Physiological and molecular responses of the Antarctic harpacticoid copepod Tigriopus kingsejongensis to salinity fluctuations - A multigenerational study.

Since Antarctica and the surrounding Southern Ocean are facing global climate change, biota inhabiting those coastal regions is now challenged by environmental fluctuations including coastal freshening. In this study, the effects of salinity range of 0-75 (practical salinity unit, PSU) on the Antarctic harpacticoid copepod Tigriopus kingsejongensis was investigated by measurement of 96 h survival rate, lifespan, and sex ratio with further analysis of multigenerational growth parameters and mRNA expressions under salinity of 15-45. Different stages of the copepods (i.e., nauplius, male, and female) generally showed tolerance to hypo- and hypersalinity, wherein female copepods were more tolerant than males when exposed to salinity fluctuations. Lifespan was significantly shortened by hypo- and hypersalinity compared to control salinity (34), but there was no significant difference in the sex ratio between salinity treatments. Multigenerational experiments across five generations revealed that exposure to salinities of 15 and 45 reduced body length compared to that in control salinity and the first generation of each salinity group. Our results provide evidence regarding T. kingsejongensis on their preferred salinity ranges, physiological limit to salinity fluctuations, and population dynamics in future salinity.

The antioxidant responses of gills, intestines and livers and blood immunity of common carp (Cyprinus carpio) exposed to salinity and temperature stressors.

Aquaculture activity is affected by various environmental factors, including water salinity and high temperatures. The present study investigated the impact of using varying water salinity (0, 5, 10, 15 and 20 ppt) on the growth behavior, immune responses and antioxidative responses of common carp. Fish were raised under optimal conditions except for water salinity for 8 weeks; fish were then subjected to high-temperature stress (32 °C) for 48 h. The results indicated a reduced final weight (FBW), weight gain (WG), specific growth rate (SGR), condition factor (CF), feed intake and feed efficiency ratio (FER) in common carp reared in 15 and 20 ppt (p < 0.05). The lowest FBW, WG, SGR, CF, feed intake and FER values were observed in fish reared in 20 ppt water salinity (p < 0.05). In gills, the superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) were markedly decreased, but malondialdehyde (MDA) levels increased in fish challenged with 15 and 20 ppt before they were subjected to heat stress (p < 0.05). After heat stress, the SOD, CAT and GPx were decreased, and the MDA increased in fish reared in varying salinity levels (p < 0.05). Before heat stress, the intestinal SOD, CAT and GPx markers were decreased by 15 and 20 ppt, while the MDA level was increased by 15 and 20 ppt (p < 0.05). Generally, heat stress lowered the SOD, CAT and GPx activity in the intestines and liver tissues but increased MDA levels in common carp stressed by varying salinity levels (p < 0.05). The most decreased lysozyme activity, SOD, CAT and GPx and increased MDA levels were observed in common carp exposed to 20 ppt before and after heat stress (p < 0.05). After heat stress, fish exposed to 15 and 20 ppt had lower NBT than the remaining groups, and fish exposed to 20 ppt had the lowest values (p < 0.05). Overall, the heat stress markedly suppressed the antioxidant and immune responses of common carp reared in hypersalinity conditions.

Physiological responses of a juvenile marine estuarine-dependent fish (Family Sparidae) to changing salinity.

Estuaries are subject to high environmental variability coupled to tidal salinity shifts. Under restricted freshwater flow and prolonged drought conditions, salinity may exceed natural ranges and thus organisms may experience stressful hypersaline conditions. This study assessed the physiology of a juvenile marine estuarine-dependent species Rhabdosargus holubi (Family: Sparidae) under changing salinity to determine the impact on respiration and survival under shock and acclimatisation exposures. Oxygen consumption was not significantly different in the 2.5 to 45 salinity range and the interaction between temperature and salinity was not significant at the moderate levels tested. This confirmed the strong osmoregulatory capabilities of marine estuarine-dependent R. holubi. However, respiration was impacted at salinities of 55-62.5. The salinity tolerance ranges of R. holubi were expanded beyond those previously observed in the laboratory, to a maximum of 77 when fish were gradually exposed to daily 20% incremental changes. This indicated the ability to adapt to hypersaline conditions that occur gradually in anthropogenically altered estuaries which is an important aspect for management decisions regarding freshwater inputs. The adaptability of Rhabdosargus holubi to hypersaline conditions in estuaries may thereby ensure the maintenance of populations in the short term under certain environmental conditions, such as those currently occurring in a freshwater-scarce South Africa. However, in the long term and at more extreme salinities (> 55), the physiology of R. holubi and similar species may be compromised, thus placing the species at risk.

