Effect of food type and concentration on the survival,longevity, and reproduction of Daphnia magna

The freshwater microalgae Ankistrodesmus falcatus and Scenedesmus incrassatulus, at three concentrations (6, 12 and 18 mg l⁻¹ t, dry weight), were tested as diets for Daphnia magna cultured in reconstituted hard water, at 19 ± 1 °C. Effects on survival, and reproductive characteristics were evaluated during a complete life-cycle. Test animals fed with the highest food concentration had the lowest survival, longevity, number of clutches, and average inter-brood times, but the total offspring was similar to that obtained with the lowest food concentration, for the same species of alga. Average longevity ranged from 40 to 85 days, with a minimum of 24 and a maximum of 119 days. The average inter-brood time ranged from 4.2 to 5.8 days, the highest values being observed at the lowest food concentration. The average total offspring was maximum for the intermediate concentrations of both algae. The maximum number of clutches ranged from 9 to 23, with the lowest values being observed at the highest food concentration. Even though both microalgae had similar effects on survival and reproduction, and the greatest differences observed were related to food concentration, it seems that S. incrassalulus is a comparatively better food for D. magna. The most suitable food level should be determined prior to carrying out chronic bioassays, and it is also an important factor in cultures for obtaining neonates for toxicological tests.     

Salinity tolerance of Gambusia affinis (Baird & Girard) and Heteropneustes fossilis (Bloch)

The present paper describes the results of a study on the salinity tolerance of two freshwater fishes, Gambusia affinis (Baird & Girard) and Heteropneustes fossilis (Bloch). The two species were treated with various concentrations of sea water and three most common salts found in the saline waters of Iraq, namely sodium chloride, calcium chloride and potassium chloride. The mortality rates following these treatments were recorded. Both species showed the highest degree of resistance for sea water and sodium chloride, and the lowest degree of tolerance to potassium chloride. Gambusia affinis was more resistant to these salts and sea water than H. fossilis .     

The life history parameters of Diaphanosoma excisum (Cladocera), grown in different culturing media

Life history parameters of Diaphanosoma excisum (SARS) were derived from culture tube experiments with media comprising mohua oil cake, mustard oil cake, cow dung and rice bran. Body length, longevity, fecundity and progeny production were highest in rice bran medium. First reproduction time (A) in different media ranged from 2 to 6 days, while the reproduction peak (T) varied from 4 to 13 days. The total offspring per female (S) was directly dependent upon the mean number of eggs per female per life span. The intrinsic (r) and finite rate (e^r) of natural increase were larger for rice bran than for other media.     

SHORT‐TERM EFFECT OF TEMPERATURE ON THE PHOTOKINETICS OF MICROALGAE FROM THE SURFACE LAYERS OF ANTARCTIC PACK ICE1

Microalgae growing within brine channels (85 psu salinity) of the surface ice layers of Antarctic pack ice showed considerable photosynthetic tolerance to the extreme environmental condition. Brine microalgae exposed to temperatures above ?5°C and at irradiances up to 350 μmol photons·m^?2·s^?1 showed no photosynthetic damage or limitations. Photosynthesis was limited (but not photoinhibited) when brine microalgae were exposed to ?10°C, provided the irradiance remained under 50 μmol photons·m^?2·s^?1. The highest level of photosynthetic activity (maximum relative electron transport rate [rETR_max]) in brine microalgae growing within the surface layer of sea ice was at approximately 18 μmol electrons·m^?2·s^?1, which occurred at ?1.8°C. Effective quantum yield of PSII and rETR_max of the halotolerant brine microalgae exhibited a temperature‐dependent pattern, where both parameters were higher at ?1.8°C and lower at ?10°C. Relative ETR_max at temperatures above ?5°C were stable across a wide range of irradiance.     

