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Brackish water ecosystems often have high primary production, intermediate salinities, and fluctuating physical conditions and therefore provide challenging environments for many of their inhabitants. This is especially true of the Baltic Sea, which is a large body of brackish water under strong anthropogenic influence. One freshwater species that is able to cope under these conditions in the northern Baltic Sea is the vendace (Coregonus albula), a small salmonid fish. Here, we review the current knowledge of its ecology and fishery in this brackish water environment. The literature shows that, by competing for resources with other planktivores and being an important prey for a range of larger species, C. albula plays a notable role in the northern Baltic Sea ecosystem. It also sustains significant fisheries in the coastal waters of Sweden and Finland. We identify the need to better understand these C. albula populations in terms of the predator–prey interactions, distributions of anadromous and sea spawning populations and other putative (eco)morphs, extent of gene exchange between the populations, and effects of climate change on their future. In this regard, we recommend strengthening C. albula‐related research and management efforts by improved collaboration and coordination between research institutions, other governmental agencies, and fishers, as well as by harmonization of fishery policies across national borders. [ABSTRACT FROM AUTHOR]

Abstract This work concerns the modelling and numerical simulation of the 3D salinity and current distribution in a very shallow Mediterranean lagoon subject to strong winds which create intensive resuspension of polluted bottom sediments. We consider wind speeds of 10 m/s and 20 m/s in the two dominant wind directions (N-NW and S-SE). This study is made for different scenarios of flow exchanges with the surrounding hydrosystems: a brackish lagoon on the North (the Etang de Berre), the Cadiere River on the East, and a brackish channel on the South (the Rove channel). The bottom shear stress (B S S) are compared to the B B S threshold given in the literature in terms of the bottom roughness. It permits to determine which kind of bottom sediments (muds and sands) will be resuspended by each wind. The bottom currents permit to predict in which direction the suspended sediments will be moved and where are the sedimentary deposit zones. It provides a guide for the specialists of remediation of the lagoon for a mechanical extraction of sediments in such zones. In addition, numerical experiments have been performed to understand how the salinity distribution depends on the flow exchanges with the two brackish surrounding hydrosystems. This new knowledge will permit the owner of this lagoon to know how to maintain efficiently the level of salinity in the suitable range. [ABSTRACT FROM AUTHOR]

Saemangeum Reservoir in South Korea is an estuarine system enclosed by a dyke construction, where seawater inflow and retained water outflow are managed by the opening/closing of sluice gates installed in the southern part of the dyke. An exchange of the reservoir water can cause spatiotemporal fluctuations in the salinity and trophic state, which are major drivers determining variation in the composition of biological communities in estuarine systems. Here, we investigated the seasonal and spatial variability in the copepod community and environmental conditions (water temperature, salinity, transparency, chlorophyll a concentration, total nitrogen, total phosphorus and Carlson’s trophic state index) based on seasonally conducted field monitoring in the Saemangeum Reservoir from July 2013 to January 2018. In addition to the role of temperature, salinity and chlorophyll a concentration in structuring the copepod community and diversity, the biological indices of copepods with respect to salinity range and trophic state, were evaluated. The spatiotemporal variability in the salinity and trophic state variables showed contrasting patterns, and chlorophyll a concentration was negatively affected by salinity, indicating that the reservoir water was being highly exchanged with opening of the sluice gates. The mean trophic state index values, however, were constant in the eutrophic state (50―70). Dominant copepods were Acartia (A. hudsonica, A. sinjiensis, Acartia spp.) and Oithona (O. davisae and Oithona spp.), which are common species in eutrophic neritic water. Variation in the copepod community was mainly associated with the seasonal succession of the dominant species rather than a spatial gradient (from around the estuary to the sluice gates); however, site-specific differences in frequencies of several non-dominant species could be detected around the estuary (Sinocalanus tenellus) and the sluice gates (Centropages spp., Tigriopus spp. and Labidocera rotunda). The copepod diversity increased with species-richness from around the estuary to the sluice gates, which could result from variation in the site-specific location of non-dominant species. The frequency of particular species was also able to discriminate in terms of the salinity range (oligohaline: A. pacifica, S. tenellus and A. sinjiensis; mesohaline: Pseudodiaptomus inopinus; and polyhaline: C. abdominalis and Centropages spp.) and the trophic state (mesotrophic: C. abdominalis, Calanus sinicus and Centropages spp.; and hypereutrophic: S. tenellus, P. inopinus and Sinocalanus spp.). The findings from this study not only identify the factors determining spatiotemporal variation in the copepod community in the Saemangeum Reservoir, but also expand the applicability of copepods as biological indicators of conditions associated with salinity range and trophic state in other enclosed estuarine systems. [ABSTRACT FROM AUTHOR]

