Tufa stromatolite ecosystems on the South African south coast

Following the first description of living marine stromatolites along the South African east coast, new investigations along the south coast have revealed the occurrence of extensive fields of actively calcifying stromatolites. These stromatolites have been recorded at regular distances along a 200-km stretch of coastline, from Cape Recife in the east to the Storms River mouth in the west, with the highest density found between Schoenmakerskop and the Maitland River mouth. All active stromatolites are associated with freshwater seepage streams flowing from the dune cordon, which form rimstone dams and other accretions capable of retaining water in the supratidal platform. Resulting pools can reach a maximum depth of about 1 m and constitute a unique ecosystem in which freshwater and marine organisms alternate their dominance in response to vertical mixing and the balance between freshwater versus marine inflow. Although the factors controlling stromatolite growth are yet to be determined, nitrogen appears to be supplied mainly via the dune seeps. The epibenthic algal community within stromatolite pools is generally co-dominated by cyanobacteria and chlorophytes, with minimal diatom contribution

Microbial Community Responses to Alterations in Historical Fire Regimes in Montane Grasslands

The influence of fire regimes on soil microbial diversity in montane grasslands is a relatively unexplored area of interest. Understanding the belowground diversity is a crucial stepping-stone toward unravelling community dynamics, nutrient sequestration, and overall ecosystem stability. In this study, metabarcoding was used to unravel the impact of fire disturbance regimes on bacterial and arbuscular mycorrhizal fungal community structures in South African montane grasslands that have been subjected to an intermediate (up to five years) term experimental fire-return interval gradient. Bacterial communities in this study exhibited a shift in composition in soils subjected to annual and biennial fires compared to the controls, with carbon and nitrogen identified as significant potential chemical drivers of bacterial communities. Shifts in relative abundances of dominant fungal operational taxonomic units were noted, with Glomeromycota as the dominant arbuscular mycorrhiza observed across the fire-return gradient. A reduction in mycorrhizal root colonisation was also observed in frequently burnt autumnal grassland plots in this study. Furthermore, evidence of significant mutualistic interactions between bacteria and fungi that may act as drivers of the observed community structure were detected. Through this pilot study, we can show that fire regime strongly impacts bacterial and fungal communities in southern African montane grasslands, and that changes to their usually resilient structure are mediated by seasonal burn patterns, chemical drivers, and mutualistic interactions between these two groups

Preliminary evidence for the organisation of a bacterial community by zooplanktivores at the top of an estuarine planktonic food web

Publisher versionAs part of a larger investigation, the effect of apex predation on estuarine bacterial community structure, through trophic cascading, was investigated using experimental in situ mesocosms. Through either the removal (filtration) or addition of specific size classes of planktonic groups, four different trophic scenarios were established using estuarine water and its associated plankton. One such treatment represented a “natural” scenario in which stable apex predatory pressure was qualified. Water samples were collected over time from each of the treatments for bacterial community evaluation. These samples were assessed through pyrosequencing of the variable regions 4 and 5 of the bacterial 16S rRNA gene and analysed at the species operational taxonomic unit (OTU) level using a community procedure. The blue-green group dominated the samples, followed by Proteobacteria and Bacteroidetes. Samples were the most similar among treatments at the commencement of the experiment. While the bacterial communities sampled within each treatment changed over time, the deviation from initial appeared to be linked to the treatment trophic scenarios. The least temporal deviation-from-initial in bacterial community was found within the stable apex predatory pressure treatment. These findings are consistent with trophic cascade theory, whereby predators mediate interactions at multiple lower trophic levels with consequent repercussions for diversity

A pivotal role for ocean eddies in the distribution of microbial communities across the Antarctic Circumpolar Current

<div><p>Mesoscale variability and associated eddy fluxes play crucial roles in ocean circulation dynamics and the ecology of the upper ocean. In doing so, these features are biologically important, providing a mechanism for the mixing and exchange of nutrients and biota within the ocean. Transient mesoscale eddies in the Southern Ocean are known to relocate zooplankton communities across the Antarctic Circumpolar Current (ACC) and are important foraging grounds for marine top predators. In this study we investigated the role of cyclonic and anti-cyclonic eddies formed at the South-West Indian Ridge on the spatial variability and diversity of microbial communities. We focused on two contrasting adjacent eddies within the Antarctic Polar Frontal Zone to determine how these features may influence the microbial communities within this region. The water masses and microbiota of the two eddies, representative of a cyclonic cold core from the Antarctic zone and an anti-cyclonic warm-core from the Subantarctic zone, were compared. The data reveal that the two eddies entrain distinct microbial communities from their points of origin that are maintained for up to ten months. Our findings highlight the ecological impact that changes, brought by the translocation of eddies across the ACC, have on microbial diversity.</p></div

Physical characteristics of adjacent warm and cold core eddies.