Growth,maturation and survival in a laboratory-reared Rhabdocoelid Turbellarian,Macrostomum orthostylum (BRAUN 1885)

Growth, maturation and survival of a free living turbellarian Macrostomum orthostylum (BRAUN), from a brackish water fish-farm, were studied in the laboratory under a constant temperature of 24 °C. The worms tolerated a wide range of salinity (1 to 30‰). Maximum growth (total length) of 1000 μm was attained in 56 days with a mean growth rate of 15.7 μm d^-1. Minimum maturation time (7 days) and highest longevity (112 days) were recorded in 9%. salinity. Survival period was considerably longer at lower salinities (1 to 10‰) and showed negative relationship with higher salinities (11 to 30‰).     

The Influence of Host Species on Some Biological and Behavioural Aspects of Dibrachys boarmiae (Hymenoptera: Pteromalidae), Parasitoid of Kermania pistaciella (Lepidoptera: Tineidae)

Dibrachys boarmiae was recently found as a parasitoid of the pistachio twig borer moth, Kermania pistaciella, an important pistachio pest in Iran. Several biological and behavioural aspects of the wasp were studied under controlled conditions using three different lepidopterous host species, K. pistaciella, Sitotroga cerealella and Galleria mellonella. Development time from egg to adult decreases from 54 days at 15°C to 12.6 days at 32.5°C. The thermal constant was estimated 270°D, and the lower development threshold was at 9.9°C. Longevity of females that had the opportunity to oviposit and access to food (honey) was on average 23 days, and 134 offspring were produced during 13 days of oviposition. Ninety percent of ovipositions occur during the first 10 days of the parasitoid's life, although no pre-oviposition period was found. If females were deprived of food, longevity as well as fecundity, were drastically reduced to 8 days and only 79 offspring respectively. Females were able to mate immediately after emergence and the sex ratio of the progeny was strongly female biased on all examined hosts, especially on the largest host G. mellonella (0.08 male). When females were kept with a male throughout their life, the total number of progeny decreased to 92 wasps on average but the sex ratio was unaffected. The parasitoid significantly preferred to attack the pre-pupal stage, and this influenced the size of clutches allocated to different host stages. The parasitoid laid larger clutches on bigger hosts.     

Marine bacterioplankton at the Weddell Sea ice edge,distribution of psychrophilic and psychrotrophic populations

Summary In the eastern Weddell Sea on several transects from ice-covered, through ice melt, to open-ocean stations, total and heterotrophic bacteria were estimated to document an enhanced bacteriological biomass expected near the ice edge. The highest numbers of bacteria were found in melted ice cores, with 4.2·10³ CFUml^–1 and 1.1·10⁷ Cells ml^–1. Although brine from pore water samples average more than one order of magnitude less cells per ml, the highest bacterial production, 2.2·10⁷ cells l^–1 day^–1, was recorded in brine samples. All quantitatively studied bacterial parameters were lower under the ice than in the ice samples but there were no clear vertical gradients in the water column. In the studied spring situation, sea ice occurrence seems to play only a minor role in the general distribution of the seawater bacterioplankton. The bacterial community structure was investigated by carrying out 29 morphological and biochemical tests on 118 isolated strains. The bacterial communities inhabiting Antarctic pack ice differ from those found in underlying seawater. Although non fermentative Gram-negative rods were always dominant in seawater, Vibrio sp. represented more than 25% of the strains isolated from some ice samples. The results clearly indicated that a large majority of the bacteria isolated from seawater must be considered psychrotrophic but that truly psychrophilic strains occurred in melted ice and brine samples.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Growth rate of the carrageenophyte Kappaphycus alvarezii (Rhodophyta, Gigartinales) in vitro

