Posts Tagged 'prokaryotes'

Marine microbial gene abundance and community composition in response to ocean acidification and elevated temperature in two contrasting coastal marine sediments

Marine ecosystems are exposed to a range of human-induced climate stressors, in particular changing carbonate chemistry and elevated sea surface temperatures as a consequence of climate change. More research effort is needed to reduce uncertainties about the effects of global-scale warming and acidification for benthic microbial communities, which drive sedimentary biogeochemical cycles. In this research, mesocosm experiments were set up using muddy and sandy coastal sediments to investigate the independent and interactive effects of elevated carbon dioxide concentrations (750 ppm CO2) and elevated temperature (ambient + 4 °C) on the abundance of taxonomic and functional microbial genes. Specific q-PCR primers were used to target archaeal, bacterial and cyanobacterial/chloroplast 16S rRNA in both sediment types. Nitrogen cycling genes archaeal and bacterial ammonia monooxygenase (amoA) and bacterial nitrite reductase (nirS) were specifically targeted to identify changes in microbial gene abundance and potential impacts on nitrogen cycling. In muddy sediment, microbial gene abundance, including amoA and nirS genes, increased under elevated temperature and reduced under elevated CO2 after 28 days, accompanied by shifts in community composition. In contrast, the combined stressor treatment showed a non-additive effect with lower microbial gene abundance throughout the experiment. The response of microbial communities in the sandy sediment was less pronounced, with the most noticeable response seen in the archaeal gene abundances in response to environmental stressors over time. 16S rRNA genes (amoA and nirS) were lower in abundance in the combined stressor treatments in sandy sediments. Our results indicated that marine benthic microorganisms, especially in muddy sediments, are susceptible to changes in ocean carbonate chemistry and seawater temperature, which ultimately may have an impact upon key benthic biogeochemical cycles.

Continue reading ‘Marine microbial gene abundance and community composition in response to ocean acidification and elevated temperature in two contrasting coastal marine sediments’

The survival, recovery, and diversification of metazoan reef ecosystems following the end-Permian mass extinction event

The Triassic Period records important ecological transitions in the aftermath of the end-Permian mass extinction and is a key interval in the evolution of modern coral reefs. There have been several critical developments in our understanding of Triassic reef evolution over the past decade: the timing of events and duration of stages have changed dramatically; the discovery of metazoan reefs in the Early Triassic; details about the environmental perturbations that drove the extinction; the relationship between tectonic activity and platform margin reef proliferation; and additional proxy evidence for the co-evolution of coral reef-builders and their photosymbionts. Here, we provide an up-to-date synthesis of reef collapse and recovery dynamics following the end-Permian extinction, specifically integrating recent discoveries. The evolution of reef ecosystems can be divided into five phases based on their composition. 1) Microbial-metazoan reefs represent survival communities that characterize the immediate extinction aftermath. 2) The re-establishment of reefs built by metazoans (small sponge biostromes and bivalve buildups) is observed in oxygenated settings in the Olenekian (Early Triassic). 3) Towards the end of the Olenekian and into the Anisian (Middle Triassic) low-diversity, “Tubiphytes”-dominated reefs formed, which represent the first Triassic platform-margin reefs; platform-margin reefs, however, are not widespread until the late Anisian. 4) Late Anisian reefs also record a composition change and increase in species richness with sponges and “Tubiphytes” as the main reef builders. 5) The first scleractinian corals (which are the main reef builder in modern marine reef ecosystems) evolved during the Anisian but are not reported as dominant reef builders until the Late Triassic. The radiation of coral reefs is posited to be coupled to the acquisition of photosymbionts (e.g., zooxanthellae). There is clearly a stepwise evolution of reef types during the Triassic; however, once each reef type appears it persists throughout the remainder of the Triassic. The survival, recovery, and diversification of reef ecosystems is, therefore, more complex than previously outlined, particularly with respect to the earliest post-extinction ecosystems. These recent advances highlight the need to thoroughly document the faunal compositions of understudied reef systems as well as to continue the exploration of Triassic ecosystems in underrepresented regions.

