Posts Tagged 'morphology'

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Resilience of the macroalgae Gongolaria barbata under ocean acidification: physiological responses and restoration perspective

Published 3 February 2026 Science Closed
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The increasing CO2 concentration is a major cause of the climate change phenomenon. Concurrently, the same increase is leading to ocean acidification (OA), which is projected to decrease seawater pH by 0.4 units by 2100. Here we investigated the potential impacts of OA on the canopy-forming brown macroalga Gongolaria barbata from the Venice Lagoon. One-year-old individuals were maintained in mesocosms under two pH levels: 8.1 (current ambient value) and 7.7 (the end-of-the-century value predicted under the current scenario of anthropogenic CO2 emissions). The physiological responses of the algae were assessed during the experiment in terms of oxygen production and consumption, and maximal PSII photochemical efficiency. At the end of the experiment, we analyzed the percentage of mature receptacles, algal growth rate and the total polyphenolic content and antioxidant capacity as indicators of the stress response. The significant decrease in polyphenolic content indicates the impairment of the defence mechanisms, which could make the algae more vulnerable to grazing under acidified conditions. Yet, conversely, our results suggest that changes in pH levels do not significantly affect the physiological processes, growth or fertility of the algae. These findings suggest that while OA may weaken defence mechanisms, the preservation of physiological and reproductive functions would still support the potential of G. barbata populations from the Venice Lagoon to act as donor sources for restoration efforts, highlighting their resistance to the acidified conditions expected in the future.

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Triple threat: ocean acidification, warming, and hyposalinity synergistically weaken shell integrity in a Mediterranean calcifying mollusk

Published 30 January 2026 Science Closed
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Highlights

  • OA, OW, and hyposalinity drive skeletal and mineralogical responses in a Mediterranean clam.
  • Combined stress makes shells less dense, more porous, and more fracture-prone.
  • Microstructural changes reveal early calcification impairments under triple stress.
  • Triple-stressor synergy compromises shell integrity and threatens fishery species resilience.

Abstract

Anthropogenic climate change is rapidly altering marine environments primarily through ocean warming, acidification, and hyposalinity, posing significant challenges for marine calcifying organisms. This study investigated the short-term effects of these stressors on the Mediterranean bivalve Chamelea gallina, a key fishery species in the Adriatic Sea, by integrating skeletal, mechanical, and mineralogical responses. Adult clams of commercial size were exposed for 21 days to eight experimental treatments manipulating two levels of temperature (18 °C vs. 22 °C), pH (8.0 vs. 7.9), and salinity (35 vs. 32), chosen to reproduce near-future climate projections and the freshwater-driven variability typical of the Adriatic Sea. Despite the short exposure duration, the combined exposure to low pH, high temperature, and reduced salinity weakens the shell of Chamelea gallina at multiple levels, compromising shell integrity, by making shells less dense, more porous, more fragile, and more susceptible to fracture, and increasing mortality. Microstructural analysis revealed smaller aragonite crystallites and lower calcium content, indicative of early impairments in the calcification process. The study highlights the occurrence of synergistic effects among stressors and reveals the vulnerability of Chamelea gallina to near-future ocean conditions, with potential cascading consequences for ecosystem functioning and fishery sustainability, given the species’ key ecological role and commercial relevance in the Adriatic Sea.

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Short-term tolerance to ocean acidification of the sub-antarctic sea-urchin arbacia dufresnii

Published 29 January 2026 Science Closed
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The accumulation of anthropogenic CO2 in the ocean is impacting the carbonate system chemistry in seawater, particularly in polar regions. Acidified seawater can impair the echinoderms internal regulation of pH due to an increase in hydrogen ions concentration, potentially affecting growth, and calcification, among other physiological activities. The goal of this work was to assess the effects of Ocean Acidification (OA) on Arbacia dufresnii, a sub-Antarctic sea urchin species. Adult specimens were exposed to three pH treatments: 7.4, 7.7, and 8.0 (control), for 21 up to 23 days. We assessed spine regeneration, a proxy of calcification, by cutting spines at the base of the shaft and evaluating the magnesium content, height, and weight of the regenerated part. The coelomic fluid was sampled for pH assessment and magnesium and calcium content analysis. The RNA/DNA ratio, a proxy of metabolic activity, was assessed in the gonads and body walls. The spine regenerated weight was significantly correlated to regenerated height but not to treatments. The coelomic fluid pH (6.77 ± 0.34) did not differ between treatments (pANOVA = 0.15). No significant differences were observed between treatments regarding RNA/DNA ratio in both body wall (pANOVA = 0.65) and gonads (pKruskal-Wallis = 0.34), the spine regenerated height (pANOVA = 0.35) and Mg regenerate content (pANOVA = 0.58). Our results suggest that A. dufresnii owns physiological mechanisms to cope with OA conditions during short-term exposure.

