table isotopes are fundamental proxies for deciphering past environmental conditions and carbon cycle perturbations. However, applying these geochemical tools with a forward-looking perspective can also help predict the resilience of marine biota in future acidified oceans. This study investigates carbon uptake and biomineralization pathways under reduced pH in two ecologically keystone calcifying species: the bivalve Mytilus galloprovincialis and the gastropod Phorcus sp. To unravel these mechanisms, we adopted a dual approach, comparing isotopic trajectories (δ13C) under strictly controlled laboratory mesocosms with observations from natural CO2 vent systems in Ischia, Italy. Our results reveal a striking discrepancy between settings. Under laboratory conditions, both species exhibited a significant depletion in shell δ13C as pH decreased, directly tracking seawater carbonate chemistry. Conversely, specimens from the volcanic vents displayed a paradoxical δ13C enrichment at low-pH sites (pH ~7.4). These divergent trajectories indicate that in complex natural environments, the geochemical signal of ocean acidification can be overridden by metabolic overprints and trophically driven vital processes. Consequently, while laboratory experiments are essential to isolate kinetic fractionation, natural analogues remain crucial to capture the biological resilience and complex ecological feedback of future oceans. Future research combining these geochemical trends with direct, in vivo physiological assessments will be essential to precisely constrain the underlying metabolic kinetics and refine predictive metabolic models.
Continue reading ‘Biological modulation of shell δ13C in Mytilus galloprovincialis and Phorcus sp.: divergent responses between CO2 vents and laboratory mesocosms’Posts Tagged 'Mediterranean'
Biological modulation of shell δ13C in Mytilus galloprovincialis and Phorcus sp.: divergent responses between CO2 vents and laboratory mesocosms
Published 17 August 2026 Science Leave a CommentTags: biological response, BRcommunity, field, laboratory, Mediterranean, mesocosms, mollusks, physiology, vents
CARIMED (CARbon, tracers, and ancillary data In the MEDiterranean Sea): a ship-based data synthesis product – overview and quality control procedures
Published 12 August 2026 Science Leave a CommentTags: chemistry, field, Mediterranean
The Mediterranean Sea (MedSea) is highly sensitive to climate-driven changes in temperature, oxygen, and pH, among other variables. To better assess these long-term trends, we developed CARIMED (CARbon, tracers, and ancillary data In the MEDiterranean Sea), the first comprehensive, harmonised data synthesis product for the MedSea. CARIMED integrates hydrographic, inorganic carbon, transient tracer, and ancillary measurements from 46 research cruises spanning the period from 1976 to 2018, containing observations for the entire water column across all MedSea sub-basins. A substantial component of the data was retrieved from fragmented or locally archived historical records, thus consolidating previously inaccessible measurements. Following global synthesis approaches, CARIMED applies a quality-controlled, and bias-adjusted framework. A key adaptation was the secondary quality control (2QC) procedure, specifically tailored to the MedSea’s unique hydrography, utilising sub-basin divisions and supplementary checks (including statistical consistency assessments) to resolve complex, often contradictory, inter-cruise offsets. This rigorous process minimised systematic biases, yielding a dataset with improved consistency, and highlights the urgent need for adapted standard operating procedures and reference materials to address the MedSea biogeochemical particularities. CARIMED delivers two complementary, freely available products: the aggregated original cruise data product (https://doi.org/10.20350/digitalCSIC/17785, García-Ibáñez et al., 2025) and the final bias-adjusted data synthesis product (https://doi.org/10.25921/cp5b-zq67, Álvarez et al., 2025; hosted at https://www.ncei.noaa.gov/access/ocean-carbon-acidification-data-system/oceans/CARIMED/, last access: 26 June 2026). This essential resource establishes a new benchmark for assessing long-term biogeochemical trends, validating regional ocean models, and supporting climate-change mitigation and adaptation strategies in this rapidly changing semi-enclosed basin.
Continue reading ‘CARIMED (CARbon, tracers, and ancillary data In the MEDiterranean Sea): a ship-based data synthesis product – overview and quality control procedures’Invasive macroalgae exert stronger effects than elevated CO₂ on seagrass (Posidonia oceanica) seedling performance and associated microbiomes
Published 11 August 2026 Science Leave a CommentTags: algae, biological response, laboratory, Mediterranean, mesocosms, multiple factors, oxygen, phanerogams, physiology, primary production, reproduction, respiration
Highlights
- Invasive macroalgae reduced P. oceanica seedling biomass and leaf development.
