the structural integrity and ecological performance of calcifying marine organisms, yet the mechanistic links between environmental acidification and compromised shell mechanical resilience remain insufficiently understood. Here, we integrate microstructural imaging, mechanical testing, and quantitative phosphoproteomics to characterize the structural, mechanical, and phosphorylation responses of Mytilus edulis to OA and examine their relationships. Adult mussels were exposed to near-future pH conditions (8.1, 7.9, 7.7) for up to 40 days. OA produced progressive disorganization of nacreous tablets and prismatic columns without altering aragonite–calcite polymorphs, indicating that acidification drives structural degradation rather than mineralogical shifts. Correspondingly, shell compressive strength declined in a pH- and time-dependent manner, with an approximately 60% reduction at pH 7.7 after 40 days. Phosphoproteomic profiling identified 3720 phosphoproteins (10,780 sites), revealing extensive acidification-induced remodeling of phosphorylation networks. Proteins corresponding to differentially phosphorylated peptides were predominantly nuclear and were enriched in kinase-, PH-, PDZ-, and RNA-recognition-domain-containing proteins. Functional analyses implicated MAPK signaling, vesicular trafficking, ion transport, glycolysis/gluconeogenesis, autophagy, and calcium-associated processes. Phosphoproteomic remodeling was associated with the deterioration of shell microstructure and compressive strength, supporting an association between mantle phosphorylation responses and compromised biomineralization under acidification. The enriched pathways and protein domains were functionally related to calcium-dependent signaling, vesicular trafficking, cytoskeletal organization, and cellular metabolism, providing testable candidates for future mechanistic validation. Together, these findings support a working model in which ocean acidification is accompanied by coordinated phosphorylation remodeling and progressive loss of shell mechanical resilience. We further propose a proof-of-concept dual-indicator framework that integrates candidate molecular sentinels with organismal metrics, providing a conceptual basis for future assessment of aquaculture resilience and ecosystem vulnerability under progressive ocean acidification.

Graphical abstract

Globally, oceans are becoming increasingly acidic and hypoxic due to anthropogenic carbon emissions increasing atmospheric CO₂, much of which is absorbed by the ocean. Recent research demonstrates that wastewater discharges, particularly in densely populated regions with large wastewater treatment plants, exacerbate ocean acidification and hypoxia (OAH). Excess nutrients contained in treated wastewater amplify OAH processes, negatively impacting marine life. In the United States, state and federal agencies have the authority to manage nutrient levels in treated sewage in order to protect marine ecosystems. This study includes a compilation of data on OAH and wastewater inputs across key areas—biological thresholds, wastewater plant data, treatment technology options, and policy recommendations—to provide guidance to regulators in reducing excess nutrients that contribute to OAH. A series of steps provided to coastal managers focuses on wastewater discharge as a concrete example of how to translate an emerging scientific understanding into a concrete policy and regulatory recommendation. Wastewater discharges that cause or contribute to OAH conditions in ocean-receiving waters have infrequently been regulated to reduce or eliminate impacts despite the efficacy of increasingly common treatment technologies. With a focus on the California Current Ecosystem (CCE), this study recommends implementing more stringent wastewater treatment plant regulations by moving to technology-based standards to limit nitrogen concentrations in treated sewage discharged off the coast. If implemented, these limitations would minimize wastewater contributions to OAH and reduce its harmful impacts, safeguarding coastal ecosystems and economies. The nutrient management framework outlined here can be replicated nationally using the Clean Water Act framework, or internationally using a similar regulatory framework. Sewage effluent discharges and overflows to the ocean occur in all coastal states and territories, and mitigating these nutrient contributions is a management issue for all coastal managers. In this study, we present a nutrient management framework that can be integrated into regional and national strategies to help coastal regions mitigate OAH impacts on marine ecosystems.