Unialgal cultures were established trom a 2.5 g branch ot a brown variant ot Kappaphycus alvarezii (Doty) Doty ex P. Silva, with the main objective to produce branches for monthly outplanting in the sea. Ditterent conditions were tested to optimize production ot branches in the laboratory. The best growth was obtained under culture conditions of 25 ± 2°C, 170–210 μmol photons m² s^?1, 14:10 LD photoperiod and salinity 32–35‰. Three culture media (Provasoli,‘F/2’and von Stosch) were tested. Deleterious ettects were observed in branches incubated continuously in full‐ or halt‐strength Provasoli's enriched seawater medium (PES). Exponential growth rates ot about 3% day^?1 were obtained using PES, pulse‐fed 24 h per week, or other diluted media used continuously (one‐quarter strength ‘F/2’and half‐strength von Stosch). Laboratory‐grown branches with mean weights from 2.97 to 4.25 g were successfully introduced into the sea at Ubatuba, SP, Brazil (23°26.9′S, 45°0.3′W) an area with mean monthly seawater temperature from 20.3 to 28.5°C (extremes: 17.0–31.0°C). Transplantation of branches produced in unialgal culture, as done in the present study, avoids the risk of introduction of unwanted species into new areas.     

Modelled and measured dynamics of viruses in Arctic winter sea-ice brines

We describe a model based on diffusion theory and the temperature-dependent mechanism of brine concentration in sea ice to argue that, if viruses partition with bacteria into sea-ice brine inclusions, contact rates between the two can be higher in winter sea ice than in seawater, increasing the probability of infection and possible virus production. To examine this hypothesis, we determined viral and bacterial concentrations in select winter sea-ice horizons using epifluorescence microscopy. Viral concentrations ranged from 1.6 to 82 x 10(6) ml(-1) of brine volume of the ice, with highest values in brines from coldest (-24 to -31 degrees C) ice horizons. Calculated virus-bacteria contact rates in underlying -1 degrees C seawater were similar to those in brines of -11 degrees C ice but up to 600 times lower than those in ice brines at or below -24 degrees C. We then incubated native bacterial and viral assemblages from winter sea ice for 8 days in brine at a temperature (-12 degrees C) and salinity ( approximately 160 psu) near expected in situ values, monitoring their concentrations microscopically. While different cores yielded different results, consistent with known spatial heterogeneity in sea ice, these experiments provided unambiguous evidence for viral persistence and production, as well as for bacterial growth, in -12 degrees C brine.     

Strong male‐biased operational sex ratio in a breeding population of loggerhead turtles (Caretta caretta) inferred by paternal genotype reconstruction analysis

Characterization of a species mating systems is fundamental for understanding the natural history and evolution of that species. Polyandry can result in the multiple paternity of progeny arrays. The only previous study of the loggerhead turtle (Caretta caretta) in the USA showed that within the large peninsular Florida subpopulation, multiple paternity occurs in approximately 30% of clutches. Our study tested clutches from the smaller northern subpopulation for the presence of multiple paternal contributions. We examined mothers and up to 20 offspring from 19.5% of clutches laid across three nesting seasons (2008–2010) on the small nesting beach on Wassaw Island, Georgia, USA. We found that 75% of clutches sampled had multiple fathers with an average of 2.65 fathers per nest (1–7 fathers found). The average number of fathers per clutch varied among years and increased with female size. There was no relationship between number of fathers and hatching success. Finally, we found 195 individual paternal genotypes and determined that each male contributed to no more than a single clutch over the 3‐year sampling period. Together these results suggest that the operational sex ratio is male‐biased at this site.     

Antiviral carbohydrates from marine red algae

The solubility of the O₂ in the Dead Sea brine was determined over the temperature range 5 °C–50 °C using a modified Winkler titration, volumetric analysis, and a polarographic sensor. The solubility at room temperature and 1 atmosphere pressure was ca. 1 mg l^–1, and the temperature coefficient 0.006 mg 1^–1° C^–1 . The data are nearly consistent with sea water solubility extrapolated to Dead Sea brine salinity.     

