Salinity Fluctuations Research Articles

Hyposalinity stress reduces mussel byssus secretion but does not cause detachment

Environmental stressors such as salinity fluctuations can significantly impact the ecological dynamics of mussel beds. The present study evaluated the influence of hyposalinity stress on the detachment and survival of attached mussels by simulating a mussel farming model in a laboratory setting. Byssus production and mechanical properties of thread in response to varying salinity levels were assessed, and histological sections of the mussel foot were analyzed to identify the changes in the byssus secretory gland area. The results showed that hyposalinity stress (20 and 15 psu) led to a significant decrease in mussel byssus secretion, delayed initiation of new byssus production, and reduced plaque adhesion strength and breaking force of byssal threads compared to the control (30 psu) (p < 0.05). The complete suppression of byssal thread secretion in mussels under salinity conditions of 10 and 5 psu, leading to lethality, indicates the presence of a blockade in byssus secretion when mussels are subjected to significant physiological stressors. Histological analysis further demonstrated a decrease in the percentage of foot secretory gland areas in mussels exposed to low salinities. However, contrary to expectations, the study found that mussels did not exhibit marked detachment from ropes in response to the reduced salinity levels during one week of exposure. Hyposalinity stress exposure reduced the byssal secretion capacity and the mechanical properties of threads, which could be a cause for the detachment of suspension-cultured mussels. These results highlight the vulnerability of mussels to hyposalinity stress, which significantly affects their byssus mechanical performance.

Unravelling the genetic mechanisms and paleoenvironmental controls of early Cretaceous Oyster Mass occurrences (OMOs), Neuquén Basin, west-central Argentina

Lower Valanginian oyster mass occurrences (OMOs) from the Neuquén Basin of Argentina are analyzed using a multidisciplinary approach, including the description of their sedimentological signature and stratigraphic contacts, assessment of taphonomical attributes, and paleontological and paleoecological characteristics. These OMOs present a wide distribution in the study area, with lateral continuity for at least 2.5 km and up to 12 m thick. They occur within a single stratigraphic interval, constrained in terms of sequence stratigraphy and biostratigraphy. Three stacked tabular OMOs separated by mudstone levels were recorded in all the studied localities. The associated lithofacies point to a mainly outer ramp paleoenvironment, below storm wave base and occasionally disturbed by exceptional, distal storm flows. Internally, the OMOs share a common vertical trend characterized, from base to top, by a gradual increase in oyster abundance and a transition from mainly reclining, disarticulated oysters to articulated, cementing oysters conforming build-ups. Hence, a mainly biogenic origin is proposed, with autobiostromes grading vertically to bioherms. This vertical trend was interpreted in terms of development stages, namely, colonization, expansion, climax and extinction, which were in turn related to specific paleoenvironmental controls. Particularly, the OMOs establishment and development were associated to low sedimentation rates, salinity fluctuations and high nutrient input as a result of high primary productivity. At a larger scale, the overall paleoenvironmental conditions and subtropical geographical position of the basin were detrimental for most reef builders typical of the Cretaceous period (e.g., corals, sponges, rudists), and could have favored oyster proliferation and OMOs development instead.

Impacts of groundwater dynamics around a macro-tidal river on agricultural soil salinity

Estuaries are vulnerable to oceanic and atmospheric climate change. Much of the research investigating climate change impacts on estuaries is focused on saltwater intrusion within surface water due to drought and rising sea levels, with implications for ecosystems and humans. Groundwater and soil near estuaries may also be influenced, as estuary salinity and hydraulic head changes can impact soils and aquifers not previously at risk of salinization. This study was conducted to address knowledge gaps related to present and future groundwater salinity distribution in a groundwater system connected to a macro-tidal estuary. The studied estuary experiences a tidal bore due to its hydraulic connection to the Bay of Fundy in Nova Scotia, Canada. A parcel of agricultural land adjacent to the estuary was selected to assess the groundwater response to episodic fluctuations in estuary water levels and salinity. Groundwater monitoring and electromagnetic surveys were conducted to map soil and groundwater salinity patterns. A numerical model of groundwater flow and solute transport informed by field data was used to investigate how varying estuary salinity due to droughts and sea-level rise could impact groundwater salinity. Results showed that, in contrast to salt wedges observed along marine coasts, the saline groundwater existed as a plume immediately around the estuary. Model simulations showed that short-term droughts had an insignificant impact on the adjacent groundwater salinity. However, permanent increases in salinity caused by sea-level rise increased the plume volume by 86 %, or an additional ∼11 m horizontally and ∼ 4.5 m vertically. Our results suggest that increased river salinity in this setting would not result in widespread salinization of porewater and agricultural soils, but more extensive salinization may be experienced in permeable aquifers or along more saline estuarine zones. Findings may inform land management decisions in regions exposed to increased salinity in the future.

