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.
Continue reading ‘Environmental impact on calcifying organisms: focus on the effects of river runoff and ocean acidification on health status and pollutant bioaccumulation’Posts Tagged 'physiology'
Environmental impact on calcifying organisms: focus on the effects of river runoff and ocean acidification on health status and pollutant bioaccumulation
Published 29 September 2026 Science ClosedTags: biogeochemistry, biological response, chemistry, corals, field, growth, Mediterranean, multiple factors, physiology, temperature, toxicants, vents
A key seawater acidification-enriched gut bacterium, Pseudoalteromonas carrageenovora P1, enhances growth performance, antioxidant status, and disease resistance in sea cucumbers under seawater acidification
Published 28 September 2026 Science ClosedTags: abundance, adaptation, biological response, BRcommunity, echinoderms, fisheries, laboratory, molecular biology, morphology, North Pacific, otherprocess, physiology, prokaryotes
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.
Thermal history and behavioural plasticity shape reef fish tolerance to marine heatwaves
Published 25 September 2026 Science ClosedTags: adaptation, biological response, field, fish, laboratory, morphology, multiple factors, North Pacific, performance, physiology, temperature
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.
Continue reading ‘Thermal history and behavioural plasticity shape reef fish tolerance to marine heatwaves’Projecting the impact of climate change on the lipid profile of the hydrocoral Millepora alcicornis: relative lipid homeostasis under warming and ocean acidification
Published 25 September 2026 Science ClosedTags: biological response, corals, laboratory, multiple factors, North Atlantic, physiology, temperature
Climate change exerts a strong impact on marine ecosystems, particularly through ocean acidification and rising water temperatures. Within this context, shifts in lipid composition have emerged as valuable stress indicators in many organisms, providing insights into the trophic ecology of ecosystems. The objective of this study was to assess the combined effects of warming and ocean acidification scenarios projected for the end of the century (+5 °C and pH 7.5) on the lipid profiles of the hydrocoral Millepora alcicornis, recently recorded for the first time in Tenerife (Canary Islands, Spain). After an 84-day experiment, corals exhibited significant reductions in total lipid content, key lipid classes and fatty acids, particularly triacylglycerides (TAG) and docosahexaenoic acid (DHA, 22:6n-3), whereas sterol esters (ST) and saturated fatty acids (SFAs) showed the opposite trend. By contrast, symbiont-derived glycolipids and C18 fatty acids characteristic of zooxanthellae were not significantly affected by environmental stress, suggesting relative stability of membrane lipid composition. Overall, the maintenance of membrane lipid composition in symbiotic algae together with evidence of lipid remodelling in the host suggests a capacity for short-term physiological acclimation of M. alcicornis under the simulated climate change conditions. However, reduced DHA availability may have important physiological implications for the colonies, justifying future studies on the molecular regulation of LC-PUFA biosynthesis and the long-term acclimation capacity of Millepora alcicornis under climate change.
Continue reading ‘Projecting the impact of climate change on the lipid profile of the hydrocoral Millepora alcicornis: relative lipid homeostasis under warming and ocean acidification’The effects of ocean warming and acidification on fatty acid contents of marine organisms: a global meta-analysis
Published 23 September 2026 Science ClosedTags: algae, biological response, fish, multiple factors, physiology, phytoplankton, review, temperature
Ocean warming and acidification pose significant threats to marine biodiversity and human nutrition by fundamentally altering the biochemical composition of marine organisms. A primary concern is the potential decline in omega-3 fatty acids (FAs) that are essential to human health and primarily obtained through seafood consumption. The influence of these climate stressors on FA content across marine food webs remains poorly understood. To address this critical knowledge gap, we conducted a global meta-analysis of 489 experiments across 143 publications and 132 marine species, quantifying the effects of warming and acidification on nutritionally important FAs in marine primary producers, invertebrates and fishes. Under warmer conditions, we detected reductions of up to 34% and 50% in omega-3 FA proportions and concentrations, respectively, and up to 53% in omega-3: omega-6 ratios, together with increases of up to 22% and 17% in saturated FA proportions and concentrations, respectively across taxa groups. Critically, these effects were intensified as warming increased. The most severe reductions in omega-3 FAs were observed in primary producers, suggesting that climate-driven changes at the base of the food web could impair trophic transfer of these micronutrients, limiting nutrient availability for higher trophic levels and ultimately humans. Ocean acidification, conversely, demonstrated a minor overall effect on FA levels, although this result was based on substantially fewer studies. Furthermore, we identified species from environments with broader temperature ranges, diatoms, herbivorous invertebrates and low-resilience fish to display larger reductions in omega-3 FA proportions under warming. Our meta-analysis further highlighted the need for long-term studies under ecologically realistic conditions to improve predictions of nutritional responses to climate change. These findings are essential for understanding how the nutritional value of species change under climate change, and can inform fisheries management, aquaculture and public health policy aimed at securing the future availability of these vital micronutrients.
