The effect of the pH level on the communities of anoxygenic phototrophic bacteria of soda lakes of the southeastern Transbaikal Region

The effect of pH on the structure of the communities of anoxygenic phototrophic bacteria (APB) was studied under laboratory conditions. Samples of natural APB communities were inoculated into media that differed in pH values, which were 7, 9.5, or 10.5. The structure of the APB communities in the obtained enrichment cultures at all pH values depended also on the mineralization levels of the media, which were the same as in the lakes from which samples were taken. The same dependence of the community structure on salinity was observed as in the case of the natural communities that had been described previously. APB were most diverse in the enrichment cultures grown at pH 9.5. The shift of the pH to either neutral or extremely alkaline values restricted the species diversity within the APB community, resulting in marked predominance of the most adapted forms. It was shown that the status of Ectothiorhodospira species within the community could serve not only as an indicator of salinity but also as an indicator of pH in soda lakes with a water mineralization of higher than 5 g/l. The statuses of various APB groups in the community as dependent on pH and salinity are discussed, as well as possible changes in these statuses due to changes in the water level and other environmental parameters in the studied lakes.     

Halotaxis of cyanobacteria in an intertidal hypersaline microbial mat

An intertidal hypersaline cyanobacterial mat from Abu Dhabi (United Arab Emirates) exhibited a reversible change in its surface colour within several hours upon changes in salinity of the overlying water. The mat surface was orange‐reddish at salinities above 15% and turned dark green at lower salinities. We investigated this phenomenon using a polyphasic approach that included denaturing gradient gel electrophoresis, microscopy, high‐performance liquid chromatography, hyperspectral imaging, absorption spectroscopy, oxygen microsensor measurements and modelling of salinity dynamics. Filaments of Microcoleus chthonoplastes, identified based on 16S rRNA sequencing and morphology, were found to migrate up and down when salinity was decreased below or increased above 15%, respectively, causing the colour change of the mat uppermost layer. Migration occurred in light and in the dark, and could be induced by different salts, not only NaCl. The influence of salinity‐dependent and independent physico‐chemical parameters, such as water activity, oxygen solubility, H₂S, gravity and light, was excluded, indicating that the observed migration was due to a direct response to salt stress. We propose to term this salinity‐driven cyanobacterial migration as ‘halotaxis’, a process that might play a vital role in the survival of cyanobacteria in environments exposed to continuous salinity fluctuations such as intertidal flats.     

The effect of the pH level on the communities of anoxygenic phototrophic bacteria of soda lakes of the southeastern Transbaikal region

The effect of pH on the structure of the communities of anoxygenic-phototrophic-bacteria (APB) was studied under laboratory conditions. Samples of natural APB communities were inoculated into media that differed in pH values, which were 7, 9.5, or 10.5. The structure of the APB communities in the obtained enrichment cultures depended on the pH values and on the mineralization levels of the media, which were the same as in the lakes from which samples were taken. The same dependence of the community structure on salinity was observed as in the case of the natural communities that had been described previously. APB were most diverse in the enrichment cultures grown at pH 9.5. The shift of the pH to either neutral or extremely alkaline values affected the species diversity within the APB community, resulting in marked predominance of the most adapted forms. It was shown that the status of Ectothiorhodospira within the community could serve as an indicator of both salinity and pH in soda lakes with a water mineralization of higher than 5 g/l. The statuses of various APB groups in the community as dependent on pH and salinity are discussed, as well as possible changes in these statuses due to changes in the water level and other environmental parameters in the studied lakes.     

Genetic Variance in the Composition of Two Functional Groups (Diazotrophs and Cyanobacteria) from a Hypersaline Microbial Mat

Examination of variation in ecological communities can lead to an understanding of the forces that structure communities, the consequences of change at the ecosystem level, and the relevant scales involved. This study details spatial and seasonal variability in the composition of nitrogen-fixing and cyanobacterial (i.e., oxygenic photosynthetic) functional groups of a benthic, hypersaline microbial mat from Salt Pond, San Salvador Island, Bahamas. This system shows extreme annual variability in the salinity of the overlying water and the extent of water coverage. Analysis of molecular variance and F_ST tests of genetic differentiation of nifH and cyanobacterial 16S rRNA gene clone libraries allowed for changes at multiple taxonomic levels (i.e., above, below, and at the species level) to inform the conclusions regarding these functional groups. Composition of the nitrogen-fixing community showed significant seasonal changes related to salinity, while cyanobacterial composition showed no consistent seasonal pattern. Both functional groups exhibited significant spatial variation, changing with depth in the mat and horizontally with distance from the shoreline. The patterns of change suggest that cyanobacterial composition was more insensitive to water stress, and consequently, cyanobacteria dominated the nitrogen-fixing community during dry months but gave way to a more diverse community of diazotrophs in wet months. This seasonal pattern may allow the mat community to respond quickly to water-freshening events after prolonged dry conditions (system recovery) and maintain ecosystem function in the face of disturbance during the wet season (system resilience).     