- Macroalgal invasion depleted carbohydrate reserves in seedling roots and rhizomes.
- Elevated CO2 increased rhizome starch but did not mitigate invasion impacts.
- Root microbiome diversity declined markedly under macroalgal invasion.
- Future CO2 enrichment unlikely to buffer invasion stress at recruitment stage.
Abstract
Seagrass seedlings are key to meadow recovery under global change, as they enable recolonization of degraded areas and provide genetic variability needed for adaptation. While invasive macroalgae increasingly threaten seagrass communities, elevated CO2 has been proposed to enhance seagrass performance and potentially buffer other stressors. Here, we conducted a mesocosm experiment to test the combined effects of two invasive macroalgae (Lophocladia trichoclados and Caulerpa cylindracea) and elevated CO2 on Posidonia oceanica seedlings. CO2 enrichment increased carbohydrate reserves in rhizomes and induced subtle shifts in root-associated microbiomes. In contrast, invasive macroalgae had consistently negative effects on seedling development and physiology and strongly altered both above- and belowground microbial communities. Despite its potential to stimulate seagrass productivity, elevated CO2 did not mitigate the detrimental impacts of invasive macroalgae. These findings indicate that future CO2 conditions may not offset invasion-driven stress at the recruitment stage, highlighting the need for targeted management efforts to limit macroalgal proliferation and support seagrass meadow regeneration.
Continue reading ‘Invasive macroalgae exert stronger effects than elevated CO₂ on seagrass (Posidonia oceanica) seedling performance and associated microbiomes’Global genome-wide patterns of genetic diversity and population structure in Coryphaena hippurus
Published 10 August 2026 Science Leave a CommentTags: biological response, fish, Indian, laboratory, Mediterranean, molecular biology, North Atlantic, North Pacific, physiology
Highlights
- Genome-wide SNPs reveal four discrete populations across ocean basins.
- Mediterranean population forms a deeply divergent and isolated lineage.
- Nuclear SNPs detect Pacific–Atlantic.
- Environmental gradients (salinity, phosphate, pH, light) shape genomic structure.
- Genetic connectivity varies within basins, revealing hidden substructure.
Abstract
The origin and maintenance of marine biodiversity remain poorly understood, particularly in highly connected oceanic environments where extensive dispersal is expected to limit population differentiation. Evolutionary processes driving population divergence or speciation frequently depend on a proper knowledge of species’ life history and its interaction with major environmental variables. Using a genome-wide approach, we investigated the global population structure of the cosmopolitan pelagic fish Coryphaena hippurus Linnaeus, 1758, generating a dataset of 8.7 million SNPs and complete mitochondrial genomes.
Our results reveal, for the first time, four genetically differentiated populations, corresponding to major oceanic basins: Atlantic, Pacific, Indian and Mediterranean Sea. The Mediterranean population exhibited a distinct genomic signature, likely resulting from historical isolation and restricted contemporary exchange through the strait of Gibraltar. Despite this structure, genome-wide analyses uncovered extensive signals of historical connectivity among basins. D-statistics and f4-ratio tests detected significant excess allele sharing, particularly between Indo-Pacific and Atlantic populations, while phylogenetic network reconstruction in TreeMix supported multiple migration events, highlighting the role of ancestral gene flow in shaping global genetic patterns.
At finer scales, a limited but significant intra-oceanic structure was detected within both Atlantic and Pacific basins. Seascape genomic analyses revealed that environmental gradients such as salinity, phosphate concentration, light availability (PAR, Kd), and pH are significantly associated with genomic variation, suggesting that ecological factors contribute to population differentiation across heterogeneous marine environments.
Annual variations of seawater carbonate system in the surface layer of the South-Eastern Mediterranean Sea
Published 7 August 2026 Science Leave a CommentTags: chemistry, Mediterranean
Seawater carbonate system measurements in the Mediterranean Sea are relatively scarce, especially in its eastern basin. This study describes the monthly variations of carbonate system parameters in the open sea and coastal water column of the eastern Mediterranean Sea during the period February 2018 to January 2019. Water samples were collected for analysis of Total Alkalinity and pHT at the shallow coastal THEMO1 and the deeper open-water THEMO2 (1,500 m bottom depth) stations off the Mediterranean coast of Israel. In the surface layer (<25 m), TA increased with salinity at a rate of +72 μmol·kg−1 and the pCO2(SW) was strongly and positively correlated with temperature. During summertime, surface waters were highly super-saturated with respect to atmospheric pCO2 (pCO2(SW) ∼ 600 μatm), while during winter they were only slightly super-saturated. The estimated net annual CO2 flux from the surface of the eastern Mediterranean Sea to the atmosphere during the study period was +2.8 Tg C·y−1, which is three times greater than a previous estimate made for this region (0.9 Tg C·y−1), and is attributed to the smaller volume of Atlantic water input in the present study compared to the previous one as well as the substantially shallower total dissolved inorganic carbon enriched core of the Levantine Intermediate Water in this study. Based on these results, it is still expected that future warming and salinization, reduced Atlantic Water influx to the eastern Mediterranean Sea, and increased stratification will increase the flux of CO2 to the atmosphere in this region.
