Coral biomineralization drives the formation of reef structures, but ocean acidification (OA) threatens this process. Coral survival requires effective skeletogenesis in early life stages, through the formation of co joined growth zones: rapid accretion deposits (RADs) and thickening deposits (TDs). Contrasting theories and lack of data on how these zones form hamper our understanding of normal coral growth and under future OA. This study describes growth patterns of RADs and TDs during the early stages of coral calcification under both normal and OA conditions. The work reveals geometric characteristics of RADs and TDs at micro- and sub-micrometer scales, as a basis for learning how OA impacts the early-formed skeletons. By combining material science approaches and Monte-Carlo simulations to model electron interactions that probe mineral phase composition, we show how TDs and RADs form simultaneously, challenging the classical “step-by-step” growth hypothesis. Unexpectedly, under normal pH, TDs comprise ≈65% amorphous calcium carbonate (ACC) and only 35% crystalline aragonite. Under OA, skeletons exhibit higher densities, with only 50% ACC. RADs are underdeveloped under OA, reducing skeletal bending resistance and increasing fracture risk. These findings reveal that the effect of OA on coral skeletogenesis is more complex than previously understood.
Continue reading ‘4D insights into coral biomineralization: effects of ocean acidification on the early skeleton development of a stony coral’Posts Tagged 'laboratory'
4D insights into coral biomineralization: effects of ocean acidification on the early skeleton development of a stony coral
Published 24 September 2025 Science ClosedTags: biological response, corals, laboratory, morphology, Red Sea, reproduction
Using boron isotopes to examine calcification fluid pH changes in marine calcifiers under environmental change
Published 23 September 2025 Science ClosedTags: biological response, calcification, laboratory, light, mollusks, multiple factors, physiology, South Pacific, temperature
CO₂-driven ocean acidification (OA) decreases seawater pH and carbonate ion concentrations, which can impact the calcification and physiology of marine calcifiers. These organisms form calcium carbonate skeletons and shells from a specialized calcification fluid that is, to varying degrees, isolated from surrounding seawater. The carbonate structures serve as archives, preserving the chemical signature of the calcification fluid, which can be analyzed using geochemical proxies. In the following thesis, I examine how different taxa respond to future ocean changes by exposing them to predicted future acidification scenarios. Additionally, I aim to understand if an organism’s resilience to the impacts of ocean acidification is linked to their ability to regulate their calcification fluid chemistry using geochemical proxies.
In Chapter 1, I investigate the geochemistry of three reservoirs important for biomineralization – seawater, the extrapallial calcification fluid (EPF), and the shell – of two commercially important bivalve species: Crassostrea virginica and Arctica islandica to understand if the boron isotope proxy is probing calcification fluid pH. Additionally, I examined the effects of three ocean acidification conditions (ambient: 500 ppm, moderate: 900 ppm, and high: 2800 ppm CO2) on the calcification and chemistry of the calcification fluid of the same three reservoirs for C. virginica. Comparisons of seawater and extrapallial fluid geochemistry indicated that the EPF has a distinct composition that differs from seawater. Additionally, our OA experiments show that EPF chemistry is significantly affected by ocean acidification, demonstrating that the biological pathways regulating or storing these ions are impacted by ocean acidification. I also found that shell δ11B does not faithfully record seawater pH, but rather was correlated with EPF pH, despite an offset from in situ microelectrode pH measurements. However, the δ11B-calculated pH values were consistently higher than microelectrode pH measurements, indicating that the shell δ11B may reflect pH at a more localized site of calcification, rather than pH of the bulk EPF.
In Chapter 2, I investigate the effects of four different seawater pH levels (8.03, 7.93, 7.83, and 7.63) on seven complexes of temperate coralline algae collected from New Zealand. I examined the photophysiology, calcification, and geochemical proxies to probe the internal carbonate chemistry of seven different species of coralline algae under simulated end-of-century ocean acidification scenarios. Under ambient conditions we found clear physiological differences between branching and encrusting species. We found that OA treatments only had a significant effect on calcification of three of the seven species, Corallina berteroi, Corallina spp., and Jania “bottlebrush.” Additionally, OA only affected the calcification fluid pH (pHCF) of two species, decreasing pHCF for both Corallina beteroi and Jania “feather.” Nonetheless, for all species pHCF was constantly upregulated compared to seawater pH, indicating a strong control over calcifying fluid chemistry. My results underscore the high resilience of coralline algae calcification under the different end-of-century ocean acidification scenarios. This tolerance to OA is related to the species’ ability to maintain a stable carbonate chemistry to support calcification as seawater pH declined.
