Posts Tagged 'respiration'

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Comparative transcriptomic analysis reveals a differential acid response mechanism between estuarine oyster (Crassostrea ariakensis) and Pacific oyster (Crassostrea gigas)

Published 2 May 2025 Science Closed
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Highlights

  • Mechanisms underlying resilience of estuarine oysters to low pH were analyzed.
  • Estuarine oysters have evolved enhanced acid-tolerance responding to low pH levels.
  • Frontloaded genes contributing to the enhanced acid-tolerance of estuarine oysters.
  • Ion transporters and translation are crucial in mitigates low pH effects in estuarine oysters.
  • Acid adaptation of estuarine oysters offers new insights into the adaptive potential of mollusks.

Abstract

Ocean and coastal acidification (OCA) poses a significant and rapidly emerging threat to mollusks. The physiological resilience of mollusks to OCA varies considerably; however, the underlying molecular mechanisms remain poorly understood. Seawater in estuaries, being more susceptible to acidification than that in open coastal zones, may enhance the tolerance of resident mollusks to low pH levels. Here, we conducted a comparative analysis between estuarine oysters (Crassostrea ariakensis) and Pacific oysters (Crassostrea gigas) using physiological phenotype and transcriptomic analyses to reveal differential acid-tolerance mechanisms in response to constant pH of 7.8. Our findings indicated that survival and respiration rates of C. ariakensis, which inhabits estuaries with fluctuating pH levels, were higher than those of C. gigas, which inhabits open coastal zones with relative stable pH conditions. Acid-responsive genes identified in C. gigas, including molecular chaperones and immune-related genes, exhibited higher constitutive expression in C. ariakensis under control conditions. Co-expression analyses revealed that C. ariakensis mitigated the effects of low pH by expressing genes involved in ion transporter activity and translation control. C. gigas activated genes associated with glycolipid metabolism while inhibiting cell division during acid stress. These findings suggested that C. ariakensis has evolved into a more energy-efficient regulatory network than C. gigas, incorporating both front-loading and responsive mechanisms to maintain acid-base homeostasis. This study is the first to investigate acid-tolerance differences between mollusks inhabiting estuarine and open coastal environments and provides critical insights into the resilience of mollusks in increasingly acidified oceans.

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Effects of ocean acidification on intestinal homeostasis and organismal performance in a marine bivalve: from microbial shifts to physiological suppression

Published 25 April 2025 Science Closed
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Ocean acidification (OA) poses significant threats to marine calcifiers through multifaceted physiological disruptions. While bivalve mollusks are particularly vulnerable, the intestinal defense mechanisms against OA-induced stress remain poorly characterized. This study systematically investigated the intimate associations between the organismal physiological toxicity responses and intestinal homeostasis of Chlamys nobilis (C. nobilis) under simulated OA situations (pH 7.3-8.0) to reveal the potential physiological and biochemical damage. The results revealed that acidification stimulated pathogenic bacteria（Mycoplasma）colonization, disrupted microbiota homeostasis, and induced oxidative responses, thereby triggering intestinal inflammation and epithelial damage. Furthermore, the filtration rates and oxygen consumption rates of C. nobilis were significantly decreased in a pH-dependent manner across all the treatments, which might result from the intestinal dysfunction and the inhibition of acetylcholinesterase activities. These findings establish a link between OA-induced intestinal dysbiosis and organismal physiology, providing novel insights into the interplay between physiological performance and intestinal homeostasis under OA scenarios. The results advance our understanding of bivalve mollusk adaptation strategies and inform predictive models for its sustainability in acidifying marine ecosystems.

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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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Food availability, but not tidal emersion, influences the combined effects of ocean acidification and warming on oyster physiological performance

Published 25 March 2025 Science Closed
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Highlights

  • Effects of pH/temperature conditions, tidal treatments, and food levels are studied.
  • Ocean acidification and warming enhance the physiological performance of oysters.
  • Food level impacts responses to future conditions and disease susceptibility.
  • Intertidal oysters increase food intake to compensate for limits during emersion.