Salinity-induced expression of pyrrolline-5-carboxylate synthetase determine salinity tolerance in Brassica spp

The objective of the present study was to assess the role of salinity-induced expression of pyrrolline 5-carboxylate synthetase (P5CS), P5CS activity, and proline accumulation on salinity tolerance in Brassica genotypes. A pot culture experiment was conducted with four Brassica genotypes viz. CS 52, CS 54, Varuna, (B. juncea) and T 9 (B. campestris) under control and two salinity levels, i.e., 1.65, 4.50 and 6.76?dS?m^?1. Proline contents increased with increasing levels of salinity, and the highest content were recorded at post-flowering stage in CS 52 and CS 54. Activity of P5CS recorded at flowering stage was highest at higher level of salinity, with CS 52 and CS 54 recording highest activity. Gene expression of P5CS, which regulates the synthesis of proline, was higher in CS 52 and CS 54 under salt stress than Varuna and T 9. Comparison of partial nucleotide as well as amino acid sequence showed conserved domains, and inter and intra generic relatedness of these genes. The study suggests that salinity-induced expression of P5CS, pyrrolline-phosphate synthetase activity and proline accumulation may serve as one of the mechanism of salinity stress tolerance in Brassica genotypes.     

Genotype-by-environment interaction for salinity tolerance in the freshwater-invading copepod Eurytemora affinis

This study examined the extent of phenotypic plasticity for salinity tolerance and genetic variation in plasticity in the invasive copepod Eurytemora affinis. Euryemora affinis is a species complex inhabiting brackish to hypersaline environments but has invaded freshwater lakes and reservoirs within the past century. Reaction norm experiments were performed on a relatively euryhaline population collected from a brackish lake with fluctuating salinity. Life history traits (hatching rate, survival, and development time) were measured for 20 full-sib clutches that were split and reared at four salinities (fresh, 5, 10, and 27 practical salinity units [PSU]). On average, higher salinities (10 and 27 PSU) were more favorable for larval growth, yielding greater survival and faster development rate. Clutches differed significantly in their response to salinity, with a significant genotype-by-environment interaction for development time. In addition, genetic (clutch) effects were evident in response to low salinity, given that survival in fresh (lake) water was significantly positively correlated with survival at 5 PSU for individual clutches. Clutches raised in fresh water could not survive beyond metamorphosis, suggesting that acclimation to fresh water could not occur in a single generation. Results suggest the importance of natural selection during freshwater invasion events, given the inability of plasticity to generate a freshwater phenotype, and the presence of genetic variation for plasticity upon which natural selection could act.     

Physiological adaptations to low temperature and brine exposure in the circumpolar amphipod Gammarus wilkitzkii

Summary The amphipod Gammarus wilkitzkii does not survive being frozen totally into solid sea ice. When the animals are cooled in air or freezing seawater, they will freeze and die at a temperature of about-4° C. However, during sea ice growth, the amphipods may tolerate to stay in the vicinity of the ice by conforming to the ambient brine in a salinity range of 34 ppt to about 60 ppt. A passive relationship between the concentrations of the haemolymph and seawater Na⁺ and Cl^-, lowers the melting point of the body fluids of the animals, thus preventing internal ice formation at low temperatures.     

Microbial eukaryote life in the new hypersaline deep-sea basin Thetis

Only recently, a novel anoxic hypersaline (thalassic) basin in the eastern Mediterranean was discovered at a depth of 3,258 m. The halite-saturated brine of this polyextreme basin revealed one of the highest salt concentrations ever reported for such an environment (salinity of 348‰). Using a eukaryote-specific probe and fluorescence in situ hybridization, we counted 0.6 × 10⁴ protists per liter of anoxic brine. SSU rRNA sequence analyses, based on amplification of environmental cDNA identified fungi as the most diverse taxonomic group of eukaryotes in the brine, making deep-sea brines sources of unknown fungal diversity and hotspots for the discovery of novel metabolic pathways and for secondary metabolites. The second most diverse phylotypes are ciliates and stramenopiles (each 20%). The occurrence of closely related ciliate sequences exclusively in other Mediterranean brine basins suggests specific adaptations of the respective organisms to such habitats. Betadiversity-analyses confirm that microeukaryote communities in the brine and the interface are notably different. Several distinct morphotypes in brine samples suggest that the rRNA sequences detected in Thetis brine can be linked to indigenous polyextremophile protists. This contradicts previous assumptions that such extremely high salt concentrations are anathema to eukaryotic life. The upper salinity limits for eukaryotic life remain unidentified.     

