Posts Tagged 'virus'

Insignificant response of bacterioplankton community to elevated pCO2 during a short-term microcosm experiment in a subtropical eutrophic coastal ecosystem

Ocean acidification, as one of the major consequences of global climate change, markedly affects multiple ecosystem functions in disparate marine environments from coastal habitats to the deep ocean. Evaluation of the responses of marine microbial community to the increasing partial pressure of CO2 (pCO2) is crucial to explore the microbe-driven biogeochemical processes in the future ocean. In this study, a microcosm incubation of eutrophic coastal water from Xiamen Bay under elevated pCO2 (about 1,000 μatm) and control (ambient air, about 380–410 μatm) conditions was conducted to investigate the effect of ocean acidification on the natural bacterioplankton community. During the 5-day incubation period, the chlorophyll a concentration and bacterioplankton abundance were not significantly affected by increased pCO2. Hierarchical clustering and non-metric multidimensional scaling analysis based on Bray-Curtis similarity among the bacterioplankton community derived from the 16S rRNA genes revealed an inconspicuous impact of elevated pCO2 on the bacterial community. During the incubation period, Proteobacteria, Bacteroidetes, Actinobacteria, Cyanobacteria, and Epsilonbacteraeota were predominant in all microcosms. Despite the distinct temporal variation in the composition of the bacterioplankton community during the experimental period, statistical analyses showed that no significant difference was found on bacterioplankton taxa between elevated pCO2 and control, indicating that the bacterioplankton at the population-level were also insensitive to elevated pCO2. Our results therefore suggest that the bacterioplankton communities in the fluctuating and eutrophic coastal ecosystems appear to be adaptable to the short-term elevated pCO2.

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Elevated pCO2 impedes succession of phytoplankton community from diatoms to dinoflagellates along with increased abundance of viruses and bacteria

Eutrophic coastal regions are highly productive and greatly influenced by human activities. Primary production supporting the coastal ecosystems is supposed to be affected by progressive ocean acidification driven by increasing CO2 emissions. In order to investigate the effects of high pCO2 (HC) on eutrophic plankton community structure and ecological functions, we employed 9 mesocosms and carried out an experiment under ambient (∼410 ppmv) and future high (1000 ppmv) atmospheric pCO2 conditions, using in situ plankton community in Wuyuan Bay, East China Sea. Our results showed that HC along with natural seawater temperature rise significantly boosted biomass of diatoms with decreased abundance of dinoflagellates in the late stage of the experiment, demonstrating that HC repressed the succession from diatoms to dinoflagellates, a phenomenon observed during algal blooms in the East China Sea. HC did not significantly influence the primary production or biogenic silica contents of the phytoplankton assemblages. However, the HC treatments increased the abundance of viruses and heterotrophic bacteria, reflecting a refueling of nutrients for phytoplankton growth from virus-mediated cell lysis and bacterial degradation of organic matters. Conclusively, our results suggest that increasing CO2 concentrations can modulate plankton structure including the succession of phytoplankton community and the abundance of viruses and bacteria in eutrophic coastal waters, which may lead to altered biogeochemical cycles of carbon and nutrients.

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Editorial: Microbial response to a rapidly changing marine environment: global warming and ocean acidification

The World Ocean is undergoing rapid and substantial changes, particularly, in terms of warming and acidification. Global sea surface temperatures have risen by 0.7°C in recent years (2005–2014) relative to pre-industrial times (1870–1899) (Gattuso et al., 2015). The ocean pH is decreasing in response to the increasing anthropogenic CO2 emissions (Ocean Acidification; OA). This clear trend of ocean warming and acidification was documented in the fifth Assessment Report (AR5) by Intergovernmental Panel on Climate Change (IPCC). The warming of the surface ocean could increase stratification, suppress transport of nutrients into the upper photic zone and alter hydrographic properties or patterns of ocean circulation. The effects of OA include the changes of seawater carbonate chemistry such as an increase in partial pressure of seawater CO2 (pCO2) concentration and a decrease in calcium carbonate (CaCO3) saturation state (Royal Society, 2005IPCC, 2014). Consequently, the warming and acidification will have substantial impacts on the growth and survival of marine organisms (e.g., Brander, 2010Doney et al., 2012Hollowed et al., 2013). In particular, microbes, as a vital component of the marine ecosystem that includes microalga (phytoplankton), protists, fungi, viruses, and the two main groups of prokaryotes (Bacteria and Archaea), are vulnerable to these environmental changes. Since these microscopic organisms drive major biogeochemical cycles and support higher food webs globally, physiological, and ecological alterations in microbial communities caused by marine environmental changes can herald changes not only in pathways of energy transfer through the food web but also in global biogeochemical cycles. Considering the microbial communities’ pivotal roles in the marine ecosystem and biogeochemical cycles, it is important to understand recent changes in microbial communities and how future changes might arise under the ongoing environmental forcing of the warming and acidifying oceans.