Abstract

Many studies on the effects of ocean acidification and warming (OAW) in intertidal mollusks overlook critical factors like tidal emersion and food availability, both of which can shape organisms’ responses. Experiments on intertidal bivalves often use constant immersion and abundant food, which likely underestimate global change impacts and underscore the need for more realistic experiments mimicking natural ecosystems. This study investigated the physiological responses of juvenile Pacific oyster Crassostrea gigas exposed for 81 days to current and OAW conditions (+3 °C, −0.3 pH units) under two tidal treatments (0 vs. 30 % emersion) and two food levels (ad libitum vs. limited). We measured growth, reproduction, food ingestion, respiration, and biochemical traits like energy reserves and membrane fatty acids. At the experiment’s end, oysters were challenged with a viral disease to assess the physiological cost of acclimation and potential trade-offs. Results showed improved oyster physiological performance under OAW with high food level. Nevertheless, food availability emerged as the predominant factor in oyster performance, limiting growth, reproduction, and energy reserves, while increasing oxygen consumption and disease susceptibility. Food deprivation attenuated the beneficial effects of OAW through antagonistic interaction, suggesting physiologically weakened oysters may struggle to adapt to environmental hazards. Finally, tidal treatment had no significant effect, implying that oysters possess physiological compensatory mechanisms, particularly in food acquisition, enabling them to meet nutritional needs during immersion periods. This study provides valuable insights for designing global climate change experiments that align with ecological realism and improves our understanding of the acclimation potential in bivalves facing rapid ocean changes.

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Combined effects of ocean acidification and copper exposure on the polyps of moon jellyfish Aurelia coerulea

Published 24 March 2025 Science Closed
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Ocean acidification (OA) can interact with Copper (Cu) pollutants and threaten marine organisms and ecosystems. In this study, we assessed the effects of OA and Cu2+, alone and in combination, on the polyps of Aurelia coerulea, a common jellyfish renowned for its complex life cycle and frequent global blooms. The results revealed that ocean acidification and Cu2+ exposure significantly inhibited the activities of catalase, Ca2+-ATPase, acid phosphatase, and alkaline phosphatase in polyps, resulting in antioxidative stress effects and a significant increase in respiratory metabolism. In addition, the combination of ocean acidification and Cu2+ exposure caused severe tissue damage to polyps, thereby impeding their predation behavior and reducing their asexual reproduction rates. These two environmental stressors showed synergistic effects on the Ca2+-ATPase activity, predation rate, reproduction rate, and injury index of polyps. Therefore, reduced seawater pH and copper contamination adversely affect the physiology, growth, and development of A. coerulea polyps, which may affect the survival and population dynamics of wild populations.

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The effects of ocean warming and elevated CO2 on the feeding behavior and physiology of two sympatric mesograzers

Published 4 March 2025 Science Closed
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Highlights

  • Combining climate stressors gives better insights into climate change effects.
  • Sympatric species respond differently to the same environmental stressors.
  • Temperature and pH did not influence the physiology and feeding of H. niger.
  • Combined effects of temperature and pH reduced feeding rate in C. filosa.
  • Rates of ammonia excretion and protein catabolism increase with warming.

Abstract

Atmospheric CO2 concentrations have increased significantly since pre-industrial times, leading to ocean warming and acidification. These environmental changes affect the physiology of marine organisms as they modify metabolic processes. Despite the critical role of temperature and pH in marine biology, studies of their combined effects are limited. This study investigated the interactive effects of ocean warming and acidification on the feeding behavior and physiology of two sympatric amphipods, Hyale niger and Cymadusa filosa. Using an orthogonal experimental design with two temperatures (27 °C and 30 °C) and two pH levels (7.8 and 7.5), we assessed feeding rates, respiration rates, ammonia excretion, and O/N ratios. Results indicated that C. filosa was less tolerant to these stressors than H. niger. While H. niger showed no significant changes between treatments, C. filosa showed reduced feeding rates and altered physiological responses to elevated temperature and decreased pH. Reducing the feeding rate of C. filosa may favor macroalgal biomass and strengthen bottom-up control in phytal communities. In addition, increased ammonia excretion in C. filosa suggests increased protein catabolism to meet energy demands at higher temperatures, despite reduced oxygen consumption. This indicates a compromised metabolism and a reduction in circulating oxygen capacity for C. filosa. The study shows heterogeneous responses to climate change, highlighting the need to assess combined environmental stressors in different species to accurately understand the impacts of climate change.