Continue reading ‘Using boron isotopes to examine calcification fluid pH changes in marine calcifiers under environmental change’Carbonate chemistry fitness landscapes inform diatom resilience to future perturbations
Published 22 September 2025 Science ClosedTags: biological response, growth, laboratory, physiology, phytoplankton, South Pacific
Marine diatoms are an abundant and ecologically important phytoplankton group susceptible to changing environmental conditions. Currently available data assessing diatom responses focus on empirical comparisons between present-day and future conditions, rather than exploring the mechanisms driving these responses. Here, we conducted high-resolution growth experiments to map the fitness of diatoms across broad carbonate chemistry landscapes. Our results reveal species-specific carbonate chemistry niches, which can be used to predict ecological shifts between species under changing conditions driven by ocean acidification or ocean alkalinity enhancement. The results demonstrate that changes in diatom fitness are almost exclusively driven by carbon dioxide and proton concentrations, with bicarbonate exerting no discernible effect. Thus, current assumptions regarding the role of bicarbonate as a primary carbon source supporting diatom growth may be overestimated. This study presents a methodological and conceptual framework as a foundation for future studies to collate data capable of predicting species-specific responses and shifts in ecological niches driven by changes in marine carbonate chemistry.
Continue reading ‘Carbonate chemistry fitness landscapes inform diatom resilience to future perturbations’Microplastic exposure under future oceanic conditions further threatens an endangered coral, Acropora cervicornis
Published 22 September 2025 Science ClosedTags: biological response, BRcommunity, corals, laboratory, morphology, multiple factors, photosynthesis, physiology, phytoplankton, plastics, South Atlantic, temperature
Microplastic pollution is ubiquitous in the oceans. However, little is known about the physiological impact of microplastics on corals, particularly under predicted future ocean conditions. This study investigated the individual impacts of microplastic exposure (MP) and predicted future ocean conditions [ocean acidification and warming (OAW)] as well as the combination of these stressors (OAW+MP) on the growth and physiology of Acropora cervicornis, a threatened Caribbean coral and its associated symbiont, Symbiodiniaceae. After 22 days, the OAW+MP treatment resulted in more pronounced physiological changes than either stressor individually or the control. OAW conditions alone had minimal impacts, despite A. cervicornis generally being sensitive to thermal stress. The OAW+MP treatment and the MP treatment also disrupted the host-symbiont relationship evidenced by the higher symbiont densities relative to the control and the OAW treatments. Additionally, the OAW+MP treatment resulted in lower chlorophyll a per symbiont cell. Microplastic handling is energetically costly, possibly leading to changes in host-symbiont signaling. Photosynthetic efficiency was only marginally lower in the OAW+MP treatment, and values did not indicate photosystem damage. Negative host health impacts were found with the OAW+MP treatment exhibiting lower skeletal growth compared to the control and lower host protein concentrations compared to the OAW treatment. These results indicate that although short term microplastic exposure alone may not pose a significant threat to coral health, when adding additional stressors, it can further threaten the health and recovery of this already vulnerable species.
Continue reading ‘Microplastic exposure under future oceanic conditions further threatens an endangered coral, Acropora cervicornis’Effects of simulated ocean acidification on the activity, escape response, and muscle physiology of marine threespine stickleback (Gasterosteus aculeatus)
Published 19 September 2025 Science ClosedTags: biological response, fish, laboratory, North Pacific, performance, physiology
Rapidly increasing anthropogenic CO2 can impose physiological challenges for fish species that are thought to be tolerant. We tested the hypothesis that elevated pCO2 will affect the routine activity and escape response by affecting energy metabolism and/or the muscle physiology of coastal fish. We exposed threespine stickleback (Gasterosteus aculeatus) to pCO2 of ~ 700 µatm (pH 7.9 representing current levels), ~ 1400 µatm (pH 7.6 representing upwelling events) and ~ 3500 µatm (pH 7.3 representing a future predicted scenario for coastal areas) for 2 weeks. Baseline activity was significantly higher in fish exposed to 1400 µatm compared to the control at both sampling points, while the escape response was lower (p < 0.05). Metabolic rate was not different (p > 0.05), but lactate dehydrogenase activity was significantly higher at 3500 µatm compared to control fish after the first week (p < 0.05), while no difference was found in muscle histology between treatments or time points. Our study demonstrates that the baseline activity and escape responses of adult marine coastal fish were temporarily affected by the current level of ocean acidification, but this was not due to changes in metabolism or muscle function, but potentially neuronal effects of high pCO2. Our study shows that ocean acidification might affect predator‐prey interactions during current upwelling events and in the future.
Continue reading ‘Effects of simulated ocean acidification on the activity, escape response, and muscle physiology of marine threespine stickleback (Gasterosteus aculeatus)’Effect of short-term exposure to ocean acidification on antioxidant response in the Patagonian scallop Zygochlamys patagonica (P.P. King, 1832) from the Southwest Atlantic Ocean
Published 19 September 2025 Science ClosedTags: biological response, laboratory, mollusks, physiology, South Atlantic
Ocean acidification (OA) can impair antioxidant responses in bivalves altering their capacity to cope with environmental changes. Here, we analyzed the effects of short-term OA exposure on antioxidant responses of an important commercial Patagonian scallop Zygochlamys patagonica (P.P. King, 1832), considering present pH variability at natural beds of scallops and OA conditions. The scallops were exposed at three levels of pH, (1) high pHT = 8.10 (mean annual pH at the sampling site), (2) medium pHT = 7.80 (minimum value of natural variability recorded at scallops’ bed close to the sampling site), and (3) low pHT = 7.50 (0.30 below medium pH value) for 4 and 17 days of experimental time. Oxidative damage and antioxidants were measured in hemolymph, gill, and mantle. Hemolymph did not show signs of oxidative damage thus, antioxidant response induction was not detected under OA exposure. Gills showed antioxidant activation at 4 days under OA which decreased by the end of the experiment, with no signs of oxidative damage. Non-enzymatic antioxidant decreased under OA in the mantle. This study supports previous evidence of bivalves’ capacity to maintain their redox homeostasis under experimental OA conditions and constitutes a cornerstone to continue elucidating this species’ strategies to cope with environmental changes.