The goal of this Research Topic was to collect studies on present and future possible changes in microbial communities with respect to environmental change and their consequences within various oceans. The topic contains 10 diverse scientific contributions on many fundamental questions related to microbial communities in oceanic environments, and report on physiological and ecological responses of microbial communities to environmental changes. The studies from a range of geographic regions were collected, from more coastal systems to open oceans, and include Tera Nova Bay in Antarctica, Mediterranean waters, the East/Japan Sea, the South China Sea, the Western Pacific Ocean, the South Pacific Ocean, and the Ross Sea of the Southern Ocean. In the context of taxonomic diversity, heterotrophic bacteria, viruses, microalga, and other prokaryotes were included in this Research Topic.

Out of the 10 works published, seven of them are focused on the phytoplankton communities, or single species of microalgae, or environmental drivers. Kim et al. describe the seasonal variability in the macromolecular composition of the sea surface in front of the Korean station in Terra Nova Bay, Ross Sea, Antarctica. They show changes in organic matter composition mainly derived by changes in phytoplankton metabolism between the productive and the non-productive season. Their study helps us to understand the effect of future climate change on the composition of organic matter derived from phytoplankton in the polar oceans. Biochemical compositions such as macromolecular and amino acids of phytoplankton in the Ross Sea, Antarctica was investigated by Jo et al.. They found distinct differences in the biochemical composition between two major bloom-forming phytoplankton groups (diatoms and Phaeocystis antarctica). They discuss how these different compositions may highlight the different strategies of these two phytoplankton communities to cope with ongoing environmental changes in the Antarctic Ocean. Kang et al. demonstrate the differences in carbon uptake rates and intracellular biochemical compositions between two different size fractions of phytoplankton to understand the ecological roles of the small phytoplankton in terms of food quantity and quality in the East/Japan Sea where the water temperature has rapidly increased. Their findings show that the increase of small phytoplankton under the warming ocean conditions could negatively affect the primary productivity and caloric content, with further consequences on the marine food webs. The photosynthetic responses to oceanic physio-chemical conditions and phytoplankton communities in the oligotrophic Western Pacific Ocean were presented by Wei et al.. Their study found that the important biotic variables influencing Fv/Fm are diatoms, Prochlorococcus, and picoeukaryotes, whilst the maximum of primary production is closely related to cyanobacteria, dinoflagellates, and Synechococcus. The detailed investigation of a chromophytic phytoplankton community using high-throughput sequencing of rbcL genes in the Western Pacific Ocean was presented by Pujari et al.. The authors found that the diversity of RuBisCO encoding rbcL gene varies with depth and across latitudes in the Western Pacific Ocean. The variation observed in chromophytic phytoplankton suggests the strong influence of environmental variables on biological production induced by oceanographic features. Thangaraj et al. investigated comprehensive proteomic profiling of diatom Skeletonema dohrnii with a change of temperature and silicate deprivation based on the iTRAQ proteomic approach, to understand the effect of the temperature and nutrient on the physiology of marine diatoms growth and photosynthesis. Their study shows that the proteome analysis for environmental stress-response of diatoms could extend our understanding for the potential impacts of climate change on the physiological adjustment to the metabolic process of phytoplankton. Sow et al. present a clear and concise description of the biogeography of Phaeocystis along a transect from the ice edge to the equator in the South Pacific Ocean, by way of high-throughput 18S rRNA gene sequencing. Their study shows that Phaeocystis could be occasionally highly abundant and diverse in the South Pacific Ocean, whereas the oceanic fronts could be the driving force for the distribution and structure of Phaeocystis assemblages in the ocean. Their work greatly expands our knowledge about the biodiversity patterns and abundances of Phaeocystis as a globally important nano-eukaryote.

