Posts Tagged 'physiology'

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Gene expression of pocillopora damicornis coral larvae in response to acidification and ocean warming

Published 27 March 2024 Science Closed
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Objectives

The endosymbiosis with Symbiodiniaceae is key to the ecological success of reef-building corals. However, climate change is threatening to destabilize this symbiosis on a global scale. Most studies looking into the response of corals to heat stress and ocean acidification focus on coral colonies. As such, our knowledge of symbiotic interactions and stress response in other stages of the coral lifecycle remains limited. Establishing transcriptomic resources for coral larvae under stress can thus provide a foundation for understanding the genomic basis of symbiosis, and its susceptibility to climate change. Here, we present a gene expression dataset generated from larvae of the coral Pocillopora damicornis in response to exposure to acidification and elevated temperature conditions below the bleaching threshold of the symbiosis.

Data description

This dataset is comprised of 16 samples (30 larvae per sample) collected from four treatments (Control, High pCO2, High Temperature, and Combined pCO2 and Temperature treatments). Freshly collected larvae were exposed to treatment conditions for five days, providing valuable insights into gene expression in this vulnerable stage of the lifecycle. In combination with previously published datasets, this transcriptomic resource will facilitate the in-depth investigation of the effects of ocean acidification and elevated temperature on coral larvae and its implication for symbiosis.

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Response of CRH system in brain and gill of marine medaka to seawater acidification

Published 26 March 2024 Science Closed
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Corticotropin-releasing hormone (CRH) is mainly secreted by the hypothalamus to regulate stress when environmental factors change. Gills contact with water directly and may also secrete CRH to maintain local homeostasis. Ocean acidification changes water chemical parameters and is becoming an important environmental stressor for marine fish. The response of brain and gill CRH systems to ocean acidification remains unclear. In this study, marine medaka were exposed to CO2-acidified seawater (440 ppm, 1000 ppm, and 1800 ppm CO2) for 2 h, 4 h, 24 h, and 7 d, respectively. At 2 h and 4 h, the expression of crh mRNA in gills increased with increasing CO2 concentration. Crh protein is expressed mainly in the lamellae cells. crhbp and crhr1 expression also increased significantly. However, at 2 h and 4 h, acidification caused little changes in these genes and Crh protein expression in the brain. At 7 d, Crh-positive cells were detected in the hypothalamus; moreover, Crh protein expression in the whole brain increased. It is suggested that CRH autocrine secretion in gills is responsible for local acid–base regulation rather than systemic mobilization after short-term acidification stress, which may help the rapid regulation of body damage caused by environmental stress.

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Adverse environmental perturbations may threaten kelp farming sustainability by exacerbating enterobacterales diseases

Published 25 March 2024 Science Closed
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Globally kelp farming is gaining attention to mitigate land-use pressures and achieve carbon neutrality. However, the influence of environmental perturbations on kelp farming remains largely unknown. Recently, a severe disease outbreak caused extensive kelp mortality in Sanggou Bay, China, one of the world’s largest high-density kelp farming areas. Here, through in situ investigations and simulation experiments, we find indications that an anomalously dramatic increase in elevated coastal seawater light penetration may have contributed to dysbiosis in the kelp Saccharina japonica’s microbiome. This dysbiosis promoted the proliferation of opportunistic pathogenic Enterobacterales, mainly including the genera Colwellia and Pseudoalteromonas. Using transcriptomic analyses, we revealed that high-light conditions likely induced oxidative stress in kelp, potentially facilitating opportunistic bacterial Enterobacterales attack that activates a terrestrial plant-like pattern recognition receptor system in kelp. Furthermore, we uncover crucial genotypic determinants of Enterobacterales dominance and pathogenicity within kelp tissue, including pathogen-associated molecular patterns, potential membrane-damaging toxins, and alginate and mannitol lysis capability. Finally, through analysis of kelp-associated microbiome data sets under the influence of ocean warming and acidification, we conclude that such Enterobacterales favoring microbiome shifts are likely to become more prevalent in future environmental conditions. Our study highlights the need for understanding complex environmental influences on kelp health and associated microbiomes for the sustainable development of seaweed farming.

