Impact of natural metazooplankton assemblage on planktonic microbial communities in a newly flooded reservoir

The grazing impact of a natural assemblage of metazoan zooplankton on pigmented flagellates (PF), heterotrophic nanoflagellates (HNF), ciliates, and non-flagellate algae and microcyanobacteria (NFAM) was measured in situ during the period of thermal stratification in a newly flooded reservoir (Reservoir de la Sep, France). Experiments were conducted with diffusion chambers in the meta- and epilimnion over a period of 7 h. The mean mortalities of PF in the epi- and metalimnion (0.08 0.02 and 0.06 ± 0.03 h^-1, respectively), of HNF (0.04 ± 0.02 and 0.05 ± 0.02 h^-1) and ciliates (0.09 ± 0.04 and 0.11 ± 0.04 h^-1) demonstrate the impact of the metazoan zooplankton, and particularly of the rotifer Asplanchna priodonta, on the components of the microbial loop. The mortality of NFAM, accounting for 14 and 18% of total mortality, remained low throughout the study. The taxa with the highest mortality were pigmented flagellates of 4-19 m, HNF, and small-sized ciliates such as Halteria sp. (0.10 ± 0.02 h^-1 at 1 m and 0.30 ± 0.38 h^-1 at 7 m) and Urotricha furcata (0.11 ± 0.05 h^-1 at 1 m and 0.12 ± 0.06 h^-1 at 7 m). Large-sized ciliates (Paradileptus elephantinus) and sessile ciliates (Suctorida, Vorticella sp.) had a very low mortality (>0.04 h^-1). After reservoir flooding, the organisms in the microbial trophic loop, favoured by the high quantities of allochthonous organic matter, are subject to a higher mortality than the phytoplankton.      

Bacterivory by heterotrophic flagellates: community structure and feeding strategies

Heterotrophic flagellates (HF) are known as most important grazers of bacteria in many aquatic ecosystem. HF cannot be treated as a black box since HF generally contain a diverse community of species significantly differing in their feeding behaviour and other ecological properties. Today it seems that the dominant taxonomic groups among heterotrophic nano- and microflagellate communities within different marine, brackish and limnetic pelagic communities (heterokont taxa, dinoflagellates, choanoflagellates, kathablepharids) and benthic communities (euglenids, bodonids, thaumatomonads, apusomonads, cercomonads) are relatively similar. HF among protista incertae sedis, often neglected in ecological studies, are abundant bacterivores in all investigated habitats. Recent studies of flagellate feeding processes indicated that there are significant species-specific differences and individual variability regarding the food uptake and food selection of bacterivorous flagellates: Variability of bacterivory is discussed regarding the prevailing feeding modes, the energy budgets, the considerable importance of slight deviations in the time budgets of feeding phases, the ingestion rates and the feeding microhabitat, respectively. The significant flexibility of the grazing impact of bacterivorous flagellate communities creates a complex top-down pressure on bacteria which should have lead to the evolution of efficient predator avoidance mechanisms in bacteria and should be at least partly responsible for the diversity of present bacteria. This revised version was published online in August 2006 with corrections to the Cover Date.     

Size-selective grazing of coastal bacterioplankton by natural assemblages of pigmented flagellates,colorless flagellates,and ciliates

