Abrupt Salinity Change Research Articles

Short-Term Effects of Abrupt Salinity Changes on Aquaculture Biofilter Performance and Microbial Communities

In recirculating aquaculture systems (RASs), ammonia excreted by fish must be converted to the less toxic nitrate before recirculation. Nitrifying microorganisms in biofilters used for this transformation can be sensitive to changes in salinity, which can present issues for systems that raise anadromous fish such as Atlantic salmon. Freshwater biofilters maintained at a low level of salinity (such as biofilters operated in coastal areas) may be better equipped to handle more drastic salinity shifts; therefore, experiments were performed on freshwater and low-salinity (3 ppt) biofilters to assess their ability to recover nitrification activity after an abrupt change in salinity (3, 20, and 33 ppt). Two-week tests showed full nitrification recovery in freshwater biofilters after a shift to 3 ppt but no ammonia oxidation in 20 or 33 ppt. Low-salinity-adapted filters (transitioned from 0 to 3 ppt) showed a small recovery (about 11%) after a shift to 20 ppt, and no activity when shifted to 33 ppt. Illumina sequencing revealed that, while nitrification was slowed or stopped with shifting salinities, the nitrifiers survived the salinity increases; conversely, the heterotrophic communities were more greatly affected and were reduced in proportion with increasing salinity. This work indicates that biofilters operated at low salinity may recover more quickly after large salinity changes, though this slight benefit may not outweigh the cost of low-level salinity maintenance. Further research into halotolerant heterotrophs in biofilms may increase the effectiveness of nitrifying biofilters under variable salinities.

Radionuclide transport in fractured chalk under abrupt changes in salinity

Internationally, it has been agreed that geologic repositories for spent fuel and radioactive waste are considered the internationally agreed upon solution for intermediate and long-term disposal. In countries where traditional nuclear waste repository host rocks (e.g., clay, salt, granite) are not available, other low permeability lithologies must be studied. Here, chalk is considered to determine its viability for disposal. Despite chalk's low bulk permeability, it may contain fracture networks that can facilitate radionuclide transport. In arid areas, groundwater salinity may change seasonally due to the mixing between brackish groundwater and fresh meteoric water. Such salinity changes may impact the radionuclides' mobility. In this study, radioactive U(VI) and radionuclide simulant tracers (Sr, Ce and Re) were injected into a naturally fractured chalk core. The mobility of tracers was investigated under abrupt salinity variations. Two solutions were used: a low ionic strength (IS) artificial rainwater (ARW; IS ∼0.002) and a high IS artificial groundwater (AGW; IS ∼0.2). During the experiments, the tracers were added to ARW, then the carrier was changed to AGW, and vice versa. Ce was mobile only in colloidal form, while Re was transported as a conservative tracer. Both Re and Ce demonstrated no change in mobility due to salinity changes. In contrast, U and Sr showed increased mobility when AGW was introduced and decreased mobility when ARW was introduced into the core. These experimental results, supported by reactive transport modeling, suggest that saline groundwater solutions promote U and Sr release via ion-exchange and enhance their migration in fractured chalk. The study emphasizes the impact of salinity variations near spent fuel repositories and their possible impact on radionuclide mobility.

Evaluating the effect of temperature on Penaeus vannamei culture in a heterotrophic system and experimentally infected with the infectious myonecrosis virus