Water mass exchange in triangle seas of the Java-Makassar-Flores (JMF): A modeling study

The ocean dynamics of the marginal seas in the Java-Makassar-Flores (JMF) Triangle seas facilitates the seasonal exchange of water masses between Java, Makassar, and Flores, which influences the occurrence of small pelagic fish. This research investigates seasonal fluctuations in sea currents, seawater temperature, salinity, and phytoplankton primary production (PPN and PPD) based on validated model output datasets from NEMO and PISCES from the INDESO simulation (2008–2015). The model demonstrated seasonal exchanges of the top 50 m of water masses in the area, where the eastward monsoon current transported freshwater (salinity<31 psμ) from the Java Sea to southern Makassar and Flores. This northwest monsoon produced a much fresher water in the southern region of Makassar and western region of Flores. During the southeast monsoon, the surface component of the Makassar throughflow, which transports saline water (salinity >34 PSU) into the Java Sea, pushes fresh Java waters westward. Seasonal salinity changes and PPN/PPD in the shelf region of southern Kalimantan correlated with substantial small pelagic fishing.

First Insights into Body Localization of an Osmoregulation-Related Cotransporter in Estuarine Annelids.

The expression of the Na+-K+-2Cl- cotransporter (NKCC), widely associated with cell volume regulation, has never been directly demonstrated in annelids. Its putative presence was firstly recovered in silico, and then using immunofluorescence, its signal was retrieved for the first time in different tissues of four species of estuarine annelids from southern Brazil that are regularly subjected to salinity fluctuations. We tested two euryhaline species (wide salinity tolerance), the nereidids Alitta yarae and Laeonereis acuta (habitat salinity: ~10-28 psu), and two stenohaline species (restricted salinity tolerance), the nephtyid Nephtys fluviatilis (habitat salinity: ~6-10 psu), and the melinnid Isolda pulchella (habitat salinity: ~28-35 psu). All four species showed specific immunofluorescent labelling for NKCC-like expression. However, the expression of an NKCC-like protein was not homogeneous among them. The free-living/burrowers (both euryhaline nereidids and the stenohaline nephtyid) displayed a widespread signal for an NKCC-like protein along their bodies, in contrast to the stenohaline sedentary melinnid, in which the signal was restricted to the branchiae and the internal tissues of the body. The results are compatible with NKCC involvement in cell volume, especially in annelids that face wide variations in salinity in their habitats.

Sea Surface Salinity Forecasting with a Comparison Studying Case of GMM-VSG and FB-Prophet Model

With the evolution of artificial intelligence, the utilization of machine learning algorithms for predicting hydrological data has gained popularity in scientific research, especially for the development and operational patterns of marine-related objects in coastal regions. Salinity analysis plays a crucial role in evaluating the resilience and health of marine ecosystems. Traditional numerical models, although accurate, require significant computational resources. Therefore, this study assesses the effectiveness of GMM-VSG proposed by Shanghai University and FB-Prophet created by Meta (Facebook) as rapid alternatives for simulating the nonlinear relationships between salinity and various parameters, like tide-induced free surface elevation, river flows, and wind speed. The algorithms were tested using an eight-year dataset collected at the MAREL buoy at the entrance to bay of Brest. Results indicate that, despite the simplicity of the input data, both algorithms successfully reproduced seasonal and semi-diurnal fluctuations in salinity. This underscores their potential as complementary tools for the ecological monitoring in estuarine environments.