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Transcriptome‐to‐phenome response of larval Eastern oysters under multiple drivers of aragonite undersaturation

Published 19 February 2025 Science Closed
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Understanding how interactive environmental challenges affect marine species is critical to long‐term ecological and economic stability under global change. Marine calcifiers are thought to be vulnerable to ocean acidification (OA; elevated pCO2); active dissolution of aragonite (Ωar) is associated with disrupted development, survivorship, and gene expression in bivalve larvae, resulting in an early life‐stage bottleneck. Dynamic carbonate chemistry in coastal systems emphasizes the importance of multiple stressors, e.g., warming and low salinity events may change organismal responses relative to OA alone. We exposed Eastern oyster larvae ( Crassostrea virginica ) to a full‐factorial experimental design using two temperatures (23°C and 27°C), salinities (17 and 27), and pCO2 levels (~700 μatm and 1850 μatm pCO2), resulting in Ωar conditions 0.3–1.7. Ωar reduced by low salinity, elevated pCO2, and low temperature, each slowed early development and reduced survival. Low salinity × elevated pCO2 was linked to severe Ωar undersaturation (< 0.5) that suppressed expression of bicarbonate transport, biomineralization and augmented expression for ciliary locomotion, proteostasis, and histone modifiers. In isolation and under moderate Ωar intensity (0.5 < Ωar < 1), larvae increased transcription for osmoregulatory activity and endocytosis under low salinity, and suppressed transcription for iron metabolism under elevated pCO2. Although shell growth and survival were affected by Ωar undersaturation, gene expression patterns of D‐stage oyster larvae and oyster juveniles suggests tolerance to dynamic estuarine environments. Genes and expression patterns that confer survival of postmetamorphosed oysters can improve our understanding of environmental‐organismal interactions and improve breeding programs enabling sustainable production.

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Contrasting species-specific stress response to environmental pH determines the fate of coccolithophores in future oceans

Published 14 February 2025 Science Closed
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Highlights

  • Molecular mechanisms dictating sensitivity of coccolithophores to pH remain elusive.
  • Coastal species was resilient to pH changes, but ancient open-ocean species was not.
  • Bloom-forming species showed unique molecular changes under stress.
  • Cellular carbon fixation will be higher under future acidification.

Abstract

Molecular mechanisms driving species-specific environmental sensitivity in coccolithophores are unclear but crucial in understanding species selection and adaptation to environmental change. This study examined proteomic and physiological changes in three species under varying pH conditions. We showed that changing pH drives intracellular oxidative stress and changes membrane potential. Upregulation in antioxidant, DNA repair and cell cycle-related protein-groups indicated oxidative damage across high (pH 8.8) and low pH (pH 7.6) compared to control pH (pH 8.2), and correlated with reduced growth rates. Upregulation of mitochondrial proteins suggested higher metabolite demand for restoring cellular homeostasis under pH-induced stress. Photosynthetic rates generally correlated with CO2 availability, driving higher net carbon fixation rates at low pH. The intracellular pH-buffering capacity of the coastal Chrysotila carterae and high metabolic adaptability in the bloom-forming Gephyrocapsa huxleyi will likely facilitate their adaptation to ocean acidification or artificial ocean alkalinisation. However, the pH sensitivity of the ancient open-ocean Coccolithus braarudii will possibly result in reduced growth and shrinking of its ecological niche.