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Trade-off between growth and reproduction in Argopecten purpuratus (L.) scallops exposed to medium-term hypoxia and acidification

Published 25 March 2024 Science Closed
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Highlights

  • •Scallops showed physiological adaptations to survive and reproduce under medium-term exposure.
  • •The most pronounced impact of hypoxia and low pH were on clearance and calcification rates.
  • •The combined effect of hypoxia and low pH produced relatively high survival (>70%).
  • •Hypoxia and low pH generated early gonad development and high reproductive potential.

Abstract

Peruvian bays that are home to aquatic organisms of commercial interest are increasingly affected by hypoxia and low pH events. These stressors produce unfavorable conditions for the aquatic fauna, leading to mass mortality events. In this study, we evaluated the ecophysiological responses of the scallop Argopecten purpuratus exposed to moderate hypoxia (20% DO saturation) and low pH (OA, pH 7.4) using a 2 × 2 factorial design. We found that a 51-day exposure to low pH (OA treatment) had greater negative effects on A. purpuratus performances than hypoxia (lower survival and decreased clearance and calcification rates), but stimulated early gonad maturation. The survival rate was 1.3-fold higher under hypoxia than under acidic treatment. The interaction between hypoxia and low pH had an antagonistic effect on survival, since the combined treatment (HOA) resulted in lower scallop mortality than the single stress treatments. Calcification was negatively affected by all stress treatments, whereas hypoxia and OA both stimulated gametogenesis. OA treatment resulted in higher frequencies of previtellogenic and vitellogenic oocytes, greater gonad coverage area, and lower frequency of atretic oocytes, suggesting higher reproductive potential. HOA was positively related to oocyte development and high frequency of post-vitellogenic and atretic oocytes. These results suggest that, due to hypoxia and low pH, feeding is reduced and energy allocation prioritizes scallop gonad maturation. This trend would have negative effects on scallop growth and calcification, while increased reproduction under environmental stress could mitigate the effect on recruitment.

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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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Ocean acidification increases susceptibility to sub-zero air temperatures in ecosystem engineers and limits poleward range shifts

Published 21 March 2024 Science Closed
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Ongoing climate change has caused rapidly increasing temperatures and an unprecedented decline in seawater pH, known as ocean acidification. Increasing temperatures are redistributing species toward higher and cooler latitudes that are most affected by ocean acidification. While the persistence of intertidal species in cold environments is related to their capacity to resist sub-zero air temperatures, studies have never considered the interacting impacts of ocean acidification and freeze stress on species survival and distribution. Here, a full-factorial experiment was used to study whether ocean acidification increases mortality in subtidal Mytilus trossulus and subtidal M. galloprovincialis, and intertidal M. trossulus following sub-zero air temperature exposure. We examined physiological processes behind variation in freeze tolerance using 1H NMR metabolomics, analyses of fatty acids, and amino acid composition. We show that low pH conditions (pH = 7.5) significantly decrease freeze tolerance in both intertidal and subtidal populations of Mytilus spp. Under current day pH conditions (pH = 7.9), intertidal M. trossulus was more freeze tolerant than subtidal M. trossulus and subtidal M. galloprovincialis. Conversely, under low pH conditions, subtidal M. trossulus was more freeze tolerant than the other mussel categories. Differences in the concentration of various metabolites (cryoprotectants) or in the composition of amino acids and fatty acids could not explain the decrease in survival. These results suggest that ocean acidification can offset the poleward range expansions facilitated by warming and that reduced freeze tolerance could result in a range contraction if temperatures become lethal at the equatorward edge.

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How do sea urchins prepare offspring to face ocean acidification? Gamete intraspecific differences and adaptability

Published 21 March 2024 Science Closed
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Introduction: Due to their relevant ecological position and well-studied biology, sea urchins are reference organisms for ocean acidification studies, at both within- and trans-generational levels. In this study, we examined gamete quality in specimens exposed to future predicted (-0.4 units) pH conditions during gametogenesis.

