Salinity Fluctuations Research Articles

Functional changes in hemocytes and antioxidant activity in gills of the ark clam Anadara kagoshimensis (Bivalvia: Arcidae) induced by salinity fluctuations.

This study describes the analysis of antioxidant enzymatic activities (catalase and superoxide dismutase) in gills and functional state of hemocytes (osmotic stability, mitochondrial membrane potential) of ark clams (Anadara kagoshimensis) from the Black Sea basin exposed to salinity stress. For this, the effects of 48h periods of exposure to low (8 ‰, 14 ‰) and high (35 ‰, 45 ‰) salinity were assessed. Our results showed that ark clams, A. kagoshimensis, possessed pronounced tolerance to hypersalinity stress and are sensitive to a short-time hyposalinity treatment. Salinity 35 ‰ inhibited production of reactive oxygen species (ROS) by hemocytes and did not affect their levels of mitochondrial membrane potential. Acclimation to 45 ‰ salinity caused significant increase in mitochondrial membrane potential accompanied with recovery of intracellular ROS levels up to controls levels. Acclimation to low salinity (8 ‰) induced an increase in both ROS and mitochondrial membrane potential levels in hemocytes. Catalase and superoxide dismutase activity in gills decreased following acclimation to low (8 ‰) and high (35 ‰) salinity. Exposure to the highest salinity levels (45 ‰) led to a decrease of superoxide dismutase activity levels, but did not influence the levels of catalase activity. Acclimation to low and high salinity was not accompanied with changes in osmotic fragility of hemocytes despite osmotic fragility curve according to changes in hemolymph osmolarity. Based upon these results, we postulate the involvement of cellular osmoregulatory mechanisms in the adaptation of the ark clam to short-term fluctuations of environmental salinity.

Interactive effects of temperature and salinity on the apoptosis, antioxidant enzymes, and MAPK signaling pathway of juvenile pufferfish (Takifugu fasciatus)

Takifugu fasciatus is an anadromous fish widely distributed in East Asia and often experiences fluctuations in temperature and salinity. This study investigated the effects of the interactions between temperature and salinity on apoptosis, antioxidant enzymes, and mitogen-activated protein kinase (MAPK) signaling pathways in the liver of T. fasciatus. The temperature (25, 21, 17, and 13 ℃) and salinity (0, 10, and 20 ppt salinity) were conducted with three replicates for each treatment. Quantitative reverse transcription-PCR (qRT-PCR), western blotting, and TdT-mediated dUTP Nick-End Labeling (Tunel) assays were used to detect mRNA expression, protein levels, and apoptosis levels. The expressions of caspase 3, 7, 9, and the apoptosis index increased in T. fasciatus as the temperature decreased, while the expression of B-cell lymphoma-2 (BCL-2) decreased. The correlation results in this study showed that after the exposure to 10 ppt salinity at 13 and 17 ℃, the glutathione peroxidase (GSH-PX) activity and malondialdehyde (MDA) concentration, caspase3, 7, and 9 expressions, and apoptosis index were decreased as compared with those in the control. In addition, there were no deaths and no significant change in apoptosis in the group at 21 ℃, and there were a small number of deaths in the 20 ppt, 25 ℃ groups. Correspondingly, MDA concentration and total superoxide dismutase (T-SOD) activity, caspase7 and 9 expressions, and apoptosis index in the liver were significantly higher in the 20 ppt, 25 ℃ groups than in the 0 ppt, 25 ℃, and 10 ppt, 25 ℃ groups. In addition, salinity had no significant influence on the expression of p-p38 MAPK and its phosphorylation ratio (p-p38/p38) at low temperatures but significantly affected its downstream transcription factors (ATF2, ElK-1, MEF2, and P53). Our study provides a reference for healthy cultures of T. fasciatus.