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Effect of ocean acidification on the oxygen consumption of the sea urchins Paracentrotus lividus (Lamarck, 1816) and Arbacia lixula (Linnaeus, 1758) living in CO2 natural gradients

Published 7 February 2025 Science Closed
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Ocean acidification (OA) stands out as one of the main threats to marine ecosystems. OA leads to a reduction in the availability of carbonate ions, which are essential for marine calcifiers such as echinoderms. We aim to understand the physiological responses of two sea urchin species, Paracentrotus lividus and Arbacia lixula to low pH conditions and determine whether their responses result from phenotypic plasticity or local adaptation. The study is divided into two parts: plasticity response over time, measuring respiration rates of individuals from the Mediterranean Sea exposed to low pH over seven days, and adaptation and plasticity under changing pH, analyzing individuals inhabiting a pH gradient in a natural CO2 vent system located in La Palma Island, Spain. Over the seven days of low pH exposure, distinct patterns in respiration rates were revealed, with both species demonstrating potential for acclimatization. Notably, P. lividus and A. lixula displayed unsynchronized acidosis/alkalosis cycles, suggesting different physiological mechanisms. Additionally, environmental history seemed to influence adaptive capacity, as specimens from fluctuating pH environments exhibited respiration rates similar to those from stable environments with heightened phenotypic plasticity. Overall, our results suggest that both species possess the capacity for metabolic plasticity, which may enhance their resilience to future OA scenarios but likely involve energetic costs. Moreover, CO2 vent systems may serve as OA refugia, facilitating long-term survival. Understanding the plastic responses versus adaptations is crucial for predicting the effects of OA on species distribution and abundance of marine organisms in response to ongoing climate change.

Continue reading ‘Effect of ocean acidification on the oxygen consumption of the sea urchins Paracentrotus lividus (Lamarck, 1816) and Arbacia lixula (Linnaeus, 1758) living in CO2 natural gradients’

Conspecific interactions between corals mediate the effect of submarine groundwater discharge on coral physiology

Published 30 January 2025 Science Closed
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Land-based inputs, such as runoff, rivers, and submarine groundwater, can alter biologic processes on coral reefs. While the abiotic factors associated with land-based inputs have strong effects on corals, corals are also affected by biotic interactions, including other neighboring corals. The biologic responses of corals to changing environmental conditions and their neighbors are likely interactive; however, few studies address both biotic and abiotic interactions in concert. In a manipulative field experiment, we tested how the natural environmental gradient created by submarine groundwater discharge (SGD) affected holobiont and symbiont metabolic rates and endosymbiont physiology of Porites rus. We further tested how the effect of SGD on the coral was mediated by intra and interspecific interactions. SGD is a natural land-sea connection that delivers nutrients, inorganic carbon, and other solutes to coastal ecosystems worldwide. Our results show that a natural gradient of nutrient enrichment and pH variability as a result of acute SGD exposure generally benefited P. rus, increasing gross photosynthesis, respiration, endosymbiont densities, and chlorophyll a content. Conspecifics in direct contact with the a neighboring coral, however, altered the relationship between coral physiology and SGD, lowering the photosynthetic and respiration rates from expected values when the coral had no neighbor. We show that the response of corals to environmental change is dependent on the types of nearby neighbor corals and how neighbors alter the chemical or physical environment around the coral. Our study underscores the importance of considering biotic interactions when predicting the physiologic responses of corals to the environment.

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The impact of climate change stressors on microbial respiration and community structure: ocean acidification and artificial upwellling