Fluorescently-labelled bacteria (FLB) were used to study the feeding strategies of a natural assemblage of estuarine protozoans and to examine whether the protozoan grazing could account for the in situ size structure of the bacterioplankton. The FLB, DTAF-stained enterococci, ranging in volume from 0.01 to 0.30 × 10^–1 µm³, were added to a natural planktonic assemblage at a density of 5.5% of the natural bacterioplankton. Initial densities (individuals ml^–1) were as follows: total natural bacteria, 2.2 × 10⁶; FLB, 1.2 × 10⁵; pigmented flagellates, 300; colorless flagellates, 250; and ciliates, 30. FLB consumption rates were determined by examining the contents of protozoan food vacuoles, and the long-term effect of grazing (over a period of 100 hours) was determined by monitoring the decline in the FLB density in experimental vessels. The average consumption rates of FLB by pigmented flagellates were similar to those by flagellates that lacked chloroplasts (0.9 and 0.6 FLB protozoan^–1 hour^–1, respectively). The ciliates consumed bacteria at an average rate that was 17-fold higher (per cell) than flagellates, and they displayed a greater preference for larger bacteria than did the flagellates. FLB of the mid-size classes (0.025–0.100 µm³) were heavily grazed by the entire protozoan assemblage; the smallest (<0.025 µm³) and the largest (>0.100 µm³) FLB escaped protozoan grazing. This had a profound effect on the resulting size distribution of FLB. At the end of a 100-hour incubation, the percentage of mid-size FLB (0.025 to 0.100 µm³) decreased 2.0–2.2-fold, while the percentage of the smallest and the largest FLB increased 2.0–2.5-fold. Resultant densities of FLB were consistent with initial clearance rates determined for the protozoan groups. The grazing rates of protozoans on FLB were species-specific; whereas some species consumed FLB, others did not demonstrate bacterivory. The results suggest that protozoan grazing has a major effect on the size distribution of coastal bacterioplankton. By selectively feeding on a particular size-class of bacteria, planktonic ciliates may consume 15–90% day^–1 of the standing stock of largest size classes of bacterioplankton. Thus, ciliates, which were present in low abundance in the field, could not balance the production of the entire bacterial community, but they may strongly influence the portion of the bacterial community represented by the largest bacterial class. The direct effect of flagellates (e.g., grazing) was limited to smaller bacteria.Offprint requests to: M. P. Shiaris.     

Relationship between the flagellates and the ciliates.

The flagellates and the ciliates have long been considered to be closely related because of their unicellular nature and the similarity in the structures of the axoneme of the flagella and cilia in both groups. Most protozoologists believe that the ciliates arose from a flagellate. The flagellates that are most similar in structure to the ciliates are the dinoflagellates and two genera of uncertain taxonomic position, Colponema and Katablepharis. Structurally, dinoflagellates have a number of similarities with ciliates. These include the similarity of the cortical alveoli in the ciliates to the thecal vesicles in the dinoflagellates, the possession of tubular cristae, the similarity of the parasomal sac of the ciliates to the pusule of the dinoflagellates, the possession of similar trichocysts and mucocysts, and some similarity in the feeding apparatus. Colponema spp. are probably related to the dinoflagellates and have many of the same similarities with the ciliates. Katablepharis spp. are very similar in structure to the swarmer (embryo) of the suctorian ciliates. Indeed, reduction in the number of cilia to two in the suctorian swarmer and elimination of the macronucleus would result in a cell that is very similar to the Katablepharis cell. The feeding apparatus of Katablepharis spp. and the rest of the ciliates consists of two concentric microtubular arrays associated with vesicles. Information available from nucleotide sequencing of rRNA places the dinoflagellates in an ancestral position to the ciliates. The rRNA of Colponema and Katablepharis spp. has not yet been investigated. The use of stop codons in mRNA is discussed in relation to phylogeny.     

Protistan bacterivory in an oligomesotrophic lake: Importance of attached ciliates and flagellates

Seasonal and depth variations of the abundance, biomass, and bacterivory of protozoa (heterotrophic and mixotrophic flagellates and ciliates) were determined during thermal stratification in an oligomesotrophic lake (Lake Pavin, France). Maximal densities of heterotrophic flagellates (1.9 × 10³ cells ml^–1) and ciliates (6.1 cells ml^–1) were found in the metalimnion. Pigmented flagellates dominated the flagellate biomass in the euphotic zone. Community composition of ciliated protists varied greatly with depth, and both the abundance and biomass of ciliates was dominated by oligotrichs. Heterotrophic flagellates dominated grazing, accounting for 84% of total protistan bacterivory. Maximal grazing impact of heterotrophic flagellates was 18.9 × 10⁶ bacteria 1^–1h^–1. On average, 62% of nonpigmented flagellates were found to ingest particles. Ciliates and mixotrophic flagellates averaged 13% and 3% of protistan bacterivory, respectively. Attached protozoa (ciliates and flagellates) were found to colonize the diatom Asterionella formosa. Attached bacterivores had higher ingestion rates than free bacterivorous protozoa and may account for 66% of total protozoa bacterivory. Our results indicated that even in low numbers, epibiotic protozoa may have a major grazing impact on free bacteria.Correspondence: C. Amblard.     

