Posts Tagged 'phanerogams'

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Extreme abiotics drive sediment biocomplexity along pH gradients in a shallow submarine volcanic vent

Published 3 January 2025 Science Closed
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Highlights

  • Shallow CO2 vents generate pH gradients that influence sediment biogeochemistry
  • Sedimentary organic matter (SOM) and prokaryotic community were analysed along a pH gradient
  • Environmental gradients drive distribution and abundance of benthic prokaryotic communities and origin of SOM
  • Vent-derived sources contributed largely to SOM up to 350 m from the vent
  • CO2-driven benthic community shifts affect spatial dynamics of SOM origin and composition with expected rebounds on biota

Abstract

Volcanic emissions in shallow vents influence the biogeochemistry of the sedimentary compartment, creating marked abiotic gradients. We assessed the spatial dynamics of the sediment compartment, as for the composition and origin of organic matter and associated prokaryotic community, in a volcanic shallow CO2 vent (Vulcano Island, Italy). Based on elemental (carbon, nitrogen content and their ratio) and isotopic composition (δ13C, δ15N and δ34S), the contribution of vent-derived organic matter (microbial mats) to sedimentary organic matter was high close to the vent, while the marine-derived end-members (seagrasses) contributed highly at increasing distance. Chemoautotrophic Campylobacterota and hyperthermophilic Achaea prevailed close to the vent, whilst phototrophic and chemoheterotrophic members dominated at increasing distance. Abiotic gradients generated by the volcanic CO2 vent drive relevant changes in the composition, origin and nutritional quality of sedimentary organic matter, and influence the structure and complexity of associated prokaryotic communities, with expected relevant impact on the entire food-web.

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Gene expression changes in the seagrass Cymodocea nodosa individuals in response to aquatic acidification

Published 2 January 2025 Science Closed
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Human activities have caused a rise in atmospheric carbon dioxide (CO2) levels, leading to greater absorption of CO2 by oceans and causing ocean acidification (OA). This phenomenon, marked by a reduction in pH, represents substantial risks to marine ecosystems, including seagrass meadows. Seagrasses are vital elements of coastal ecosystems, performing important functions in carbon storage, stabilizing shorelines, and preserving biodiversity; however, reactions to OA are not well understood, especially in molecular terms. This research study examined alterations in gene expression within seagrass meadows, namely Cymodocea nodosa, in reaction to simulated OA conditions. A climate chamber system was used to adjust CO2 levels to simulate future projections of OA, specifically following the RCP 8.5 scenario. Gene expression dynamics were assessed by collecting samples at different time intervals across a 36-h period. Research has demonstrated that genes related to photosynthesis are suppressed quickly after being exposed to increased amounts of CO2. Gene expression levels were found to change often over time, which is crucial for adaptation and acclimatization. However, antioxidant genes have varied responses to OA, with CAT and SOD being downregulated in distinct ways. Our findings offer valuable insights into the molecular mechanisms of seagrass responses to OA. They highlight the significance of examining short-term responses when evaluating the susceptibility of coastal ecosystems to climate change.

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Local effects of Sargassum beds on the seawater carbonate system and plankton community

Published 30 December 2024 Science Closed
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Highlights

  • The ecological effect of the sargassum beds depends on seaweed biomass.
  • The biomass of the sargassum beds in Weizhou Island reached its peak in spring.
  • Sargassum beds significantly influenced the carbonate system and DOC pool in spring.
  • Sargassum beds is more likely to alter phytoplankton communities than zooplankton.