Seasonal drivers of productivity and calcification in the coral Platygyra carnosa in a subtropical reef

Scleractinian corals are increasingly subjected to local stressors combined with global changes. In subtropical areas, corals exhibit metabolic plasticity and resilience in response to variability and extremes in local temperature, salinity, and light; however, the physiological mechanisms by which corals acclimate or adapt to these changing conditions remain disputed. We assessed the physiological status of the coral Platygyra carnosa during a two-year in situ monitoring survey. To obtain metabolic rates (respiration and photosynthesis), photochemical efficiency (Fv / Fm), and biocalcification measurements, non-invasive techniques such as underwater respirometry, Pulse Amplitude Modulated (PAM) fluorometry, total alkalinity measurements, and digital photography were used. Our findings show clear seasonality in water quality parameters, which affected coral health. Elevated temperatures during the summer were below the maximum monthly mean < 31°C) but reduced the energetic productivity of corals (-44% relative to winter). Fluctuations in salinity (25–38 ppt) and pH (7.65–8.44) were linked to rainfall and reduced calcification rates. The conditions during the spring were favorable for coral metabolism and calcification (+20% relative to summer). Overall, our research demonstrates that the metabolic plasticity of P. carnosa in response to shifts in seawater quality allows this species to survive ongoing environmental change. Our in situ observations provide fundamental insights into coral response mechanisms under changing environmental conditions and contribute to projections of coral health under future scenarios of global change.

Solid-State Fermentation of Plant Feedstuff Mixture Affected the Physiological Responses of European Seabass (Dicentrarchus labrax) Reared at Different Temperatures and Subjected to Salinity Oscillation.

This study aimed to evaluate the effects of dietary inclusion of plant feedstuff mixture (PFM) pre-treated by solid-state fermentation (SSF) on the physiological responses of European seabass. For that purpose, two diets were formulated to contain: 20% inclusion level of non-fermented plant ingredients mixture (20Mix) and 20Mix fermented by A. niger in SSF conditions (20Mix-SSF). Seabass juveniles (initial body weight: 20.9 ± 3.3 g) were fed the experimental diets, reared at two different temperatures (21 and 26 °C) and subjected to weekly salinity oscillations for six weeks. Growth performance, digestive enzyme activities, humoral immune parameters, and oxidative stress indicators were evaluated. A reduction in weight gain, feed intake, and thermal growth coefficient was observed in fish fed the fermented diet (20Mix-SSF). Salinity oscillation led to an increase in weight gain, feed efficiency, daily growth index, and thermal growth coefficient, regardless of dietary treatment. Higher rearing temperatures also increased daily growth index. No dietary effect was observed on digestive enzymes activities, whereas rearing temperature and salinity oscillation modulated digestive enzyme activities. Oxidative stress responses were significantly affected by experimental diets, temperature, and salinity conditions. Catalase and glutathione peroxidase activities showed an interactive effect. Fish reared at 21 °C showed higher enzymatic activity when fed the 20Mix-SSF. Conversely, fish reared at 26 °C showed higher GPx activity when fed the 20Mix diet. Fish reared at 26 °C showed reduced peroxidase and lysozyme activities, while salinity fluctuation led to increased lysozyme activity and decreased ACH50 activity. ACH50 activity increased in fish fed the 20Mix-SSF. Overall, the dietary inclusion of PFM fermented by A. niger was unable to mitigate the impact of environmental stress on physiological performance in European seabass. In fact, fermented feed caused an inhibition of growth performances and an alteration of some physiological stress indicators.

Complete mitochondrial genome of the Spanish toothcarp, Aphanius iberus (Valenciennes, 1846) (Actinopterygii, Aphaniidae) and its phylogenetic position within the Cyprinodontiformes order

BackgroundThe Spanish toothcarp (Aphanius iberus Valenciennes, 1846) is a small fish endemic to the eastern coastline of the Iberian Peninsula and is currently listed as “Endangered” (category IUCN: EN). It mainly inhabits brackish waters which can exhibit large fluctuations in temperature and salinity throughout the year. The genetics of A. iberus are not well-known since most studies have only evaluated the genetic structure of the species under a conservation framework in order to identify its potential conservation units. Different phylogenetic relationships of Aphanius have been published based on some particular genes. In the present study, the entire mitochondrial genome of A. iberus was obtained for the first time in the context of an A. iberus reference genome and a hypothesis regarding its phylogenetic position was considered.Methods and resultsThe mitogenome (a circular doble-stranded DNA sequence of 16,708 bp) was reconstructed and aligned against 83 Cyprinodontiformes and two outgroup taxa to identify the phylogenetic position of A. iberus. PartitionFinder was first used to test for the best evolutionary model and the phylogenetic analyses were performed using two methods: Maximun-Likelihood Approximation (IQ-Tree) and Bayesian inference (MrBayes). Our results show that A. iberus forms a sister group with Orestias ascotanensis, a cyprinodontiform species native to South America.ConclusionsThe results were congruent with the traditional morphometric reconstructed trees and with a geological vicariant hypothesis involving Cyprinodontiformes where Aphaniidae is shown as a monophyletic family separated from the family Cyprinodontidae. The information gathered from this study is not only valuable for improving our understanding of the evolutionary history of A. iberus, but for future genomic studies involving the species.