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The widely distributed snail species Theodoxus fluviatilis (Linneaus, 1758) is rather diverse in shell size and patterning. It has formed regional subgroups in northern Germany that appear separate in either fresh- or brackish water, yet, according to literature, are indistinguishable by morphology, anatomy or mtRNA markers. Tolerance towards challenging salinities, however, is distinct. The question as to whether the observed difference in salinity tolerance is a result of local adaptation or of phenotypic plasticity remains. In this study, physiological limits to salinity stress and tolerance shift abilities were compared between individuals from both subgroups in a salinity transfer experiment and acclimation regime followed by a survival analysis. Brackish water animals struggled in freshwater but performed much better than freshwater individuals when directly transferred into higher salinities. With acclimation to their challenging salinities, individuals of both subgroups achieved shifts in the slopes of their reaction norms and were able to survive salinity levels otherwise lethal to them. Even with this shift freshwater animals were not able reach the tolerance levels of brackish water individuals. The results indicate that phenotypic plasticity as well as genetic adaptation may determine osmotolerance in regional subgroups of T. fluviatilis. [ABSTRACT FROM AUTHOR]

The most suitable sturgeon species for culture in artificial systems are freshwater and non-migratory species: sterlet - Acipenser ruthenus - and Siberian sturgeon - Acipenser baerii, recently introduced in Romania. The experiment aimed at establishing the age and salinity thresholds to be taken into account in attempting to rear (Siberian sturgeon - Acipenser baerii) in a recirculating system using Black Sea water. From the point of view of adaptability in general, in about a week the individuals adapted to the captive breeding conditions of NIMRD's recirculating system. The specimens also easily adapted to manipulation during measurements, showing calm handling behavior. The food used was very easily accepted, the active feeding behavior being observed even in the presence of the staff. Throughout the experiment, the fish were active. The survival rate was 100%. However, adaptability to the brackish environment has posed problems. The experimental batch became more sedentary and ingested significantly less food compared to the control group, when salinity exceeded 3‰. Upon reaching the 7‰ threshold, all individuals were already completely refusing food, which is why it was decided to stop sea water input. The return to freshwater caused the resumption of feeding behavior in just a week, calling for further research on the osmoregulatory mechanisms of A. baerii. [ABSTRACT FROM AUTHOR]

Wittrockiella is a small genus of filamentous green algae that occurs in habitats with reduced or fluctuating salinities. Many aspects of the basic biology of these algae are still unknown and the phylogenetic relationships within the genus have not been fully explored. We provide a phylogeny based on three ribosomal markers (ITS, LSU, and SSU rDNA) of the genus, including broad intraspecific sampling for W. lyallii and W. salina, recommendations for the use of existing names are made, and highlight aspects of their physiology and life cycle. Molecular data indicate that there are five species of Wittrockiella. Two new species, W. australis and W. zosterae, are described, both are endophytes. Although W. lyallii and W. salina can be identified morphologically, there are no diagnostic morphological characters to distinguish between W. amphibia, W. australis, and W. zosterae. A range of low molecular weight carbohydrates were analyzed but proved to not be taxonomically informative. The distribution range of W. salina is extended to the Northern Hemisphere as this species has been found in brackish lakes in Japan. Furthermore, it is shown that there are no grounds to recognize W. salina var. kraftii, which was described as an endemic variety from a freshwater habitat on Lord Howe Island, Australia. Culture experiments indicate that W. australis has a preference for growth in lower salinities over full seawater. For W. amphibia and W. zosterae, sexual reproduction is documented, and the split of these species is possibly attributable to polyploidization. [ABSTRACT FROM AUTHOR]

