Brachionus Plicatilis Research Articles

Hyposalinity and incremental micro-zooplankton supply in early-developed Nemopilema nomurai polyp survival, growth, and podocyst reproduction

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 591:117-128 (2018) - DOI: https://doi.org/10.3354/meps12204 Hyposalinity and incremental micro-zooplankton supply in early-developed Nemopilema nomurai polyp survival, growth, and podocyst reproduction Song Feng1,2, Jianing Lin3,4, Song Sun1,2,5,6,*, Fang Zhang1,2, Chaolun Li1,2 1CAS Key Laboratory of Marine Ecology and Environmental Sciences, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, PR China 2Laboratory for Marine Ecology and Environmental Science, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, PR China 3State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, PR China 4Laboratory of Riverine Ecological Conservation and Technology, Chinese Research Academy of Environmental Sciences, Beijing 100012, PR China 5Jiaozhou Bay Marine Ecosystem Research Station, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, PR China 6University of Chinese Academy of Sciences, Beijing 100049, PR China *Corresponding author: sunsong@qdio.ac.cn‑Advance View was available online September 5, 2017; subsequently updated October 27, 2017 ABSTRACT: Early-developed polyps of the giant jellyfish Nemopilema nomurai that are sexually produced during the rainy season form the principal recruitment for benthic population stages, regulating the mass outbreaks of medusae that occur in east Asian marginal seas. Their survival, development and subsequent asexual reproduction are likely facilitated by hyposaline seawater and potentially enhanced micro-zooplankton around the estuaries that comprise the major nurseries of medusae. In this study, 8-tentacled polyps that developed from planulae were incubated at 11 salinities from low to high (8, 11, 13, 15, 18, 20, 23, 25, 28, 31, 33) with 3 feeding frequencies (once every 3 d, once every 9 d, unfed; Brachionus plicatilis concentration: 0.16 mg C l-1) at a constant temperature (19°C). Survival rate of early-developed polyps increased 3-fold at salinities 11 to 20, >80% greater than at salinities 25 to 33. The composition of fully developed polyps, somatic growth, and podocyst diameter positively depended on food supply, except at salinity 8. The potential podocyst production of polyp colonization reached normal peak at salinity 20 in the group that was fed once every 3 d. Excystments were significantly restricted at salinity <20. These findings confirm that estuarine areas with salinities from 11 to 20 are appropriate for N. nomurai polyp colonization, where prospectively increasing micro-zooplankton supply rooted in frequent eutrophication may benefit polyps. An asexual reproduction strategy also corresponded with autumn salinity fluctuations. The intensity of diluted water and monsoonal rainfall, as well as plankton supply around the estuaries in autumn may fundamentally affect polyp abundance and size, determining the population size of medusae in the following spring. KEY WORDS: Polyps · Low salinity · Survival · Growth · Podocyst reproduction Full text in pdf format PreviousNextCite this article as: Feng S, Lin J, Sun S, Zhang F, Li C (2018) Hyposalinity and incremental micro-zooplankton supply in early-developed Nemopilema nomurai polyp survival, growth, and podocyst reproduction. Mar Ecol Prog Ser 591:117-128. https://doi.org/10.3354/meps12204 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 591. Online publication date: March 19, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

Comparative ecotoxicity of polystyrene nanoparticles in natural seawater and reconstituted seawater using the rotifer Brachionus plicatilis

