Large Variations In Salinity Research Articles

The costs of living on the coast: Reduction in body size and size‐specific reproductive output in coastal populations of a widespread amphibian

Abstract Body size is a critical component of organismal biology. Body size is known to be influenced by a plethora of environmental conditions, among which exposure to large scale variations of salinity has been comparatively overlooked. Yet, exposure to salinity is known to affect energetic allocation toward growth and reproduction. In this study, we investigated the morphological differences between inland and coastal individuals of spined toads (Bufo spinosus) in Western France. We measured adult morphology both outside and during the reproductive season on 190 individuals, and assessed reproduction in pairs originating from inland (N = 20) and coastal (N = 30) environments. Overall, we found that adult coastal toads were smaller and lighter than inland individuals. Reproductive correlates of these differences included lower fecundity and smaller egg size (but higher egg density) in coastal females. Interestingly, these differences were not allometric correlates of body size, as coastal females invested proportionally less in all components of reproduction (fecundity, egg size and egg protection). These results suggest altered resource allocation to growth and reproduction in coastal amphibians, which may be related to the marked spatial gradient of salinity (measured in reproductive ponds) and the associated costs of osmoregulation (higher osmolality in coastal individuals), for which local adaptation and higher tolerance to salinity remains to be tested. Read the free Plain Language Summary for this article on the Journal blog.

Temporal variation in composition, abundance and biomass of the fish fauna after impact on subtropical transitional water

Transitional waters are characterized by large variations in salinity, temperature, turbidity, among other factors, such as tidal cycle, wind action and rainfall, that are constantly changing over time. The distribution of biota in these environments is regulated by these natural variations and also by human activities, such as pollution, overexploitation of resources, acceleration of urbanization, suppression of habitats and changes in hydrological dynamics. The objective of this study was to analyze the temporal dynamics of the fish fauna of the Saco dos Limões Cove, state of Santa Catarina, Brazil, after the construction of a highway. Fish community was evaluated over five years by annual and monthly variation in species richness, abundance and biomass. A total of 17,993 individuals were collected, distributed in 33 families, 59 genera and 79 species. The evaluated years were similar to each other in species composition. Community descriptors varied over time but did not show seasonal trends. In all years, abundance was higher than biomass, indicating both the disturbance and the ecosystem function as a nursery in the studied area. This was corroborated by the large number of juveniles of dominant species (Genidens genidens, Eucinostomus gula and Eucinostomus argenteus).

Genetic Mechanisms and Identification of Low-Resistivity Pay Zones: A Case Study of Pengyang Area, Ordos Basin, China

The Triassic Yanchang Formation in the Pengyang area of Ordos Tianhuan depression is an important oil and gas formation. However, most of the oil pays in the study formations are low-resistivity or low-contrast reservoirs with low permeability, bringing challenges to the reservoir identification and evaluation by well logs. In this paper, we first measured the nuclear magnetic resonance (NMR), phase permeability, cation exchange capacity (CEC), and X-ray diffraction for core samples. Then, the genetic types for the low-resistivity pays were analyzed based on the experiment results, water analysis, and well log data collected. It was found that large variations of formation water salinity, high irreducible water saturation, and clay conductivity are the primary genetic types. Further, the random forest (RF) algorithm with sensitive parameter inputs was used to identify the oil, oil and water, and water layers. The anomaly of spontaneous potential (∆SP) that characterizes water salinity, the relative value of gamma ray log (∆GR) that describes the bound water content, resistivity, density, and acoustic logs were taken as sensitive logs according to the genetic analysis. Finally, this identification method was verified by comparison with the traditional crossplot method and oil test results. The identification accuracy of the RF is 90%, far higher than that by the crossplot method.