Abstract

Sargassum beds are recognized as important habitats for fostering species diversity and capturing blue carbon, exerting significant influence on seawater chemistry and planktonic communities. However, there is still much to uncover about the interactions between these biogenic habitats and seawater chemistry, as well as their impact on plankton communities in the water column. To address this gap, we conducted a study on the functions of natural Sargassum beds in various seasons around the northern part of Weizhou Island in the South China Sea. Our research involved quantifying carbonate chemistry, carbon stock potential, and seawater plankton communities in two distinct areas: the core area in the interior regions of the seaweed beds and the non-core areas at its periphery or external. Our findings revealed an estimated 3.7 km2 of benthic Sargassum, with an overall biomass of 21.2 Gg km−2, reaching its peak productivity in spring, equivalent to 1.14 Pg C km−2. Notably, during spring, the seaweed beds significantly influenced the exchange of CO2 at the air-sea interface, leading to reduced pCO2 (41 μatm) in the core area compared to the non-core area (p < 0.05), thus enhancing the local carbon sequestration capacity. Additionally, we observed significant regional differences in the concentration of dissolved organic carbon (DOC) only during the spring season, indicating the capacity of Sargassum to alter the DOC pool around its habitat. We anticipate that seaweed deposition will become a more frequent occurrence towards the end of the growth period, with increasing fragments facilitating a transition towards phytoplankton-dominated marine ecosystems. Furthermore, the fixation of extra CO2 by seaweed may lead to a pH increase, providing a refuge for copepods from ocean acidification. In summary, our observations suggest that the Sargassum beds plays a substantial role in nearshore carbon cycling and ecological impact, surpassing previous documentation.

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Coexisting mangrove-coral habitats: trends in seawater chemistry and coral diversity

Published 20 December 2024 Science Closed
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Coral reefs face unprecedented threats from climate change, with rising temperatures, ocean acidification, and other stressors endangering their survival. Coexisting mangrove-coral (CMC) habitats provide a natural laboratory to study coral resilience under extreme conditions. However, these habitats are rare and understudied, leaving gaps in understanding their biogeochemical and ecological dynamics. This thesis examines how mangrove proximity influences seawater chemistry, coral diversity, and morphology. A global review identified differences in seawater chemistry between habitat types and regions, driven by biogeochemical processes and freshwater inputs. Edge habitats, particularly in the Great Barrier Reef (GBR), were identified as understudied. An empirical study at Pioneer Bay, GBR, revealed significant spatial and temporal variations in seawater chemistry along a gradient from mangroves to open reefs. Corals near mangroves experienced greater fluctuations in pH, temperature, and oxygen, stabilizing with distance. Tidal flushing mitigated extremes, fostering coral resilience. Mangrove proximity significantly influenced benthic communities, coral morphology, and biodiversity. Extreme conditions near mangroves favored resilient corals like *Porites*, while intermediate sites supported the highest diversity due to nutrient influx and moderate disturbances. Farther sites were dominated by complex coral communities. Edge CMC habitats play a vital role in supporting coral adaptation to climate change. However, intensifying stressors threaten even resilient systems, underscoring the need for long-term monitoring and adaptive management to protect these critical biodiversity hotspots.

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The influence of macrophytes on diurnal pH variability in subtropical estuaries: a mesocosm study

Published 4 December 2024 Science Closed
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Highlights

  • Macrophytes influence estuary water column pH levels.
  • Floating macrophytes decrease pH and submerged macrophytes increase pH.
  • Diurnal pH variability is more pronounced in submerged macroalgae.
  • Floating macrophytes exhibit lower diurnal variability.

Abstract

Coastal ecosystems are increasingly threatened by anthropogenic impacts, particularly from land-based activities that drive eutrophication. This research investigated eutrophication and the unique challenges facing southern hemisphere coastal ecosystems. We used a mesocosm study to measure the influence of a macroalga (Rhizoclonium riparium) and a floating macrophyte (Pistia stratiotes), on diurnal pH variability. Diurnal pH variability was more pronounced in the presence of macroalgae due to the direct release of metabolic byproducts into the water column during photosynthesis and respiration. In contrast, floating macrophyte treatments had lower diurnal pH variability, as metabolic byproducts are released into the atmosphere through floating foliage. Floating macrophytes influenced overall water column pH levels, resulting in an acidification effect, becoming more pronounced as macrophyte biomass increased. The study highlighted the importance of nutrient management and its association with macrophytes, to preserve the delicate balance of estuaries, and ensure the sustainable functioning of these critical ecosystems. Further in situ research is recommended to validate and expand on the mesocosm findings.