Causing economic losses in Brazil and Indonesia between 2002 and 2011 of over US$ 1 billion, infectious myonecrosis (IMN) constitutes a disease of mandatory notification to WHO (World Health Organization) and is responsible for constant damages in the production of the marine shrimp Penaeus vannamei. Although environmental factors such as high thermal amplitude, high concentration of nitrogen compounds and abrupt changes in salinity can alter the infection rate of this disease, there are still no studies. Thus, the present work aimed to evaluate the influence of temperature on the infectivity of IMNV in P. vannamei culture in a heterotrophic system. The experiment lasted 42 days, divided into two stages: (i) subjecting the shrimps to different temperatures (26 °C, 29 °C, 32 °C, and 35 °C) for 21 days; and (ii) viral challenge with IMNV via intramuscular injection (100 μL) also for 21 days, with evaluation of the shrimps by nested-PCR, histopathology and total and differential hemocyte count. The results obtained indicated that shrimps submitted to the highest temperatures evaluated (32 °C and 35 °C) had the highest post-viral challenge survival rates (85.42% and 93.75%, respectively), with less presence of lesions suggestive of IMN, although these shrimps were still positive by nested-PCR. No significant differences were observed in total hemocyte counts between pre- and post-challenge treatments (P > 0.05). In conclusion, the use of a temperature of 35 °C reduced mortality and viral load but altered the feed absorption, generating a reduction in zootechnical performance.

Effects of Salinity on Lipid Composition in Juvenile Pinc Salmon Oncorhynchus gorbuscha (Salmonidae)

Lipid and fatty acid modifications induced by the effects of various salinity patterns on the juvenile pink salmon Oncorhynchus gorbuscha (the Olkhovka River and the White Sea) within the experiment have been revealed. Concentrations of steroids, saturated fatty acids, and signaling molecules such as phospholipids (phosphatidylserine and phosphatidylinositol) and arachidonic acid under the hyperosmotic stress-related effects (keeping the fish for 1 h in the seawater after the time of transfer from the freswater) tend to increase. Decreases in phosphatidylcholine and n-6 saturated, monounsaturated, and polyunsaturated fatty acids are recorded in the juvenile pink salmon fish kept for 24 h in the seawater after the time of transfer them from the freswater, while the levels of phosphatidylethanolamine and n-3 polyunsaturated fatty acids (especially eicosapentaenoic and docosahexaenoic acids), on the contrary, tend to rise significantly. Lipid composition modifications in the juvenile pink salmon fish kept under the hypoosmotic stress conditions (24 h in freshwater after 24 h in seawater) induce stabilization of functioning the cell membrane structure, since the levels of bioeffectors including phosphatidylserine, phosphatidylinositol, and arachidonic, eicosapentaenoic, and docosahexaenoic acids tend to decrease. A reduced amount of lipids (triacylglycerols) stored as an energy reserve is shown for all the experimental fish groups. The outcomes indicate the high levels of adaptive potential of the juvenile pink salmon fish kept under the effects of abrupt salinity change in the water environments and their readiness for downstream migration not long before leaving the nests.

The combined effect of seawater salinity and duration on the survival and growth of eelgrass Zostera marina

Abrupt changes in salinity are considered a key cause of seagrass bed degradation. In the study, we first quantified the effects of different combinations of salinity and duration on the responses of Zostera marina shoots in terms of survivorship, morphology, growth and physiology. The recovery potential (recovery of shoots from salinity stress to be returned to original salinity level) of Z. marina shoots was assessed. The LT50 (lethal time that caused an increase in mortality to 50 % of that of the control) and EC50 (effect concentration, i.e., salinity level that caused a decrease in growth to 50 % of that of the control) were calculated to reveal the quantitative relationship between salinity and duration that resulted in limiting effects on the survival and growth of Z. marina shoots. Z. marina shoots were exposed to different combinations of water salinity [20, 25, 30 (control), 35, 40, and 45 PSU] and duration (5, 10, 15 and 20 days), and then the shoots were transferred to the control condition for 30 days under laboratory conditions. The results showed that the survival rate of shoots at the end of recovery was significantly lower than those of shoots at the end of direct salinity stress at the hypersalinity levels of 40 and 45 PSU, indicating that short-term periods of increase in water salinity would lead to long-term effects on the survival of Z. marina shoots. The total leaf area of shoots at the end of recovery was significantly higher than those of shoots at the end of direct salinity stress at salinity levels of 25–35 PSU, indicating a significant recovery potential following the salinity stress. However, a poor recovery potential was found under combinations of hypersalinity (40–45 PSU) and duration of 20 days. Regression analysis revealed that the relationship between salinity and duration was a strong power function that could limit the growth of Z. marina. Pearson correlation analysis showed that the survival and growth of Z. marina shoots exposed to different salinity levels were significantly correlated with leaf soluble sugar contents when the duration was higher than 5 days. This study will further enhance our understanding of seagrass bed degeneration induced by abrupt changes in salinity.

