Disturbances due to increased salinity and the resilience of zooplankton communities: the potential role of the resting egg bank

When faced with disturbances such as increased salinity, aquatic communities inhabiting inland coastal systems change and may or may not be resilient after salinity decreases. The purpose of this study was to assess the potential role of the resting egg bank for zooplankton community resilience. We predicted that (1) hatching of resting eggs is inhibited by increased salinities and (2) resting eggs remain viable when exposed to salinity and hatch when returned to freshwater. At the community level, we evaluated the hatching responses and the short-term viability of resting eggs exposed to a salinity gradient. The hatching of resting eggs was inhibited at higher salinities (16.0 and 32.0 g l^?1). However, some resting eggs remained viable and hatched when returned to freshwater. Additionally, combining our experimental results to previously published field data, we observed that the pattern of hatching during exposure to salinity matches the temporal succession observed in the zooplankton community at our model system, after increased salinity. The recovery of zooplankton communities after disturbances involving increased salinity is likely facilitated by the presence of an egg bank. This finding has important implications for the recovery of zooplankton communities and the management of aquatic systems vulnerable to salinization worldwide.     

Long-term droughts change the hatching patterns of zooplankton resting eggs from permanent and temporary lakes

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Impact of water regime and fish predation on zooplankton resting egg production and emergence

The emergence of zooplankton from ephemeral areas upon re-wettinghas been suggested as a significant contributor to billabongproductivity. Sixteen experimental billabongs were designedto test two hypotheses (i) that changing the pattern of floodingalters zooplankton abundance within billabongs, and (ii) thepresence of small planktivorous fish alters the zooplanktoncommunity structure and diversity within billabongs. Resultsindicated that flooding caused microcrustaceans to increasein abundance but not rotifers. This response was not modifiedby changing the time of flooding. The presence of the planktivorousfish had only a small influence on the structure of rotiferassemblages, whereas microcrustacean assemblages became dominatedby juveniles. Emergence of rotifers and microcrustaceans fromsediment taken from the experimental billabongs and incubatedunder controlled conditions indicated the existence of a largereservoir of resting stages. The number of resting stages inthe sediment had not been modified by changing the season offlooding in the experimental billabongs, but it was modifiedby permanent inundation, which may have removed environmentalcues. The presence of planktivorous fish also appeared to influencethe number of resting stages that accumulated in the sediment.Emergence under stable laboratory conditions was rapid. Thiswas not the case under more variable natural conditions.     

Abundance,composition and spatial variation in the egg bank of a tropical zooplankton community

The semi‐aquatic grasshopper Cornops aquaticum (Bruner, 1906) is native to South America, with a distribution from the Argentinian pampas to the Gulf of Mexico, and is currently being proposed as a biological control agent for the invasive water hyacinth (Eichhornia crassipes) in South Africa. This study reports results of a neutral molecular marker (microsatellites) study on C. aquaticum within its native range. The data were analysed for levels of diversity and structure within/between South American populations, and correlations between host plant, geography and environmental/climatic variables were investigated. We found no evidence to support associations between host plant use and microsatellite genotypes (hypothesis 1). High levels of gene flow and weak genetic clustering of populations indicate a lack of differentiation, therefore an interaction between climate and local genotype (hypothesis 2) seems unlikely. Our results suggest that C. aquaticum may not have “tightly” coevolved with its host Eichhornia spp. (Pontederiaceae) as originally thought, and that instar variation might be due to the effect of local climate on phenotype (hypothesis 3) or possibly a locally adaptive trait.     

Vertical migration, hatching rates, and distribution of egg stages in freshwater zooplankton

In shallow, thermally stratifield lakes, the developing eggs carried by pelagic crustacean zooplankton are exposed to regularly alternating higher and lower temperatures during daily vertical migration. Rate summation techniques for determining the duration of egg developiment suggest that (1) the distribution of egg stages in the population will not change because of the alternating temperatures, and (2) the majority of young animals will not be hatched or released in the warmer, upper waters of the lake. This latter result is probably positively adaptive, but it may be brought about entirely mechanistically by the more rapid development in warmer waters.     