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The role of benthic TA and DIC fluxes on carbon sequestration in seagrass meadows of Dongsha Island

Published 27 November 2024 Science Closed
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Coastal blue carbon ecosystems sequester carbon, storing it as plant biomass and particulate organic matter in sediments. Recent studies emphasize the importance of incorporating dissolved inorganic and organic forms into carbon assessments. As sediment-stored organic matter decomposes, it releases dissolved inorganic carbon (DIC) and total alkalinity (TA), both of which are critical for regulating the partial pressure of CO2 (pCO2) and thus carbon sequestration. This study investigated the role of benthic DIC and TA fluxes in carbon sequestration within seagrass meadows in Dongsha Island’s inner lagoon (IL) during the winter and summer seasons. Chamber incubation experiments revealed elevated benthic DIC and TA fluxes compared to global averages (107 ± 75.9 to 119 ± 144 vs. 1.3 ± 1.06 mmol m−2 d−1 for DIC, and 69.7 ± 40.7 to 75.8 ± 81.5 vs. 0.52 ± 0.43 mmol m−2 d−1 for TA). Despite DIC fluxes being approximately 1.5 times higher than TA fluxes, water pCO2 levels remained low (149 ± 26 to 156 ± 18 µatm). Mass balance calculations further indicated that benthic DIC was predominantly reabsorbed into plant biomass through photosynthesis (−135 to −128 mmol m−2 d−1). Conversely, TA accumulated in the water and was largely exported (−60.3 to −53.7 mmol m−2 d−1), demonstrating natural ocean alkalinity enhancement (OAE). This study highlights the crucial role of IL seagrass meadows in coastal carbon sequestration through net autotrophy and carbonate dissolution. Future research should explore the global implications of these processes and assess the potential of natural OAE in other coastal blue carbon ecosystems.

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The unique biogeochemical role of carbonate-associated organic matter in a subtropical seagrass meadow

Published 18 November 2024 Science Closed
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The particulate organic matter buried in carbonate-rich seagrass ecosystems is an important blue carbon reservoir. While carbonate sediments are affected by alkalinity produced or consumed in seagrass-mediated biogeochemical processes, little is known about the corresponding impact on organic matter. A portion of particulate organic matter is carbonate-associated organic matter. Here, we explore its biogeochemistry in a carbonate seagrass meadow in central Florida Bay, USA. We couple inorganic stable isotope analyses (δ34S, δ18O) with a molecular characterization of dissolved and carbonate associated organic matter (21 tesla Fourier-transform ion cyclotron resonance mass spectrometry). We find that carbonate-associated molecular formulas are highly sulfurized compared to surface water dissolved organic matter, with multiple sulfurization pathways at play. Furthermore, 97% of the formula abundance of surface water dissolved organic matter is shared with carbonate-associated organic matter, indicating connectivity between these two pools. We estimate that 9.2% of the particulate organic matter is carbonate-associated, and readily exchangeable with the broader aquatic system as the sediment dissolves and reprecipitates.

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Exploring the leaf regeneration cycles response of Zostera japonica to ocean acidification

Published 16 October 2024 Science Closed
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Highlights

  • The leaf regeneration cycles response of Z. japonica to OA was conducted.
  • 10 d represented a critical response node, 100 d was a critical adaptation point.
  • From response to adaptation, Z. japonica increased production and carbon fixation.
  • High‑carbon fixation of Z. japonica owed to three carbon acquisition strategies.

Abstract

Ocean acidification is one of the major global environmental problems facing humankind today, and it has far-reaching impacts on marine organisms and the entire marine ecosystem. Zostera japonica, an important supporting species of intertidal seagrass beds, exhibits high photosynthetic productivity and plays an important role in the carbon cycle of nearshore waters. However, little is known about the characteristics, processes, and mechanisms of its response to ocean acidification. In this study, we conducted a 120-day acidification experiment in Z. japonica; here, plants underwent four leaf regeneration cycles to reveal the response mechanism of Z. japonica to ocean acidification (OA). We found that acidification significantly affected the seedling stage of Z. japonica, impacting leaf regeneration cycles by altering physiological and molecular responses. In one leaf regeneration cycle, the short-term exposure to CO2 affected the seagrass parameters, such as the regulation of inorganic carbon uptake modes and the regulation of photosynthesis between the dark and light reactions, with the potential to affect the carbon sinks of the marine organisms. The long-term effects on the regulation of antioxidant enzymes and antioxidant metabolites, caused an improvement in the marine life adaptation to OA. In a comparison of the different leaf regeneration cycles, the response pattern of Z. japonica showed an offset of the acidification during the short cycles and an adaption to the acidification during the long cycles. This study revealed the response mechanism of Z. japonica to OA at different time scales and could provide a theoretical basis for accurately assessing the impact of OA on seagrass and the entire seagrass bed ecosystem.