Continue reading ‘Effect of short-term exposure to ocean acidification on antioxidant response in the Patagonian scallop Zygochlamys patagonica (P.P. King, 1832) from the Southwest Atlantic Ocean’Effects of ocean acidification on intestinal homeostasis and organismal performance in a marine bivalve: from microbial shifts to physiological suppression
Published 18 September 2025 Science ClosedTags: biological response, BRcommunity, community composition, laboratory, molecular biology, mollusks, morphology, North Pacific, otherprocess, performance, physiology, prokaryotes
Highlights
- OA stimulates the colonization of the pathogenic bacterium Mycoplasma.
- Microbiota dysbiosis and oxidative damage trigger intestinal inflammation.
- OA causes significant epithelial damage to the intestines of C. nobilis.
- Physiological suppression of C. nobilis is decreased in a pH-dependent manner.
Abstract
Ocean acidification (OA) poses significant threats to marine calcifiers through multifaceted physiological disruptions. While bivalve mollusks are particularly vulnerable, the intestinal defense mechanisms against OA-induced stress remain poorly characterized. This study systematically investigated the intimate associations between the organismal physiological toxicity responses and intestinal homeostasis of Chlamys nobilis (C. nobilis) under simulated OA situations (pH 7.3–8.0) to reveal the potential physiological and biochemical damage. The results revealed that acidification stimulated pathogenic bacteria(Mycoplasma)colonization, disrupted microbiota homeostasis, and induced oxidative responses, thereby triggering intestinal inflammation and epithelial damage. Furthermore, the filtration rates and oxygen consumption rates of C. nobilis were significantly decreased in a pH-dependent manner across all the treatments, which might result from the intestinal dysfunction and the inhibition of acetylcholinesterase activities. These findings establish a link between OA-induced intestinal dysbiosis and organismal physiology, providing novel insights into the interplay between physiological performance and intestinal homeostasis under OA scenarios. The results advance our understanding of bivalve mollusk adaptation strategies and inform predictive models for its sustainability in acidifying marine ecosystems.
Continue reading ‘Effects of ocean acidification on intestinal homeostasis and organismal performance in a marine bivalve: from microbial shifts to physiological suppression’Opposing physiological performances of two coexisting gastropods to changing ocean climate
Published 18 September 2025 Science ClosedTags: adaptation, biological response, growth, laboratory, mollusks, morphology, multiple factors, otherprocess, physiology, South Pacific, temperature
The impact of climate change on the structure of ecological communities will be influenced by how different species respond to changing environmental conditions. In this study, we investigated the effects of increased temperature (summer Control, 21 °C; HT, 24 °C) and elevated CO2 levels (Control, 400 ppm; OA, 1000 ppm) on two species of co-occurring temperate gastropods – Turbo undulatus and Austrocochlea odontis. Biological responses to simulated future conditions were measured as growth rates (shell and tissue) and metabolic rates across thermal ramps (temperatures ranging from 15 °C to 38 °C) after 8 weeks of exposure. We found that T. undulatus exposed to HT, OA or HT × OA conditions had a higher metabolic rate throughout their thermal curve than control conditions. In addition, the temperature at which individuals had maximum metabolic rate (TMMR) was higher in animals acclimated to HT × OA than in other conditions, potentially demonstrating acclimation. In contrast, A. odontis showed antagonistic effects in response to OA and HT; metabolism was lowest under OA but highest under HT. Furthermore, TMMR was reduced in A. odontis exposed to HT and the combination of HT x OA. In terms of growth, T. undulatus exposed to HT and HT × OA grew three times more in shell length and ∼20-30% in weight compared to the control group or those exposed to only OA. In contrast, no treatment had a significant effect on growth in A. odontis. Overall, our findings suggest that the impact of ocean acidification and heating on metabolic function can differ between coexisting species, possibly depending on their evolutionary and life history strategies, and these differential responses could have significant implications for the structure of ecological communities.
