Posts Tagged 'prokaryotes'

Impact of ocean acidification on the intestinal microbiota of the marine sea bream (Sparus aurata L.)

Within a scenario of increasing atmospheric CO2 and ocean acidification (OA), it is highly relevant to investigate its impacts not only on fish performance but also on fish intestinal microbiome and how that reflects on host performance and health. The main objective of this study was to establish if the intestinal microbiota of the sea bream (Sparus aurata) was affected by high level of CO2 in line with the predictions for this century. The bacterial communities of the intestinal fluid were characterized in animals kept at the present-day level of CO2 (400 μatm) and in animals switched to high CO2 (1200 μatm) for 1 month. Bacterial taxa identification was based on molecular methods, using the DNA coding for the 16S ribosomal RNA and primers targeting the regions V1–V3. Amplicons obtained from DNA samples of animals in the same tank were combined, cloned to obtain a bacterial DNA library, and the clones were sequenced. No significant differences were found between the two treatments for alpha diversity. However, beta diversity analysis revealed distinct dysbiosis in response to hypercapnia, with phylum Firmicutes absent from the bacterial communities of fish exposed to 1200 μatm CO2, whereas Proteobacteria relative abundance was increased at elevated CO2, due to the presence of Gammaproteobacteria (Vibrionaceae and Alteromonadaceae), a class not present in the control samples. This study provides a first glimpse at the impact of OA in fish intestinal microbiota and highlights potential downstream effects to the general condition of fishes under hypercapnia.

Continue reading ‘Impact of ocean acidification on the intestinal microbiota of the marine sea bream (Sparus aurata L.)’

Response of N2O production rate to ocean acidification in the western North Pacific

Ocean acidification, induced by the increase in anthropogenic CO2 emissions, has a profound impact on marine organisms and biogeochemical processes. The response of marine microbial activities to ocean acidification might play a crucial role in the future evolution of air–sea fluxes of biogenic gases such as nitrous oxide (N2O), a strong GHG and the dominant stratospheric ozone-depleting substance. Here, we examine the response of N2O production from nitrification to acidification in a series of incubation experiments conducted in subtropical and subarctic western North Pacific. The experiments show that when pH was reduced, the N2O production rate during nitrification measured at subarctic stations increased significantly while nitrification rates remained stable or decreased. Contrary to previous findings, these results suggest that the effect of ocean acidification on N2O production during nitrification and nitrification rates are probably uncoupled. Collectively, these results suggest that if seawater pH continues to decline at the same rate, ocean acidification could increase marine N2O production during nitrification in the subarctic North Pacific by 185 to 491% by the end of the century.

Continue reading ‘Response of N2O production rate to ocean acidification in the western North Pacific’

Ulva prolifera green-tide outbreaks and their environmental impact in the Yellow Sea, China

The Ulva prolifera green tides in the Yellow Sea, China, which have been occurring since 2007, are a serious environmental problem attracting worldwide attention. Despite extensive research, the outbreak mechanisms have not been fully understood. Comprehensive analysis of anthropogenic and natural biotic and abiotic factors reveals that human activities, regional physicochemical conditions and algal physiological characteristics as well as ocean warming and biological interactions (with microorganism or other macroalgae) are closely related to the occurrence of green tides. Dynamics of these factors and their interactions could explain why green tides suddenly occurred in 2007 and decreased abruptly in 2017. Moreover, the consequence of green tides is serious. The decay of macroalgal biomass could result in hypoxia and acidification, possibly induce red tide and even have a long-lasting impact on coastal carbon cycles and the ecosystem. Accordingly, corresponding countermeasures have been proposed in our study for future reference in ecosystem management strategies and sustainable development policy.

Continue reading ‘Ulva prolifera green-tide outbreaks and their environmental impact in the Yellow Sea, China’

Ocean acidification and warming effects on the physiology, skeletal properties, and microbiome of the purple-hinge rock scallop


• Is the physiology of Crassadoma gigantea affected by warming and acidification?

• Warming and acidification reduced shell strength & increased total lipid content.

• Exposed scallops reorganized fatty acids to sustain metabolic functions.

• Treatments lead to differences in microbiome community composition.

• This was the first multi-stressor experiment on Crassadoma gigantea.

• This was the first multi-stressors experiment to define a core microbiome in a bivalve.


