Protozoan communities in chalk streams

This study assessed the individual effects of three mayflies (Paraleptophlebia sp., Ephemerella subvaria McDunnough and Epeorus sp.) and one caddisfly (Psilotreta sp.) on periphyton communities associated with clay tiles and leaves. Algal densities were estimated for leaf discs and tiles from experimental chambers (with individual grazers) and control chambers (i.e., no grazers). Scanning electron micrographs (SEM) of leaf discs and tiles also were taken for all mayfly grazing experiments. Densities of algae on leaf discs were two to five times lower than on tiles. Mouthpart morphology influenced how different insects grazed the periphyton community. Paraleptophlebia had typical collector-gatherer mouthparts and had no effect on diatom densities associated with leaves whereas diatom densities on grazed tiles were higher than densities on tiles from control chambers. Epeorus had brusher mouthparts and had little impact on diatom densities regardless of substratum type. The other two grazers had the blade-like mandibles of a scraper. Psilotreta did not reduce the numerical abundance of diatoms on either substratum, but did alter community structure by significantly reducing densities of stalked Gomphonema olivaceum and large species of Navicula and Nitzschia; densities of smaller diatoms (Achnanthes spp) increased. However, E. subvaria reduced densities of most algal species regardless of size on both substrata and also significantly altered community structure. SEMs of substrata grazed by mayflies showed reductions in fungal hyphae on all grazed leaf discs, decreases in filamentous algal forms on grazed tiles, and greatly shortened stalks of G. olivaceum (Paraleptophlebia only). Thus, periphyton communities are different on leaves versus tiles and grazers with different mouthpart morphologies have varying effects on both algal and heterotrophic microbial community structure.     

Ciliated Protozoan communities in a fluvial ecosystem

The ciliated protozoan communities in the Llobregat River (Barcelona, Spain) were studied for one year. Samples were taken from 11 different stations. The physical-chemical factors of the water as well as the qualitative and quantitative nature of the ciliate populations were considered. 105 species of ciliates, grouped in 13 orders, were found.The species which constantly appeared at all 11 stations (although not every month) were Litonotus fasciola, Trithigmostoma cucullulus, Cyclidium glaucoma, Glaucoma scintillans, Vorticella microstoma, Oxytricha sp., Stylonychia mytilus, Aspidisca costata and Aspidisca lynceus. The index of diversity at the different stations, and the affinity between the most abundant species, were also determined.     

Effect of wall shear rate on biofilm deposition and grazing in drinking water flow chambers

The effect of four-wall shear rates (34.9, 74.8, 142.5, and 194.5 s(-1)) on bacterial deposition on glass slides in drinking water flow chambers was studied. Biofilm image acquisition was performed over a 50-day period. Bacterial accumulation and surface coverage curves were obtained. Microscopic observations allowed us to obtain information about the dynamics and spatial distribution of the biofilm. During the first stage of biofilm formation (210-518 h), bacterial accumulation was a function of the wall shear rate: the higher the wall shear rate, the faster the bacterial deposition (1.1 and 1.9 x 10(4) bacterial cells . cm(-2) for wall shear rates of 34.9 and 142.5 s(-1), respectively). A new similarity relationship characteristic of a non-dimensional time and function of the wall shear rate was proposed to describe initial bacterial deposition. After 50 days of exposure to drinking water, surface coverage was more or less identical under the entire wall shear rates (7.44 +/- 0.9%), suggesting that biofilm bacterial density cannot be controlled using hydrodynamics. However, the spatial distribution of the biofilm was clearly different. Under low wall shear rate, aggregates were composed of bacterial cells able to "vibrate" independently on the surface, whereas, under a high wall shear rate, aggregates were more cohesive. Therefore, susceptibility to the hydraulic discontinuities occurring in drinking water system may not be similar. In all the flow chambers, significant decreases in bacterial biomass (up to 77%) were associated with the presence of amoebae. This grazing preferentially targeted small, isolated cells.     

Amoebic grazing of freshwater Synechococcus strains rich in phycocyanin

Fifteen strains of naked amoebae were presented with 19 strains of Synechococcus on an agar surface. After 14 days of incubation, each of the 285 combinations yielded one of three responses. 42.1% of combinations showed clearing (digestion) of the Synechococcus (C), 56.5% of combinations showed no clearing of the Synechococcus (N) while 1.4% of combinations showed partial clearing of the Synechococcus (P). In general, the Synechococcus strains showed variability in their susceptibility to digestion by the amoebae and the amoebae showed variability in their ability to digest the Synechococcus strains. There was no evidence for amoebae actively selecting profitable prey and equivalent-sized Synechococcus strains were ingested at the same rate, irrespective of their fate. There was some evidence of 'size-selective' grazing in that amoebae ingested the smaller Synechococcus strains at higher rates than the larger strains. However, there was no correlation between prey size and their ultimate fate. These data suggest that amoebae are not selective with regard to the ingestion of synechococci, but that 'selection' occurs at the digestion stage, i.e. whether the synechococci are digested or not.     