Methods: Egg physical characteristics, biochemical composition, and fatty acid profiles were assessed after two and six months of exposure, while sperm viability and velocity were analyzed after six months of exposure. Considering the documented intraspecific variability in response to ocean acidification, this study involved two populations of Paracentrotus lividus. One population was sampled from the highly variable lagoon of Venice (Site 1), while the other was obtained from a coastal area (Site 2) characterized by more stable environmental conditions and facing minimal anthropogenic stress.

Results: A different response was highlighted in the two sites. Noteworthy trends emerged, especially in the fatty acid profile and sperm traits. Although adults were fed the same diet, Site 1 eggs contained more high-energetic fatty acids than Site 2, potentially boosting the survival odds for the next generation. Moreover, Site 1 sperms displayed higher viability but slower motility compared to those from Site 2. Within sites, a significant difference between time points and a change in the fitness strategy of sea urchin females emerged when comparing eggs spawned after two and six months of exposure to reduced pH. The effects of time and exposure pH are more pronounced in animals from Site 1, suggesting a higher adaptability of this population rather than negative effects of ocean acidification.

Discussion: Overall, our findings suggest that sea urchins have the potential to acclimate to reduced pH and to produce gametes of the same quality as controls held at the currently natural pH. Our findings emphasize the relevance of combining investigations of gamete quality characteristics, particularly egg biochemistry and fatty acid composition, and considering site variability to fully understand the transgenerational response potential of sea urchins to ocean acidification.

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Effects of ocean acidification and polystyrene microplastics on the oysters Crassostrea gigas: an integrated biomarker and metabolomic approach

Published 19 March 2024 Science Closed
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Highlights

  • Exposure to SPS-MPs alone can cause stronger oxidative stress than LPS-MPs.
  • Exposure to OA can inhibit antioxidant enzyme activity and increase clearance rate.
  • Antagonistic effects were mainly occurred between MPs and OA.
  • The strongest toxic effect was found in combined exposure of SPS-MPs and OA.
  • Energy and antioxidant-related metabolites were altered after combined exposure.

Abstract

The adverse impacts of microplastics (MPs) or ocean acidification (OA) on mollusks have been widely reported, however, little is known about their combined effects on mollusks. The oysters Crassostrea gigas were exposed to two sizes of polystyrene MPs with 1 × 104 particles/L (small polystyrene MPs (SPS-MPs): 6 μm, large polystyrene MPs (LPS-MPs): 50–60 μm) at two pH levels (7.7 and 8.1) for 14 days. The antagonistic effects between MPs and OA on oysters were mainly observed. Single SPS-MPs exposure can induce CAT enzyme activity and LPO level in gills, while LPS-MPs exposure alone can increase PGK and PEPCK gene expression in digestive glands. Ocean acidification can increase clearance rate and inhibit antioxidant enzyme activity, whereas combined exposure of OA and SPS-MPs can affect the metabolomic profile of digestive glands. This study emphasized that the potential toxic effects of MPs under the scene of climate change should be concerned.

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Effects of reduced seawater pH and oil contamination on bacterial communities and biochemical markers of estuarine animal hosts

Published 18 March 2024 Science Closed
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Ecosystem functioning depends on complex interactions between microorganisms, hosts, and the environment. Changes in environmental conditions (e.g., ocean acidification) in combination with anthropogenic pollution have been shown to affect the composition and function of free-living microbial communities, but little is known about the effects these stressors on host-associated communities. This study aims to characterize the response of host-associated bacterial communities of the bottom-dwelling polychaete Hediste diversicolor and the epibenthic gastropod Peringia ulvae to oil contamination and reduced seawater pH. The independent and interactive effects of both stressors were simulated under controlled conditions. The response of host-associated bacterial communities was assessed using the high-throughput sequencing of the 16S rRNA gene and several biochemical markers related to host metabolic pathways, e.g., neurotransmission, anaerobic metabolism, biotransformation, oxidative stress, and energy consumption. In H. diversicolor, reduced seawater pH was associated with a high relative abundance of Cyanobacteria, while in P. ulvae oil contamination was associated with a reduction in the relative abundance of Chitinophagales. In P. ulvae, enrichment with oil hydrocarbon-degrading bacteria suggests a possible role of these organisms in the dispersion of oil hydrocarbon degraders. Furthermore, oil supplementation shifted some specific biochemical markers of gastropods related to oxidative stress and energy consumption, which suggests host stress. In general, the bacterial communities and biochemical markers of the gastropod were more affected by stressors than those of the polychaete. Overall, this study contributes to a better understanding of the response of host-associated bacterial communities of benthic macrofauna to anthropogenic contamination and environmental change.

