Posts Tagged 'phanerogams'

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.

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Handling the heat: ocean acidification mitigates the effects of marine heatwaves on Posidonia oceanica seedlings 

Published 8 July 2025 Science Closed
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Ocean acidification (OA) and marine heatwaves (MHWs) are key drivers of marine ecosystem changes that can interact and influence marine organisms. Seagrasses, including the long-lived Posidonia oceanica endemic to the Mediterranean Sea, are widely distributed along coastal habitats, forming highly valuable underwater meadows. The germination and survival of the early life stages of P. oceanica are strongly affected by environmental changes. To assess the impact of warming and acidification on its future, we conducted a multifactorial experiment where P. oceanica seedlings were grown under OA conditions for six months and then exposed to a seawater warming event. Seedlings’ performance was investigated by analyzing photo-physiology, antioxidant capacity, energetic metabolism and transcriptomic profiles. The Weighted Gene Correlation Network Analysis (WGCNA) was used to integrate phenotypic plant traits with transcriptomic results to identify central genes involved in plant responses to OA and temperature exposure. Results demonstrated that prolonged OA exposure enhances P. oceanica seedling resilience to MHW. Specifically, seedlings regulated their antioxidant systems and transcriptomic machinery to better cope with thermal stress. Under current CO2 concentrations, elevated temperatures induced stress in P. oceanica seedlings, impacting photosynthesis and respiration. However, OA could mitigate the impact of warming in the future, enhancing P. oceanica‘s resilience to global stressors.

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Seaweed responses to ocean acidification: global impacts on growth, biochemical composition, and CO2 mitigation potential

Published 3 July 2025 Science Closed
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Ocean acidification, driven by the absorption of elevated atmospheric CO2 levels, significantly affecting the growth and nutritional composition of marine biota, including seaweeds. The increasing expansion of the cultivation of seaweed is a promising method for removing carbon dioxide through both government and private sectors. There are notable comprehensive assessments that evaluated the effectiveness of seaweed farming to achieve significant climate change mitigation and it ended with positive outcome. Hence the present article reviews about the global impacts of ocean acidification on seaweed communities including growth dynamics, nutritional trends, and their potential for CO2 mitigation. The ecological consequences of ocean acidification and providing an overview of its status. Amplified CO2 levels affect seaweed physiology and ecosystem dynamics that have an influence on biodiversity, carbon cycling, and nutrient flows. The review highlights the trends in seaweed growth under elevated CO2 conditions, through identification of both opportunities and challenges for maintenance of productivity and nutritional quality. Seaweeds exhibit potential for CO2 sequestration, that whorls to offset carbon emissions through aquaculture practices. Furthermore, integrated seaweed farming practices can enhance environmental benefits, such as biodiversity conservation, nutrient remediation, and improved carbon storage. Finally, yet importantly this article emphasizes the necessity for targeted research that aimed at optimization of seaweed cultivation techniques, decipher species-specific responses to ocean acidification, and leveraging biotechnological advancements for maximation in mitigation of CO2. The findings underscore the role of seaweed aquaculture as a sustainable strategy to combat climate change and protect marine ecosystems.

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Biophysical model of eelgrass and water quality in Coos Bay, OR shows greater mitigation potential for ocean acidification than hypoxia