Published 14 January 2025 Science Closed
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Microbial community respiration significantly influences the oceans capacity to sequester CO2 in marine ecosystems. Despite its pivotal role, there remains limited understanding of the variability and magnitude of community respiration in marine ecosystems, especially regarding its sensitivity to climate change stressors. This knowledge gap hinders a comprehensive grasp of its contribution to the global carbon cycle. Traditional in situ approaches for measuring community respiration are subject to several methodological limitations, particularly that of sensitivity in oligotrophic ecosystems, which cover more than 40% of the Earth’s ocean surface. These limitations thus contribute significantly to the uncertainty in global estimates of carbon budgets. To address these challenges, enzymatic techniques such as ETSvitro offer a fast and sensitive method to assess respiratory activity rates at spatial scales that are difficult to cover using conventional approaches. The method involves reducing the tetrazolium salt, INT, within the respiratory chain under substrate saturation levels (i.e., NADH, NADPH, and succinate). However, the reliability of the ETSvitro method has been questioned because it measures potential respiratory activity rather than actual respiration. In response to these concerns, another enzymatic technique, ETSvivo, emerged presumably as a more realistic estimate of actual respiration. Unlike ETSvitro, ETSvivo measures INT under in vivo conditions, utilizing substrates naturally available inside the cell. Nevertheless, before these methods can be considered feasible proxies for community respiration, further evaluation is needed to determine their universal applicability in marine ecosystems. In this thesis, our objective was to improve our understanding of community respiration by addressing its methodological limitations and investigating the drivers responsible for its variability. We paid particular attention to planktonic community structure and the impact of two climate change stressors: ocean acidification and changes in nutrient fertilization. Simulating a typical ETSvivo assay in eight independent experiments using surface coastal and open ocean waters from the Canary region, we observed that INT alone significantly influences the physiological status of bacteria. Bacteria are considered the primary contributors to respiration in oligotrophic environments, but their physiological status is largely affected by the inherent toxicity of INT. Consequently, we question the applicability of the ETSvivo method as a proxy for community respiration in oligotrophic regions. On the other hand, we explore the temporal variability of respiratory metabolism through two mesocosm experiments conducted in the oligotrophic waters of the subtropical Eastern North Atlantic. In the first mesocosms experiment, we investigated the impact of changing community structure and biomass on the temporal variability of community respiration measured through the Winkler method (R), ETS activity, and their ratio (R/ETS) in response to increasing CO2 concentrations and nutrient fertilization (e.g., due to local upwelling events). Our results suggest that community respiration and ETS activity do not respond to CO2 during oligotrophic conditions. However, following fertilization, community respiration increased in the two high CO2 mesocosms coinciding with an increase in microplankton, primarily diatoms. Simultaneously, the R/ETS ratio showed no correlation with community structure or biomass, indicating its variability makes it unsuitable for application with communities undergoing abrupt changes in trophic conditions. In light of these findings, the second mesocosm experiment explored the influence of different upwelling intensities and frequencies (singular pulse versus recurring upwelling) on community respiration. Our results demonstrate that community respiration is sensitive to changes in upwelling intensities but more significantly to the mode in which nutrients are supplied to oligotrophic waters. The planktonic community structure significantly influenced the observed variability in community respiration, revealing notable differences under varying upwelling intensities.The results of this thesis underscore the significance of mitigating methodological uncertainties to achieve precise measurements of respiration rates. It is crucial to adequately assess the impact of climate change-induced stressors, especially ocean acidification and changes in nutrient fertilization, along with planktonic community structure, as drivers of temporal variability. This thorough examination is essential for gaining a deeper understanding and, consequently, making more accurate predictions of community respiration in marine ecosystems.

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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.

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Adaptation to warming and high CO2 influences diatom response norms and multi-trait variations across CO2 gradients 

Published 6 January 2025 Science Closed
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Understanding how phytoplankton response to elevated CO2 and/or warming through long-term genotypic adaptation is critical for predicting future phytoplankton distribution and community structure. In this study, we conducted a 4.5-year experimental evolution with the model marine diatom Phaeodactylum tricornutum Bohlin under four environmental regimes: ambient conditions, high CO2, warming, and combined high CO2 + warming. Following this long-term adaptation, we exposed the populations to a broad CO2 gradient in a short-term (7-day) experiment, assessing their multi-trait responses. Our results demonstrate that P. tricornutum Bohlin populations adapted to different regimes exhibit significant multi-trait variation across CO2 gradients. Notably, the variability driven by long-term adaptation exceeded that induced by short-term CO2 changes. Furthermore, both long-term adaptation and short-term CO2 exposure altered trait co-variations, highlighting the complex interplay between environmental history and immediate conditions. This study emphasizes the importance to assess long-term genetic changes in marine phytoplankton under global change, as short-term experiments alone may underestimate their capacity for adaptation and the broader implications for marine ecosystems under future climate scenarios.