Continue reading ‘Opposing physiological performances of two coexisting gastropods to changing ocean climate’Selective breeding boosts oyster resilience to ocean acidification via energy budget modulation
Published 12 September 2025 Science ClosedTags: biological response, fisheries, growth, laboratory, mitigation, mollusks, mortality, North Pacific, physiology
Natural pH variability in coastal-estuarine systems exacerbates OAX events through frequent pCO2 spikes, posing severe threats to bivalves and ecosystems they support. While selective breeding has improved growth performance in oysters, its capacity to enhance tolerance to acidic stress remains poorly understood. Here, we evaluated the physiological performance of wild and recently selectively bred oyster variety (Guihao No. 1) under the simulation of recurrent OAX scenarios. In comparison to wild oysters, selectively bred oysters exhibited significantly higher survival rates, fast shell growth, and improved condition index. Energy metabolism suggests that selective breeding confers enhanced stress resilience in oysters by optimizing feeding capacity, increasing oxygen uptake, and reducing ammonia excretion rates. This metabolic efficiency supports more effective protein and glycogen turnover, as evidenced by elevated O:N ratios, and ultimately results in higher SFG. PCA analysis demonstrated that enhanced energy metabolism (CMA, NKA), antioxidant capacity (low MDA), and immune activity (high ACP, AKP) contributed to improved growth and resilience of selectively bred oysters when exposed to OAX, whereas wild oysters showed metabolic suppression and oxidative damage. These results highlight the role of selective breeding in promoting stress tolerance through optimized energy allocation and defense mechanisms, offering valuable guidance for climate-resilient oyster aquaculture in acidifying oceans.
Continue reading ‘Selective breeding boosts oyster resilience to ocean acidification via energy budget modulation’Transgenerational plasticity responses differ across genetically distinct families in the Sydney rock oyster, Saccostrea glomerata
Published 12 September 2025 Science ClosedTags: adaptation, biological response, laboratory, mollusks, morphology, otherprocess, reproduction, respiration, South Pacific
Across the globe, marine organisms need to rapidly respond to climate change. Acclimation through the mechanism of transgenerational plasticity (TGP) is now at the forefront of research, providing hope that some marine organisms may persist into the future. To date, however, because most studies have focussed on the average phenotypic species response to climate change, we do not know whether phenotypic responses vary among genotypes. Here, we take a next critical step in TGP research to assess whether TGP responses to ocean acidification (OA) differ among genotypes of the culturally significant and iconic Sydney Rock Oyster (SRO), Saccostrea glomerata. Adults of four genetically distinct families of the SRO were exposed to ambient (410 μatm) and elevated (1000 μatm) pCO2 for 9 weeks during reproductive conditioning. Following this exposure, we performed a within family cross of each family and measured the percentage development, abnormality, shell length and respiration rate of D-veliger larvae after 48 hours in the same ambient and elevated pCO2 treatments. We found significant variability in TGP responses among families to elevated pCO2, with positive, negative, and neutral responses in larval offspring. How well we understand the adaptive potential of oysters and their capacity to mount fast responses through TGP to climate change will determine our ability to ensure the sustainability of SRO populations, marine food security and the cultural heritage of this iconic species. Combined approaches quantifying both genetic and non-genetic TGP responses are needed to determine the total adaptive potential of other marine organisms to climate change.
Continue reading ‘Transgenerational plasticity responses differ across genetically distinct families in the Sydney rock oyster, Saccostrea glomerata’Biological and genomic responses of juvenile Pacific oysters (Crassostrea gigas) to a changing ocean
Published 11 September 2025 Science ClosedTags: biological response, laboratory, molecular biology, mollusks, morphology, multiple factors, North Pacific, reproduction, temperature
Climate change, fueled by greenhouse gas emissions, is causing global atmospheric and oceanic temperatures to rise, accompanied by increased levels of carbon dioxide (CO₂) in the ocean, which has led to ocean acidification (OA). During warmer months, climate stressors (e.g. elevated temperatures), host physiology (e.g. reproductive efforts), and opportunistic pathogens like Vibrio spp. and Ostreid herpesvirus 1 (OsHV-1), coincide with each other, and exacerbate interactions into global phenomenon called oyster summer mortality syndrome, a multifactorial disease affecting oysters, particularly Crassostrea gigas (EFSA Panel on Animal Health and Welfare, 2015; Petton et al., 2015; Pernet et al., 2014). While many marine species, including bivalves (such as oysters, mussels, clams, and scallops), are adversely affected by heat and OA individually, there is relatively limited research on the combined effects of these stressors on either somatic growth or genomic responses. In this study, I investigated the individual and combined effects of temperature and pCO2 on various growth and genomic responses of juvenile Pacific oysters (Crassostrea gigas) (mean ± SD shell height: 16.6 ± 1.7 mm, wet weight: 0.47 ± 0.12 g for growth responses and shell height: 15.2 ± 1.3 mm, wet weight: 0.42 ± 0.09 g for genomic responses). Two factors (temperature and pCO2) at two levels (average summer level and IPCC-projected (RCP 8.5) future summer level) were tested in a fully-crossed experimental design, using six replicate tanks per treatment and 24 oysters per tank. Oysters were sampled at regular intervals (every 2 or 4 weeks) over 16 weeks to examine various shell biometrics (shell height, shell length, shell width, wet total weight, wet and dry shell weights, wet and dry soft-tissue weights, fan ratio, cup ratio, weight ratio) and condition index. A different subset of oysters were sampled at regular intervals (every 2 or 4 weeks) over 16 weeks for transcriptomic (RT-qPCR) analysis. Fourteen genes of interest (GOIs)—covering immunity, cellular stress, and metabolism responses—were chosen for study. The results showed that oysters were significantly impacted mostly by high temperature rather than high pCO2, both in individual and combined treatments, when analyzing both the growth and genomic results.
