Fossil Holocene Ostracoda from the Itapeva Lake, Southern Brazilian coastal plain

Holocene ostracods from a core obtained in the Itapeva Lake, Rio Grande do Sul coastal plain, are studied in this paper. Twenty-six species belonging to 22 genera and 13 families were registered in nine samples analyzed, two of them new: Cytherella eros sp. nov. and Loxoconcha itapevensis sp. nov. The taxonomic composition of the assemblages varies along the core, being Cyprideis multidentataHartmann the most abundant and frequent species (273 specimens), followed by Cytheretta punctata Sanguinetti (56 specimens) and L.itapevensis sp. nov. (51 specimens). Variation in richness and diversity observed along the core probably results from sedimentary and hydrological changes during the evolution of the Itapeva Lake. The results obtained in this work reinforce the importance of ostracods in the study of coastal paleoenvironments. Keywords: barrier-lagoon system, biostratinomy, micropaleontology, Quaternary.

Metagenomic Insights Into Ecosystem Function in the Microbial Mats of a Large Hypersaline Coastal Lagoon System

The hypersaline lagoon system of Araruama (HLSA) is one of the largest in the world and one of the most important sources of evaporative salt in Brazil. The biogeochemical characteristics of this lagoon system led it to be considered a Precambrian relic. The HLSA also harbors extensive microbial mats, but the taxonomic and metabolic attributes of these mats are poorly understood. Our high-throughput metagenomics analyses demonstrated that the HLSA microbial mats are dominated by Proteobacteria, Cyanobacteria, and Bacteroidetes. Among Proteobacteria, Deltaproteobacteria comprises approximately 40% of the total population and it includes sulfate-reducing bacteria such as Desulfobacterales, Desulfuromonadales, and Desulfovibrionales. Differing in composition and function of their reaction centers, other phylogenetic diverse anoxygenic phototrophic bacteria were detected in the HLSA microbial mats metagenomes. The presence of photolithoautotrophs, sulfate reducers, sulfide oxidizers, and aerobic heterotrophs suggests the existence of numerous cooperative niches that are coupled and regulated by microbial interactions. We suggest that the HLSA microbial mats hold microorganisms and the necessary machinery (genomic repertoire to sustain metabolic pathways) to promote favorable conditions (i.e., create an alkaline pH microenvironment) for microbially mediated calcium carbonate precipitation process. Metagenome-assembled genomes (Ca. Thiohalocapsa araruaensis HLSAbin6 sp. nov. and Ca. Araruabacter turfae HLSAbin9 gen. nov. sp. nov.) obtained support the relevance of Sulfur metabolism and they are enriched with genes involved in the osmoadaptive networks, hinting at possible strategies to withstand osmotic stress. Metabolically versatile bacteria populations, able to use multiple nutrient sources and osmolytes, seem to be a relevant attribute to survive under such stressful conditions.

Vulnerability Analysis of the Riumar Dune Field in El Garxal Coastal Wetland (Ebro Delta, Spain)

The aim of this work is to apply a vulnerability index in the dune field located in the Riumar urban zone at the mouth of the Ebro River. This dune field represents the natural barrier of the El Garxal coastal lagoon system. The index used integrates the dimensions of exposure, susceptibility, and resilience from the analysis of 19 variables. The results obtained show moderate susceptibility and high resilience, which are in line with the behavior of this dune field during the last sea storms (Gloria in January 2020 and Philomena in January 2021, among others) that have tested the capacity of this system to cope with the effects of these storms. Therefore, increasing the knowledge of the factors affecting the vulnerability of the dunes can be helpful in the management and conservation of these coastal environments.