The impact of nanoplastics using model polystyrene nanoparticles (PS NPs), anionic (PS-COOH) and cationic (PS-NH2), has been investigated on the marine rotifer Brachionus plicatilis, a major component of marine zooplanktonic species. The role of different surface charges in affecting PS NP behaviour and toxicity has been considered in high ionic strength media. To this aim, the selected media were standardized reconstituted seawater (RSW) and natural sea water (NSW), the latter resembling more natural exposure scenarios. Hatched rotifer larvae were exposed for 24h and 48h to both PS NPs in the range of 0.5–50μg/ml using PS NP suspensions made in RSW and NSW. No effects on lethality upon exposure to anionic NPs were observed despite a clear gut retention was evident in all exposed rotifers. On the contrary, cationic NPs caused lethality to rotifer larvae but LC50 values resulted lower in rotifers exposed in RSW (LC50=2.75±0.67µg/ml) compared to those exposed in NSW (LC50=6.62±0.87µg/ml). PS NPs showed similar pattern of aggregation in both high ionic strength media (RSW and NSW) but while anionic NPs resulted in large microscale aggregates (Z-average 1109 ± 128nm and 998±67nm respectively), cationic NP aggregates were still in nano-size forms (93.99 ± 11.22nm and 108.3 ± 12.79nm). Both PDI and Z-potential of PS NPs slightly differed in the two media suggesting a role of their different surface charges in affecting their behaviour and stability. Our findings confirm the role of surface charges in nanoplastic behaviour in salt water media and provide a first evidence of a different toxicity in rotifers using artificial media (RSW) compared to natural one (NSW). Such evidence poses the question on how to select the best medium in standardized ecotoxicity assays in order to properly assess their hazard to marine life in natural environmental scenarios.

Trade-offs in rotifer diapausing egg traits: survival, hatching, and lipid content

The production of diapausing eggs is an ecological strategy commonly used by zooplanktonic organisms to cope with adverse conditions in time-varying habitats. Traits related to diapause (e.g., the time spent in diapause, the hatching fraction of diapausing eggs, or the amount of reserves allocated to them) should be combined by natural selection to favor adaptation to particular habitat conditions, especially in relation to their hydrology. Indeed, trade-offs between these traits are likely to occur due to resource allocation. Here, we studied population differentiation in survival, hatching propensity, and the amount of lipid reserves stored in diapausing eggs of the rotifer Brachionus plicatilis. We studied populations from ponds varying in hydrological conditions and used pond area as a proxy of water permanence. We found differences among B. plicatilis populations in the three traits studied, but no relationship with pond area. A significant negative relationship between diapausing egg survival in the sediment and hatching fraction was observed. We also found a negative relationship between lipid content and survival. These trade-offs are discussed in relation to the risks experienced by the rotifers in a given habitat, their ability for long-term survival, and the potential to disperse and recolonize new habitats.

Free ammonia offers algal crop protection from predators in dairy wastewater and ammonium-rich media

Cost-effective methods for protecting crops from grazing organisms like rotifers are needed to reduce the risk of pond crashes in mass algal cultures. We present a novel strategy to optimize the exposure time to free ammonia, via control of media pH, in both defined media and dairy anaerobic digester effluent to suppress rotifers and maintain algal productivity. We tested five different free ammonia exposure times (0, 1, 2, 6, and 12h) and found a significant nonlinear effect of exposure time (p<0.0001) but not pH (p>0.9) on rotifer survival. In both media types, 6–12h of elevated free ammonia significantly reduced Brachionus plicatilis rotifer survival with no negative effects on Nannochloropsis oculata, while shorter exposure times were insufficient to inhibit rotifers, leading to severe algal culture crashes. These results suggest that algal crops can be protected from rotifers, without productivity loss, by elevating free ammonia for 6 or more hours.

Interspecies Interactions Reverse the Hazard of Antibiotics Exposure: A Plankton Community Study on Responses to Ciprofloxacin hydrochloride

