Posts Tagged 'phanerogams'

Invasive macroalgae exert stronger effects than elevated CO₂ on seagrass (Posidonia oceanica) seedling performance and associated microbiomes

Published 11 August 2026 Science Leave a Comment
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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.

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Ocean acidification influence on Cymodocea nodosa seedling development

Published 5 August 2026 Science Leave a Comment
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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.

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pH–salinity-driven regulation in carbon utilization kinetics of the intertidal seagrass Zostera japonica along China’s coastline

Published 27 July 2026 Science Closed
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Highlights

  • We innovatively define two biophysical parameters (pH change rate and acceleration) of Zostera japonica photosynthesis.
  • pH change acceleration is sensitive to the regulation of carbon utilization pathways during Z. japonica photosynthesis.
  • A progressive pH–salinity-driven regulation mode of carbon utilization pathways in Z. japonica photosynthesis is summarized.
  • The impact of ocean acidification and alkalization on seagrass is characterized from a new biophysical standpoint.

Abstract

Seagrass carbon concentration mechanisms are modulated by seawater pH and salinity, yet their progressive regulation in photosynthetic inorganic carbon utilization pathways remain poorly characterized. This study novelly mathematically characterized first-order (pH change rate) and second-order (pH change acceleration) derivatives from pH-drift experiments in the intertidal seagrass Zostera japonica along China’s coastline. The pH change-based method effectively highlights the dissolved inorganic carbon (DIC) utilization and biomass accumulation of seagrass, while pH change acceleration is sensitive to the progressive switch of DIC utilization pathways during Z. japonica photosynthesis. As pH increases, six significant regulations emerge that have ecophysiological significance: a. primary regulation via reaching the CO2 compensation point; b. extracellular carbonic anhydrase (exCA) activity dropping to negligible levels; c. diminished efficiency of proton pump-mediated extracellular acidification in supplying CO2; d. regulation via reaching the bicarbonate saturation point; e. regulation via reaching the bicarbonate compensation point; and f. regulation via enhanced respiratory CO2 into seawater temporarily stimulating photosynthesis as a feedback. We summarize a progressive and universal pH–salinity-driven regulation mode reflecting different combinations of DIC utilization pathways and their respective intensities. Specifically, seawater pH modulates the mode’s fluctuating thresholds, while salinity governs the amplitude. Unexpectedly, elevated salinity serves as an effective stimulant for Z. japonica to maintain strong DIC utilization intensity in high pH (> 9.1) environments. Ocean acidification could increase pH change acceleration by 166%, enhancing carbon fixation, whereas artificial ocean alkalinity enhancement (Ca(OH)2 supplementation and olivine-seawater weathering) could reduce it by 165% and 105%, respectively, risking mortality of Z. japonica. Additionally, the salinity-dependent braking point (where acceleration drops to zero) serves as a critical threshold for seagrass photosynthesis and a new factor for transplantation-based restoration.

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Response of Zostera japonica rhizosphere bacteria to ocean acidification

Published 24 July 2026 Science Closed
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Abstract

Amidst global climate change, the escalating atmospheric CO2 levels have intensified ocean acidification (OA), significantly impacting the structure and function of marine ecosystems. Seagrass beds, representative nearshore ecosystems, play a pivotal role in carbon sequestration, biodiversity preservation, and nearshore environmental equilibrium. Rhizosphere microorganisms within seagrass beds, essential components of the ecosystem, drive material cycling and energy flow. Their community structure and functions demonstrate heightened sensitivity to environmental variations. While previous studies have primarily focused on the effects of ocean acidification on seagrass hosts, limited attention has been given to the rhizosphere. Therefore, this study selected Zostera japonica as the focal species and systematically evaluated changes in the structure and function of the rhizosphere bacterial community across varying acidification levels (400 ppm, 1,000 ppm, 2,000 ppm CO2) within an ocean acidification context. The results revealed a significant decline in the richness and diversity of the rhizosphere bacterial community under acidification, accompanied by shifts in community composition characterized by an increase in the relative abundance of Bacteroidota and Tenacibaculum with escalating acidification levels. In high acidification conditions, bacterial network interactions exhibited a trend toward simplification; yet the number of key taxonomic units increases, and there was a shift in community assembly from stochastic to deterministic processes. Functional predictions indicated the enhancement of microbial carbon sequestration and nitrogen fixation under acidification, while denitrification and specific sulfur metabolism pathways were inhibited. This implies that in acidified environments, the rhizosphere bacterial community may enhance carbon and nitrogen fixation to uphold nutrient supply.