Quantification of dissolved metabolites in environmental samples through cation‐exchange solid‐phase extraction paired with liquid chromatography–mass spectrometry

AbstractSmall, biologically produced, organic molecules called metabolites play key roles in microbial systems where they directly mediate exchanges of nutrients, energy, and information. However, the study of dissolved polar metabolites in seawater and other environmental matrices has been hampered by analytical challenges including high inorganic ion concentrations, low analyte concentrations, and high chemical diversity. Here we show that a cation‐exchange solid‐phase extraction (CX‐SPE) sample preparation approach separates positively charged and zwitterionic metabolites from seawater and freshwater samples, allowing their analysis by liquid chromatography–mass spectrometry. We successfully extracted 69 known compounds from an in‐house compound collection and evaluated the performance of the method by establishing extraction efficiencies (EEs) and limits of detection (pM to low nM range) for these compounds. CX‐SPE extracted a range of compounds including amino acids and compatible solutes, resulted in very low matrix effects, and performed robustly across large variations in salinity and dissolved organic matter concentration. We compared CX‐SPE to an established SPE procedure (PPL‐SPE) and demonstrate that these two methods extract fundamentally different fractions of the dissolved metabolite pool with CX‐SPE extracting compounds that are on average smaller and more polar. We use CX‐SPE to analyze four environmental samples from distinct aquatic biomes, producing some of the first CX‐SPE dissolved metabolomes. Quantified compounds ranged in concentration from 0.0093 to 49 nM and were composed primarily of amino acids (0.15–16 nM) and compatible solutes such as trimethylamine N‐oxide (0.89–49 nM) and glycine betaine (2.8–5.2 nM).

Mapping mineralogical heterogeneities at the nm-scale by scanning electron microscopy in modern Sardinian stromatolites: Deciphering the origin of their laminations

Stromatolites are found throughout the geological record and have received strong attention because they provide precious information about paleoenvironments and microbial paleobiodiversity. However, while this information is interpreted based on our knowledge about modern analogs, the latter remains incomplete. Here, we investigated the environmental and biological information recorded by modern stromatolites in Mari Ermi, a coastal pond in Western Sardinia that experiences severe seasonal evaporation and large salinity variations. For this purpose, we combined a variety of analytical tools, allowing to characterize the mineralogical composition of these stromatolites from the bulk, centimeter-scale to the nanometer-scale and assess the spatial distribution of the mineral phases. In particular, we used quantified x-ray elemental maps provided by energy dispersive x-ray spectrometry analyses coupled with scanning electron microscopy (SEM-EDXS). These maps were processed using an innovative data treatment allowing (i) mineral phase recognition, (ii) assessment of the mineral formula of each phase and (iii) mapping of their spatial distribution with a spatial resolution down to a hundred nanometers. Overall, this proved as an efficient approach to unravel mineralogical heterogeneities and detect informative mineral phases overlooked by bulk analyses. Mari Ermi stromatolites were mostly composed of magnesian calcite with an average Mg/Ca of ~0.1–0.2 as indicated by bulk analyses. However, microscopy observations revealed variable Mg-contents of calcite with a specific distribution, the most Mg-enriched calcites (Mg/Ca up to ~0.5) being systematically distributed around microbial remnants. Moreover, Mari Ermi stromatolites comprised an alternation of Mg-richer and Mg-poorer laminae, which paralleled the varying enrichment in microbial remnants of alternating laminae. The combination of SEM-EDXS, focused ion beam milling and transmission electron microscopy allowed to detect several minor phases, hardly or not detected at all by bulk analyses, such as aragonite, a variety of clay minerals as well as a gypsum-like phase. An additional calcium sulfate phase, best interpreted as S-apatite (cesanite), was detected by SEM-EDXS. Overall, this mineral assemblage and its definite spatial distribution record only discrete stages of the evaporation of Mari Ermi lagoon. Moreover, microorganisms seem to have a major control on Mg substitution in calcite. As a result, the dynamics of microbial populations, influenced by the salinity variations induced by evaporation in the lagoons, generates the formation of laminae in Mari Ermi stromatolites.