Plain Language Summary
This study investigated annual variations in atmospheric CO2 flux from the surface of the eastern Mediterranean Sea based on monthly seawater sampling and carbon chemistry analyses conducted at two locations off the Mediterranean coast of Israel from February 2018 to January 2019. The results indicate that the southeastern Mediterranean Sea was a net source of CO2 to the atmosphere. This behavior was largely driven by seasonal changes in seawater temperature, which controls the saturation concentration of dissolved CO2 in seawater. During summer months, warm surface waters were a strong source of CO2 to the atmosphere, while during winter they were a weak sink. The study estimates that approximately 2.8 million tons of carbon were released annually from the sea to the atmosphere during the study period. This revised and more comprehensive estimate is ∼3 times higher than previous estimates reported for the same region. The increase is suggested to result from recent changes in regional circulation, particularly a reduced inflow of Atlantic Ocean waters into the eastern Mediterranean Sea. Based on these findings, continued warming, increasing salinity, and enhanced stratification of the eastern Mediterranean Sea are expected to further intensify CO2 release to the atmosphere in the future.
Continue reading ‘Annual variations of seawater carbonate system in the surface layer of the South-Eastern Mediterranean Sea’Ocean acidification influence on Cymodocea nodosa seedling development
Published 5 August 2026 Science ClosedTags: biological response, laboratory, Mediterranean, phanerogams, physiology, vents
Ocean acidification may positively affect seagrasses, although the response of the early life stages remains generally unknown. This study investigated the effect of OA and seed origin on the viability, morphometry, and chemical content of Cymodocea nodosa seedlings, using a field experiment along a natural-low pH gradient created by submarine vents in Vulcano Island, Italy. After four months of exposure, seedlings under increased pCO2 showed a reduction in the viability but a higher development exhibiting a lower C leaf content, independently of their origin. Results indicate compensating responses which may favour the plant acclimation in early life stages to future acidification scenarios.
Continue reading ‘Ocean acidification influence on Cymodocea nodosa seedling development’Exploring the multiple functions of polyphenols in Mediterranean macroalgae: insights, gaps, and future directions from a systematic review
Published 30 July 2026 Science ClosedTags: algae, biological response, Mediterranean, physiology, review
Macroalgae are a cornucopia of bioactive molecules whose synthesis is modulated in response to environmental variables, allowing macroalgal adaptation and survival. Among these metabolites, polyphenols are worthy of attention because they may represent an informative archive of environmental conditions, given their involvement in several ecological and biochemical functions. This systematic review synthesized the literature from the last two decades on phenolic compounds in Mediterranean macroalgae, focusing on their functional roles, taxonomic distribution, geographical occurrence, and responses to abiotic and biotic stressors, with particular attention to their potential as ‘early indicators’ of environmental change. Using a Scopus-based search strategy, nearly 6000 records were screened and studies on brown, red, and green macroalgae published between 2003 and September 2025 across the Mediterranean basin were retained.
The reviewed literature highlighted that polyphenols are widely involved in antioxidant defense, photoprotection, stress tolerance, and interspecific interactions, supporting the resilience of macroalgae in a rapidly changing Mediterranean Sea. At the same time, the review emphasizes the significant biotechnological potential of these compounds in the pharmaceutical, cosmetic, food, and agricultural sectors. Overall, the evidence indicates that fluctuations in polyphenol content often reflect rapid physiological responses to environmental stress, suggesting that these compounds may function as early indicators of ecological change in Mediterranean macroalgae.
Despite growing evidence, several important gaps remain. Research from the eastern Mediterranean basin is still limited, most studies focus on only a few model genera, and long-term field studies examining multiple environmental stressors are rare. Future research should therefore include a wider range of geographic areas and species, adopt standardized analytical methods, and investigate how polyphenols respond to combined environmental drivers. This would help clarify and validate their use as early indicators of ecological change.