Published 30 June 2025 Science Closed
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Seagrass beds provide important ecosystem services and are valued, in part, for their potential to mediate stressors such as ocean acidification and hypoxia (OAH) for sensitive species. However, the susceptibility of seagrasses to anthropogenic impacts and recent declines motivate the need to better understand the drivers of seagrass and the water quality consequences that occur with variation in seagrass abundance. To meet this need, we leveraged existing monitoring data (water quality and seagrass), hydrodynamic circulation model, and biogeochemical model framework with seagrass submodel, to produce a biophysical model of Coos Bay estuary, Oregon, U.S. The model includes biogeochemical processes involving water quality, plankton, seagrass, and sediment-water interactions. Ecosystem models like this are useful for evaluating complex estuarine systems because they allow us to extend our understanding of system dynamics beyond existing observations and perform experiments to identify the processes driving observed patterns. We used the biophysical model of Coos Bay to evaluate the dynamics of water quality and native eelgrass (Zostera marina) under three eelgrass abundance scenarios (zero eelgrass, current extent, and maximum observed extent) to elucidate the relationship between eelgrass and OAH. Including eelgrass in the Coos Bay model produced results that more closely resembled water quality observations – dissolved oxygen (DO) and pH were more dynamic in simulations with eelgrass, often having both higher highs and lower lows. While there were some areas of the estuary where DO improved with the addition of eelgrass to the model there was overall a small net increase in harmful DO conditions (based on a salmon physiological threshold). In contrast, ocean acidification conditions, pH and calcium carbonate saturation state for aragonite (Ω), were improved (based on oyster requirements) with the addition of eelgrass – although the magnitude of improvement differed seasonally and spatially. Our new model represents a useful tool – one which accounts for and controls the relevant physical and biogeochemical processes – to evaluate conditions that confer resilience or enhance vulnerability to OAH in an important Pacific Northwest coastal estuary and results can inform the OAH-related dynamics occurring in other eastern boundary current estuaries.

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Microbe-host associations as drivers of benthic carbon and nitrogen cycling in a changing Mediterranean Sea

Published 14 April 2025 Science Closed
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Seagrasses, such as the endemic Mediterranean species Posidonia oceanica, are critical components of coastal marine ecosystems, providing essential ecosystem services, including carbon sequestration, nutrient cycling, and habitat formation. P. oceanica forms extensive meadows that serve as biodiversity hotspots and play a crucial role in mitigating climate change through long-term carbon storage. Despite their ecological significance, the interactions between P. oceanica and associated organisms, as well as their combined contributions to biogeochemical cycling, remain poorly understood, particularly under changing environmental conditions. This thesis explores the carbon and nitrogen cycling processes within the P. oceanica holobiont, focusing on the epiphytic and microbial communities, microbial driven metabolic processes, and the interaction between P. oceanica and larger associated invertebrates, such as the sponge Chondrilla nucula. Through field and laboratory experiments, this work demonstrates the significant role of epiphytic algae in the primary production of the seagrass holobiont, contributing a substantial portion of net primary production. Nitrogen cycling processes such as N₂ fixation, nitrification, and denitrification in the seagrass phyllosphere were quantified, revealing their importance in meeting the N demands of the seagrass holobiont, especially under natural ocean acidification conditions. Experiments near marine CO₂ vents indicated that ocean acidification accelerates net primary production and nitrogen cycling, while the structure of the microbial community associated with P. oceanica leaves remains largely stable. The facultative mutualism between P. oceanica and the sponge C. nucula further highlights the complexity of the seagrass holobiont. P. oceanica releases dissolved organic carbon, which meets a portion of the sponge’s respiratory carbon demand. Conversely, C. nucula releases dissolved inorganic nitrogen, including ammonium and nitrate generated by microbial nitrification, which supports seagrass growth. Stable isotope analysis suggests that the association facilitates nutrient exchange, with P. oceanica preferentially absorbing sponge-derived ammonium, while epiphytes may benefit from sponge-produced nitrate. This dynamic reduces seasonal fluctuations in productivity, stabilizing the seagrass ecosystem during periods of senescence. Sponge-associated nitrification contributes to the nitrogen budget of the seagrass holobiont, potentially reducing nutrient limitations in oligotrophic Mediterranean waters. The microbiome of C. nucula plays a key role in these processes, harboring nitrifiers that mediate the production of nitrate. High-throughput sequencing revealed taxonomic diversity among microbes associated with both the sponge and seagrass, including microorganisms involved in carbon and nitrogen cycling processes. These microbial communities not only mediate nutrient exchange within the seagrass-sponge association but also contribute to the overall resilience and productivity of the ecosystem. This thesis highlights the intricate interactions within the P. oceanica holobiont and its nested ecosystem with C. nucula. These findings underscore the importance of microbial and epiphytic communities in maintaining the resilience and productivity of seagrass meadows, particularly in nutrient-poor environments like the Mediterranean Sea. This research enhances our understanding of the biogeochemical processes that support seagrass ecosystem stability and provides valuable insights to guide conservation efforts in the face of climate change and anthropogenic pressures.