The ecotoxicological effects of Ciprofloxacin hydrochloride (CIP) were tested on population densities of plankton assemblages consisting of two algae (Isochrysis galbana and Platymonas subcordiformis) and a rotifer (Brachionus plicatilis). The I. galbana showed a significant decrease in densities when concentrations of CIP were above 2.0 mg L−1 in single-species tests, while P. subcordiformis and B. plicatilis were stable in densities when CIP were less than10.0 mg L−1. The equilibrium densities of I. galbana in community test increased with CIP concentrations after falling to a trough at 5.0 mg L−1, showed a completely different pattern of P. subcordiformis which decreased with CIP concentrations after reaching a peak at 30.0 mg L−1. The observed beneficial effect was a result of interspecies interactions of trophic cascade that buffered for more severe direct effects of toxicants. The community test-based NOEC of CIP (2.0 mg L−1), embodying the indirect effects, was different from the extrapolated one derived by single-species tests (0.5 mg L−1), but all lacked confidence interval. A CIP threshold concentration of obvious relevance to ecological interaction was calculated with a simplified plankton ecological model, achieving a value of 1.26 mg L−1 with a 95% bootstrapping confidence interval from 1.18 to 1.31 mg L−1.

Toxic effects of combined effects of anthracene and UV radiation on Brachionus plicatilis

Anthracene is a typical polycyclic aromatic hydrocarbon, with photo activity, can absorb ultraviolet light a series of chemical reactions, aquatic organisms in the ecosystem has a potential light induced toxicity. In this paper, the effects of anthracene and UV radiation on the light-induced toxicity of Brachionus plicatilis were studied. The main methods and experimental results were as follows: (1) The semi-lethal concentration of anthracene in UV light was much lower than that in normal light, The rotifers have significant light-induced acute toxicity. (2) Under UV irradiation, anthracene could induce the increase of ROS and MDA content in B. plicatilis, and the activity of antioxidant enzymes in B. plicatilis significantly changed, Where SOD, GPx activity was induced within 24 hours of the beginning of the experiment. And the content of GPX and CAT was inhibited after 48 hours. Therefore, the anthracite stress induced by UV radiation could more strongly interfere with the ant oxidative metabolism of B. plicatilis, and more seriously cause oxidative damage, significant light-induced toxicity.

Empirical evidence for fast temperature-dependent body size evolution in rotifers

Organisms tend to decrease in size with increasing temperature by phenotypic plasticity (the temperature-size rule; ectotherms) and/or genetically (Bergmann’s rule; all organisms). In this study, the evolutionary response of body size to temperature was examined in the cyclically parthenogenetic rotifer Brachionus plicatilis. Our aim was to investigate whether this species, already known to decrease in size with increasing temperature by phenotypic plasticity, presents a similar pattern at the genetic level. We exposed a multiclonal mixture of B. plicatilis to experimental evolution at low and high temperature and monitored body size weekly. Within a month, we observed a smaller size at higher temperature, as compared to body size at lower temperature. The pattern was consistent for the size of both mature females and eggs; rotifers kept at high temperature evolved to be on average 14% (after 2 weeks) and 3% (after 3 weeks) smaller than the ones kept at low temperature (10 and 5% in the case of eggs, respectively). We therefore found that B. plicatilis is genetically programmed to adjust its body size-to-environmental temperature.

Potential use of an ultrasound antifouling technology as a ballast water treatment system

The aim of this study was to investigate, at a laboratory scale, the potentialities of an ultrasound-based treatment initially designed to eliminate fouling, as a ballast water treatment system. Therefore, early life stages of three different zooplanktonic species (Amphibalanus amphitrite, Brachionus plicatilis and Artemia salina) were exposed to ultrasound waves (20–22kHz). The experimental set up included static assays with variations of time exposure (30s, 60s and 30s on/60s off/30s on), material of tanks (stainless steel, galvanized steel and plastic) and position of the ultrasound source. Results showed that the treatment efficacy increased from 30 to 60s and no differences were registered between 60s-continuous exposure and pulse exposure. The highest efficacy was observed in Experiment I (metal-to-metal contact assay) with a mortality value of 93–95% for B. plicatilis and A. salina. It consisted of organisms located inside stainless steel tubes that were located in direct contact with the ultrasound source and treated for 60s. Further, we found that, generally, A. amphitrite and B. plicatilis were the most resistant species to the ultrasound treatment whereas A. salina was the most sensitive. We further discuss that US may unlikely be used for commercial vessels, but may be used to treat ballast water in smaller ballast tanks as on board of mega yachts.