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Short periods of decreased water flow may modulate long-term ocean acidification in reef-building corals

Published 14 March 2024 Science Closed
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Ocean acidification (OA) poses a major threat to reef-building corals. Although water flow variability is common in coral reefs and modulates coral physiology, the interactive effects of flow and OA on corals remain poorly understood. Therefore, we performed a three-month OA experiment investigating the effect of changes in flow on coral physiology. We exposed the reef-building corals Acropora cytherea, Pocillopora verrucosa, and Porites cylindrica to control (pH 8.0) and OA (pH 7.8) conditions at moderate flow (6 cm s-1) and monitored OA effects on growth. Throughout the experiment, we intermittently exposed all corals to low flow (2 cm s-1) for 1.5 h and measured their photosynthesis:photosynthesis (P:R) ratio under low and moderate flow. On average, corals under OA calcified 18 % less and grew 23 % less in surface area than those at ambient pH. We observed species-specific interactive effects of OA and flow on coral physiology. P:R ratios decreased after 12 weeks of OA in A. cytherea (22 %) and P. cylindrica (28 %) under moderate flow, but were unaffected by OA under low flow. P:R ratios were stable in P. verrucosa. These results suggest that short periods of decreased water flow may modulate OA effects on some coral species, indicating that flow variability is a factor to consider when assessing long-term effects of climate change.

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The tolerance of two marine diatoms to diurnal pH fluctuation under dynamic light condition and ocean acidification scenario

Published 14 March 2024 Science Closed
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Highlights

  • Growth rates of two diatoms remained insensitive to fluctuating pH or seawater acidification.
  • Fluctuating pH enhanced the light-saturated photosynthetic rate of the diatom Thalassiosira weissflogii by 20%.
  • Photosynthetic rates of two diatoms remained unaltered in response to acute pH changes ranging from 7.2 to 8.4.

Abstract

Coastal waters undergo dynamic changes in seawater carbonate chemistry due to natural and anthropogenic factors. Despite this, our current understanding of how coastal phytoplankton respond to fluctuating pH is limited. In the present study, we investigated the physiological responses of two coastal diatoms Thalassiosira pseudonana and Thalassiosira weissflogii to seawater acidification and diurnally fluctuating pH under natural solar irradiance. Seawater acidification did not significantly impact the growth, maximum and effective quantum yield of PSII, and photosynthetic rates of the two species. However, it did increase the maximum relative electron transport rate of T. weissflogii by 11%. Overall, fluctuating pH had neutral or positive effects on both species. It enhanced the light-saturated photosynthetic rate of T. weissflogii by 20% compared to cells grown under seawater acidification condition. Results from the short-term pH exposure experiment revealed that the photosynthetic rates of both species remained unaffected by acute pH changes, indicating their tolerance to varying pH. Nevertheless, it is crucial to consider dynamic pH when predicting changes in primary production in coastal waters, given the interplay of various environmental drivers.