Continue reading ‘The survival, recovery, and diversification of metazoan reef ecosystems following the end-Permian mass extinction event’

Ocean acidification of a coastal Antarctic marine microbial community reveals a critical threshold for CO2 tolerance in phytoplankton productivity

High-latitude oceans are anticipated to be some of the first regions affected by ocean acidification. Despite this, the effect of ocean acidification on natural communities of Antarctic marine microbes is still not well understood. In this study we exposed an early spring, coastal marine microbial community in Prydz Bay to CO2 levels ranging from ambient (343 μatm) to 1641 μatm in six 650 l minicosms. Productivity assays were performed to identify whether a CO2 threshold existed that led to a decline in primary productivity, bacterial productivity, and the accumulation of Chlorophyll a (Chl a) and particulate organic matter (POM) in the minicosms. In addition, photophysiological measurements were performed to identify possible mechanisms driving changes in the phytoplankton community. A critical threshold for tolerance to ocean acidification was identified in the phytoplankton community between 953 and 1140 μatm. CO2 levels ≥ 1140 μatm negatively affected photosynthetic performance and Chl a-normalised primary productivity (csPP14C), causing significant reductions in gross primary production (GPP14C), Chl a accumulation, nutrient uptake, and POM production. However, there was no effect of CO2 on C : N ratios. Over time, the phytoplankton community acclimated to high CO2 conditions, showing a down-regulation of carbon concentrating mechanisms (CCMs) and likely adjusting other intracellular processes. Bacterial abundance initially increased in CO2 treatments ≥ 953 μatm (days 3–5), yet gross bacterial production (GBP14C) remained unchanged and cell-specific bacterial productivity (csBP14C) was reduced. Towards the end of experiment, GBP14C and csBP14C markedly increased across all treatments regardless of CO2 availability. This coincided with increased organic matter availability (POC and PON) combined with improved efficiency of carbon uptake. Such changes in phytoplankton community production could have negative effects on the Antarctic food web and the biological pump, resulting in negative feedbacks on anthropogenic CO2 uptake. Increases in bacterial abundance under high CO2 conditions may also increase the efficiency of the microbial loop, resulting in increased organic matter remineralisation and further declines in carbon sequestration.

Continue reading ‘Ocean acidification of a coastal Antarctic marine microbial community reveals a critical threshold for CO2 tolerance in phytoplankton productivity’

Solar UVR sensitivity of phyto- and bacterioplankton communities from Patagonian coastal waters under increased nutrients and acidification

The effects of ultraviolet radiation (UVR) under future expected conditions of acidification and increase in nutrient inputs were studied on a post-bloom phytoplankton and bacterioplankton community of Patagonian coastal waters. We performed an experiment using microcosms where two environmental conditions were mimicked using a cluster approach: present (ambient nutrients and pH) and future (increased nutrients and acidification), and acclimating the samples for five days to two radiation treatments (full solar radiation [+UVR] and exclusion of UVR [–UVR]). We evaluated the short-term (hours) sensitivity of the community to solar UVR through chlorophyll afluorescence parameters (e.g. the effective photochemical quantum yield of PSII [ΦPSII]) at the beginning, at the mid-point and at the end of the acclimation period. Primary production and heterotrophic bacterial production (HBP) were determined, and biological weighting functions were calculated, at the beginning and at the end of the acclimation period. Mid-term effects (days) were evaluated as changes in taxonomic composition, growth rates and size structure of the community. Although the UVR-induced inhibition on ΦPSII decreased in both clusters, samples remained sensitive to UVR after the 5 days of acclimation. Also, under the future conditions, there was, in general, an increase in the phytoplankton carbon incorporation rates along the experiment as compared to the present conditions. Bacterioplankton sensitivity to UVR changed along the experiment from inhibition to enhancement of HBP, and future environmental conditions stimulated bacterial growth, probably due to indirect effects caused by phytoplankton. Those changes in the microbial loop functioning and structure under future global change conditions might have important consequences for the carbon pump and thus for the carbon sequestration and trophodynamics of Patagonian coastal waters.