Identification of 28 cytochrome P450 genes from the transcriptome of the marine rotifer Brachionus plicatilis and analysis of their expression

Whole transcriptomes of the rotifer Brachionus plicatilis were analyzed using an Illumina sequencer. De novo assembly was performed with 49,122,780 raw reads using Trinity software. Among the assembled 42,820 contigs, 27,437 putative open reading frame contigs were identified (average length 1235bp; N50=1707bp). Functional gene annotation with Gene Ontology and InterProScan, in addition to Kyoto Encyclopedia of Genes and Genomes pathway analysis, highlighted the metabolism of xenobiotics by cytochrome P450 (CYP). In addition, 28 CYP genes were identified, and their transcriptional responses to benzo[α]pyrene (B[α]P) were investigated. Most of the CYPs were significantly upregulated or downregulated (P<0.05) in response to B[α]P, suggesting that Bp-CYP genes play a crucial role in detoxification mechanisms in response to xenobiotics. This study sheds light on the molecular defense mechanisms of the rotifer B. plicatilis in response to exposure to various chemicals.

Haemolytic activity and reactive oxygen species production of four harmful algal bloom species

Based on haemolytic activity and reactive oxygen species (ROS) production of Chattonella marina, Chattonella antiqua, Heterocapsa circularisquama, Alexandrium tamiyavanichii and Karenia mikimotoi, the species were categorized into four types. (1) H. circularisquama: haemolytic activity was detected in both cell suspension and cell-free culture supernatant, but with greater activity in cell suspension than in the supernatant suggesting the presence of both cell surface and secreted haemolytic agents. (2) A. tamiyavanichii: equal haemolytic activities were detected in both the cell suspension and cell-free culture supernatant suggesting the presence of only secreted haemolytic agents. (3) K. mikimotoi: haemolytic activity was detected only in the cell suspension, indicating haemolytic agents occur only on the cell surface. (4) C. marina and C. antiqua: no significant haemolytic activity was detected in either cell suspension or cell-free culture supernatant, but high ROS were detected in the cell suspensions. Heterocapsa circularisquama and K. mikimotoi showed lethal effects on rotifers (Brachionus plicatilis), whereas A. tamiyavanichii, C. marina and C. antiqua had no effect. Our results suggest that H. circularisquama, K. mikimotoi and A. tamiyavanichii produce haemolytic agents with distinct characteristics, whereas C. marina and C. antiqua have an extremely potent ability to produce ROS.

Experimental evolution of bet hedging in rotifer diapause traits as a response to environmental unpredictability

The adaptive response of organisms to unpredictable environments is increasingly recognized as a central topic in fundamental and applied evolutionary ecology. Selection due to environmental unpredictability can act on multiple traits of an organism's life cycle to reduce the impact of high environmental variance. The aim of this research was to study how unpredictability selects for diapause traits: 1) the timing of sex (a proxy of the timing of diapausing egg production), and 2) the diapausing egg hatching fraction (a proxy of diapause duration). We used an experimental evolution approach with the facultative sexual rotifer Brachionus plicatilis. Laboratory populations experiencing two contrasting regimes of environmental fluctuation (predictable versus unpredictable) evolved divergently over a short time span (&lt; 77 days). The populations under the unpredictable regime showed an earlier initiation of sexual reproduction and a lower hatching fraction of diapausing eggs than populations under the predictable regime. These findings demonstrate empirically the existence of bet‐hedging strategies in B. plicatilis regarding both traits, consistent with theoretical predictions of bet‐hedging evolution under conditions of unpredictable environmental variance. Given that scenarios of increased environmental variability are expected to occur in the near future, a comprehensive understanding of the role of bet‐hedging strategies is necessary for predicting population responses to environmental change.