Importance

Against the background of escalating global climate change and ocean acidification, seagrass beds, as crucial blue carbon sink ecosystems, face formidable challenges to their ecological functions and stability. Rhizosphere microorganisms of seagrasses, serving as the “second genome” of the seagrass host, play a central role in material cycling, nutrient supply, and system stability within seagrass beds. They are a key biological component that supports seagrass adaptation to environmental changes. Therefore, investigating the response and adaptation mechanisms of seagrass rhizosphere bacterial communities under ocean acidification is essential for deepening our understanding of the stability and resilience of seagrass bed ecosystems.

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Fish trait-based indicators of mercury bioaccumulation under natural ocean acidification: insights from a mediterranean CO₂ vent system

Published 22 July 2026 Science Closed
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Highlights

  • Low pH conditions at CO₂ vents increase THg bioavailability and fish exposure.
  • Functional traits explain THg patterns better than species identity.
  • Under low pH, less-mobile benthic fish accumulate more THg than highly-mobile fish.
  • Trophic position drives stronger THg biomagnification at low pH sites.

Abstract

Ocean acidification is not an isolated climate-related threat to marine organisms, as it may act in combination with other stressors such as trace element contamination. Here, we took advantage of naturally acidified conditions and mercury spill-out from the shallow CO2 vent of Vulcano Island (Italy) to test whether fish functional traits explain contaminant dynamics better than species identity under ocean acidification scenarios. Specifically, we investigated if trophic group and mobility influence total mercury (THg) bioaccumulation and trophic transfer in fish inhabiting Cymodocea nodosa seagrass meadows under low and ambient pH conditions. Low-mobility benthic fish, mainly represented by invertebrate feeders and small piscivores, exhibited higher THg concentration at the vent site than at reference sites, while highly mobile zooplanktivorous fish showed no significant differences, highlighting the importance of fish mobility and local trophic benthic pathways in shaping contaminant exposure and bioaccumulation. Moreover, the relationship between trophic position and THg concentration in fish was stronger in the low pH site, indicating enhanced trophic transfer and biomagnification when Hg availability is higher. In contrast, weak or absent biomagnification in the reference sites suggests that Hg transfer depends more on contaminant availability and food web structure than trophic position alone. Overall, these findings indicate that functional traits better predict Hg bioaccumulation patterns than species identity, supporting trait-based approach to assess contaminant dynamics in future ocean acidification scenarios.

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Anthropogenic stressors and amphipod size influence herbivory on eelgrass in San Francisco Bay