Effects of low salinity stress on osmoregulation and gill transcriptome in different populations of mud crab Scylla paramamosain

Animals living in estuaries suffer from rapid and continuous salinity fluctuations, while the global warming and extreme precipitation aggravate this situation. Osmoregulation is important for estuarine animals adapt to salinity fluctuations. The present study investigated the effects of low salinity stress on osmoregulation and gill transcriptome in two populations of mud crab from Hangzhou Bay and Zhangzhou Bay of China, respectively. Crabs were transferred from salinity 25 ppt to 5 ppt for 96 h. Edematous swelling in gill filaments was caused by low salinity stress and was more serious in Zhangzhou Bay population. Gill Na+/K+-ATPase activity increased (p < 0.01) in both populations under the low salinity stress and was significantly higher (p < 0.01) in Hangzhou Bay population than in Zhangzhou Bay population. According to transcriptome analysis, there were 191 genes differentially expressed under the low salinity stress in gill tissue of both populations. Several ion transport and energy metabolism related pathways, as well as the arginine and proline metabolism pathway, were enriched by these genes. On the other hand, 272 genes were identified to differentially express between two populations under the low salinity stress, but not under the control salinity. The enrichment analysis showed that these genes were mainly related to ion transport, energy metabolism, osmolytes metabolism and methyltransferase activity. In conclusion, the present study suggested that mud crab exploited a combination of extracellular anisosmotic regulation and intracellular isosmotic regulation for osmoregulation under the low salinity stress. Hangzhou Bay population showed a greater osmoregulatory capacity, which is probably due to the enhanced ion transport, energy supply, and osmolytes regulation. Meanwhile, epigenetic modification might also contribute to an inherent osmoregulation ability for Hangzhou Bay population to response to salinity fluctuation rapidly.

Larval Fish Spatiotemporal Dynamics of Different Ecological Guilds in Yangtze Estuary

Estuaries, as important fish nursery habitats, usually include a variety of larval fishes of different ecological guilds and exhibit complicated changing environmental conditions. We carried out a survey to examine the spatiotemporal dynamics of different ecological guild larval fishes and their relationships with environmental factors in the springs and summers from 2018 to 2020 in the Yangtze Estuary (China). The aims of the study were to provide detailed information on the characteristics of the larval fish assemblage and to explore the spatiotemporal variation in different ecological guild species and the effects of environmental variables on assemblage structure. More than 140,000 fish larvae from 26 families and 99 species were gathered during the six cruises, with the spring being the most prolific. The assemblage was dominated by a few species and was divided into three ecological guilds. Engraulidae was the most abundant family, followed by Cyprinidae and Gobiidae. Hemiculter bleekeri (freshwater), Pseudolaubuca sinensis (freshwater), Coilia mystus (brackish water), and Engraulis japonicas (marine) were the predominant species. Seasonal variations in larval fish assemblage structure were closely influenced by temperature, and the fluctuation in salinity mainly determined the spatial distribution of the larval fish community. Freshwater flows also played an important role in shaping the larval fish assemblage structure and dynamics. The conclusions improve the understanding of the ecological dynamics of larval fish assemblages in environmentally heterogeneous areas and may be applicable to other estuary ecosystems.

Morphology of Coscinodiscus radiatus Ehrenberg (Bacillariophyta) from Kara-Bogaz-Gol Bay (Caspian Sea)

The study of morphology of Coscinodiscus radiatus from Kara-Bogaz-Gol Bay (the Caspian Sea) revealed that among the investigated parameters, the valve diameter was the most variable (variation coefficient CV = 21.2%) at a salinity of 50 to 262‰. The number of areolae in 10 µm on the valve mantle was the least variable characters (CV = 9.6%). The variability of the aforementioned quantitative traits, in comparison with the literature data was revealed. An increase in the valve diameter of C. radiatus at a salinity of 60‰ was noted and a decrease – at a salinity of 216–262‰. Calculation of correlation coefficient between the analyzed morphometric characters revealed a stable positive correlation between the valve diameter and the number of areolae in 10 μm on the valve. Mass development in the Bay conditions allows to characterize C. radiatus not only as a marine euryhaline species occurring in desalinated sea areas, but also as a halophile capable of tolerating wide fluctuations in salinity.

