Number Of Ciliates Research Articles

Benthic ciliates in Adriatic Sea lagoons

Sediment samples were collected from four sandy and muddy bottom sites at both Sacca di Goro lagoon (northern Adriatic Sea) and Lesina lagoon (southern Adriatic Sea) on one occasion in May and one occasion in July in order to make a comparative study of ciliate abundance and diversity. The temperature, pH, dissolved oxygen, and redox potential were measured at the time of collection, the water content of the sediments was determined, and samples subjected to granulometric analysis. The ciliated protozoa in sub-samples from the top centimeter of sediment were identified to genus and species level and enumerated. Ciliates belonging to 38 and 33 species were found in the sediment of Sacca di Goro and Lesina, respectively, the diversity of ciliates varying widely between stations. Total ciliate numbers ranged from 32 to 759 cm −2 and from 2 to 256 cm −2 at Sacca di Goro and Lesina, respectively; the ciliate biomass ranged from 1.1 to 30.3 μg C cm −2 in the samples collected at Sacca di Goro, and from 0.01 to 157 μg C cm −2 in the samples collected at Lesina lagoon. Aspidisca lynceus, Aspidisca steini, Chilodonella uncinata, Frontonia marina, Pleuronema marinum, Strombidinopsis minimum, Strombidium sp., and Urotricha sp., were observed at the two lagoons but not in all stations; Keronopsis flavicans and Trachelostyla pediculariformis were often numerous at Goro lagoon, A. lynceus, Condylostoma patulum and Tracheloraphis teissieri were the most abundant ciliates observed at Lesina lagoon.

Top-down impact by copepods on ciliate numbers and persistence depends on copepod and ciliate species composition

Experiments with the copepods Acartia clausi, Centropages hamatus and Pseudocalanus sp. were performed to assess the species-specific effect of these copepods on the development of monospecific algae (Nephroselmis pyrifomis) and ciliate communities (Strombidium vestitum, Strombidium conicum, Strombidium sp. and Lohmanniella oviformis). It was hypothesized that potentially switching copepods like A. clausi will stabilize the algal community by switching between ciliate and algal food, in contrast to copepods with stereotypic filter feeding behaviour (Pseudocalanus sp.). In treatments with Pseudocalanus sp. and C. hamatus, all ciliate species were wiped out in 2 days, resulting in blooms of N. pyriformis. In treatments with A. clausi, two of the ciliate species were able to persist, but the combined ciliate and copepod community was not able to control the algal bloom. Ciliates became abundant in control treatments without copepods, but only S. vestitum and S. conicum seemed able to establish grazing control. Hence, when evaluating the role ofciliates in food webs, their actual numbers and species composition should be taken into account. Likewise, the species composition of copepods may be crucial; these experiments demonstrate that small filter feeding copepods may have tremendous impact on ciliate numbers.

Relative importance of nanoflagellates and ciliates as consumers of bacteria in a coastal sea area dominated by oligotrichous Strombidium and Strobilidium

To examine the relative importance of nanoflagellates and ciliates as grazers of bacteria, we examined seasonal changes in their consumption of bacteria in a coastal sea, where the oligotrichous ciliates Strombidium and Strobilidium are dominant throughout the year. The numbers of these 2 dominant taxa accounted for 16 to 71% (average 55%) of the total ciliate numbers. Other ciliate taxa which seasonally dominated were photosynthetic Myrionecta rubra, the aloricate oligotrichs Laboea and Lohmaniella, the loricate oligotrichs Tintinnopsis, Cyttarocylis, and scuticociliates. Fluorescently labelled 0.5 µm diameter beads were used to determine grazing rates. Bacterivory was detected for nano- flagellates, Strombidium, Strobilidium, Lohmaniella, Tintinnopsis and Cyttarocylis. Ingestion rates on bacteria by nanoflagellates ranged between 0.3 and 2.2 bacteria protistan cell -1 h -1 . Ingestion rates of the dominant ciliate taxa Strombidium and Strobilidium, when feeding on bacteria, varied from 7 to 34 bac- teria protistan cell -1 h -1 , though the rates were low relative to those of other dominant ciliate taxa (14 to 50 bacteria protistan cell -1 h -1 ). Significant relationships (p < 0.01) were found between the cell numbers of bacteria and ingestion rates of nanoflagellates, and between the cell numbers of bacteria and inges- tion rates of Strombidium, whereas the relationship between the cell numbers of bacteria and ingestion rates of the total ciliates was not significant. Turnover rates of bacteria due to grazing by the total ciliates (0 to 0.63% d -1 ) were lower than those by nanoflagellates (1 to 15% d -1 ). Thus, it is likely that the dominant ciliates in the bay are not important grazers of bacteria, and that the main grazers of bacteria are nanoflagellates.