Channeling of bacterioplanktonic production toward phagotrophic flagellates and ciliates under different seasonal conditions in a river

The objective of this study was to analyze the flux of biomass through the communities of bacteria and phagotrophic protists in the cold and warm conditions occurring seasonally in Butrón River. Bacterial and heterotrophic protistan (flagellate and ciliate) abundance was determined by epifluorescence direct counts; protistan grazing on planktonic bacteria was measured from fluorescently labeled bacteria uptake rates; and the estimate of bacterial secondary production was obtained from [³H]thymidine incorporation rates. The abundance of bacterial, flagellate, and ciliate communities was similar during cold and warm situations. However, we observed that estimates of dynamic parameters, i.e., secondary bacterial production and protistan grazing, in both situations were noticeably different. In the warm situation, grazing rates of flagellates and ciliates (bacteria per protist per hour) were, respectively, 7 times and 18 times higher than those determined in the cold situation, and the grazing rates of the protistan communities (bacteria per protists present in 1 ml of water per hour) increased up to 5 times in the case of flagellates and 42 times in the case of ciliates. Estimates of bacterial secondary production were also higher during the warm situation, showing a ninefold increase. The percentage of bacterial production preyed upon by flagellates or ciliates was not significantly different between the two conditions. These results showed that in the different conditions of a system, the flux of biomass between the trophic levels may be quite different although this process may not be reflected in the abundance of each community of bacteria, flagellates, and ciliates.Offprint requests to: J. Iriberri.     

Size-selective grazing on bacteria by natural assemblages of estuarine flagellates and ciliates

The small average cell size of in situ bacterioplankton, relative to cultured cells, has been suggested to be at least partly a result of selection of larger-sized cells by bacterivorous protozoa. In this study, we determined the relative rates of uptake of fluorescence-labeled bacteria (FLB), of various cell sizes and cell types, by natural assemblages of flagellates and ciliates in estuarine water. Calculated clearance rates of bacterivorous flagellates had a highly significant, positive relationship with size of FLB, over a range of average biovolume of FLB of 0.03 to 0.08 microns3. Bacterial cell type or cell shape per se did not appear to affect flagellate clearance rates. The dominant size classes of flagellates which ingested all types of FLB were 3- to 4-microns cells. Ciliates also showed a general preference for larger-sized bacteria. However, ciliates ingested a gram-positive enteric bacterium and a marine bacterial isolate at higher rates than they did a similarly sized, gram-negative enteric bacterium or natural bacterioplankton, respectively. From the results of an experiment designed to test whether the addition of a preferentially grazed bacterial strain stimulated clearance rates of natural bacterioplankton FLB by the ciliates, we hypothesized that measured differences in rates of FLB uptake were due instead to differences in effective retention of bacteria by the ciliates. In general, clearance rates for different FLB varied by a factor of 2 to 4. Selective grazing by protozoa of larger bacterioplankton cells, which are generally the cells actively growing or dividing, may in part explain the small average cell size, low frequency of dividing cells, and low growth rates generally observed for assemblages of suspended bacteria.     

黑色素染色法在纤毛虫和鞭毛虫研究中的使用与改进

介绍并分析了前人在纤毛虫研究中使用过的黑色素染色法,得出作者自己的改进法及其复染法。报告了黑色素改进法的步骤及操作细节,并示出此法显示纤毛虫和鞭毛虫的效果。     

Short-term variations of virus-like particles in a tropical lake: relationship with microbial communities (bacteria, ciliates and flagellates)