Phenanthrene mineralization along a natural salinity gradient in an Urban Estuary,Boston Harbor,Massachusetts

The effect of varying salinity on phenanthrene and glutamate mineralization was examined in sediments along a natural salinity gradient in an urban tidal river. Mineralization was measured by trapping¹⁴CO₂ from sediment slurries dosed with trace levels of [¹⁴C]phenanthrene or [¹⁴C]glutamate. Sediments from three sites representing three salinity regimes (0, 15, and 30%.) were mixed with filtered column water from each site. Ambient phenanthrene concentrations were also determined to calculate phenanthrene mineralization rates. Rates of phenanthrene mineralization related significantly to increasing salinity along the transect as determined by linear regression analysis. Rates ranged from 1 ng/hour/g dry sediment at the freshwater site to > 16 ng/hour/g dry sediment at the 30 salinity site. Glutamate mineralization also increased from the freshwater to the marine site; however, the relationship to salinity was not statistically significant.To examine the effect of salinity on mineralizing activities, individual sediments were mixed with filtered water of the other two sites. Slurries were also made with artificial seawater composed of 0, 15, or 30 g NaCl/ liter to substitute for overlying water. Rates of phenanthrene mineralization in the 0 ambient salinity sediments were not affected by higher salinity waters. Activities in the 15 and 30 ambient salinity sediments, however, were significantly inhibited by incubation with 0 salinity water. The inhibition, in large part, appears to be due to the decreased NaCl concentration of the water phase. Glutamate mineralization was affected in a similar manner, but not as dramatically as phenanthrene mineralization. The results suggest that phenanthrene degraders in low salinity estuarine sediments subject to salt water intrusion are tolerant to a wide range of salinities but phenanthrene degradation in brackish waters is mainly a function of obligate marine microorganisms.     

Bacterial growth on N,N-dimethylformamide: implications for the biotreatment of industrial wastewater

The degradation of N,N-dimethylformamide (DMF) by bacterial consortia was investigated under aerobic, fermentative and nitrate-reducing conditions and a variety of salt concentrations (0.2%, 4% and 7% NaCl w/v) and pH values (5 and 7). Optimization of degradation conditions was studied to provide information and recommendations for large-scale biological treatment processes. Under aerobic conditions, mineralization of DMF (200 mg l⁻¹, 2.7 mM) was achieved under all combinations of salinity and pH. The rate of bacterial growth decreased with increasing salinity. Changes in the salt concentration and pH still resulted in mineralization and unchanged yield of bacterial cells. At 0.2% NaCl and either pH 5 or 7, growth occurred on DMF in the range 0.2–1 g l⁻¹. However, cell yield decreased with increasing concentrations of DMF. Under conditions of 0.2% NaCl, pH 7 and 4% NaCl, pH 5, growth on DMF at 5 g l⁻¹ resulted in the production of an intermediate that was detected using gas chromatography (GC). It is proposed that the intermediate was dimethylamine, and its persistence in growth media was attributed to suppressed growth as a result of an increase in pH. A culture capable of degrading DMF under nitrate-reducing conditions was obtained at 0.2% NaCl and pH 7, but not at more saline and acidic conditions. Growth and degradation of DMF were considerably slower under these conditions compared with aerobic conditions. Fermentative degradation of DMF was not observed. Journal of Industrial Microbiology & Biotechnology (2000) 25, 8–16. Received 14 July 1999/ Accepted in revised form 30 March 2000     

The Phototrophic Community Found in Lake Khilganta (an Alkaline Saline Lake Located in the Southeastern Transbaikal Region)