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Interactive effects of CO2, temperature, and nitrate limitation on the growth and physiology of strain CCMP 1334 of the marine cyanobacterium Synechococcus (Cyanophyceae)

Published 13 December 2024 Science Closed
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The marine cyanobacterium Synecococcus sp. (CCMP 1334) was grown in a continuous culture system on a 12:12 h light:dark cycle at all combinations of low and high pCO2 (400 and 1000 ppmv, respectively), nutrient availability (nitrate-limited and nutrient-replete conditions), and temperatures of 21, 24, 28, 32, and 35°C. The maximum nutrient-replete growth rate was ~1.15 day−1 at 32–35°C. Median nutrient-replete growth rates were higher at 1000 ppmv than at 400 ppmv pCO2 at all temperatures. Carbon:nitrogen ratios were independent of pCO2 at a fixed relative growth rate (i.e., growth rate ÷ nutrient-replete growth rate) but decreased with increasing temperature. Carbon:chlorophyll a ratios were decreased monotonically with increasing temperature and were higher under nitrate-limited than nutrient-replete conditions. Ratios of phycoerythrin to chlorophyll a were independent of growth conditions. Productivity indices were independent of temperature and nutrient limitation but were consistently higher at 1000 ppmv than 400 ppmv pCO2. Both growth rates and dark respiration rates were positively correlated with temperature, and the associated Q10 values were 2.2 and 2.3, respectively. A model of phytoplankton growth in which cellular carbon is allocated to structure, storage, or the light or dark reactions of photosynthesis accounted for the general patterns of cell composition and growth rate. This strain of Synechococcus appears well suited to changes in environmental conditions that are expected as the climate warms in response to anthropogenic emissions of CO2.

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Synergistic effects of ocean acidification and sulfamethoxazole on immune function, energy allocation, and oxidative stress in Trochus niloticus

Published 9 December 2024 Science Closed
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Highlights

  • Dual stress of OA and SMX may harm survival and reproduction in T. niloticus.
  • OA increased immune and antioxidant responses in T. niloticus.
  • SMX exposure boosted antioxidant responses and oxygen consumption.
  • Exposure to OA combined with SMX impaired cellular energy allocation in T. niloticus.

Abstract

Ocean acidification, a major consequence of climate change, poses significant threats to marine organisms, particularly when combined with other environmental stressors such as chemical pollution. This study investigated the physiological responses of Trochus niloticus to a 28-day exposure of ocean acidification and/or sulfamethoxazole, a commonly detected antibiotic in the South China Sea. Exposure to either acidification or sulfamethoxazole individually triggered adaptive responses through immune activation, antioxidant reactions, and metabolic adjustments. However, concurrent exposure resulted in significant adverse effects, including compromised immunity, oxidative damage, and disrupted energy budget. These findings provide new insights into how ocean acidification interacts with antibiotic pollution to synergistically impact marine gastropods, suggesting that multiple stressors may pose greater threats to T. niloticus populations than single stressors alone.

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Comparative physiological and transcriptome analyses reveal the responses to ocean acidification challenge of Mactra veneriformis with different shell colors

Published 6 December 2024 Science Closed
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Mactra veneriformis is highly susceptible to ocean acidification (OA) due to its low shell hardness during its rapid growth period. In this study, oxygen consumption rate, ammonia excretion rate, and transcriptome sequencing of mantle tissue analyses were conducted in white and purple shell-color populations of M. veneriformis under OA stress (pH = 7.6). The findings indicated a significant rise in oxygen consumption rates and ammonia excretion rates following acidification in both the two shell colors, while the clams with purple color showed comparatively lower basal metabolic levels. Transcriptomic analyses demonstrated the expression of key genes related to fatty acid synthesis were significantly inhibited, whereas genes involved in calcification, osmoregulation, and immune response were upregulated under OA exposure in the two shell-color groups. However, some genes such as CA and HSP showed a population-specific response between the two shell-color populations. KEGG enrichment analysis revealed that the MAPK signaling pathway and protein processing in the endoplasmic reticulum were significantly enriched in the two acidification groups. This study provides valuable insights into the response of M. veneriformis to OA stress and also helps to predict the future breeding of valuable strains of M. veneriformis.