三门湾浮游动物的季节变动及微型浮游动物摄食影响

2002年8月、11月、2003年2月和5月,在三门湾进行了4个航次生物、化学和水文等专业综合调查。根据采集的浮游动物样品的分析鉴定及海上现场实验结果,对浮游动物的群落组成、生物量、丰度、多样性指数的分布和季节变动及其浮游动物对浮游植物的摄食影响进行研究。结果表明,三门湾浮游动物有67属,89种,16类浮游幼体,主要可划分为4个生态类群：以近岸低盐类群为主,其优势种为中华哲水蚤Calanus sinicus、真刺唇角水蚤Labidocera etwhaeta、捷氏歪水蚤Tortanus derjugini、太平洋纺锤水蚤Acartiapacifica、中华假磷虾Pseudeuphausia sinica和百陶箭虫Sagitta bedoti等。半咸水河口类群、暖水性外海类群和广布种相对较少。浮游动物生物量和丰度的平面分布趋势除了夏季有所差异外,其它季节基本一致。2月份和5月份,浮游动物生物量和丰度,从湾顶向湾口呈逐渐增加趋势;8月份,湾口区生物量最高,而丰度高值区出现在湾顶部;11月份,生物量和丰度的平面分布相对均匀。浮游动物种类多样性指数有明显的季节变化,其动态变化与浮游动物种数和丰度的变化一致。微型浮游动物对浮游植物存在摄食压力,且有季节变化,摄食率的变化在0．18．0．68d^-1,微型浮游动物的摄食率低于相同季节的浮游植物生长率。微型浮游动物对浮游植物摄食压力的变化范围为16．1％-49．1％d^-1,对初级生产力摄食压力的变化在58．3％-83．6％d^-1。11月份,微型浮游动物对浮游植物和初级生产力的摄食压力均出现最高值。     

管理措施对牧鸡生长性能及草地蝗虫数量的影响

蝗灾作为威胁草地生态系统的主要灾害之一,给草地畜牧业发展带来严重影响,如何经济、有效和安全抑制蝗虫数量显得尤为紧迫。通过野外调查就草地牧鸡放牧强度、补饲量以及放牧方式对牧鸡生长性能和蝗虫发生数量的影响进行探讨。结果发现,高山草地利用牧鸡放牧可有效控制蝗虫发生数量,长期连续牧鸡捕食能有效将蝗虫数量控制在经济阈值之下;不同放牧强度(15只/hm2和13只/hm2)和补饲程序对蝗虫种群数量没有显著差异,但对牧鸡生长性能有明显影响;自由放牧和限时放牧均能控制蝗虫数量,但限时放牧牧鸡日增重和最终活重均高于自由放牧。综合防治蝗虫和养育牧鸡来看,每公顷草场初次放牧15只牧鸡,限时放牧和适当增加补饲量可达到控制蝗虫和获得较高禽肉生产之双赢目的。     

Molecular Size and Chain Length Distribution in Acanthamoeba Cellulose*

SYNOPSIS Evidence obtained by total hydrolysis, partial acetolysis, periodate oxidation, as well as treatment with amylase, emulsin, and Trichoderma virideβ-(1→4)-glucanase, verified that the alkali insoluble component of Acanthamoeba castellanii was pure β-(1→4)-glucan. The weight average chain length of the cellulose varied from DP = 3170 to DP = 4130 (mean DP = 3480) with polysaccharide obtained from seven seemingly identical cultures. Isolation of the cyst-wall cellulose by nondegrading means indicated that alkali extraction was not depolymerizing the polysaccharide. Fractionation of cellulose obtained from a single culture produced fractions from DP = 550 to DP = 4550 (mean DP = 3280; 98.7% of the original cellulose), indicating that the cellulose is polydisperse.     