Three of the 10 published works have focused on the response of viruses, prokaryotes or microbial communities to environmental stress. The response of viruses to two anthropogenic stressors (OA and eutrophication) was presented by Malits et al.. Their study demonstrates that the effect of OA on viral dynamics and viral-mediated mortality varies depending on the nutrient regime of the studied systems. It helps us to understand how viral-mediated mortality of microbes (VMMM) can be modified with environmental forcing. Another work looks into the contribution of grazers and viruses in controlling ecologically distinct prokaryotic sub-groups (i.e., high nucleic acid (HNA) and low nucleic acid (LNA) cells) along a cross-shore nutrient gradient in the northern South China Sea (Hu et al.). Their study shows how the nutrient regime influences the fate of ecologically relevant prokaryotic groups in the actual context of global warming and the anticipated oligotrophication of the future ocean. Sörenson et al. address the resilience of a marine microbial community, cultivated in an outdoor photobioreactor, when exposed to a naturally occurring seasonal stress. Differential gene expression analyses suggest that community function at warm temperatures is based on concomitant utilization of inorganic and organic carbon assigned to autotrophs and heterotrophs, while at colder temperatures, the uptake of organic carbon was performed primarily by autotrophs. Overall, the microbial community maintains a similar level of diversity and function within and across autotrophic and heterotrophic levels, confirming the cross-scale resilience theory.

The topics of the papers published in this Research Topic range from viruses, prokaryotes to phytoplankton and cover microbial communities from the various oceans. The studies confirm that the changes already occurring in ocean environments affect the metabolism and physiology of microbial communities, and further suggest that future changes will impact the physiological and ecological function or strategy of the microbial community in the marine ecosystem. Since most of these studies focus on the response of a single taxonomic population of microbes to environmental changes, our special issue highlights the need for studies to understand how ecological interactions occurring within and among the microbial community in the changing ocean will affect ecosystem structure and function. Finally, we hope that the group of papers that we have drawn together here will be a valuable addition to the accumulating observational evidence of how microbial communities are responding to the climate-related changes and consequently useful for evaluating and predicting the ongoing and future responses of marine ecosystems associated with the global climate change.

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Viral-mediated microbe mortality modulated by ocean acidification and eutrophication: consequences for the carbon fluxes through the microbial food web

Anthropogenic carbon emissions are causing changes in seawater carbonate chemistry including a decline in the pH of the oceans. While its aftermath for calcifying microbes has been widely studied, the effect of ocean acidification (OA) on marine viruses and their microbial hosts is controversial, and even more in combination with another anthropogenic stressor, i.e., human-induced nutrient loads. In this study, two mesocosm acidification experiments with Mediterranean waters from different seasons revealed distinct effects of OA on viruses and viral-mediated prokaryotic mortality depending on the trophic state and the successional stage of the plankton community. In the winter bloom situation, low fluorescence viruses, the most abundant virus-like particle (VLP) subpopulation comprising mostly bacteriophages, were negatively affected by lowered pH with nutrient addition, while the bacterial host abundance was stimulated. High fluorescence viruses, containing cyanophages, were stimulated by OA regardless of the nutrient conditions, while cyanobacteria of the genus Synechococcus were negatively affected by OA. Moreover, the abundance of very high fluorescence viruses infecting small haptophytes tended to be lower under acidification while their putative hosts’ abundance was enhanced, suggesting a direct and negative effect of OA on viral–host interactions. In the oligotrophic summer situation, we found a stimulating effect of OA on total viral abundance and the viral populations, suggesting a cascading effect of the elevated pCO2 stimulating autotrophic and heterotrophic production. In winter, viral lysis accounted for 30 ± 16% of the loss of bacterial standing stock per day (VMMBSS) under increased pCO2 compared to 53 ± 35% in the control treatments, without effects of nutrient additions while in summer, OA had no significant effects on VMMBSS (35 ± 20% and 38 ± 5% per day in the OA and control treatments, respectively). We found that phage production and resulting organic carbon release rates significantly reduced under OA in the nutrient replete winter situation, but it was also observed that high nutrient loads lowered the negative effect of OA on viral lysis, suggesting an antagonistic interplay between these two major global ocean stressors in the Anthropocene. In summer, however, viral-mediated carbon release rates were lower and not affected by lowered pH. Eutrophication consistently stimulated viral production regardless of the season or initial conditions. Given the relevant role of viruses for marine carbon cycling and the biological carbon pump, these two anthropogenic stressors may modulate carbon fluxes through their effect on viruses at the base of the pelagic food web in a future global change scenario.