Continue reading ‘The effects of ocean warming and acidification on fatty acid contents of marine organisms: a global meta-analysis’Pre-harvest thermal and pH stress modulate macronutrient digestibility and protein bioaccessibility of the sea cucumber Isostichopus badionotus under in vitro gastrointestinal digestion
Published 18 September 2026 Science ClosedTags: biological response, echinoderms, fisheries, laboratory, multiple factors, physiology
Highlights
- Thermal stress modulates protein digestibility and bioaccessibility in I. badionotus.
- Induction at 28 °C maximized protein digestibility and intestinal bioaccessibility.
- Sublethal 34 °C for 12 h peaked digestibility; longer exposure caused decline.
- Intestinal bioaccessibility was the most sensitive indicator to pre-harvest stress.
- Pre-harvest thermal and pH stress can alter the macronutrient nutritional quality in I. badionotus.
Abstract
The impact of in vivo thermal and pH stress on the macronutrient nutritional quality of the sea cucumber Isostichopus badionotus remains poorly understood from a food-nutrition perspective. This study investigated how acute induction temperatures (16–36 °C) and sublethal thermal exposure (34 °C, 3–48 h), combined with two ambient pH levels (7 and 8), modulate in vitro protein, lipid and carbohydrate digestibility and protein bioaccessibility of the sea cucumber I. badionotus, a collagen-rich tropical food, using the standardized static INFOGEST gastrointestinal simulation. In the acute induction experiment, protein digestibility, total bioaccessibility and intestinal bioaccessibility were strongly affected by temperature, with a narrow optimum at 28 °C (digestibility ∼58–66%; intestinal bioaccessibility ∼64–68% at both pH levels). Lipid digestibility varied within a relatively narrow range across treatments, whereas carbohydrate digestibility showed a marked temperature × pH interaction, with higher values at 28 and 36 °C under alkaline conditions. In the sublethal-stress experiment, protein digestibility and bioaccessibility followed a time-dependent pattern, with a peak at 12 h followed by a decline at 24–48 h, consistent with patterns of progressive collagen oxidation reported in other holothuroids. Across both experiments, intestinal bioaccessibility was the most responsive nutritional indicator to pre-harvest stress. These results demonstrate that pre-harvest thermal and pH stress can qualitatively alter the macronutrient nutritional quality of I. badionotus, with implications for harvest timing, processing optimization and seafood quality management under ongoing ocean warming and acidification.
Graphical abstract
Live sea cucumbers (Isostichopus badionotus) were exposed in vivo to controlled thermal and pH stress (16–36 °C, pH 7–8; 6 h acute induction and 3–48 h sublethal exposure), inducing proteolysis, oxidative responses, heat-shock protein expression and structural remodeling of the collagen-rich body-wall matrix. Samples were then subjected to standardized INFOGEST in vitro digestion (oral, gastric and intestinal phases with pepsin, pancreatin and bile salts), followed by dialysis at 12–14 kDa to quantify intestinal bioaccessibility. A narrow optimum at 28 °C and a sublethal window around 12 h at 34 °C tended to maximize protein digestibility and intestinal bioaccessibility, whereas conditions outside this window were associated with increased oxidative crosslinking and reduced protein quality.
Coral acclimatization to novel, co-varying stressors is associated with fitness trade-offs
Published 18 September 2026 Science ClosedTags: adaptation, biological response, calcification, corals, field, morphology, mortality, multiple factors, North Atlantic, oxygen, photosynthesis, physiology, respiration, temperature
Reef-building corals are under pressure to acclimatize and/or adapt to multiple co-occurring stressors, including climate change and declines in water quality. However, their capacity to do so is largely unknown. Yet, some corals naturally persist in habitats with multi-stressor conditions which can provide crucial insight into coral adaptive capacity under future ocean conditions. To assess the role of phenotypic plasticity and local adaptation in coral acclimatory responses to novel conditions, we reciprocally transplanted two coral species (Siderastrea siderea, branching Porites) between an inland bay characterized by multiple, co-varying stressors, including warmer seawater temperatures, higher pollution and more variable temperatures, pH and dissolved oxygen concentrations, and an environmentally less extreme, more stable fringing reef. We measured key phenotypic traits (e.g., calcification, tissue biomass, metabolic rates, chlorophyll concentrations) of all transplant groups after 0, 4 and 12 months. Reef-origin corals demonstrated high plasticity when transplanted to the bay, as both species maintained high survival and calcification, and matched bay natives’ other phenotypic traits. Yet, reef-to-bay transplants of both species had reduced photosynthesis-to-respiration ratios in the bay, highlighting the risk of metabolic trade-offs unless compensated for through increased heterotrophy. Conversely, bay-origin corals had enhanced photosynthetic performance but lower calcification on the reef. Reaction norms provided stronger evidence for environmental specialization in bay-origin than reef-origin corals, which could limit their use as stress-tolerant source corals for reef restoration. Overall, our findings suggest multi-stressor variability may promote specialized genotypes, rather than increased phenotypic plasticity, though this may also depend on predictability of environmental variability.