Heterogeneity of alkaline lacustrine source rocks of the lower Permian Fengcheng Formation in the Mahu Sag, Junggar Basin, northwestern China

The alkaline lacustrine source rocks in the lower Permian Fengcheng Formation in the Mahu Sag, Junggar Basin, China, exhibit significant heterogeneity. However, most previous studies have focused on the vertical variability of the source rocks, and the lateral variability is poorly understood. This study investigated recently drilled samples of the Fengcheng Formation in the Manan area to assess the lateral variability of the source rocks. The geochemical characteristics of the Fengcheng Formation source rocks in the Manan area are variable, with low–high abundances of organic matter, which comprises types I–III kerogen that is mature to high-mature. These features differ from the typical Fengcheng Formation source rocks in the Wuxia–Fengcheng area, which have a high abundance of organic matter with substantial hydrocarbon and shale oil generation potential. Biomarker data show that the organic matter in the Fengcheng Formation source rocks in the Manan area is a mixture of higher plants, algae, and bacteria, which differs from the Wuxia–Fengcheng area where algae and bacteria are dominant. The Fengcheng Formation source rocks in the Manan area were deposited in an oxic to anoxic environment characterized by large variations in water salinity and stratification. Mudstones were deposited rather than carbonate rocks. This differs from the strongly reducing, hypersaline, and water-stratified depositional environment of the Fengcheng Formation source rocks in the Wuxia–Fengcheng area. These two areas are separated by the Dazhuluogou Fault, and there are no alkaline lacustrine deposits in the Manan area. The distribution of the alkaline lacustrine source rocks was controlled by the paleogeography and sedimentary environment, which was characterized by significant spatial heterogeneity.

Spectrophotometric determination of nitrate in small volume of seawater samples using a simple resorcinol method.

A simple resorcinol method to determine nitrate (NO3-) in seawater using a microplate reader with a 48-well plate was established. The method involved the nitration of resorcinol in sulfuric acid to form a pink product that was detected at 505nm. Reagent concentrations were optimized, and the effect of salinity on NO3- determination was investigated. The detection limit of this method was 0.8µM, while the upper limit of the linear range was 100µM. The recoveries ranged from 91.5 to 109.7% for spiked seawater samples with different salinities. The proposed method was compared with two reference methods, and the results revealed a good correlation. Compared to conventional methods that require the preparation of reactants, the proposed method used aqueous solutions as reagents for the reaction, which was simpler and more convenient. Compared to the methods that used organic solvents for the direct determination of NO3-, the proposed method was suitable for estuarine and coastal water samples with large salinity variations. All results indicated that the proposed method can satisfy the requirements of laboratory analysis and demonstrate high application potential for use in field determination.

Hydrogeochemical insights into the signatures, genesis and sustainable perspective of nitrate enriched groundwater in the piedmont of Hutuo watershed, China

Groundwater nitrate contamination has been a global issue threatening water supply, especially in arid and semiarid piedmonts. An extensive hydrogeochemical investigation was performed in an intensively human-impacted semiarid piedmont in North China. Groundwater is nearly neutral to alkaline in nature with large variations of salinity. The concentration of nitrate in groundwater ranges from 4.89 mg/L to 402.40 mg/L with 64.29% of values beyond the permissible limit of 50 mg/L recommended by World Health Organization. Hydrogeochemistry changes gradually from fresh HCO3-Ca type waters to moderately saline Cl-Ca type with the increase of nitrate content in groundwater. Anthropogenic inputs from residential land usage are responsible for the nitrate enrichment and salinity increase. The Entropy-weighted water quality index value ranges from 29 to 327 with a mean of 82, and 21.43% of sampled groundwaters under the categories from medium to extremely poor quality for drinking purpose. Non-carcinogenic risks posed by nitrate, nitrite and ammonia via dermal and oral pathways were assessed for infants, children, adult females and males. The overall non-carcinogenic risk of investigated groundwaters ranges from 2.91 × 10−1 to 2.38 × 101 (mean of 4.00 × 100) for infants, 1.29 × 10−1 to 1.06 × 101 (mean of 1.78 × 100) for children, 5.74 × 10−2 to 4.70 × 100 (mean of 7.90 × 10−1) for adult females, and 4.24 × 10−2 to 3.47 × 100 (mean of 5.83 × 100) for adult males. Health risks vary but all population groups are at risk. These health threats are mainly posed by nitrate through the oral ingestion pathway, with minors being more susceptible. Therefore, measures including awareness improvement of local residents, environmental protection, differential water supplies based on water quality, and targeted water treatment are recommended to achieve sustainable groundwater resource development in arid and semiarid piedmonts.