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Ocean acidification induces changes in virus–host relationships in Mediterranean benthic ecosystems

Acidified marine systems represent “natural laboratories”, which provide opportunities to investigate the impacts of ocean acidification on different living components, including microbes. Here, we compared the benthic microbial response in four naturally acidified sites within the Southern Tyrrhenian Sea characterized by different acidification sources (i.e., CO2 emissions at Ischia, mixed gases at Panarea and Basiluzzo and acidified freshwater from karst rocks at Presidiana) and pH values. We investigated prokaryotic abundance, activity and biodiversity, viral abundance and prokaryotic infections, along with the biochemical composition of the sediment organic matter. We found that, despite differences in local environmental dynamics, viral life strategies change in acidified conditions from mainly lytic to temperate lifestyles (e.g., chronic infection), also resulting in a lowered impact on prokaryotic communities, which shift towards (chemo)autotrophic assemblages, with lower organic matter consumption. Taken together, these results suggest that ocean acidification exerts a deep control on microbial benthic assemblages, with important feedbacks on ecosystem functioning.

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A review of the potential effects of climate change on disseminated neoplasia with an emphasis on efficient detection in marine bivalve populations


  • Ocean warming is likely to favour disseminated neoplasia outbreaks.
  • The effect of seasonality on disseminated neoplasia seems species specific.
  • Detailed prevalence and environmental data are required to understand outbreak dynamics.
  • State of the art detection methods will be of key importance to obtain insights.


Climate change not only directly impacts marine environments by shifting water temperatures, salinity, pH and dissolved oxygen concentrations, but may also indirectly contribute to the emergence of additional ecosystem stressors, such as infectious diseases, including bivalve disseminated neoplasia. Disseminated neoplasia, a form of cancer found in some bivalves – recently discovered to be transmissible in at least six species – has been shown to impair bivalve health and fitness, with occasional mass outbreaks causing high levels of mortality. As the ability of the host bivalve to respond to disseminated neoplasia, and the survival and transmissibility of disseminated neoplasia both depend on environmental factors, it is crucial to understand the interaction between climate change and disseminated neoplasia epidemiology. Furthermore, with bivalves being species of high ecological and economic importance, there is a rising need for the development of efficient disseminated neoplasia detection tools in order to explore potential effects, mitigate and potentially prevent deleterious disseminated neoplasia outbreaks. Therefore, in this study, we reviewed the current knowledge of climate impacted environmental parameters on disseminated neoplasia and identified good practices and methodology for the detection of transmissible disseminated neoplasia in the wild. By exploring the potential effects changing climate has on disseminated neoplasia dynamics, we identified future research directions in order to advance the field. This included using state of the art disease detection methods and taking in account species’ ecological niches to understand the dynamic of disseminated neoplasia outbreaks in the wild and to investigate whether disseminated neoplasia is present in freshwater ecosystems. Finally, we provided a comprehensive step-by-step guideline for an evidence-based detection of this disease in marine ecosystems.

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Potential impact of global climate change on benthic deep-sea microbes

Benthic deep-sea environments are the largest ecosystem on Earth, covering ∼65% of the Earth surface. Microbes inhabiting this huge biome at all water depths represent the most abundant biological components and a relevant portion of the biomass of the biosphere, and play a crucial role in global biogeochemical cycles. Increasing evidence suggests that global climate changes are affecting also deep-sea ecosystems, both directly (causing shifts in bottom-water temperature, oxygen concentration and pH) and indirectly (through changes in surface oceans’ productivity and in the consequent export of organic matter to the seafloor). However, the responses of the benthic deep-sea biota to such shifts remain largely unknown. This applies particularly to deep-sea microbes, which include bacteria, archaea, microeukaryotes and their viruses. Understanding the potential impacts of global change on the benthic deep-sea microbial assemblages and the consequences on the functioning of the ocean interior is a priority to better forecast the potential consequences at global scale. Here we explore the potential changes in the benthic deep-sea microbiology expected in the coming decades using case studies on specific systems used as test models.