Filtration rate and bioremediatory potential of the tropical blacklip rock oyster Saccostrea lineage J

The tropical blacklip rock oyster Saccostrea lineage J is an emerging aquaculture species displaying fast growth rates, large sizes and resilience to fluctuations in temperature and salinity, all characteristics that suggest it would be well-suited to bioremediatory applications. To investigate their bioremediatory potential, the present study aimed to (1) determine the influence of temperature (20, 24, 28, 32°C) on the filtration rate of Saccostrea lineage J and (2) describe and quantify uptake in total nitrogen (TN), total phosphorus (TP), total suspended solids (TSS) and chlorophyll a (chl a), using prawn pond effluent and 2 levels of oyster stocking density. The results demonstrated that higher water temperatures promote a faster filtration rate and identified an optimal performance range of 24 to 32°C for a filtration rate of 12.68 to 15.20 l h-1 g-1. In addition, the highest density (0.66 oysters l-1) of stocked oysters resulted in significant reduction of all water quality parameters, with TN reduced by 13%, TP by 16%, TSS by 95% and chl a by 29% when compared to unstocked controls after 3 h. Tissue analysis of 10 oysters with a mean whole weight of 75.4 g revealed a mean of 0.09 g of nitrogen per oyster. Scaling these values suggests that 1.20 kg of nitrogen is removed per tonne of harvested oysters. This study is the first to investigate the bioremediatory potential of Saccostrea lineage J and demonstrates their potential to improve aquaculture wastewater treatment practices and bioremediation.

Effects of hypo-osmotic stress on osmoregulation, antioxidant response, and energy metabolism in sea cucumber Holothuria moebii under desalination environment

With global climate changing, hypo-salinity events are increasing in frequency and duration because of continuous rainfall and freshwater inflow, which causes reduced cytosolic osmolarity and cellular stress responses in aquatic animals. Sea cucumbers are considered stenohaline because they lack osmoregulatory organs and are vulnerable to salinity fluctuations. In this study, we performed multiple biochemical assays, de novo transcriptomics, and widely targeted metabolomics to comprehensively explore the osmoregulatory mechanisms and physiological responses of sea cucumber Holothuria moebii to hypo-osmotic stress, which is a representative specie that is frequently exposed to hypo-saline intertidal zones. Our results found that H. moebii contracted their ambulacral feet and oral tentacles, and the coelomic fluid ion concentrations were reduced to be consistent with the environment. The microvilli of intestines and respiratory trees underwent degeneration, and the cytoplasm exhibited swelling and vacuolation. Moreover, the Na+, K+, and Cl− concentrations and Na+/K+-ATPase activity were significantly reduced under hypo-osmotic stress. The decrease in protein kinase A activity and increase in 5′-AMP level indicated a significant inhibition of the cAMP signaling pathway to regulate ion concentrations. And small intracellular organic molecules (amino acids, nucleotides and their derivatives) also play crucial roles in osmoregulation through oxidative deamination of glutamate, nucleotide catabolism, and nucleic acid synthesis. Moreover, lysosomes and peroxisomes removed oxidative damage, whereas antioxidant metabolites, such as N-acetyl amino acids and glutathione, were increased to resist oxidative stress. With prolonged hypo-osmotic stress, glycerophospholipid metabolism was enhanced to maintain membrane stability. Furthermore, acyl-CoA-binding protein activity was significantly inhibited, and only a small amount of acylcarnitine was significantly accumulated, which indicated a disruption in energy metabolism. PPAR signaling pathway and choline content were up-regulated to promote fatty acid metabolism under hypo-osmotic stress. Overall, our results provide new insights into the osmoregulatory mechanisms and physiological responses of sea cucumbers to hypo-osmotic stress.

Impacts of extreme river discharge on coastal dynamics and environment: Insights from high-resolution modeling in the German Bight

The intricate relationship between extreme river discharge and its consequential effects on coastal basins’ environment and dynamics remains a subject of profound significance. The impact of extreme river discharge on coastal basin dynamics and environment is a complex phenomenon, particularly relevant in the context of the German Bight. The inflow of freshwater from rivers into the German Bight plays a crucial role in driving the complex thermohaline circulation. Addressing the challenges posed by local hydro-meteorological extremes, compounded by strong wind waves, currents and tides is vital for comprehensive impact assessment. Utilizing the Geesthacht Coupled cOAstal model SysTem (GCOAST) with high-resolution configuration, we investigate the sensitivity of the thermohaline properties to the river forcings. By incorporating river discharge as lateral land forcing in a coupled hydrodynamic and wave model, we conducted five sensitivity experiments. Our findings reveal that the simulated temperatures closely match measurements in all experiments. The salinity, however, is remarkably sensitive to the variation of freshwater from the rivers Elbe and Ems in the German Bight, causing the haline stratification. The statistical evaluation, as demonstrated by the Taylor diagram at the Marnet DB station, underscores the skill of the Mesoscale Hydrologic Model (mHM) in generating the freshwater discharge that drives the thermohaline characteristics of the German Bight, especially during events like the June 2013 flooding. Significantly, the use of climatological runoff proves to be ineffective in simulating stratification during extreme flooding events. In essence, this investigation enhances our understanding of the pivotal role played by high-frequency river freshwater buoyancy. It emerges as a driving force behind salinity fluctuations during extreme floods, providing valuable insights into coastal dynamics within the German Bight.