The short-term dynamics of virus-like particles (VLPs) abundance, bacterioplankton, ciliates and flagellates were analyzed in a small tropical lake, during a rainy day (June 9–10, 2003) and a dry day (February 18–19, 2004), with intervals of 3 h between the samplings. Frequent sampling in intervals of 15 min were conducted. During the rainy day, the VLP mean abundance was 7.0×108 mL⁻¹ and bacterial density was 5.75×107 mL⁻¹. During the dry day, VLP and bacterial mean were 5.78×108 and 4.1×107 mL⁻¹, respectively. The virus/bacterium rate (VBR) varied from 11 to 18 on the rainy day and from 4 to 22 on the dry day. The density of VLP was higher during the night, especially on the dry day, suggesting a virucidal action of the solar radiation on them. When registered in intervals of 15 min, the densities were not associated with the fluctuations of bacteria or chlorophyll a (Chl a), but a strong negative correlation between VLP and protozooplankton was observed (Spearman: R=−0.71; p=0.04), possibly associated with the occurrence of viral lyses on these organisms. The variations of VBR in the system, indicate that the elevated densities and fluctuations of VLP is suggestive of an active and important participation of these biological entities in the dynamics of the microbial communities in the studied environment.     

Densities and distribution of flagellates and ciliates in the chemocline of saline,meromictic Lake Shunet (Siberia,Russia)

The vertical and seasonal distributions of the phytoflagellate Cryptomonas spp., and its most common, the planktonic ciliate predators (Oligotrichida, Scuticociliatida, Hypotrichida and Prostomatida) were investigated in chemocline region of small saline, meromictic lake Shunet (Siberia, Russia) during 2003 and 2005. The lake has a pronounced chemocline, with abundance of purple and green sulphur bacteria. Vertical distribution of the Cryptomonas populations near the oxic/anoxic boundary layer was studied at close intervals in water sampled using a hydraulically operated thin-layer sampler. In both summer and winter, Cryptomonas peaked in water stratum 5–10 cm above anoxic zone or in the anoxic zone water column in the chemocline (about 5 m). Ciliate densities and biomass were also much higher in chemocline than in mixolimnion. The range of diurnal migration of Cryptomonas population was not very wide, and it was restricted to layers with high light intensity. The ciliates were sometimes detected above the upper border of the anoxic zone but also several centimetres below this zone.     

Benthic flagellates and ciliates in fine freshwater sediments: Calibration of a live counting procedure and estimation of their abundances

Despite the recognized importance of protozoans (flagellates and ciliates) as predators of bacteria, there are very few estimates of their abundance in fine sediments of freshwater lakes. This is due, in part, to the lack of a standard methodology. Because of the low concentration of protists in relation to particles, epifluorescence counts can not always be used. Instead, dilution followed by live counting was used to solve the masking by sediment particles. One to twenty 1 sample aliquots were diluted with filtered lake water in a Palmer-Maloney counting slide. Four to eight replicates were sufficient to minimize the counting error, while minimizing effort. The method is highly replicable and could potentially be calibrated for different sediment types because sediment masking depends on the mean particle size of the sediment. When this method was applied in a survey of benthic sites in Quebec lakes, flagellate abundances were found to range from 100 to 180,000 cells ml^–1, while ciliate numbers ranged from 26 to 11,000 cells ml^–1. Bacteria are 105 to 10⁷ times more abundant than protists and, thus, the impact of these protists on sediment bacterial dynamics is likely to be minimal.     

Improvement of silver impregnation technique (protargol) to obtain morphological features of protists ciliates, flagellates and opalinates