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Alterations in microbial community composition with increasing fCO2: a mesocosm study in the eastern Baltic Sea (update)

Ocean acidification resulting from the uptake of anthropogenic carbon dioxide (CO2) by the ocean is considered a major threat to marine ecosystems. Here we examined the effects of ocean acidification on microbial community dynamics in the eastern Baltic Sea during the summer of 2012 when inorganic nitrogen and phosphorus were strongly depleted. Large-volume in situ mesocosms were employed to mimic present, future and far future CO2 scenarios. All six groups of phytoplankton enumerated by flow cytometry ( <  20 µm cell diameter) showed distinct trends in net growth and abundance with CO2 enrichment. The picoeukaryotic phytoplankton groups Pico-I and Pico-II displayed enhanced abundances, whilst Pico-III, Synechococcus and the nanoeukaryotic phytoplankton groups were negatively affected by elevated fugacity of CO2 (fCO2). Specifically, the numerically dominant eukaryote, Pico-I, demonstrated increases in gross growth rate with increasing fCO2 sufficient to double its abundance. The dynamics of the prokaryote community closely followed trends in total algal biomass despite differential effects of fCO2 on algal groups. Similarly, viral abundances corresponded to prokaryotic host population dynamics. Viral lysis and grazing were both important in controlling microbial abundances. Overall our results point to a shift, with increasing fCO2, towards a more regenerative system with production dominated by small picoeukaryotic phytoplankton.

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Combined effects of elevated pCO2 and warming facilitate Cyanophage infections

Elevated pCO2 and warming are generally expected to influence cyanobacterial growth, and may promote the formation of blooms. Yet, both climate change factors may also influence cyanobacterial mortality by favoring pathogens, such as viruses, which will depend on the ability of the host to adapt. To test this hypothesis, we grew Plectonema boryanum IU597 under two temperature (25 and 29°C) and two pCO2 (400 and 800 μatm) conditions for 1 year, after which all treatments were re-exposed to control conditions for a period of 3 weeks. At several time points during the 1 year period, and upon re-exposure, we measured various infection characteristics of it associated cyanophage PP, including the burst size, latent period, lytic cycle and the efficiency of plaquing (EOP). As expected, elevated pCO2 promoted growth of P. boryanumequally over the 1 year period, but warming did not. Burst size increased in the warm treatment, but decreased in both the elevated pCO2 and combined treatment. The latent period and lytic cycle both became shorter in the elevated pCO2 and higher temperature treatment, and were further reduced by the combined effect of both factors. Efficiency of plaquing (EOP) decreased in the elevated pCO2 treatment, increased in the warm treatment, and increased even stronger in the combined treatment. These findings indicate that elevated pCO2 enhanced the effect of warming, thereby further promoting the virus infection rate. The re-exposure experiments demonstrate adaptation of the host leading to higher biomass build-up with elevated pCO2 over the experimental period, and lower performance upon re-exposure to control conditions. Similarly, virus burst size and EOP increased when given warm adapted host, but were lower as compared to the control when the host was re-exposed to control conditions. Our results demonstrate that adaptation but particularly physiological acclimation to climate change conditions favored viral infections, while limited host plasticity and slow adaptation after re-exposure to control conditions impeded host biomass build-up and viral infections.

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Influence of ocean acidification and deep water upwelling on oligotrophic plankton communities in the subtropical North Atlantic: Insights from an in situ mesocosm study

Oceanic uptake of anthropogenic carbon dioxide (CO2) causes pronounced shifts in marine carbonate chemistry and a decrease in seawater pH. Increasing evidence indicates that these changes – summarized by the term ocean acidification (OA) – can significantly affect marine food webs and biogeochemical cycles. However, current scientific knowledge is largely based on laboratory experiments with single species and artificial boundary conditions, whereas studies of natural plankton communities are still relatively rare. Moreover, the few existing community-level studies were mostly conducted in rather eutrophic environments, while less attention has been paid to oligotrophic systems such as the subtropical ocean gyres.