Recent Advances in Halophilic Protozoa Research.

Most research on microorganisms adapted to hypersaline habitats has focused on Archaea and Bacteria, with microbial eukaryotes receiving much less attention. Over the past 15 yr, our knowledge of phagotrophic microbial eukaryotes, i.e. protozoa, from hypersaline habitats has greatly improved through combinations of microscopy, molecular phylogenetics, environmental sequencing, transcriptomics and growth experiments. High salinity waters from salterns, other landlocked water masses and deep hypersaline anoxic basins contain unique and diverse halophilic protozoan assemblages. These have the potential to exert substantial grazing pressure on prokaryotes and other eukaryotes. They represent many separate evolutionary lineages; species of Heterolobosea, Bicosoecida, and Ciliophora have been most intensively characterized, with several proven to be extreme (or borderline extreme) halophiles. Transcriptomic examinations of the bicosoecid Halocafeteria (and the heteroloboseid Pharyngomonas) indicate that high-salt adaptation is associated with a subtle shift in protein amino acid composition, and involves the differential expression of genes participating in ion homeostasis, signal transduction, stress management, and lipid remodeling. Instances of gene duplication and lateral transfer possibly conferring adaptation have been documented. Indirect evidence suggests that these protozoa use "salt-out" osmoadaptive strategies.

Bacterial and Archaeal Diversity in Hypersaline Cyanobacterial Mats Along a Transect in the Intertidal Flats of the Sultanate of Oman.

Hypersaline intertidal zones are highly dynamic ecosystems that are exposed to multiple extreme environmental conditions including rapidly and frequently changing parameters (water, nutrients, temperature) as well as highly elevated salinity levels often caused by high temperatures and evaporation rates. Microbial mats in most extreme settings, as found at the coastline of the subtropical-arid Arabian Peninsula, have been relatively less studied compared to their counterparts around the world. We report, here, for the first time on the diversity of the bacterial and archaeal communities of marine microbial mats along an intertidal transect in a wide salt flat with strongly increased salinity employing Illumina MiSeq technology for amplicon sequencing of 16S rRNA gene fragments. Microbial communities were dominated by typical halotolerant to halophilic microorganisms, with clear shifts in community composition, richness, and diversity along the transect. Highly adapted specialists (e.g., Euhalothece, Salinibacter, Nanohaloarchaeota) were mainly found at the most extreme, upper tidal sites and less specialized organisms with wide tolerance ranges (e.g., Lyngbya, Rhodovibrio, Salisaeta, Halobacteria) in intermediate sites of the transect. The dominating taxa in the lower tidal sites were typical members of well-stabilized mats (e.g., Coleofasciculus, Anaerolineaceae, Thaumarchaeota). Up to 40% of the archaeal sequences per sample represented so far unknown phyla. In conclusion, the bacterial richness and diversity increased from upper towards lower tidal sites in line with increasing mat stabilization and functional diversity, opposed to that of cyanobacteria only and archaea, which showed their highest richness and diversity in upper tidal samples.

The differential role of renoguanylin in osmoregulation and apical Cl-/HCO3- exchange activity in the posterior intestine of the Gulf toadfish (Opsanus beta).