Identification of free amino acids (FAA) that are important as major intracellular osmolytes in the estuarine Hong Kong oyster, Crassostrea hongkongensis

Crassostrea hongkongensis (Hong Kong oyster), a commercially valuable bivalve thriving in the estuaries along the northern coast of the South China Sea, is threatened by the increase of salinity during the dry season. It is essential to improve its hyper-salinity tolerance, which requires a clear understanding of the mechanism to regulate its osmotic balance. For this purpose, 25 free amino acids (FAA), the most critical intracellular osmolyte in bivalves, were quantified in gill, adductor muscle, and hemolymph of C. hongkongensis during abrupt salinity changes (18–6, 12, 24 and 30‰) by high-performance liquid chromatography-tandem mass spectrometry. Taurine, alanine and glycine were dominant FAA, contributing to total FAA contents that varied with salinities, no matter in gill, muscle or hemolymph. Under hypo-osmotic stress, total FAA contents decreased in gill and adductor muscle but increased in hemolymph, probably resulting from the extrusion of some FAA from tissues to prevent swelling of cells. And taurine contributed most significantly to the hypo-salinity response, which was mainly reflected by the remarkable increase in hemolymph at 8 h after the exposure to 6‰. By contrast, total FAA contents increased in gill, muscle, and hemolymph when transferred to hyper-salinity, suggesting the assumption that it increases the osmolality and subsequently prevents the cell shrinking. Alanine and glycine contributed most significantly to hyper-salinity response. Of the two, the former was more sensitive to hyper-osmotic stress for its rapid increase in gill within 8 h after the exposure to 24 and 30‰. An inverse pattern with most FAA was presented by ornithine, the intermediate of the urea cycle, which was probably associated with the FAA metabolism. This study identified the major FAA as intracellular osmolytes in C. hongkongensis and would benefit the further understanding of the regulatory mechanisms of oyster salinity acclimation.

Effects of salinity on survival, reproductive performance, population growth, and life stage composition in the calanoid copepod Acartia bilobata

Copepods are a critical live prey item for most marine finfish larvae in the natural environment. The calanoid copepod belonging to species Acartia is a potential live food for the larval rearing of marine finfishes because of their higher productivity and tolerance to wide range of salinities. The present study was conducted to determine the effect of salinity on production parameters to standardize the optimal salinity for Acartia bilobata culture. For selecting the optimal salinity range, the adult copepods were exposed to abrupt salinity change from 30 g L−1 to ten salinity levels, including 0, 5, 10, 15, 20, 25, 30, 35, 40 and 45 g L−1 and their survival estimated after 24 h. Further, the effect of salinity (15, 20,25,30, and 35 g L−1) on egg production, hatching success and population growth were studied. Following sudden salinity change, A. bilobata could tolerate a wide range of salinities from 15 to 35 g L−1, and no copepod survived below 10 g L−1 and above 35 g L−1. Average daily egg production was significantly higher at 25 and 30 g L−1 (32 ± 1 and 34 ± 2 eggs female−1 day−1). A remarkably low egg hatching success was recorded at 15 g L−1 salinity; however, all other tested salinities showed similar egg hatching success. Different salinity levels did not affect the sex ratio of A. bilobata. A significantly higher total population number (1539 ± 75) and intrinsic population growth rate (0.50 ± 0.00) was observed at 30 g L−1, followed by 25 g L−1 salinity. The lowest mean population (518 ± 19) and population growth rate (0.39 ± 0.00) were recorded at 15 g L−1 salinity. The study results suggested that 25–30 g L−1 is the optimal salinity range to achieve maximal production of A. bilobata.