The valves morphology of the diatom Coscinodiscus radiatus Ehrenberg (Bacillariophyta) from marine and hypersaline ecosystems

The study of morphology of Coscinodiscus radiatus from the Kara-Bogaz-Gol Bay (the Caspian Sea) revealed that at a salinity of 50 to 262‰ among the investigated characters, valve diameter (variation coefficient CV = 21.2%) was the most variable. The number of areolae on the valve mantle in 10 μm (CV = 9.6%) was the least variable characters. Some quantitative characters (valve diameter and number of areolae on the valve mantle in 10 μm) revealed variability compared to the literature data, based on the study of species from marine waters. An increase in the valve diameter of C. radiatus was noted at a salinity of 60‰, a decrease – at a salinity of 262‰. C. radiatus can be characterize as halophilous capable of tolerate fluctuations in salinity.

Testing macroecological hypotheses in sandy beach populations: the wedge clam Donax hanleyanus in South America

Large-scale spatial and temporal variability in environmental conditions may result in differences in life-history traits, population demography, and abundance of sandy-beach species. We analyzed the effects of salinity, chlorophyll a (chl a), and sea surface temperature (SST) on population parameters of the wedge clam Donax hanleyanus from 75 South American sandy beaches covering a 15° latitudinal range. Generalized modeling results showed that between-beach differences in abundance, population structure, growth performance, productivity, mortality, and individual shell mass were mainly explained by salinity fluctuations, with chl a and SST as secondary contributors, overriding, in most cases, local habitat features (Dean’s parameter, grain size, slope). Our results provide valuable insights into macroscale ecological processes, setting a basis to delineate conservation guidelines at large spatial scales that respond to the potential effects of climate variability and change on sandy beach populations.

Exploring the diversity of microeukaryotic communities in New England tide pools

Though historically understudied, due in large part to most species being uncultivable, microbial eukaryotes (i.e. protists) are abundant and widespread across diverse habitats. Recent advances in molecular techniques, including metabarcoding, allow for the characterization of poorly known protist lineages. This study surveys the diversity of SAR (Stramenopila, Alveolata, and Rhizaria), a major eukaryotic clade that is estimated to represent about half of all eukaryotic diversity. SAR lineages use varied metabolic strategies like mixotrophy in dinoflagellates (Alveolata), parasitism in apicomplexans (Alveolata) and labyrinthulids (Stramenopila), and life cycle stages that include encystment and attachment (e.g. in ciliates, Alveolata) to survive in highly dynamic habitats. Using metabarcoding primers designed specifically to target a portion of the 18S small subunit ribosomal RNA (SSU-rRNA) gene of SAR lineages, we compare protist community composition from tide pools in Acadia National Park, Maine, USA. We characterize over 500 lineages, here operational taxonomic units (OTUs), many of which are found abundant in the tide pool environment. We also find that communities vary by month sampled and exhibit patterns by size (i.e. macro-, micro-, and nano-sized). Taken together, these data allow us to further catalog protist diversity in extreme environments (e.g. those subject to extreme fluctuations in temperature and salinity during tidal cycles). Such data are critical in the explorations of biodiversity patterns among microorganisms on our rapidly changing planet.

A Study on Periodic Fluctuations of Salinity in Coastal Water of Toyama Bay

A Study on Periodic Fluctuations of Salinity in Coastal Water of Toyama Bay

Contribution of microphytobenthos to the carbon sink in brackish and freshwater tidal flats of the Yangtze Estuary