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Shifting seagrass-oyster interactions alter species response to ocean warming and acidification

Published 16 October 2024 Science Closed
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  1. A major challenge in biodiversity research is the incorporation of species interactions into frameworks describing population and community response to global edfnmental change (GEC). Mutualisms are a type of species interaction especially sensitive to changing environmental conditions, and the breakdown of facilitative species interactions could amplify the negative impacts of novel climate regimes on focal species.
  2. Here, we investigate how reciprocal interactions between two coastal foundation species, the eastern oyster (Crassostrea virginica) and eelgrass (Zostera marina) shift in sign and magnitude in response to ocean warming (+1.5°C) and acidification (−0.4 pH) via a manipulative co-culture experiment in mesocosms.
  3. Under ambient environmental conditions, oysters facilitated eelgrass leaf growth and clonal reproduction by 35% and 38%, respectively. Simultaneously, eelgrass decreased the oyster condition index (the ratio of tissue to shell biomass) by 35%, indicating greater allocation of energy to shell growth instead of soft tissues at ambient conditions. Varying sensitivities of each species to ocean warming and/or acidification treatments led to complex shifts in species interactions that were trait dependent. As such, community outcomes under future conditions were influenced by species interactions that amplified and mitigated species response to environmental change.
  4. Synthesis: Given that species interaction effect sizes were similar in magnitude to effect sizes of warming or pH treatments, our results underscore the need to identify key species and interaction types that strongly influence community response to GEC. Specifically, for macrophyte-bivalve interactions, understanding how physiological limitations on growth are impacted by environmental heterogeneity and co-culture will support the successful restoration of natural populations and the rapid expansion of aquaculture.
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Low pH enhances germination of eelgrass (Zostera marina L.) seeds despite ubiquitous presence of Phytophthora gemini

Published 28 August 2024 Science Closed
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Highlights

  • Lowered pH levels positively influence eelgrass seed germination, indicating a potential adaptive response to ocean acidification.
  • Despite favorable germination conditions, the virulence of Phytophthora gemini remains unaffected, leading to widespread infection in eelgrass populations regardless of pH levels.
  • The study shows the persistent threat of Phytophthora gemini to eelgrass restoration efforts, emphasizing the need for innovative disease management strategies alongside considerations of ocean acidification impacts on coastal ecosystems.

Abstract

Seagrasses are foundation species in coastal ecosystems promoting biodiversity and community structure. Future marine carbonate chemistry under ocean acidification may enhance seagrass physiology, but little is known about how reproductive ecology and disease will integrate into future ocean conditions. A novel pathogen, Phytophthora gemini, infects >90% of eelgrass, Zostera marina, surveyed in Northern Atlantic and Mediterranean populations reducing annual germination 6-fold. Our study investigated the combined effects of ocean acidification and P. gemini infection on germination of eelgrass seeds. We conducted a two-level factorial experiment crossing four pH levels (∆0, – ∆0.3, – ∆0.6, -∆0.9; relative to the average pH at the sampling site) with three infection levels (infected, non-infected, exposed) to determine germination rate and infection response. Prior to experimentation, flowering shoots were collected and held in flow-through seawater tanks where seeds ripened naturally. Once collected, seeds were held in copper sulfate solution (27.37 ± 1.57 ppt) and stored in darkness to mimic winter dormancy (4 oC). Before the start of the experiment, viable seeds were cultured on oomycete selective growth media to determine infection status. By the end of the experiment, 100% of tested seeds, regardless of treatment, contained P. gemini. Germination rate significantly increased with decreased pH. Our findings indicate that P. gemini is not inhibited by ecologically relevant changes to carbonate chemistry and standard handling practices can result in effective and highly virulent disease transmission. These results confirm perennial populations of eelgrass are susceptible to infection and alerts conservationists to additional considerations necessary for successful eelgrass restoration.