Broadening the adaptation of Sepia pharaonis to low salinity through a graded salinity reduction approach

Sepia pharaonis, commonly known as the pharaoh cuttlefish, is a valued cephalopod in aquaculture. However, its sensitivity to salinity fluctuations has constrained its cultivation, especially in regions with varying salinity and during rainy seasons. To address this, our study implemented a graded salinity reduction approach, enabling S. pharaonis to acclimate to an environment with a salinity of 20. Despite a reduction in growth parameters such as mantle length and body weight in the Low-Salinity Acclimation group (LSA), the survival rates were largely consistent with the control group. After the acclimation process, the LSA group demonstrated a strikingly high survival rate of nearly 100% in salinity ranges from 18 to 24, a span previously thought to be deadly for non-acclimated S. pharaonis. Our evaluations indicate that the serum osmotic pressure and ion concentration of S. pharaonis decline with decreasing seawater salinity. During this process, there were significant alterations in the Na+/K+-ATPase activity and the content of free amino acids, suggesting their crucial role in low-salt osmoregulation. Overall, this study not only highlights the potential of the graded salinity reduction method to enhance the adaptability of S. pharaonis to fluctuating salinities, but also underscores the potential of graded salinity reduction as an innovative approach to enhance the resilience of aquaculture species.

Glycine betaine modulates extracellular polymeric substances to enhance microbial salinity tolerance

High salinity inhibits microbial activity in the bioremediation of saline wastewater. To alleviate osmotic stress, glycine betaine (GB), an osmoprotectant, is added to enhance the secretion of extracellular polymeric substances (EPS). These EPS are pivotal in withstanding environmental stressors, yet the intricate interplay between GB supplementation and microbial responses through EPS modifications—encompassing composition, molecular architecture, and electrochemical features—remains elusive in hypersaline conditions. Here we show microbial strategies for salinity endurance by investigating the impact of GB on the dynamic alterations of EPS properties. Our findings reveal that GB supplementation at 3.5% salinity elevates the total EPS (T-EPS) content from 12.50 ± 0.05 to 24.58 ± 0.96 mg per g dry cell weight. The observed shift in zeta potential from −28.95 to −6.25 mV at 0% and 3.5% salinity, respectively, with GB treatment, indicates a reduction in electrostatic repulsion and compaction. Notably, the EPS protein secondary structure transition from β-sheet to α-helix, with GB addition, signifies a more compact protein configuration, less susceptible to salinity fluctuations. Electrochemical analyses, including cyclic voltammetry (CV) and differential pulse voltammetry (DPV), reveal GB's role in promoting the release of exogenous electron shuttles, such as flavins and c-type cytochromes (c-Cyts). The enhancement in DPV peak areas (QDPV) with GB addition implies an increase in available extracellular electron transfer sites. This investigation advances our comprehension of microbial adaptation mechanisms to salinity through EPS modifications facilitated by GB in saline habitats.

Modeling Dynamic Processes in the Black Sea Pelagic Habitat—Causal Connections between Abiotic and Biotic Factors in Two Climate Change Scenarios