The guanylin family of peptides are effective regulators of intestinal physiology in marine teleosts. In the distal intestinal segments, they inhibit or reverse fluid absorption by inhibiting the absorptive short-circuit current (Isc). The present findings demonstrate that mRNA from guanylin and uroguanylin, as well as at least one isoform of the guanylin peptide receptor, apical guanylyl cyclase-C (GC-C), was highly expressed in the intestine and rectum of the Gulf toadfish (Opsanus beta). In the posterior intestine, GC-C, as well as the cystic fibrosis transmembrane conductance regulator and basolateral Na(+)/K(+)/2Cl(-) cotransporter, which comprise a Cl(-)-secretory pathway, were transcriptionally upregulated in 60 parts per thousand (ppt). The present study also shows that, in intestinal tissues from Gulf toadfish held in 35 ppt, renoguanylin (RGN) expectedly causes net Cl(-) secretion, inhibits both the absorptive Isc and fluid absorption, and decreases HCO3(-) secretion. Likewise, in intestinal tissues from Gulf toadfish acclimated to 60 ppt, RGN also inhibits the absorptive Isc and fluid absorption but to an even greater extent, corresponding with the mRNA expression data. In contrast, RGN does not alter Cl(-) flux and, instead, elevates HCO3(-) secretion in the 60-ppt group, suggesting increased apical Cl(-)/HCO3(-) exchange activity by SLC26a6. Overall, these findings reinforce the hypotheses that the guanylin peptide system is important for salinity acclimatization and that the secretory response could facilitate the removal of solids, such as CaCO3 precipitates, from the intestine.

Esophageal desalination is mediated by Na⁺, H⁺ exchanger-2 in the gulf toadfish (Opsanus beta).

Esophageal desalination is a crucial step in the gastrointestinal water absorption pathway, as this pre-intestinal processing establishes the osmotic conditions necessary for water absorption. Previous work has shown that esophageal Na(+) absorption is amiloride sensitive; however, it is as yet unclear if Na(+), H(+) exchangers (NHE) or Na(+) channels (ENaC) are responsible. The purpose of the current study was therefore to investigate the roles that NHE isoforms may play in this process in a marine teleost, the gulf toadfish (Opsanus beta), as well as what role NHE isoforms may play in the downstream intestinal Na(+) transport. A combination of symmetrical current clamp and asymmetrical voltage clamp experiments showed the esophagus to contain both an ion absorptive current (I(sc)=0.83±0.68) and serosal side negative transepithelial potential (TEP=-4.9±0.6). (22)Na uptake (J(Na)(m→s)) was inhibited by 0.5 mM EIPA, with no effect of 0.1 mM amiloride, 1 mM furosemide or 1 mM thiazide. A Cl(-) free saline reduced J(Na)(m→s) by 40% while also reducing conductance and reversing TEP. These results suggest that both transcellular and paracellular components contribute to esophageal Na(+) transport, with transcellular transport mediated by NHE. The NHE1, NHE2 and NHE3 genes were amplified and tissue distribution analysis by real-time PCR showed high NHE2 expression levels in the esophagus and stomach. Little NHE3 expression was observed throughout the gastrointestinal tract, and NHE2 expression was absent from the intestine. Hypersalinity (60 ppt) had no effect on the expression profile of NHE2, slc4a2, scl26a6, CAc or V-type ATPase (ß-subunit), suggesting that esophageal desalination is less flexible in response to osmotic stress than the intestine.

Characteristics of the ichthyofauna of a temperate microtidal estuary with a reverse salinity gradient, including inter-decadal comparisons.