Summary and overview of the CYCLOPS P addition Lagrangian experiment in the Eastern Mediterranean

CYCLOPS was a European Framework 5 program to further our understanding of phosphorus cycling in the Eastern Mediterranean. The core of CYCLOPS was a Lagrangian experiment in which buffered phosphoric acid was added to a <4×4 km patch of water together with SF6 as the inert tracer. The patch was followed for nine days in total. Results obtained prior to the experiment showed that the system was typically ultra-oligotrophic and P-starved with DON:DOP, PON:POP and DIN:DIP all having ratios greatly in excess of 16:1 in surface waters. To our surprise, we found that although the added phosphate was rapidly taken up by the microbial biota, there was a small but significant decrease in chlorophyll a and no increase in primary production, together with an increase in heterotrophic bacterial activity, ciliate numbers and in the gut fullness and egg numbers in the zooplankton community. A microcosm experiment carried out using within-patch and out-of-patch water showed that the phytoplankton community were N and P co-limited while the bacteria and micrograzers were P-limited. Thus this system tends to N and P co-limitation of phytoplankton productivity in summer possibly caused by bioavailable DIN being converted into non-bioavailable forms of DON. On the basis of the data collected within the programme it was concluded that this behavior could be explained by three non-mutually exclusive processes described as (1) trophic by-pass in which the added phosphate gets directly to the grazing part of the predatory food chain from the heterotrophic bacteria bypassing the phytoplankton compartment phosphate, (2) trophic tunnelling in which phosphate is rapidly taken up by both phytoplankton and bacteria via rapid luxury consumption. This causes an immediate change in the phosphorus content but not the abundance of the prey organisms. The added P then “reappears” as responses at the predator level much more rapidly than expected, and (3) mixotrophic by-pass in which inorganic nutrients, including the added P, are taken up by mixotrophic ciliates directly, bypassing the phytoplankton. For details of the results of this study and the processes described, the readers are referred to the relevant papers within this volume. The implications of these results for nutrient cycling in the Eastern Mediterranean are discussed. In particular it is noted that the efficient and rapid grazing observed in this study might explain why the system although impacted by anthropogenic nutrient input has shown little or no measurable change in microbial productivity since added nutrients are rapidly transferred out of the photic zone via the by-pass and tunnelling processes and are exported from the basin. It is also suggested that fish productivity is higher than has been suggested by conventional food chain models due to this grazing. Two possible reasons for the unusual P-starved nature of the basin are presented.

A parasitic scuticociliate infection in the Norway lobster ( Nephrops norvegicus)

A histophagous ciliate infection was discovered in a number of Norway lobsters ( Nephrops norvegicus) from the Clyde Sea Area, Scotland. Silver-carbonate staining of cultured ciliates revealed an oral apparatus and additional structural features that are morphologically similar to scuticociliates in the genus Mesanophrys, which are known to parasitize crustaceans. However, ribosomal DNA sequences (ITS1/5.8S/ITS2) of the ciliate were identical to Orchitophyra stellarum, a parasitic scuticociliate of sea stars with a different morphology from Mesanophrys spp. and to the ciliate from N. norvegicus. Associated pathology included degeneration and necrosis of the myocardial heart muscle, and large numbers of ciliates in the gill filaments.