Continue reading ‘Coral acclimatization to novel, co-varying stressors is associated with fitness trade-offs’TNF-NF-κB signaling mediates immune-biomineralization crosstalk during shell repair under ocean acidification in Mytilus edulis
Published 17 September 2026 Science ClosedTags: biological response, laboratory, molecular biology, mollusks, morphology, North Pacific, physiology
Highlights
- Day-15 shell closure ≠ functional repair: pH 7.7 disrupts microstructure, delays crystallization, and causes ∼87% strength loss.
- Hemocytes: early divergence (pH 7.9 inflammatory vs. pH 7.7 stress), late convergence with weak effectors; mantle upregulates immunity, suppresses OXPHOS/ECM.
- TNF-NF-κB (TNFSF14/TRAF6/IκBα) mediates immune-mineralization crosstalk, linking immunity to repair impairment.
- Multi-tissue dysregulation causes repair failure – not a single bottleneck, but decoupling of recruitment from deposition.
Abstract
Ocean acidification (OA) impairs biomineralization in bivalves, but its effects on immune-biomineralization crosstalk during shell repair remain unknown. Here, we exposed adult Mytilus edulis bearing standardized shell perforations to three pH levels (8.1, 7.9, and 7.7) for up to 40 days. OA slowed early repair and caused microstructural disorganization and an approximately 87% reduction of compressive strength at pH 7.7, yet the damaged area appeared largely closed by day 15, suggesting a decoupling between morphological closure and functional recovery. In addition, transcriptomic profiling of hemocytes and mantle tissue, based on an average of 6.5 Gb of clean reads per sample mapped to the M. edulis reference genome (NCBI Assembly GCF_000511035.1), revealed that these shell-level defects were accompanied by coordinated immune and metabolic reprogramming. Hemocytes, the primary immune effector cells of bivalves, exhibited pH- and time-dependent shifts with moderate acidification (pH 7.9) promoting inflammatory transcripts, whereas severe acidification (pH 7.7) suppressed these signals while upregulating stress-associated pathways; both treatments consistently downregulated lysosomal proteases and NF-κB negative regulators. The mantle, a primarily mineralizing organ, paradoxically upregulated immune-related genes while suppressing oxidative phosphorylation and extracellular matrix pathways. This tissue-level imbalance, with hemocytes recruited but functionally constrained and mantle metabolically suppressed yet immunologically activated, points to TNF-NF-κB pathway modulation as a key mediator of shell repair under acidification. Our findings demonstrate that visible shell closure masks underlying structural and mechanical failure, and that immune regulation, rather than simple suppression or activation, critically shapes the repair outcome. These results advocate for multifunctional indicators beyond closure area to assess shell integrity in acidified marine environments.
Continue reading ‘TNF-NF-κB signaling mediates immune-biomineralization crosstalk during shell repair under ocean acidification in Mytilus edulis’Brood chamber carbonate chemistry in the oyster Ostrea edulis is dynamically shaped by warming, acidification, and ventilation
Published 14 September 2026 Science ClosedTags: biological response, BRcommunity, laboratory, mollusks, performance, physiology, reproduction
Brooding organisms can modify the chemical environment experienced by developing offspring, potentially altering their exposure to climate change. In marine systems, however, the carbonate chemistry of brood chambers, and the mechanisms governing it, remain poorly resolved. Here, we combine high-resolution pH and CO2 measurements of the empty brood chamber (i.e., mantle cavity above gills) in the European flat oyster (Ostrea edulis) while also tracking valve gape to quantify how warming, ocean acidification, and ventilation interact to shape the internal environment experienced by larvae during incubation. Brood chamber pH was consistently lower than that of the surrounding seawater and responded to external conditions in a state-dependent manner governed by ventilation and respiration. When oysters were actively ventilating, brood chamber chemistry tracked ambient seawater with a persistent offset, whereas valve closure led to rapid CO2 accumulation and pronounced declines in pH. These dynamics generated highly variable and behaviorally mediated exposure regimes, in which metabolic processes distorted ambient chemical signals over short timescales. Paired pH and CO2 measurements provided preliminary constraints on aragonite saturation state (Ωar), revealing that brood chambers can remain undersaturated (Ωar < 1) for prolonged periods even in ventilating oysters and while overlying seawater remains favorable. Together, these results demonstrate that brood chambers function as dynamic microenvironments in which larval exposure to ocean acidification is governed not only by external conditions, but also by behavior. Because warming enhances metabolic CO2 production and intensifies acidification within the chamber, future climate change is likely to amplify both the magnitude and variability of larval exposure. These findings help explain the apparent resilience of brooding species to ocean acidification, while also highlighting potential limits as environmental conditions move beyond historical bounds.