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Ocean acidification effects on growth, survival and physiological immunity of farmed Larimichthys crocea

Published 29 January 2026 Science Closed
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Ocean acidification has become a significant global ecological issue, particularly in coastal regions with intensive aquaculture. Fish farming is a crucial component of global food security, yet research on the impact of acidification on the aquaculture performance of economically important teleosts remains limited. In this study, we reared the fast-growing large yellow croaker (Larimichthys crocea) for 30 days under three different pH conditions: severe acidification (LA, pH 7.4), moderate acidification (MA, pH 7.8), and control (HA, pH 8.1). We comprehensively evaluated growth performance, survival rate, tissue structure, antioxidant enzyme activity, and innate immunity. The results showed that the LA group exhibited suppressed growth (significantly lower than the MA group, p < 0.05), elevated cortisol and T4 levels (p < 0.05), and trends of reduced antioxidant enzyme and innate immune enzyme activities, along with organ-specific pathological changes (vacuolation, structural loosening) in gills, liver, kidneys, and intestines, though most indices showed no significant difference from the HA group. Notably, the MA group showed optimal growth performance, stable physiological and immune responses. In conclusion, while acidification did not markedly affect the survival rate of L. crocea, severe acidification (pH 7.4) induces stress responses and tissue damage. These findings suggest that L. crocea exhibits a certain degree of tolerance to the acidification conditions tested, as several physiological parameters were not significantly affected. However, when considering the overall set of observations, including histological alterations across multiple tissues and changes in plasma and tissue parameters, long-term exposure to severe acidification (pH 7.4) appears to induce tissue damage and stress-related physiological disturbances, indicating potential health risks. This study provides empirical evidence regarding the potential risk posed by projected ocean acidification on L. crocea aquaculture and supports the development of climate change adaptation strategies for coastal mariculture.

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Transgenerational effects of extreme weather on Manila clam resilience: implications for aquaculture sustainability

Published 27 January 2026 Science Closed
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Highlights

  • SAE+MHW synergistically impaired clams during reproduction.
  • Progeny exhibited lasting developmental delays and high mortality.
  • Long-term physiological dysfunction persisted into later life stages.
  • Compound extremes threaten bivalve aquaculture resilience.

Abstract

Extreme environmental events, including sea acidity extremes (SAE) and marine heatwaves (MHW), pose increasing threats to coastal aquaculture species. This study examined the individual and combined effects of SAE and MHW on Manila clams (Ruditapes philippinarum) and their transgenerational impacts. Adults exposed to SAE+MHW showed reduced survival, decreased condition index, lower clearance rate (CR) and assimilation efficiency (AE), elevated ammonia excretion (ER), and negative scope for growth, indicating disrupted energy budgets. Reproductive output and gonadal development were also compromised. Offspring from stressed parents exhibited lower larval survival, stunted shell growth, reduced metamorphic success, smaller settlement size, reduced juvenile (6-month-old) survival rate and disrupted energy homeostasis, revealing persistent transgenerational impacts on development and energy homeostasis. These findings suggest that parental exposure to synergistic SAE+MHW alters energy allocation and may involve epigenetic mechanisms, ultimately impairing offspring fitness. Overall, our study demonstrates that compound extreme events can severely affect metabolic resilience and cross-generational performance in Manila clams, highlighting the need for multigenerational assessments, selective breeding, and aquaculture strategies to enhance climate resilience.