The structure of the phototrophic community found in Lake Khilganta (the Agin-Buryat Autonomous Area), a shallow saline soda lake (depth, 35–45 cm; water mineralization, 45 g/l; alkalinity, 30 mg-equiv/l; pH 9.5) has been studied. The bottom of the lake is covered with a 10- to 15-mm microbial mat, whose basis is formed by the filamentous cyanobacterium Microcoleus chthonoplastes. The mat exhibits pronounced layering and contains a significant amount of minerals. Six zones, which have characteristic colors and consistencies and are composed of intermittent layers, have been identified along the vertical profile. Live phototrophic bacteria have been found in the three upper zones. The bulk of the cyanobacteria is concentrated in the upper zone. In the lower zones, the development of purple bacteria has been observed. The diurnal dynamics of the vertical distribution of phototrophic microorganisms, which results from variations in the physicochemical environmental parameters, is described. Ectothiorhodospira sp. are dominant among the anoxyphotobacteria present. Their number, determined according to the inoculation method, is 10⁶–10⁷ cells/ml. The purple bacteria of the genera Allochromatium, Thiocapsa, and Rhodovulum are also present. Experiments with isolated pure cultures have shown that the anoxygenic photosynthetic bacteria of Lake Khilganta are halotolerant and alkalitolerant or alkaliphilic. In liquid enrichment cultures, at pH 9.5, the ratio of anoxyphotobacteria species is close to that observed in the lake. When the pH is increased to 10.4, it is Ectothiorhodospira, which is the most adapted to life under increased mineralization and alkalinity, that predominantly develops. Photosynthetic activity has been observed in the three upper mat zones and constitutes, on average, 1.5 g C/(m²h); the share of anoxygenic photosynthesis accounts for 75–95% of the total productivity. The main role in sulfide oxidation belongs to the phototrophic anoxyphotobacteria and cyanobacteria. In terms of the physicochemical conditions and structure of the phototrophic community, Lake Khilganta is similar to shallow saline water bodies of marine origin. The main differences consist in the increased alkalinity and in the consequent prevalence of alkaliphilic and alkalitolerant microorganisms and in the absence of representatives of the neutrophilic group of green sulfur bacteria.__________Translated from Mikrobiologiya, Vol. 74, No. 3, 2005, pp. 410–419.Original Russian Text Copyright © 2005 by Kompantseva, Sorokin, Gorlenko, Namsaraev.     

The role of water level and salinity in the regulation of Juncus gerardi populations in former ricefields in southern France

Abstract. In the Rhône delta (southern France) Juncus gerardi is a dominant, strongly aggregating species in artificially flooded former rice fields. In order to explain this pattern, the effects of water depth, salinity and their interaction were measured on (1) seed germination and seedling development and (2) vegetative growth of J. gerardi in a controlled-environment experiment. The germination pattern of J. gerardi was affected by salinity. Low salinity (2 g/l NaCl) delayed germination while moderate salinity (12 g/l NaCl) reduced germination rate. In contrast, the germination of J. gerardi was not affected in the range of water depths tested (i.e. 0–10cm). Salinity negatively affected the development of below-ground parts, shoots and inflorescences. This negative effect of salinity on the vegetative growth of J. gerardi was amplified when combined with flooding. Flooding with fresh water (0–20 cm depth) did not limit biomass production during the experiment. However, a decrease in the ratio of below-ground/above-ground dry weight at deeper water depths suggests a limitation of the vegetative propagation of J. gerardi under prolonged flooding conditions. This hypothesis is supported by the negative correlation between the cover of J. gerardi and water depth found in an abandoned rice field. The limitation on seedling recruitment imposed by salinity and the depression of vegetative growth of J. gerardi due to a combination of salinity and water depth could explain the aggregate distribution of J. gerardi in former rice fields.     

Taxonomic and ecological characterization of cyanobacteria from some brackish and saline lakes of Southern Transbaikal Region

The species composition of cyanobacteria from 12 lakes of Southern Transbaikal Region was studied. In the studied lakes, a total of 28 species of cyanobacteria were detected, including 10 species previously not retrieved from the lakes of Southern Transbaikal Region. The morphological and ecophysiological characteristics, as well as the phylogenetic position, of pure cyanobacterial cultures were determined. According to the results of 16S rRNA sequencing, the Cya 1, Cya 2, and Cya 10 cultures were identified as representatives of the genus Phormidium; the Cya 5 and Cya 6 cultures were assigned to the genus Nodularia. On the basis of its morphological properties, the Cya 4 culture was identified as Pseudanabaena frigida. The studied microorganisms were moderate alkaliphiles and could grow within a broad salinity range (0–100 g/l NaCl).     