Continue reading ‘Solar UVR sensitivity of phyto- and bacterioplankton communities from Patagonian coastal waters under increased nutrients and acidification’

Faunal succession and geochemical analysis of carbonate facies changes along the late Permian mass extinction boundary in the Nanpanjiang Basin, South China: a potential argument for ocean acidification and its implications

The late Permian mass extinction is considered the largest extinction event in Earth’s history with over 90% of marine and 70% of terrestrial species becoming extinct as a result (Lehrmann et al., 2015). The Nanpanjiang Basin in southern China contains multiple drowned carbonate platforms that are a record of the Permian-Triassic boundary. Data of two subsections from the Tianwan section of the Tian’e platform in the Nanpanjiang Basin consist of Permian carbonates, the altered truncation surface of the Permian-Triassic boundary as well as Triassic microbialites. Analysis of 1) faunal succession, 2) faunal dominance, 3) stable isotopes and 4) diagenetic structures contributes to the understanding of the environmental conditions during the late Permian to early Triassic. Data collected shows a trend from skeletal packstone to microbial boundstone from the Permian to Triassic respectively. Stable isotope analysis of δ13C and δ18O data up section both show large excursions at the extinction boundary.

Continue reading ‘Faunal succession and geochemical analysis of carbonate facies changes along the late Permian mass extinction boundary in the Nanpanjiang Basin, South China: a potential argument for ocean acidification and its implications’

Ocean acidification changes the structure of an Antarctic coastal protistan community

Antarctic near-shore waters are amongst of the most vulnerable in the world to ocean acidification. Microbes occupying these waters are critical drivers of ecosystem productivity, elemental cycling and ocean biogeochemistry, yet little is known about their sensitivity to ocean acidification. An unreplicated, six-level dose-response experiment was conducted using 650 L incubation tanks (minicosms) adjusted to fugacity of carbon dioxide (ƒCO2) from 343 to 11 641 μatm. The minicosms were filled with near-shore water from Prydz Bay, East Antarctica and the protistan composition and abundance was determined by microscopy analysis of samples collected during the 18 day incubation. No CO2-related change in the protistan community composition was observed during the initial 8 day acclimation period under low light. Thereafter, the response of protists to ƒCO2 were species-specific for both heterotrophic and autotrophic protists. The response by diatoms was related to cell size, large cells increasing in abundance with low to moderate ƒCO2 (634–953 μatm). Similarly, the abundance of Phaeocystis antarctica increased with increasing ƒCO2 peaking at a ƒCO2 of 634 μatm. Above this threshold the abundances of large diatoms and Phaeocystis antarctica fell dramatically, and small diatoms dominated, therefore culminating in a significant shift in the composition of the protistan community. The threshold CO2 level at which the composition changed agreed with that previously measured at this location, indicating it remains consistent among seasons. This suggests that near-shore microbial communities are likely to change significantly near the end of this century if anthropogenic CO2 release continues unabated, with profound ramifications for near-shore Antarctic ecosystems.

Continue reading ‘Ocean acidification changes the structure of an Antarctic coastal protistan community’

Low pH reduces the virulence of black band disease on Orbicella faveolata

Black band is a deadly coral disease found worldwide, which may become more virulent as oceanic conditions continue to change. To determine the effects of climate change and ocean acidification on black band disease virulence, Orbicella faveolata corals with black band were exposed to different temperature and pH conditions. Results showed a significant decrease in disease progression under low pH (7.7) conditions. Low pH also altered the relative abundance of the bacterial community of the black band disease consortium. Here, there was a significant decrease in Roseofilum, the cyanobacterium that typically dominates the black band mat. These results indicate that as oceanic pH decreases so may the virulence of a worldwide coral disease.

Continue reading ‘Low pH reduces the virulence of black band disease on Orbicella faveolata’


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