Data on the fish fauna of the Leschenault Estuary on the lower west coast of Australia were collected and used as a model to elucidate the characteristics of permanently open estuaries with a reverse salinity gradient, which undergo seasonal changes similar to many other estuaries with Mediterranean climate. Focus was placed on determining (1) the relationships of the number of species, density, life cycle category and species composition of fishes with region (within estuary), season and year and salinity, (2) whether species are partitioned along the lengths of such systems and (3) the extent and significance of any inter-decadal changes in species composition. The analyses and interpretation involved using multi-factorial permutational multivariate analysis of variance (PERMANOVA) and analysis of similarity (ANOSIM) designs, and three new or recently published visualization tools, i.e. modified non-metric multidimensional scaling (nMDS) plots, coherent species curves and segmented bubble plots. The base, lower, upper and apex regions of the Leschenault Estuary, along which the salinity increased in each season except in winter when most rainfall occurs, were sampled seasonally for the 2 years between winter 2008 and autumn 2010. Estuarine residents contributed twice as many individuals, but less than half the number of species as marine taxa. While the numbers of marine species and estuarine residents declined between the base or lower and apex regions, the individuals of marine species dominated the catches in the base region and estuarine residents in the other three regions. Ichthyofaunal composition in each region underwent conspicuous annual cyclical changes, due to time-staggered differences in recruitment among species, and changed sequentially along the estuary, both paralleling salinity trends. Different groups of species characterized the fauna in the different regions and seasons, thereby partitioning resources among species. The ichthyofauna of the apex region, in which salinities reached 54 and temperatures 36° C, recorded the highest maximum density and, in terms of abundance, was dominated (90%) by three atherinid species, emphasizing the ability of this family to tolerate extreme conditions. Comparisons between the data for 2008-2010 and 1994 demonstrate that the spotted hardyhead Craterocephalus mugiloides and the common hardyhead Atherinomorus vaigiensis had colonized and become abundant in the Leschenault Estuary in the intervening period. This represents a southwards extension of the distribution of these essentially tropical species during a period of increasing coastal water temperatures as a result of climate change. The abundance of weed-associated species, e.g. the western gobbleguts Ostorhinchus rueppellii and the soldier Gymnapistes marmoratus, increased, whereas that of the longfinned goby Favonigobius lateralis decreased, probably reflecting increases in eutrophication and siltation, respectively.

Larval fish assemblages in selected Brazilian estuaries: Species-environment relationships under different anthropogenic influences.

We investigate the effects of spatial changes in environmental conditions and anthropogenic influences on larval fish communities in two tropical estuaries with varying levels of human impact. Our findings revealed a distinct structure of larval fish assemblages between the two estuaries located in northeastern Brazil, and we observed that eutrophication, characterized by high concentrations of nutrients, had adverse effects on the abundance and richness of larval fish assemblages. Additionally, we observed that a decrease in rainfall had an impact on larval fish assemblages, particularly during the dry season, when intermittent upstream rivers lead to changes in salinity and species composition within the estuaries. This study contributed to evaluating the community descriptors of two tropical estuaries under different levels of human influence, providing insights into the vulnerability of larval fish assemblages to climate change, specifically in relation to human influences and hypersalinity and the effects of marinization in shallow tropical estuaries in this region.

Transcriptomic profiles and diagnostic biomarkers in the Mediterranean seagrasses Posidonia oceanica and Cymodocea nodosa reveal mechanistic insights of adaptative strategies upon desalination brine stress.

Seawater desalination by reverse osmosis is growing exponentially due to water scarcity. Byproducts of this process (e.g. brines), are generally discharged directly into the coastal ecosystem, causing detrimental effects, on benthic organisms. Understanding the cellular stress response of these organisms (biomarkers), could be crucial for establishing appropriate salinity thresholds for discharged brines. Early stress biomarkers can serve as valuable tools for monitoring the health status of brine-impacted organisms, enabling the prediction of long-term irreversible damage caused by the desalination industry. In this study, we conducted laboratory-controlled experiments to assess cellular and molecular biomarkers against brine exposure in two salinity-sensitive Mediterranean seagrasses: Posidonia oceanica and Cymodocea nodosa. Treatments involved exposure to 39, 41, and 43 psu, for 6 h and 7 days. Results indicated that photosynthetic performance remained unaffected across all treatments. However, under 43 psu, P. oceanica and C. nodosa exhibited lipid oxidative damage, which occurred earlier in P. oceanica. Additionally, P. oceanica displayed an antioxidant response at higher salinities by accumulating phenolic compounds within 6 h and ascorbate within 7 d; whereas for C. nodosa the predominant antioxidant mechanisms were phenolic compounds accumulation and total radical scavenging activity, which was evident after 7 d of brines exposure. Finally, transcriptomic analyses in P. oceanica exposed to 43 psu for 7 days revealed a poor up-regulation of genes associated with brassinosteroid response and abiotic stress response, while a high down-regulation of genes related to primary metabolism was detected. In C. nodosa, up-regulated genes were involved in DNA repair, cell cycle regulation, and reproduction, while down-regulated genes were mainly associated with photosynthesis and ribosome assembly. Overall, these findings suggest that 43 psu is a critical salinity-damage threshold for both seagrasses; and despite the moderate overexpression of several transcripts that could confer salt tolerance, genes involved in essential biological processes were severely downregulated.