Effects of fixatives on ciliates as related to cell size

Abundances of ciliate size classes and of phototrophic ciliates were compared between 2% formaldehyde and 1 % Lugol's preserved samples collected over 1 year at a coastal Mediterranean site. Large cells and Mesodinuim rubrum were poorly preserved in formaldehyde. A correction factor for ciliate numbers in formaldehyde samples of 1.6 for M. rubrum and of 1.3 for other naked dilates was found at our study site, where most ciliates were <30 μm equivalent spherical diameter (ESD). Commercially produced Lugol's appears inferior to laboratory prepared solutions.

Microzooplankton dynamics during the development of the spring bloom in the north-east Atlantic

Microzooplankton community composition, abundance, biomass and grazing impact were assessed, along with measurements of ciliate growth and mortality, during the onset of the spring bloom in the north-east Atlantic. The study was undertaken as part of the UK Biogeochemical Ocean Flux Study during 1 May to 15 June 1990. The microzooplankton community was composed of protozoans and metazoan developmental stages with respective mixed-layer depth integrated biomass values ranging from 127 to 638 and 74 to 394 mg C m−2. High numbers of aloricate ciliates (up to 35,000 cells l−1) dominated the microzooplankton community during early May prior to the onset of the spring bloom. Ciliate abundance then declined rapidly during mid-May with community growth rates ranging from −0·71 to 0·23 d−1. High abundances of metazoplankton (up to 400 l−1) were also recorded at this time and may have contributed to the decline in ciliate numbers. In late May and early June the protozoan community comprised a more even mix of dinoflagellates, tintinnids and aloricate ciliates. Phytoplankton mortality rates, measured using a dilution technique, ranged from 0·2 to 0·5 d−1. The microzooplankton consumed 8 to 44 μg C l−1 d−1, equivalent to between 16 and 40% of the chlorophyll biomass and 38 and 154% of primary production. These high rates of herbivory reflect the predominance of small (&lt;5 μm in length) phytoplankton cells present throughout the first half of the study and support previous studies demonstrating the microzooplankton to be the main grazers of phytoplankton in the north-east Atlantic. However, there is also evidence that a disparity between predator and prey may have prevented a response by the microzooplankton to rapid increases in phytoplankton biomass and production during the spring bloom.

Some aspects of interrelations between fungi and other biota in forest soil

Interrelations of fungal mycelium with other soil biota are of paramount importance in forestry and soil ecology. Here we present the results of statistical analysis of a comprehensive data set collected in the first (and the only) British fungus sanctuary over a period of four months. The variables studied included a number of soil properties, bacteria, protozoan flagellates, ciliates and amoebae, microbial and plant feeding nematodes, various microarthropods, and two fungal biomarkers--glomalin and ergosterol. One way ANOVA showed that the dynamics of the microbiota studied was influenced by seasonal changes. Superimposed on these changes, however, was variability due to biological interactions and habitat characteristics. Two fungal biomarkers, ergosterol and glomalin, were differently influenced by other biota and abiotic variables. The results indicate that the dynamics of soil fungi is influenced not only by soil microarthropods, but also by those found in forest litter. The overall outcome, therefore, is likely to be very complex and will depend upon specific conditions of any particular ecosystem.