The brackish habitat colonization by the red swamp crayfish Procambarus clarkii (Girard, 1852) has aroused lively interest among many biologists. Here, we focused on its salinity tolerance by carrying out laboratory experiments and histomorphological observations on its antennal glands. Adult crayfish of similar size were subject to increasing salinity levels up to 35%o in a recirculating system. Only one male molted, and no specimens died during the experiment (only 3 females and 1 male). The antennal gland tissue organization (mainly regarding labyrinth and nephridial tubules) in the treated crayfish showed alterations if compared with the control specimens. We never found sexual differences in both laboratory experiments and histological observations. Our data highlighted the P. clarkii ability to survive in high salinity levels. This tolerance ought to be investigated in order to improve our understanding of mechanisms driving the coastal brackish area colonization by P. clarkii. [ABSTRACT FROM AUTHOR]

Apomictic reproduction without alternation of generations has been reported in Ulva prolifera Müller from some brackish environments, and few genetic and phenotypic variations are expected in such apomictic populations. We collected 534 specimens of U. prolifera throughout the year from brackish lakes and a river and genotyped all the samples using a nuclear-encoded hsp90 gene sequence. In total, 14 genotypes were detected, 12 of which were heterozygous ( n = 531), and the genotype composition differed between the lakes and estuaries as well as between the high and low brackish sites. We tried to induce discharge of zoids from the collected thalli, and the phenotypes of zoids were examined in total 309 specimens. The flagellum number of the zoids differed among the eight most frequently encountered genotypes, i.e., six genotypes released only biflagellate zoids, whereas the other two produced quadriflagellate zoids. The ratio of specimens that produced positively phototactic zoids, which varied among the genotypes regardless of the flagellum number, was relatively high in the high-salinity brackish regions. The parthenogenetic thallus had the same genotype, flagellum number, and direction of phototaxis relative to the parental thallus in all the genotypes examined, which suggested clonal apomictic reproduction. Apomixis induction through outcrossing between genetically different entities has been reported in other algae and this may have occurred many times in U. prolifera . [ABSTRACT FROM AUTHOR]

In recent years, voices in Jordan became lauder to exploit the fresh to brackish deep groundwater overlain by fresh groundwater bodies. In this article the implications of such a policy on the existing fresh water bodies are worked out through studying the sources of salinity in the different aquifer systems and the potentials of salinity mobilization by artificial changes in the hydrodynamic regimes. It is concluded that extracting the groundwater of deep aquifers overlain by fresh water bodies, whether the deep groundwater is fresh to brackish, brackish or salty, is equivalent to extracting groundwater from the overlying fresh groundwater bodies because of the hydraulic connections of the deep and the shallow aquifers’ groundwaters. The consequences are even more complicated and severe because exploiting the deep groundwater containing brackish or salty water will lead to refilling by fresh groundwater leaking from the overlying aquifers. The leaking water becomes salinized as soon as it enters the pore spaces of the emptied deep aquifer matrix and by mixing with the deep aquifer brackish or saline groundwater. Therefore, the move to exploit the deep groundwater is misleading and damaging the aquifers and is unjust to future generation's rights in the natural wealth of Jordan or any other country with similar aquifers’ set-up. In addition, desalination produces brines with high salinity which cannot easily be discharged in the highlands of Jordan (with only very limited access to the open sea) because they will on the long term percolate down into fresh water aquifers. [ABSTRACT FROM AUTHOR]

We investigated the effect of salinity on larval development and survival rate to metamorphosis in the common spadefoot toad Pelobates fuscus (Laurenti, 1768). Our hypothesis was that higher salinity would decrease tadpole survival rate and body size at metamorphosis, and delay metamorphosis. The response of the tadpoles was evaluated through an experimental design with three salinity treatments of 2, 4, and 8‰ compared to a control (deionized water). Survival varied across the treatments: neither of the tadpoles in 8‰ salinity treatment survived the experiment, nor achieved metamorphosis. Salinity levels of 2 and 4‰ had no significant influence on the mean time to metamorphosis, body mass and SVL at metamorphosis. Our results suggest that P. fuscus tadpoles have a tolerance threshold for brackish water up to 4‰, above which survival is impaired. [ABSTRACT FROM AUTHOR]