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Thalassia hemprichii may benefit from ocean acidification and slightly increased salinity in the future

Published 13 February 2025 Science Closed
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Highlights

  • Thalassia hemprichii highly adapted to acidified environments.
  • The effect of elevated salinity on the physiology and growth of Thalassia hemprichii is not linearly.
  • Ocean acidification could further enhance the resilience of Thalassia hemprichii to high salinity.
  • Both acidification and slight salinity increased the photosynthetic activity of Thalassia hemprichii.

Abstract

Since the industrial revolution, the direct impacts of elevated CO2 concentrations, such as ocean acidification, and indirect impacts, such as extreme drought events, have synergistically influenced coastal ecosystems, including seagrass meadow. Consequently, investigating the individual and combined effects of ocean acidification and extreme drought-induced increased salinity on seagrasses is crucial for enhancing the management and monitoring of these ecosystems. This study used a two-factor crossover indoor simulation experiment to thoroughly examine the effects of seawater acidification at pH 7.7 and elevated salinity levels at 43‰ and 51‰ on the physiological responses and growth status of the dominant tropical seagrass species Thalassia hemprichii. The results indicated that seawater acidification at pH 7.7 significantly enhanced the growth rate and photosynthetic activity of T. hemprichii across all salinity levels. A salinity of 43‰ activated certain antioxidant enzymes without inducing severe osmotic stress in T. hemprichii and positively influenced leaf photosynthetic activity, with a 15.6% increase in growth rate compared to the CK group. The extreme salinity of 51‰ imposed osmotic stress, leading to increase in reactive oxygen species and decreased photosynthetic activity and a 52% decrease in growth rate compared to seagrasses in the CK group. Under future scenarios of ocean acidification and frequent extreme droughts, T. hemprichii inhabiting enclosed marine environments may exhibit greater adaptability and secure an ecologically competitive edge. Our findings underscore the importance of conserving declining meadows, forecasting the ecological trajectory of these ecosystems, and managing salinity in lagoons for the well-being of seagrass ecosystems.

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Global environmental change mediated response of wetland plants: evidence from past decades

Published 11 February 2025 Science Closed
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Highlights

  • Wetland plant research on climate change responses showed an upward trend.
  • Plant growth affected negatively by increase in CO2, temperature and sea level.
  • Extreme weather events harmed wetland plant landscapes.
  • Collaborative research is needed for sustainability of wetland plants

Abstract

Wetland ecosystems are critically affected by global environmental changes, yet understanding the impact of these changes on wetland plants remains a challenge. This review article employs a comprehensive approach, including bibliographic analysis, utilization of various climate models for historical data retrieval, and extensive literature survey, to investigate the response of wetland plants to environmental shifts over the past decades. The analysis conducted in this study uncovers a multitude of climatic parameters that exhibit an influence on the dynamics of wetland vegetation. Results indicated a significant positive trend in atmospheric CO2 concentration, leading to increased water use efficiency in some plant species, particularly C3 plants. However, C4 plants did not show the same positive response. Nitrous oxide growth rate showed a weaker, less consistent trend than CO2, highlighting the need for further investigation into the complex factors influencing Nitrous oxide emissions from wetlands. Methane growth rate and global mean sea level demonstrated a strong positive linear trend. Ocean pH exhibited a statistically significant downward trend (acidification), while sea surface temperature showed a moderate but statistically significant upward trend. Glacier mass balance revealed a significant negative trend. Although some plants may benefit from increased CO2 initially, but the combined effects of rising sea levels, ocean acidification, and temperature changes pose substantial threats to the overall health and diversity of wetland plant life.