Isolation mediates persistent founder effects on zooplankton colonisation in new temporary ponds

Understanding the colonisation process in zooplankton is crucial for successful restoration of aquatic ecosystems. Here, we analyzed the clonal and genetic structure of the cyclical parthenogenetic rotifer Brachionus plicatilis by following populations established in new temporary ponds during the first three hydroperiods. Rotifer populations established rapidly after first flooding, although colonisation was ongoing throughout the study. Multilocus genotypes from 7 microsatellite loci suggested that most populations (10 of 14) were founded by few clones. The exception was one of the four populations that persisted throughout the studied hydroperiods, where high genetic diversity in the first hydroperiod suggested colonisation from a historical egg bank, and no increase in allelic diversity was detected with time. In contrast, in another of these four populations, we observed a progressive increase of allelic diversity. This population became less differentiated from the other populations suggesting effective gene flow soon after its foundation. Allelic diversity and richness remained low in the remaining two, more isolated, populations, suggesting little gene flow. Our results highlight the complexity of colonisation dynamics, with evidence for persistent founder effects in some ponds, but not in others, and with early immigration both from external source populations, and from residual, historical diapausing egg banks.

Inclusion of copepod Acartia tonsa nauplii in the feeding of Centropomus undecimalis larvae increases stress resistance

This research represents the first result of studies of the common snook Centropomus undecimalis larvae from broodstock matured in captivity in Brazil. The aim of this study was to evaluate if the inclusion of Acartia tonsa nauplii improves stress resistance of common snook larvae. The larvae were fed with: rotifers Brachionus plicatilis (10 to 15 mL-1); A. tonsa nauplii (0.25 to 0.5 mL-1) and rotifers (5 to 7.5 mL-1), and A. tonsa nauplii (0.12 to 0.25 mL-1). The average percentage of survival of the treatments was 11.9%. At 20 days of age, larvae were subjected to thermal stress. Subsequently, the stress resistance was evaluated. Common snook larvae fed B. plicatilis+A. tonsa reached a higher weight and length (7.5 ± 0.00 mg and 9.1 ± 0.23 mm, respectively) and resisted more heat stress (87.4%) than larvae fed other foods, indicating that the feed mixture is satisfactory as a starter diet for larvae of common snook. However, more research is needed to confirm these results.

Growth inhibitory and antifeedant effects of sublethal concentrations of toosendanin on the rotifer Brachionus plicatilis

Toosendanin has been suggested as a potential agent for controlling zooplankton contamination in microalgal cultivation. Growth inhibitory and antifeedant influences of toosendanin on the rotifer Brachionus plicatilis were investigated. Sublethal concentrations of toosendanin (1.76–2.59 mg m−3) reduced population abundance of rotifers, decreased the lorica length and width, and shrank the body size of survivors notably. No changes were observed in the amictic egg sizes, although the egg production per female rotifer was decreased by toosendanin. Exposure to toosendanin for 4 h significantly decreased the rotifer chlorophyll consumption per individual, indicating the antifeedant effect on rotifers. Analysis on the digestive enzymes showed that exposure to toosendanin had no effect on cellulose activity, but reduced the activities of diastase, pepsase and tryptase in rotifer homogenate. In addition, the half-saturation constant (Km) of tryptase was increased and the maximum velocity (Vmax) of pepsase was decreased by toosendanin, suggesting the direct inhibition of these two proteases by toosendanin in B. plicatilis. This may contribute to the feeding deterrent property of toosendanin on rotifers. The present study heralds the very beginning of studies regarding the toxic mechanism of toosendanin on rotifers, and will accelerate its potential uses for zooplankton extermination in microalgal cultivation.

Performance of Debaryomyces hansenii as a Diet for Rotifers for Feeding Zebrafish Larvae.