Seasonal and spatial distribution of ciliates in the sandy hyporheic zone of a lowland stream

The seasonal and spatial distribution of abundance and biomass as well as the taxonomic composition of ciliates inhabiting the sandy hyporheic zone of a lowland stream were studied. The mean abundances varied between 0 and 895 cells ml −1 sediment, and the mean ciliate biomass ranged between 0 and 5.3 μg C ml −1 sediment. Ciliate numbers and biomasses were greatest at the sediment surface and declined significantly with increasing sample depth. Abundance and biomass varied seasonally, with maximum values in late autumn and early winter and minimum values in early summer. The community was dominated by small representatives of the Hymenostomatia and Peritrichia. Ciliate community composition changed with depth from a very diverse community at the sediment surface to a less diverse one at greater sediment depths. Ciliate abundance and biomass were two orders of magnitude lower in the channel water than in the hyporheic zone. Although representatives of all sediment taxa could also be found in the channel water, the greatest concentrations of Peritrichia and Suctoria were in the hyporheic zone. The species of the sandy Ladberger Mühlenbach sediment were ubiquitous; there was no single ciliate fauna that proved to be typical for this kind of freshwater biotope.

Podite carrying ciliates dominate the benthic ciliate community in the kelp forest

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 36:305-310 (2004) - doi:10.3354/ame036305 Podite carrying ciliates dominate the benthic ciliate community in the kelp forest Ingrid Gismervik* Section of Marine Biology and Limnology, University of Oslo, PO Box 1069 Blindern, 0316 Oslo, Norway *Email: ingrid.gismervik@bio.uio.no ABSTRACT: The ciliate fauna on the kelp Laminaria hyperborea and 5 of its epiphytes was sampled in April and August, off the north-west coast of Norway. The lamina of the kelp carried few (old lamina) or no ciliates (new lamina), while podite carrying cyrtophorids of the order Dysteriida prevailed in April on the epiphytes. The highest number of ciliates was found on Ectocarpus sp. (total ciliate number of 20352 ± 5040 ciliates g-1 fresh weight, FW), with species of the genus Dysteria (8008 ± 1928 g-1 FW) and 1 species of the genus Hartmannula (Hartmannula angustipilosa; 8767 ± 5202 g-1 FW) being dominant. In August, the abundance of ciliates was greatly reduced on all epiphytes, although more taxa were observed. Aspidisca spp. (4829 ± 987 g-1 FW) dominated total numbers (6080 ± 1118 ciliates g-1 FW) on Ectocarpus sp. The infraciliature of 7 species from the family Dysteridae, including Agnathodysteria littoralis, Trochilia sigmoides and Dysteria monostyla, is described. The dysterids and H. angustipilosa carry a flexible podite by which they attach to the surface. The podite may be the key to success in this wave- and current-exposed environment. KEY WORDS: Benthic ciliates · Dysteria spp. · Cyrtophorids · Kelp forest · Epiphytes · Abundance Full article in pdf format PreviousExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 36, No. 3. Online publication date: September 14, 2004 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2004 Inter-Research.

Evaluation of double formalin—Lugol's fixation in assessing number and biomass of ciliates: an example of estimations at mesoscale in NE Atlantic

Ciliated protozoa are potential grazers of primary and bacterial production and act as intermediaries between picoplankton and copepods and other large suspension feeders. Accurate determination of ciliate abundance and feeding mode is crucial in oceanic carbon budget estimations. However, the impact of different fixatives on the abundance and cell volume of ciliates has been investigated in only a few studies using either laboratory cultures or natural populations. Lugol's solution and formalin are the most commonly used fixatives for the preservation of ciliates samples. In the present study, the aim was to compare 0.4% Lugol's solution and 2% borated-formalin fixation and evaluate the need of counting duplicate samples each using a different fixative. For this, a large number of samples ( n=110) from the NE Atlantic was analyzed in the frame of POMME program (Multidisciplinary Mesoscale Ocean Program). We established a statistically significant relationship ( p<0.0001) between Lugol's and formalin fixed samples for both abundance ( r 2=0.50) and biomass ( r 2=0.76) of aloricate ciliates which showed that counts were higher in Lugol's solution by a factor of 2 and a non-taxon specific cell-loss in formalin. However, loricate ciliate abundance in our samples which were represented primarily by Tintinnus spp. did not show any difference between the two treatments. Abundance and biomass of mixotrophic ciliates (chloroplast-bearing cells) were for various reasons underestimated in both treatments. Our results show that unique fixation by formalin may severely underestimate ciliates abundance and biomass although their population may not alter. For this reason, Lugol's solution is best for the estimation of their abundance and biomass. However, for counts of mixotrophs and the evaluation of the ecological role of ciliates in carbon flux, double fixation is essential. Compromises regarding the fixatives have lead to severe underestimations of mixotrophs in studies conducted by now.