Continue reading ‘Exploring the multiple functions of polyphenols in Mediterranean macroalgae: insights, gaps, and future directions from a systematic review’Climate change and ocean acidification outweigh local stressors in Mediterranean mussels: a multi-method convergence analysis
Published 15 July 2026 Science ClosedTags: biological response, BRcommunity, field, laboratory, Mediterranean, metals, mollusks, multiple factors, physiology
Highlights
- Climate change explains ∼40% of biological stress variance in Mediterranean mussels.
- Ocean acidification drives 67% of metal bioavailability changes via pH-metal speciation.
- 64% of climate effects on biomarkers operate indirectly through metal bioaccumulation.
- Multi-method convergence (LMG, GAM, SEM, Bayesian Networks) confirms stressor ranking.
- Only SSP1-2.6 keeps biological stress below the chronic-stress threshold through 2050.
Abstract
Marine coastal ecosystems face concurrent pressure from climate change and anthropogenic contamination, yet their relative contributions to biological stress remain poorly quantified. Here we present a decade-long (2014–2023) biomonitoring study on Mytilus galloprovincialis in the Ligurian Sea (NW Mediterranean), integrating quarterly biomarker measurements, heavy metal bioaccumulation data (12 metals), and high-resolution oceanographic records at a control site (Gorgona Island Marine Protected Area) and an offshore regasification terminal.
Biological stress variance was partitioned using five complementary analytical frameworks — Lindeman–Merenda–Gold (LMG) variance decomposition, Hierarchical and Generalised Additive Models (HGAM/GAM), Structural Equation Modelling (SEM), and Bayesian Networks — applied to four biomarkers: DNA damage, lysosomal membrane stability, gill tissue integrity, and immune response. A campaign-specific T0 baseline normalisation isolated environmental signals from initial population variability.
Climate change emerged as the dominant driver, consistently explaining ∼40% of variance across all methods, significantly exceeding metal bioaccumulation (∼30%), terminal influence (∼13%), and seasonal effects (∼2%). Ocean acidification was the primary climate mechanism, influencing 67% of analysed metals. Causal mediation analysis revealed that 64% of the climate effect operates indirectly through enhanced metal bioaccumulation (Climate→Metals→Biomarkers), while 36% acts directly. Climate and biological stress indices co-varied strongly (ρ = 0.78, p < 0.001), with marine heatwaves coinciding with peak biomarker responses.
Under IPCC Shared Socioeconomic Pathway (SSP) scenarios, the Biological Stress Index is projected to cross chronic-stress thresholds by 2035–2040 under the high-emission scenario (SSP5-8.5) and the intermediate-emission scenario (SSP2-4.5), with only the low-emission scenario (SSP1-2.6) maintaining stress below critical levels through 2050.
These findings challenge pollution-centric monitoring paradigms and demonstrate that CO2 mitigation now constitutes the highest-leverage intervention for marine invertebrate health in the Mediterranean.
Graphical abstract
This graphical abstract illustrates the main findings of a decade-long field study (2014–2023) on the effects of climate change and metal contamination on Mytilus galloprovincialis in the Ligurian Sea (NW Mediterranean). Three panels summarise the causal chain from environmental drivers to biological outcomes. The first panel depicts the key oceanographic trends recorded at the study site: ocean warming (+0.41°C/decade), acidification (−0.020 pH units/decade), deoxygenation, and a doubling of marine heatwave frequency after 2018. The second panel shows how pH decline enhances the bioavailability of 67% of the metals analysed, driving a predominantly indirect pathway (64%) from climate stressors to biological stress, mediated by metal bioaccumulation, as revealed by structural equation modelling and Bayesian network analysis. The final panel presents the four biomarkers used to compute the Biological Stress Index (BSI), its strong temporal correlation with the Climate Change Index (ρ = 0.78), and BSI projections to 2050 under three IPCC emission scenarios, showing that only SSP1-2.6 keeps BSI below the chronic-stress threshold throughout the projection period.