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Changes in isotope fractionation during nitrate assimilation by marine eukaryotic and prokaryotic algae under different pH and CO2 conditions

Published 13 March 2024 Science Closed
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The impact of environmental factors on nitrogen (N) and oxygen (O) isotope effects during algal nitrate assimilation causes uncertainty in the field application of sedimentary N isotope records and nitrate isotopes to understand the marine nitrogen cycle. Ocean acidification is predicted to change nitrogen cycling including nitrate assimilation, but how N and O isotope effects during algal nitrate assimilation vary in response to changes in seawater pH and partial pressure CO2 (pCO2) remains unknown. We measured N and O isotope effects during nitrate assimilation and physiological states of the marine diatom Thalassiosira weissflogii and Synechococcus under different pH (8.1 or 7.8) and pCO2 (400 or 800 μatm) conditions. Low pH and/or high pCO2 equally decreased N and O isotope effects during nitrate assimilation by diatoms possibly due to reducing cellular nitrate efflux/uptake ratio and decreased isotope effects for nitrate uptake, whereas they did not affect those by Synechococcus with low intracellular nitrate concentration and limited nitrate efflux. Our results provide compelling experimental evidence showing different changes in N and O isotope effects during nitrate assimilation by marine eukaryotic and prokaryotic phytoplankton at low pH and/or high pCO2. These findings suggest new insight into environmental controls on variability in the isotope effect during algal nitrate assimilation, and have implications for improving a predictive understanding of N and O isotope tools in acidified oceans.

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Ocean acidification impact on the uptake of trace elements by mussels and their biochemical effects

Published 13 March 2024 Science Closed
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Highlights

  • Copper and cerium bioavailability may increase under ocean acidification.
  • Ocean acidification impacts metal accumulation in mussel gills.
  • Biochemical responses in M. galloprovincialis altered by trace metals and OA.
  • Complex interplay of oxidative stress markers affected by OA and metals.

Abstract

This study delves into the intricate interplay between ocean acidification (OA), metal bioaccumulation, and cellular responses using mussels (Mytilus galloprovincialis) as bioindicators. For this purpose, environmentally realistic concentrations of isotopically labelled metals (Cd, Cu, Ag, Ce) were added to investigate whether the OA increase would modify metal bioaccumulation and induce adverse effects at the cellular level. The study reveals that while certain elements like Cd and Ag might remain unaffected by OA, the bioavailability of Cu and Ce could potentially escalate, leading to amplified accumulation in marine organisms. The present findings highlight a significant rise in Ce concentrations within different mussel organs under elevated pCO2 conditions, accompanied by an increased isotopic fractionation of Ce (140/142Ce), suggesting a heightened potential for metal accumulation under OA. The results suggested that OA influenced metal accumulation in the gills of mussels. Conversely, metal accumulation in the digestive gland was unaffected by OA. The exposure to both trace metals and OA affects the biochemical responses of M. galloprovincialis, leading to increased metabolic capacity, changes in energy reserves, and alterations in oxidative stress markers, but the specific effects on other biomarkers (e.g., lipid peroxidation, some enzymatic responses or acetylcholinesterase activity) were not uniform, suggesting complex interactions between the stressors and the biochemical pathways in the mussels.

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Increased light intensity enhances photosynthesis and biochemical components of red macroalga of commercial importance, Kappaphycus alvarezii, in response to ocean acidification

Published 12 March 2024 Science Closed
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Highlights

  • Effects of light availability and pCO2 on Kappaphycus alvarezii were examined.
  • Moderate increases in light intensity and pCO2 had positive effects on K. alvarezii.
  • OA and high light promoted carbon accumulation, but they had negative impacts on nitrogen.

Abstract

The concentration of atmospheric carbon dioxide (CO2) has increased drastically over the past several decades, resulting in the pH of the ocean decreasing by 0.44 ± 0.005 units, known as ocean acidification (OA). The Kappaphycus alvarezii (Rhodophyta, Solieriaceae), is a commercially and ecologically important red macroalga with significant CO2 absorption potential from seawater. The K. alvarezii also experienced light variations from self-shading and varied cultivation depths. Thus, the aim of present study was to investigate the effects of two pCO2 levels (450 and 1200 ppmv) and three light intensities (50, 100, and 150 μmol photons·m−2·s−1) on photosynthesis and the biochemical components in K. alvarezii. The results of the present study showed that a light intensity of 50 μmol photons·m−2·s−1 was optimal for K. alvarezii photosynthesis with 0.663 ± 0.030 of Fv/Fm and 0.672 ± 0.025 of Fv’/Fm’. Phycoerythrin contents at two pCO2 levels decreased significantly with an increase in light intensity by 57.14–87.76%, while phycocyanin contents only decreased from 0.0069 ± 0.001 mg g−1 FW to 0.0047 ± 0.001 mg g−1 FW with an increase in light intensity at 1200 ppmv of pCO2. Moreover, moderate increases in light intensity and pCO2 had certain positive effects on the physiological performance of K. alvarezii, specifically in terms of increasing soluble carbohydrate production. Although OA and high light levels promoted total organic carbon accumulation (21.730 ± 0.205% DW) in K. alvarezii, they had a negative impact on total nitrogen accumulation (0.600 ± 0.017% DW).