Continue reading ‘Brood chamber carbonate chemistry in the oyster Ostrea edulis is dynamically shaped by warming, acidification, and ventilation’Ocean acidification and nanoplastics disrupt mussel calcification in synergy: a multi-omics analysis
Published 14 September 2026 Science ClosedTags: biological response, calcification, laboratory, molecular biology, mollusks, multiple factors, North Pacific, physiology, plastics
Highlights
- Ocean acidification disrupts calcium homeostasis in the mantle of mussels.
- Ocean acidification and N-NPs together intensify the inhibition of calcification.
- Surface charge determines distinct, mechanism-specific response pathways.
- Both omics reveal key roles for calcium transport, CA, and ECM synthesis.
Abstract
Ocean acidification (OA) and nanoplastics (NPs) increasingly co-occur in coastal ecosystems, yet their combined mechanistic impacts on calcifying invertebrates remain poorly resolved. Here, the mussel Mytilus coruscus was exposed for 30 days to factorial combinations of OA (pH 7.7 vs 8.1), surface-modified polystyrene NPs at a concentration of 100 μg/L (positively and negatively charged), and experimental shell damage to assess effects on shell repair, ion homeostasis, and energy metabolism. OA reduced shell repair quality by thinning repair layers, increasing porosity, and lowering calcium content, effects that were further enhanced by co-exposure to NPs, particularly negatively charged particles. OA and NPs jointly altered Ca2+ and Mg2+ levels, alkaline phosphatase activity, Ca2+Mg2+-ATPase activity, and key indicators of energy metabolism, including ATP content and cellular energy allocation. Transcriptomic and proteomic analyses revealed enrichment of ion transport, extracellular matrix, TGF-β signaling and other pathways, with divergent patterns linked to NPs surface charge. Together, these results suggest that nanoplastic surface charge under OA may impair mussel shell repair through associated alterations in ion homeostasis and energy metabolism. These findings highlight that particle surface properties shape how organisms respond to combined environmental stressors in acidifying marine environments.
Continue reading ‘Ocean acidification and nanoplastics disrupt mussel calcification in synergy: a multi-omics analysis’Environmental regulation and disruption of shell biomineralization in bivalves and gastropods: a mechanistic review
Published 10 September 2026 Science ClosedTags: biological response, molecular biology, mollusks, physiology, reproduction, review
Molluscan shells are increasingly threatened by a complex array of environmental stressors—climate-related drivers, changes in seawater chemistry, contaminants, and biotic cues. This review provides a mechanistic synthesis of how these stressors disrupt the biomineralization process across life stages. We develop a conditional hierarchical response framework from the reviewed evidence. The framework links ionoregulatory and acid-base disturbances with molecular, microstructural, and shell-level responses, while allowing for compensatory, nonlinear, species-specific, and life-stage-specific outcomes. This molecular disruption manifests as defects in calcium carbonate (CaCO3) crystalline microstructure, which may in turn compromise shell macro-scale physical properties (strength, hardness, growth). We synthesize combined and context-dependent effects of co-occurring stressors and distinguish formally tested interactions from qualitative comparisons of combined treatments. Future research must leverage integrated multi-omics, advanced in vivo imaging, and multi-stressor experimental designs to unravel candidate molecular and physiological thresholds and predict adaptive potential. This framework may help identify testable mechanisms, evidence gaps, and context-dependent vulnerabilities relevant to conservation.
Highlights
- A conditional framework links molecular, microstructural, and shell-level responses.
- Early stages often show high sensitivity, although direct ontogenetic comparisons remain limited.
- Energy limitation is a recurrent, but often indirectly inferred, physiological constraint.