Microbial river-to-sea continuum: gradients in benthic and planktonic diversity, osmoregulation and nutrient cycling

BackgroundCoastal aquatic ecosystems include chemically distinct, but highly interconnected environments. Across a freshwater-to-marine transect, aquatic communities are exposed to large variations in salinity and nutrient availability as tidal cycles create periodic fluctuations in local conditions. These factors are predicted to strongly influence the resident microbial community structure and functioning, and alter the structure of aquatic food webs and biogeochemical cycles. Nevertheless, little is known about the spatial distribution of metabolic properties across salinity gradients, and no study has simultaneously surveyed the sediment and water environments. Here, we determined patterns and drivers of benthic and planktonic prokaryotic and microeukaryotic community assembly across a river and tidal lagoon system by collecting sediments and planktonic biomass at nine shallow subtidal sites in the summer. Genomic and transcriptomic analyses, alongside a suite of complementary geochemical data, were used to determine patterns in the distribution of taxa, mechanisms of salt tolerance, and nutrient cycling.ResultsTaxonomic and metabolic profiles related to salt tolerance and nutrient cycling of the aquatic microbiome were found to decrease in similarity with increasing salinity, and distinct trends in diversity were observed between the water column and sediment. Non-saline and saline communities adopted divergent strategies for osmoregulation, with an increase in osmoregulation-related transcript expression as salinity increased in the water column due to lineage-specific adaptations to salt tolerance. Results indicated a transition from phosphate limitation in freshwater habitats to nutrient-rich conditions in the brackish zone, where distinct carbon, nitrogen and sulfur cycling processes dominated. Phosphorus acquisition-related activity was highest in the freshwater zone, along with dissimilatory nitrate reduction to ammonium in freshwater sediment. Activity associated with denitrification, sulfur metabolism and photosynthesis were instead highest in the brackish zone, where photosynthesis was dominated by distinct microeukaryotes in water (Cryptophyta) and sediment (diatoms). Despite microeukaryotes and archaea being rare relative to bacteria, results indicate that they contributed more to photosynthesis and ammonia oxidation, respectively.ConclusionsOur study demonstrates clear freshwater–saline and sediment–water ecosystem boundaries in an interconnected coastal aquatic system and provides a framework for understanding the relative importance of salinity, planktonic-versus-benthic habitats and nutrient availability in shaping aquatic microbial metabolic processes, particularly in tidal lagoon systems.72ugw57JLuZNUPngo1htqPVideo abstract

The Seasonal Variation of the Anomalously High Salinity at Subsurface Salinity Maximum in Northern South China Sea from Argo Data

The large variations in salinity at the salinity maximum in the northern South China Sea (NSCS), as an indicator for the changes in the Kuroshio intrusion (KI), play an important role in the hydrological cycle. The high salinity here is more than 34.65 at the salinity maximum and is intriguing. In the past, the salinity was difficult to trace in the entire NSCS over long periods due to a lack of high-quality observations. However, due to the availability of accumulated temperature and salinity (T-S) profiles from the Argo program, it is now possible to capture subsurface-maximum data on a large spatiotemporal scale. In this study, the salinity maximum distributed in the subsurface of 80 to 200 m at a density of 23.0–25.5 σθ was extracted from decades of Argo data (on the different pressure surfaces, 2006–2019). We then further studied the spatial distribution and seasonal variation of the salinity maximum and its anomalously high salinity. The results suggest that a high salinity (salinity > 34.65, most of which is located at the shallow depths < 100 m) at the subsurface salinity-maximum layer often occurs in the NSCS, especially near the Luzon Strait, which accounts for about 23% of the total salinity maximum. In winter, the anomalously high salinity at the shallow subsurface salinity maximum can extend to the south of 17° N, while it rarely reaches 18° N and tends to locate at deeper waters in summer. The T-S values of the anomalously high-salinity water are between the mean T-S values in the NSCS and north Pacific subsurface water, implying that the outer sea water gradually mixes with the South China Sea water after passing through the Luzon Strait. Finally, our results show that the factors play an important role in the appearance and distribution of the anomalously high salinity at the subsurface salinity maximum, including the strength of the Kuroshio intrusion, the local wind stress curl and the anticyclonic eddy shedding from the loop current.