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Quantifying the impacts of multiple stressors on the production of marine benthic resources

Published 11 March 2024 Science Closed
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Coastal ecosystems are among the most heavily affected by climate change and anthropogenic activities, which impacts their diversity, productivity and functioning and puts many of the key ecosystem services that they provide at risk. Although empirical studies have moved beyond single-stressor-single-species experiments with limited extrapolation potential and have increasingly investigated the cumulative effects of simultaneously occurring multiple stressors, consistent generalities have not yet been identified. Upscaling from controlled experiments to natural ecosystems, therefore, remains an unsolved challenge. Disentangling the independent and cumulative effects of multiple stressors across different levels of biological complexity, revealing the underlying mechanisms and understanding how coastal ecosystems may respond to predicted scenarios of global change is critical to manage and protect our natural capital.

In this thesis, I advance multiple stressor research by applying complementary approaches to quantify the impact of multiple stressors on marine benthic resources and thereby help predict the consequences of expected climate change for coastal habitats. First, I present the newly developed experimental platform QIMS (Quantifying the Impacts of Multiple Stressors) that overcomes some of the shortfalls of previous multiple stressor research (Chapter 2). Second, in a novel empirical study, I investigate the independent and combined effects of moderate ocean warming and acidification on the functioning and production of mussels and algae, considering the effects of interspecific interactions in the presence or absence of the respective other species (Chapter 3). Third, I synthesise monitoring data from Dublin Bay (representative of a typical metropolitan estuary) using conditional interference and a Bayesian Network model and provide alternative system trajectories according to different climate change scenarios. From this new model, I deepen the understanding of the complex linkages between environmental conditions and the diversity and functioning of Dublin Bay to support local decision making and management (Chapter 4).

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Physiological impacts of CO2-Induced acidification and UVR on invasive alga Caulerpa racemosa

Published 11 March 2024 Science Closed
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Anthropogenically increasing atmospheric CO2 causes changes in the carbon chemistry of seawater. With these changes, the HCO3− and CO2 concentration of seawater increases, while the pH decreases. CO2-induced ocean acidification by interacting with ultraviolet radiation (UVR) affects the metabolic pathways of seaweeds such as photosynthesis, growth, and nutrient uptake in a species-specific manner. This study was designed to determine the future ecological success of Caulerpa racemosa, an invasive species in the Mediterranean. In laboratory culture, C. racemosa was exposed to CO2-induced low pH (pH: 7.7) with or without UVR (UVA: 1.2 W m−2; UVB: 0.55 W m−2) and its physiological responses were investigated. Maximum quantum yield of photosystem-II (Fv/Fm) and light utilization efficiency (α) of C. racemosa was negatively affected by low pH and UVR. However, low pH increased the rETRmax (maximum relative electron transfer rate) of C. racemosa. This increased rETRmax indicated that the photosynthesis of C. racemosa was not photosynthetically saturated at the ambient inorganic carbon pool. This could be an advantage in competing with other species in the predicted future ocean acidification. The combined effect of low pH and UVR affected the rETRmax of C. racemosa in different ways along with the incubation time. The synergistic effect observed in the first two weeks turned into an antagonistic effect in the last two weeks. The data obtained from this study suggest that incubation time is the most effective factor in the response of C. racemosa to CO2-induced low pH and moderate-level UVR. In addition, our results support the hypothesis that C. racemosa may be one of the species that will benefit from CO2-induced ocean acidification.