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Effects of pH on growth and anatomical characters of tapeseagrass (Enhalus acoroides (Linnaeus f.) Royle)

Published 14 January 2026 Science Closed
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Enhalus acoroides (Linnaeus f.) Royle or tape seagrass plays a vital role in tropical seagrass meadows, especially in Thailand. While ocean acidification negatively affects many marine species, it may benefit tropical seagrasses. E. acoroides relies on seed dispersal for sexual reproduction, and pH variations may influence seedling development. This study examined the effects of pH levels (6, 7, 8, and 9) on E. acoroides seedling growth over 8 weeks in controlled aquariums. All treatments showed 100% seed germination during the first week. By week 2, no significant differences in biomass were observed, but by week 8, seedlings at pH 6 had the highest dry weight (0.21±0.01 g), as well as the greatest leaf number (5.64±0.15 leaves), leaf length (23.39±2.06 mm), and leaf width (4.74±0.14 mm). One-way ANOVA revealed significant differences in growth by week 8. Lower pH levels enhanced shoot and root growth, while higher pH increased root number but reduced root length. Chlorophyll content analysis showed no correlation with pH after 8 weeks. Anatomical examination revealed tannin cells, starch granules, and thick cell walls in the mesophyll, with an enlarged exodermis in lower pH treatments, suggesting an adaptation for stabilizing in muddy, acidic conditions. These findings indicate that pH influences the growth and adaptation of E. acoroides seedlings, highlighting the species resilience to acidification. Its adaptive capacity is crucial for management, as E. acoroides can survive acidification and continue providing habitat, preserving ecosystem balance.

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Modeling the spatiotemporal effects of ocean acidification and warming on Atlantic sea scallop growth to guide adaptive fisheries management

Published 7 January 2026 Science Closed
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Highlights

  • We spatially couple a scallop bioenergetic model to a regional oceanographic model.
  • Our model reproduces observed growth patterns using temperature, food, and pCO2.
  • Mid-century warming enhances scallop growth except in the south.
  • By 2100, scallops grow faster but reach smaller sizes under warming and acidification.
  • This tool can inform adaptive fisheries management under climate change.

Abstract

Climate-ready fisheries management requires reliable predictions of species responses to changing conditions across large-scale environmental gradients. Bioenergetic frameworks, such as Dynamic Energy Budget (DEB) models, relate physiological processes to environmental conditions, enabling predictions of organismal growth under projected climate change conditions. Here, we provide the first large-scale coupling of a DEB model to downscaled regional oceanographic simulations to resolve spatiotemporal changes and reveal how climate stressors emerge at relevant biogeographic, economic, and oceanographic scales. We calibrated our DEB model for the Atlantic sea scallop (Placopecten magellanicus) with forcing from a realistic oceanographic and biogeochemical model for the Northeast U.S. continental shelf to predict the effects of ocean acidification (OA) and warming on individual growth historically and over the next century. Our model reproduced observed historical patterns in scallop age at harvest size and maximum size. At mid-century (2035–2050), scallop growth was projected to increase in most areas except the southern Mid-Atlantic, and OA effects were limited to the deep Gulf of Maine. By the end of the century (2080–2095) under a high emissions scenario, scallops were predicted to grow faster but attain smaller maximum sizes. Our results highlight that warming stress is more acute than previously accounted for, particularly in the southern Mid-Atlantic. While warming stress emerges in the south first, OA stress emerges before warming in the north. Together, these emerging stressors compress the spatial range for optimal growth. Altogether, our findings demonstrate the utility of the spatially coupled DEB model as a tool to inform adaptive fisheries management.

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Shell proteome plasticity assists oyster larval biomineralization in adverse carbonate chemistry

Published 30 December 2025 Science Closed
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Bivalve planktonic development is a critical phase during which larvae must secrete the first calcium carbonate shell, the prodissoconch I (PD I). As PD I formation is in close contact with seawater, this process can be negatively affected by adverse seawater carbonate chemistry. It is hypothesized that bivalves can regulate shell formation under environmental stress through biologically controlled biomineralization involving a complex extracellular shell proteome. However, the plasticity of this regulatory mechanism during PD I development is unknown. We assessed the PD I shell proteome of the Hong Kong oyster (Magallana hongkongensis) in carbonate chemistry that was adverse or favorable for biomineralization to understand the regulatory capacity of larval shell formation. While survival rates were not affected in adverse carbonate chemistry, there were significant changes, including the upregulation of several calcium-binding proteins and downregulation of proton-generating processes and putative calcification inhibitors. With 198 sequences, the oyster larval shell proteome was twice to over six times larger than those reported for other bivalve species at the same developmental stage. However, in adverse carbonate chemistry, the oyster larval shells were thinner and smaller, and protein diversity decreased to 131 sequences, with overall lower functional redundancy and reduced expression of structural proteins, indicating potential trade-offs. The proteomic and shell structural data also suggest that direct cellular control and biologically induced mechanisms, which will require further investigation, may be involved in PD I formation.