<p><b>(A)</b> Real Time of Merged Sea Level Anomalies (MSLA obtained from <a href="http://www.aviso.oceanobs.com/" target="_blank"><u>http://www.aviso.oceanobs.com</u></a><i>)</i> showing the position of the warm (positive anomaly) and cold core (negative anomaly) eddies. The positive anomaly is centred 28°E and 49°S, while a negative anomaly, presumed to be a cold Antarctic eddy was observed between 48.45°-51°S and 28.30°-32°E. <b>(B)</b> Sampling locations of adjacent cold- (▲) and warm-core eddies (■) situated within the Antarctic Polar Front Zone (APFZ) of Southern Ocean. Samples collected from the Subantarctic, APFZ and Antarctic domains are indicated (●). CTD (conductivity, temperature and depth) and uCTD (underway CTD) sampling stations are indicated on the map along with temperature data in ^oC. Isotherms are at 0.25°C intervals. <b>(C)</b> Vertical cross section of temperature across both the warm and cold-core eddy. The grey dashed line demarcates the boundaries between the two features. Surface property plots across both warm and cold-core eddies (again separated by a red line), demonstrating surface temperature and Chl-a concentration (mg.m^-3). <b>(D)</b> Temperature and salinity (T/S) profiles highlighting the cold-core eddy (blue), the core of the warm eddy and the Subantarctic Front (SAF) domain (red), the APFZ (green) and Antarctic waters (black). The profiles characterize the nature of both eddies in relation to the surrounding ocean environment.</p

Bacterial diversity and community structure in the Southern Ocean eddies.

<p><b>(A)</b> Phylogenetic classification of bacterial taxa. The data is expressed as the relative percentage of phyla and subphyla present within the cold eddy (n = 5 samples), warm eddy (n = 9 samples). Error bar represents standard error mean between samples. <b>(B)</b> Relative abundance of dominant bacterial species (B_OTUs). The bacterial 16S rRNA datasets were classified at the species level (OTU_0.03) with the Silva reference database (Version 123) using the Mothur platform. SAF: Subantarctic Front; APFZ: Antarctic Polar Frontal Zone; A: Antarctic.</p

Microphytoplankton diversity in the Southern Ocean eddies.

<p>Chloroplast OTUs (C_OTUs) were extracted from 16S sequence datasets and the relative abundance of the top 10 dominant C_OTUs in each sample are represented in the bar graph. C_OTUs were identified using the PhytoREF reference database. SAF: Subantarctic Front; APFZ: Antarctic Polar Frontal Zone; A: Antarctic.</p

Comparison across the warm-core (Subantarctic) and cold-core (Antarctic) eddies during the 2012 survey.

<p>Comparison across the warm-core (Subantarctic) and cold-core (Antarctic) eddies during the 2012 survey.</p

Non-metric Multidimensional Scaling (nMDS) ordination of microbial communities in cold- vs warm-core Southern Ocean eddies.

<p>NMDS plots of bacterial <b>(A)</b> and algal <b>(B)</b> communities were based on a Bray–Curtis dissimilarity matrix (stress = 0.984). The ordination plots were derived from the 16S rRNA bacterial and chloroplast OTUs classified at the species (97%) level using the Mothur software platform. The significance of the dissimilarity between microbial communities was statistically confirmed (p = <0.05) using the Analysis of Similarity (ANOSIM) test using the Vegan package in the R platform.</p

Sea surface height (SSH) variability for the period 2000–2009 for the South-West Indian Ridge (SWIR).

<p>The region of interest in this study is the southward extension of variability centred along 30°E from 50–58°S. The black lines represent the 3500 isobath and demarcate the location of the SWIR in relation to this region of high ocean variability.</p