The paper contributes to the Sustainable Development Goals (SDGs) targeting Life Below Water by introducing user-friendly modeling approaches. It delves into the impact of abiotic factors on the first two trophic levels within the marine ecosystem, both naturally and due to human influence. Specifically, the study examines the connections between environmental parameters (e.g., temperature, salinity, nutrients) and plankton along the Romanian Black Sea coast during the warm season over a decade. The research develops models to forecast zooplankton proliferation using machine learning (ML) algorithms and gathered data. Water temperature significantly affects copepods and “other groups” of zooplankton densities during the warm season. Conversely, no discernible impact is observed on dinoflagellate Noctiluca scintillans blooms. Salinity fluctuations notably influence typical phytoplankton proliferation, with phosphate concentrations primarily driving widespread blooms. The study explores two scenarios for forecasting zooplankton growth: Business as Usual, predicting modest increases in temperature, salinity, and constant nutrient levels, and the Mild scenario, projecting substantial temperature and salinity increases alongside significant nutrient decrease by 2042. The findings underscore high densities of Noctiluca scintillans under both scenarios, particularly pronounced in the second scenario, surpassing the first by around 70%. These findings, indicative of a eutrophic ecosystem, underscore the potential implications of altered abiotic factors on ecosystem health, aligning with SDGs focused on Life Below Water.

Community stability of free-living and particle-attached bacteria in a subtropical reservoir with salinity fluctuations over 3 years

Changes in salinity have a profound influence on ecological services and functions of inland freshwater ecosystems, as well as on the shaping of microbial communities. Bacterioplankton, generally classified into free-living (FL) and particle-attached (PA) forms, are main components of freshwater ecosystems and play key functional roles for biogeochemical cycling and ecological stability. However, there is limited knowledge about the responses of community stability of both FL and PA bacteria to salinity fluctuations. Here, we systematically explored changes in community stability of both forms of bacteria based on high-frequency sampling in a shallow urban reservoir (Xinglinwan Reservoir) in subtropical China for 3 years. Our results indicated that (1) salinity was the strongest environmental factor determining FL and PA bacterial community compositions – rising salinity increased the compositional stability of both bacterial communities but decreased their α-diversity. (2) The community stability of PA bacteria was significantly higher than that of FL at high salinity level with low salinity variance scenarios, while the opposite was found for FL bacteria, i.e., their stability was higher than PA bacteria at low salinity level with high variance scenarios. (3) Both bacterial traits (e.g., bacterial genome size and interaction strength of rare taxa) and precipitation-induced factors (e.g., changes in salinity and particle) likely contributed collectively to differences in community stability of FL and PA bacteria under different salinity scenarios. Our study provides additional scientific basis for ecological management, protection and restoration of urban reservoirs under changing climatic and environmental conditions.

State of Surface and Vertical Salinity in Puttalam Lagoon during North-East Monsoon

Puttalam Lagoon which covers 226 km2 located in Sri Lanka‘s Northwest coast, plays an important role in aquaculture and lagoon capture fisheries. Kala oya and Mee oya are the major freshwater sources which empties into the Lagoon by eastern bank. Salinity variability is an important environmental variable in lagoon system that has an impact on aquaculture and aquatic resources. During the Northeast monsoon (NEM) in 2021, the spatial and vertical fluctuation of salinity in the lagoon was studied using SBE 19plus V2 CTD profiler. Field measurements show that the vertical salinity stratification in the lagoon was substantial during the study period. The lagoon has a significant spatial variability of salinity, ranging from 15 psu to 26 psu and Kala Oya river mouth has a salinity of 22 psu which impacted by freshwater and sea water circulation. The Salinity stratification in eastern section of the lagoon where the Kala Oya and Mee Oya streamflow reach is observed with surface salinity of 15 psu. During the NEM season, the average discharge of Kala Oya and Mee Oya to the lagoon was 10.8 m3/s and 9.4 m3/s, respectively, with a mean monthly precipitation of 48.89 mm. Fresh water from the Kala and Mee oya rivers flows into the lagoon during the season, while low evaporation and significant rainfall led the salinity to decline during the wet season, influencing the structure and function of lagoon ecosystems. The study reveals that a significant area of the lagoon is covered by the 20-30 psu salinity range, which is more appropriate for brackish water fisheries, particularly for shrimp and prawns during NEM. &#x0D; Keywords: Salinity, CTD profiling, Northeast Monsoon, Freshwater

Fatty acid profiles reveal dietary variability of a large calanoid copepod Limnocalanus macrurus in the northern Baltic Sea