Comparative transcriptome analysis of Portunus trituberculatus in response to Vibrio parahaemolyticus and low salinity

Vibrio parahaemolyticus is a common pathogen of marine crustaceans and is responsible for large losses in aquaculture. Salinity is an important environmental factor, and abrupt changes in salinity can affect the immunity of crustaceans. In this study, we carried out a transcriptomic analysis under pathogenic infection and low salt stress, and conducted a comparative analysis of the differentially expressed genes (DEGs) after stimulation by the two factors. Illumina sequencing technology was used for the transcriptome sequencing of 27 hepatopancreas samples, and 178.77 G sequencing data and an average of 44,142,119 clean reads per sample were obtained. A total of 3,047 and 3,710 DEGs were found after V. parahaemolyticus infection and low salt stress, which included a number of innate immunity genes, such as Toll-like receptor (TLR), anti-lipopolysaccharide factor (ALF), lectin, and hemocyanin. In addition, 2,016 common DEGs were found, accounting for 42.52% of the total DEGs. Among these, 169 DEGs were up-regulated after pathogenic infection and down-regulated after low salt stress, and were mainly enriched in starch and sucrose metabolism, nitrogen metabolism, amino sugar and nucleotide sugar processes, and other pathways. Collectively, these results provide data support for the analysis of the immune mechanism of crabs against V. parahaemolyticus and will also help to clarify the molecular mechanism by which salinity affects immunity.

Salinity-induced transcriptome profiles in marine and freshwater threespine stickleback after an abrupt 6-hour exposure.

Saltwater and freshwater environments have opposing physiological challenges, yet, there are fish species that are able to enter both habitats during short time spans, and as individuals they must therefore adjust quickly to osmoregulatory contrasts. In this study, we conducted an experiment to test for plastic responses to abrupt salinity changes in two populations of threespine stickleback, Gasterosteus aculeatus, representing two ecotypes (freshwater and ancestral saltwater). We exposed both ecotypes to abrupt native (control treatment) and non‐native salinities (0‰ and 30‰) and sampled gill tissue for transcriptomic analyses after 6 h of exposure. To investigate genomic responses to salinity, we analyzed four different comparisons; one for each ecotype (in their control and exposure salinity; (1) and (2), one between ecotypes in their control salinity (3), and the fourth comparison included all transcripts identified in (3) that did not show any expressional changes within ecotype in either the control or the exposed salinity (4)). Abrupt salinity transfer affected the expression of 10 and 1530 transcripts for the saltwater and freshwater ecotype, respectively, and 1314 were differentially expressed between the controls, including 502 that were not affected by salinity within ecotype (fixed expression). In total, these results indicate that factors other than genomic expressional plasticity are important for osmoregulation in stickleback, due to the need for opposite physiological pathways to survive the abrupt change in salinity.

Observation of Abrupt Changes in the Sea Surface Layer of the Adriatic Sea

We observed interannual changes in the temperature and salinity of the surface layer of the Adriatic Sea when measured during the period 2005–2020. We observed non-stationarity and a positive linear trend in the series of mixed layer depth, heat storage, and potential energy anomalies. This non-stationarity was related to the climate regime that prevailed between 2011 and 2017. We observed significant changes in the interannual variability of salinity above and below the mixed layer depth and a positive difference in the surface barrier layer. In an effort to reconstruct the cause of this phenomenon, a multi-stage investigation was conducted. The first suspected culprit was the change in wind regime over the Mediterranean and Northeast Atlantic regions in September. Using the growing neural gas algorithm, September wind fields over the past 40 years were classified into nine distinct patterns. Further analysis of the CTD data indicated an increase in heat storage, a physical property of the Adriatic Sea known to be strongly influenced by the inflow of warm water masses controlled by the bimodal oscillating system (BiOS). The observed increase in salinity confirmed the assumption that BiOS activity affects heat storage. Unexpectedly, this analysis showed that an inverse vertical salinity profile was present during the summer months of 2015, 2017, and 2020, which can only be explained by salinity changes being a dominant factor. In addition, the aforementioned wind regime caused an increase in energy loss through latent energy dissipation, contributing to an even larger increase in salinity. While changes in the depth of the mixed layer in the Adriatic are usually due to temperature changes, this phenomenon was primarily caused by abrupt changes in salinity due to a combination of BiOS and local factors. This is the first record of such an event.