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Review of the protist Labyrinhula spp. and its relationship to seagrass disease under the influence of anthropogenic activities

Published 5 August 2024 Science Closed
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Anthropogenic activities are driving significant changes in coastal ecological environments, increasingly spotlighting microorganisms associated with seagrass bed ecosystems. Labyrinthula is primarily recognized as a saprophytic protist associated with marine detritus, and it also acts as an opportunistic pathogen affecting marine algae, terrestrial plants and mollusks, especially in coastal environments. The genus plays a key role in the decomposition of marine detritus, facilitated by its interactions with diatoms and through the utilization of a diverse array of carbohydrate-active enzymes to decompose seagrass cell walls. However, human activities have significantly influenced the prevalence and severity of seagrass wasting disease (SWD) through factors such as climate warming, increased salinity and ocean acidification. The rise in temperature and salinity, exacerbated by human-induced climate change, has been shown to increase the susceptibility of seagrass to Labyrinthula, highlighting the adaptability of pathogen to environmental stressors. Moreover, the role of seagrass in regulating pathogen load and their immune response to Labyrinthula underscore the complex dynamics within these marine ecosystems. Importantly, the genotype diversity of seagrass hosts, environmental stress factors and the presence of marine organisms such as oysters, can influence the interaction mechanisms between seagrass and Labyrinthula. Besides, these organisms have the potential to both mitigate and facilitate pathogen transmission. The complexity of these interactions and their impacts driven by human activities calls for the development of comprehensive multi-factor models to better understand and manage the conservation and restoration of seagrass beds.

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Acidification alleviates the inhibition of hyposaline stress on physiological performance of tropical seagrass Thalassia hemprichii

Published 4 July 2024 Science Closed
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Highlights

  • Thalassia hemprichii highly adapts to acidification and hyposalinity environments.
  • Acidification and hyposalinity had interaction effects on physiology of the seagrass.
  • Acidification and hyposalinity had no interaction effects on growth of the seagrass.
  • Acidification mitigates the inhibitory effects of hyposaline stress for the seagrass.

Abstract

Since the Industrial Revolution, increasing atmospheric CO2 concentrations have had a substantial negative impact influence on coastal ecosystems because of direct effects including ocean acidification and indirect effects such as extreme rainfall events. Using a two-factor crossover indoor simulation experiment, this study examined the combined effects of acidification and hyposaline stress on Thalassia hemprichii. Seawater acidification increased the photosynthetic pigment content of T. hemprichii leaves and promoted seagrass growth rate. Hyposaline stress slowed down seagrass growth and had an impact on the osmotic potential and osmoregulatory substance content of seagrass leaves. Acidification and salinity reduction had significant interaction effects on the photosynthesis rate, photosynthetic pigment content, chlorophyll fluorescence parameters, and osmotic potential of T. hemprichii, but not on the growth rate. Overall, these findings have shown that the hyposaline stress inhibitory effect on the T. hemprichii physiological performance and growth may be reduced by acidification.

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Impact of climate change on carbon and nitrogen balance in Zostera Marina L. (Eelgrass)