The effects of single and multiple climate-driven stressors exposures on the seagrass Posidonia oceanica: phenological, cellular, and genetic adaptations
Published 10 July 2026 Science ClosedTags: adaptation, biological response, Mediterranean, phanerogams
Posidonia oceanica is a foundation seagrass species endemic to the Mediterranean Sea, where it forms highly productive meadows that support biodiversity, coastal protection and long-term blue carbon storage. However, these ecosystems are increasingly threatened by the combined effects of climate change and local anthropogenic pressures, including ocean warming, marine heatwaves, ocean acidification, hypersalinity and thermal pollution. Despite growing evidence of the vulnerability of P. oceanica to environmental change, the mechanisms underlying its acclimation capacity, resilience and potential vulnerability thresholds remain only partially understood, particularly under multiple-stressor scenarios.This study investigates the responses of P. oceanica to climate change-related stressors across multiple levels of biological organization, integrating evidence from meta-analysis, controlled mesocosm experiments, molecular analyses and field observations. Special attention is given to the role of environmental history in shaping population-specific responses, comparing plants exposed to contrasting environmental conditions and assessing their phenological, physiological, metabolic and molecular performance under single and combined stressors.By linking organismal, molecular and meadow-scale responses, this work provides new insights into the capacity of P. oceanica to cope with future climate scenarios and local anthropogenic disturbances. The findings contribute to identifying resilience mechanisms and vulnerability patterns in Mediterranean seagrass ecosystems, supporting the development of more effective monitoring, management and conservation strategies under ongoing global change.
Continue reading ‘The effects of single and multiple climate-driven stressors exposures on the seagrass Posidonia oceanica: phenological, cellular, and genetic adaptations’Skeletal porosity of a cold-water coral increases with decreasing aragonite saturation state along a depth gradient in the Mediterranean Sea
Published 29 June 2026 Science ClosedTags: biogeochemistry, biological response, BRcommunity, chemistry, corals, laboratory, Mediterranean, physiology
Background
Cold-water corals (CWCs) are key ecosystem engineers that create complex three-dimensional habitats much like tropical reefs, but in deep, cold seas. However, like other reef-building systems, they are increasingly threatened by climate change and ocean acidification. CWC communities in the Mediterranean Sea may be especially vulnerable because these waters absorb more atmospheric CO2 than the global ocean, making it a mesocosm that mirrors broader global trends affecting marine life. Since calcification is energetically costly and likely becomes even more demanding as pH and carbonate ion availability decline, understanding how the decrease in aragonite saturation state (Ωarag) affects biomineralization is essential for predicting the future of these corals.
Results
Here, we investigated skeletal structural and compositional changes of the scleractinian CWC Desmophyllum dianthus along an Ωarag gradient in the Mediterranean Sea using specimens collected between 400 and 1200 m depth. Our findings indicate that skeletal porosity increases at the macro-scale with decreasing Ωarag, while micro- and nano-scale structural and compositional features remained unaffected.
Conclusions
The persistence of micro- and nano-scale skeletal features across an 800 m depth gradient suggests that D. dianthus maintains tight biological control over mineralization at these scales, even as Ωarag declines. This control does not extend to the macro-scale, where increasing porosity alters the skeleton’s overall architecture under lower Ωarag. D. dianthus thus appears to preserve the fundamental “building blocks” of its skeleton while changing its larger-scale structure, a decoupling that may make macro-scale porosity an early marker of acidification stress in CWCs.
Continue reading ‘Skeletal porosity of a cold-water coral increases with decreasing aragonite saturation state along a depth gradient in the Mediterranean Sea’Will the Mediterranean sea be a cul-de-sac for marine gastropods under climate change?
Published 23 June 2026 Science ClosedTags: biological response, BRcommunity, communitymodeling, individualmodeling, Mediterranean, modeling, mollusks, North Atlantic, physiology, reproduction
Marine ecosystems are undergoing rapid transformation under climate change, yet the responses of many marine invertebrates remain vastly understudied. In particular, for many benthic gastropods there is a striking imbalance between their traditional appreciation by shell collectors—and, consequently, their consistent representation in Natural History Collections—and the limited attention they receive in ecological and conservation studies. Focusing on the northeastern Atlantic and the Mediterranean, the cowries Luria lurida, Naria spurca, Zonaria pyrum and the frog-shell Talisman scrobilator are emblematic examples of this knowledge gap, despite being frequently mentioned as species of conservation concern. Using long-term occurrence records spanning more than a century, we modelled past and present distributions of these species and explored their potential responses to future climate scenarios through a multi-temporal Species Distribution Modelling framework. Our results show that intermediate climatic conditions—both in time (2050–2060 vs. 2090–2100) and scenario intensity (moderate SSP2-4.5 versus high-emission SSP5-8.5)—may represent a critical transition phase, leading to habitat contractions without compensatory gains in newly emerging suitable areas. The Mediterranean Sea is expected to increasingly function as a cul-de-sac, with the dominant circulation patterns strongly limiting outward movements towards cooler regions for species relying on planktic larvae for dispersal. Furthermore, incorporating larval sensitivity to reduced pH suggests that large areas of the Atlantic Ocean may actually result unsuitable for larval persistence, substantially reducing the habitat effectively available for completion of the full life cycle; this highlights the need to account for connectivity, life-history constraints and juvenile-stage sensitivity when assessing climate-driven range shifts in shelled organisms with planktic larvae.