Ocean acidification (OA) poses a significant threat to the ability of marine calcifying organisms—such as mollusks, corals, crustaceans, and plankton—to form and maintain their calcium carbonate-based shells. While some species show greater sensitivity to OA than others, the impacts on benthic marine calcifiers remain inadequately understood. This study investigates the shell density, weight, and thickness of the ostracode species Paracyprideis pseudopunctillata (subphylum Crustacea), which inhabits the continental shelves of the Arctic Ocean. Using microfocus X-ray computed tomography (microXCT) scans, we generated detailed morphometric measurements of specimens collected from both surface and down-core sediment samples to assess variations in shell properties over time. To our knowledge, this is the first study to examine the natural variability of ostracode shell characteristics in a specific region over an extended time period. For each specimen, we calculated a CT number, an index of relative calcium carbonate density, using a previously published equation. Our findings show that most living specimens of P. pseudopunctillata in the Beaufort Sea showed no overt signs of OA-related shell compromise or degradation. Shell density remained consistent between 1969 and 2018 CE, with consistent CT numbers suggesting that corrosive bottom waters are not a persistent feature in this area of the Beaufort Sea continental shelf. This is supported by a timeseries of discrete pH and carbonate saturation measurements. To help quantify diagenetic impacts on ostracode shells, we compared this calibration dataset with measurements of well-preserved adult specimens from downcore intervals of a box core (MR22, MT1, 1-29 cm) and a multicore (HLY1302 MC29, 25-35 cm), both collected from the same location, representing 2018 to 1955 CE and 1953 to 1925 CE, respectively. The CT numbers from these specimens were also consistent, which confirmed the preservation state of most specimens. However, several specimens had low CT numbers, and these shells show surficial evidence of post-mortem diagenesis. We aimed to quantify the extent of diagenesis, which has important implications for paleoenvironmental reconstructions. These findings provide important baseline data for understanding the variability of modern ostracode shell density of fossil and alive-collected specimens.

Ocean acidification (OA) and microplastic (MP) pollution are widespread marine stressors, yet their interactive effects on seafood quality and molecular metabolism remain unclear. This study investigated the combined effects of OA (pH 7.7) and MPs (2 and 200 μg/L) on the Pacific oyster (Magallana gigas). OA was the primary driver of textural deterioration, significantly reducing springiness and chewiness, while combined stress synergistically depleted protein and lipid reserves. Distinct lipid remodeling strategies were identified: OA induced DHA accumulation potentially associated with membrane stabilization, whereas MPs triggered EPA and ARA upregulation associated with stress and immune responses. The flavor profile was severely compromised, characterized by depletion of umami amino acids, nucleotide redistribution, and altered succinate contribution. Transcriptomic analysis revealed that high MP exposure activated genome maintenance and DNA repair-associated pathways, including the Fanconi anemia pathway, superimposed on OA-associated metabolic suppression. Concurrent upregulation of nucleotide salvage (APRT, HPRT) and amino acid catabolic genes (GLS, GDH) suggests increased utilization of flavor metabolites for energetic demands. These findings support a bioenergetic trade-off in which oysters exposed to OA and MPs reallocate resources from nutritional and sensory quality toward cellular maintenance and stress adaptation, highlighting underrecognized consequences of climate change and plastic pollution for seafood quality.

Across the world’s oceans, lakes, and rivers, climate change is reshaping fisheries and aquaculture systems on which billions of people depend for food and millions rely for their livelihoods. This narrative review summarizes peer-reviewed and selected literature published between 2008 and 2026 on climate impacts, adaptation options, and critical knowledge gaps in marine and freshwater fisheries, with a particular focus on tropical and African inland fisheries. This review shows that warming, acidification, deoxygenation, and altered hydrology are disrupting fish physiology; shifting the distribution of marine species poleward by over 70 km per decade, at rates that vary greatly by taxon, depth, and area; and destroying critical habitats. Although this rapid poleward shift is well documented in open marine environments, it contrasts sharply with landlocked or fragmented freshwater systems, where horizontal migration is physically constrained, a contrast central to the concept of climate entrapment developed in this review. In scenarios characterized by high emissions, tropical fisheries may see a reduction of up to 40% in their maximum catch potential, a statistic relevant to specific tropical Exclusive Economic Zones based on bioclimate-envelope forecasts, which should not be interpreted as a global or universal result. This figure is a model-derived projection under a bioclimate-envelope framework rather than an observed trend, and the realized outcome will depend on future emission pathways. These biophysical changes compound already serious pressures, overfishing, habitat loss, and pollution, and the burden falls heaviest on those least responsible: small-scale fishers, women, and indigenous communities. We introduce the concept of climate entrapment to describe the distinct vulnerability of freshwater fisheries: trapped by fragmented habitats and hydrological barriers, fish stocks cannot migrate to more secure waters as conditions deteriorate. While there are promising adaptation strategies, major gaps remain in understanding what works, for whom, and under what conditions. We conclude with priority recommendations for research, policy, and practice.