Fluxes associated with brine motion in growing sea ice

Summary Laboratory and field studies have demonstrated that fluid motion occurs at two locations in growing sea ice: in a network of brine channels and within the skeletal layer at the ice-water interface. Brine channel fluxes estimated using brine channel areal density from natural sea ice and channel velocities from laboratory studies are compared with recent measurements reported in the literature. Fluxes into the porous skeletal layer of sea ice may be estimated using rates of nutrient uptake by ice algae and adjacent seawater nutrient concentrations. Both approaches indicate fluxes of the order of 10^-6 cc cm^-2 s^-1 (l m^-2 h^-1), which are about equal to fluxes reported in bioirrigated sediments. Fluxes of this magnitude indicate a very short residence time for the liquid phase in the skeletal layer, suggesting that this fluid motion may be important in maintaining the ice algae community.     

The influence of salinity on the kinetics of NH inf4 sup+ uptake in Spartina alterniflora

Summary The effects of short- and long-term exposure to a range in concentration of sea salts on the kinetics of NH _inf4 ^sup+ uptake by Spartina alterniflora were examined in a laboratory culture experiment. Long-term exposure to increasing salinity up to 50 g/L resulted in a progressive increase in the apparent K_m but did not significantly affect V_max (mean V_max=4.23±1.97 mole·g^–1·h^–1). The apparent K_m increased in a nonlinear fashion from a mean of 2.66±1.10 mole/L at a salinity of 5 g/L to a mean of 17.56±4.10 mole/L at a salinity of 50 g/L. These results suggest that the long-term effect of exposure to total salt concentrations within the range 5–50 g/L was a competitive inhibition of NH _inf4 ^sup+ uptake in S. alterniflora. No significant NH _inf4 ^sup+ uptake was observed in S. alterniflora exposed to 65 g/L sea salts. Short-term exposure to rapid changes in salinity significantly affected both V_max and K_m. Reduction of solution salinity from 35 to 5 g/L did not change V_max but reduced K_m by 71%. However, exposing plants grown at 5 g/L salinity to 35 resulted in an decrease in V_max of approximately 50%. Exposure of plants grown at 35 g/L to a total sea salt concentration of 50 g/L for 48h completely inhibited uptake of NH _inf4 ^sup+ . For both experiments, increasing salinity led to an increase in the apparent K_m similar to that found in response to long-term exposure. Our data are consistent with a conceptual model of changes in the productivity of S. alterniflora in the salt marsh as a function of environmental modification of NH _inf4 ^sup+ uptake kinetics.     