Growth results revealed that somatic growth, weight ratio and condition indices were negatively impacted by high temperature and minimally impacted by elevated pCO2. I found that shell growth in higher temperature conditions was growing at a faster rate than in ambient temperatures, but the amount of wet tissue in high temperature condition oysters was minimal, resulting in a higher weight ratio. Similarly, condition indices were drastically different when comparing the two temperature treatments, not pCO2. Unsupervised hierarchical clustering with principal component analysis revealed numerous clusters when comparing somatic growth, with most clusters relating to week, pCO2, and temperature. Genomic results revealed that nine of the GOIs (i.e. heat shock protein 23, heat shock protein 70, hypoxia-inducible factor 1-alpha inhibitor, V-type proton ATPase catalytic subunit A, multidrug resistance 1, toll-like receptor 7, transforming growth factor, protein kinase R, macrophage expressed protein 1) were significantly upregulated by temperature, compared to only two GOIs (metallothionein and 6-phosphofructokinase) that were significantly upregulated by pCO2. Heat shock 23 and heat shock 70 genes were deemed as being the most suitable for routine monitoring as early-warning signs of oyster summer mortality. Unsupervised hierarchal clustering with principal components analysis revealed only two major clusters when comparing genomic responses, driven primarily by temperature.
My results indicate that juvenile oysters are much more sensitive to heat exposure than high pCO2, with no additive effect of the two factors. Understanding how oyster growth and genes respond to both individual and combined climate-change stressors is crucial for improving predictions of oyster performance under future climate scenarios and for enhancing the sustainability of shellfish aquaculture systems that are increasingly affected by heatwaves and low-pH upwelling events. Ongoing research is essential to investigate oyster responses in controlled, environmentally-relevant, multi-stressor experiments, providing deeper insights into the potential impacts of concurrent climate change stressors and extremes on both natural and cultivated oyster populations.
Continue reading ‘Biological and genomic responses of juvenile Pacific oysters (Crassostrea gigas) to a changing ocean’The effects of ocean acidification on the epiphytic bacterial community of Sargassum thunbergii via high-throughput sequencing
Published 11 September 2025 Science ClosedTags: abundance, adaptation, algae, biological response, BRcommunity, community composition, laboratory, molecular biology, nitrogen fixation, North Pacific, otherprocess, physiology, prokaryotes
Marine macroalgae and their epiphytic bacteria have established a symbiotic relationship. Although the effects of ocean acidification (OA) on macroalgae have been extensively studied, its impact on these epiphytic bacteria remains unclear. This study investigated the OA-induced shifts in the epiphytic bacterial community of Sargassum thunbergii from Qingdao’s intertidal zone using 16S rDNA sequencing. The results indicated that elevated CO2 altered bacterial community structure and function, reducing diversity while maintaining dominant taxa but significantly changing their relative abundances. The abundances of Proteobacteria, Firmicutes, and Verrucomicrobiota declined, whereas Campylobacterota, Desulfobacterota, and Spirochaetota increased. The specific phyla like Cloacimonadota, Calditrichota and Entotheonellaeota also emerged. These shifts were linked to the environmental adaptability and stress resistance of epiphytic bacteria as well as the metabolic activities of the host algae, particularly in protein and fatty acid degradation.
Functional predictions revealed that OA primarily affected nitrogen and sulfur metabolism in the epiphytic bacterial community, with effects intensifying over time. Specifically, nitrogen fixation increased, while dark oxidation of sulfur compounds, dark sulfite oxidation, and dark sulfur oxidation decreased. In conclusion, ocean acidification directly induced changes in the abundance of epiphytic bacterial taxa with varying stress resistance and adaptability. Simultaneously, it promoted shifts in bacterial taxa closely associated with the host algal metabolic activities, ultimately reshaping the epiphytic bacterial community on S. thunbergii. These findings provided new insights into the macroalgae-epiphytic bacteria interactions under ocean acidification and provided important guidance for macroalgal cultivation.
Continue reading ‘The effects of ocean acidification on the epiphytic bacterial community of Sargassum thunbergii via high-throughput sequencing’No effect of ocean acidification on individual-level variation in behaviour and susceptibility to predation in a Great Barrier Reef damselfish
Published 9 September 2025 Science ClosedTags: biological response, fish, laboratory, mortality, performance, South Pacific
1) Ocean acidification, caused by rising carbon dioxide (CO2) in the atmosphere, has been reported to negatively impact a wide variety of behaviours in fishes, including activity, exploration, and predator avoidance.