This doctoral thesis presents a multi-scale and interdisciplinary investigation into the impacts of climate change and anthropogenic pressures on coastal marine ecosystems, integrating the regional dynamics of the Adriatic Sea and the broader context of the Mediterranean Sea. This research combines long-term environmental data analysis with physiological and biochemical studies on key indicator species to elucidate the complex, and often synergistic, nature of the major threats facing these vulnerable environments. The first part of the work highlights a shift in the Adriatic Sea’s physical and biogeochemical regime, from historical eutrophication toward contemporary oligotrophic conditions. The combined effects of reduced Po River runoff and climate-driven warming, particularly during summer, modify the hydrography of the entire basin. These changes have cascading effects, clearly visible in the clam Chamelea gallina. Northern populations, while showing short-term resilience (e.g., higher survival in air), exhibit a lower condition index and higher bioaccumulation of trace metals, which activate costly metabolic defense mechanisms. This energetic stress makes the populations more vulnerable to additional pressures, possibly aligning with the recurrent mass mortality events. The second part of this work was conducted at the Panarea CO2 vents, which constitute a natural laboratory for assessing future global change impacts. Through the study of the coral Balanophyllia europaea, it is found that ocean acidification (OA), especially when combined with ocean warming, significantly impairs coral tissue regeneration, with species-specific responses. A crucial finding was that OA appears to stimulate a response mediated by the coral’s microbiome, enhancing its bacterial degradation capacity and reducing the presence of PAHs in coral tissues. Collectively, this work demonstrates that synergistic stressor interactions pose the greatest threat to marine ecosystems. While evidence of resilience emerges through physiological and microbial adaptations, the findings emphasize the urgent need for integrated management strategies that address cumulative impacts across scales.

This convergent mixed methods study examined the impact of a new phenomena based (PhBL) lesson plan—grounded by social constructivism and the NGSS framework—on 1) student ability to explain and contextualize a phenomenon, and 2) assess student perceptions of PhBL compared to traditional science instruction. This addressed the shift towards science education reform that better prepares K-12 students for the STEM pipeline and creates student agency surrounding human impact on the environment. Ocean acidification was the selected phenomenon for this study as it was culturally and locally relevant to the participants—sixth-grade science students at a Pacific Island public middle school. Findings revealed apparent differences in the distribution of inductive codes, showing treatment group students acquiring more diverse knowledge of ocean acidification as assessed by graphic organizers and field notes. Findings also showed an increase in student ability to construct accurate explanations of ocean acidification and contextualizations in both treatment and control groups, as assessed by the pre/post-tests. But the treatment group students exhibited the larger increase, alluding to PhBL creating the more effective learning environment. Using the Constructivist Learning Environment Survey (CLES), the instrument revealed no significant differences in perceptions between control and treatment group students. However, treatment group students expressed overall positive experiences and opinions towards PhBL via interview questions—and provided insight that would help inform future PhBL.

Highlights

• First discovery of Pseudoalteromonas enrichment in A. japonicus gut under acidification.
• The dominant strain P. carrageenovora P1 was successfully isolated.
• P. carrageenovora P1 activates host antioxidant and immune pathways to bolster stress resilience.
• P. carrageenovora P1 significantly enhances resistance to V. splendidus 21,915 infection in A. japonicus.