The zebrafish larval stage is a critical moment due to high mortality rates associated with inadequate supplies of nutritional requirements. Larval feeding has important challenges associated with such factors as small mouth gape (≈100 μm), the low activity of digestive enzymes, and the intake of live food. A common zebrafish live food at the onset of exogenous feeding is rotifers, mainly Brachionus plicatilis. These rotifers should be fed with other microorganisms such as microalgae or yeast, mostly from the Saccharomyces genus. In the laboratory, the culture of microalgae is more expensive than the culture of yeast. The aim of this study was to evaluate the performance of Debaryomyces hansenii as a diet for rotifers in comparison to a microalgae-based diet (Rotigrow®). To achieve this aim, we assessed the rotifer total protein content, the rotifers fatty acid profile, zebrafish larval growth performance, the expression of key growth, and endocrine appetite regulation genes. The total protein and fatty acids content were similar in both rotifer cultures, averaging 35% of dry matter (DM) and 18% of DM, respectively. Interestingly, the fatty acids profile showed differences between the two rotifer cultures: omega-3 fatty acids were only observed in the Microalgae/rotifer, whereas, omega-6 fatty acids presented similar levels in both rotifer cultures. No differences were observed in the larval body length distribution or mortalities between the rotifer cultures. However, gh, igf-1, and cck gene expression showed significantly higher upregulation in zebrafish fed the Microalgae/rotifer diet compared with those fed the Debaryomyces/rotifer diet. In conclusion, D. hansenii could be an alternative diet for rotifer used as a live food in zebrafish larvae at the onset of exogenous feeding. The gene responses observed in this work open up the opportunity to study the effect of omega-3 supply on growth regulation in zebrafish.

Plankton community and the relationship with the environment in saline lakes of Onon-Torey plain, Northeastern Mongolia.

The plankton community of sixteen saline lakes located on Onon-Torey plain (Northeastern Mongolia) during the filling phase and the raising of the water level was investigated in July 2011. Thirty-five taxa of phytoplankton and thirty-one species of zooplankton were found. For phytoplankton, blue-green algae (Merismopedia elegans, Anabaenopsis elenkinii, Arthrospora fusiformis, Spirulina major, Lyngbya sp., Oscillatoria sp.) and green algae (Monoraphidium minutum, Tetrastrum komarekii, Ankyra ocellata, Oocystis sp.) were dominant. For zooplankton, Filinia longiseta, Brachionus plicatilis, B. variabilis, Hexarthra mira (Rotifera), Daphnia magna, Moina brachiata, M. mongolica (Cladocera), Arctodiaptomus bacillifer, Mixodiaptomus incrassatus, Metadiaptomus asiaticus (Copepoda) dominated. Mineralization, active hydrogen ratio, dissolved oxygen and water temperature were the main factors influencing the diversity, structure and distribution of plankton organisms in the steppe lakes during low water level. The RDA analysis for phytoplankton and zooplankton from different lakes was carried out for selected two groups which included lakes and a subset related species. The first group is of oligohaline and mesohaline lakes in which mostly green algae, rotifers and copepods inhabit. The second group is of mesohaline and polyhaline lakes with mainly blue-green algae, some crustaceans and rotifers inhabiting. High abundance and biomass of Spirulina major, Oscillatoria sp. and Brachionus variabilis were observed in lakes with high mineralization, pH and temperature.

Metal stress in zooplankton diapause production: post-hatching response.

Aquatic organisms commonly respond to harsh conditions by forming diapausing stages, which enable populations to survive adverse periods forming egg banks. Production of diapausing eggs is frequently observed in monogonont rotifers, previously changing from asexual to partial sexual reproduction (mixis). In despite that zooplankton are frequently used in ecotoxicological assessment because of their sensitivity to various toxicants and their important role in the ecosystems, toxicity evaluations often consider the directly exposed population produced by parthenogenetic reproduction, exclusively. We assessed experimentally effects of exposure to metals on mixis delay and fitness of hatchlings of the rotifer Brachionus plicatilis obtained from a brackish water lagoon with high metal content, especially copper. We show that sub-lethal concentrations of copper affected traits related to sexual reproduction and diapausing egg production in the rotifer. Copper addition did not delay the start of mixis, suggesting that rapid initiation of mixis is promoted in risky environments, according to the hypothesis of mixis as an escape strategy. Higher investment in mixis was obtained when individuals were exposed to metal. Addition of copper negatively affected the hatching success of diapausing eggs and performance of hatchlings. Nevertheless, these effects were greater for individuals formed in non-metal conditions, suggesting an adaptive advantage of populations from natural sediments exposed to copper. These results highlight the ecological and evolutionary consequences of the presence of metals in freshwater environments by modulating diapause adaptive efficacy and the selective process in egg banks.