Seasonal dynamics of zooplankton and grazing impact of microzooplankton on phytoplankton in Sanmen Bay, China

The species composition, biomass, abundance and species diversity of zooplankton were determined for samples collected from 12 stations in Sanmen Bay, China, in four cruises from August 2002 to May 2003. Growth of phytoplankton and grazing rates of microzooplankton were measured using the dilution technique. The spatial and temporal variation of zooplankton and its relationship with environmental factors were also analyzed. The results showed that a total of 89 species of zooplankton belonging to 67 genera and 16 groups of pelagic larvae were found in Sanmen Bay. The coastal low-saline species was the dominant ecotype in the study area, and the dominant species were Calanus sinicus, Labidocera euchaeta, Tortanus derjugini, Acartia pacifica, Pseudeuphausia sinica and Sagitta bedoti. Maximum biomass was recorded in August, followed by November and May, and the lowest biomass was recorded in February. Similarly, the highest abundance of zooplankton was observed in August, followed by May, November, and February. Grazing pressure of microzooplankton on phytoplankton in Sanmen Bay existed throughout the year, although the grazing rate of microzooplankton on phytoplankton varied with the season. Estimates for growth rate of phytoplankton ranged from 0.25 d^?1 to 0.89 d^?1, whereas grazing rate of microzooplankton ranged between 0.18 d^?1 and 0.68 d^?1 in different seasons. The growth rate of phytoplankton exceeded the grazing rate of microzooplankton in all the seasons. Grazing pressure of microzooplankton on phytoplankton ranged from 16.1% d^?1 to 49.1% d^?1, and the grazing pressure of microzooplankton on primary production of phytoplankton ranged from 58.3% d^?1 to 83.6% d^?1 in different seasons.     

Seasonal dynamics of zooplankton and grazing impact of microzooplankton on phytoplankton in Sanmen Bay, China

The species composition, biomass, abundance and species diversity of zooplankton were determined for samples collected from 12 stations in Sanmen Bay, China, in four cruises from August 2002 to May 2003. Growth of phytoplankton and grazing rates of microzooplankton were measured using the dilution technique. The spatial and temporal variation of zooplankton and its relationship with environmental factors were also analyzed. The results showed that a total of 89 species of zooplankton belonging to 67 genera and 16 groups of pelagic larvae were found in Sanmen Bay. The coastal low-saline species was the dominant ecotype in the study area, and the dominant species were Calanus sinicus, Labidocera euchaeta, Tortanus derjugini, Acartia pacifica, Pseudeuphausia sinica and Sagitta bedoti. Maximum biomass was recorded in August, followed by November and May, and the lowest biomass was recorded in February. Similarly, the highest abundance of zooplankton was observed in August, followed by May, November, and February. Grazing pressure of microzooplankton on phytoplankton in Sanmen Bay existed throughout the year, although the grazing rate of microzooplankton on phytoplankton varied with the season. Estimates for growth rate of phytoplankton ranged from 0.25 d⁻¹ to 0.89 d⁻¹, whereas grazing rate of microzooplankton ranged between 0.18 d⁻¹ and 0.68 d⁻¹ in different seasons. The growth rate of phytoplankton exceeded the grazing rate of microzooplankton in all the seasons. Grazing pressure of microzooplankton on phytoplankton ranged from 16.1% d⁻¹ to 49.1% d⁻¹, and the grazing pressure of microzooplankton on primary production of phytoplankton ranged from 58.3% d⁻¹ to 83.6% d⁻¹ in different seasons.     

Protozoan and metazoan communities treating a simulated petrochemical industry wastewater in a rotating disc biological reactor

The microfauna of adhered biofilms treating a simulated petrochemical plant wastewater was investigated in relation to the organic loading and the toxicity. Experiments in a six-compartment laboratory rotating biological reactor were performed at organic loadings of 0.99, 1.38 and 1.97g/l.day. The concentration of organic compounds in the artificial wastewater (phenol, acetophenone and styrene), toxicity of the wastewater, number of representative types of microfauna, their biomass and species diversity were monitored along the reactor. During this study 25 species were identified and attributed to seven classes of the three types Sarcomastigophora, Ciliophora and Nemathelminthes. Eight species from 18 ciliates have been reported in the literature as being commonly found inhabitants of aerobic wastewater treatment plants. An inverse relationship between the number of microfauna representatives and the organic loading was found. The presence of the most common species was related to the reactor operating conditions. A correlation between the toxicity of the wastewater measured by the Paramecium express-test and the distribution and abundance of microfauna was established. This express-test made it possible to predict the biological quality of the biofilm of activated sludge. Therefore, it is recommended as one of the control parameters to monitor systems of biological wastewater treatment.     

