Spatio-temporal variability in the Cladocera assemblage of a subtropical hypersaline lagoon

Cladocera represent an important zooplankton group because of their seasonal prominence in terms of abundance and their contribution in controlling primary production (phytoplankton). On a global scale, there are few studies on Cladocera in hypersaline environments. The present work aims to evaluate the spatio-temporal variation of the Cladocera assemblage across a salinity gradient in the habitats of the Araruama Lagoon. Samples were collected in random months over a period of four years at 12 fixed stations in the Araruama Lagoon using a WP2 plankton net equipped with a flow meter. Our results do not reveal significant influence of the tide and seasonal variation as factors affecting the Cladocera assemblage. Five Cladocera species were found in the Araruama Lagoon, only in stations 11 and 12 where they reached an average of 1,799 ± 3,103 ind. m-3. The mean of the Shannon Diversity Index was 0.45 ± 0.2. The species that stood out in terms of frequency and abundance were: Penilia avirostris (frequency of occurrence: 71%), followed by Pseudevadne tergestina (41%). The same species also stood out in terms of relative abundance, Penilia avirostris (87%) and Pseudevadne tergestina (11%). The absence of Cladocera in the innermost parts of the lagoon suggests that their entrance to these locations is possibly inhibited by the salinity and temperature gradient of the lagoon, being the main factors influencing the dynamics of the Cladocera assemblages.

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.

First hematologic and serum biochemistry record of black drum Pogonias cromis (Linnaeus, 1766) in a Neotropical hypersaline Lagoon

This study is a pioneer in describing the first hematological parameters and serum biochemistry record of black drum, Pogonias cromis (Linnaeus, 1766) in a Neotropical hypersaline Lagoon. We collected a total of 32 individuals of P. cromis, with a total length (TL) ranging between 160 and 710mm, and total weight (TW) ranging between 24 and 39.8g. Blood samples were taken and the presence of granulocytes, lymphocytes, and monocytes indicated that P. cromis had developed an immune system. Increased levels of thrombocytes with decreased levels of the lymphocytes, may be due to an increased frequency of lymphocytes among the leukocytes, which is also seen in the trend of higher levels of lymphocytes associated with an increased leukocyte count. The mean count of red blood cells (1.97 ± 0.07 106 mm³) was relatively low, whilst the hematocrit (37.4 ± 0.9%) and mean corpuscular volume (195.8 ± 1.9 fL) were higher when compared with those of other species of marine fish. High total plasma protein values (6.3 ± 0.1 g/dL) suggest an osmotic imbalance, which could be due to the stress of the environment. The relatively high values of ALT and AST (90 ± 0.7 and 229 ± 4.5 U/L, respectively) and urea (24.7 ± 0.6 mg/dL), and the low levels of creatinine (0.10 ± 0.02 mg/dL), suggest possible liver dysfunction in this species in this ecosystem. This work indicates the use of hematological analysis of P. cromis could be used as an effective biomarker for environmental risk assessments.

FISHING IN THE LARGEST PERENE HYPERSALINE LAGOON IN SOUTH AMERICA, WITH NOTES ON CURRENT REGULATIONS

Araruama Lagoon (Rio de Janeiro) is the largest hypersaline lagoon in South America. The aim of this study was to survey fishing landings, capture areas and production at this lagoon, in addition to analyzing data from the Pescarte Census. Fishing landings were monitored daily by community agents from March to August/2009, through the Petrobras Mosaico Program. Thirteen landing points were identified in five municipalities, totaling 8,096 recorded landings, and accumulating 469.1 tonnes. São Pedro da Aldeia (39.6%), Arraial do Cabo (27.7%) and areas in the central region (37.6%) and the south coast (29.1%) of the lagoon presented the highest landings and catch volumes. Twelve species were identified, mainly Pogonias courbina (48.9%) and Penaeus spp (33.8%), and gillnets were the most important fishing gear. Very few studies have addressed fishing at Araruama Lagoon, leading to current planning measures supported by little data. We advocate a participatory review of current regulations, to better address gillnet fishing and the capture of different fish species. This study is the result of research financed by the Pescarte Environmental Education Project, a mitigation measure required by the Federal Environmental Licensing, conducted by IBAMA.

Microstructure and mineral composition of Holocene stromatolites from Lagoa Vermelha, a hypersaline lagoon in Brazil: Insights into laminae genesis

ABSTRACT Stromatolites are domes, columns, or nearly flat crusts of laminated sedimentary rocks, usually consisting of Ca-Mg carbonates. Stromatolites result from lithification of microbial mats, which are benthic microbial ecosystems where microorganisms arrange themselves in layers according to their physiology. Despite a century of research, the hypothesis of stromatolite genesis by lithification of microbial mats remains controversial, and a convincing explanation for how stromatolites arise from microbial mats is still lacking. In this work, we analyze in detail a stromatolite from Lagoa Vermelha, a coastal hypersaline lagoon in Rio de Janeiro State, Brazil. The stromatolite presents a laminated core and thrombolitic regions at the periphery. Both thrombolitic and laminated facies consist of fine-grained authigenic minerals with minor contributions of bioclasts and quartz grains. X-ray diffraction shows aragonite, high-magnesium calcite (HMC) containing about 17% MgCO3, a very-high-Mg calcite (VHMC) containing 29–46% MgCO3, and small amounts of quartz and pyrite. Scanning electron microscopy of polished samples coupled to energy-dispersive X-ray analysis (EDS) showed that each lamina was composed of 1–4 distinct mineral phases embedded within each other, indicating sequential steps of precipitation of Ca-Mg carbonates under distinct biogeochemical conditions. The coexistence of different phases in a single lamina suggests that several processes contribute to mineral deposition as the incipient stromatolite laminae are left behind by microorganisms from the lower layers of the microbial mat when they grow and/or move upwards.