Responses of the rotifer Brachionus plicatilis to flame retardant (BDE-47) stress

A series of short-term toxicological tests were conducted on the rotifer Brachionus plicatilis to assess the toxicity of the flame retardant 2,2′,4,4′-tetrabrominated biphenyl ether (BDE-47). BDE-47 increased mortality, morphological damage, and altered population dynamics and fecundity of rotifer. Antioxidant enzymes were differentially changed to maintain the balance between antioxidant and pro-oxidant activity. However, with increases in the concentration of BDE-47, the metabolic and antioxidant activity decreased. Moreover, the reactive oxygen species (ROS) and malondialdehyde contents increased and the ratio between glutathione and glutathione-SH decreased, indicating oxidative stress. The addition of the ROS-inhibitor N-acetylcysteine alleviated the degree of damage and stimulated the activity of xenobiotic-metabolizing and antioxidant system, which suggested that ROS were the most important loop in the stress response.

Impact of water input on plankton temporal dynamics from a managed shallow saline lake

La Salada is a shallow saline lake located in the SW of the Pampas subject to significant water management, so the primary objective was to assess whether the water input and physicochemical parameters have an impact on the plankton assemblages over a two year period (2013–dry and 2014–wet). The plankton community structure and physicochemical variables showed substantial changes over the study period. La Salada hosted a plankton community characterized by low diversity and small sized organisms. The nanoplanktonic fraction organisms (2–20 μm) dominate the phytoplankton community. Ochromonas sp. showed the maximum abundance throughout the whole study period. The zooplankton community was dominated by rotifers, with a lack of cladocerans. Halotolerant species, e.g. the rotifer Brachionus plicatilis and the cyclopod Apocyclops sp. were the main species. The seasonal temperature and conductivity dynamics influence the plankton abundance dynamics in La Salada. The increment of nutrients and decrease of conductivity caused by the water input led to an increase in plankton biomass and shaped its composition. These findings emphasize that interactions between plankton, salinity, and nutrients are sensitive to the water input and they improve the understanding of the impact of adequate management decisions.

Use of commercial probiotics for the improvement of water quality and rotifer density in outdoor mass culture tanks

An experimental study was carried out to evaluate the efficacy of three commercially available probiotics P1, P2 and P3 consisting of mainly Bacillus spp. and nitrifying bacteria against Vibrio loads in mass culture tanks of the rotifer Brachionus plicatilis. Triplicate tanks were maintained for each of the probiotic treatment as well as for control group. All the tanks were inoculated with 50 rotifers ml-1 and were fed with Nannochloropsis oculata at a density of 1 x 107 cells ml-1. Every alternate day, all the experimental tanks were treated with probiotics at a concentration of 1 x 104 cfu ml-1 and the experiment was carried out for one week. The study showed a significant increase in rotifer density (p&lt;0.05) in all the tanks treated with the probiotics and a maximum density of 400 nos. ml-1 was observed in the tanks treated with P3. After 5th and 6th day of culture, total elimination of Vibrios was also recorded in the tanks treated with P3 and P2 respectively. The study revealed that P3, with a combination of Bacillus, Thiobacillus, Acetobacter and Paracoccus supplemented with enzymes, was found to be most effective in the enhancement of rotifer density and also in the elimination of Vibrios in rotifer mass culture tanks.