Coping with salinity extremes: Gill transcriptome profiling in the black-chinned tilapia (Sarotherodon melanotheron).

Steeper and sometimes extreme salinity gradients increasingly affect aquatic organisms because of climate change. Hypersalinity habitats demand powerful physiological adaptive strategies. Few teleost species have the capacity to spend their whole life cycle in salinities way over seawater levels. Focusing on the multifunctional gill, we unraveled the tilapia S. melanotheron key strategies to cope with different environmental conditions, ranging from freshwater up to hypersaline habitats. De novo transcriptome assembly based on RNAseq allowed for the analysis of 40,967 annotated transcripts among samples collected in three wild populations at 0, 40 and 80 ‰. A trend analysis of the expression patterns revealed responses across the salinity gradient with different gene pathways involved. Genes linked to ion transport, pH regulation and cell surface receptor signaling were mainly upregulated in the high salinity habitat. We identified tight junction proteins that were critical in high salinity habitats and that were different from the well-known tightening junctional proteins identified and expressed in fresh water. Expression profiles also suggest a change in the vascular tone that could be linked to an osmorespiratory compromise not only in fresh water, but also in high salinity environments. A striking downregulation of genes linked to the immune system and to the heat shock response was observed suggesting an energetic trade-off between immunity and acclimation/adaptation in the hypersaline habitat. The high expression of transcripts coding for immune and heat shock response in the freshwater habitat suggests the establishment of powerful mechanisms to protect gills from environmental threats and to maintain protein integrity. Non-directional expression trends were also detected with an upregulation of genes only in the hypersaline habitat (80 ‰) or only in the marine habitat (40 ‰). Unravel physiological strategies in S. melanotheron populations will help to better understand the molecular basis of fish euryhalinity in salinity-contrasted environments.

The combined effects of salinity and ammonia on the growth behavior, stress-related markers, and hepato-renal function of common carp (Cyprinus carpio).

One of the most critical factors affecting aquaculture efficiency is the capability of releasing ammonia from the water. By applying a high salinity strategy, this study provides a prompt approach for removing high ammonia levels and relieving its adverse impacts on common carp. The study investigated five groups with triplicates where the control was kept with fresh water, and the remaining four groups stressed with different salinity levels (5, 10, 15, and 20 ppt) for 8 weeks. Then fish were exposed to unionized ammonia (NH3 ) stress (0.5 ppm) for 6 h. The final weight (FBW) and weight gain (WG) showed lower values in fish stressed with 15 and 20 ppt salinity levels than fish reared in 0 and 5 ppt salinity levels (p < 0.05). The lowest FBW and WG and the highest feed conversion ratio were shown in fish grown in 20 ppt (p < 0.05). The survival rate was markedly lowered by 15 and 20 ppt salinity levels (p < 0.05), while no significant differences were observed among 0, 5, and 10 ppt salinity levels (p > 0.05). Liver condition-related indices (alanine aminotransferase, aspartate aminotransferase, and alanine aminotransferase) were markedly increased in fish grown in 15 and 20 ppt before or after ammonia stress (p < 0.05). The results showed higher creatinine levels in fish raised in 15 and 20 ppt than the remaining salinity levels, with the highest value in fish of 20 ppt salinity before and after ammonia stress (p < 0.05). Markedly the blood glucose and cortisol levels were upraised in fish reared in 10, 15, and 20 ppt before and after ammonia stress (p < 0.05). The glucose level was not significantly different in fish reared in 5 ppt than 0 and 10 ppt salinity levels (p < 0.05). Generally, the blood glucose and cortisol levels were decreased markedly after ammonia stress than before ammonia stress (p < 0.05). Interestingly, total protein, albumin, and globulin levels were increased in common carp reared in different salinity levels after ammonia stress (p < 0.05). In conclusion, ammonia toxicity combined with high salinity resulted in a regulatory effect on the hepato-renal function and stress-related markers in common carp.

