Posts Tagged 'prokaryotes'

In situ responses of the sponge microbiome to ocean acidification

Climate change is causing rapid changes in reef structure, biodiversity, and function, though most sponges are predicted to tolerate conditions projected for 2100. Sponges maintain intimate relationships with microbial symbionts, with previous studies suggesting that microbial flexibility may be pivotal to success under ocean acidification. We performed a reciprocal transplantation of the coral reef sponges Coelocarteria singaporensis and Stylissa cf. flabelliformis between a control reef site and an adjacent CO2 vent site in Papua New Guinea to explore how the sponge microbiome responds to ocean acidification. Microbial communities of C. singaporensis, which differed initially between sites, did not shift towards characteristic control or vent microbiomes, even though relative abundances of Chloroflexi and Cyanobacteria increased and that of Thaumarchaeota decreased seven months after transplantation to the control site. Microbial communities of S. cf. flabelliformis, which were initially stable between sites, did not respond specifically to transplantation but collectively exhibited a significant change over time, with a relative increase in Thaumarchaeota and decrease in Proteobacteria in all treatment groups. The lack of a community shift upon transplantation to the vent site suggests that microbial flexibility, at least in the adult life-history stage, does not necessarily underpin host survival under ocean acidification.

Continue reading ‘In situ responses of the sponge microbiome to ocean acidification’

Rhodoliths holobionts in a changing ocean: host-microbes interactions mediate coralline algae resilience under ocean acidification

Life in the ocean will increasingly have to contend with a complex matrix of concurrent shifts in environmental properties that impact their physiology and control their life histories. Rhodoliths are coralline red algae (Corallinales, Rhodophyta) that are photosynthesizers, calcifiers, and ecosystem engineers and therefore represent important targets for ocean acidification (OA) research. Here, we exposed live rhodoliths to near-future OA conditions to investigate responses in their photosynthetic capacity, calcium carbonate production, and associated microbiome using carbon uptake, decalcification assays, and whole genome shotgun sequencing metagenomic analysis, respectively. The results from our live rhodolith assays were compared to similar manipulations on dead rhodolith (calcareous skeleton) biofilms and water column microbial communities, thereby enabling the assessment of host-microbiome interaction under climate-driven environmental perturbations.

Continue reading ‘Rhodoliths holobionts in a changing ocean: host-microbes interactions mediate coralline algae resilience under ocean acidification’

Independent and interactive effects of reduced seawater pH and oil contamination on subsurface sediment bacterial communities

Ocean acidification may exacerbate the environmental impact of oil hydrocarbon pollution by disrupting the core composition of the superficial (0–1 cm) benthic bacterial communities. However, at the subsurface sediments (approximately 5 cm below sea floor), the local biochemical characteristics and the superjacent sediment barrier may buffer these environmental changes. In this study, we used a microcosm experimental approach to access the independent and interactive effects of reduced seawater pH and oil contamination on the composition of subsurface benthic bacterial communities, at two time points, by 16S rRNA gene-based high-throughput sequencing. An in-depth taxa-specific variance analysis revealed that the independent effects of reduced seawater pH and oil contamination were significant predictors of changes in the relative abundance of some specific bacterial groups (e.g., Firmicutes, Rhizobiales, and Desulfobulbaceae). However, our results indicated that the overall microbial community structure was not affected by independent and interactive effects of reduced pH and oil contamination. This study provides evidence that bacterial communities inhabiting subsurface sediment may be less susceptible to the effects of oil contamination in a scenario of reduced seawater pH.

Continue reading ‘Independent and interactive effects of reduced seawater pH and oil contamination on subsurface sediment bacterial communities’

Temperature driven changes in benthic bacterial diversity influences biogeochemical cycling in coastal sediments

Marine sediments are important sites for global biogeochemical cycling, mediated by macrofauna and microalgae. However, it is the microorganisms that drive these key processes. There is strong evidence that coastal benthic habitats will be affected by changing environmental variables (rising temperature, elevated CO2), and research has generally focused on the impact on macrofaunal biodiversity and ecosystem services. Despite their importance, there is less understanding of how microbial community assemblages will respond to environmental changes. In this study, a manipulative mesocosm experiment was employed, using next-generation sequencing to assess changes in microbial communities under future environmental change scenarios. Illumina sequencing generated over 11 million 16S rRNA gene sequences (using a primer set biased toward bacteria) and revealed Bacteroidetes and Proteobacteria dominated the total bacterial community of sediment samples. In this study, the sequencing coverage and depth revealed clear changes in species abundance within some phyla. Bacterial community composition was correlated with simulated environmental conditions, and species level community composition was significantly influenced by the mean temperature of the environmental regime (p = 0.002), but not by variation in CO2 or diurnal temperature variation. Species level changes with increasing mean temperature corresponded with changes in NH4 concentration, suggesting there is no functional redundancy in microbial communities for nitrogen cycling. Marine coastal biogeochemical cycling under future environmental conditions is likely to be driven by changes in nutrient availability as a direct result of microbial activity.