Ocean Circulation Drives the Variability of the Carbon System in the Eastern Tropical Atlantic

The carbon system in the eastern tropical Atlantic remains poorly known. The variability and drivers of the carbon system are assessed using surface dissolved inorganic carbon (DIC), alkalinity (TA) and fugacity of CO2 (fCO2) measured in the 12° N–12° S, 12° W–12° E region from 2005 to 2019. A relationship linking DIC to temperature, salinity and year has been determined, with salinity being the strongest predictor. The seasonal variations of DIC, ranging from 80 to 120 μμmol kg−1, are more important than the year-to-year variability that is less than 50 μμmol kg−1 over the 2010–2019 period. DIC and TA concentrations are lower in the northern part of the basin where surface waters are fresher and warmer. Carbon supply dominates over biological carbon uptake during the productive upwelling period from July to September. The lowest DIC and TA are located in the Congo plume. The influence of the Congo is still observed at the mooring at 6° S, 8° E as shown by large salinity and chlorophyll variations. Nevertheless, this site is a source of CO2 emissions into the atmosphere.

Subcritical Phase Separation and Occurrence of Deep-Seated Brines at the NW Caldera Vent Field, Brothers Volcano: Evidence from Fluid Inclusions in Hydrothermal Precipitates

The northwestern caldera wall of Brothers volcano in the southern Kermadec arc features several clusters of hydrothermal venting in a large area that extends from near the caldera floor (~1700 mbsl) almost up to the crater rim (~1300 mbsl). Abundant black smoker-type hydrothermal chimneys and exposed stockwork mineralization in this area provide an excellent archive of hydrothermal processes that form seafloor massive sulfide deposits. Using sulfate precipitates from chimneys and stockwork recently recovered by remotely operated vehicles, we conducted fluid inclusion microthermometry and Sr isotope studies to determine the role of phase separation and mixing between vent fluid and seawater. The variability in the vast majority of fluid inclusion salinities (i.e., 0.1–5.25 wt.% NaCl eq.) and entrapment temperatures of up to 346°C are indicative of phase-separated hydrothermal fluids. Large salinity variations in samples with entrapment temperatures mostly below the boiling temperature for the sample’s depth show that the majority of fluids ascending below the NW Caldera are phase separating in the subsurface and cooling, prior to discharge. In several samples, entrapment temperatures of over 343°C suggest that phase-separating fluids have at least sporadically exited the seafloor at the NW Caldera site. Isobaric-isenthalpic mixing trends between coexisting phase-separated vapors and brines with seawater are consistent with phase-separated fluids at near-seafloor pressures of ~170 bar and suggest that the vast majority of the ascending fluids continue to phase separate to within tens to hundreds of meters below seafloor prior to mixing with seawater. A small subset of the most saline fluid inclusions (up to 18.6 wt.% NaCl eq.) is unlikely formed by near-seafloor phase separation and is considered to be produced either by supercritical phase separation or by the contribution of a magmatic brine from near the magmatic-hydrothermal interface. 87Sr/86Sr values of sulfate samples range from 0.7049 (i.e., near hydrothermal end-member) to 0.7090 (i.e., near seawater) and show that the crystals grew from vapor- and brine-derived fluids in a hydrothermally dominated mixing regime. Our work provides new insights into mineral growth conditions, mixing regimes, and in particular, the extent and character of subseafloor phase separation during the formation of hydrothermal vents and their underlying stockwork in seawater-dominated, arc-related hydrothermal systems.

Trophic transfer of trace elements in a euryhaline fish, the turbot Scophthalmus maximus: Contrasting effects of salinity on two essential elements

Trace elements can be accumulated from coastal environment by aquatic organisms from their food and be transferred throughout the food webs. Studying the effects of salinity on the trophic transfer of trace elements in a euryhaline fish, able to deal with large variations in salinity, is therefore key to understand their dynamics in aquatic environments. In this context, we investigated the potential influence of salinity on the trophic transfer of two essential elements (Mn and Zn) in the euryhaline fish, the turbot Scophthalmus maximus using radiotracer techniques. After acclimation to three salinities (10, 25 and 38), turbots were fed with radiolabelled pellets (54Mn and 65Zn). Kinetic parameters of depuration were determined after a 21-d period and trophic transfer factors were calculated. Trophic transfer of Mn at the highest salinity was significantly lower than for the other conditions whereas salinity did not significantly influenced Zn trophic transfer. Differences in the processes involved in the regulation (homeostasis) of the two tested trace elements may explain the contrasting influence of seawater salinity for Mn and Zn.