Here we report from a recent in situ mesocosm experiment off the coast of Gran Canaria in the eastern subtropical North Atlantic, where we investigated the influence of OA on the ecology and biogeochemistry of plankton communities in oligotrophic waters under close-to-natural conditions. This paper is the first in this Research Topic of Frontiers in Marine Biogeochemistry and provides (1) a detailed overview of the experimental design and important events during our mesocosm campaign, and (2) first insights into the ecological responses of plankton communities to simulated OA over the course of the 62-day experiment.

One particular scientific objective of our mesocosm experiment was to investigate how OA impacts might differ between oligotrophic conditions and phases of high biological productivity, which regularly occur in response to upwelling of nutrient-rich deep water in the study region. Therefore, we specifically developed a deep water collection system that allowed us to obtain ~85 m3 of seawater from ~650 m depth. Thereby, we replaced ~20% of each mesocosm’s volume with deep water, and thus successfully simulated a deep water upwelling event that induced a pronounced plankton bloom.

Our study revealed significant effects of OA on the entire food web, leading to a restructuring of plankton communities that emerged during the oligotrophic phase, and was further amplified during the bloom that developed in response to deep water addition. Such CO2-related shifts in plankton community composition could have consequences for ecosystem productivity, biomass transfer to higher trophic levels, and biogeochemical element cycling of oligotrophic ocean regions.

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Change in Emiliania huxleyi virus assemblage diversity but not in host genetic composition during an ocean acidification mesocosm experiment

Effects of elevated pCO2 on Emiliania huxleyi genetic diversity and the viruses that infect E. huxleyi (EhVs) have been investigated in large volume enclosures in a Norwegian fjord. Triplicate enclosures were bubbled with air enriched with CO2 to 760 ppmv whilst the other three enclosures were bubbled with air at ambient pCO2; phytoplankton growth was initiated by the addition of nitrate and phosphate. E. huxleyi was the dominant coccolithophore in all enclosures, but no difference in genetic diversity, based on DGGE analysis using primers specific to the calcium binding protein gene (gpa) were detected in any of the treatments. Chlorophyll concentrations and primary production were lower in the three elevated pCO2 treatments than in the ambient treatments. However, although coccolithophores numbers were reduced in two of the high-pCO2 treatments; in the third, there was no suppression of coccolithophores numbers, which were very similar to the three ambient treatments. In contrast, there was considerable variation in genetic diversity in the EhVs, as determined by analysis of the major capsid protein (mcp) gene. EhV diversity was much lower in the high-pCO2 treatment enclosure that did not show inhibition of E. huxleyi growth. Since virus infection is generally implicated as a major factor in terminating phytoplankton blooms, it is suggested that no study of the effect of ocean acidification in phytoplankton can be complete if it does not include an assessment of viruses.

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Special edition of Estuarine, Coastal and Shelf Science – “Ocean acidification in the Mediterranean Sea: pelagic mesocosm experiments”

The topic of ocean acidification has received extensive attention in a recently published special edition of the journal Estuarine, Coastal and Shelf Science. Volume 186, Part A presents a series of 12 research papers focusing on pelagic mesocosm experiments conducted in the Mediterranean Sea in 2012 and 2013. Plankton plays a key role in the global carbon cycle. It is therefore important to project the evolution of plankton community structure and function in a future high-CO2 world. Several results from experiments conducted at the community level have shown increased rates of community primary production and shifts in community composition as a function of increasing pCO2. However, the great majority of these – experiments have been performed under high natural or nutrient-enriched conditions and very few data are available in areas with naturally low levels of nutrient and chlorophyll i.e. oligotrophic areas such as the Mediterranean Sea, although they represent a large and expanding part of the ocean surface. In the frame of the European Mediterranean Sea Acidification in a changing climate project (MedSeA;, large-scale in situ mesocosms (9 x 50 m3, 12 m deep) have been used to quantify the potential effects of CO2 enrichment in two coastal areas of the Mediterranean Sea: the bay of Calvi (Corsica, France) in June/July 2012 and the bay of Villefranche (France) in February/March 2013. These two experiments gathered the expertise of more than 25 scientists from 7 institutes and 6 countries (France, Greece, Spain, UK, Italy, Belgium, US).