不同放牧强度对荒漠草原蝗虫群落的影响

采用无底样框法对四子王旗荒漠草原不同放牧强度下的蝗虫群落进行了取样调查,比较了不同放牧强度下荒漠草原蝗虫群落的丰富度、多样性和均匀度指数及群落中蝗虫种类和数量随季节的动态变化,并对蝗虫种群分布与植物群落特征进行了相关性分析。结果表明,在不同放牧强度下蝗虫的群落结构及时间动态均存在一定差异,说明放牧活动对蝗虫群落结构有明显影响,其中,轻度放牧和重度放牧样地中蝗虫种群总数显著高于其他样地。不同种类的蝗虫群落与放牧强度之间关系表现复杂。     

Modelling epilithic biofilms combining hydrodynamics,invertebrate grazing and algal traits

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The Cell Cycle and Induced Amitosis in Acanthamoeba*

The small soil ameba, Acanthamoeba castellanii strain HR, with a mean generation time of 18 hr in axenic culture, requires 24 min for nuclear mitosis. This is followed immediately by nuclear DNA synthesis that is initiated in late telophase and lasts for 20 min. Evidence is presented that amitosis can be induced in susceptible amebas only during a portion of the cell cycle.     

Stratification and dynamics of microbial loop communities in Lake Fryxell, Antarctica

1. Lake Fryxell, situated in the McMurdo Dry Valleys, Antarctica, offers the opportunity to study microbial loop processes in the absence of crustacean zooplankton and other higher organisms. This is the first study of Lake Fryxell to provide detailed temporal and vertical variations of microbial loop organisms.
2. Protozoan communities are concentrated around the chemocline (9–10 m) in Lake Fryxell. Phototrophic nanoflagellates (PNAN), heterotrophic nanoflagellates (HNAN) and ciliates formed deep maxima of 14 580, 694 and 58 cells mL−1 respectively. Although abundance and biomass at the chemocline was high, diversity of protozoa was low, Plagiocampa accounting for> 80% of the total ciliate biomass.
3. In the mixolimnion (4.5–8 m), protozoa were less abundant, but more diverse, with 24 ciliate morphotypes being identified within this region of the water column. Inter-annual variability of protozoan biomass and abundance was greater in the mixolimnion than at the chemocline due to more variable nutrient and prey concentrations.
4. Physicochemical gradients in Lake Fryxell were very stable because the perennial ice cover reduced wind driven currents. As a consequence, ciliate species occurred in distinct depth strata, Monodinium being most abundant directly beneath the ice cover, Askenasia having maximum abundance at 8 m and Plagiocampa dominating ciliate biomass at the chemocline. The lack of vertical mixing reduced seasonal successions of PNAN and ciliate species. Three cryptophyte species dominated the PNAN community at all times (>79% of total biomass).     

细菌生物被膜基质的研究进展

细菌生物被膜(biofilm)附着在生物或者非生物表面,由细菌及其分泌的糖、蛋白质和核酸等多种基质组成的细菌群落,是造成病原细菌持续性感染、毒力和耐药性的重要原因之一.细菌的生物被膜基质由复杂的胞外聚合物(extracellular polymeric substances,EPS)构成,影响生物被膜的结构和功能.本文...     

The green alga Dicytosphaeria ocellata and its organic extracts alter natural bacterial biofilm communities

Surfaces immersed in the marine environment are under intense fouling pressure by a number of invertebrates and algae. The regulation of this fouling can often be attributed to the bacterial biofilm that quickly develops on the surface of any available substratum in the ocean. The bacterial community composition on the surface of the green alga Dictyosphaeria ocellata was investigated and compared to those found on two other green algae, Batophora oerstedii and Cladophoropsis macromeres, and on a reference surface from three sites along the Florida Keys. Although the bacterial community composition of D. ocellata was not consistent across the sites, it was significantly different from the other algae and the reference surface at two of the three sites tested. Methanol extracts of D. ocellata significantly affected the abundance of bacteria and composition of the bacterial community on Phytagel? plates when compared to solvent controls, suggesting that the alga regulates the bacterial community by producing active metabolites.     