Ore-forming mechanism and physicochemical evolution of Gutaishan Au deposit, South China: Perspective from quartz geochemistry and fluid inclusions

The Gutaishan is an important gold deposit of the Jiangnan Orogen in South China. The deposit is characterized by multiphase alteration/mineralization, including barren quartz (pre-ore Stage I) quartz + dolomite + pyrite + arsenopyrite (Stage II), quartz + dolomite + native gold + pyrite + arsenopyrite + stibnite (Stage III), and quartz + dolomite ± pyrite (Stage IV).Cathodoluminescence (CL) observations show that each of Stage II and III quartz comprises two sub-stages (Stage II: QII1 and QII2; Stage III: QIII1 and QIII2), and Stage IV quartz (QIV) contains no sub-stages. QIII1 has distinct core-rim texture, with the CL intensity decreasing from core to rim. QII1, QII2, QIII2 and QIV are texturally more homogeneous. Variations of aluminium concentration correlate with the CL intensity and reveal the determinated of pH in fluids during Stage II and III, with marked decline to Stage IV. Fluid inclusions (FIs) trapped in quartz are liquid-rich and CO2-rich, suggesting a CO2-H2O-NaCl fluid system. Fluid inclusion microthermometry data suggest that the ore-forming fluids were under conditions of medium-low salinity (Stage II: 1.02–11.46 wt% NaCl equiv.; Stage III: 0.83–9.84 wt% NaCl equiv.; Stage IV: 4.39–8.10 wt% NaCl equiv.) and temperature (Stage II: 190–285 °C; Stage II: 170–270 °C; Stage II: and 163–240 °C), consistent with the low Ti content (<10 ppm) in the quartz. Fluid boiling, coupled with decrease of temperature, may have controlled gold precipitation at Gutaishan, based on the coexistence of liquid-rich and CO2-rich FIs with similar homogenization temperatures and large salinity variations. Integrating regional tectonic evolution, previous H–O–S–Pb data, and close temporal and spatial relationship with the Baimashan granite rocks, we propose that the Gutaishan gold mineralization may have been genetically linked to the Mesozoic magmatism related to the Baimashan granite rocks formed in an extensional setting during subduction of the Paleo-Pacific plate.

Assessing proxy signatures of temperature, salinity, and hypoxia in the Baltic Sea through foraminifera-based geochemistry and faunal assemblages

Abstract. Current climate and environmental changes strongly affect shallow marine and coastal areas like the Baltic Sea. This has created a need for a context to understand the severity and potential outcomes of such changes. The context can be derived from paleoenvironmental records during periods when comparable events happened in the past. In this study, we explore how varying bottom water conditions across a large hydrographic gradient in the Baltic Sea affect benthic foraminiferal faunal assemblages and the geochemical composition of their calcite tests. We have conducted both morphological and molecular analyses of the faunas and we evaluate how the chemical signatures of the bottom waters are recorded in the tests of several species of benthic foraminifera. We focus on two locations, one in the Kattegat (western Baltic Sea) and one in Hanö Bay (southern Baltic Sea). We show that seawater Mn∕Ca, Mg∕Ca, and Ba∕Ca (Mn∕Casw, Mg∕Casw, and Ba∕Casw) variations are mainly controlled by dissolved oxygen concentration and salinity. Their respective imprints on the foraminiferal calcite demonstrate the potential of Mn∕Ca as a proxy for hypoxic conditions, and Ba∕Ca as a proxy for salinity in enclosed basins such as the Baltic Sea. The traditional use of Mg∕Ca as a proxy to reconstruct past seawater temperatures is not recommended in the region, as it may be overprinted by the large variations in salinity (specifically on Bulimina marginata), Mg∕Casw, and possibly also the carbonate system. Salinity is the main factor controlling the faunal assemblages: a much more diverse fauna occurs in the higher-salinity (∼32) Kattegat than in the low-salinity (∼15) Hanö Bay. Molecular identification shows that only Elphidium clavatum occurs at both locations, but other genetic types of both genera Elphidium and Ammonia are restricted to either low- or high-salinity locations. The combination of foraminiferal geochemistry and environmental parameters demonstrates that in a highly variable setting like the Baltic Sea, it is possible to separate different environmental impacts on the foraminiferal assemblages and therefore use Mn∕Ca, Mg∕Ca, and Ba∕Ca to reconstruct how specific conditions may have varied in the past.