Estuarine and coastal wetlands have great potential as carbon sinks; however, the carbon fluxes that occur in unvegetated tidal flats remain largely unknown. The CO2 flux of tidal flats is mainly controlled by CO2 uptake by microphytobenthos (MPB) and CO2 emission by sediment respiration. In this study, a brackish tidal flat (B-TF) and a freshwater tidal flat (F-TF) in the Yangtze Estuary were selected to investigate the effects of salinity on MPB growth (indicated by the content of chlorophyll a and pheopigment) and the CO2 flux of tidal flats (during daytime). The results showed that the sediment salinity at the B-TF was 5-19 times higher than that at the F-TF, depending on the season. Diatoms showed a dominant saltwater community at the B-TF and a freshwater community at the F-TF. Over spring, autumn, and winter, CO2 absorbed by the MPB was on average 113 and 230% of the CO2 emitted through sediment respiration of the B-TF and F-TF, respectively, showing a CO2 sink capacity. High salinity in winter inhibited sediment respiration and improved the physiological status of the MPB, making the B-TF a strong CO2 sink, whereas the F-TF was a strong CO2 sink in summer. The freshwater and dissolved (SiO32-) silicon input to the estuary via the river had significant effects on MPB growth and sediment respiration, which were also influenced by light, temperature, and pH. Our study highlights the importance of estuarine salinity fluctuations in the CO2 sinks of estuarine tidal flats, which should be given additional attention when assessing the role of tidal flats in CO2 mitigation.

염분 변화에 따른 명태(Gadus Chalcogrammus)의 스트레스 반응; 혈액생리학적 변화 및 유전자 발현

The study evaluated the change of stress indicators in plasma and mRNA expression levels of stress-related genes in head-kidney and liver of walleye pollock, Gadus chalcogrammus according to acute salinity fluctuation. Walleye pollocks were exposed for 24 hours in five groups, as salinity are 34, 30, 25, 20, and 15 psu. The levels of hematocrit (Ht), glutamic oxaloacetate transaminase (GOT), cortisol, glucose, and superoxide dismutase (SOD) in plasma were increased as the salinity of the breeding water decreased. Ht increased with 37.5 ± 1% at 20 psu. GOT with 41.0 ± 5.03 U/L, cortisol with 882.73 ± 32.73 ng/mL, and glucose with 67.67±11.6 ng/dL increased a significant difference at 25 psu. The SOD activity levels in plasma were highest at 15 psu with 3.51 ± 0.13 U/mL. Plasma hemoglobin (Hb) and glutamic pyruvic transaminase (GPT) did not show a statistically significant difference according to salinity, but showed a tendency to increase as the salinity decreased. Total protein (TP) levels in plasma were the highest with 5.9 ± 0.61 g/dL at 25 psu. The relative mRNA expression of stress-related genes was investigated in the head-kidney and liver of walleye pollocks, and the mRNA expression of steroidogenic acute regulatory protein (StAR) and heat shock protein 70 (HSP70) increased, as the salinity decreased from 25 psu, whereas glucocorticoid receptor (GR) mRNA expression decreased as the salinity decreased. These results suggest that walleye pollocks become stressed-condition to salinity below 25 psu, but homeostasis can be maintained up to 15 psu in short-term.

Laser beam scintillations of LIDAR operating in weak oceanic turbulence

The formulation of light detection and ranging (LIDAR) systems is derived and examined for the scintillation index, evaluated on-axis, of laser beams in horizontal links in the ocean with weak turbulence by utilizing the Rytov method. These scintillation indices, obtained for the Gaussian beam which is collimated, the limits of plane and spherical waves, are depicted versus the source size, target size, and parameter of the normalized reflector size. It is found that the source size, target size, and normalized reflector size parameter, lessening the scintillation index evaluated on-axis, are approximately 0.44 cm, 56 × 10 − 4 c m , and 2.2, respectively. Additionally, by using these values that minimize the scintillation index, the variation of the scintillations is shown against the propagation distance, radius of reflector, temperature and salinity fluctuation effects, mean squared temperature, and turbulent kinetic energy dissipation rate per unit mass of fluid at various selected source size and radius of reflector values.