Genetic variance in the composition of two functional groups (diazotrophs and cyanobacteria) from a hypersaline microbial mat

Examination of variation in ecological communities can lead to an understanding of the forces that structure communities, the consequences of change at the ecosystem level, and the relevant scales involved. This study details spatial and seasonal variability in the composition of nitrogen-fixing and cyanobacterial (i.e., oxygenic photosynthetic) functional groups of a benthic, hypersaline microbial mat from Salt Pond, San Salvador Island, Bahamas. This system shows extreme annual variability in the salinity of the overlying water and the extent of water coverage. Analysis of molecular variance and F(ST) tests of genetic differentiation of nifH and cyanobacterial 16S rRNA gene clone libraries allowed for changes at multiple taxonomic levels (i.e., above, below, and at the species level) to inform the conclusions regarding these functional groups. Composition of the nitrogen-fixing community showed significant seasonal changes related to salinity, while cyanobacterial composition showed no consistent seasonal pattern. Both functional groups exhibited significant spatial variation, changing with depth in the mat and horizontally with distance from the shoreline. The patterns of change suggest that cyanobacterial composition was more insensitive to water stress, and consequently, cyanobacteria dominated the nitrogen-fixing community during dry months but gave way to a more diverse community of diazotrophs in wet months. This seasonal pattern may allow the mat community to respond quickly to water-freshening events after prolonged dry conditions (system recovery) and maintain ecosystem function in the face of disturbance during the wet season (system resilience).     

The effect of light, salinity, and nitrogen availability on lipid production by Nannochloropsis sp

We examined responses of batch cultures of the marine microalga Nannochloropsis sp. to combined alterations in salinity (13, 27, and 40 g/l NaCl) and light intensity (170 and 700 μmol photons/m²·s). Major growth parameters and lipid productivity (based on total fatty acid determination) were determined in nitrogen-replete and nitrogen-depleted cultures of an initial biomass of 0.8 and 1.4 g/l, respectively. On the nitrogen-replete medium, increases in light intensity and salinity increased the cellular content of dry weight and lipids due to enhanced formation of triacylglycerols (TAG). Maximum average productivity of ca. 410 mg TFA/l/d were obtained at 700 μmol photons/m²·s and 40 g/l NaCl within 7 days. Under stressful conditions, content of the major LC-PUFA, eicosapentaenoic acid (EPA), was significantly reduced while TAG reached 25% of biomass. In contrast, lower salinity tended to improve major growth parameters, consistent with less variation in EPA contents. Combined higher salinity and light intensity was detrimental to lipid productivity under nitrogen starvation; biomass TFA content, and lipid productivity amounted for only 33% of DW and ca. 200 mg TFA/l/day, respectively. The highest biomass TFA content (ca. 47% DW) and average lipid productivity of ca. 360 mg TFA/l/day were achieved at 13 g/l NaCl and 700 μmol photons/m²·s. Our data further support selecting Nannochloropsis as promising microalgae for biodiesel production. Moreover, appropriate cultivation regimes may render Nannochloropsis microalgae to produce simultaneously major valuable components, EPA, and TAG, while sustaining relatively high biomass growth rates.     

Effect of different salinities of a dynamic water system on biofilm formation

AISI-1020 carbon steel coupons were fixed onto a water circulation loop in order to study the effect of varying NaCl concentrations on formation of biofilms by natural populations of microorganisms. Overall, we observed a reduction in the number of bacteria attached to the metal surfaces as NaCl levels increased. At 12.85 and 80 g/l NaCl, the respective bacterial counts were: 1.7×10⁹ CFU/cm² and 7.5×10² CFU/cm² for aerobic species; 1.3×10⁴ CFU/cm² and 2.1×10 CFU/cm² for anaerobic species; and 1.8×10³ CFU/cm² and 4.6×10 CFU/cm² for sulfate-reducing species. However, the opposite trend was observed for the numbers of iron-reducing bacteria: 4.1×10⁶ CFU/cm² at 12.85 g/l NaCl and 7.5 10⁸ CFU/cm² at 80 g/l NaCl, respectively. Fungal counts remained constant throughout the experimental period. The salt concentration at which the maximum corrosion rate was observed was 35 g/l. In view of the marked loss of metal mass recorded at this salinity, AISI-1020 carbon steel proved to belong to the group of alloys less resistant to corrosion. Journal of Industrial Microbiology & Biotechnology (2000) 25, 45–48. Received 07 December 1999/ Accepted in revised form 25 April 2000     