Published 14 June 2024 Science Closed
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Seagrasses face vulnerability to both global stressors like Ocean Acidification (OA) and climate warming compounded by local stressors such as eutrophication that reduces light availability, leading to a complex dynamic of positive and negative effect on their growth and survival. Increased dissolved aqueous CO2 (CO2(aq)) benefits seagrasses by enhancing photosynthetic and growth rates, but it may increase nutrient demand, potentially depleting nutrient supply, especially in oligotrophic environments. In this study, the long-term impact of CO2 on Zostera marina L. (eelgrass) were investigated across a gradient of CO2(aq) concentrations (55 – 2200 µM CO2(aq)) and leaf area indices (LAI). The focus was on quantify changes in carbon (C) and nitrogen (N) content, composition, and metabolism in response to CO2-stimulated photosynthesis and growth. Absolute growth rates, shoot sizes, leaf density, sucrose concentrations, and carbon and nitrogen growth demands increased with increasing CO2(aq) availability. However, there was no notable decline in biomass-specific N content of leaf at higher CO2(aq) concentrations primarily due to dilution effects caused by carbon accumulation in thicker leaves, rather than N-limitation. Rather than increasing plant survival in the context of CO2(aq) enrichment, this study found that nutrient enrichment of the sediment reduced plant survival as a result of NH4 +toxicity. In contrast, the high H2S concentrations reaching millimolar levels in sediment, which was stimulated by organic carbon addition, was not particularly toxic to eelgrass. CO2 effects on N uptake were complicated by changes in canopy architecture due to increasing leaf area index (LAI), affecting N uptake patterns of leaves and roots. Combining a nutrient uptake model with the radiative transfer GrassLight (v2.14) model, this study explored how CO2-driven photosynthesis affected N uptake patterns and requirements for growth. Model predictions across varying LAIs and CO2(aq) concentrations indicated low N demand for eelgrass under all CO2(aq) conditions, with roots playing a key role in N acquisition as CO2(aq) concentrations increased. Overall, my results highlight the importance of photosynthesis in regulating N metabolism and acquisition between the above- and belowground components, and suggest that most eelgrass meadows are unlikely to experience N limitation, even in high CO2(aq) environments.

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Accelerated nitrogen cycling on Mediterranean seagrass leaves at volcanic CO2 vents

Published 22 March 2024 Science Closed
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Seagrass meadows form highly productive and diverse ecosystems in coastal areas worldwide, where they are increasingly exposed to ocean acidification (OA). Efficient nitrogen (N) cycling and uptake are essential to maintain plant productivity, but the effects of OA on N transformations in these systems are poorly understood. Here we show that complete N cycling occurs on leaves of the Mediterranean seagrass Posidonia oceanica at a volcanic CO2 vent near Ischia Island (Italy), with OA affecting both N gain and loss while the epiphytic microbial community structure remains largely unaffected. Daily leaf-associated N2 fixation contributes to 35% of the plant’s N demand under ambient pH, while it contributes to 45% under OA. Nitrification potential is only detected under OA, and N-loss via N2 production increases, although the balance remains decisively in favor of enhanced N gain. Our work highlights the role of the N-cycling microbiome in seagrass adaptation to OA, with key N transformations accelerating towards increased N gain.

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Cool-edge populations of the kelp Ecklonia radiata under global ocean change scenarios: strong sensitivity to ocean warming but little effect of ocean acidification

Published 9 February 2024 Science Closed
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Kelp forests are threatened by ocean warming, yet effects of co-occurring drivers such as CO2 are rarely considered when predicting their performance in the future. In Australia, the kelp Ecklonia radiata forms extensive forests across seawater temperatures of approximately 7–26°C. Cool-edge populations are typically considered more thermally tolerant than their warm-edge counterparts but this ignores the possibility of local adaptation. Moreover, it is unknown whether elevated CO2 can mitigate negative effects of warming. To identify whether elevated CO2 could improve thermal performance of a cool-edge population of E. radiata, we constructed thermal performance curves for growth and photosynthesis, under both current and elevated CO2 (approx. 400 and 1000 µatm). We then modelled annual performance under warming scenarios to highlight thermal susceptibility. Elevated CO2 had minimal effect on growth but increased photosynthesis around the thermal optimum. Thermal optima were approximately 16°C for growth and approximately 18°C for photosynthesis, and modelled performance indicated cool-edge populations may be vulnerable in the future. Our findings demonstrate that elevated CO2 is unlikely to offset negative effects of ocean warming on the kelp E. radiata and highlight the potential susceptibility of cool-edge populations to ocean warming.

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The vulnerability of World Heritage seagrass habitats to climate change