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Ocean acidification and food availability impacts on the metabolism and grazing in a cosmopolitan herbivorous protist Oxyrrhis marina

Published 8 March 2024 Science Closed
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The heterotrophic dinoflagellate Oxyrrhis marina is an essential microzooplankton in coastal waters, linking the energy transfer from phytoplankton to higher trophic levels. It is of general significance to investigate how it responds and acclimates to ocean acidification (OA), especially under varied availabilities of food. Here, O. marina was exposed and acclimated to three pCO2 levels (LC: 415, MC:1000, HC:1500 μatm) for 60 days, and then was further grown under the CO2 levels with different levels of food (the microalgae Dunaliella salina) availability for about 8 generations. The OA treatments did not significantly hamper its growth and ingestion rates even under the reduced food availability and starvation (deprived of the microalgae), which significantly reduced its growth rate. While the impacts of OA on the growth and ingestion rates of O. marina were insignificant, the OA treatments appeared to have resulted in a faster decline of the heterotrophic dinoflagellate cells during the starvation period. Nevertheless, the acidic stress under the elevated pCO2 of 1000 or 1500 μatm decreased its respiration by about 53% or 59% with the high and by about 26% or 23% with the low food availability, respectively. Such OA-repressed respiration was also significant during the starvation period. On the other hand, the OA treatments and deprivation of the microalgae synergistically reduced the cellular quota of particulate organic C, N and P, resulting in a reduction of food value of the heterotrophic dinoflagellate as prey. In conclusion, our results show that O. marina is highly resilient to future ocean acidification by reducing its respiration and sustaining its ingestion of microalgae.

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Phosphorus deficiency regulates the growth and photophysiology responses of an economic macroalga Gracilariopsis lemaneiformis to ocean acidification and warming

Published 4 March 2024 Science Closed
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Ocean acidification and warming caused by elevated CO2 are urgent problems facing the marine ecological environment. With the strengthening of environmental governance in China, anthropogenic inputs of terrestrial phosphorus into the coastal ocean have drastically decreased, resulting in frequent phosphorus deficiency in seawater. These environmental factors in the future may affect algal growth, photosynthesis and yield. As an important economic macroalga suitable for large-scale cultivation, Gracilariopsis lemaneiformis is also potentially affected by the coupling of ocean acidification, warming and phosphorus deficiency. In this study, G. lemaneiformis was cultured outdoors under two pCO2 levels (LC, 400 μatm; HC, 1000 μatm), two temperatures (LT, 20 ℃; HT, 24 ℃) and two phosphorus concentrations (LP, 0.1 μmol L−1; HP, 10 μmol L−1) to investigate its growth and photosynthetic performance. The results showed that LP significantly decreased the relative growth rates (RGR) and the maximum photosynthesis rate (Pm) of G. lemaneiformis both under LC and HC conditions. Under P depletion condition, the effects of warming and ocean acidification on the growth and photosynthetic performance of G. lemaneiformis showed an opposite trend, that is, HC caused a decrease in the growth, Pm, maximum relative electron transfer rate (rETRmax) and light utilization efficiency (α) from the rapid light response curve of G. lemaneiformis, and HT improved these parameters. Under LP condition, HC significantly inhibited the RGR of G. lemaneiformis in the LT group but had no significant effect on RGR in the HT group. Additionally, under LP condition, HC insignificantly affected PE and PC contents in the LT group, but significantly reduced these contents in the HT group. These findings suggest that phosphorus deficiency results in a decline in the growth of G. lemaneiformis and, under LP condition, the inhibition effect of ocean acidification on the growth of G. lemaneiformis could be mitigated by warming. This study provides scientific guidance for the field cultivation and selective breeding of G. lemaneiformis in phosphorus-deficient seawater under global climate change.

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Ocean acidification alters shellfish-algae nutritional value and delivery

Published 1 March 2024 Science Closed
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Highlights

  • Ocean acidification promotes microalgae growth.
  • The nutrient value of microalgae is positively altered under acidifying conditions.
  • Nutrient changes in primary producers can have indirect effects through trophic transfer.
  • Fatty acid content of food sources affects shellfish macromolecular ratios.