Nutrient dynamics and successional changes in a lentic freshwater biofilm

SUMMARY 1. Colonisation, species composition, succession of microalgae and nutrient dynamics in biofilms grown under light and dark conditions were examined during the initial phases of biofilm development in a lentic freshwater environment.
2. Biofilms were developed on inert (perspex) panels under natural illuminated and experimental dark conditions and the panels were retrieved for analysis after different incubation periods. Analysed parameters included biofilm thickness, algal density, biomass, chlorophyll a , species composition, total bacterial density and nutrients such as nitrite, nitrate, phosphate and silicate.
3. Biofilm thickness, algal density, biomass, chlorophyll a and species richness were significantly higher in light-grown biofilms, compared with dark-grown biofilms. The light-grown biofilms showed a three-phased succession pattern, with an initial domination of Chlorophyceae followed by diatoms (Bacillariophyceae) and finally by cyanobacteria. Dark-grown biofilms were mostly dominated by diatoms.
4. Nutrients were invariably more concentrated in biofilms than in ambient water. Nutrient concentrations were generally higher in dark-grown biofilms except in the case of phosphate, which was more concentrated in light-grown biofilms. Significant correlations between nutrients and biofilm parameters were observed only in light-grown biofilms.
5. The N : P ratio in the biofilm matrix decreased sharply in the initial 4 days of biofilm growth; ensuing N-limitation status seemed to influence biofilm community structure. The N : P ratios showed significant positive correlations with the chlorophycean fraction in both light and dark-grown biofilms, and low N : P ratio in the older biofilms favoured cyanobacteria. Our data indicate that nutrient chemistry of biofilm matrix shapes community structure in microalgal biofilms.     

乐清湾浮游动物的季节变动及摄食率

2002年8月、11月、2003年2月和5月,在乐清湾进行了4个航次生物、化学和水文等专业综合调查。根据采集的浮游动物样品的分析鉴定及海上现场实验结果,对浮游动物的群落组成、生物量、丰度、多样性指数的分布和季节变动及其浮游动物对浮游植物的摄食率进行研究。结果表明,乐清湾已鉴定的浮游动物有56属,75种,17类浮游幼体,主要可划分为4个生态类群,以近岸低盐类群为主,其优势种为真刺唇角水蚤Labidoceraeuchaeta、太平洋纺锤水蚤Acartiapacifica、驼背隆哲水蚤Acrocalanusgibber、中华假磷虾Pseudeuphausiasinica和百陶箭虫Sagittabedoti等,半咸水河口类群、暖水性外海种和广布种的种数相对较少。浮游动物生物量和丰度的平面分布趋势基本一致,有明显季节变化。2月份和5月份,浮游动物生物量和丰度,从湾顶向湾口呈逐渐增加趋势;8月份,生物量和丰度的分布与2月份、5月份的分布趋势不同,从湾顶向湾口,生物量和丰度逐渐降低;11月份,生物量和丰度的平面分布相对均匀。浮游动物种类多样性指数有明显的季节变化,其动态变化与浮游动物种数和丰度的变化一致。微型浮游动物对浮游植物存在摄食压力,且摄食率有季节变化,摄食率的变化在0.15~0.48d-1。     

Modeling the influence of nutrients, turbulence and grazing on Pfiesteria population dynamics

A semi-idealized marine ecosystem model, designed as a heuristic tool for exploring the population dynamics of non-inducible versus toxic forms of Pfiesteria is described. The model is based on empirical evidence suggesting that these differing functional types of Pfiesteria also differ substantially in terms of what they eat and how they utilize it to optimize their growth. Non-inducible strains are similar to other mixotrophic dinoflagellates, whereas toxic strains may consume organic matter and detritus, produce toxins and attack fish. In our model formulation we represent these differences in a simplified way: the non-inducible strain is kleptochloroplastidic and it can take up DIN, but it cannot utilize DON, whereas the toxic strain is heterotrophic, it cannot utilize DIN, but it can utilize DON directly. These differences give rise to very different impacts on prey and nutrient concentrations in our model. Under high DIN/DON ratio conditions, the non-inducible cells grew much faster and were therefore more likely to bloom, but this advantage is substantially mitigated when the DIN/DON ratio is low. A turbulence parameterization was also incorporated into our model. The effect of this was to reduce the grazing rate of Pfiesteria when turbulence levels are high. According to our model, increased turbulence is more detrimental to the toxic functional type because it grows more slowly. The further imposition of microzooplankton grazing in the model showed that top-down control effects can be very significant, which is consistent with both laboratory and field studies and the general idea that plankton blooms can only happen in the absence of substantial grazing control. In general, our model results suggest that non-toxic blooms are more likely to occur in more turbulent inorganic-nutrient rich conditions, which are often found in more open coastal and estuarine waters that are subject to high inorganic loading. In contrast, toxic blooms are more likely to occur in calm, organic-nutrient rich conditions, which are often found in shallow, protected tributaries that are subject to high organic nutrient loading. Our model results also support the idea that the absence of strong grazing pressure is a prerequisite to bloom formation for both non-inducible and toxic strains of Pfiesteria. These results are generally consistent with observed patterns of toxic Pfiesteria blooms in Chesapeake Bay, the Neuse River of North Carolina and many other coastal and estuarine environments.