2) These effects have been documented at the population level, but many animal species naturally show large and repeatable individual-level differences in behaviour. How environmental stressors, such as ocean acidification, affect behavioural variation at the individual level remains largely unknown but is critically important to understand adaptation given natural selection operates on variation at the individual rather than population level.
3) Using a statistical approach allowing variation in means and variation in variance to be modeled within a single framework, we quantified individual-level differences across five behaviours in the coral reef damselfish Pomacentrus amboinensis (emergence time, activity level, time spent sheltering, thigmotaxis, novel object inspection). We measured behaviour in a novel environment assay, twice before (CO2 ~450 µatm) and twice following acclimation to predicted end-of-century ocean acidification conditions (~1,100 µatm).
4) Following behavioural assays, we tested individual survival in a live predation experiment. We used predatory rock cod, Cephalopholis microprion, acclimated to the same CO2 treatments as Ambon damsel and examined predictors of survival probability.
5) All behaviours in damselfish were moderately and significantly repeatable, with no marked differences in repeatability estimates between the ambient CO2 and elevated CO2 treatment groups. Exposure to end-of-century ocean acidification conditions had no effect on any of the five behaviours measured, both in terms of group means and residual (within-individual) variance.
6) The probability of survival in the predation trials was similar for damselfish in the elevated and ambient CO2 treatment groups. Smaller damselfish as well as those that spent a greater amount of time inspecting a novel object (i.e., bolder individuals) had a lower probability of survival regardless of their CO2 treatment.
7) Our results challenge assumptions about the impacts of ocean acidification on coral reef fish behaviour and susceptibility to predation, both at the population and individual level. They also provide support for a trade-off between boldness and predation risk in fish.
Continue reading ‘No effect of ocean acidification on individual-level variation in behaviour and susceptibility to predation in a Great Barrier Reef damselfish’Ocean acidification disrupts the biomineralization process in the oyster Crassostrea virginica via intracellular calcium signaling dysregulation
Published 3 September 2025 Science ClosedTags: biological response, laboratory, molecular biology, mollusks, morphology, North Atlantic, physiology, reproduction
Anthropogenically increased atmospheric carbon dioxide (pCO2) leads to ocean acidification, disrupting calcification in marine calcifiers by reducing the saturation state of calcium carbonate. Calcium is not only a crucial component in the shell and skeleton structure but also serves as an essential second messenger for regulating biomineralization across many species. Ocean acidification is well-studied as causing shell dissolution in a diversity of bivalve species by disordering calcium deposition. However, it remains unclear whether the calcium-mediated signaling pathway regulating biomineralization is also affected. This study assessed eastern oyster (Crassostrea virginica) to determine how calcium signaling responds to elevated pCO₂ and influences shell formation. Under elevated pCO2, increased intracellular calcium concentration was found in primary epithelial cell cultures from oyster mantle. Meanwhile, we observed upregulation of calmodulin, a primary sensor of intracellular calcium, while its downstream effector, calcineurin, was downregulated. In addition, four conserved shell matrix proteins (SMPs), representing shell construction conditions, were significantly upregulated in the CO2-exposed mantle cells. In vivo, larval C. virginica exhibited developmental stage-dependent alterations in calcium signaling and SMPs disarrangement stimulated by pCO2. We hypothesize that dysregulation of calcium signaling disrupts the expressions of SMPs and causes oyster shell deformation. Pharmaceutical blockage of the calcium-calmodulin binding induced abnormal expression of related genes and shell matrix changes consistent with those caused by elevated pCO2, both in vivo and in vitro. Importantly, calcineurin restored SMPs expression in CO2-treated mantle cells. These findings suggest that shell deformities under ocean acidification are related to disruption of the calcium-calmodulin signaling pathway, inhibiting calcineurin activity and affecting SMPs production.
Continue reading ‘Ocean acidification disrupts the biomineralization process in the oyster Crassostrea virginica via intracellular calcium signaling dysregulation’Projected cooling and pCO2 conditions in upwelling zones and their influence on a prominent rocky shore ecosystem engineer
Published 3 September 2025 Science ClosedTags: biological response, calcification, growth, laboratory, mollusks, multiple factors, physiology, South Pacific, temperature
HIGHLIGHTS
- End-of-century projections point to intensified OA and cooling in upwelling zones
- Projected OA enhanced growth, calcification, and byssus production in P. purpuratus
- However, projected cooling reversed OA effects on most of these biological traits
- These findings highlight the relevance of cooling and its strong interaction with OA
ABSTRACT
By the end of the century, upwelling zones are expected to undergo distinct changes due to the accumulation of greenhouse gases in the atmosphere. These changes include an intensification of the winds causing upwelling, further reducing sea surface temperatures (cooling), and an intensification of ocean acidification (OA). While only a few studies have evaluated the influence of cooling conditions in these systems, even fewer have assessed the combined effects of cooling and projected OA. This study addressed this gap by exposing juveniles of the intertidal purple mussel (Perumytilus purpuratus), a prominent intertidal ecosystem engineer, to distinct temperatures and pCO2 levels. Using a mesocosm system and a 2×2 factorial design, groups of purple mussels were exposed to current (15°C) and projected cooling conditions (10°C), and current and projected pCO2 levels (500 and 1500 μatm, respectively). After two months, we quantified mussel growth, calcification, byssus thread production, clearance, and metabolic rates. Growth, calcification, and byssus thread production rates were consistently affected by temperature and by the interaction between temperature and pCO2: At current temperatures (15°C) all these variables increased in response to OA, but when exposed to projected cooling conditions (10°C), these trends reversed and declined with OA. Mussel clearance rates followed the same trend, but in this case the only significant factor was the interaction between variables. Meanwhile, metabolic rates declined with temperature. A close examination of the variation among treatments suggests that the main changes were consistently associated with a sharp decline in most response variables to a combination of cooling and high pCO2 conditions. Hence, projected end of the century cooling and OA are likely to have direct (negative) effects on this habitat-forming species. Indirectly, the combination of these stressors may weaken mussel bed structure and reduce habitat complexity, thereby halting the benefits provided to associated intertidal communities.