'Ancient' DNA in the resting egg bank of a microcrustacean can serve as a palaeolimnological database

Recent work on the diapausing egg banks of zooplankton, such as Daphnia (Crustacea: Anomopoda), indicates that these eggs can remain viable for decades while, theoretically, DNA can remain intact for even longer periods (i.e. centuries or millennia). We isolated diapausing eggs of Daphnia from a 30 m long sediment core taken from a hypereutrophic, northern German lake (Belauer See), with some eggs found in dated core material as old as 4500 years. Using microsatellite markers, we analysed the genetic structure of the resting eggs dated as old as ca. 200 years, and found that, although levels of heterozygosity remained remarkably stable, significant genetic differentiation (Nei's D = 0.36; F(ST) = 0.15) between recent and 'ancient' resting eggs (including allele frequency shifts and private alleles) was detected. These shifts represent either species-level changes in this complex (i.e. species-specific characters of ephippia are not always robust), or intraspecific shifts in genetic variation, or a combination of both. This study demonstrates that the egg banks of aquatic zooplankton can serve as repositories of both genetic (intrapopulational) and ecological (interspecific) information. The use of molecular markers, such as microsatellites, on diapausing egg/seed banks may open new avenues of enquiry related to tracking the long-term genetic (and/or species) shifts that are associated with long-term environmental changes.     

Estimating population birth rates of zooplankton when rates of egg deposition and hatching are periodic

Summary I present a general method of computing finite birth and death rates of natural zooplankton populations from changes in the age distribution of eggs and changes in population size. The method is applicable to cases in which eggs hatch periodically owing to variable rates of oviposition. When morphological criteria are used to determine the age distribution of eggs at the beginning and end of a sampling interval, egg mortality can be incorporated in estimates of population birth rate. I raised laboratory populations of Asplanchna priodonta, a common planktonic rotifer, in semicontinuous culture to evaluate my method of computing finite birth rate. The Asplanchna population became synchronized to a daily addition of food but grew by the same amount each day once steady state was achieved. The steady-state rate of growth, which can be computed from the volume-specific dilution rate of the culture, was consistent with the finite birth rate predicted from the population's egg ratio and egg age distribution.     

Effect of egg storage duration and egg turning during storage on egg quality and hatching of broiler hatching eggs

In commercial hatcheries, it is common to store eggs before incubation. One practice to improve hatchability consists in egg turning during this storage. This work aims to highlight the effects of turning on the physicochemical aspects of eggs and, consequently, how this turning can influence the hatching of chicks. An experiment was conducted to evaluate the effects of storage duration and egg turning during storage on egg quality, hatchability, and residual analysis. A total of 7 500 hatching eggs were collected from a 55-week-old commercial Cobb500 breeder flock and storage according to the treatments. The experiment was completely randomized in a 3 × 2 factorial design with three storage periods (4, 8, and 12 days) and egg turning (180° turn of eggs once a day) or no turning during storage, totaling six treatments. Regardless of turning, eggs stored for 4 days weighed more than turned eggs stored for 8 and 12 days, which were similar (P < 0.05). Non-turned eggs experienced an increase in relative shell weight with increased storage duration, and non-turned eggs stored for 4 and 8 days differed from non-turned eggs stored for 12 days (P < 0.05). Albumen pH of turned eggs stored for 4 and 8 days was lower than that of non-turned eggs stored for the same durations (P < 0.05). Albumen pH of turned eggs increased as storage duration increased (P < 0.05). Egg turning increased hatching by 2.02% over that of non-turning (P < 0.05). Eggs stored for 12 days, irrespective of turning, had higher late embryonic mortality (P < 0.05) compared to the other treatments. It was concluded that turning eggs during pre-incubation storage was adequate to improve hatchability of fertile eggs. Storing fertile eggs for 12 days is harmful to egg quality and increases embryo mortality even if eggs were turned.     