Saline to freshwater invasions have become increasingly common in recent years. A key hypothesis is that rates of freshwater invasions have been amplified in recent years by increased food concentration, yet this hypothesis has remained unexplored. We examined whether elevated food concentration could enhance freshwater tolerance, and whether this effect evolves following saline to freshwater invasions. We examined physiological response to salinity and food concentration in a 2 × 2 factorial design, using ancestral brackish and freshwater invading populations of the copepod Eurytemora affinis. We found that high food concentration significantly increases low-salinity tolerance. This effect was reduced in the freshwater population, indicating evolution following the freshwater invasion. Thus, ample food could enable freshwater invasions, allowing subsequent evolution of low-salinity tolerance even under food-poor conditions. We also compared effects of food concentration on freshwater survival between two brackish populations from the native range. Impacts of food concentration on freshwater survival differed between the brackish populations, suggesting variation in functional properties affecting their propensity to invade freshwater habitats. The key implication is that high food concentration could profoundly extend range expansions of brackishwater species into freshwater habitats, potentially allowing for condition-specific competition between saline invaders and resident freshwater species. [ABSTRACT FROM AUTHOR]

- In the coastal areas of the Baltic Sea, there are two forms of perch ( Perca fluviatilis). One of the forms is migratory and spawns in streams entering the Baltic Sea. The other form is resident and spawns in brackish water. Both forms utilise the coastal habitat for foraging. We examined the spawning success of the two forms in fresh and brackish water (7‰, equal to salinity in the south Baltic Sea). The experiments showed that hatching success was equally high in freshwater and in brackish water despite female origin. The survival of yellow-sac and free swimming fry was significantly reduced in brackish water, which was independent if the fish was of migratory or brackish resident origin. Further, growth rate of perch fry was severely reduced in brackish water. The results indicate that perch has not developed any tolerance to brackish water in the young life stages. The migratory life strategy of perch can thus be explained by higher survival of fry in freshwater. [ABSTRACT FROM AUTHOR]

The effects of two different environmental salinities [brackish water (BW), 12‰; sea water (SW), 39‰] and initial stock densities [low (LD), 1.0 g L−1; high (HD), 2.0 g L−1] on growth, osmoregulation, stress and energy metabolism of the fry Pagrus pagrus were investigated over a period of 45 days. Pagrus pagrus ( n=80, 5.51 ± 0.25 g mean initial body weight) were randomly divided in eight groups. Growth, weight gain and specific growth rate increased in BW-acclimated fish compared with SW-acclimated fish. No differences were observed between the two stock densities tested at either environmental salinity. Plasma osmolality was lowest in BW-acclimated specimens, but the stock density had no effect on this parameter. Branchial Na+,K+-ATPase activity was positively correlated with environmental salinity, but unaltered at the renal level. Plasmatic parameters were enhanced by salinity and stocking conditions. At the hepatic level, triglyceride values were enhanced in BW-acclimated fish maintained at LD. Muscle metabolites (glycogen, glucose and lactate) increased in BW- compared with SW-acclimated fish; stock density had no influence. Our data suggest that changes in metabolic parameters could be correlated with the higher growth rates observed in P. pagrus acclimated to BW, while no significant effects due to the stocking density used were observed. [ABSTRACT FROM AUTHOR]