Effect of Abrupt Salinity Change in the Survival of Asian Green Mussel Perna viridis (Linnaeus, 1758) Spats

Salinity is one of the key environmental factors that affects the growth and survival of marine organisms including mussels. Five different salinity levels (40, 30, 20, 10 and 5 ppt) were used to test the effect of abrupt salinity change in the survival of hatchery-produced spats of Asian green mussel Perna viridis (Linnaeus, 1758). Spats were stocked with a density of 30 individuals per 6-L tank. Salinity manipulation was conducted after 2 days from the date of stocking. Based on the results, abrupt change and prolonged exposure to lower salinities particularly of 5 and 10 ppt (up to 5 days) are detrimental to P. viridis spats. The critical time for P. viridis spats wherein they could seclude themselves from the persistent lower salinities is 28 hours from its exposure. After which, mortality could be high at about 50% and will continue in the succeeding days if low salinity persists. Critically, no single spat can survive until the 4th day of continuous exposure to very low salinity of 5 ppt. Nevertheless, surviving individuals could still recover if salinity will return to optimum levels. Additionally, spats can readily adjust to abrupt change up to 10 ppt from the optimum salinity level as seen in the high survival in 20 and 40 ppt.

Using computed tomography (CT) to reconstruct depositional processes and products in the subaqueous glaciogenic Champlain Sea basin, Ottawa, Canada

In this study, depositional conditions in the glaciogenic Champlain Sea basin were inferred solely from evidence of computed tomography (CT). CT-scan images and Hounsfield unit (HU) profiles of two continuous cores in Ottawa, Canada, provided the data to identify five lithologically distinct, mud-dominated stratal units. Distinctively, all strata exhibit a repeating pattern of HU values. The upward increase and then decrease in HU values within each bed suggests upward increasing and then decreasing silt content, which collectively, is interpreted to reflect the consistent waxing followed by waning flow conditions during a single cycle of glaciogenic meltwater discharge. Mud rhythmites at the base of the succession (Unit 1) and beds of well-stratified mud at the top (Unit 4a) exhibit well-developed parallel-stratification in the lower part of each bed; they are characterized by a range of ~250–350 HU. This wide range in HU values reflects the effective partitioning of silt-rich and clay-rich parts in each bed, and therefore bed-surface and near-bed transport processes that sorted sediment mostly by grain size, followed by low-energy sediment fallout. The silt-rich part of each bed was deposited by glaciogenic meltwater-sourced hyperpycnal flows, which due to the freshwater composition of the basin, or at least in the upper part of the water column, were able to plunge to the basin floor and sort particles along the bed. In comparison, beds of bioturbated mud (Unit 2), banded mud (Unit 3), and diffusely stratified or structureless mud (Unit 4a) have a narrower range of ~50–120 HU, indicative of poorer particle sorting. These conditions, most clearly illustrated by the bioturbation, indicate a change to a seawater basin that caused meltwater inflows to instead form buoyant, sediment-laden hypopycnal flows, which aided by clay-silt particle flocculation and/or settling-driven convection, resulted in sediment deposition directly from suspension. In addition to characteristic sedimentary structures and textures, beds within each unit also exhibit similar thickness, which often doubles or triples in the abrupt transition from one unit to the next. These changes most probably reflect abrupt and systemic changes in deglacial dynamics and its control on sediment supply that often coincide with equally abrupt changes in salinity in the Champlain Sea basin.

Early and abrupt salinity reduction impacts European eel larval culture.