Resting egg banks can facilitate recovery of zooplankton communities after extended exposure to saline conditions

1. Salinisation has had a major effect on the diversity of biota associated with freshwater wetlands. However, there is no information available about whether elements of the biotic communities would be able to recover if the concentration of salts within secondarily salinised wetlands was lowered to levels more typical of freshwater wetlands. 2. We tested the hypothesis that dormant eggs of zooplankton are able to persist in wetlands with elevated salinities for extended periods of time by using zooplankton communities that had developed in mesocosms exposed to either salt concentrations of 13 500 mg L^?1 or freshwater (<300 mg L^?1) for a period of 22 months. We measured the response of the zooplankton community as concentration was reduced along a gradient of decreasing salinity from 13 500 mg L^?1 to freshwater. 3. In the freshwater mesocosms, the zooplankton community was abundant and taxon rich. In comparison at the start of the experiment in the high salinity mesocosms, the zooplankton community had low abundances and very few taxa. Numbers remained low in these mesocosms until salinity was reduced to <2500 mg L^?1. Below this, there was a rapid increase in the abundance, and richness of zooplankton and communities became similar to the communities in the freshwater mesocosms. 4. These results indicate that dormant eggs of zooplankton are able to persist in wetlands exposed to high salinity levels for up to 22 months and provide a means for zooplankton communities to rapidly respond once a wetland returns to freshwater. 5. It is likely that if the underlying causes of secondary salinisation in wetlands are addressed, it will be possible to undertake restoration activities that allow the rapid return of some components of their biotic communities.     

The effect of acid mine drainage on the hatching success of branchiopod egg banks from endorheic wetlands in South Africa

Endorheic wetlands are abundant in South Africa, and are more commonly referred to as pans. The pan environment experiences daily and seasonal fluctuations in physico-chemical conditions, caused by variable hydroperiods. Branchiopod crustaceans are a unique group of fauna which are able to survive this variability through the production of dormant egg banks. The endorheic nature of these wetlands makes them more vulnerable to anthropogenic activities. A decrease in the hatching success of branchiopods could be detrimental to the biodiversity and ecosystem functioning of these wetlands. Pans were selected from regions where increasing mining activities are a potential risk. The sediment collected from selected pans was inundated with two saline solutions of 1,000 and 1,500 mg/l, respectively, which served as controls. A third solution of decanted acid mine drainage (AMD) was used to determine hatching success with exposure to AMD. Findings showed that AMD had a negative effect on the hatching success from egg banks. Recovery experiments were performed to assess whether egg banks could recover from AMD exposure upon first inundation. Recovery rates were low and support the concern that affected wetlands will suffer a loss of biodiversity.     

Environmental exposure to uranium in a population living in close proximity to gold mine tailings in South Africa

BackgroundGold mining activities in South Africa resulted in contamination of residential environment with uranium-rich wastes from mine tailings. Health of the people living around the mine tailings could be affected by uranium exposure due to its hazardous chemotoxic and radiological properties.MethodsWe conducted a cross-sectional study to assess i) uranium (U) concentrations in individual hair samples of children and adults living in close proximity to mine tailings in Northeast- Soweto in Johannesburg, South Africa, and ii) the association between U concentrations in hair and various factors, including zone of residence, socio-demographic and housing characteristics. Sampling sites were divided into three zones based on the distance between a dwelling and a cluster of mine tailings (zone 1: <= 500 m, zone 2: 2–3 km away, zone 3: 4–5 km away). U concentrations in hair samples were measured using inductively coupled plasma mass spectrometry. To test the association between U concentrations and selected factors we used robust regression models with log-transformed U concentrations.ResultsAmong 128 subjects with available U measurements, 63 (49%) were children (ages 7–15 years) of which 38 were girls, the remaining 65 (51%) were adult females. Mean (median) U concentration in hair samples was 143 (92) µg/kg. In the mutually adjusted analyses, only an inverse association between age and U concentration in hair remained statistically significant, with geometric mean in children being 2.1 times higher compared to adults (P < 0.001). There was no evidence of an association between zones and U concentration (P = 0.42).ConclusionsThere was little evidence of association between U concentration in hair and distance from the mine tailings within the 5 km range, but overall concentrations were elevated compared to general population samples in other parts of the world. Children had statistically significantly higher geometric mean of uranium concentration in hair compared to adults. The results are important for improvement of mining waste policies and implementation of health monitoring and protective measures in populations at risk.Article categoryResearch Article     