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Sea-air CO2 exchanges, pCO2 drivers and phytoplankton communities in the southwestern South Atlantic Ocean during spring

Published 3 December 2024 Science Closed
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Highlights

  • The southwestern Brazilian margin behaved as a weak CO2 outgassing zone in austral spring of 2014.
  • Haptophytes were conspicuous along the entire study area, while Trichodesmium was prominent at SBB and diatoms at SBS.
  • CaCO3 production was observed at SBB, whereas seawater dilution dominated the changes of sea surface pCO2 at SBS.
  • Nitrification by Trichodesmium likely allowed increased contribution of haptophytes seen at open ocean oligotrophic waters.
  • Net respiration was the main biogeochemical process regulating sea-air CO2 exchanges in the study area.

Abstract

Hydrographic properties and carbon dioxide partial pressure (pCO2) were measured through underway survey of surface waters during spring 2014, mainly along the Surface Haline Front in the continental shelf-break domain in the southwestern South Atlantic Ocean margin. Additionally, discrete seawater surface samples were collected along the ship track to identify the phytoplankton community and measure seawater chemical properties. This study aims to identify the drivers of the marine CO2‑carbonate chemistry and the role played by the phytoplankton composition on changes in the surface marine carbonate properties and the sea-air CO2 exchanges in two biogeochemical provinces (i.e., South Brazil Bight – SBB, and Southern Brazilian Shelf – SBS) governed by the dynamics of the Brazil Current system in the South Atlantic Ocean. The water masses identified on the surface of the region were Tropical Water (mostly present at offshore regions), Subtropical Shelf Water (mostly present over the continental shelf and slope), and Plata Plume Water (present in the south coastal domain of the SBS). On average, the study area behaved as a weak net CO2 outgassing zone of 1.2 ± 2.3 mmol m−2 d−1 during the spring, despite some subregions behaving as CO2 ingassing zones. The CO2 uptake verified in the SBB was related with mesoscale activity bringing cold waters in the region while CO2 uptake in the continental shelf domain of SBS was associated with the presence of cooler and fresher Plata Plume Water. Changes in total alkalinity and dissolved inorganic carbon at surface were mainly governed by CaCO3 production in SBB and seawater dilution in SBS, although other processes may also have influenced on their spatial variability. The dominant phytoplankton groups were haptophytes (31 %), Trichodesmium (21 %), and picocyanobateria (28 %), corresponding to Synechococcus (17 %) and Prochlorococcus (11 %). The dominance of the diatom group was associated with a decrease in sea surface pCO2 (mainly at coastal zones at southern areas), although the sea-air CO2 exchanges were regulated by cooling process due the presence of Plata Plume Water in that region. Changes in surface pH were related to high concentration of Trichodesmium slicks at offshore zones with the highest microalgae concentration, leading to pH drops of up to 0.4. Trichodesmium slicks likely allowed the development of haptophytes in offshore oligotrophic waters due to its role on N2 fixation. An increase of ∼20 % in the dominance of haptophytes contribution was verified in that situation, which was likely in a post-bloom development stage, since an increased dissolved inorganic carbon content was observed, associated with a prevalence of net respiration processes.

Continue reading ‘Sea-air CO2 exchanges, pCO2 drivers and phytoplankton communities in the southwestern South Atlantic Ocean during spring’

Symbiodiniaceae algal symbionts of Pocillopora damicornis larvae provide more carbon to their coral host under elevated levels of acidification and temperature

Published 25 November 2024 Science Closed
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Climate change destabilizes the symbiosis between corals and Symbiodiniaceae. The effects of ocean acidification and warming on critical aspects of coral survical such as symbiotic interactions (i.e., carbon and nitrogen assimilation and exchange) during the planula larval stage remain understudied. By combining physiological and stable isotope techniques, here we show that photosynthesis and carbon and nitrogen assimilation (H13CO3− and 15NH4+) in Pocillopora damicornis coral larvae is enhanced under acidification (1000 µatm) and elevated temperature (32 °C). Larvae maintain high survival and settlement rates under these treatment conditions with no observed decline in symbiont densities or signs of bleaching. Acidification and elevated temperature both enhance the net and gross photosynthesis of Symbiodiniaceae. This enhances light respiration and elevates C:N ratios within the holobiont. The increased carbon availability is primarily reflected in the 13C enrichment of the host, indicating a greater contribution of the algal symbionts to the host metabolism. We propose that this enhanced mutualistic symbiotic nutrient cycling may bolster coral larvae’s resistance to future ocean conditions. This research broadens our understanding of the early life stages of corals by emphasizing the significance of symbiotic interactions beyond those of adult corals.