Cu is a major active component in anti-fouling paints, which may reach toxic levels in areas with intense boat traffic and therefore is a metal of environmental concern. The bioavailability of metals is influenced by factors such as salinity and organic matter measured as total organic carbon (TOC). The influence of these two factors was studied, with a focus on brackish water conditions, by exposing a marine and a brackish water clone of the red macroalga Ceramium tenuicorne to Cu in different combinations of artificial seawater (salinity 5–15‰) and TOC (0–4mg/L) in the form of fulvic acid (FA). In addition, the toxicity of Cu to both clones was compared in salinity 10‰ and 15‰. The results show that by increasing TOC from 0 to 2 and 4mg/L, Cu was in general less toxic to both algal clones at all salinities tested (p<0.05). The effect of salinity on Cu toxicity was not as apparent, both a positive and negative effect was observed. The brackish water clone showed generally to be more sensitive to Cu in salinity 10‰ and 15‰ than the marine counterpart. In conclusion, FA reduced the Cu toxicity overall. The Cu tolerance of both strains at different salinities may reflect their origin and their adaptations to marine and brackish water. [Copyright &y& Elsevier]

The effect of environmental salinity on hematological parameters of great sturgeon Huso huso juveniles was studied. Five-month-old juveniles (mean body weight 28.3 ± 2.1 g) were subjected to 0, 3, 6, 9, and 12 ppt salinities. The hematological parameters were assessed after a period of 20 days rearing at these salinities. After transfer from fresh water to brackish water, red blood cells, hematocrit, haemoglobin and mean corpuscular haemoglobin decreased, but mean corpuscular volume increased. Mean corpuscular haemoglobin concentration, white blood cells, monocyte counts, and eosinophil counts showed no significant variations with increase in environmental salinity. An increase was found in lymphocyte counts according to the increase of salinity from 0 to 12 ppt, while the fresh water control group maintained basal levels. Decrease in neutrophil counts was observed in great sturgeon with increase in environmental salinity. These data show significant effect of salinity on the blood parameters of great sturgeon. [ABSTRACT FROM AUTHOR]

Estuarine copepods experience strong and frequent salinity variations caused by alternating tides. Salinity is known to be a major parameter in the ecology of copepods from brackish waters but its effects on small scale behavior are relatively unclear. In this study, we used two-dimensional laboratory filming techniques to record swimming paths of the three reproductive stages (i.e. male, non-ovigerous female and ovigerous female) of Eurytemora affinis from the Seine estuary, under different salinity conditions. We show that the probability density of both the instantaneous swimming speed and the duration of the two most frequent swimming states (i.e. break and slow swimming) followed a power-law trend regardless of the salinity. Increase in salinity (i.e. 5, 15, 25 and 30) steadily decreased the instantaneous speed of E. affinis reproductive stages. At the extreme salinity of 0.5, the mean speed decreased for non-ovigerous females and ovigerous females but increased for males, when compared with higher salinities. Maximum speed was observed at salinity 0.5 for males and at salinity 5 for non-ovigerous females and ovigerous females. Low swimming speeds were associated with break events of high frequency and long duration. High swimming speeds were exhibited with cruising states of high frequency and break events of short duration. This supports laboratory and field studies indicating a preference of E. affinis for low to medium salinities. [ABSTRACT FROM PUBLISHER]

Abstract: This study serves for the definition of baseline isotopic signatures of vertebrates living in the Schlei fjord, a brackish water inlet in the north German plain, where the salinity decreases from its mouth at the Baltic Sea towards the inland locations. The Viking trade centre Haithabu and its immediate successor, the town of Schleswig, are located at opposite banks of the Schlei and constitute a settlement continuum from the 9th until the 13th century. This development not only includes a relocation of the settlement site, but also a change in economy and social structure, and witnesses the metamorphosis from an international trading locality to the rise and decline of a prototypical medieval town with town charter. In this paper, stable isotope ratios of bone collagen and bone structural carbonate of 141 vertebrate bone finds mainly of fish, birds, and sea mammals from both sites are reported to provide the baseline food web in this brackish water environment, which is the prerequisite for our ongoing studies aiming at the reconstruction of human subsistence strategies as well as the geographic origin of humans, animals, food stuffs, and raw materials in order to complete the historical picture of emerging medieval towns in a complex palaeoecosystem. In particular, we are able to show how a combination of stable isotopes from bone collagen and carbonate is capable of defining the salinity gradients in the aquatic environment. [Copyright &y& Elsevier]