Effects of high pH on a natural marine planktonic community

A natural planktonic community was incubated for 2 wk to study its response to differ- ent levels of pH, ranging from 8 to 9.5. A general increase in phytoplankton biomass was observed over time in the pH 8 to 9 incubations. In the pH 9.5 incubation, the phytoplankton biomass decreased close to detection limit during the first week; however, at the termination of the experi- ment, the initial biomass level was regained. In the pH 8 and 8.5 incubations, the diatoms Cerataulina pelagica, Cylindrotheca closterium and Leptocylindrus minimus became numerous, whereas in the pH 9 and 9.5 incubations, C. closterium solely made up the diatom biomass at the termination of the experiment. Photosynthetic dinoflagellates of the genus Ceratium, which were initially abundant, did not grow well in any of the incubations, probably due to the low nutrient concentrations. The proto- zooplankton biomass increased over time in the pH 8 to 9 incubations. In the pH 9.5 incubation, the protozooplankton biomass decreased close to detection limit during the first 3 d of the experiment and stayed at that level until the termination of the experiment. The biomass increase found in the pH 8 to 9 incubations was due to an increase in the number of ciliates, because the heterotrophic dinoflagellate number remained almost constant. Most protozooplankton species incubated at pH 9.5 died; however, the ciliate Myrionecta rubra survived at almost the same cell number as in the lower pH incubations. Overall a species succession occurred among both phototrophic and heterotrophic protists when pH approached 9. In the pH 9.5 incubation, the number of different protist taxa was reduced from 34 at the start of the experiment to 10 at the termination of the experiment. In conclu- sion, our study indicates that elevated pH (>9) in nature will affect the entire plankton community mainly by reducing the species richness and by favouring algal blooms due to loss of grazing.

Standing crop of planktonic ciliates in the East China Sea and their potential grazing impact and contribution to nutrient regeneration

Abstract The spatial distribution and standing crop of the ciliate community were investigated in the East China Sea during February to March 1993, September to October 1993, and July to August 1994. During these three periods, the ciliate community was dominated by aloricate forms, accounting for 50–93% of the total number of ciliates. All aloricate ciliates were assigned to three groups based on their trophic function: autotrophic ciliates (AC), mixotrophic ciliates (MC), and heterotrophic ciliates (HC). Sometimes AC constituted a sizable part of the ciliate community in abundance, but they were always less important in terms of biomass. MC, represented by oligotrichs of the genera Strombidium, Tontonia, and Laboea, were always a significant component in the upper water column and usually dominated during stratified periods in summer and autumn. HC were mainly comprised of oligotrichs of the genera Strombidium, Strobilidium, and Lohmaniella. They were common and most abundant in winter. Tintinnid ciliates (TC) were a minor component of the ciliate community, but they included of a large number of species, i.e. 74 species from 27 genera for all intact loricae in all seasons. The standing crop of total ciliates varied with depth and season from 4180 cells l −1 and 6.25 μg C l −1 . Integrated values of total ciliates, ranging from 7.9 to 54.3×10 6 cells m −2 in abundance and from 8.5 to 136.3 mg C m −2 in biomass, were similar to those recorded from tropical and subtropical oligotrophic systems. Based on the results obtained by this first quantitative investigation on planktonic ciliates, their production, ingestion and excretion were calculated. Potential ingestion rates and their impact on reported primary production ranged, respectively, from 14% to 86%, except for the inner shelf where the impact was only 3% in the inner shelf waters in winter. NH4+ excretion rates of ciliates were estimated to be 0.1– 63.8 mg N m −2 d −1 , equivalent to 0.1–93.8% of the nitrogen requirement by primary producers. These values suggest that the nitrogen excretion by ciliates could be significant contribution to sustainable primary productivity during summer and autumn.