Ocean acidification drives species-specific and time-dependent pigment responses in three phytoplankton taxa
Published 9 September 2026 Science ClosedTags: biological response, BRcommunity, growth, laboratory, light, multiple factors, photosynthesis, physiology, phytoplankton, respiration
Phytoplankton are primary producers in marine ecosystems and play a central role in biogeochemical cycles, yet their physiological responses to altered seawater pH vary among taxa and over time. Here, we examined the effects of sustained pH manipulation on pigment composition, growth, and dark respiration in three ecologically important phytoplankton taxa – a diatom (Pseudo-nitzschia spp.), a dinoflagellate (Heterocapsa pygmaea), and a haptophyte (Emiliania huxleyi) – during a 15-day controlled laboratory experiment. Cultures were maintained at pH 8.1, 7.8, and 7.5, representing present-day and enhanced acidification conditions. Responses to pH were species-specific and strongly time-dependent. Growth and cell-specific respiration rates showed relatively small and often transient differences among pH treatments, suggesting short-term metabolic adjustment under altered pH. In contrast, pigment composition exhibited clearer and more consistent pH-related responses, primarily expressed as shifts in temporal patterns rather than uniform directional changes. In Pseudo-nitzschia spp. and H. pygmaea, several key pigments displayed pronounced pH-dependent trajectories, whereas E. huxleyi showed greater temporal variability and weaker separation among pH treatments. Overall, these results demonstrate that photophysiological traits respond sensitively to sustained pH changes even when population-level growth and respiration remain comparatively stable, highlighting pigment composition as a potentially sensitive indicator of short-term phytoplankton acclimation to ocean acidification.
Continue reading ‘Ocean acidification drives species-specific and time-dependent pigment responses in three phytoplankton taxa’Elevated pCO2 impairs overall byssus attachment strength in the blue mussel (Mytilus edulis) without altering byssus thread quality
Published 8 September 2026 Science ClosedTags: biological response, BRcommunity, laboratory, mollusks, North Atlantic, physiology
Increasing atmospheric carbon dioxide (CO2) is driving global ocean acidification (OA). This process may threaten the persistence of bed-forming mussels by weakening the byssal system that anchors them to the seafloor. Here, blue mussels (Mytilus edulis) were exposed to present-day (∼460 ppm pCO2) normocapnic and projected end-century (∼1200 ppm pCO2) hypercapnic conditions for four weeks at 12 °C. Byssus production, thread morphology, whole-byssus mechanics and the underlying physiological condition index (CI) were quantified. Unlike previous studies, this study analysed the byssus as an intact functional unit. This approach better reflects its mechanical performance in situ. Median thread production fell by 50% under elevated pCO2 and the number of individuals producing no threads at all increased from 3% to 23% of the population. Thread diameter and plaque area were unaffected. Whole byssus tensile testing revealed a distinctive mechanical pattern (elastic loading, force plateau, and structural failure) regardless of environmental CO2 concentration. Whole byssus attachment strength scaled linearly with thread number in both treatments, and the mechanical work required to detach mussels under hypercapnia dropped by 42%. Elevated pCO2 reduced mussel condition index by 19% relative to the control, indicating an energetic burden. These results show that near-future ocean acidification weakens mussel attachment primarily by lowering individual physiological condition, which directly drives the reduction in total attachment energy, rather than by lowering individual thread quality. This likely results from a shift in energy use away from thread production, as seen in poorer mussel condition. As a result, mussels may become more prone to being dislodged by waves or predators. The findings of this study indicate that ocean acidification can reduce the overall strength of M. edulis beds, with important effects on rocky shore ecosystems and the viability of mussel farming in a changing climate.
Continue reading ‘Elevated pCO2 impairs overall byssus attachment strength in the blue mussel (Mytilus edulis) without altering byssus thread quality’Shark responses to ocean acidification: physiological buffering, behavioural vulnerability, and comparative insights from teleost fishes
Published 8 September 2026 Science ClosedTags: biological response, fish, performance, physiology, review
Highlights
- Sharks maintain acid-base balance under elevated CO₂ via effective buffering.
- Physiological compensation carries energetic costs that constrain aerobic scope.
- Olfactory-mediated foraging is more OA-sensitive than baseline locomotor function.
- Multi-stressor effects (warming + OA) amplify biological impacts across life stages.
- Evidence is biased toward benthic species; pelagic sharks remain understudied.