Reducing water salinity towards iso-osmotic conditions is a common practice applied in euryhaline fish farming to limit osmoregulation costs and enhance growth. In this respect, the present study investigated the timing of salinity reduction in an abrupt manner during European eel (Anguilla anguilla) larval culture by examining associated impacts on morphological and molecular levels. Larvae from 3 different parental combinations (families) were reared at constant 36 psu for 6days (control) or subjected to a direct reduction to 18 psu on 1, 2, or 3days post-hatch. Overall, salinity reduction enhanced growth and survival, resulting from more efficient energy resource utilization. In the control group, expression of growth-related igf2 remained constant, demonstrating a steady growth progression, while igf1 expression increased over time only for the salinity reduced treatments, potentially qualifying as a useful biomarker for growth performance. Even though each parental combination seems to have a different capacity to cope with salinity alterations, as observed by family-driven water-transport-related aquaporin (aqp1, aqp3) gene expression, it could be inferred that the abrupt salinity change is generally not stressful, based on non-upregulated heat shock proteins (hsp70, hsp90). However, the applied salinity reduction (irrespective of timing) induced the development of pericardial edema. As such, we conclude that despite the positive effect of salinity reduction on early growth and survival, the long-term benefit for eel larval culture lies in establishing a protocol for salinity reduction, at a precise developmental time point, without causing pericardial malformations.

Impact of abrupt salinity changes on activitiy of metabolic enzymes, antioxidant enzymes and cortisol content in serum and liver of <italic>Lateolabrax maculatus</italic>

<italic>Lateolabrax maculatus</italic> is an important economic fish species in China. It is a eurysaline species and can survive and grow in water environment with varieties of salinity. It is of practical significance to study the tolerance and adaptability of <italic>L</italic>. <italic>maculatus</italic>, because it usually suffers from sudden increase or decrease of salinity in aquaculture environment. This work investigated the effects of abrupt salinity changes on the activitiy of metabolic enzymes and antioxidant enzymes and cortisol content in liver of <italic>L</italic>. <italic>maculatus</italic> by simulating salinity changes of water for its breeding. The salinity was reduced from 18 to 0 and remained for 7 d, and then increased to 33 sharply after acclimation and remained for 7 d. Correspondingly, in the other treatment, the salinity increased from 18 to 33, and then decreased to 0 sharply after acclimation and remained for 7 d. Samples were taken on 0, 0.5, 1, 3,7 d after the start of the experiment, respectively. The activitiy of alkaline phosphatase, acid phosphatase, glutamic-pyruvic transaminase, glutamic-oxalacetic transaminase, superoxide dismutase, catalase, glutathione peroxidase in serum and liver of <italic>L</italic>.<italic>maculatus</italic> was tested, and cortisol (COR) content in serum was monitored as well. Results showed that the abrupt salinity changes would have impact on activitiy of metabolic enzymes and antioxidant enzymes, and COR content of <italic>L</italic>.<italic>maculatus</italic>. The activitiy of enzymes and COR content showed a trend of increasing firstly and then declining with time prolonging under most situations of abrupt salinity changes. These results showed that <italic>L</italic>.<italic>maculatus</italic> had a stress reaction during the abrupt changing of salinity, and could adapt to the change within 3-7 days, which indicated that <italic>L</italic>.<italic>maculatus</italic> had a substantial tolerance and adaptability to the abrupt changes in salinity. The changes of morphological characteristics, metabolic enzyme activity, antioxidant enzyme activity and COR content showed that <italic>L</italic>.<italic>maculatus</italic> could more rapidly adapt to sudden drop in salinity and was more adaptable to low-salinity environment.

Sandpipers go with the flow: Correlations between estuarine conditions and shorebird abundance at an important stopover on the Pacific Flyway.