Continue reading ‘Will the Mediterranean sea be a cul-de-sac for marine gastropods under climate change?’A basin-wide assessment of pH changes in the Mediterranean Sea based on reanalysis products
Published 19 June 2026 Science ClosedTags: biogeochemistry, chemistry, Mediterranean, modeling, regionalmodeling
Ocean acidification, driven by increasing atmospheric CO2 concentrations, poses a growing threat to marine ecosystems and biogeochemical processes. The Mediterranean Sea, characterized by complex circulation patterns and distinct hydrographic sub-basins, represents a sensitive region for assessing basin-scale pH variability. However, long-term in situ pH observations remain spatially sparse and unevenly distributed, limiting the assessment of coherent spatiotemporal trends across the basin. Here, we present a basin-wide spatiotemporal assessment of pH trends in the Mediterranean using an 18-year biogeochemical reanalysis dataset from the Copernicus Marine Environment Monitoring Service. Our analysis reveals a consistent vertical structuring of pH trends, with negative trends in surface waters and contrasting, often neutral to weakly positive tendencies at depth. The magnitude and vertical extent of these trends vary regionally and are closely linked to local circulation regimes, water-mass formation processes, and remineralization dynamics. In deep-water formation regions such as the Adriatic, Ionian, and Aegean Seas, negative pH trends extend throughout much of the water column, whereas in the Levantine Basin, mesoscale circulation structures confine pH changes primarily to a relatively thin surface layer. These results demonstrate that basin-scale analyses based on high-quality, publicly accessible biogeochemical reanalysis products, such as CMEMS, can provide a spatially integrated perspective on long-term pH variability, complementing existing observational records by bridging spatial and temporal gaps. The framework presented here offers a reproducible approach for systematically assessing depth and region resolved pH trends.
Continue reading ‘A basin-wide assessment of pH changes in the Mediterranean Sea based on reanalysis products’Physical-chemical gradients, CO2 venting dynamics and microbial community composition in a shallow Mediterranean CO2-rich hydrothermal system
Published 19 June 2026 Science ClosedTags: biogeochemistry, biological response, chemistry, community composition, Mediterranean, otherprocess, physiology, prokaryotes, vents
Shallow-water CO2-rich hydrothermal systems provide natural laboratories for studying localized ocean acidification under realistic environmental conditions. Here, we present a multidisciplinary characterization of the Calent mound CO2-rich system (Columbretes Islands, Western Mediterranean), based on oceanographic surveys conducted in 2020 and 2021. Localized pH anomalies were detected directly above active vents, reaching maximum reductions of 1.12 pH units, whereas water-column temperature anomalies were minimal and subsurface sediment temperatures exceeded ambient seawater by 5.67 °C. Gas analyses indicated high CO2 concentrations (0.094 ± 0.008 mol L− 1), with heterogeneous degassing regimes, ranging from sporadic to continuous emissions and an average flux of 189.4 ± 15.4 kg CO2 m− 2 yr− 1 at the active vent field. Vent fluids were significantly enriched in dissolved inorganic nutrients, particularly silicate, phosphate, nitrate+nitrite, and ammonium. Benthic microbial mats hosted metabolically diverse prokaryotic and eukaryotic communities, including hydrothermal-associated taxa such as Zetaproteobacteria, Campylobacterota, and Nitrosophaeria, consistent with iron, sulfur, and ammonia oxididation metabolisms. Several microbial core taxa persisted across years despite shifts in relative abundance. These findings demonstrate that Calent mound sustains an intense yet highly localized biogeochemical environment within the photic zone, where CO2 venting and nutrient inputs jointly influence carbonate chemistry and microbial community structure.
Continue reading ‘Physical-chemical gradients, CO2 venting dynamics and microbial community composition in a shallow Mediterranean CO2-rich hydrothermal system’Shifts of tentacles-associated prokaryotes of Anemonia viridis along a natural pH gradient
Published 18 June 2026 Science ClosedTags: biological response, BRcommunity, cnidaria, community composition, laboratory, Mediterranean, molecular biology, otherprocess, physiology, prokaryotes, sediment
Highlights
- A. viridis tentacle microbiomes were studied under changing natural pH conditions.