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Aquaculture of seaweeds (Saccharina latissima, Ulva spp., Gracilaria spp.) significantly improves the growth of co-cultivated bivalves in mesotrophic, but not eutrophic, estuaries

Published 29 December 2025 Science Closed
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The co-cultivation of seaweeds with bivalve shellfish is a potential strategy for protecting bivalve crops against anthropogenic coastal acidification and hypoxia. We co-cultivated seaweeds and bivalves using a succession of seaweed species according to season (winter, Saccharina latissima → spring, Ulva spp. → summer, Gracilaria spp.) together with eastern oysters (Crassostrea virginica) and blue mussels (Mytilus edulis). Bivalves and seaweeds were deployed in two estuaries that contrasted in trophic state, one mesotrophic and one eutrophic. In all five experiments in the mesotrophic system, cocultivation with seaweeds significantly increased weight- and/or shell-based growth of bivalves (p < 0.05). Growth rate increases for C. virginica were modest, with weight-based growth improving by 17–21% and shell-based growth improving by 3–27% with seaweed co-culture of all macroalgal species. For M. edulis, the effect was large; co-culture with S. latissima caused 47% and 114% increases in shell- and weight-based growth rates, respectively. In the four experiments in the eutrophic estuary, co-culture with seaweeds did not significantly improve bivalve growth. Seaweed cultivation significantly improved water quality metrics (increased pH and dissolved oxygen (DO); p < 0.05 in all cases) in and around the seaweed sites at both locations, although increases in pH and DO were modest, and even in control treatments, there were no prolonged periods of harmful pH or DO levels. An abundance of macroalgal detritus may have bolstered the diets of co-cultivated bivalves in the mesotrophic estuary, a hypothesis supported by lower chlorophyll a concentration, and therefore lower planktonic food levels, at that site. Given that seaweeds display species-specific allelopathic effects against phytoplankton, it is also possible that the presence of seaweeds altered the phytoplankton community to the benefit of the bivalves. Regardless, the findings here demonstrate that co-cultivation with seaweeds can accelerate the growth of bivalves.

Continue reading ‘Aquaculture of seaweeds (Saccharina latissima, Ulva spp., Gracilaria spp.) significantly improves the growth of co-cultivated bivalves in mesotrophic, but not eutrophic, estuaries’

Ecological stability of late Maastrichtian benthic foraminifera amidst Deccan volcanism

Published 29 December 2025 Science Closed
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Highlights

  • Benthic foraminifera assemblage at Bidart reveal a stable, mesotrophic late Maastrichtian seafloor.
  • K/Pg boundary at Bidart shows signs of ecological stress and taphonomic dissolution.
  • Deccan-induced calcification stress was restricted to surface ocean and had minimal impact on benthic foraminifera.
  • Robust test ratio and fragmentation index together serve as effective taphonomic proxies.

Abstract

The late Maastrichtian witnessed profound disruptions in biogeochemical cycles, leading to the fifth mass extinction at the Cretaceous–Paleogene (K/Pg) boundary. At Bidart section (France), the final ∼60 kyr of the Maastrichtian coincide with mercury (Hg) peaks, low magnetic susceptibility, evidence of biological stress and taphonomic alteration in planktic foraminifera, indicative of an ocean acidification event. While this event primarily appears to be a surface-ocean phenomenon, previous studies also documented a minor rise in benthic foraminiferal test fragmentation beginning 0.5 m below the K/Pg boundary, with a pronounced spike at the boundary itself.