Salinity Variation in a Mangrove Ecosystem: A Physiological Investigation to Assess Potential Consequences of Salinity Disturbances on Mangrove Crabs.

Dimitri Theuerkauff, Georgina A. Rivera-Ingraham, Jonathan A.C. Roques, Laurence Azzopardi, Marine Bertini, Mathilde Lejeune, Emilie Farcy, Jehan-Hervé Lignot, and Elliott Sucré (2018) Salinity is one of the main environmental factors determining coastal species distribution. However, in the specific case of mangrove crabs, salinity selection cannot be understood through ecological approaches alone. Yet understanding this issue is crucial in the context of mangrove conservation, since this ecosystem is often used as biofilter of (low- salinity) wastewater. Crabs are keystone species in this mangrove ecosystem and are differentially affected by salinity. We hypothesize that crab salinity selection may be partly explained by specific salinity-induced physiological constraints associated with osmoregulation, energy and redox homeostasis. To test this, the response to salinity variation was analysed in two landward mangrove crabs: the fiddler crab Tubuca urvillei, which inhabits low-salinity areas of the mangrove, and the red mangrove crab Neosarmatium meinerti, which lives in areas with higher salinity. Results confirm that both species are strong hypo-/hyper-osmoregulators that deal easily with large salinity variations. Such shifts in salinity do not induce changes in energy expenditure (measured as oxygen consumption) or in the production of reactive oxygen species. However, T. urvillei is physiologically suited to habitats with brackish water, since it presents i) high hemolymph osmolalities over a wider range of salinities and lower osmoregulatory capacity in seawater, ii) high Na+/K+-ATPase (NKA) activity in the posterior osmoregulatory gills and iii) a thicker osmoregulatory epithelium along the posterior gill lamellae. Therefore, while environmental salinity alone cannot directly explain fiddler and red mangrove crab distributions, our data suggest that salinity selection is indeed influenced by specific physiological adjustments.

Depositional history of the Late Barremian deposits (Sidi Aïch Formation) in central Tunisia and adjacent parts of Algeria: A geostatistical revelation

The lithofacies analysis of the Sidi Aïch Formation and equivalents in Tunisia and adjacent parts of Algeria was carried out using probabilistic and quantitative approach as Discrete Time Markov Chain (DTMC) and entropy functions coupled with detailed sedimentary analyses with a view to decipher the Late Barremian depositional history. The Late Barremian successions exhibit asymmetric, fining-upward and retrograding to aggrading cycles in both outcrop and borehole data. Complete cycles typically start with intraformational conglomerates or trough and planar cross-stratified coarse sands, overlain by fine-grained sands, which are succeeded, in turn, by laminated sands, silts, clays and carbonates, and ends with paleosoils. Such ideal succession of lithofacies is observed at Zemlet el Baidha Hill in Tunisia and OuM.1 borehole in northeast Algeria marked by high values of entropy. The entropy analysis indicates deposition in a neritic environment with interplay of fluvial (and rarely alluvial) processes. The facies associations observed at Zemlet el Baidha Hill document evidences of wave and tide dominated coast with complex-gradient of environments that graded from neritic (upper to lower shoreface) to coastal settings (lagoons, embayments, restricted bays, mires, swamps etc.). The architecture of lithofacies appears to have been controlled by autocyclic processes (effects of local tectonics, basin bathymetry, lateral redistribution of deposits by longshore waves and tide currents) and allocyclic processes (global decrease of relative sea-level and sediments supply). Due to large salinity variations, wave action, ephemeral and local aspects of these marginal environments, the ichnodiversity was often limited in time and space, and inhibited the development of fossils during the onset of deposition of Sidi Aïch Formation and its equivalents.

