Microbial mats and their palaeoenvironmental analysis in offshore - shelf facies of the Los Molles Formation (Toarcian - Lower Callovian) in the Chacay Melehue area, Neuquén Basin, Argentina.

This contribution presents the first study focused on the analysis of microbial mats in the Los Molles Formation (Toarcian - Early Callovian), Neuquén Basin, Argentina. This unit mainly represents offshore-to-shelf environments affected by storms and density currents. The Los Molles Formation is one of the oldest source rocks in the Neuquén Basin and constitutes an unconventional shale gas reservoir of great economic importance. The aim of this work was to identify the microbial activity from the description and interpretation of microbially induced sedimentary structures (MISS), to determine the paleoenvironmental and paleoecological conditions under which they formed, and to establish a possible relationship between these structures and the trace fossil Trichichnus. Samples from the levels with MISS were analyzed and described from macroscopic and binocular observations, petrographic microscope thin sections, and SEM samples with EDS analyses. The results showed several levels of microbial mats presenting diverse MISS, including biolaminations and Kinneyia-like wrinkles structures that were described at the macroscopic level. In thin sections, biolaminations, filament-like microstructures with different degrees of development, oriented grains and pyrite were observed. SEM images and EDS analyses showed different types of filaments, coccoids and EPS with high concentrations of carbon. These results revealed that the studied levels fulfill the established biogenicity criteria, guaranteeing that they have a bacterial origin. The abundance of the trace fossil Trichichnus sp. throughout the section and the proximity to some Kinneyia-like wrinkle structures levels suggests that the same organisms may have generated them. Furthermore, they revealed that the Los Molles Formation, at the time of its deposition, experienced paleoecological and paleoenvironmental conditions appropriate for the establishment and development of microbial mats. The extensive levels of microbial mats in the study area suggest that they may have been a source of organic matter for the generation of hydrocarbons from the Los Molles Formation.

A fjord-like tropical ecosystem, Pacific coast of Costa Rica: overview of research in Golfo Dulce / Un ecosistema tropical similar a un fiordo, costa del Pacífico de Costa Rica: panorama de la investigación en el Golfo Dulce

Abstract Introduction: Coastal ecosystems worldwide are under the influence of local, regional and global stressors, such as pollution, eutrophication and climate change. Golfo Dulce is a relatively pristine and accessible deep tropical ecosystem that provides opportunities for comparative and collaborative research. Objective: To summarize published reports on past research conducted in this ecosystem, identify topics for further study, and suggest new research issues. Methods: A search was made on the web for reports based on research conducted in Golfo Dulce and published in scientific journals. Reports focusing on environmental parameters and on the biota were included. Results: A total of 123 studies that include data from Golfo Dulce are cited. The four topics more frequently addressed were reports based on the results of the R/V Victor Hensen expedition (1993-1994) and follow-up work on microbiology, studies on water parameters, research on vertebrates, and zooplankton studies. The reports focusing on vertical profiles of oxygen and temperature are discussed in detail, followed by those on the biota. Conclusions: Golfo Dulce has low oxygen concentrations below 50 m and is frequently anoxic at the 200 m deep basin with occasional formation of H2S. However, the ecosystem contains a relatively high diversity of identified organisms, from bacteria to whales. Of particular relevance for future studies are multidisciplinary surveys aiming at obtaining data on primary productivity, the diversity and biomass of the main groups of planktonic, demersal and benthic organisms, and the frequency and magnitude of the influx of deep offshore waters over the sill into the basin. These data, as well as the information gathered in the past, are essential for updating the trophic model developed more than 25 years ago and in support of new predictive models on the functioning of the ecosystem.

Resumen Introducción: Los ecosistemas costeros alrededor del mundo están bajo la influencia de tensores locales, regionales y globales, como la contaminación, la eutroficación y el cambio climático. El Golfo Dulce es un profundo ecosistema tropical relativamente inalterado y accesible, que provee oportunidades para la investigación comparativa y colaborativa. Objetivo: Resumir los informes publicados sobre investigaciones pasadas realizadas en el ecosistema, identificar tópicos para estudios futuros y sugerir nuevas áreas de investigación. Métodos: Se hizo una búsqueda en la red de informes basados en investigaciones hechas en Golfo Dulce y publicadas en revistas científicas. Fueron incluidos aquellos informes sobre parámetros ambientales y la biota. Resultados: Un total de 123 estudios que incluyen datos sobre Golfo Dulce son citados. Los cuatro tópicos citados con más frecuencia fueron: Los resultados de la expedición del R/V Victor Hensen (1993-1994) y estudios de seguimiento sobre microbiología, informes sobre parámetros acuáticos, investigaciones sobre vertebrados y estudios sobre zooplancton. Los informes sobre perfiles de oxígeno y temperatura son presentados con mayor detalle, seguidos por aquellos sobre la biota. Conclusiones: Golfo Dulce tiene bajas concentraciones de oxígeno por debajo de 50 m y es usualmente anóxico a 200 m en el fondo, con formación ocasional de H2S. Sin embargo, el ecosistema contiene una diversidad de organismos identificados relativamente alta, desde bacterias hasta ballenas. De relevancia particular para futuros estudios es, entre otros, la conducción, de muestreos multidisciplinarios orientados a obtener datos sobre productividad primaria, la diversidad y biomasa de los principales grupos de organismos planctónicos, demersales y bénticos, así como la frecuencia y magnitud del flujo de agua oceánica hacia el interior. Estos datos, así como los obtenidos en el pasado, son esenciales para actualizar el modelo trófico desarrollado hace más de 25 años, o en apoyo de nuevos modelos predictivos de funcionamiento del ecosistema.