- Notable shifts in the abundance of specific taxa emerged in the acidified sites.
- Differences in seawater emphasized the host’s unique microbial signature.
- Rickettsiales predominance suggested a specialized ecological role in symbiosis.
- Further research is needed to discern the role of microbes for host resilience.
Abstract
Marine hydrothermal vents are extreme environments that naturally select for organisms with strong resistance and the ability to cope with special conditions of acidification. Sea anemones are an interesting example that are able to buffer intracellular pH conditions. In this study, the influence of a natural pH gradient on microbial communities associated with Anemonia viridis (Cnidaria, Anthozoa) tentacles was investigated. We hypothesized that exposure to a natural pH gradient would be associated with changes in the structure and activity of A. viridis-associated microbial communities, potentially contributing to the host’s resilience in hydrothermal environments. Microbial enzymatic activities within anemones’ tentacles were investigated by incubation with fluorogenic compounds. The leucine amino peptidase activity was highest in the tentacles of specimens living in more acidified sites. A microbial biodiversity loss was observed in bacterial symbionts from less acidified to more acidified sites, with a reduction of relative abundance in certain groups (i.e., Planctomycetota, Firmicutes, and Desulfobacterota). Results obtained by a metabarcoding approach provided interesting insights into the taxonomic shifts of the A. viridis holobiont system in naturally acidified environments.
Continue reading ‘Shifts of tentacles-associated prokaryotes of Anemonia viridis along a natural pH gradient’High-resolution reconstruction of the pH-upregulation and its seasonal drivers in the temperate coral Cladocora caespitosa
Published 12 June 2026 Science ClosedTags: biological response, chemistry, corals, laboratory, Mediterranean
Ocean acidification (OA) and associated changes in seawater carbonate chemistry, combined with thermal stress, hampers coral calcification. By upregulating pH and dissolved inorganic carbon, corals can optimize their calcification, giving them some resilience to OA. Little is known about the seasonal- and interannual‑scale impacts of thermal stress and OA on pH upregulation and calcification in the temperate coral Cladocora caespitosa, despite it being the only zooxanthellate reef builder in the Mediterranean Sea. δ¹¹B and B/Ca were determined seasonally in C. caespitosa skeletons from two NW Mediterranean sites to reconstruct the effect of seawater temperature and pH on the carbonate chemistry of the coral calcifying fluid (CF), at a bimonthly resolution from June 2013 to August 2017 (Columbretes Islands, Spain), and June 2016 to February 2022 (Villefranche-sur-Mer, France). Cladocora caespitosa displayed a similar pH upregulation strategy to most tropical corals, albeit with an apparently lower sensitivity to seasonal environmental change. Temperature was the main driver of seasonal variability in the CF composition and coral calcification, with seawater pH having a comparatively lower seasonal variability, and acting on longer timescales. While longer coral records and investigations into inter-population variability would still be beneficial in order to fully understand the response of C. caespitosa to environmental change, our records constitute an important first step in understanding the biomineralization strategy of this ecologically important coral species.
Continue reading ‘High-resolution reconstruction of the pH-upregulation and its seasonal drivers in the temperate coral Cladocora caespitosa’Optimization of UV-Vis spectrophotometer (OCaPI) parameters for measuring the pH and pCO2 of the ocean carbonate system in seawater to assess ocean acidification (Mediterranean Sea)
Published 9 June 2026 Science ClosedTags: chemistry, Mediterranean
Automating the measurement of carbonate system parameters is essential for improving our understanding of biogeochemical processes in marine regions. The portable OCaPI (Ocean Carbon Parameters Instrument) is designed to perform simultaneous and accurate measurements of hydrogen ion concentration (pH) and partial pressure of carbon dioxide (pCO2)1 in the ocean environment. Optimizing the parameters of the UV-Vis spectrophotometer (integration time, scan-to-average, boxcar) facilitates the quantification of ocean acidification, with significantly improved measurement accuracy and reliability. The results obtained are consistent with existing techniques and offer a simplified approach to data collection, even under challenging conditions. This work, based on design principles, performance, and preliminary results obtained in the Mediterranean Sea, paves the way for the integration of these optimized techniques into long-term monitoring programs. This will contribute to a better understanding of the impacts of climate change on marine ecosystems and to improved management in the face of ocean acidification.