Published 23 January 2024 Science Closed
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Seagrass is an important natural attribute of 28 World Heritage (WH) properties. These WH seagrass habitats provide a wide range of services to adjacent ecosystems and human communities, and are one of the largest natural carbon sinks on the planet. Climate change is considered the greatest and fastest-growing threat to natural WH properties and evidence of climate-related impacts on seagrass habitats has been growing. The main objective of this study was to assess the vulnerability of WH seagrass habitats to location-specific key climate stressors. Quantitative surveys of seagrass experts and site managers were used to assess exposure, sensitivity and adaptive capacity of WH seagrass habitats to climate stressors, following the Climate Vulnerability Index approach. Over half of WH seagrass habitats have high vulnerability to climate change, mainly from the long-term increase in sea-surface temperature and short-term marine heatwaves. Potential impacts from climate change and certainty scores associated with them were higher than reported by a similar survey-based study from 10 years prior, indicating a shift in stakeholder perspectives during the past decade. Additionally, seagrass experts’ opinions on the cumulative impacts of climate and direct-anthropogenic stressors revealed that high temperature in combination with high suspended sediments, eutrophication and hypoxia is likely to provoke a synergistic cumulative (negative) impact (p < .05). A key component contributing to the high vulnerability assessments was the low adaptive capacity; however, discrepancies between adaptive capacity scores and qualitative responses suggest that managers of WH seagrass habitats might not be adequately equipped to respond to climate change impacts. This thematic assessment provides valuable information to help prioritize conservation actions, monitoring activities and research in WH seagrass habitats. It also demonstrates the utility of a systematic framework to evaluate the vulnerability of thematic groups of protected areas that share a specific attribute.

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Adaptive responses of eelgrass (Zostera marina L.) to ocean warming and acidification

Published 21 December 2023 Science Closed
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Highlights

  • Ocean warming (OW) and acidification (OA) affect seagrass stability.
  • Zostera marina L.’s response to OW and OA was studied using multi-omics analysis.
  • Plant performance varied under different OW and OA combinations.
  • OA’s effects on genes and metabolism depended on temperature.
  • OA and OW interactions triggered diverse metabolic shifts in Z. marina.

Abstract

Ocean warming (OW) and ocean acidification (OA), driven by rapid global warming accelerating at unprecedented rates, are profoundly impacting the stability of seagrass ecosystems. Yet, our current understanding of the effects of OW and OA on seagrass remains constrained. Herein, we investigated the response of eelgrass (Zostera marina L.), a representative seagrass species, to OW and OA through comprehensive transcriptomic and metabolomic analyses. The results showed notable variations in plant performance under varying conditions: OW, OA, and OWA (a combination of both conditions). Specifically, under average oceanic temperature conditions for eelgrass growth over the past 20 years —from May to November—OA promoted the production of differentially expressed genes and metabolites associated with alanine, aspartate, and glutamate metabolism, as well as starch and sucrose metabolism. Under warming condition, eelgrass was resistant to OA by accelerating galactose metabolism, along with glycine, serine, and threonine metabolism, as well as the tricarboxylic acid (TCA) cycle. Under the combined OW and OA condition, eelgrass stimulated fructose and mannose metabolism, glycolysis, and carbon fixation, in addition to galactose metabolism and the TCA cycle to face the interplay. Our findings suggest that eelgrass exhibits adaptive capacity by inducing different metabolites and associated genes, primarily connected with carbon and nitrogen metabolism, in response to varying degrees of OW and OA. The data generated here support the exploration of mechanisms underlying seagrass responses to environmental fluctuations, which hold critical significance for the future conservation and management of these ecosystems.

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Ocean acidification impairs seagrass performance under thermal stress in shallow and deep water

Published 24 November 2023 Science Closed
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Highlights

  • Shallow and deep plants were exposed to ocean acidification and thermal stress;
  • Plants were unaffected by ocean acidification when not exposed to thermal stress;
  • Ocean acidification reduced plant performance under thermal stress;
  • Deep plants showed higher levels of heat stress at genetic and physiological levels;
  • Warming may play a key role in structuring future seagrass meadows.

Abstract

Despite the effects of ocean acidification (OA) on seagrasses have been widely investigated, predictions of seagrass performance under future climates need to consider multiple environmental factors. Here, we performed a mesocosm study to assess the effects of OA on shallow and deep Posidonia oceanica plants. The experiment was run in 2021 and repeated in 2022, a year characterized by a prolonged warm water event, to test how the effects of OA on plants are modulated by thermal stress. The response of P. oceanica to experimental conditions was investigated at different levels of biological organization. Under average seawater temperature, there were no effects of OA in both shallow and deep plants, indicating that P. oceanica is not limited by current inorganic carbon concentration, regardless of light availability. In contrast, under thermal stress, exposure of plants to OA increased lipid peroxidation and decreased photosynthetic performance, with deep plants displaying higher levels of heat stress, as indicated by the over-expression of stress-related genes and the activation of antioxidant systems. In addition, warming reduced plant growth, regardless of seawater CO2 and light levels, suggesting that thermal stress may play a fundamental role in the future development of seagrass meadows. Our results suggest that OA may exacerbate the negative effects of future warming on seagrasses.