Published 15 July 2026 Science Closed
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Seagrasses provide valuable ecosystem functions, yet they are declining globally due to anthropogenic stressors. Understanding how global climate stressors like ocean acidification interact with local environmental conditions (e.g., increased nutrient pollution) to affect ecosystem dynamics can be used to inform management of these habitats. In San Francisco Bay, it is unknown how stressor interactions will affect herbivory by Ampithoe valida, an invasive amphipod that exhibits novel feeding behavior by directly consuming the tissue of Zostera marina (eelgrass), which has been linked to negative impacts on local meadows. The goal of this study was to determine how anthropogenic stressors and amphipod size influence A. valida herbivory on eelgrass in San Francisco Bay to evaluate the ecological implications for eelgrass habitats. To further understand this relationship, feeding assays first examined food preferences of A. valida of three sizes on eelgrass of two ages and epiphytic algae. Secondly, a mesocosm experiment exposed A. valida of medium and large sizes to levels of ocean acidification expected with accelerating climate change and eelgrass to levels of nutrient pollution possible from point sources along shorelines, to test if these combined stressors affect A. valida direct herbivory of eelgrass. Additionally, A. valida were collected in the field during peak eelgrass growing season in summer and early fall to determine their size distributions and provide context to the experiments. Results found that A. valida largely prefer epiphytic algae over eelgrass regardless of their size. When offered only eelgrass, medium to large individuals consumed the tissue, whereas small individuals exhibited near-zero consumption. Although small A. valida were most abundant in field collections, medium-sized individuals were also present in moderate numbers, suggesting amphipods of this size may be the primary contributors to direct eelgrass consumption in San Francisco Bay, with high-consuming large individuals less common. Mesocosm results indicated that increased nutrients reduced eelgrass aboveground morphology (leaf size) and biomass, while tissue nutrient content increased, suggesting that although nutrients were taken up, they were not used for growth. Finally, feeding assays revealed that the effects of reduced pH and nutrient additions on A. valida eelgrass herbivory varied with grazer size and experimental context. In the no-choice assay, medium-sized individuals increased consumption under reduced pH relative to ambient pH, while large individuals consumed more of the highest nutrient-enriched eelgrass tissue. In contrast, the choice assay showed higher eelgrass consumption under ambient pH relative to reduced pH, and no effect of nutrient additions. This suggests that under reduced pH A. valida may shift their feeding behavior depending on environmental context, potentially increasing consumption through compensatory feeding on lower-quality tissue when food options are limited or reducing consumption when alternative refugia and higher-quality resources are available. This also indicates that ocean acidification may primarily alter eelgrass grazing behavior among mid sized A. valida, while nutrient enrichment may increase grazing pressure from larger individuals, potentially exacerbating eelgrass vulnerability in San Francisco Bay given reduced plant performance under high-nutrient conditions.

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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 Closed
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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.

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High-resolution temporal biogeochemical variations in a seagrass-coral cohabitate ecosystem: day-night, rain, and coral spawning

Published 14 May 2026 Science Closed
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Highlights

  • Seagrass-coral habitats act as CO2 sources driven by intense nighttime respiration
  • High-resolution data enable predictive modeling of DIC, DOC, and POC dynamics
  • Metabolic cues govern DIC, while temperature and alkalinity regulate POC and DOC
  • Episodic coral spawning and rainfall trigger rapid ocean acidification
  • Short-term disturbances dramatically shift organic and inorganic nutrient loads

Abstract

Seagrass meadows and coral reefs are global hotspots for productivity, yet they are often studied in isolation despite their intense biogeochemical connectivity. Significant gaps remain in understanding how coupled inorganic and organic processes within the water column drive blue carbon services in such mixed habitats, particularly during rapid environmental disturbances. Here, we investigated a unique, intertwined ecosystem in the Dongsha Atoll, where massive Porites corals are distributed on seagrass meadows, creating a natural laboratory for studying water column carbon biogeochemistry. During a 10-day sampling period, we collected continuous hydrological and discrete biogeochemical data at two- to four-hour intervals. Our results reveal that the dissolved inorganic carbon (DIC) covaried with dissolved oxygen and pH in strong diurnal patterns, which were governed by photosynthesis and respiration. As an outcome, variable but mostly high pCO2 values (141–2070 μatm) indicate the seagrass meadow was a source of CO2 to the atmosphere due to strong night-time respiration. Particulate organic carbon (POC) increased with temperature but showed no diurnal pattern. Dissolved organic carbon (DOC) showed a weak diurnal pattern and was linked to variations in POC and total alkalinity, highlighting the tight coupling between the organic production of the meadow and the inorganic chemistry of the calcification framework. Additionally, coral spawning led to a surge in organic content and changed inorganic nutrient levels. Rainfall events significantly acidified the ocean and enhanced submarine groundwater discharge to the seagrass-coral habitat. The distinctive contributions of this study are the extremely high temporal resolution of discrete samples, allowing the simultaneous tracking of multiple organic and inorganic pools during natural disturbances. The high-resolution data provide fundamental information for parametrizing models that explain DIC, POC, and DOC, which yield insights into organic carbon cycling in seagrass meadow-coral habitats.