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Ocean acidification and viral replication cycles: Frequency of lytically infected and lysogenic cells during a mesocosm experiment in the NW Mediterranean Sea

The frequency of lytically infected and lysogenic cells (FLIC and FLC, respectively) was estimated during an in situ mesocosm experiment studying the impact of ocean acidification on the plankton community of a low nutrient low chlorophyll (LNLC) system in the north-western Mediterranean Sea (Bay of Villefranche, France) in February/March 2013. No direct effect of elevated partial pressure of CO2 (pCO2) on viral replication cycles could be detected. FLC variability was negatively correlated to heterotrophic bacterial and net community production as well as the ambient bacterial abundance, confirming that lysogeny is a prevailing life strategy under unfavourable-for-the-hosts conditions. Further, the phytoplankton community, assessed by chlorophyll a concentration and the release of >0.4 μm transparent exopolymeric particles, was correlated with the occurrence of lysogeny, indicating a possible link between photosynthetic processes and bacterial growth. Higher FLC was found occasionally at the highest pCO2-treated mesocosm in parallel to subtle differences in the phytoplankton community. This observation suggests that elevated pCO2 could lead to short-term alterations in lysogenic dynamics coupled to phytoplankton-derived processes. Correlation of FLIC with any environmental parameter could have been obscured by the sampling time or the synchronization of lysis to microbial processes not assessed in this experiment. Furthermore, alterations in microbial and viral assemblage composition and gene expression could be a confounding factor. Viral-induced modifications in organic matter flow affect bacterial growth and could interact with ocean acidification with unpredictable ecological consequences.

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Shifts in the microbial community in the Baltic Sea with increasing CO2

Ocean acidification, due to dissolution of anthropogenically produced carbon dioxide is considered a major threat to marine ecosystems. The Baltic Sea, with extremely low salinity and thus low pH buffering capacity, is likely to experience stronger variation in pH than the open ocean with increasing atmospheric carbon dioxide. We examined the effects of ocean acidification on the microbial community during summer using large volume in situ mesocosms to simulate present to future and far future scenarios. We saw distinct trends with increasing CO2 in each of the 6 groups of phytoplankton with diameters below 20 μm that we enumerated by flow cytometry. Of these groups two picoeukaryotic groups increased in abundance whilst the other groups, including prokaryotic Synechococcus spp., decreased with increasing CO2. Gross growth rates increased with increasing CO2 in the dominant picoeukaryote group sufficient to double their abundances whilst reduced grazing allowed the other picoeukaryotes to flourish at higher CO2. Significant increases in lysis rates were seen at higher CO2 in these two picoeukaryote groups. Converting abundances to particulate organic carbon we saw a large shift in the partitioning of carbon between the size fractions which lasted throughout the experiment. The heterotrophic prokaryotes largely followed the algal biomass with responses to increasing CO2 reflecting the altered phytoplankton community dynamics. Similarly, higher viral abundances at higher CO2 seemed related to increased prokaryote biomass. Viral lysis and grazing were equally important controlling prokaryotic abundances. Overall our results point to a shift towards a more regenerative system with potentially increased productivity but reduced carbon export.

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Impact of CO2 leakage from sub-seabed carbon dioxide capture and storage (CCS) reservoirs on benthic virus–prokaryote interactions and functions