Autophagy contributes to increase the content of intracellular free amino acids in hard clam (Mercenaria mercenaria) during prolonged exposure to hypersaline environments.

Marine bivalves in intertidal zones and land-based seawater ponds are constantly subjected to a wide range of salinity fluctuations due to heavy rainfall, intense drought, and human activities. As osmoconformers, bivalves rely primarily on rapid release or accumulation of free amino acids (FAAs) for osmoregulation. Euryhaline bivalves are capable of withstanding hyposaline and hypersaline environments through regulation of physiology, metabolism, and gene expression. However, current understanding of the molecular mechanisms underlying osmoregulation and salinity adaptation in euryhaline bivalves remains largely limited. In this study, RNA-seq, WGCNA and flow cytometric analysis were performed to investigate the physiological responses of hard clams (Mercenaria mercenaria) to acute short-term hyposalinity (AL) and hypersalinity (AH), and chronic long-term hyposalinity (CL) and hypersalinity (CH) stress. We found that amino acids biosynthesis was significantly inhibited and aminoacyl-tRNA biosynthesis was augmented to decrease intracellular osmolarity during hyposaline exposure. Under CH, numerous autophagy-related genes (ATGs) were highly expressed, and the autophagy activity of gill cells were significantly up-regulated. A significant decrease in total FAAs content was observed in gills after NH4Cl treatment, indicating that autophagy was crucial for osmoregulation in hard clams during prolonged exposure to hypersaline environments. To prevent premature or unnecessary apoptosis, the expression of cathepsin L was inhibited under AL and AH, and inhibitors of apoptosis was augmented under CL and CH. Additionally, neuroendocrine regulation was involved in salinity adaption in hard clams. This study provides novel insights into the physiological responses of euryhaline marine bivalves to hyposaline and hypersaline environments.

Compositional Changes in Sediment Microbiota Are Associated with Seasonal Variation of the Water Column in High-Altitude Hyperarid Andean Lake Systems.

The lacustrine systems of La Brava and La Punta, located in the Tilopozo sector in the extreme south of Salar de Atacama, are pristine high-altitude Andean lakes found along the central Andes of South America. This shallow ecosystem suffers from permanent evaporation, leading to falling water levels, causing it to recede or disappear during the dry season. This dynamic causes physicochemical changes in lakes, such as low nutrient availability, pH change, and dissolved metals, which can influence the composition of the microbial community. In this study, we used a metataxonomic approach (16S rRNA hypervariable regions V3 to V4) to characterize the sedimentary microbiota of these lakes. To understand how the water column affects and is structured in the microbiota of these lakes, we combined the analysis of the persistence of the water column through satellite images and physicochemical characterization. Our results show a significant difference in abiotic factors and microbiota composition between La Punta and La Brava lakes. In addition, microbiota analysis revealed compositional changes in the ecological disaggregation (main and isolated bodies) and antagonistic changes in the abundance of certain taxa between lakes. These findings are an invaluable resource for understanding the microbiological diversity of high Andean lakes using a multidisciplinary approach that evaluates the microbiota behavior in response to abiotic factors. IMPORTANCE In this study, we analyzed the persistence of the water column through satellite images and physicochemical characterization to investigate the composition and diversity in High Andean Lake Systems in a hyperarid environment. In addition to the persistence of the water column, this approach can be used to analyze changes in the morphology of saline accumulations and persistence of snow or ice; for example, for establishing variable plant cover over time and evaluating the microbiota associated with soils with seasonal changes in plants. This makes it an ideal approach to search for novel extremophilic microorganisms with unique properties. In our case, it was used to study microorganisms capable of resisting desiccation and water restriction for a considerable period and adapting to survive in ecological niches, such as those with high UV irradiation, extreme drought, and high salt concentration.

Detection of a bibenzyl core scaffold in 28 common mangrove and associate species of the Indian Sundarbans: potential signature molecule for mangrove salinity stress acclimation.