A detailed investigation of benthic foraminifera in biozone CF1 at Bidart section (France) reveals a diverse and balanced assemblage preceding the K/Pg boundary, with minimal taphonomic alterations. At the K/Pg boundary, infaunal populations diminished, diversity declined sharply, test fragmentation intensified, yet paradoxically, the absolute abundance of genera rose markedly. Preferential preservation is evident in the dominance of robust taxa (Cibicidoides spp., Coryphostoma spp.), while a high fragmentation index reflects strong taphonomic dissolution and time-averaging. A plausible explanation for this could be CO2-rich waters mixing into the ocean interior over 100–1,000 years, driving dissolution during the ∼10,000-year deposition of the K/Pg boundary red clay. The stark contrast between the planktic and benthic census and morphometric data at Bidart section clearly constrains any Deccan-related calcification stress to the surface mixed layer. Lastly, the integrated planktic and benthic considerations re-emphasize a need to carefully separate taphonomic signals from true ecological stress.

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Compound hypoxia with heat or acidification stress induces synergistic and additive effects on coral physiology

Published 26 December 2025 Science Closed
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As climate change accelerates, coastal marine ecosystems are increasingly exposed to co-occurring stressors whose combined effects are nonlinear and difficult to predict. Deoxygenation is a rapidly intensifying yet underrecognized threat to coral reefs that interacts with heat and acidification to alter coral physiology and stress resilience. However, the effects of hypoxia-related compound events on corals are largely unknown, underscoring the need for multi-stressor studies. Here, we conducted two extended-exposure experiments (12–17 days) across the coral species Porites furcata, Porites astreoides and Siderastrea siderea, to disentangle the individual and combined effects of low dissolved oxygen (hypoxia) with either heat or acidification. We measured eight phenotypic traits related to growth, metabolism, and symbiosis health to test whether hypoxia imposes energetic constraints or other physiological stress that amplify the effects of heat or acidification. Standardized effect size analysis across 24 stressor–trait combinations revealed 13 additive, 10 synergistic, and only one antagonistic response. Hypoxia consistently suppressed dark respiration by 37–49% across species and altered photophysiology in the two Porites species, whereas acidification alone had minimal effects, particularly in S. siderea. Heat stress caused the most pronounced declines across nearly all traits, and when combined with hypoxia, it produced the highest number of synergistic interactions. In contrast, the combination of hypoxia and acidification largely resulted in additive responses, suggesting that independent physiological mechanisms underlie these effects. All corals showed strong metabolic depression under hypoxia which is likely beneficial as a short-term adaptive response but may impose energetic constraints in the long-term. These findings highlight deoxygenation as critical yet often overlooked drivers of coral reef vulnerability. More multi-stressor experiments across a range of species are urgently needed to improve predictions of reef resilience under future ocean conditions, where compound stress events are expected to become more frequent and severe.

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Short-term focus: phased response of Zostera marina seedlings to the combined stress of marine heatwave and ocean acidification

Published 25 December 2025 Science Closed
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Marine heat wave (MHW) and ocean acidification (OA) caused by global climate change occur frequently and intensify, which cause damage to the stability of seagrass bed. However, the understanding of the phased-impacts of sudden temperature and acidification changes on seagrass is limited. The study conducted phenomic, transcriptomic and metabolomic analyses to investigate the short-term response mechanisms of Zostera marina seedlings to sudden temperature and acidification incerease. The results showed that Z. marina seedlings activated an integrated metabolic response involving fatty acid metabolism, carbohydrate metabolism and amino acid metabolism to modulate cell membrane properties, enhance thermotolerance and maintain developmental stability. What is noteworthy is that the continuous high expression of the ABC transporters play a crucial role in resisting stress. The study is helpful to clarify the short-term phased response of Z. marina seedlings to the combination of MHW and OA, and have significant importance for the protection and restoration of seagrass beds.

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Effects of long-term ocean acidification exposure on the structural, mineralogical, and mechanical properties of sea urchin (Echinometra spp.) skeletons at a natural volcanic CO2 seep

Published 23 December 2025 Science Closed
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Two decades of mesocosm studies document generally negative effects of ocean acidification (OA) on adult sea urchin growth, feeding performance, skeletal structure, and strength. Whether experimental observations hold true in natural systems will determine whether they can be extrapolated to predict responses under ecologically relevant contexts. Here, we employ a suite of imaging, chemical, and mechanical techniques to examine the skeletal properties of two closely related sea urchin species (genus Echinometra) living at a natural carbon dioxide (CO2) seep in Japan. Test plates and spines from urchins living under elevated CO2 conditions were thinner, more porous, and had less biomineral than those at reference sites; however, tooth structure was resilient to elevated CO2. The magnesium content of the test and spines did not differ between sites; however, they exhibited reduced nanohardness and became more brittle under elevated CO2. Together, altered structural and mechanical properties may compromise the protective function of urchin skeletons at the CO2 seep. These responses have implications for ecosystem structure if urchin function is suppressed at the population level. Future work might explore the repeatability of these findings across successive species and localities to recognize generality, its limits, and the conditions that mediate the influence of OA.