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The role of seagrass in modifying dissolved oxygen and pH in coastal systems: a meta-analysis

Published 26 March 2026 Science Closed
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Highlights

  • Seagrass productivity drives diel pH–DO variation, enhancing local buffering capacity
  • Oxygen–pH coupling highlights seagrass role in mitigating acidification during photosynthesis
  • Studies should integrate temperature, salinity, and light to parse biological drivers
  • Expanded geographic scope, especially tropics and Global South, is urgently needed
  • Standardized pH scales and advanced sensors to improve comparability and monitoring

Abstract

Seagrass meadows, highly productive ecosystems, can influence local water chemistry by increasing dissolved oxygen in the water column and removing dissolved CO2 thus raising pH. This study provides the first quantitative synthesis of literature comparing pH and dissolved oxygen (DO) between systems with and without seagrasses. Through a systematic literature review and meta-analysis, we collated and analysed data from 63 studies reporting pH values and 70 studies reporting DO. Across studies, seagrass habitats were associated with slightly higher mean pH relative to non-seagrass habitats. Seagrass habitats showed the highest mean pH (8.11 ± 0.30) and the greatest diel variability (0.47 ± 0.65) of all habitats investigated with unvegetated areas exhibiting lower mean pH and reduced variability. The diel pH range was also significantly higher in seagrass habitats (p = 0.024). The pooled standardized mean difference was small (0.15), indicating a modest overall effect of seagrass presence on pH across studies. Although mean DO concentrations were slightly lower in seagrass habitats compared to other vegetated systems, they experienced fewer hypoxic events (12% of values < 2 mg/L) compared to other vegetated systems (55%). Generalized additive models identified DO as the strongest predictor of pH, with minor contributions from temperature and salinity. Overall, seagrass habitats are associated with increasing average pH and reducing hypoxia across multiple sites and regions. However, the magnitude and direction of effects vary widely among studies (I2 = 97%). These findings indicate that seagrass influences on water chemistry are context-dependent and likely driven by interactions among biological processes and local environmental conditions. Key knowledge gaps were identified; including the need for a greater focus on H+ concentration and the need for more research on seagrass ecosystems in underrepresented geographical regions.

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Novel in situ CO2 enrichment system reveals seagrass meadows are a refugium against coastal acidification for North Atlantic bivalves

Published 18 March 2026 Science Closed
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While the accumulation of anthropogenic CO2 in the atmosphere is causing a decline in global ocean pH, many eutrophic estuaries are already experiencing acidification due to accelerated respiration driving the consumption of dissolved oxygen (DO) and production of CO2, decreasing available carbonate ions (CO32-) and threatening marine calcifiers. Here, a novel in situCO2 enrichment system was constructed to examine the effects of coastal acidification on the growth and survival of two species of North Atlantic bivalves (Argopecten irradians and Crassostrea virginica) in two distinct estuarine habitats: a seagrass meadow and an unvegetated sandy bottom in an open water estuary. The in-situ system captured natural diel dynamics as ambient chambers displayed chemistry nearly identical to the surrounding water, while CO2-enriched, acidified chambers maintained a consistent ~Δ 0.3–0.5 pH offset. At the unvegetated sandy bottom site, A. irradians and C. virginica displayed significant reductions in growth and survival in the acidified chambers (pHT = 7.3–7.5; saturation state of aragonite, ΩAr = 0.6–0.9) relative to ambient conditions (pHT = 7.6–7.9; ΩAr = 1.6–2). At the seagrass site, while growth of A. irradians and C. virginica in the acidified treatments (pHT = 7.3–7.7; ΩAr = 0.7) receiving the same delivery of CO2 was, again, significantly slowed compared to the control (pHT = 7.5–8.1; ΩAr = 2 – 2.8), the growth reduction, mortality rates, and levels of acidification were attenuated compared to the sandy bottom experiment, evidencing the ability of seagrass to buffer seawater and serve as a potential acidification refuge for bivalves. Collectively, the novel experimental CO2 enrichment system constructed for this project demonstrates that coastal acidification can have deleterious effects on marine bivalve populations, and that future conditions as well as the habitat refuge offered by seagrasses must be considered when developing management and restoration plans for temperate estuaries. 