Continue reading ‘Symbiodiniaceae algal symbionts of Pocillopora damicornis larvae provide more carbon to their coral host under elevated levels of acidification and temperature’

The role of rolling corals and free-living calcifying coralline algae in the management of greenhouse gas CO2 in the Colombian Caribbean

Published 25 November 2024 Science Closed
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The ongoing increase in anthropogenic CO₂ emissions since the industrial revolution has accelerated ocean acidification (OA) by introducing CO₂ into seawater, forming carbonic acid and reducing pH levels. This acidification threatens marine calcifiers by weakening their capacity to build calcium carbonate structures and promoting the dissolution of existing skeletons. Nonetheless, calcifying organisms may contribute to mitigating OA effects. This study explores the roles of corals (rolling Siderastrea radians, a seagrass dweller) and free-living calcifying coralline algae (back reef) in CO₂ mitigation in seawater. Field experiments were conducted on Isla Grande (Corales del Rosario and San Bernardo National Natural Park, Colombian Caribbean), to observe the diel variations in photosynthesis and calcification of these uncommon reef builders across different times of the day. Results demonstrate diel shifts influenced by photosynthesis/respiration and calcification/dissolution, with free-living coralline algae exhibiting higher productivity and calcification rates than corals during the day. Notably, free-living coralline algae displayed pronounced hysteresis, reflecting high sensitivity to light. These findings underscore the significant role of free-living coralline algae in marine carbon cycling, suggesting a more substantial impact on CO₂ mitigation than previously recognized. Conserving free-living coralline algae and their habitats is thus critical for supporting marine ecosystem health and resilience amidst global change, warranting further research into their metabolic responses to inform conservation strategies.

Continue reading ‘The role of rolling corals and free-living calcifying coralline algae in the management of greenhouse gas CO2 in the Colombian Caribbean’

Effects of ocean acidification on the interaction between calcifying oysters (Ostrea chilensis) and bioeroding sponges (Cliona sp.)

Published 18 November 2024 Science Closed
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Ocean acidification can negatively affect a broad range of physiological processes in marine shelled molluscs. Marine bioeroding organisms could, in contrast, benefit from ocean acidification due to reduced energetic costs of bioerosion. Ocean acidification could thus exacerbate negative effects (e.g. reduced growth) of ocean acidification and shell borers on oysters. The aim of this study was to assess the impact of ocean acidification on the oyster Ostrea chilensis, the boring sponge Cliona sp., and their host-parasite relationship. We exposed three sets of organisms 1) O. chilensis, 2) Cliona sp., and 3) O. chilensis infested with Cliona sp. to pHT 8.03, 7.83, and 7.63. Reduced pH had no significant effect on calcification, respiration and clearance rate of uninfested O. chilensis. Low pH significantly reduced calcification leading to net dissolution of oyster shells at pHT 7.63 in sponge infested oysters. Net dissolution was likely caused by increased bioerosion by Cliona sp. at pHT 7.63. Additionally, declining pH and sponge infestation had a significant negative antagonistic effect (less negative than predicted additively) on clearance rate. This interaction suggests that sponge infested oysters increase clearance rates to cope with higher energy demand of increased shell repair resulting from higher boring activity of Cliona sp. at low seawater pH. O. chilensis body condition was unaffected by sponge infestation, pH, and the interaction of the two. The reduction in calcification rate suggests sponge infestation and ocean acidification together would exacerbate direct (reduced growth) and indirect (e.g., increased predation) negative effects on oyster health and survival. Our results indicate that ocean acidification by the end of the century could have severe consequences for marine molluscs with boring organisms.

Continue reading ‘Effects of ocean acidification on the interaction between calcifying oysters (Ostrea chilensis) and bioeroding sponges (Cliona sp.)’

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