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Interactive effects of ocean acidification and benthic biofilm composition on the early development of the European abalone Haliotis tuberculata

Published 23 December 2025 Science Closed
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Ocean acidification (OA) and associated shifts in carbonate chemistry represent major threats to marine organisms, particularly calcifiers. OA effects can be influenced by other environmental variables, including the biotic environment. This study investigated the individual and interactive effects of OA and algal density, acting through biofilm composition, on post-larval and juvenile abalone (Haliotis tuberculata). In a three-month factorial experiment, abalone were exposed from metamorphosis onward to two pH conditions (ambient 8.0 and reduced 7.7) and two initial densities of the green alga Ulvella lens on settlement plates. Biofilm biomass and composition were characterised using spectral reflectance and HPLC pigment analysis. Biological (density, length), physiological (respiration rate), behavioural (hiding response) and shell parameters (colour, surface corrosion, strength) of abalone were measured throughout the experiment. Biofilm biomass and composition remained relatively stable under both pH conditions, though greater variability in algal biomass occurred at low initial Ulvella density. Post-larval density and total length decreased significantly under low pH, while high Ulvella density reduced juvenile length at 80 days, likely due to competition between algal groups. A pH × Ulvella interaction affected shell fracture resistance and colouration, but not metabolism or behaviour, indicating that juvenile abalone maintained vital functions. Overall, the results confirm the sensitivity of early H. tuberculata stages to moderate OA (−0.3 pH units) and highlight indirect macroalgal effects through changes in diatom communities. In natural environments, the capacity of abalone to cope with future OA will depend on complex trade-offs between direct acidification effects and food-related biotic interactions.

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Ocean acidification reduces juvenile snow crab, Chionoecetes opilio, survival but does not affect growth or morphometrics

Published 18 December 2025 Science Closed
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Highlights

  • Snow crab were reared at 3 pHs for 396 days.
  • Low pH did not affect size at molt.
  • Low pH did not affect intermolt period.
  • Survival was lower at a pH of 7.5 than at ambient or pH 7.8.
  • Snow crab are moderately sensitive to ocean acidification.

Abstract

Anthropogenic release of CO2 and its subsequent dissolution in the oceans results in a decrease in the pH of seawater, known as ocean acidification, which can negatively affect marine organisms. Little is known about the response of snow crab, Chionoecetes opilio, to reduced pH. Juvenile snow crab were captured in the Bering Sea and exposed to three different pH treatments (Ambient (pH ∼7.95), pH 7.8, and pH 7.5) for 396 days at a constant temperature of 4 °C with thirty crabs randomly assigned to each treatment. Crabs were checked daily for molting or mortality. Wet mass and carapace morphometrics were measured after every molt. Reduced pH did not affect the intermolt duration, the carapace width after each molt, or wet mass of the crabs after each molt, giving no indication that growth rate was changed by reduced pH. There also was no change in morphometrics caused by reduced pH. However, the mortality rate of crabs held at pH 7.5 was 40 % higher than those held at pH 7.8 or Ambient. Such a substantial increase in mortality without accompanying sublethal effects is surprising; individuals susceptible to reduced pH might have died early in the experiment, or that differences in growth rate might have become apparent with longer exposure. Regardless, juvenile snow crab are somewhat sensitive to ocean acidification, although, consistent with studies at other life-history stages, snow crab may be more resistant to changes in pH than other Alaska crab species.