Abstract

The sea cucumber (Apostichopus japonicus) is a key mariculture species of high economic value in East Asia. However, Ocean acidification, resulting from the increased uptake of anthropogenic CO₂ by seawater, severely impairs its growth, survival, and reproductive performance, thereby threatening the sustainable development of this aquaculture industry. The gut microbiota play a critical role in host adaptation to environmental stress; however, their involvement in mediating A. japonicus responses to seawater acidification remains unclear. Therefore, this study first compared the gut microbial communities of juvenile and adult A. japonicus under acidified and ambient seawater conditions. The results showed that Pseudoalteromonas abundance was significantly enriched under seawater acidification, from which the dominant strain, Pseudoalteromonas carrageenovora P1, was screened and isolated. This strain, when supplied as a dietary supplement under seawater acidification, improved A. japonicus growth performance and intestinal morphology, activated the Keap1-Nrf2-ARE and NF-κB pathways, enhanced antioxidant capacity and immune function, and increased resistance against Vibrio splendidus 21915 infection. Moreover, P. carrageenovora P1 modulated gut microbial structure by promoting beneficial bacteria such as Lutibacter while suppressing potential pathogens, including Vibrio, thereby maintaining intestinal homeostasis under acidification stress. This study reveals the important value of the gut microbiota of A. japonicus in regulating environmental tolerance of benthic invertebrates, and also provides a scientific reference for stress resistance regulation and health maintenance in A. japonicus aquaculture under seawater acidification.

Mangrove ecosystems are critical blue carbon sinks, yet the role of submarine groundwater discharge (SGD) in carbon outwelling and coastal acidification buffering remains a major knowledge gap. This study integrates radium isotopes (²²⁴Ra and ²²⁸Ra) and carbonate system parameters to quantify SGD-driven carbon fluxes and their impacts on ocean acidification buffering in Tieshan Bay, a mangrove-fringed semi-enclosed bay in Beibu Gulf, China. Field measurements revealed SGD fluxes of (3.93 ± 1.52) × 10⁷ m³/d (11.6 ± 4.5 cm/d), delivering 31-fold more dissolved inorganic carbon [DIC, (1.06 ± 0.13) × 10⁸ mol/d] and 21-fold more total alkalinity [TA, (7.25 ± 0.89) × 10⁷ mol/d] than local rivers. Notably, SGD exhibited a low TA/DIC ratio (0.68 ± 0.14), which mechanistically weakens the bay’s buffering capacity against acidification by reducing the efficiency of the carbonate system to neutralize atmospheric CO₂. Furthermore, bicarbonate dominated SGD-derived DIC (84.7% ± 14.3%), enhancing long-term carbon sequestration potential but concurrently suppressing carbonate saturation states via dilution of carbonate ions [SGD: (27.4 ± 28.1) µmol/L vs. bay: (80.3 ± 22.4) µmol/L]. These findings demonstrate SGD’s dual role as a major carbon outwelling vector and a driver of coastal acidification, redefining blue carbon budgets in mangrove ecosystems.