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Enhanced carbon burial in seagrass meadows under ocean acidification revealed by carbon dioxide vents

Published 16 March 2026 Science Closed
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Seagrass meadows are natural carbon sinks, yet the effect of ocean acidification on their carbon burial capacity remains poorly understood. Here we investigated natural carbon dioxide vents in Ischia, Italy to assess how seawater pH influences carbon burial in an area dominated by the seagrass Posidonia oceanica. Organic carbon burial rates (mean ± standard error) between 1954 – 2021 were low under ambient conditions (1.5 ± 0.5 g m-2 yr-1) but increased sharply under acidified conditions (7 ± 1 g m-2 yr-1), reaching sevenfold higher values under extreme acidification (10 ± 3 g m-2 yr-1). Stable isotopes suggest that these patterns reflect changes in the relative contribution of seagrass, macroalgae, and epiphytes to buried carbon. These findings reveal that ocean acidification can substantially alter coastal carbon cycling, potentially through shifts in community composition, with important implications for understanding past and future feedbacks between seagrass ecosystems and the marine carbon cycle.

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Spatial dynamics of aragonite saturation state and blue carbon stocks in seagrass meadows of the Palk Bay, Southeast Coast of India

Published 19 January 2026 Science Closed
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Seagrass meadows are increasingly recognized for their role in mitigating climate change through blue carbon sequestration and their influence on local carbonate chemistry. This study investigates the spatial variability of aragonite saturation state (Ωarag) and assesses the blue carbon storage potential of seagrass meadows along the Palk Bay, Southeast Coast of India. Subsurface water samples were collected across multiple seagrass-dominated stations between May and June 2024. Key seawater carbonate system parameters, including pH, temperature, total alkalinity (TA), and salinity, were measured to calculate Ωarag using CO2SYS software. Sediment cores were analyzed for organic carbon content and bulk density to estimate carbon stock. Results revealed significant spatial variation in Ωarag, influenced by seagrass density, species composition (Cymodocea serrulata and C. rotundata), and hydrodynamic conditions. Stations with dense C. serrulata beds showed elevated Ωarag values, suggesting local amelioration of acidification stress. The mean carbon stock was estimated at 1.97 Mg C/ha−1, with higher values in more mature (> 60% cover) and dense seagrass patches. These findings highlight the dual ecological function of seagrass meadows in enhancing local carbonate saturation and functioning as effective carbon storage systems, underlining their significance in coastal ecosystem-based climate mitigation strategies.

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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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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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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.

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Can ocean acidification alleviate carbon deficiency in eelgrass Zostera marina clonal ramets under conditions of nutrients, sulfate and ocean acidification?

Published 16 October 2025 Science Closed
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Highlights

  • The ratio of Chl a/b is reduced by the interaction between CO2 and NO3-N.
  • The interaction between CO2 and NO3-N reduces the soluble sugar contents in leaves.
  • CO2 promotes the content of soluble protein in leaves while reduces that in roots.
  • CO2 reduces both the SOD activities of the rhizomes and the eelgrass mortality rate.
  • Eelgrass has complex carbon supply and conversion mechanisms to ensure its survival.