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Exploring structural integrity of coralline algae in response to the environmental changes associated with the PETM: a tale of functional resistance

Published 11 December 2025 Science Closed
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Coralline algae are key benthic components of shallow-marine ecosystems globally and as habitat-formers they support high biodiversity levels. Experiments on living coralline algae show internal growth changes in response to warming and higher CO2. These growth changes are leading to weakened structural integrity and increased breakage impacting their ecological function of habitat formation. Short-term experiments, though, raise questions about long term acclimation over multiple generations. Coralline algae have an extensive fossil record across the Cenozoic. Analysing growth changes within the geological record, specifically across hyperthermals, geologically abrupt environmental changes in the Earth’s history characterized by rapid ocean warming, acidification and sea level rise, can complement modern experiments. This allows us to quantify the vulnerability and response of habitat formers, such as coralline algae, to long-term environmental change. We evaluated cellular structure and structural integrity in species of the genera Sporolithon and Lithothamnion from Meghalaya, NE India (Eastern Tethys) before and during the Paleocene-Eocene Thermal Maximum, PETM (~55.8 Ma), the most pronounced hyperthermal of the Cenozoic. Cellular structural changes were not uniform between species, some species showed increased stress and strain due to larger cell sizes during the PETM, while other species revealed negligible changes in cell sizes. Unexpectedly, stresses and strains experienced by these Palaeogene taxa are comparable to contemporary species of the study genera. These findings suggest a resilience to long term warming and lower pH conditions resulting in a resistance to breakage. However, species differences in environmental change responses potentially highlight variations in phenotypic plasticity.

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Asymmetric effects of acidification and warming on foundation species and their predators in the California rocky intertidal zone

Published 11 December 2025 Science Closed
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The effects of climate change on marine organisms act through multiple pathways, as ocean warming and acidification can affect both their physiology and interspecies interactions. Asymmetries in species-specific physiological responses to climate change may alter the strength of interactions, such as those between predator and prey, which will have cascading effects on ecosystem structure. How foundation species and their interactions are affected by climate change will profoundly affect their community due to their dominance. I assessed the physiological responses of two common California rocky intertidal consumer–resource pairs across multiple trophic levels. I measured metabolic rates after four weeks of exposure to a range of nine pH levels (7.2–8.0) at two temperature levels (ambient, +4°C). At the lowest trophic level, I examined the effects of climate change on a primary producer foundation species, Silvetia compressa (golden rockweed), and its herbivore, Tegula eiseni, under differing upwelling regimes in early and late spring. Rockweed responded more to acidification than warming, decreasing photosynthetic rates in early spring and increasing rates during late spring. Their snail consumer, however, responded most strongly to temperature—increasing both respiration rates and calcification under warm conditions in late spring. In addition to species specific responses to climate stressors, the rockweed–snail pair had context-dependent responses based on background environmental conditions. Greater upwelling during late spring, combined with a younger snail population could explain differences in responses between early and late spring. Next, I examined asymmetries between a calcifying foundation species, Mytilus californianus, and its whelk predator, Nucella emarginata. Specifically, mussels were generally resistant to acute exposure to ocean warming and acidification, while whelks were highly sensitive to temperature. Whelks decreased their calcification, respiration, shell extension, and probability of drilling a mussel under warmer conditions. Across both experiments, I observed asymmetries in response to changes in pH and temperature between consumer and resource, which can shift ecosystems between bottom-up and top-down processes. Overall, I showed that mesopredators, such as herbivorous and carnivorous snails, appeared to be the most sensitive to changes in temperature relative to their foundation species prey. Climate change may reshape rocky intertidal communities by altering predation patterns on foundation species, which could either facilitate or threaten the survival of other associated species in a changing environment.

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Morphological adjustments enable sea urchins to sustain calcified structure function under ocean acidification

Published 10 December 2025 Science Closed
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Ocean acidification can reduce the size of calcified structures produced by marine calcifiers, raising questions about their competitiveness and persistence in future oceans. Yet, size reduction in calcified structures may represent a plastic response to ocean acidification if these structures remain functional. To test this hypothesis and examine whether morphological plasticity can influence the functionality of calcified structures, we assessed the effects of ocean acidification on the morphological, mechanical and chemical properties of the calcified structures of a sea urchin species prevailing at natural CO2 vents. We found that the rigid shells covering sea urchins’ bodies (‘tests’) were thinner and that they had smaller teeth and lower spine density at vents, but the mechanical performance of these calcified structures (mechanical resilience, wear resistance and bending strength) was maintained, possibly mediated by the capacity of sea urchins to sustain acid-base balance for calcification (i.e. increased Na/Ca). Our findings suggest that such morphological shifts in calcified structures may enable sea urchins to maintain structural performance under ocean acidification. Since ocean acidification is a slow process relative to the life cycle of sea urchins, some sea urchin species may acclimate, or even adapt, to ocean acidification so that their populations and ecological functions can persist in a future high-CO2 world.