Abstract

The ecological effects of climate change and ocean acidification (OA) have been extensively studied. Various microalgae are ecologically important in the overall pelagic food web as key contributors to oceanic primary productivity. Additionally, no organism exists in isolation in a complex environment, and shifts in food quality may lead to indirect OA effects on consumers. This study aims to investigate the potential effects of OA on algal trophic composition and subsequent bivalve growth. Here, the growth and nutrient fractions of Chlorella sp., Phaeodactylum tricornutum and Chaetocetos muelleri were used to synthesize and assess the impact of OA on primary productivity. Total protein content, total phenolic compounds, and amino acid (AA) and fatty acid (FA) content were evaluated as nutritional indicators. The results demonstrated that the three microalgae responded positively to OA in the future environment, significantly enhancing growth performance and nutritional value as a food source. Additionally, certain macromolecular fractions found in consumers are closely linked to their dietary sources, such as phenylalanine, C14:0, C16:0, C16:1, C20:1n9, C18:0, and C18:3n. Our findings illustrate that OA affects a wide range of crucial primary producers in the oceans, which can disrupt nutrient delivery and have profound impacts on the entire marine ecosystem and human food health.

Continue reading ‘Ocean acidification alters shellfish-algae nutritional value and delivery’

Probing the role of carbonic anhydrase in shell repair mechanisms in the eastern oyster Crassostrea virginica under experimental acidification stress

Published 29 February 2024 Science Closed
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Highlights

  • Shell repair dramatically decreased in oysters after chronic high pCO2 exposure.
  • Carbonic anhydrase (CA) inhibition further reduces shell repair.
  • Oysters increased hemocyte intracellular pH under low pH seawater.
  • Ability to increase intracellular pH of hemocytes was lost when CA was inhibited.
  • CA plays a role in maintaining calcification under low pH.

Abstract

The reduction in pH from atmospheric inputs of CO2 (ocean acidification, OA) threatens marine calcifiers, including the eastern oyster (Crassostrea virginica), that precipitate biogenic CaCO3 for shell formation. Recent investigations have demonstrated that alterations in gene expression enable bivalves to respond to episodic low pH. Evidence generated from several studies highlighted the importance of upregulating genes related to biomineralization, ion transport, and acid-base balance such as carbonic anhydrase (CA) genes. Two experiments were designed to evaluate the effect of acidification on calcification processes and to probe the specific role of CA in oyster resilience to low pH. First, adult oysters were exposed to eight months of chronic acidification stress (pH ∼7.3, pCO2 ∼3300 ppm) or control conditions (pH ∼7.9, pCO2 ∼500 ppm) before shells were artificially damaged and shell repair monitored. Results showed a dramatic decrease in shell regeneration after chronic high pCO2 exposure (only 30% of oysters regrew any shell) suggesting that mechanisms that promote calcification under high pCO2 conditions may not be sustainable for extended periods of time. To further explore these mechanisms, a second experiment was designed by focusing on the role of CA in mitigating acidification stress. Here, adult oysters received an injection of acetazolamide in dimethyl sulfoxide (DMSO) to inhibit CA or DMSO (control) before rearing in control (pH ∼8.1, pCO2 ∼340 ppm) or acidified (pH ∼7.3, pCO2 ∼3300 ppm) conditions. After three weeks, oyster shells were damaged and shell repair monitored. Oysters incubated at low pH seawater with CA inhibition had the least amount of shell regeneration at the end of 21-day regrowth period. Interestingly, oysters were able to increase intracellular pH (pHi) of hemocytes under low pH conditions; however, this ability was significantly diminished with CA inhibition. Results highlight the role of CA in maintaining calcification under low pH conditions by establishing an intracellular environment favorable to calcium carbonate precipitation.

Continue reading ‘Probing the role of carbonic anhydrase in shell repair mechanisms in the eastern oyster Crassostrea virginica under experimental acidification stress’

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