Impacts of high-quality coal mine drainage recycling for replenishment of aquatic ecosystems in arid regions of China: Bacterial community responses

Coal mine water is usually recycled as supplementary water for aquatic ecosystems in arid and semiarid mining regions of China. To ensure ecosystem health, the coal mine water is rigorously treated using several processes, including reverse osmosis, to meet surface water quality standards. However, the potential environmental impacts of this management pattern on the ecological function of receiving water bodies are unclear. In this study, we built several microcosm water ecosystems to simulate the receiving water bodies. High-quality treated coal mine drainage was mixed into the model water bodies at different concentrations, and the sediment bacterial community response and functional changes were systematically investigated. The results showed that the high-quality coal mine drainage could still shape bacterial taxonomic diversity, community composition and structure, with a concentration threshold of approximately 50%. Moreover, both the Mantel test and the structural equation model indicated that the salinity fluctuation caused by the receiving of coal mine drainage was the primary factor shaping the bacterial communities. 10 core taxa in the molecular ecological network influenced by coal mine drainage were identified, with the most critical taxa being patescibacteria and g_Geothermobacter. Furthermore, the pathway of carbohydrate metabolism as well as signaling molecules and interactions was up-regulated, whereas amino acid metabolism showed the opposite trend. All results suggested that the complex physical-chemical and biochemical processes in water ecosystems may be affected by the coal mine drainage. The bacterial community response and underlying functional changes may accelerate internal nutrient cycling, which may have a potential impact on algal bloom outbreaks.

Salinity appears to be the main factor shaping spatial COI diversity of Corbicula lineages within the Chinese Yangtze River Basin

AbstractAimTo date, few studies have examined the phylogenetics of Corbicula clams in their native range and the environmental parameters influencing their distribution, although this could provide great insights into the biological adaptation and invasion dynamics of Corbicula clams. We sought to identify the genetic lineages of native Corbicula clams and elucidate the environmental factors shaping the distributions of identified lineages.LocationChina, mainly the Yangtze River Basin.MethodsThe alignment comprised 558 COI sequences including samples from China and 222 COI sequences from published studies. This dataset was used to generate phylogenetic trees and compare population diversity. We used dbRDA method to assess the relationship between these COI data and environmental factors measured to identify the important factors affecting Corbicula's distribution.ResultsThe COI phylogenetic tree delineated the monophyly of 3 major COI clades and 77 distinct COI haplotypes in the Yangtze River Basin. The invasive lineage C/S (FW17) was not identified in our sampling in China, while invasive lineages A/R (FW5 = Hap6), B (FW1 = Hap17) and Rlc (FW4 = Hap43) were identified, abundant and widely distributed in the middle and lower reaches of Yangtze River. Focusing on populations from Yangtze River Basin, both the COI haplotype and nucleotide diversity in the lakes along the Yangtze River increased with longitude, except for the river mouth population. The AMOVA tests showed significant differentiation between the middle and lower reaches of the Yangtze River and among populations. The dbRDA results suggested that the parameter chloride explained most of the spatial COI haplotype distribution variation in the Yangtze River Basin, with the three invasive lineages tolerating broad fluctuations of salinity (chloride levels ranging from 4 to 60 mg/L).ConclusionsThe Corbicula COI haplotypes found within the Yangtze River Basin had distinct distribution preferences, with the invasive androgenetic lineages being the most abundant and widely distributed. Genetic diversity was higher in this native region than in invaded areas in Europe and America, while it decreased with increasing distance from the river mouth. Salinity appeared to be the main environmental factor shaping the COI haplotype distribution of Corbicula lineages within their native range.

Discordant pattern between realised and fundamental saline niches in two supralittoral Ochthebius species (Coleoptera: Hydraenidae)

Abstract Determining the saline niche of the congeneric and co‐existing species that inhabit supralittoral rockpools subjected to extremely fluctuating saline conditions is a crucial concern to understand their spatial distributions and occurrence, and to predict their ability to face increasing environmental instability due to climate change. Therefore, we compared the realised and fundamental saline niches of Ochthebius quadricollis and Ochthebius lejolisii (Coleoptera: Hydraenidae) on the Mediterranean coast of the Iberian Peninsula. A realised niche was determined using field data on the abundance of the adults and larvae of both species. A fundamental niche was addressed with laboratory experiments by measuring the survival of the adults and larvae and the egg‐hatching success exposed to different salinity treatments (35, 60, 90, 110, 140 and 170 g L−1). Our study found a discordant pattern between realised and fundamental niches. Both species are euryhalines and support extreme salinity fluctuations from 1.80 to almost 140 g L−1, and O. quadricollis larvae in the field withstand up to 180 g L−1. However, physiological tolerance was greater in O. lejolisii than in O. quadricollis, and O. lejolissi adults survived in the laboratory at 170 g L−1 for more than 3 days with 30% egg‐hatching success, whereas O. quadricollis showed a maximum survival time of 2 days and no egg‐hatching success at that salinity. The larvae and eggs of both species were more tolerant than adults. The two studied species exhibited high physiological capacity to tolerate extremely fluctuating salinity, which will be exacerbated by climate change.