Continue reading ‘Projected cooling and pCO2 conditions in upwelling zones and their influence on a prominent rocky shore ecosystem engineer’The swimming performance of mollies and their interaction with tiger barb fish when exposed to concurrent low pH and elevated temperature
Published 2 September 2025 Science ClosedTags: biological response, BRcommunity, fish, laboratory, multiple factors, performance, temperature
The global climate change and ocean acidification brought about by the anthropogenic release of carbon dioxide gas into the air is considered one of the greatest problems facing marine life. In this research, the interactions between two species of fish (the gold mollies and tiger barb) were investigated under two different environmental conditions, an elevated temperature of 28 °C and a low pH of 5 and a normal pH of 7 and a normal temperature of 24 °C. The mollies at pH 7 and a temperature of 24 °C exhibited scary interactions with the tiger barb. They were scared and ran fast away from the tiger barb. At the same time, the mollies at pH 5 and a temperature of 28 °C interacted normally as though both species were one species showing behavioral changes due to these two stressors (pH 5 and elevated temperature 28 °C). This could be the only research that has addressed how the kinematics and swimming interactions of two species of fish changed in response to elevated temperature and low pH.
Continue reading ‘The swimming performance of mollies and their interaction with tiger barb fish when exposed to concurrent low pH and elevated temperature’pHT measurements of TRIS buffer solutions in an artificial seawater matrix in the salinity range 5–40 and temperature range 5–40 °C. Part 1: measurements and data fitting
Published 2 September 2025 Science ClosedTags: chemistry, laboratory, methods
Highlights
- A function for calculation of ASW/TRIS buffer pHT for S 5–40 and T 5–40 °C is given.
- Reproducibility is assessed using measurements made by three metrology institutes.
- The function allows deriving pHT values for pure ASW (i.e. zero TRIS molality).
- The function is compatible with reference work of DelValls and Dickson (1998).
- Metrological traceability of ASW/TRIS buffers pHT values is discussed.
Abstract
Spectrophotometric measurements of seawater total pH (pHT) contribute to the knowledge of the oceanic carbonate system, and hence to the assessment of the ocean carbon cycle and the monitoring of ocean acidification. Spectrophotometric measurements rely on the characterization of the indicator dye’s second dissociation constant, obtained from measurements on solutions of known pHT. Therefore, Harned cell potentiometric measurements were performed on equimolal TRIS buffers (i.e. buffers containing equal molalities of 2-amino-2-(hydroxymethyl)-1,3-propanediol (TRIS, CAS reference number 77–86-1) and TRIS hydrochloride (TRIS.HCl)), made in an artificial seawater (ASW) matrix. Buffer solutions were prepared in an ASW matrix of nominal practical salinities from 5 to 40, and Harned cell measurements were performed on these solutions at temperatures from 5 °C to 40 °C. This provides, for the first time, pHT values of ASW/TRIS buffers that are consistent for the entire ranges of salinity relevant for oceanographic measurements, and for a wide range of temperature. The work presented includes a comparison of results from three National Metrology Institutes to assess reproducibility, and provides a function allowing the calculation of equimolal ASW/TRIS buffers pHT as a function of salinity, temperature and TRIS buffer molality. This function can be used to derive pHT values for zero TRIS molality, thus representing a pure ASW (i.e. a chemical environment unaffected by the presence of TRIS and TRIS.HCl), and referring to a true pHT scale. These values are needed for the characterization of the second dissociation constant of the dye with perspective of traceability to the International System of units.