Abstract
Ocean acidification (OA), driven by increasing atmospheric carbon dioxide (CO₂), is a major component of global ocean change with widespread implications for marine organisms. Sharks (elasmobranchs) are often assumed to be relatively resilient to OA due to their distinctive physiology, including strong acid–base regulation and urea-based osmoconformation. However, empirical evidence evaluating this assumption remains limited and fragmented. This review synthesizes current knowledge on the physiological, behavioural, and sensory responses of sharks to OA within a comparative framework that incorporates insights from teleost fishes. A systematic literature search following PRISMA guidelines identified studies examining OA effects across shark species and life stages. Available evidence indicates that sharks generally maintain extracellular acid-base balance under elevated CO₂, demonstrating effective physiological buffering. However, this compensation is not without cost. Energetic trade-offs, reduced aerobic scope under multi-stressor conditions, and alterations in metabolic and oxidative responses have been reported. Behavioural and sensory-mediated processes, particularly olfactory-driven foraging, appear more sensitive to OA, with impairments emerging even in the absence of obvious physiological failure. Responses are highly species-specific and often amplified by co-occurring stressors such as warming. Despite these findings, current data are strongly biased toward small, benthic species, with limited representation of pelagic taxa and long-term responses. Sharks cannot be considered uniformly resilient to OA; rather, their responses are context-dependent, energetically constrained, and potentially consequential at population and ecosystem levels. Future research integrating long-term, multi-stressor, and mechanistic approaches will be critical for improving predictions of shark responses under ongoing ocean change.
Continue reading ‘Shark responses to ocean acidification: physiological buffering, behavioural vulnerability, and comparative insights from teleost fishes’Physiology and hydrodynamics influence the susceptibility of reef-building corals to ocean acidification
Published 3 September 2026 Science ClosedTags: biological response, community composition, corals, growth, laboratory, otherprocess, physiology
Ocean acidification (OA) poses a major future threat to tropical coral reefs. This is primarily due to its effects on reef-building coral species, which vary in their susceptibility to this climate change stressor. However, the potential factors underlying the range of susceptibilities observed among reef-building corals remain poorly understood. Therefore, this doctoral thesis investigates the influence of species-specific physiology and water flow conditions on coral susceptibility to OA. Using an experimental, multi-scale approach, the present thesis addresses this knowledge gap in a total of four studies and focuses on the physiological response of three major reef-building coral genera (Acropora, Pocillopora, and Porites) to prolonged exposure of OA conditions (> three months).
The results showed that (1) variable decreases in coral growth under OA were mediated by differential changes in maintenance and cellular stress parameters. This physiological interplay was genus-specific for Acropora and Pocillopora, and was species-specific for Porites spp. Moreover, assessments of the combined effects of OA and changes in water flow conditions indicated that (2) temporarily reduced water flow may mitigate OA effects on Acropora and Porites spp. Still, simultaneous changes in seawater chemistry and flow led to changes in coral physiology with complex and species-specific patterns. Finally, at the microscale, characterisation of the effects of OA and water flow on the concentration boundary layer (CBL) at the coral surface revealed that (3) OA was an overall weak modulator of this layer, regardless of flow conditions and CBL variability among species. Despite minor OA effects, however, the results also suggested that the CBL had a limited OA-buffering capacity due to thin pH gradients across the CBL. Nonetheless, low flow potentially enhanced CBL sheltering from acidified seawater by elevating pH at the coral surface.
In summary, this thesis provides evidence that both species physiology and water flow conditions shape coral susceptibility to OA in species-specific patterns and contributes novel insights into the potential links, between colony and CBL levels, involved in shaping it. Furthermore, the findings of this thesis showcase the potential of low-flow environments as refugia for coral species under OA and highlight the importance of including reef hydrodynamics in future OA scenarios, which will require consideration of different spatial and temporal scales. Altogether, the knowledge provided here may help improve projections of coral community dynamics under future OA and inform conservation efforts.
Continue reading ‘Physiology and hydrodynamics influence the susceptibility of reef-building corals to ocean acidification’Biological impacts of ocean change in upwelling systems: from organismal responses to fishery outcomes
Published 3 September 2026 Science ClosedTags: arthropoda, biological response, calcification, crustaceans, echinoderms, fisheries, laboratory, mollusks, mortality, physiology
Climate change is altering marine ecosystems through concurrent changes in temperature, carbonate chemistry, and dissolved oxygen. These changes are particularly important in coastal upwelling systems, where organisms already experience naturally variable environmental conditions. This dissertation integrates synthesis, experimentation, and modeling to evaluate how ocean change influences marine invertebrates and the fisheries they support. First, I conducted a meta analysis examining the effects of ocean acidification and deoxygenation on marine invertebrates. Both stressors produced broadly negative effects on fitness-related
traits, including survival, growth, development, and reproduction. Although vulnerability varied among taxa, responses were not strongly structured across broad taxonomic groups, suggesting that species-specific traits and environmental history are important determinants of sensitivity. Second, I investigated the effects of multi-stressor upwelling conditions on juvenile Dungeness crab (Metacarcinus magister). Crabs maintained net calcification across a range of moderate conditions but exhibited significant declines under the most severe treatments, indicating threshold responses to environmental stress. Short-term environmental variability had little effect relative to mean conditions, suggesting that exposure severity is a stronger driver of performance than exposure pattern. Finally, I incorporated experimentally observed reductions in calcification into a size-structured yield-per
recruit model to evaluate potential fishery consequences. Reduced growth delayed attainment of legal harvest size and decreased projected fishery yield, demonstrating how sublethal physiological responses can scale to population and management-relevant outcomes. Together, these chapters show that ocean change can affect biological systems across levels of organization, from individual performance to fishery productivity. By linking broad patterns of vulnerability to species-specific responses and applied fishery outcomes, this dissertation provides a framework for understanding and managing the impacts of global change in coastal
marine ecosystems.