Abstract

Carbon deficiency in the eelgrass caused by nutrient eutrophication and high concentrations of sulfate causes eelgrass mortality; however, ocean acidification provides sufficient carbon. Thus, it is inferred that ocean acidification might reduce the carbon deficiency. To verify this hypothesis, eelgrass clonal ramets were exposed to 72—h combined conditions of ocean acidification (CO2), nitrate (NO3-N), ammonia (NH4-N), phosphate (PO4-P) and sulfate (SO4-S). The pigment contents were affected by nutrients; however, the Chl a/b ratio was inhibited by the interaction between CO2 and NO3-N and was promoted by interaction between NO3-N and NH4-N. The soluble protein contents in leaves were increased by CO2; however, the soluble protein contents in roots were reduced by CO2. The soluble sugar contents in the leaves had negatively correlation with the interaction between NO3-N and CO2. Moreover, the SOD activities of the rhizomes were inhibited by CO2. All these findings suggest that ocean acidification does not seem to effectively alleviate the deficiency of soluble carbon in eelgrass under eutrophication and high concentrations of sulfate; however, the eelgrass mortality rate was inhibited by CO2 and the interaction between PO4-P and SO4-S. Thus, eelgrass has extremely complex carbon supply and conversion mechanisms to ensure its survival under composite conditions or eelgrass has another mechanism of death in eutrophication.

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In-situ measurements reveal alkalinity release from cold-temperate seagrass meadows

Published 25 September 2025 Science Closed
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Highlights

  • Cold-temperate seagrass meadows are net sources of alkalinity
  • Alkalinity generation exceeds soil organic carbon accumulation by fourfold
  • Seagrasses buffer ocean acidification locally during the day
  • Alkalinity generation in seagrasses is lower than in mangroves and saltmarshes

Abstract

Understanding the carbon sequestration potential of blue carbon ecosystems is important to inform climate policies and to guide restoration and protection efforts. Alkalinity generation is an often overlooked carbon sequestration mechanism, especially in seagrass meadows. Here, we quantified total alkalinity (TA) and dissolved inorganic carbon (DIC) fluxes in two cold-temperate Zostera marina seagrass meadows in Sweden using 24-hour in-situ chamber incubations at the end of the high-productivity season. The seagrass meadows were similar net sources of TA (16 ± 45 mmol m-2 d-1 in Smalsund, 17 ± 16 mmol m-2 d-1 in Bökevik), whereas DIC fluxes were highly variable (34 ± 59 mmol m-2 d-1 in Smalsund, -43 ± 35 mmol m-2 d-1 in Bökevik). Fluxes followed a diurnal cycle consistent with photosynthesis-respiration cycles. As a result, seagrass meadows ameliorated ocean acidification locally during the day, but not during the night. The large CO2 uptake provided higher buffering levels compared to mangroves and saltmarshes. The TA fluxes were comparable to those reported for Mediterranean and tropical seagrass meadows, but 16-times lower than in mangrove forests and 5-times lower than in saltmarshes. Alkalinity generation in these cold-temperate seagrasses exceeded soil organic carbon stocks accumulation by fourfold, potentially contributing to their carbon sequestration potential and warranting inclusion in seagrass meadow carbon budgets.

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Short-term and long-term ocean acidification effects on seagrass performance: evidence from shallow CO2 vents

Published 8 August 2025 Science Closed
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Highlights

  • Cymodocea nodosa performance under in-situ ocean acidification has been evaluated.
  • Morphology of long-term acidified plants does not differ from that of control plants.
  • Higher performance was found in short-term acidified plants.
  • The response of apical shoots was particularly enhanced.