Eutrophication, climate-induced warming, and salinity fluctuations are altering the fatty acid profiles and the availability of essential polyunsaturated fatty acids (PUFAs) in marine zooplankton communities. Limnocalanus macrurus Sars G.O., 1863 is a large calanoid copepod inhabiting the low-salinity areas in the Baltic Sea, where it is a major source of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) to commercially important fish. L. macrurus is sensitive to warming, eutrophication and hypoxia. As an opportunistic feeder, it is capable of dietary shifts, which affects its fatty acid profiles. Although much studied in boreal lakes, there are only a few studies on the fatty acid profiles of the Baltic Sea populations. This study aimed to compare the fatty acid profiles of L. macrurus in three basins of the Baltic Sea, in relation to the community fatty acids and environmental variables. We collected samples of L. macrurus and filtered plankton community for gas chromatographic fatty acid analyses in August 2021 on R/V Aranda. The nutritional quality of L. macrurus to consumers was lower in the Gulf of Finland (GoF) compared to the Gulf of Bothnia, indicated by the low levels of DHA and EPA, as well as the low n-3/n-6 ratio of PUFAs. The lower ratio of 18:1n-7 to 18:1n-9 implied higher degree of omnivory in GoF. In contrast, a diatom marker 16:1n-7 had high proportion in the Bothnian Bay. High temperatures in GoF may have restricted feeding in the upper water column, possibly forcing a shift towards cyanobacteria or seston-based diet, as interpreted from a high proportion of 18:2n-6 and 18:3n-3. We conclude that the ability of L. macrurus to utilize multiple food sources increases its resilience to environmental change, while the consequences on the nutritional quality may have further cascading effects on the food webs.

Effects of Erythromycin on Nereis succinea and the Intestinal Microbiome across Different Salinity Levels.

The exposure of aquatic organisms to pollutants often occurs concomitantly with salinity fluctuations. Here, we reported the effects of erythromycin (0.250, 7.21, and 1030 μg/L) on marine invertebrate N. succinea and its intestinal microbiome under varying salinity levels (5‰, 15‰, and 30‰). The salinity elicited significant effects on the growth and intestinal microbiome of N. succinea. The susceptibility of the intestinal microbiome to erythromycin increased by 8.7- and 6.2-fold at salinities of 15‰ and 30‰, respectively, compared with that at 5‰ salinity. Erythromycin caused oxidative stress and histological changes in N. succinea intestines, and inhibited N. succinea growth in a concentration-dependent manner under 30‰ salinity with a maximum inhibition of 25%. At the intestinal microbial level, erythromycin enhanced the total cell counts at 5‰ salinity but reduced them at 15‰ salinity. Under all tested salinities, erythromycin diminished the antibiotic susceptibility of the intestinal microbiome. Two-way ANOVA revealed significant interactive effects (p < 0.05) between salinity and erythromycin on various parameters, including antibiotic susceptibility and intestinal microbial diversity. The present findings demonstrated the significant role of salinity in modulating the impacts of erythromycin, emphasizing the necessity to incorporate salinity fluctuations into environmental risk assessments.

Salinity-induced succession of phototrophic communities in a southwestern Siberian soda lake during the solar activity cycle

A variety of lakes located in the dry steppe area of southwestern Siberia are exposed to rapid climatic changes, including intra-century cycles with alternating dry and wet phases driven by solar activity. As a result, the salt lakes of that region experience significant fluctuations in water level and salinity, which have an essential impact on the indigenous microbial communities. But there are few microbiological studies that have analyzed this impact, despite its importance for understanding the functioning of regional water ecosystems. This work is a retrospective study aimed at analyzing how solar activity-related changes in hydrological regime affect phototrophic microbial communities using the example of the shallow soda lake Tanatar VI, located in the Kulunda steppe (Altai Region, Russia, southwestern Siberia). The main approach used in this study was the comparison of hydrochemical and microscopic data obtained during annual field work with satellite and solar activity data for the 12-year observation period (2011–2022). The occurrence of 33 morphotypes of cyanobacteria, two key morphotypes of chlorophytes, and four morphotypes of anoxygenic phototrophic bacteria was analyzed due to their easily recognizable morphology. During the study period, the lake surface changed threefold and the salinity changed by more than an order of magnitude, which strongly correlated with the phases of the solar activity cycles. The periods of high (2011–2014; 100–250 g/L), medium (2015–2016; 60 g/L), extremely low (2017–2020; 13–16 g/L), and low (2021–2022; 23–34 g/L) salinity with unique biodiversity of phototrophic communities were distinguished. This study shows that solar activity cycles determine the dynamics of the total salinity of a southwestern Siberian soda lake, which in turn determines the communities and microorganisms that will occur in the lake, ultimately leading to cyclical changes in alternative states of the ecosystem (dynamic stability).