Estuaries of major rivers provide important stopover habitat for migratory birds throughout the world. These estuaries experience large amounts of freshwater inputs from spring runoff. Understanding how freshwater inputs affect food supply for migrating birds, and how birds respond to these changes will be essential for effective conservation of critical estuarine habitats. We estimated trends over time in counts of Western Sandpiper (Calidris mauri) and Pacific Dunlin (Calidris alpina pacifica) during northward migration on the Fraser River estuary, British Columbia, Canada, where shorebirds feed extensively on intertidal biofilm and invertebrates. We also examined whether counts were correlated with a suite of environmental variables related to local conditions (precipitation, temperature, wind speed and direction, solar radiation, tidal amplitude, and discharge rates from the Fraser River) during a total of 540 surveys from 1991 to 2019. Counts of Western Sandpiper declined ~54% (−2.0% per annum) over the entire study period, and 23% from 2009 to 2019 (−0.9% per annum). Counts of Pacific Dunlin did not show a statistically significant change over the study period. Counts of shorebirds were lower when discharge from the Fraser River was high, which we propose results from a complex interaction between the abrupt changes in salinity and the estuarine food web related to the quantity or quality of intertidal biofilm. Counts were also higher when tidal amplitude was lower (neap tides), potentially related to longer exposure times of the mudflats than during spring tides. Effects of wind are likely related to birds delaying departure from the stopover site during unfavorable wind conditions. The negative trend in migrating Western Sandpipers is consistent with declines in nonbreeding areas as observed in Christmas Bird Counts. Understanding causes of population change in migratory shorebirds highlights the need for research on mechanistic pathways in which freshwater inputs affect food resources at estuarine stopovers.

Understanding structure/function relationships in nitrifying microbial communities after cross-transfer between freshwater and seawater

In this study, nitrification before and after abrupt cross-transfer in salinity was investigated in two moving bed biofilm reactors inoculated with nitrifying cultures that had adaptation to freshwater (FR) and seawater salinities (SR). FR and SR MBRRs were exposed to short and long term cross-transfer in salinity, and the functional capacity of nitrifying microbial communities was quantified by the estimation of ammonia and nitrite oxidation rates. Salinity induced successions were evaluated before and after salinity change by deep sequencing of 16S rRNA gene amplicons and statistical analysis. The bacterial community structure was characterized and Venn diagrams were included. The results indicated that after salinity cross-transfer, the FR was not significantly recovered at seawater salinity whereas SR showed high resistance to stress caused by low-salt. Succession and physiological plasticity were the main mechanisms of the long-term adaption of the nitrifying communities exposed to abrupt salinity changes. Independently of salinity, some nitrifiers presented high physiological plasticity towards salinity and were very successful at both zero and full seawater salinity. SR culture is robust and suitable inoculum for ammonium removal from recirculating aquaculture systems and industrial wastewaters with variable and fast salinity changes. Our findings contradict the current perspective of the significance of salinity on the structure of nitrifying communities.

Marine or freshwater? Accessing the paleoenvironmental parameters of the Caldas Bed, a key marker bed in the Crato Formation (Araripe Basin, NE Brazil)

The Aptian Crato Formation is world renowned for its well-preserved fossils in microbially-induced laminated limestones, which are regarded as one of the main Cretaceous Konservat-Lagerstätte of the geological record. Detailed stratigraphic investigation and mapping of the up to 90-m-thick Crato Formation at the eastern border of the Araripe Plateau allowed recognition of a regionally persistent fossil-bearing muddy interval, herein defined as the Caldas Bed. At its type locality, it is defined as an up to 2-m-thick coarsening-upward succession of grey/green mudstone and interbedded sandy siltstone and claystone. The 0.85- to 2-m-thick interval was recognized in several localities along the outcrop belt, and it is bounded by sharp, lower (Konservat-Lagerstätte limestone) and upper (sandstone and heterolithic facies) contacts. Despite previous literature data suggesting the presence of marine mollusks, the bed contains freshwater bivalves, small gastropods, spinicaudatans, plant remains, trace fossils, and rare ostracods. The Caldas Bed records benthic paleocommunities representing a short-term isochronous regional freshening event, marked by abrupt changes in sedimentation pattern, bathymetry, salinity, oxygenation and water chemistry.