Continue reading ‘pHT measurements of TRIS buffer solutions in an artificial seawater matrix in the salinity range 5–40 and temperature range 5–40 °C. Part 1: measurements and data fitting’Simulated ocean acidification affects shark tooth morphology
Published 29 August 2025 Science ClosedTags: biological response, fish, laboratory, morphology
Changing ecological factors pose a challenge to many organisms. Global changes and the associated environmental changes have major impacts on marine organisms and threaten the biodiversity of marine ecosystems. It has been shown in previous experimental studies that ocean acidification caused by anthropogenic CO2 release into the atmosphere and subsequent dissolution in seawater will have a significant impact on various marine organisms. Here, we investigated the corrosive effects from acidification on the morphology of isolated shark teeth in an eight-week incubation at a pH of 7.3, the expected seawater pH in the year 2300. The typical littoral blacktip reef shark (Carcharhinus melanopterus), which is often kept in display aquaria under controlled conditions, has been used for this purpose, greatly facilitating minimally invasive sampling for in-situ investigation. The teeth of this typical Requiem Shark species are orthodont teeth, which show strong serration in the teeth of the upper jaw. Using scanning electron microscopy (SEM) we could observe the corrosive effects of acidification on the different tooth structures, such as the root, primary and secondary serrations and the crown of the blacktip reef sharks teeth. Our results show that ocean acidification will have significant effects on the morphological properties of teeth, including visible corrosion on the crown, degradation of root structures, and loss of fine serration details under low pH conditions which could lead to changes in foraging efficiency, energy uptake, and ultimately elasmobranch fitness in future oceans.
Continue reading ‘Simulated ocean acidification affects shark tooth morphology’Acclimation mechanisms of reef-building coral Acropora gemmifera juveniles to long-term CO2-driven ocean acidification
Published 27 August 2025 Science ClosedTags: adaptation, biological response, corals, laboratory, molecular biology, morphology, North Pacific, otherprocess, physiology, reproduction
Ocean acidification (OA) is a major threat to the sexual recruitment of reef-building corals. Acclimation mechanisms are critical but poorly understood in reef-building corals to OA during early life stages. Here, Acropora gemmifera, a common Indo-Pacific coral cultured in in situ seawater from Luhuitou reef at three levels of pCO2 (pH 8.14, 7.83, 7.54), showed significantly delayed larval metamorphosis and juvenile growth, but adapted to long-term high pCO2. Differentially expressed genes (DEGs) emerged as a time- and dose-dependent mode of short-term response (3 days post settlement, d p.s.) and long-term acclimation (40 d p.s.), with more DEGs responding to high pCO2 (pH 7.54) than to medium pCO2 (pH 7.83). High pCO2, a presumed threatening seawater baseline for A. gemmifera juveniles, activated DNA repair, macroautophagy, microautophagy and mitophagy mechanisms to maintain cellular homeostasis, recycle cytosolic proteins and damaged organelles, and scavenge reactive oxygen species (ROS) and H+, but at the cost of delayed development through cell cycle arrest associated with epigenetic and genetic regulation at 3 d p.s.. However, A.gemmifera juveniles acclimated to high pCO2 by up-regulating cell cycle, transcription, translation, cell proliferation, cell-extracellular matrix, cell adhesion, cell communication, signal transduction, transport, binding, Symbiodiniaceae symbiosis, development and calcification from 3 d p.s. to 40 d p.s., when energy reallocation and metabolic suppression occurred for high demand but short-term energy limitation in coral cells undergoing flexible symbiosis. All results indicate that acclimation mechanisms of complicated gene expression improve larval and juvenile resilience to OA for coral population recovery and reef restoration.
Continue reading ‘Acclimation mechanisms of reef-building coral Acropora gemmifera juveniles to long-term CO2-driven ocean acidification’Impacts of ocean acidification on survival of the brown mussel (Perna perna) in Brazil
Published 27 August 2025 Science ClosedTags: adaptation, biological response, fisheries, growth, laboratory, mollusks, morphology, mortality, otherprocess, South Atlantic
The impacts of ocean acidification (OA) on seafood are recognized globally as a major threat, and OA is explicitly mentioned in the United Nations 2030 Agenda for Sustainable Development. One target of Goal 14 (SDG 14.3), life below water, is to minimize and address the impacts of OA using all levels of scientific cooperation. In 2018, the International Atomic Energy Agency launched a Coordinated Research Project (CRP), which gathered researchers from 13 different countries and aimed to evaluate the quantitative and qualitative impacts of OA on seafood. The Brazilian brown mussel Perna perna (Linné, 1858) was selected as the target species for these experiments. Low pH can disrupt the life cycle, affect survival and growth rates, and lead to a decline in mussel populations over time. Based on an agreed protocol within the CRP network, brown mussels were exposed to pH scenarios covering the present and future range of pH variability at the sampling site. The impacts on mortality, growth rate, and morphological parameters of juvenile mussels (seed) were evaluated after a 15-wk exposure in the laboratory, followed by an 8-wk recovery period in situ. Although no effect was detected for growth rate and allometric relationships during the laboratory experiment, mussel mortality was significantly higher at low pH. This effect on mortality disappeared when mussels were transferred to the field for a recovery period, and the acclimation to low pH had no carry-over effect on growth, allometric relationships, or sensory quality. Evidence of impacts from chronic lowering of pH is still needed to address species adaptation for long-term changes, which limit the prognostic power of short-term experiments.
Continue reading ‘Impacts of ocean acidification on survival of the brown mussel (Perna perna) in Brazil’