THE SHORT‐TERM EFFECT OF IRRADIANCE ON THE PHOTOSYNTHETIC PROPERTIES OF ANTARCTIC FAST‐ICE MICROALGAL COMMUNITIES1

Although sea‐ice represents a harsh physicochemical environment with steep gradients in temperature, light, and salinity, diverse microbial communities are present within the ice matrix. We describe here the photosynthetic responses of sea‐ice microalgae to varying irradiances. Rapid light curves (RLCs) were generated using pulse amplitude fluorometry and used to derive photosynthetic yield (Φ_PSII), photosynthetic efficiency (α), and the irradiance (E_k) at which relative electron transport rate (rETR) saturates. Surface brine algae from near the surface and bottom‐ice algae were exposed to a range of irradiances from 7 to 262 μmol photons · m^?2 · s^?1. In surface brine algae, Φ_PSII and α remained constant at all irradiances, and rETR_max peaked at 151 μmol photons · m^?2 · s^?1, indicating these algae are well acclimated to the irradiances to which they are normally exposed. In contrast, Φ_PSII, α, and rETR_max in bottom‐ice algae reduced when exposed to irradiances >26 μmol photons · m^?2 · s^?1, indicating a high degree of shade acclimation. In addition, the previous light history had no significant effect on the photosynthetic capacity of bottom‐ice algae whether cells were gradually exposed to target irradiances over a 12 h period or were exposed immediately (light shocked). These findings indicate that bottom‐ice algae are photoinhibited in a dose‐dependent manner, while surface brine algae tolerate higher irradiances. Our study shows that sea‐ice algae are able to adjust to changes in irradiance rapidly, and this ability to acclimate may facilitate survival and subsequent long‐term acclimation to the postmelt light regime of the Southern Ocean.     

POPULATION DYNAMICS OF MICROALGAE IN THE UPPER LAND-FAST SEA ICE AT A SNOW-FREE LOCATION

The population dynamics of interior ice microalgae were investigated at a snow-free site on annual land-fast sea ice in McMurdo Sound, Antarctica, during the austral spring and summer of 1995 – 96. A dynamic successional sequence was observed with life history transformations playing an important role. During late November and early December (austral spring), cryo- and halotolerant dinoflagellates and chrysophytes bloomed in brine channels within the upper ice. At this time, competition and grazing pressure are low because of the inability of most marine species to grow under the extreme environmental conditions found in the upper ice during the austral spring. In November and December, dinoflagellates, chrysophytes, and prasinophytes contributed an average of 66%, 44%, and < 1% of the phytoflagellate biomass, respectively. Both the dinoflagellates and the chrysophytes encysted in December, with cyst formation most intense just prior to surface melt and flushing of the ice. The cysts appear to be an adaptation for survival and dispersal in the plankton during ice decay and/or overwintering in the sea ice. In January (austral summer), when ice temperatures were similar to those in the water column, pennate diatoms replaced flagellates as the photosynthetic dominants in the upper sea ice. The upper land-fast sea ice undergoes dramatic seasonal changes in light availability, temperature, brine salinity, and inorganic nutrient availability. Ephemeral blooms of cyst-forming phytoflagellates exploit this habitat in the austral spring, when both inorganic nutrients and light are available but temperatures <− 2° C and brine salinities elevated.     

舟山海域大中型浮游动物群落时空变化及受控要素

为更好地保护舟山海域的渔业资源和生态环境,了解舟山海域浮游动物组成的时空变化,于2014年到2017年对舟山海域33个站位开展4个季节的生态综合调查,结果表明:4个航次共鉴定出浮游动物成体88种和浮游幼体19类,优势种共12种,浮游动物的优势种更替和群落特征季节变化明显,春夏、夏秋、秋冬、冬春相邻季节优势种更替率分别为75%、80%、100%和60%;平均生物量为夏季(176.34 mg/m³)>春季(120.20 mg/m³)和秋季(86.28 mg/m³)>冬季(7.21 mg/m³);平均丰度为夏季(143.97个/m³)>春季(86.30个/m³)>秋季(21.38个/m³)和冬季(26.86个/m³);平均多样性指数:夏季(3.03)>秋季(2.82)>春季(2.05)>冬季(1.71)。舟山海域浮游动物群落具有明显的季节和区域差异,温度、盐度、Chl a和营养盐是影响舟山浮游动物群落时空变化的主要环境因素,其中春季浮游动物群落空间分布主要受盐度的影响,夏季主要受温度、盐度和Chl a的影响,秋季主要受Chl a的影响,冬季主要受悬浮物和溶解氧的影响,而营养盐对每个季节的浮游动物群落分布都有一定的影响。