Continue reading ‘Optimization of UV-Vis spectrophotometer (OCaPI) parameters for measuring the pH and pCO2 of the ocean carbonate system in seawater to assess ocean acidification (Mediterranean Sea)’Microbial communities associated with two populations of the sponge Chondrilla nucula under present and projected climate conditions in the Aegean Sea
Published 25 May 2026 Science ClosedTags: biological response, BRcommunity, community composition, laboratory, Mediterranean, molecular biology, otherprocess, porifera, prokaryotes
This data paper describes bacterial and fungal communities associated with the sponge Chondrilla nucula collected from two Eastern Mediterranean populations (North and South Aegean Sea) and maintained under controlled common-garden conditions simulating present and projected climate scenarios over a period of 3 months. Microbial composition was characterised using two complementary ribosomal marker approaches: Illumina (MiSeq) sequencing of the 16S rRNA gene for Bacteria and Oxford Nanopore (MinION) sequencing of a long 18S-ITS-28S rRNA fragment for Fungi. A total of 24 sponge libraries (3 climate conditions x 2 populations x 4 biological replicates) along with six control libraries (water from three experimental tanks, extraction and PCR blanks) were constructed for each group of microsymbionts. The resulting reads were processed using custom and publicly available bioinformatic pipelines and databases, followed by initial taxonomic assignment. This dataset represents the first fungal community associated with C. nucula and the first bacterial community for this species from the Aegean Sea.
Continue reading ‘Microbial communities associated with two populations of the sponge Chondrilla nucula under present and projected climate conditions in the Aegean Sea’Combined effects of ammonium and pH on sea urchin embryogenesis: insights for sediment quality assessment
Published 30 April 2026 Science ClosedTags: biological response, echinoderms, laboratory, Mediterranean, multiple factors, physiology, reproduction, sediment, toxicants
Highlights
- Reduced pH enhances ammonium toxicity on sea urchin embryos in filtered seawater.
- In elutriates ammonium is a major driver of P. lividus embryotoxicity.
- Data support setting ammonium thresholds in sediment quality frameworks.
- Ocean acidification potentially increases ammonium toxicity for sea urchin larvae.
Abstract
Ammonium is a key component of coastal marine systems, originating from both natural and anthropogenic sources, with possible toxic effects on marine organisms depending on the concentration and pH. This study evaluates, for the first time, the combined effects of ammonium and seawater acidification on early development of the sea urchin Paracentrotus lividus under both laboratory conditions and exposure to environmental matrices derived by dredged sediments from harbor area. Embryos were incubated with increasing concentrations of ammonium in filtered seawater at pH 8.1 and 7.6, as well as in sediment elutriates from the Pescara harbor (Adriatic Sea, Italy), selected as a case study with relevant concentrations of ammonium (0.1–3.5 mg/L). A combined effect between ammonium and pH was observed, with increasing ammonium toxicity by ∼20% at pH 7. Moreover, in sediment elutriates, ammonium affect sea urchin embryo development, with EC50 ranging between 1.388 and 1.538 mg/L NH4+ at pH 8.1 and 7.6, respectively, without significant differences due to pH. Chemical analyses of sediments confirmed low levels of trace metals and organic pollutants, indicating that ammonium is the primary driver of embryotoxicity without a direct toxic effect of other contaminants. The results further underscore the need to integrate ammonium assessment into sediment quality frameworks and for management strategies, particularly in the context of future ocean acidification, to safeguard the early life stages of sensitive marine invertebrates.
Continue reading ‘Combined effects of ammonium and pH on sea urchin embryogenesis: insights for sediment quality assessment’Unravelling marine benthic functioning shifts under ocean acidification
Published 10 April 2026 Science ClosedTags: algae, biological response, BRcommunity, calcification, community composition, crustaceans, field, Mediterranean, mollusks, morphology, otherprocess, photosynthesis, physiology, porifera, respiration, vents
Ocean acidification (OA) driven by increasing atmospheric CO2 is altering marine biodiversity. However, impacts of OA on ecosystem functioning at the community level, including calcification, primary production and nutrient uptake, remain largely unknown. Here, we conducted community transplant experiments at natural CO2 vents to assess how declining pH affects marine community species composition, biomass, and key ecosystem processes over time. Our results indicate that community shifts caused by declining pH lead to decreased biomass and calcification rates, while photosynthesis and nutrient uptake rates increased. By leveraging OA field model systems and in situ measurements of ecosystem functioning, this study provides critical insights into how OA-induced biodiversity loss reshapes the structure and functioning of temperate marine coastal ecosystems.
Continue reading ‘Unravelling marine benthic functioning shifts under ocean acidification’