The effects of constant and changing temperatures on the period from egg hatching to egg laying in Tanymastix stagnalis

The main duration of time from egg hatching to egg laying (D) in this anostracan crustacean increases at lower constant temperatures. The mean number of eggs per female lay between 25 and 50. In both regularly changing temperature experiments D was significantly increased (P<.05). This may be due to an increase in length of adult life which would also account for the increase in number of eggs per female to about 100. The relation of the results to the life and survival strategy of the animal in Ireland in discussed.     

Effect of incubation and preservation on resting egg hatching and mixis in the derived clones of the rotifer Brachionus plicatilis

The marine rotifer Brachionus plicatilis typicus (Clone 8105A, Univ. of Tokyo) was cultured in 500 ml beakers to form resting eggs. Tetraselmis tetrathele was used as a culture food. Just after formation, resting eggs were exposed to various temperature (5–25 °C) and light regimes (24L: OD and OL : 24D). When eggs were exposed to light just after formation, the eggs hatched sporadically over a month. No hatching was observed for six months when eggs were preserved under dark conditions regardless of the temperature. These eggs hatched simultaneously after being exposed to light and eggs preserved at 5 °C showed twice as high hatching rate (40%) as that of eggs preserved at 15–25 °C (24%). Clones from resting eggs that were kept under different temperature and light regimes were reared individually to the third generation. Incubation at 25 °C with lighting produced the highest (5.4% and 5.2 %) rate of mictic females during their 2nd and 3rd generations, respectively. The lowest rates (0 and 1.5%) were found when the eggs were kept at 5 °C in total darkness for six months. A lower rate of amictic female production was found in clones with higher rates of mixis.     

Effect of incubation temperature on the hatching of rotifer resting eggs collected from sediments

Sediment samples from Loch Leven, Scotland, were incubated at 5°C, 10°C and 15°C to induce hatching of rotifer resting eggs. The emergent animals were identified and counted. The temperature which induced hatching varied among the nine species studied. These results are discussed in relation to seasonality and temperature preferences previously recorded for the most abundant species. Resting egg densities of 2.2–13.9 eggs cm^–3 were recorded in the upper 5 cm of sediment.     

Mineralogy and geochemistry of tailings from a gold mine in northeastern Thailand

Mineralogical and geochemical characteristics of tailings from a gold mine in northeastern Thailand were investigated in relation to acid mine drainage (AMD) and the release potentials of toxic elements. The tailings can be divided into upper tailings and lower tailings. The upper tailings usually contain pyrrhotite, pyrite ± chalcopyrite, calcite, quartz, andradite and diopside. The lower tailings mainly contain goethite, quartz, chlorite, muscovite, calcite and hematite ± pyrrhotite. These assemblages clearly relate to the original types of gold deposit prior to mining and mineral processing. The upper tailings are defined as potential acid forming (PAF), whereas the lower tailings are classified as non-acid forming (NAF). Regarding heavy metals, apart from high Mn level, the other heavy metals appear to have low concentrations in the upper tailings. On the other hand, the lower tailings contain high contents of As, Cu and Pb, which appear to be higher than the National Total Threshold Limit Concentrations. Goethite, the main mineral assemblage in the lower tailings, reveals characteristic of arsenic adsorbent. As a result, the tailing pond is recommended to be covered to prevent the oxidizing processes of the upper tailings; otherwise, AMD generation may take place soon after the mine closure. Land reclamation and monitoring plans must be planned very well and carried out with great care since arsenic contamination has been reported in steam water close to the tailing dam.     