Coral reef community structure and photophysiology differ between upwelling and non-upwelling locations on the Pacific Coast of Costa Rica
Published 28 August 2026 Science ClosedTags: biological response, community composition, corals, echinoderms, field, North Pacific, otherprocess, photosynthesis, physiology
Reef-building corals and coralline algae form the calcium carbonate frameworks that underpin tropical coral reefs, yet in some locations, coral cover has declined by ~50% in recent decades due to marine heatwaves and other stressors. Identifying refugia environments, such as upwelling systems, that may buffer stress, promote recovery, and could enhance resilience by promoting physiological plasticity that supports thermotolerance is therefore critical. Here, we compared benthic community composition, coral percent cover, and photophysiology between an upwelling location in the Gulf of Papagayo and a non-upwelling location in Sámara on the Pacific coast of Costa Rica. Waters in Papagayo were cooler, more acidic, and had higher chlorophyll-a concentrations. Reefs at this location exhibited higher crustose coralline algae, higher sea urchin abundance, and lower macroalgae cover, compared to Sámara. Papagayo also showed higher stony coral cover, driven by Pocillopora spp., while Sámara was dominated by massive, heat-tolerant Porites spp. Photophysiological parameters were significantly different between locations. Specifically, photosynthetic efficiency (Fv′/Fm′) was 10–45% higher, and maximum photosynthetic rate (Pmax) was 20–40% lower in corals from Papagayo than in those from Sámara. These results reveal that two locations differing in environmental regime within a relatively small geographic area also differ in coral community composition and photophysiological features. Although further research is needed to resolve whether these environmental contrasts shape the observed biological differences, the observed patterns are consistent with the hypothesis that such regimes may support reef persistence or refugia, providing a basis for future work to test this hypothesis directly.
Continue reading ‘Coral reef community structure and photophysiology differ between upwelling and non-upwelling locations on the Pacific Coast of Costa Rica’Elucidating impact of ocean acidification on coral exoskeletons using an in-situ (S)TEM platform
Published 25 August 2026 Science ClosedTags: biological response, corals, field, methods, mitigation, mortality, physiology
Scleractinian (stony) corals can build highly ordered aragonite (CaCO3) exoskeletons, which are vital for marine ecosystems, coastal stability, and of cultural and economic importance through supporting fisheries and tourism. However, they face multiple challenges through global climate change, unsustainable human activity, and coral-specific diseases. In the latter category, Stony Coral Tissue Loss Disease (SCTLD) has recently emerged as one of the most destructive coral diseases, spreading rapidly and causing widespread tissue mortality across many marine species [1]. We have recently started exploring remnant effects of this disease on Montastraea cavernosa exoskeletons, abundant throughout the Caribbean Sea, Gulf of Mexico, and Atlantic Ocean. Indeed, through use of multi-scale electron diffraction characterization techniques, we find that their skeletogenisis is impacted by this disease from the micro- through atomic scale [2]. Notably, at the nanoscale we observe pockets of more soluble amorphous calcium carbonate (ACC) within centers of calcification (CoCs; i.e. the center of the three-dimensional fans containing arranged elongated aragonite crystals) for healthy corals, which appear absent in STCLD-afflicted corals. At the atomic level, we reveal planar defects in diseased coral, which are much lower in density in healthy corals, presumably inflicted through dysregulation processes after tissue death.
Yet, the most severe threat to global coral reefs and their exoskeletons is climate change. As oceans increase the uptake of anthropogenic CO2 primarily from burning fossil fuels, ocean acidity has increased. The reduction in pH because of this Ocean Acidification (OA) not only reduces the rate of net ecosystem calcification, but also increases net dissolution of skeletons. At current trends, most coral exoskeletons are expected to dissolve starting in 2050 [3]. Currently, it is unclear how exactly (the onset of) dissolution proceeds and affects their aragonitic framework. Given our expertise in characterization of coral skeletons, herein we discuss a developed in-situ platform to investigate OA effects at the nanoscale.