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Seasonal temperature variation in Zostera marina seedlings under ocean acidification

Published 24 November 2023 Science Closed
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Objective: To investigate the responses of Zostera marina seedlings to the individual and combined stresses of seasonal temperature increase and ocean acidification (OA) caused by global climate change and anthropogenic factors. This data will help in efforts to protect and restore seagrass beds in temperate coastal zones of China.

Methods: A mesoscale experimental system was utilized to analyze stress response mechanisms at multiple levels – phenotype, transcriptome, and metabolome – during the seedling stage of Z. marina, a dominant temperate seagrass species in China. The study monitored the seedlings under varying conditions: increased seasonal temperature, OA, and a combination of both.

Results: Findings revealed that under high-temperature conditions, carotenoid biosynthesis was stimulated through the upregulation of specific metabolites and enzymes. Similarly, the biosynthesis of certain alkaloids was promoted alongside modifications in starch, sucrose, and nitrogen metabolism, which improved the plant’s adaptation to OA. Unique metabolic pathways were activated under OA, including the degradation of certain amino acids and modifications in the citric acid cycle and pyruvate metabolism. When subjected to both temperature and OA stresses, seedlings actively mobilized various biosynthetic pathways to enhance adaptability and resilience, with distinct metabolic pathways enhancing the plant’s response under diversified stress conditions. In terms of growth, all treatment groups exhibited significant leaf length increase (p < 0.05), but the weakest growth index was observed under combined stress, followed by the thermal treatment group. Conversely, growth under OA treatment was better, showing a significant increase in wet weight, leaf length, and leaf width (p < 0.05).

Conclusion: Seasonal temperature increase was found to inhibit the growth of Z. marina seedlings to some extent, while OA facilitated their growth. However, the positive effects of OA did not mitigate the damage caused by increased seasonal temperature under combined stress due to seedlings’ sensitivity at this stage. Our findings elucidate differing plant coping strategies under varied stress conditions, contingent on the initial environment. This research anticipates providing significant data support for the adaptation of Z. marina seedlings to seasonal temperature fluctuations and global oceanic events like OA, propelling the effective conservation of seagrass beds.

Continue reading ‘Seasonal temperature variation in Zostera marina seedlings under ocean acidification’

Microbial associates of an endemic Mediterranean seagrass enhance the access of the host and the surrounding seawater to inorganic nitrogen under ocean acidification

Published 21 November 2023 Science Closed
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Seagrasses are important primary producers in oceans worldwide. They live in shallow coastal waters that are experiencing carbon dioxide enrichment and ocean acidification. Posidonia oceanica, an endemic seagrass species that dominates the Mediterranean Sea, achieves high abundances in seawater with relatively low concentrations of dissolved inorganic nitrogen. Here we tested whether microbial metabolisms associated with P. oceanica and surrounding seawater enhance seagrass access to nitrogen. Using stable isotope enrichments of intact seagrass with amino acids, we showed that ammonification by free-living and seagrass-associated microbes produce ammonium that is likely used by seagrass and surrounding particulate organic matter. Metagenomic analysis of the epiphytic biofilm on the blades and rhizomes support the ubiquity of microbial ammonification genes in this system. Further, we leveraged the presence of natural carbon dioxide vents and show that the presence of P. oceanica enhanced the uptake of nitrogen by water column particulate organic matter, increasing carbon fixation by a factor of 8.6–17.4 with the greatest effect at CO2 vent sites. However, microbial ammonification was reduced at lower pH, suggesting that future ocean climate change will compromise this microbial process. Thus, the seagrass holobiont enhances water column productivity, even in the context of ocean acidification.

Continue reading ‘Microbial associates of an endemic Mediterranean seagrass enhance the access of the host and the surrounding seawater to inorganic nitrogen under ocean acidification’

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