Ocean acidification and increased ocean temperature from elevated atmospheric carbon dioxide can significantly influence the physiology, growth and survival of marine organisms. Despite increasing research efforts, there are still many gaps in our knowledge of how these stressors interact to affect economically and ecologically important species. This project is the first to explore the physiological effects of high pCO2 and temperature on the acclimation potential of the purple-hinge rock scallop (Crassadoma gigantea), a widely distributed marine bivalve, important reef builder, and potential aquaculture product. Scallops were exposed to two pCO2 (365 and 1050 μatm) and temperature (14 and 21.5 °C) conditions in a two-factor experimental design. Simultaneous exposure to high temperature and high pCO2 reduced shell strength, decreased outer shell density and increased total lipid content. Despite identical diets, scallops exposed to high pCO2 had higher content of saturated fatty acids, and lower content of polyunsaturated fatty acids suggesting reorganization of fatty acid chains to sustain basic metabolic functions under high pCO2. Metagenomic sequencing of prokaryotes in scallop tissue revealed treatment differences in community composition between treatments and in the presence of genes associated with microbial cell regulation, signaling, and pigmentation. Results from this research highlight the complexity of physiological responses for calcifying species under global change related stress and provide the first insights for understanding the response of a bivalve’s microbiome under multiple stressors.

Continue reading ‘Ocean acidification and warming effects on the physiology, skeletal properties, and microbiome of the purple-hinge rock scallop’

Life in the freezer : the role of dimethylsulfoniopropionate (DMSP) in the physiological and biochemical adaptations of Antarctic microalgae

Marine microalgae are the fuel of the Antarctic ecosystem and changes in primary production can impact the entire food web, as well as the nutritional value at the base of the food web which is dependant not only on biomass but also the macromolecular content of the individual species. Primary production by Antarctic microalgae is also of key importance in the biogeochemical cycling of carbon and sulfur. Antarctica has a unique and dynamic environment where microalgae are evolutionarily adapted to live in freezing temperatures under extreme and oscillating environmental gradients exposing them to solar, osmotic, oxidative and nutrient stress. This thesis investigated the physiological and biochemical adaptations of Antarctic microalgae, focusing on the role dimethylsulfoniopropionate (DMSP) plays in surviving in the harsh Antarctic environment. This thesis provides new knowledge into who are the DMSP producers in Antarctica, the spatial dynamics and role of DMSP in natural Antarctic microbial communities. In a screening study, 16 species of Antarctic microalgae were characterised by their growth rates, physiological health, carbon content, DMSP production and DMSP lyase activity. We found that DMSP production and rates of lyase activity were species-specific, varying within taxa, and that diatom species can produce significant levels of DMSP, in the same magnitude as known DMSP producing haptophytes, 𝘗𝘩𝘢𝘦𝘰𝘤𝘺𝘴𝘵𝘪𝘴 𝘴𝘱𝘱.. In a descriptive study, we take a geographical look at the DMSP content and lyase activity, macromolecular profiles and productivity of three different Antarctic microalgal communities from three unique Antarctic environments; the open ocean to the sea ice and a hypersaline lake. We reveal that species diversity is reduced with more challenging environmental conditions and the species with the greatest phenotypic plasticity dominate in harsher settings. This thesis found that macromolecular content of microalgae changes based on environment, whereby sea-ice microalgae were higher in caloric value due to heavy investment in lipids compared to pelagic species. Using manipulative laboratory studies, we delivered new insight into the response of DMSP to environmental stress and future climate change scenarios as well as macromolecular responses at the species and community levels. Exposure to hypersaline conditions did not induce increased DMSP production, potentially due to the salinity shift being too rapid. In addition, there was no significant change in DMSP or macromolecular concentrations in response to ocean acidification at the species level, however there was a difference at the community level due to a shift in community composition.

Continue reading ‘Life in the freezer : the role of dimethylsulfoniopropionate (DMSP) in the physiological and biochemical adaptations of Antarctic microalgae’

Marine microbial community dynamics and responses to ocean acidification

Marine microbes, including both eukaryotes and prokaryotes, are the basal components of marine food webs and play a fundamental role in global biogeochemical cycling. Marine phytoplankton are responsible for approximately 50% of Earth’s primary production, while heterotrophic bacteria and archaea modulate carbon and nutrient cycling in the marine environment. The structure and function of marine microbial communities are closely coupled. Consequently, understanding the factors which govern the distribution of marine microbes through space and time has key implications for food webs and biogeochemical cycling. The development of high-throughput sequencing technologies has revolutionised marine microbial ecology by facilitating the profiling of microbial communities in high taxonomic resolution. In this thesis high-throughput sequencing of the 16S and 18S rRNA genes was used to achieve two major aims. The first aim was to investigate the ecological processes which underpin microbial community assembly in the marine environment. The second aim was to investigate the responses of marine microbial communities to near- future ocean acidification.