Bibenzyl derivatives comprising two benzene rings are secondary plant metabolites with significant therapeutic value. To date, bibenzyl derivatives in the Plant kingdom have been primarily identified in bryophytes, orchids, and Cannabis sativa. The metabolic cost investment by plant species for the synthesis of these bioactive secondary metabolites is rationalized as a mechanism of plant defense in response to oxidative stress induced by biotic/abiotic factors. Bibenzyl derivatives are synthesized from core phenylpropanoid biosynthetic pathway offshoots in plant species. Mangrove and mangrove associate species thrive under extreme ecological niches such as a hypersaline intertidal environment through unique adaptive and acclimative characteristics, primarily involving osmotic adjustments followed by oxidative stress abatement. Several primary/secondary bioactive metabolites in mangrove species have been identified as components of salinity stress adaptation/acclimation/mitigation; however, the existence of a bibenzyl scaffold in mangrove species functioning in this context remains unknown. We here report the confirmed detection of a core bibenzyl scaffold from extensive gas chromatography-mass spectrometry and gas chromatography-flame ionization detection analyses of 28 mangrove and mangrove associate species from the Indian Sundarbans. We speculate that the common presence of this bibenzyl core molecule in 28 mangrove and associate species may be related to its synthesis via branches of the phenylpropanoid biosynthetic pathway induced under high salinity, which functions to detoxify reactive oxygen species as a protection for the maintenance of plant metabolic processes. This finding reveals a new eco-physiological functional role of bibenzyls in unique mangrove ecosystem.

Analysis of a hypersaline drought-prone estuary reveals low density and diversity of fish eggs and larvae.

We analyzed fish eggs and larvae in an estuary under severe drought conditions. We detected an inverse salinity gradient, with values increasing from the mouth to the upper estuary. Egg densities decreased from the estuarine mouth to the upstream areas following the salinity increase for all three mesh net sizes. This pattern was also found for the density of larvae, which decreased in estuarine regions with hypersalinity (38 to 62). The low diversity constituted only nine fish species, which were classified as anadromous (Anchoa hepsetus), estuarine and marine (Bathygobius soporator, Hippocampus reidi, Eucinostomus sp., and Diapterus auratus), marine estuarine-opportunist (Caranx latus and Bardiella rochus), and marine stragglers (Echeneis naucrates and Haemulon sp.). In addition, we observed an oversimplification of the assemblage to include stress-tolerant estuarine and marine species. Our baseline results suggest that this hypersaline estuarine ecosystem has lower densities and diversity than a healthy mangrove system.

Study of Wetland Soils of the Salar de Atacama with Different Azonal Vegetative Formations Reveals Changes in the Microbiota Associated with Hygrophile Plant Type on the Soil Surface.

Salar de Atacama is located approximately 55 km south of San Pedro de Atacama in the Antofagasta region, Chile. The high UV irradiation and salt concentration and extreme drought make Salar de Atacama an ideal site to search for novel soil microorganisms with unique properties. Here, we used a metataxonomic approach (16S rRNA V3-V4) to identify and characterize the soil microbiota associated with different surface azonal vegetation formations, including strict hygrophiles (Baccharis juncea, Juncus balticus, and Schoenoplectus americanus), transitional hygrophiles (Distichlis spicata, Lycium humile, and Tessaria absinthioides), and their various combinations. We detected compositional differences among the soil surface microbiota associated with each plant formation in the sampling area. There were changes in soil microbial phylogenetic diversity from the strict to the transitional hygrophiles. Moreover, we found alterations in the abundance of bacterial phyla and genera. Halobacteriota and Actinobacteriota might have facilitated water uptake by the transitional hygrophiles. Our findings helped to elucidate the microbiota of Salar de Atacama and associate them with the strict and transitional hygrophiles indigenous to the region. These findings could be highly relevant to future research on the symbiotic relationships between microbiota and salt-tolerant plants in the face of climate change-induced desertification. IMPORTANCE The study of the composition and diversity of the wetland soil microbiota associated with hygrophilous plants in a desert ecosystem of the high Puna in northern Chile makes it an ideal approach to search for novel extremophilic microorganisms with unique properties. These microorganisms are adapted to survive in ecological niches, such as those with high UV irradiation, extreme drought, and high salt concentration; they can be applied in various fields, such as biotechnology and astrobiology, and industries, including the pharmaceutical, food, agricultural, biofuel, cosmetic, and textile industries. These microorganisms can also be used for ecological conservation and restoration. Extreme ecosystems are a unique biological resource and biodiversity hot spots that play a crucial role in maintaining environmental sustainability. The findings could be highly relevant to future research on the symbiotic relationships between microbiota and extreme-environment-tolerant plants in the face of climate change-induced desertification.