Marine environments that are subjected to seasonal changes are increasingly exposed to various factors, such as water pollution, climate change, coastal development, and human impacts. Therefore, this study examined seasonal changes in the main physicochemical parameters of seawater around Dangli Island, Langkawi, Malaysia to better understand the environmental conditions that affect the local marine ecosystem. This study examined seasonal variations in the main physicochemical parameters of seawater such as salinity, temperature, conductivity, pH, dissolved oxygen (DO), Total Ammoniacal Nitrogen (TAN), and Orthophosphate (PO₄³⁻) between twelve monitoring stations D1–D12 around Dangli Island during the Southwest and Northwest Monsoons. The results showed a significant difference between the Southwest Monsoon (SWM) season, which exhibited higher salinity up to 31.16 ppt, temperature up to 30.62°C, and conductivity, while the Northwest Monsoon (NEM) was recorded with cooler temperatures as low as 28.73°C and a slight increase in dissolved oxygen in some areas. This phenomenon causes the ocean to absorb CO₂ and control ocean acidification. Warmer waters during NEM can reduce CO₂ solubility, while cooler, oxygen-rich SWM conditions increase CO₂ uptake, potentially increasing acidification. By studying and understanding how these seasonal conditions affect ocean chemistry, it can help assess the long-term impacts of climate change on the marine environment of Dangli Island and allow us to prepare early conservation strategies for the future. These factors can be influenced by seasonal variations and upwelling phenomena. Two-way ANOVA results demonstrated that all physicochemical parameters have no significant difference between sampling stations (p > 0.05). In addition, there have high significant differences between monsoon seasons (p < 0.05) except for conductivity and DO level. The variations in the physicochemical properties of seawater around Dangli Island reveal the influences of rainfall, river discharges, and upwelling phenomenon on stratification shifts that show the differences in the distribution of seawater physicochemical parameters. These findings also provide valuable insights and help to conserve the marine environment, offering a basis for future research and environmental management strategies around Dangli Island.

Marine heatwaves are becoming more frequent and intense, driving mass fish mortalities and reshaping marine ecosystems, yet the capacity of fishes to tolerate heatwaves remains unclear. We quantified physiological condition and behavioural responses of juvenile warm-water (Abudefduf vaigiensis) and cool-water (Microcanthus strigatus) fishes from three natural climate analogues—an ambient temperate reef, an ocean warming analogue, and a combined warming and extreme acidification analogue—before and during the 2023 global marine heatwave, and under a + 3 °C simulated heatwave in the laboratory. In the laboratory, warm-water fish from the warm reef began the experiment in leaner condition than cool reef fish but increased their bite rates under heatwave conditions, compensating for elevated metabolic demand and maintaining body condition. Cool-water fish showed no behavioural adjustment to the heatwave, and body condition diverged by reef origin: cool reef fish lost weight across all treatments while warm- and extreme-origin fish maintained condition, suggesting tolerance was conferred by prior thermal history rather than acute behavioural responses. In the field, warm-water fish were leaner and had lower protein content during the 2023 heatwave than before it, while cool-water fish from the extreme reef had lower body condition than those from the cool reef prior to the heatwave. Our findings suggest that behavioural plasticity can facilitate warm-water fish tolerance to heatwaves at their cold leading edges, while thermal history supports heatwave tolerance in cool-water fish within their core ranges. Populations inhabiting naturally extreme climate analogues may therefore harbour pre-adapted, climate-resilient fish in a future ocean.

Early life stages play a key role in structuring marine benthic communities, yet the mechanisms controlling recruitment in confined habitats remain poorly understood. In particular, the relative importance of substrate stability and visual cues under low-exchange, low-light conditions is unresolved. We investigated zoobenthic recruitment on 8 natural rock types differing in mineral composition, grain size, and surface reflectance, in simulated interstitial sub-boulder conditions in the Ligurian Sea (NW Mediterranean). After 90 d immersion, recruitment was dominated by spirorbid and serpulid polychaetes. Settlement intensity differed markedly among lithotypes, decreasing from granitoids (239.4 ± 37.7 spirorbids and 23.9 ± 3.4 serpulids) to marbles (128.7 ± 45.5 and 13.6 ± 4.8, respectively) and highly porous travertines (55.4 ± 18.5 and 8.4 ± 2.8), in agreement with their estimated dissolution rates. These results suggest that substrate stability is a primary driver of recruitment under confined conditions, likely mediated by localized acidification and enhanced dissolution of calcareous substrates. Within lithotypes, differences in recruitment were also associated with surface reflectance: specifically, a clear preference for darker surfaces emerged within marbles, whereas the colour effect was overridden by structural or mineralogical traits within the heterogeneous matrix of granitoids. These findings indicate that both chemical stability and optical properties contribute to recruitment patterns, although their relative importance varies with environmental context. The modulation of the early colonization in these restricted sub-boulder environments provide a valuable hypothetical framework to investigate the effects of large-scale environmental stressors like future ocean acidification scenario.