Effect of Salinity on the Growth Parameters of Halotolerant Microalgae, &lt;i&gt;Dunaliella spp.&lt;/i&gt;

: Dunaliella strains (T35, T36 and T37) were isolated from saline river of Namibia. The effects of salinity stress on their growth and pigment content was investigated. The specific growth rate (µ) of Dunaliella was established in a controlled environment. NaCl concentration has a strong effect on the growth rate and generation time of these halotolerant microalgae. Dunaliella strains were shown to withstand large variations of salinity of the growth medium, 0.5 - 4.0 M NaCl. The optimum conditions for their growth were 1.0 M NaCl at 30 oC, pH 7.5 to 9.0 and 45 µmol m-2 s-1. Increasing salinity from 1.0 to 4.0 M NaCl decreased cell density by 40 %. Increased cellular chlorophyll content was observed form 2 to 14 days of inoculation for all the three strains investigated. However, after day 10 of inoculation there was no significant difference in the pigment content per cell in all strains (p ≤ 0.05). This study shows that there is a good relationship between growth rate and efficient photosynthetic apparatus during the cultivation.

The zooplankton of the shallow lakes of the semi-arid region of southern South America

The southern region of South America is arid and semi-arid, with an east–west gradient of precipitation. Most of its aquatic ecosystems are temporary lakes, with large variations in level and salinity. Although some ecological aspects of these lakes have been studied, the information on the relations between zooplankton and water chemistry, predation, effects of human activities, and the trophic status is scarce and scattered. The objective of this study was to determine the zooplanktonic composition, density, and biomass and their relationships with environmental variables in lakes of different phytogeographic regions of this region (Argentinian central pampa), subjected to different anthropic influences. Samples were taken from ten lakes with a salinity gradient between 0.38 and 115.5 g∙L−1 . The chemical composition revealed a distinction between sodic-bicarbonated and sodic-chlorinated lakes. We recorded 19 crustaceans and 30 rotifers and found inverse relationships between the richness and density and salinity and concentrations of most ions. Bicarbonated lakes were subsaline and characterized by greater richness and density, caused by rotifers. The most frequent species were Brachionus caudatus and Keratella tropica , and the crustaceans Bosmina huaronensis and Microcyclops anceps . The sodic-chlorinated lakes had lower richness and densities, and with distinguishable hyposaline and mesosaline populations with a predominance of neotropical endemic crustaceans, such as Moina eugeniae and Boeckella poopoensis , and hypersaline lakes with a predominance of Artemia permisilis . The biomass did not differ, but lakes with introduced fish fauna (subsaline and hyposaline) had smaller zooplankton, indicating the importance of the top down-effect in the zooplankton community structure.

Life Under Exceptional Conditions—Isotopic Niches of Benthic Invertebrates in the Estuarine Maximum Turbidity Zone

The estuarine maximum turbidity zone (MTZ) can be assumed to be a stressful environment featuring special conditions of great biological importance with an excess of organic matter, high-deposition rates, large variations in salinity, and dredging activities. Under such harsh conditions, populations may remain below the carrying capacity and competition is assumed to be of little importance, as predicted by the stress-gradient hypothesis. Therefore, we hypothesized that invertebrates of similar feeding types may utilize the same resources. To test our hypothesis, we chose the three most abundant taxa classified in literature as deposit feeders (Bathyporeia pilosa, Boccardiella ligerica, Marenzelleria sp.) and two taxa classified as predominately predacious (Palaemon longirostris, Crangon crangon) and determined their isotopic niches based on a stable isotope analysis for the MTZ of the Elbe Estuary (Germany). We expected the isotopic niches of similar feeding types to show a clear overlap if our hypothesis was true. Our results showed that the isotopic niches of no two taxa overlapped within each feeding group, indicating different resource use and the absence of competition. The sediment analysis revealed that two of the deposit feeders inhabited significantly different mean grain sizes. The lack of overlap of isotopic niches within each feeding group may be due to differences in habitat and feeding behavior in the case of the deposit feeders and due to different migration behavior in the case of the predominately predacious species. However, competition may have occurred in the past, resulting in a divergence of feeding niches during evolution.