In situ filamentous communities from the Ediacaran (approx. 563 Ma) of Brazil.

Precambrian filamentous microfossils are common and diverse. Nevertheless, their taxonomic assignment can be difficult owing to their overall simple shapes typically lacking in diagnostic features. Here, we report in situ communities of well-preserved, large filamentous impressions from the Ediacaran Itajaí Basin (ca 563 Ma) of Brazil. The filaments are uniserial (unbranched) and can reach up to 200 µm in width and up to 44 mm in length. They occur as both densely packed or sparsely populated surfaces, and typically show a consistent orientation. Although simple in shape, their preferred orientation suggests they were tethered to the seafloor, and their overall flexibility (e.g. bent, folded and twisted) supports a biological (rather than sedimentary) affinity. Biometric comparisons with modern filamentous groups further support their biological affinity, suggesting links with either large sulfide-oxidizing bacteria (SOB) or eukaryotes. Other morphological and palaeoecological characteristics further corroborates their similarities with modern large filamentous SOB. Their widespread occurrence and association with complex Ediacaran macrobiota (e.g. frondose organisms, Palaeopascichnus) suggest that they probably played an important role in the ecological dynamics of these early benthic communities by providing firm substrates for metazoans to inhabit. It is further hypothesized that the dynamic redox condition in the latest Ediacaran, with the non-continuous rise in oxygen concentration and periods of hypoxia, may have created ideal conditions for SOB to thrive.

SSU-rRNA Gene Sequencing Survey of Benthic Microbial Eukaryotes from Guaymas Basin Hydrothermal Vent.

Microbial eukaryotes have important roles in marine food webs, but their diversity and activities in hydrothermal vent ecosystems are poorly characterized. In this study, we analyzed microbial eukaryotic communities associated with bacterial (Beggiatoa) mats in the 2,000 m deep-sea Guaymas Basin hydrothermal vent system using 18S rRNA gene high-throughput sequencing of the V4 region. We detected 6,954 distinct Operational Taxonomic Units (OTUs) across various mat systems. Of the sequences that aligned with known protistan phylotypes, most were affiliated with alveolates (especially dinoflagellates and ciliates) and cercozoans. OTU richness and community structure differed among sediment habitats (e.g. different mat types and cold sediments away from mats). Additionally, full-length 18S rRNA genes amplified and cloned from single cells revealed the identities of some of the most commonly encountered, active ciliates in this hydrothermal vent ecosystem. Observations and experiments were also conducted to demonstrate that ciliates were trophically active and ingesting fluorescent bacteria or Beggiatoa trichomes. Our work suggests that the active and diverse protistan community at the Guaymas Basin hydrothermal vent ecosystem likely consumes substantial amounts of bacterial biomass, and that the different habitats, often defined by distances of just a few 10s of cm, select for particular assemblages and levels of diversity.

Sulphur-cycling bacteria and ciliated protozoans in a Beggiatoaceae mat covering organically enriched sediments beneath a salmon farm in a southern Chilean fjord.

The colourless mat covering organically enriched sediments underlying an intensive salmon farm in Estero Pichicolo, southern Chile, was surveyed by combined 454 PyroTag and conventional Sanger sequencing of 16S/18S ribosomal RNA genes for Bacteria and Eukarya. The mat was dominated by the sulphide-oxidizing bacteria (SOB) Candidatus Isobeggiatoa, Candidatus Parabeggiatoa and Arcobacter. By order of their abundances, sulphate-reducing bacteria (SRB) were represented by diverse deltaproteobacterial Desulfobacteraceae, but also within Desulfobulbaceae, Desulfuromonadaceae and Desulfovibrionaceae. The eukaryotic PyroTags were dominated by polychaetes, copepods and nematodes, however, ciliated protozoans were highly abundant in microscopy observations, and were represented by the genera Condylostoma, Loxophyllum and Peritromus. Finally, the abundant Sulfurimonas/Sulfurovum also suggest the occurrence of zero-valence sulphur oxidation, probably derived from Beggiatoaceae as a result of bacteriovorus infaunal activity or generated as free S(0) by the Arcobacter bacteria. The survey suggests an intense and complex sulphur cycle within the surface of salmon-farm impacted sediments.