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Posidonia bonsai: dwarf morphotypes of Posidonia oceanica in CO2 vents and non-vents areas suggest a novel growth strategy

Published 10 December 2025 Science Closed
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Highlights

  • Dwarf Posidonia oceanica shoots occur in vents and no-vents areas at Ischia, Palinuro and Ustica.
  • Dwarf shoots have a biomass reduced from 82 % to 97 % than normal-sized shoots.
  • Bonsai shoots also lack cyclic annual sheath-thickness pattern (lepidochronology).
  • Bonsai shoots occur in dead matte areas of the meadows, or behind regular terminal shoots.
  • Bonsai shoots suggest a novel growth strategy, likely to favour rapid substrate colonization.

Abstract

Dwarf shoots of the Mediterranean seagrass Posidonia oceanica, referred to as “Posidonia bonsai”, described in shallow hydrothermal vents, showed markedly reduced size and altered phenology, that were attributed to the extreme environmental conditions associated with ocean acidification and H2S emissions of these vent systems. Here we report new records of Posidonia “bonsai” from CO2 vent off the Ischia Island and non-vent areas with normal pH conditions at Ischia, and Ustica islands and at Palinuro. At Ustica and Palinuro, bonsai shoots we found exclusively on rocky bottoms, while at Ischia they occurred on the dead P. oceanica matte, both within vent systems and in control areas. Bonsai shoots exhibited a reduced number of leaves, significantly shorter leaf length and width, resulting in a drastic reduction of total leaf surface area (84–95 % lower) and biomass (82–97 % lower) compared to nearby regular-sized shoots. In addition, bonsai shoots lacked the typical annual cycle of leaf sheath thickness observed in normal shoots (lepidochronological cycle), as previously observed in bonsai from other sites. The high number of sheaths recorded per rhizome length, suggests high leaf production and turnover. The occurrence of bonsai shoots on dead matte at the meadow margins and in small clearings, or behind regular terminal shoots on creeping rhizomes in hard bottoms, leads to hypothesize that Posidonia bonsai represents a novel growth and colonization strategy, probably trigged by stressful conditions, not limited to ocean acidification, and point out the remarkable phenotypic plasticity of this seagrass.

Continue reading ‘Posidonia bonsai: dwarf morphotypes of Posidonia oceanica in CO2 vents and non-vents areas suggest a novel growth strategy’

Resistance of the cold-water coral Dendrophyllia cornigera to single and combined global change stressors

Published 28 November 2025 Science Closed
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Current knowledge of the consequences on global change in deep marine ecosystems is still limited, especially since environmental pressures do not act separately, and their potential interactions are mostly unknown. Cold-water corals (CWC) play a significant role in the deep sea, being ecosystem engineers supporting high biodiversity. However, global change may impact CWCs, compromising their integrity and survival. In this study, a nine-month aquaria experiment was conducted on the CWC Dendrophyllia cornigera from the NW Iberian Shelf (NE Atlantic Ocean). The aim was to assess the individual and combined effects of elevated temperature (12 vs. 15 °C), low pH (~ 7.99 vs. 7.69 pHT) and low oxygen (~ 6.4 vs. 4.7 mL L−1), based on the IPCC RCP 8.5 scenario. During the experiment, coral survival, skeletal growth, tissue cover and respiration were monitored as response variables. No significant effects were found on any of the response variables for either individual or combined stressors, pointing to the resistance of D. cornigera to different global change scenarios. Such a physiological resistance may support D. cornigera persistence under future conditions where other CWCs with narrower tolerance ranges may face greater limitations. However, further research is needed to assess potential trade-offs to cope with environmental change, which might impact the long-term survival capacity of this species.

Continue reading ‘Resistance of the cold-water coral Dendrophyllia cornigera to single and combined global change stressors’

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