Abstract

Future ocean acidification conditions have the potential to affect seagrasses, although predicting the outcomes remains challenging due to the complexity of ecological interactions. This study aimed at evaluating the effects of ocean acidification on the morphology and physiology of the seagrass Cymodocea nodosa. A field manipulative experiment was conducted (Aeolian Islands, Italy) at a natural low pH site, where shallow submarine CO2 seeps occur, and other control pH sites. The effects of long-term acidification (by comparing untouched plants from control pH to the low pH sites) and a short-term acidification (by comparing transplanted plants from control pH sites to low pH site with translocated control pH plants) were evaluated. The evidence provided suggest that the seagrass may be considered a low pH tolerant seagrass, as the long-term acidification only determined an increase in photopigment concentrations, while the short-term acidification led to the increase in morphology, biomass and pigments, counteracting the negative effects due to cutting manipulation. These enhancements were more pronounced in apical shoots, suggesting a high clonal specialization. Our study provides evidence of morphological and physiological acclimation of C. nodosa in response to acidified conditions, suggesting that future ocean acidification scenarios could also favour this autochthonous seagrass species.

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Mangrove-driven acidification and shell dissolution on intertidal oyster reefs in a subtropical estuary

Published 4 August 2025 Science Closed
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Tropicalization, resulting from warmer minimum temperatures, has allowed mangroves to expand poleward and increase in abundance in historical ranges. Since 1984, mangrove abundance on intertidal oyster reefs in Mosquito Lagoon, Florida, USA, has increased by 198% due to tropicalization. Oysters provide abundant ecosystem services including engineering reef habitat and water filtration, but shells are prone to dissolution in acidic conditions. Mangroves are associated with soil acidification and therefore may alter the pH of oyster reef sediment. The goal of this research was to determine if mangroves acidify oyster reef porewater (i.e. water within the sediment) and determine if mangrove-correlated acidification caused oyster shell dissolution as indicated by shell mass loss. Porewater, up to 10 cm depth, was collected monthly for 2 yr, and the pH was compared between 4 habitats: mudflats, oyster-dominated reefs (oyster reefs), transitioning reefs (oyster reefs with mangroves), and mangrove-dominated sites (mangrove islands). Porewater was more acidic with mangroves present. Transitioning reefs had a mean pH of 7.13 compared to oyster-dominated reefs (mean pH: 7.52). To measure shell dissolution, bags containing 10 pre-weighed oyster shells were deployed and re-weighed after 6, 12, and 24 mo. After 24 mo, mangrove-dominated sites lost more shell mass (8% loss) compared to oyster-dominated sites (1% loss). Transitioning reefs had intermediate shell mass loss. Combined, these data suggest that mangrove expansion on intertidal oyster reefs can negatively impact oysters. With oyster reef habitats in global decline, understanding new sources of degradation, including mangrove-driven acidification, is crucial to supporting conservation and restoration efforts.

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Impact of ocean acidification on fish health and marine ecosystem dynamics

Published 11 July 2025 Science Closed
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Ocean acidification (OA) causes an increase in carbon dioxide (CO2) and a reduction in the pH of ocean waters. This chapter reviews the current literature to investigate the adverse effects of OA on fish health and marine ecosystem dynamics. OA poses serious threats to marine biodiversity and ecosystem dynamics. Fish experience severe physiological problems such as impaired growth, development, tissue damage, Impaired behavioral changes, sensory and brain functions, and disruption in predator-prey interactions due to acidification with a 74% decline in survival rates of egg and larval stages. Besides affecting fish, OA also affects marine ecosystem dynamics: reducing calcification rates in calcifying species, increasing seagrass production, causing effects on habitat-forming species, and disrupting the food web. Vulnerable species, such as coral reef fish, show high sensitivity, risking the stability of their habitats. The United Nations recognized the OA as a threat to marine biodiversity through the Convention on Biodiversity. The future research needs to focus on understanding fish and marine animals’ adaptive mechanisms to OA, its interaction with other stressors, and global collaboration to address the underlying causes of OA.

Continue reading ‘Impact of ocean acidification on fish health and marine ecosystem dynamics’

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