Daphnia magna Straus is a freshwater organism that can strive in environments with a salinity of up to 12 psu, although its life cycle and survival are significantly affected by increasing salinities. Saline environments are not devoid of chemical contaminant influences, such as toxic metals; for freshwater species this could be another stress factor aside from that caused by salinity. In this study, we assessed the acute (48 h) toxicity produced by hexavalent chromium [Cr(VI)] in neonates of a D. magna strain previously acclimated to different salinities induced by adding NaCl to reconstituted hard water. The Mean Lethal Concentration (CL50) values determined for Cr(VI) were 0.14±0.12, 1.35±0.34, 1.79±0.41, 2.0±0.21, 2.02±0.075, and 2.6±0.23 mg l-1 for salinities of 0.3, 1, 2, 3, 4, and 5 psu, respectively, evidencing that D. magna's sensitivity to Cr(VI) decreased with increasing salinity. The increase in tolerance could be due to a possible antagonic effect of NaCl on Cr(VI) rather than due to a reduction in Cr(VI) bioavailability due to the NaCl concentration. Although it was not demonstrated that the stress produced by salinity increased the sensitivity to the exposed toxicant, care must be exerted in inferring that the impact of contaminants, such as toxic metals, could be lower on freshwater species that sporadically or permanently strive in brackish water environments. [ABSTRACT FROM AUTHOR]

A new method for classifying soft-bottom zoobenthic assemblages along the Finnish coasts (northern Baltic Sea) is presented and tested against traditional physicochemical monitoring data in the complex Archipelago Sea. Although multivariate methods for assessing the state of the marine environment have become widely used, few numerical indices can operate over a wide salinity range. We compare indices currently in use and propose a new index, BBI (brackish water benthic index), for the low-saline and species-poor Baltic coastal waters. BBI offers a salinity-corrected tool for classification of the soft-bottom zoobenthos under the demands of the European Union Water Framework Directive. [ABSTRACT FROM AUTHOR]

Diatoms in surface sediments from a data set of 27 brackish lakes and nine fjords in Jutland, Denmark (range 0.2 – 31 g·L–1 total dissolved solids (TDS)), were analysed using multivariate methods to determine response to measured parameters (depth, total phosphorus (TP), total nitrogen (TN), TN/TP, salinity, water body type). Water body type, salinity, depth and TP together explained 25.3% of the variation in the diatom data and were all independently significant predictors. A diatom–salinity model (r2jack = 0.887, root mean square error of prediction = 0.246 log salinity, g·L–1) was developed from the 36 sample training set and applied to fossil diatom assemblages in three sediment cores from the east Vejlerne wetland, Denmark, a nature reserve created after the damming of an embayment of the polyhaline Limfjord (~26 g·L–1 TDS) in the late 19th century. The diatom–inferred salinity reconstructions reflect the known salinity history of the Limfjord and the freshwater–subsaline Vejlerne lakes, and appear sensitive to documented North Sea storms in the 16th and 17th centuries, which had major impacts on the brackish Limfjord herring fishery. Diatom–salinity models may be useful tools in long-term studies of coastal and estuarine areas to test hypotheses concerning aquatic resources and ecological, hydrographic, and cultural change. [ABSTRACT FROM AUTHOR]

Presents the results of an effort to monitor a population of Enochrus bicolor (Fabricius) over a 4-year period (March 1997-March 2001) from a coastal brackish pool in S.E. Essex. This water beetle, together with Ochthebius marinus (Payk.), O. viridis Peyrhiff, O. punctatus Steph., Hygrotus parallelogrammus (Ahrens), Berosus affinis Brulle, Agabus conspersus, (Marsham), Rhantus frontalis (Marsham), R. suturalis (MacLeay), Paracymus aeneus (Germar), and Haliplus apicalis Thompson, are all taxa of conservation interest. Enochrus bicolor was present in most months, with greatest adult abundances being recorded in August and September each year. Correlation analysis and the development of regression models indicated that the highest abundances of E. bicolor coincided with maximum water temperature in the late summer-early autumn. However, when the natural seasonal signal was removed by standardizing the series, a relatively weak association with the relative abundance of E. bicolor and conductivity was observed. The conservation of E. bicolor and other organisms associated with brackish water habitats subject to irregular marine inundation is considered.