Continue reading ‘Temperature driven changes in benthic bacterial diversity influences biogeochemical cycling in coastal sediments’

High-resolution time-series reveals seasonal patterns of planktonic fungi at a temperate coastal ocean site (Beaufort, North Carolina, USA)

There is a growing awareness of the ecological and biogeochemical importance of fungi in coastal marine systems, while highly diverse fungi have been discovered in these marine systems, still little is known about their seasonality and associated drivers in coastal waters. Here, we examined fungal communities over three years of weekly samples at a dynamic, temperate coastal site (Piver’s Island Coastal Observatory (PICO), Beaufort NC USA). Fungal 18S rRNA gene abundance, OTU richness and Shannon’s diversity exhibited prominent seasonality. Fungi 18S rRNA gene copies peak in abundance during the summer and fall, with positive correlations with chlorophyll a, SiO4 and oxygen saturation. Diversity (measured using Internal Transcribed Spacer: ITS libraries) was highest during winter and lowest during summer; it was linked to temperature, pH, chlorophyll a, insolation, salinity, and DIC. Fungal community ITS libraries were dominated throughout the year by Ascomycota with contributions from Basidiomycota, Chytridiomycota and Mucoromycotina, with seasonal patterns linked to water temperature, light, and the carbonate system. Network analysis revealed that while co-occurrence and exclusion existed within fungal network, exclusion dominated the fungi and phytoplankton network, in contrast with reported pathogenic and nutritional interactions between marine phytoplankton and fungi. Compared with the seasonality of bacterial community in the same samples, the timing, extent and associated environmental variables for fungi community are unique. These results highlighted the fungal seasonal dynamics in coastal water and improve our understanding of the ecology of planktonic fungi.

Continue reading ‘High-resolution time-series reveals seasonal patterns of planktonic fungi at a temperate coastal ocean site (Beaufort, North Carolina, USA)’

Plankton community respiration and ETS activity under variable CO2 and nutrient fertilization during a mesocosm study in the subtropical North Atlantic

The enzymatic electron transport system (ETS) assay is frequently used as a proxy of respiratory activity in planktonic communities. It is thought to estimate the maximum overall activity of the enzymes associated with the respiratory ETS systems in both eukaryotic and prokaryotic organisms. Thus, in order to derive actual respiration rates (R) from ETS it is necessary to determine empirical R/ETS conversion algorithms. In this study we explore the temporal development of R and ETS activity in natural plankton communities (from bacteria to large phytoplankton) enclosed in mesocosms, treated with different CO2 concentrations. The experiment lasted 30 days, during which abrupt changes in community structure and biomass occurred through a sharp transition from oligotrophy (phase I) to highly eutrophic conditions (phase II) after nutrient-induced fertilization (day 18). R and ETS did not show any response to CO2 under oligotrophic conditions, but R increased significantly more in the two high CO2 mesocosms after fertilization, coinciding with a sharp rise in large phytoplankton (mostly diatoms). R and ETS were significantly correlated only during the eutrophic phase. The R/ETS ranged more than 3 fold in magnitude during the experiment, with phase-averaged values significantly higher under oligotrophic conditions (0.7-1.1) than after nutrient fertilization (0.5-0.7). We did not find any significant relationship between R/ETS and community structure or biomass, although R correlated significantly with total biomass after fertilization in the four mesocosms. Multiple stepwise regression models show that large phytoplankton explains most of the variance in R during phases I (86%) and II (53%) and of ETS (86%) during phase II, while picophytoplankton contributes up to 73% to explain the variance in the ETS model during phase I. Our results suggest that R/ETS may be too variable in the ocean as to apply constant values to different communities living under contrasting environmental conditions. Controlled experiments with natural communities, like the present one, would help to constrain the range of variability of the R/ETS ratio, and to understand the factors driving it.

Continue reading ‘Plankton community respiration and ETS activity under variable CO2 and nutrient fertilization during a mesocosm study in the subtropical North Atlantic’

Contrasting effects of acidification and warming on dimethylsulfide concentrations during a temperate estuarine fall bloom mesocosm experiment

The effects of ocean acidification and warming on the concentrations of dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) were investigated during a mesocosm experiment in the Lower St. Lawrence Estuary (LSLE) in the fall of 2014. Twelve mesocosms covering a range of pHT (pH on the total hydrogen ion concentration scale) from 8.0 to 7.2, corresponding to a range of CO2 partial pressures (pCO2) from 440 to 2900µatm, at two temperatures (in situ and +5°C; 10°C and 15°C) was monitored during 13 days. All mesocosms were characterized by the rapid development of a diatom bloom dominated by Skeletonema costatum, followed by its decline upon the exhaustion of nitrate and silicic acid. Neither the acidification nor the warming resulted in a significant impact on the abundance of bacteria over the experiment. However, warming the water by 5°C resulted in a significant increase of the average bacterial production (BP) in all 15°C mesocosms as compared to 10°C, with no detectable effect of pCO2 on BP. Variations in total DMSP (DMSPt=particulate+dissolved DMSP) concentrations tracked the development of the bloom although the rise in DMSPt persisted for a few days after the peaks in chlorophyll a. Average concentrations of DMSPt were not affected by acidification or warming. Initially low concentrations of DMS (<1nmolL−1) increased to reach peak values ranging from 30 to 130nmolL−1 towards the end of the experiment. Increasing the pCO2 reduced the averaged DMS concentrations by 66% and 69% at 10°C and 15°C, respectively, over the duration of the experiment. On the other hand, a 5°C warming increased DMS concentrations by an average of 240% as compared to in situ temperature, resulting in a positive offset of the adverse pCO2 impact. Significant positive correlations found between bacterial production rates and concentrations of DMS throughout our experiment point towards temperature-associated enhancement of bacterial DMSP metabolism as a likely driver for the mitigating effect of warming on the negative impact of acidification on the net production of DMS in the LSLE and potentially the global ocean.

Continue reading ‘Contrasting effects of acidification and warming on dimethylsulfide concentrations during a temperate estuarine fall bloom mesocosm experiment’


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Ocean acidification in the IPCC AR5 WG II

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