The effects of salinity on aquatic plant germination and zooplankton hatching from two wetland sediments

1. The effect of increasing salinity on the emergence of zooplankton eggs and the germination of aquatic plant seeds from the sediment of two wetlands was examined. Salinity was found to cause reductions in species richness and abundance of aquatic plants and zooplankton at salinities between 1000 and 5000 mg L^?1. Aquatic plants also had an associated decrease in above ground biomass. 2. Individual taxa showed different responses to salinity, and four response patterns were identified: (i) increased number of organisms emerging at 1000 mg L^?1; (ii) decreased number of organisms emerging above 1000 mg L^?1; (iii) decreased number of organisms emerging between 300 and 1000 mg L^?1; (iv) no difference in number of organisms emerging across the range of salinities. Response patterns (iii) and (iv) were common to both plants and zooplankton, whereas response patterns (i) and (ii) were only identified for zooplankton. 3. Results indicate that there is potential for the increasing salinity in Australian rivers and wetlands to decrease the species richness of aquatic communities resulting in loss of wetland biodiversity.     

Sex, parthenogenesis and genetic structure of rotifers: microsatellite analysis of contemporary and resting egg bank populations

Cyclically parthenogenetic rotifers are a valuable model for investigating the relationship between reproductive mode and population structure, although advances in this field have been hindered by low allozyme variability in these organisms. A high genotypic diversity is predicted after population establishment, which would be eroded by clonal selection during the parthenogenetic phase. The resting egg bank, produced sexually, is presumed to store high levels of genetic diversity, with subsequent effects on planktonic population structure. Here, we provide the first application of microsatellite markers to a rotifer planktonic population and its associated resting egg bank. Seven polymorphic microsatellite loci were screened in populations of the rotifer Brachionus plicatilis in a temporary pond to analyse: (i) the genetic structure of the resting egg bank; (ii) the changes in the genetic structure of rotifer populations during the parthenogenetic phase; and (iii) the population structure after its initiation from resting eggs. Microsatellites proved to be a useful tool for clone identification, revealing a surprisingly high clonal diversity in rotifer populations. The last sample in the parthenogenetic phase showed evidence of clonal selection, as indicated by a low observed clonal diversity and the appearance of linkage disequilibria. The resting egg bank, analysed comprehensively for the first time in any zooplankter, is in Hardy-Weinberg and linkage equilibrium, and contains a high genotypic diversity. Unexpectedly, the resting egg bank differed from the planktonic population in its allelic composition, suggesting that resting egg hatching is biased.     

Differential responses of a mine tailings Pseudomonas isolate to cadmium and lead exposures

We examined cadmium and lead resistance in Pseudomonas sp. S8A, an isolate obtained from mine tailings-contaminated soil. Resistant to soluble metal concentrations up to 200 mg l⁻¹ cadmium and 300 mg l⁻¹ lead, S8A produced both exopolymer and biosurfactant. Upon growth, this pseudomonad diverged into two morphologically distinct colony subtypes; small and round or large and flat. In the presence of lead and in the no metal control the large morphotype appeared only in late stationary phase. With cadmium the large morphotype appeared immediately following exposure. Results show that the large morphotype produced greater amounts of surfactant than the small morphotype, suggesting a unique subpopulation response to cadmium toxicity. Results also indicate that an unidentified 28 kDa protein was expressed following exposure to >10 mg l⁻¹ cadmium. This study demonstrates new links between surfactant production, differential subpopulation response and metal exposure.     

铅锌尾矿上自然定居植物

在凡口1#铅锌尾矿库内共有10种植物自然定居,这些植物主要生长在尾矿库的边缘区域.植物在尾矿上的生长、分布明显受到表层尾矿某些物理性质如稳定状况、含水量等的影响,尾矿中的营养物质含量与植物的生长高度以及群落盖度有一定的关系.杜虹花(Callicarpa pedunculata)体内的Pb、Zn、Cu和Cd含量大小顺序为叶>根>茎,而盐肤木(Rhuschinensis)和美丽胡枝子(Lespedeza