The research on ciliates, flagelates and opalinates have been widespread by the utilization of techniques employing silver impregnation (protargol), modified by several authors. However, these are time consuming and its results are variable. The present work is a variant of the technique described by Tuffrau (1964, 1967) showing some adaptations made in our laboratory. The organisms can be preserved by different fixatives (alcoholic Bouin, Stieve's fluid, 2.5% glutaraldehyde and others) and then rinsed in destilled water followed by a fast clarification by 3% sodium hypochloride. If the organism is very sensitive to hypochloride, 4% sodium lauryl sulfate may be used and then washed 3 times in distilled water. The protista can be adhered to the glass slides with Mayer's glycerinated-albumin (1 glycerin vol. to 1 or 2 albumin vol.), diluted in water at a proportion of 1:10 Cv/v., or with 1% polylysine followed by fast washes with distilled water. After the slide preparation, they were covered with a layer of 0,8% Silver proteinate. Right after that, the slide has to be placed in a glass tray lined with moist tissue and covered to prevent the proteinate to dry. The tray was placed in a incubator at 40 degrees - 50 degrees C for 30 minutes. The slides are rinsed for 1 minute. with warm (35 degrees C) distilled water. The development of the material should be done with 0.4% hydroquinone with a maximum incubation time of 1 minute. It should be developed gradually, controlling the silver impregnation intensity by observation under optical microscope. Next, rinse in distilled water for 1 minute, and then, fix in 2,5% Sodium thiosulfate. Rinse the slide for two minutes before dehydrating it in an alcoholic serial 50-100 degrees. Finally rinse the slides in xylene. Mount the slides with Entellan MerckTM or Canada balsam.     

Reproductive success of the rotifer Brachionus calyciflorus feeding on ciliates and flagellates of different trophic modes

SUMMARY 1. The nutritional value of the bacterivorous ciliate Tetrahymena pyriformis and the algivorous ciliate Coleps sp., as well as the heterotrophic flagellate Chilomonas paramecium and the autotrophic flagellate Cryptomonas ovata , were investigated in population growth experiments using the rotifer B. calyciflorus . The two ciliates, both flagellates, which were of similar size, shape and mobility, were each offered as a sole diet and as a supplement to the alga Monoraphidium minutum , known to support reproduction of B. calyciflorus .
2. To further test nutritional differences between the prey organisms, prey selection experiments were conducted in which B. calyciflorus was able to select between the bacterivorous and algivorous ciliate, and between the heterotrophic and autotrophic flagellate.
3. The results demonstrated that both ciliates and the heterotrophic flagellate were not sufficient to support reproduction of B. calyciflorus when offered as a sole diet. They were, however, a good supplement to algal prey (except for the bacterivorous ciliate T. pyriformis ). In the prey selection experiments, B. calyciflorus positively selected for the algivorous Coleps sp. and the autotrophic C. ovata.
4. Overall, ciliates and heterotrophic flagellates may enhance survival of B. calyciflorus , but reproduction of the rotifer is likely to rely on algal prey. Both higher population growth of B. calyciflorus when fed the algivorous Coleps and the autotrophic Cryptomonas, along with their positive selection, give evidence for prey specific differences in nutrition, with algivorous or autotrophic prey species tending to be of higher nutritional value.     

飞来峡水库蓄水初期营养状态及浮游生物分布特征

于2000年丰水期和枯水期调查分析了新建河流型水库-飞来峡水库在蓄水初期的营养状态及浮游生物特征。结果表明:水库处于营养累积高峰期,已开始回落,但流域上游大量含磷废水使水库中磷含量继续上升,目前属于中营养型。共记录到浮游植物29种(属),以蓝藻门、绿藻门、硅藻门种类较多,其中丰水期以蓝藻和绿藻为主,枯水期是硅藻占优势,除大坝附近外,浮游植物两个季节密度变化不大,为0.39×10⁶cells·L^-1.浮游动物53种(属),其中包括僧帽溞和透明薄皮溞两种嗜寒性种类,丰度为52ind.·L^-1,枯水期高于丰水期,数量以轮虫和无节幼体为多。     

Man's impact on a newly formed reservoir

A newly formed reservoir in the southwestern part of the United States was analyzed for man's impact on the eutrophication of the impoundment. The analysis of the ¹⁴C net productivity (mg ¹²C/m² per day) indicated that the area studied was naturally eutrophic. Significant differences in net production were observed among the sites, as the area where man's recreational activities are highly concentrated had a significantly higher production rate than the other sites investigated. Mean monthly estimate of production for all the sites, and monthly and yearly estimates for the area studied are also included.     