Atmospheric CO2 emissions are a global concern due to their predicted impact on biodiversity, ecosystems functioning, and human life. Among the proposed mitigation strategies, CO2 capture and storage, primarily the injection of CO2 into marine deep geological formations has been suggested as a technically practical option for reducing emissions. However, concerns have been raised that possible leakage from such storage sites, and the associated elevated levels of pCO2 could locally impact the biodiversity and biogeochemical processes in the sediments above these reservoirs. Whilst a number of impact assessment studies have been conducted, no information is available on the specific responses of viruses and virus–host interactions. In the present study, we tested the impact of a simulated CO2 leakage on the benthic microbial assemblages, with specific focus on microbial activity and virus-induced prokaryotic mortality (VIPM). We found that exposure to levels of CO2 in the overlying seawater from 1,000 to 20,000 ppm for a period up to 140 days, resulted in a marked decrease in heterotrophic carbon production and organic matter degradation rates in the sediments, associated with lower rates of VIPM, and a progressive accumulation of sedimentary organic matter with increasing CO2 concentrations. These results suggest that the increase in seawater pCO2 levels that may result from CO2 leakage, can severely reduce the rates of microbial-mediated recycling of the sedimentary organic matter and viral infections, with major consequences on C cycling and nutrient regeneration, and hence on the functioning of benthic ecosystems.

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Ocean acidification effect on prokaryotic metabolism tested in two diverse trophic regimes in the Mediterranean Sea

Notwithstanding the increasing amount of researches on the effect of ocean acidification (OA) on marine ecosystems, no consent has emerged on its consequences on many prokaryote-mediated processes. Two mesocosm experiments were performed in coastal Mediterranean areas with different trophic status: the summer oligotrophic Bay of Calvi (BC, Corsica, France) and the winter mesotrophic Bay of Villefranche (BV, France). During these experiments, nine enclosures (∼54 m3) were deployed: 3 unamended controls and 6 elevated CO2, following a gradient up to 1,250 μatm. We present results involving free-living viral and prokaryotic standing stocks, bacterial carbon production, abundance of highly active cells (CTC+), and degradation processes (beta-glucosidase, chitinase, leucine-aminopeptidase, lipase and alkaline phosphatase activities).

The experiments revealed clear differences in the response of the two prokaryotic communities to CO2 manipulation. Only abundances of heterotrophic prokaryotes, viruses and lipase activity were not affected by CO2 manipulation at both locations. On the contrary, the percent of CTC+ was positively correlated to CO2 only in BC, concomitantly to a bulk reduction of [3H]-leucine uptake. The other tested parameters showed a different response at the two sites suggesting that the trophic regime of the systems plays a fundamental role on the effect of OA on prokaryotes through indirect modifications of the available substrate.

Modified degradation rates may affect considerably the export of organic matter to the seafloor and thus ecosystem functioning within the water column. Our results highlight the need to further analyse the consequences of OA in oligotrophic ecosystems with particular focus on dissolved organic matter.

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Effect of ocean warming and acidification on a plankton community in the NW Mediterranean Sea

The effect of ocean warming and acidification was investigated on a natural plankton assemblage from an oligotrophic area, the bay of Villefranche (NW Mediterranean Sea). The assemblage was sampled in March 2012 and exposed to the following four treatments for 12 days: control (∼360 μatm, 14°C), elevated pCO2 (∼610 μatm, 14°C), elevated temperature (∼410 μatm, 17°C), and elevated pCO2 and temperature (∼690 μatm, 17°C). Nutrients were already depleted at the beginning of the experiment and the concentrations of chlorophyll a (chl a), heterotrophic prokaryotes and viruses decreased, under all treatments, throughout the experiment. There were no statistically significant effects of ocean warming and acidification, whether in isolation or combined, on the concentrations of nutrients, particulate organic matter, chl a and most of the photosynthetic pigments. Furthermore, 13C labelling showed that the carbon transfer rates from 13C-sodium bicarbonate into particulate organic carbon were not affected by seawater warming nor acidification. Rates of gross primary production followed the general decreasing trend of chl a concentrations and were significantly higher under elevated temperature, an effect exacerbated when combined to elevated pCO2 level. In contrast to the other algal groups, the picophytoplankton population (cyanobacteria, mostly Synechococcus) increased throughout the experiment and was more abundant in the warmer treatment though to a lesser extent when combined to high pCO2 level. These results suggest that under nutrient-depleted conditions in the Mediterranean Sea, ocean acidification has a very limited impact on the plankton community and that small species will benefit from warming with a potential decrease of the export and energy transfer to higher trophic levels.

Continue reading ‘Effect of ocean warming and acidification on a plankton community in the NW Mediterranean Sea’

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