Two studies were performed towards the first aim of this thesis. In the first study, the microbial biogeography of the South Pacific Gyre was characterised across three depths at 22 stations along a 2,000 km longitudinal transect of the region. Microbial community composition was homogenous across horizontal spatial scales in the surface waters of the South Pacific Gyre, but varied significantly between surface waters and the deep chlorophyll maximum. A null model approach was used to unveil the ecological processes driving microbial community assembly in the region. Microbial communities in the surface waters were assembled primarily through the deterministic process of homogeneous selection, indicating that selection pressures were sufficient to overwhelm the influence of dispersal effects and ecological drift across vast horizontal spatial distances in the region. Dispersal limitation was comparatively more influential in the assembly of microbial communities between the surface waters and the deep chlorophyll maximum, indicating that stochastic processes play a significant role in microbial community assembly between these contiguous water masses.

In the second study, the bacterioplankton and protist biogeography of the Southland Front system was characterised in surface waters at 24 stations spanning four water masses. Both bacterioplankton and protist communities displayed significant structuring according to water mass, although this effect was most pronounced in bacterioplankton communities. A null model approach revealed that bacterioplankton communities were primarily assembled through homogeneous selection, while protist communities were primarily assembled through dispersal limitation and ecological drift across the Southland Front system. These findings highlight that distinct ecological processes can underpin the assembly of co- occurring bacterioplankton and protist communities, and that hydrographic features such as oceanic fronts play an important role in structuring both bacterioplankton and protist communities.

Two studies were conducted towards the second aim of this thesis. In the first study, the effect of ocean acidification and warming on bacterioplankton communities was investigated at the fringe and ultra-oligotrophic centre of the South Pacific Gyre using trace-metal clean deckboard incubation experiments. Bacterioplankton community composition and function were resistant to ocean acidification alone, and combined with warming, at the fringe of the South Pacific Gyre. Subtle but significant responses of bacterioplankton community composition to ocean acidification were observed at the ultra- oligotrophic centre of the South Pacific Gyre. These results suggest that bacterioplankton community responses to ocean acidification may be modulated by nutrient regimes. Nonetheless, the findings of this study did not diverge substantially from the narrative that bacterioplankton communities are resistant to near-future acidification.

In the second study, the effect of ocean acidification on both prokaryotic and eukaryotic biofilm communities was investigated at the Shikine-Jima CO2 seep system in Japan. The composition of both prokaryotic and eukaryotic communities was profoundly affected by ocean acidification through early successional stages, though these responses were not associated with shifts in community diversity or evenness. Notably, the relative abundance of the nuisance algae Prymnesium sp. and Biddulphia biddulphiana were enhanced under high CO2 conditions. These findings suggest that benthic biofilm communities may be vulnerable to near-future ocean acidification, and that changes in biofilm community composition may contribute to the reorganisation of coastal ecosystem observed at CO2 seeps globally.

In its entirety, this thesis significantly contributes to our understanding of the spatial dynamics of marine microbial communities by revealing the highly deterministic nature of bacterioplankton community assembly in the coastal waters and central gyre of the South Pacific Ocean. Furthermore, the findings of this thesis highlight the dominance of stochastic processes in structuring marine protist communities across short spatial scales, which may contribute to challenges in correlating abiotic environmental variables with marine protist community composition through space. The resistance of bacterioplankton communities to ocean acidification at the fringe of the South Pacific Gyre, and subtle responses to ocean acidification at the ultra-oligotrophic centre of the South Pacific Gyre broadly support the notion that bacterioplankton communities are resilient to near-future ocean acidification. In contrast, the composition of both prokaryotic and eukaryotic biofilm communities was profoundly affected by ocean acidification, leading to the proliferation of harmful algae with potentially severe consequences for coastal marine environments.

Continue reading ‘Marine microbial community dynamics and responses to ocean acidification’

Changes in the metabolic potential of the sponge microbiome under ocean acidification

Anthropogenic CO2 emissions are causing ocean acidification, which can affect the physiology of marine organisms. Here we assess the possible effects of ocean acidification on the metabolic potential of sponge symbionts, inferred by metagenomic analyses of the microbiomes of two sponge species sampled at a shallow volcanic CO2 seep and a nearby control reef. When comparing microbial functions between the seep and control sites, the microbiome of the sponge Stylissa flabelliformis (which is more abundant at the control site) exhibits at the seep reduced potential for uptake of exogenous carbohydrates and amino acids, and for degradation of host-derived creatine, creatinine and taurine. The microbiome of Coelocarteria singaporensis (which is more abundant at the seep) exhibits reduced potential for carbohydrate import at the seep, but greater capacity for archaeal carbon fixation via the 3-hydroxypropionate/4-hydroxybutyrate pathway, as well as archaeal and bacterial urea production and ammonia assimilation from arginine and creatine catabolism. Together these metabolic features might contribute to enhanced tolerance of the sponge symbionts, and possibly their host, to ocean acidification.

Continue reading ‘Changes in the metabolic potential of the sponge microbiome under ocean acidification’

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Ocean acidification in the IPCC AR5 WG II

OUP book