新建水库轮虫和甲壳类浮游动物动态特征

于2000~2003年调查了新建水库飞来峡水库(1999年蓄水)轮虫和甲壳类浮游动物的动态特征。共检到轮虫68种,枝角类18种和桡足类13种。轮虫、枝角类和桡足类的丰度均不高,分别为0.2~88.6,0.1~13和0.4~13.8 ind.L-1,最高丰度均出现在蓄水后的第4年(2002年3月)。在水库开始蓄水之后,轮虫先以螺形龟甲轮虫(Keratella cochlearis)为优势种;然后在蓄水后的第4年(2002年3月)由于长圆疣毛轮虫(Synchaeta pectinata)种群密度大幅度上涨,长圆疣毛轮虫取缔螺形龟甲轮虫成为优势种;此后,随着长圆疣毛轮虫种群回落,螺形龟甲轮虫又成为优势种。对于枝角类来说,水库蓄水初期,短尾秀体氵蚤(Diaphanosoma brachyurum)和长额象鼻氵蚤(Bosmina longirostris)交替成为枝角类的优势种;在蓄水后的第4年,长额象鼻氵蚤种群密度上涨,成为绝对优势种;此后,长额象鼻氵蚤种群回落,但仍然为绝对优势种。对于桡足类来说,在调查期间均以桡足幼体为主,成体丰度很低。飞来峡水库属河流型水库,在调查期间滞留时间为1.3~14.2 d,高的稀释和平流损失率造成浮游动物丰度很低。滞留时间的变化与轮虫、枝角类和桡足类种群波动密切相关;叶绿素a对它们的种群波动影响则不明显,但与长圆疣毛轮虫和长额象鼻氵蚤均显著正相关。在相对较长的滞留时间(14.2 d)和较丰富的食物的条件下,长圆疣毛轮虫和长额象鼻氵蚤种群密度大幅度上涨,并使总浮游动物丰度在蓄水后的第4年出现最高值。     

Structure and seasonal dynamics of the protozoan community (heterotrophic flagellates,ciliates, amoeboid protozoa) in the plankton of a large river (River Danube,Hungary)

Seasonal dynamics of all major protozoan groups were investigated in the plankton of the River Danube, upstream of Budapest (Hungary), by bi-weekly sampling over a 1-year long period. Sixty-one heterotrophic flagellate, 14 naked amoeba, 50 testate amoeba, 4 heliozoan and 83 ciliate morphospecies were identified. The estimated abundance ranges of major groups throughout the year were as follows: heterotrophic flagellates, 0.27–7.8×10⁶ ind. l^?1; naked amoebae, max. 3300 ind. l^?1; testaceans, max. 1600 ind. l^?1; heliozoans, max. 8500 ind. l^?1; ciliates, 132–34,000 ind. l^?1. In terms of biovolume, heterotrophic flagellates dominated throughout the year (max. 0.58 mm³ l^?1), and ciliates only exceeded their biovolume in summer (max. 0.76 mm³ l^?1). Naked amoeba and heliozoan biovolume was about one, and testacean biovolume 1–3, orders of magnitude lower than that of ciliates. In winter, flagellates, mainly chrysomonads, had the highest biomass, whilst ciliates were dominated by peritrichs. In 2005 from April to July a long spring/summer peak occurred for all protozoan groups. Beside chrysomonads typical flagellates were choanoflagellates, bicosoecids and abundant microflagellates (large chrysomonads and Collodictyon). Most abundant ciliates were oligotrichs, while Phascolodon, Urotricha, Vorticella, haptorids, Suctoria, Climacostomum and Stokesia also contributed significantly to biovolume during rapid succession processes. In October and November a second high protozoan peak occurred, with flagellate dominance, and slightly different taxonomic composition.     

The changing role of terrestrial and autochthonous organic matter in newly flooded lakes

Examination of the gut contents of mud-dwelling animals in three newly flooded lakes shows terrestrial organic matter to be a major component, particularly during filling of the lake basin. After filling is complete, a fall-off in total biomass of fauna is usually accompanied by significant reduction in the proportion of terrestrial detritus in favour of algal food. It is concluded that newly formed lakes pass through two phases. During flooding they are dependent on the terrestrial ecosystem. This is followed by a switch, immediately after filling, to more self-sustained autochthonous-based food chains.