The bacterial influencing mechanisms of salinity fluctuations in a brackish-water lake on the dissolved organic matter characteristics of pore water

The dissolved organic matter (DOM) components in lake water have been widely studied; however, few previous studies have considered the growth of Phragmites australis in brackish lakes. It has not been well understood how salinity variations influence the DOM compositions in pore water and its bacterial mechanisms in lakes with Phragmites australis. This experiment included three salinity groups (1,200 mg/L, 3,600 mg/L, and 6,000 mg/L) to study the interactions between bacteria and DOM in pore water under a salinity gradient. The results showed that the maximum fluorescence intensity (Fmax) of DOM measured by excitation-emission fluorescence spectroscopy decreased with increasing salinity. Higher salinity reduced the Fmax of protein-like substances and resulted in DOM becoming more aromatic. Salinity affected DOM composition due to the responses of functional bacterial communities. Thiobacillus was salt-tolerant and dominated in the sediments, and its relative abundance was negatively correlated with the Fmax of protein-like components. The relative abundance of Flavobacterium showed a positive correlation with salinity and a negative correlation with the Fmax of the fulvic acid-like component. Pseudomonas, Brevundimonas, and Polaromonas were negatively correlated with salinity and the Fmax of the fulvic acid-like component, while being positively correlated with the Fmax of tyrosine-like and aromatic protein substances. Higher salinity inhibited the metabolism gene modules of tryptophan and tyrosine. The results of this study may offer a novel perspective on comprehending the biochemical cycling of fluorescent DOM, encompassing tryptophan-like, tyrosine-like, and fulvic acid-like components in brackish lakes with fluctuating salinity.

Synergistic effect of silicon availability and salinity on metal adsorption in a common estuarine diatom

Increasing nitrogen and phosphorus discharge and decreasing sediment input have made silicon (Si) a limiting element for diatoms in estuaries. Disturbances in nutrient structure and salinity fluctuation can greatly affect metal uptake by estuarine diatoms. However, the combined effects of Si and salinity on metal accumulation in these diatoms have not been evaluated. In this study, we aimed to investigate how salinity and Si availability combine to influence the adsorption of metals by a widely distributed diatom Phaeodactylum tricornutum. Our data indicate that replete Si and low salinity in seawater can enhance cadmium and copper adsorption onto the diatom surface. At the single-cell level, surface potential was a dominant factor determining metal adsorption, while surface roughness also contributed to the higher metal loading capacity at lower salinities. Using a combination of non-invasive micro-test technology, atomic force microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy, we demonstrate that the diversity and abundance of the functional groups embedded in diatom cell walls vary with salinity and Si supply. This results in a change in the cell surface potential and transient metal influx. Our study provides novel mechanisms to explain the highly variable metal adsorption capacity of a model estuarine diatom.

The Dynamics of Soil Mesofauna Communities in a Tropical Urban Coastal Wetland: Responses to Spatiotemporal Fluctuations in Phreatic Level and Salinity

Coastal wetlands, vital for ecological diversity, have been significantly altered by anthropogenic activities, particularly in the Caribbean. These changes have created a complex mosaic of habitats and physicochemical conditions, further stressed by climate variability and sea-level rise. This study, conducted in Las Cucharillas Natural Reserve, a tropical urban coastal wetland in Puerto Rico, aimed to determine the effects of spatiotemporal variations in phreatic levels and salinity on soil mesofauna assemblages, crucial bio-indicators of environmental change. In 2020 and 2021, soil samples were collected from five diverse habitat types during different hydroperiods. Each sample was taken under four randomly selected plant types and processed using lighted Tullgren–Berlese extractors. Phreatic level and salinity were also measured. A total of 43 families were quantified, underscoring distinct habitat differences, similarities, and overall ecosystem diversity. Moderate correlations between phreatic levels, salinity, and mesofauna richness and abundance were determined. Peak richness and abundance were quantified at shallow (−0.03 to −0.07 m) and slightly moderate (−0.12 to −0.17 m) phreatic levels where oligohaline salinity (&gt;0.5 to 5.0 ppt) prevails. The study highlights the adaptability of mesofauna to environmental shifts and their potential as biosensors for effective coastal wetland management amid climatic and anthropogenic pressures.