Salinity variation modulates cellular stress response to ZnO nanoparticles in a sentinel marine bivalve, the blue mussel Mytilussp.

Zinc oxide nanoparticles are released into marine environments from industrial, medical and consumer uses sparking concerns about their potential ecotoxicological effects. Ecological hazard assessment of nZnO in marine ecosystems is hindered by the lack of understanding of the potential interactive effects of nZnO toxicity with other common abiotic stressors, such as salinity fluctuations, in marine organisms. To close this gap in our knowledge, we carried out a comprehensive biomarker-based assessment of the combined effects of salinity and nZnO in a sentinel marine bivalve, the blue mussels Mytilus edulis. The mussels were exposed for 21 days to clean seawater (control), an environmentally relevant concentration (100 μg Zn l−1) of nZnO or dissolved Zn (to identify the toxic effects attributable to Zn2+ toxicity) under the normal (15), low (5) and fluctuating (5–15) salinity regimes. The selected molecular and biochemical markers focused on the oxidative stress, apoptosis, detoxification system and inflammation in the gills and the digestive gland of the mussels. Biomarker analysis showed different effects of nZnO and dissolved Zn on biomarkers of oxidative stress, xenobiotic detoxification and apoptosis but similar effects of both pollutants on the levels of metallothioneins and inflammatory markers. Exposure to nZnO led to elevated levels of lipid peroxidation, upregulation of p53 and p38 stress kinases and apoptosis-related genes, most notably in the gills. Exposure to dissolved Zn led to accumulation of protein carbonyls and activated redox-sensitive detoxification enzymes (NADPH-P450 reductase and glutathione-S-transferase) in the mussels. The ambient salinity had significant effects the cellular adverse effects of nZnO in the mussels. The nZnO-induced cellular stress was detectable under the normal (15) and fluctuating (5–15) salinity conditions in the studied brackish water population of the mussels. At low salinity (5), nZnO toxicity signal was almost completely dampened. These findings indicate that chronic osmotic stress close to the tolerance limits of M. edulis prevails over the effects of the environmentally relevant nZnO and dissolved Zn concentrations in combined exposures. These stressor interactions might ameliorate the cellular toxicity of nZnO in the mussels but limit applicability of cellular stress biomarkers for detecting the toxic effects of nanopollutants in low salinity habitats.

Applications and limitations of portable density meter measurements of Na-Ca-Mg-K-Cl-SO4 brines

Knowledge of brine density and mineral saturation states under different temperatures contributes to understanding Earth systems, including dissolution and crystallization of chemical sediments, mixing water bodies with variable density, and mineral resource development and evolution. However, these interpretations often rely on geochemical measurements with low accuracies at high salinities. Here, we test the utility of density measurments to advance understanding of brine geochemistry. We demonstrate the accuracy and limits of determining a brine's density and halite saturation state at multiple temperatures with rapid and relatively inexpensive portable density meter measurements. Density measurements at different temperatures are used to create samples' equations of state, which are used to extrapolate measurements. This methodology presents multiple opportunities. We use brine samples from around the world to show that density and equation of state data provide semi-quantitative information about sample composition and temperature-sensitive mineral precipitation. Importantly, density measurements can be used to evaluate error-prone geochemical measurements. We illustrate applications with brine samples from the Bonneville Salt Flats, a landscape in Utah, USA, that is valued for mineral resources and recreation opportunities. We developed system-scale equations of state for these saline pan samples and their halite-saturated counterparts. We evaluated methodological limitations with duplication tests and by determining if diurnal fluctuations in salinity and halite saturation in a shallow pool's brine and shallow groundwater in contact with a halite crust were detectable. Average daily changes in halite saturation of shallow pool brine of approximately 3 kg m−3 were clearly detected, while diurnal halite saturation fluctuations in the shallow halite crust brine of 0.4 to 0.7 kg m−3 were near method limits. Because of their accuracy, low cost, and applications, portable density meter measurements of brines are invaluable in studying brine systems.