Response of cyanobacteria to arsenic toxicity

Arsenic content of cyanobacterial biomass, soil and water samples from arsenic-contaminated area of eastern India were estimated. It was found that arsenic content in cyanobacterial biomass (276.9 μg g⁻¹) was more than soil (19.01 μg g⁻¹) or water sample (244.13 μg L⁻¹). Shallow tube well water showed more arsenic (244.13 μg L⁻¹) than deep tube well water (146.13 μg L⁻¹). Arsenic resistant genera recorded from the contaminated area were Oscillatoria princeps, Oscillatoria limosa, Anabaena sp. and Phormidium laminosum. Among these, P. laminosum was isolated and exposed to different concentration of Arsenic in vitro (0.1–100 ppm) to study the toxicity level of arsenic. Modulation in stress enzymes and stress-related compounds were studied in relation to lipid peroxidase, catalase, super oxide dismutase (SOD), ascorbate peroxidase (APX), reduced glutathione and carotenoids in arsenic exposed biomass to understand the resistance mechanism of the genus both in laboratory condition as well as in natural condition. Arsenic content of cyanobacterial biomass from contaminated area was more (276.9 μg g⁻¹) than laboratory exposed sample (37.17 μg g⁻¹), indicating bioconcentration of arsenic in long-term-exposed natural biomass. Overall, more activity of catalase was recorded in cyanobacterial biomass of natural condition whereas SOD and APX were at higher level in laboratory culture.     

Influence of Salinity Concentration on Aquatic Insect Community Structure: A Mesocosm Experiment in the Dead Sea Basin Region

Salinity varies considerably among temporary pools in the Dead Sea Basin, Israel. We experimentally assessed the effects of four salinity levels (0, 10, 20 and 30 g NaCl per liter) on the aquatic insect community in this basin in an artificial pool experiment. Each salinity level was randomly assigned to six pools (total=24 pools). Salinity did not affect total insect abundance but strongly affected abundance and distributions of different species, and consequently, community structure. Of 13 taxa colonizing the pools, 12 were Diptera including 10 mosquito species. Five taxa were sufficiently common to assess abundance in relation to salinity. Polypedilum nubiferum Skuse (Diptera: Chironomidae) was largely salinity intolerant being abundant only in the freshwater. Ephydra flavipes Macquart (Diptera: Ephydridae) was most abundant at the highest salinity level and was rare in freshwater. Ochlerotatus caspius Pallas (Diptera: Culicidae) abundance tended to be highest at 10 g/l and lowest at 30 g/l although the differences were not statistically significant. Anopheles multicolor Cambouliu (Diptera: Culicidae) was relatively euryhaline although numbers dropped significantly at the highest salinity. Cleon dipterum Linnaeus (Baetidae: Ephemeroptera) was also euryhaline and showed no significant differences in abundance across salinities. For the mosquito species, we also estimated survival to pupation. Survival to pupation was significantly lower for O. caspius in freshwater, but was not statistically significantly different across salinities for A.␣multicolor. Species diversity was highest at the two lowest salinities tested and then dropped with increasing salinity. Evenness was not significantly different across salinities. Community similarity generally decreased with increasing salinity differences though dissimilarity was greatest when comparing freshwater to other salinities. Thus, regional diversity is likely increased when there is a range of salinities among pools.     

Successional Changes in the Microbial Community of the Alkaline Lake Khilganta during the Dry Season

Microbial processes in a shallow, saline, alkaline Lake Khilganta (Southern Siberia) were studied during the dry season. During the drought, a crust was formed on the lake surface, where low rates of production processes were observed, with predominance of anoxygenic photosynthesis at 2.3 mg C/(dm³ day). The rates of microbial processes increased after short-term rains. During this period, a thin cyanobacterial mat was formed on the bottom, in which filamentous cyanbacteria Geitlerinema spp. predominated and the rate of oxygenic photosynthesis was up to 18 mg C/(dm³ day). Subsequent water evaporation and salinity increase resulted in altered community types and their activity. Red spots emerged on the mat surface, where anoxygenic prototrophic members of the genus Ectothiorhodospira predominated. Anoxygenic photosynthesis became the main production process in microbial mats, with the rate of 60 mg C/(dm³ day). At salinity increase to 200 g/L, the water remained in small depressions on the bottom, where extremophilic green algae Dunaliella sp. predominated, and the rate of oxygenic photosynthesis was 0.877 mg C/(dm³ day). These changes in the type and activity of microbial communities is an example of succession of microbial communities in Southern Siberia saline lakes during drought.     