As proof of concept, we sandwiched crushed geological aragonite nanoparticles between own fabricated SiNx-based chips, compatible with a Protochips Atmosphere gas cell holder [4]. Thereafter, we introduced water vapor at 14 Torr at room temperature (∼60% relative humidity) for 10 minutes to create a hydrated environment for the particles (Fig. 1b). In a third step, we introduced gaseous CO2 at a pressure of 1 atm (Fig. 1c). The formed unstable carbonic acid produces HCO3– and H+, which increases acidity (i.e. lowers pH). Indeed, we observe rapid dissolution of aragonite particles after CO2. While we expect roughly a pH ∼4 in this system, this experimental observation matches theoretical expectations that aragonite would dissolve under these conditions (Fig 1c-f). We further observe nucleation and growth of new particles in a dendritic fashion in the vicinity of the dissolved particles (Fig 1c-f). Likely, this is crystallization of calcite, the most stable crystalline polymorph of CaCO3, induced by local dissolution of aragonite [5]. Although pCO2 in the oceans is expected to be much lower (∼400 – 500 µatm) and thus dissolution timescales are expected to shift, this illustrates our platform can capture aragonite dissolution.
To expand our platform methodology, using conventional Ga+ FIB-methods, we prepared a lamella of geological aragonite with a thinned region (∼100 nm), which was then transferred on top of a SiNx-based chip, and attached this in one of the corners between the Si support and the SiNx layer (Fig. 2a). We were able to sandwich the lamella between both chips when observing the cell in the TEM (Fig 2b,c). Next, we will target healthy and STCLD-afflicted coral sections to investigate how nanoscale dissolution proceeds at/near more soluble areas including defects due to the devastating OA process. This understanding may allow for more accurate forecasting of marine ecosystem collapse, enabling targeted mitigation strategies, protecting food supplies, and predicting climate feedback loops [6].
Fig. 1. In-situ OA platform experiment showing TEM snapshots of: a) Initial geological aragonite nanoparticles. Inset: selected area diffraction pattern indicating aragonite spots. b) Introduction of water vapor (14 Torr) after 10 min. The white arrow indicates an apparent hydration layer surrounding the large particle. c) Introduction of CO2 at 1 atm pressure after 10 s. d) 60s e) 90s and f) 150s. White arrows in c-f) mark the outer layer of the large particle dissolving in time, red arrows illustrate growth of new crystals.
Fig. 2. a) SEM image of geological aragonite lamella attached to SiNx chip. b) TEM image of lamella after cell assembly (top and bottom chip). c) In-situ selected area diffraction pattern of the lamella.
Continue reading ‘Elucidating impact of ocean acidification on coral exoskeletons using an in-situ (S)TEM platform’Calcium carbonate formation in coastal macroalgal ecosystems via multiple pathways
Published 24 August 2026 Science ClosedTags: algae, biological response, BRcommunity, community composition, otherprocess, photosynthesis, physiology, review
Calcium carbonate formation in coastal macroalgal ecosystems via multiple pathways
Highlights
- Focused on a novel inorganic carbon sequestration pathway of non-calcifying macroalgae.
- Clarified algae-bacteria synergistic driving mechanism for calcium carbonate precipitation.
- Systematically sorted out potential mineralizing microbial taxa within the phycosphere and their core metabolic pathways.
Abstract
Macroalgae are dominant primary producers that drive carbon sequestration in coastal ecosystems. Macroalgal carbon sequestration primarily refers to the long-term storage of macroalgae-derived organic carbon in the ocean. However, calcium carbonate (CaCO3) formation is frequently observed in non-calcifying macroalgal environments, suggesting the existence of an overlooked inorganic carbon process in macroalgal ecosystems. Here, we introduce multiple pathways that may drive CaCO3 formation in macroalgal ecosystems. These include the effects of macroalgal photosynthesis and carbon-concentrating mechanisms on the seawater carbonate system, the role of phycosphere interfacial properties in facilitating CaCO3 nucleation, and the macroalgae-bacteria synergy that promotes CaCO3 formation. We identified several current knowledge gaps—the unclear carbon sequestration or source effect of CaCO3 formation in macroalgal ecosystems and the stability of CaCO3 minerals in macroalgal ecosystems—that require further investigation. This review advances the understanding of macroalgal carbon cycling beyond organic pathways and emphasizes the importance of a comprehensive assessment of macroalgal carbon sequestration, including that of inorganic carbon.