Effect of a short-term sodium chloride bath on juvenile pikeperch (Sander lucioperca) welfare

This study aimed to determine the impact of immersing pikeperch (body weight approximately 94 g) in an aqueous solution of sodium chloride on gasometric, hematological, and biochemical indicators. The impact of the sodium chloride concentration (NaCl 10, 15, and 20 g L−1), immersion time (30 or 60 min) and time of blood sampling (0 h – blood drawn immediately following fish immersion; 24 h – blood drawn one full day after manipulation) was analyzed. The immersion protocol did not bring significant stress for tested fish as none of the tested parameters was different when compared to results obtained in a blank control group. The immersion times tested impacted the gasometric indicators and blood acid-base balance (0 h). The levels of most of the whole blood and plasma biochemical indicators analyzed (Na+, Cl-, glucose, lactate, total protein, globulin) differed significantly in fish exposed to 15 g L−1 and 20 g L−1 of NaCl from those in the blank control group. These changes were short-term and after 24 h the values of these indicators did not differ from those confirmed in the control group. Significant increases in the levels of hemoglobin, hematocrit, and red blood cells were confirmed in groups 10 g NaCl L−1/30 min/0 h and 20 g NaCl L−1/30 min/0 h and these changes persisted 24 h following immersion. Significant increases in the number of white blood cells (0 h) were confirmed in all groups, and this persisted for 24 h following immersion. The current study revealed transient, dose- and time-dependent stress reactions in pikeperch subjected to abrupt changes in water salinity and indicated that this species has significant recovery abilities in response to salinity shifts of short duration.

Using osmotic shock to control invasive aquatic species

Coastal estuaries are especially vulnerable to the arrival and establishment of invasive aquatic species (IAS) as they are often the receiving locations of ship-based introductions. Rapid response tools, such as mechanical or chemical treatments to capture, remove, and contain of IAS, are needed to prevent subsequent spread into adjacent marine and freshwater systems. Abrupt salinity change, created when infrastructure in estuaries situated at the proximity of river mouths is operated, offers a novel, low-cost and environmentally friendly method for potentially controlling IAS. We investigated the use of osmotic shock to control the invasive brackish water clam Rangia cuneata that is quickly spreading through Europe. Clams were exposed in the laboratory to eight salinity concentrations ranging from 0.5 to 32.0‰ and monitored for 60 days. Saline shock, but not freshwater shock, could control R. cuneata. Salinities >26‰ killed 95% R. cuneata in two weeks. All specimens exposed to full strength seawater (32‰) were killed within 30 days. At lower salinities, clams collected from the most freshwater locality (1.2‰) showed lower mortality than clams from the most saline site (3.1‰). Furthermore, even modest increases in salinity during spawning periods of R. cuneata may prevent recruitment. Given the vulnerability of coastal estuaries to introduction of IAS, saline flushing presents a novel and effective management tool for many species.

Extracellular polymeric substances mediate the coaggregation of aquatic biofilm-forming bacteria

Coaggregation, a phenomenon contributing to biofilm formation, occurs among biofilm bacteria from different aquatic environments. However, not much is known about molecules involved in aggregation. In this study, freshwater, estuarine and marine biofilm bacteria were evaluated for aggregation capabilities, and their cell-bound extracellular polymeric substances (CB-EPS), known to play an important role in biofilm formation, were characterized for functional groups, and sugar composition via Fourier-transform infrared spectroscopy and high-pressure liquid chromatography. Biofilm-forming potential of estuarine and freshwater biofilm bacteria was higher as indicated by their coaggregation scores, attributed to CB-EPS with distinct sugar types, compared to marine. Most of the biofilm bacteria lost their ability to coaggregate after removal of CB-EPS, indicating its importance in coaggregation. Estuarine (Bacillus indicus, Bacillus cereus), and freshwater (Exiguobacterium spp., B. cereus) bacterial pairs, retained their aggregation capability probably via expression of lipids and proteins, suggesting their ability to rebuild themselves by expressing specific biomolecules under stressed conditions. A similar expression pattern was observed when these strains were exposed to abrupt salinity change (environmental stressor), indicating modulation of cell surface chemistry as a strategy to protect biofilm bacteria in harsh conditions. Unravelling role of these biomolecules as cues for settlement of macrofoulers is a step ahead.