Differentially Expressed miRNAs and mRNAs in Regenerated Scales of Rainbow Trout (Oncorhynchus mykiss) under Salinity Acclimation.

In order to explore the potential effects of salinity acclimation on bone metabolism of rainbow trout (Oncorhynchus mykiss), transcriptional information of regenerated scales under salinity acclimation (sea water, SW) was compared to those of fish under fresh water (FW) environments. According to the high-throughput sequencing results, a total of 2620 significantly differentially expressed genes (DEGs) were identified in the data of SW vs. FW. Compared with the FW group, six significantly downregulated and 44 significantly upregulated miRNAs were identified in the SW scales (p < 0.05). Furthermore, a total of 994 significantly differentially expressed target genes (DETGs) were identified from the 50 significantly differentially expressed miRNAs (DE miRNAs). Gene ontology analysis of the aforementioned DETGs was similar to the results of the differentially expressed genes (DEGs) obtained from mRNA-seq data, these genes were mainly related to ion metabolism. KEGG enrichment analysis of the DEGs and DETGs suggested that many significantly enriched pathways were related to the energy metabolism pathway.

Intestinal osmoregulatory mechanisms differ in Mediterranean and Atlantic European sea bass: A focus on hypersalinity.

European sea bass (Dicentrarchus labrax) migrate towards habitats where salinity can reach levels over 60‰, notably in Mediterranean lagoons. D. labrax are genetically subdivided in Atlantic and Mediterranean lineages and have evolved in slightly different salinities. We compared Atlantic and West-Mediterranean populations regarding their capacity to tolerate hypersalinity with a focus on the involvement of the intestine in solute-driven water reabsorption. Fish were analyzed following a two-week transfer from seawater (SW, 36‰) to either SW or hypersaline water (HW, 55‰). Differences among lineages were observed in posterior intestines of fish maintained in SW regarding NKA activities and mRNA expressions of nkaα1a, aqp8b, aqp1a and aqp1b with systematic higher levels in Mediterranean sea bass. High salinity transfer triggered similar responses in both lineages but at different magnitudes which may indicate slight different physiological strategies between lineages. High salinity transfer did not significantly affect the phenotypic traits measured in the anterior intestine. In the posterior intestine however, the size of enterocytes and NKA activity were higher in HW compared to SW. In this tissue, nka-α1a, nkcc2, aqp8ab and aqp8aa mRNA levels were higher in HW compared to SW as well as relative protein expression of AQP8ab. For aqp1a, 1b, 8aa and 8b, an opposite trend was observed. The sub-apical localization of AQP8ab in enterocytes suggests its role in transepithelial water reabsorption. Strong apical NKCC2/NCC staining indicates an increased Na+ and Cl- reuptake by enterocytes which could contribute to solute-coupled water reuptake in cells where AQP8ab is expressed.

Hypersalinity drives convergent bone mass increases in Miocene marine mammals from the Paratethys.

Pachyosteosclerosis-a condition that creates dense, bulky bones-often characterizes the early evolution of secondarily aquatic tetrapods like whales and dolphins1-3 but then usually fades away as swimming efficiency increases.4 Here, we document a remarkable reversal of this pattern, namely the convergent re-emergence of bone densification in Miocene seals, dolphins, and whales from the epicontinental Paratethys Sea of eastern Europe and central Asia. This phenomenon was driven by imbalanced remodeling and inhibited resorption of primary trabeculae and coincided with hypersaline conditions-the Badenian salinity crisis-that affected the Central Paratethys between 13.8 and 13.4 Ma.5 Dense bones acting as ballast would have facilitated efficient swimming in the denser and more buoyant water and hence were likely adaptive in this setting. From the Central Paratethys, pachyosteosclerosis subsequently spread eastward, where it became a defining feature of the endemic late Miocene whale assemblage.6,7.