盐分对河口淡水、微咸水沼泽湿地土壤甲烷产生潜力的影响

海平面上升导致河口区盐水入侵现象日益明显,深刻影响着河口潮汐淡水、微咸水湿地生物地球化学循环。采集闽江河口区淡水、微咸水短叶茳芏潮汐沼泽湿地表层土样,室内添加盐度为5,10,15,21 g/L的人造海水、Na Cl溶液及盐度为0的去离子水,通过室内泥浆厌氧培养试验,对比研究海水和Na Cl溶液对淡水、微咸水沼泽湿地土壤甲烷产生潜力的影响。与对照相比,1—12 d培养期内4个盐度的海水处理均显著抑制河口淡水、微咸水沼泽湿地甲烷产生潜力,抑制率在93%以上,盐度10—21 g/L的3个海水处理对于河口淡水、微咸水沼泽湿地甲烷产生潜力的抑制效应无显著差异。Na Cl溶液只有在盐度达到15和21 g/L才显著抑制淡水、微咸水沼泽湿地甲烷产生潜力,且抑制率最多为80.9%,盐度为5、10 g/L的Na Cl溶液对淡水、微咸水沼泽湿地甲烷产生潜力的抑制作用不显著,抑制率多小于30%。伴随着盐水入侵而发生的硫酸盐还原作用及离子胁迫作用对河口淡水、微咸水沼泽湿地甲烷产生具有显著的抑制效应。     

Natural and recombinant luminescent microorganisms in biotoxicity testing of mineral waters

We have developed methods of biotesting mineral waters involving use of natural or recombinant luminescent strains with elimination of the effect of degree of mineralization and pH. To overcome the adverse effect of high salt concentrations, disguising the action of chemical pollutants, a special method of mineral water sample preparation is proposed. In this method, the marine luminescent bacterium Photobacterium phosphoreum (Microbiosensor B-17 677f) is used as a test object. Samples to be analyzed are supplemented with NaCl depending on their natural degree of mineralization to adjust it to 30 g/l. Another approach, more universal and efficient, involves pH adjustment in the samples to 7.5. This value is suitable for application of both Microbiosensor B-17 677f and the recombinant Escherichia coli strain harboring the cloned lux operon of P. leiognathi (Ecolum-9). It has been shown that this treatment, retaining the natural luminescence level of the bacterial biosensors, allows bioluminescent detection of exogenous pollutants added to the samples, including benzene and Cr(VI).     

Effect of salinity stress on the life history variables of Branchipus schaefferi Fisher, 1834 (Crustacea: Anostraca)

Background

Freshwater anostracans inhabit ephemeral water bodies in which as the water level decreases due to evaporation the salt concentration increases. Thus, for most anostracans salinity becomes the major stress factor.

Results

We tested five concentrations of NaCl (0 to 8 g/l) on the life table demography of Branchipus schaefferi fed Chlorella (alga). Age-specific survivorship curves of male and female B. schaefferi showed nearly a similar pattern in that increased salt concentration resulted in decreased survivorship. The age-specific reproduction (m_x) of females showed several peaks of cyst production at 0 and 1 g/l salinity while in treatments containing salt at 4 or 8 g/l, there were fewer peaks. Average lifespan, life expectancy at birth, gross and net reproductive rates, generation time and the rate of population increase were all significantly influenced by the salt concentration in the medium. The highest value of net reproductive rate (970 cysts/female) was in treatments containing 0 g/l of salt, while the lowest was 13 cysts/female at 8 g/l. The rate of population increase (r) varied from 0.52 to 0.32 per day depending on the salt concentration in the medium.

Conclusion

The low survival and offspring production of B. schaefferi at higher salinity levels suggests that this species is unlikely to colonize inland saline water bodies. Therefore, the temporary ponds in which it is found, proper conservative measures must be taken to protect this species.