Continue reading ‘Global environmental change mediated response of wetland plants: evidence from past decades’

Seagrass influence on mitigating ocean acidification and warming impacts on tropical calcifying macroalgae

Published 28 January 2025 Science Closed
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Highlights

  • OA and warming reduce calcium carbonate for marine calcifiers.
  • Seagrass can capture excess carbon, possibly mitigating OA effects.
  • 12-week study tested algae with/without seagrass under increasing stress.
  • M. rosea was affected by OA and warming; H. opuntia by temperature alone.
  • Mesophyllum sp. was resilient, and seagrass did not reduce OA impacts.
  • Light, flow, combining OA and warming, likely to impact coralline algae

Abstract

Ocean acidification (OA) and warming pose significant threats to marine ecosystems, particularly by reducing calcium carbonate availability for marine calcifiers. Given that seagrasses can capture and store excess carbon, this study aimed to investigate whether seagrasses can mitigate the impacts of OA and elevated temperatures on three calcifying macroalgae: Mastophora rosea, Halimeda opuntia, and Mesophyllum sp. A 12-week mesocosm experiment was conducted, where the algae were cultured with and without seagrass under gradually increasing stress conditions: ambient conditions, OA alone for four weeks, OA combined with elevated (but non-stressful) temperatures (28°C) for four weeks, and OA plus a stress-inducing temperature (31°C) for two weeks. Results indicated that OA and warming negatively affected M. rosea, while H. opuntia was more strongly impacted by temperature alone. Mesophyllum sp. exhibited resilience to both OA and elevated temperatures. Contrary to expectations, the presence of seagrass did not mitigate the negative effects of OA and warming on these calcifying macroalgae species.

Continue reading ‘Seagrass influence on mitigating ocean acidification and warming impacts on tropical calcifying macroalgae’

Ocean acidification and global warming may favor blue carbon service in a Cymodocea nodosa community by modifying carbon metabolism and dissolved organic carbon fluxes

Published 9 January 2025 Science Closed
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Highlights

  • 45-days mesocosm experiment with whole-benthic community to mimic nature conditions
  • Global warming (GW) and ocean acidification (OA) modify C dynamics on seagrasses.
  • OA enhances GPP and NCP and synergistic effects when combined with GW.
  • DOC production decreased with OA and GW separately, but increased when combined.
  • Climate change potentially increases the blue carbon service of C. nodosa populations.

Abstract

Ocean acidification (OA) and global warming (GW) drive a variety of responses in seagrasses that may modify their carbon metabolism, including the dissolved organic carbon (DOC) fluxes and the organic carbon stocks in upper sediments. In a 45-day full-factorial mesocosm experiment simulating forecasted CO2 and temperature increase in a Cymodocea nodosa community, we found that net community production (NCP) was higher under OA conditions, particularly when combined with warming (i.e., synergistic effect). Moreover, under OA conditions, an increase in aboveground biomass and photosynthetic shoot area was recorded. Interestingly, DOC fluxes were reduced when exposed to OA; however, an increase occurred when both factors acted together (i.e., antagonistic effect), which was attributable to increased DOC release by plants. Our results suggest that C. nodosa populations in temperate latitude may favor blue carbon service in future scenarios of OA and GW by increasing the NCP, the DOC export with lower labile:recalcitrant ratio, and accumulating more organic carbon in upper sediments. These findings offer additional arguments for the urgent need to protect and conserve this valuable ecosystem.

Continue reading ‘Ocean acidification and global warming may favor blue carbon service in a Cymodocea nodosa community by modifying carbon metabolism and dissolved organic carbon fluxes’

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