Encystment-inducing factors in the ciliate Euplotes elegans.

Although starvation is considered one of the most important induces of ciliate encystment, its nature has been unclear. Euplotes is a well-known ciliate genus, but the relationship in Euplotes between encystment and food has not been reported. The encystment of Euplotes elegans is facilitated when it is transferred to Chalkley's solution without bacteria as food. A higher ciliate density also facilitates encystment. Thus, starvation and ciliate density needed to be examined. Ciliates were inoculated into 3 treatments: Chalkley's solution with formaldehyde-fixed bacteria as nutritive particles (FFB group), with polystyrene latex particles as non-nutritive particles (PLP group), and without particles (control group). Cysts appeared fastest and ciliate numbers increased in the FFB group. Although the encystment kinetics of the PLP group was similar to that of the control group, the encystment rate of the PLP group was lower than that of the control group in the earliest phase. This suggests that the ciliates were temporarily deceived into feeding on PLP, because they had food vacuoles containing PLP during the earliest phase of incubation. A cell-free old culture solution from a stationary phase, which probably contained excreted substances from high-density ciliates, also facilitated encystment.

Effect of propylene glycol and undegradable protein source on rumen fermentation, blood metabolism and milk production in lactating dairy cows

Eight lactating Holstein cows were divided into two groups (n = 4) and used in a double reversal trial with three periods of 14 days each, to evaluate diets containing propylene glycol (PG) and ruminally undegradable protein (RUP) blend on milk yield and composition, ruminal fermentation and blood metabolism. The control diet contained 20% chopped Sudangrass hay, 20% cubed alfalfa hay, 12% corn silage, and 48% of the respective concentrate mixtures (dry matter basis). The experimental diet (PG + RUP) partially replaced the concentrate mixture from the control diet with 1.4% PG and 2.1% RUP. Both diets contained about 16% crude protein and 71% total digestible nutrients. Dry matter intake was similar between the two diets. Daily production of milk, milk lactose and milk solids-not-fat increased by 9.0%, 11.3% and 9.3%, respectively (P < 0.1), for cows fed diets with PG + RUP; milk composition was unchanged. Although the concentration of ruminal total volatile fatty acids was unchanged, the proportion of propionic acid increased, and the proportion of acetic acid decreased with PG + RUP. The concentration of ruminal ammonia nitrogen and number of ciliate protozoa was not significantly affected by PG + RUP. The concentration of glucose in blood plasma increased, the concentration of urea nitrogen was unaffected, and the concentration of some essential free amino acids decreased with PG + RUP. It is suggested that these changes might be caused predominantly by PG, and the addition of PG may exert a favorable effect on milk production through increased metabolism.

Population dynamics of active and total ciliate populations in arable soil amended with wheat.

Soil protozoa are characterized by their ability to produce cysts, which allows them to survive unfavorable conditions (e.g., desiccation) for extended periods. Under favorable conditions, they may rapidly excyst and begin feeding, but even under optimal conditions, a large proportion of the population may be encysted. The factors governing the dynamics of active and encysted cells in the soil are not well understood. Our objective was to determine the dynamics of active and encysted populations of ciliates during the decomposition of freshly added organic material. We monitored, in soil microcosms, the active and total populations of ciliates, their potential prey (bacteria and small protozoa), their potential competitors (amoebae, flagellates, and nematodes), and their potential predators (nematodes). We sampled with short time intervals (2 to 6 days) and generated a data set, suitable for mathematical modeling. Following the addition of fresh organic material, bacterial numbers increased more than 1,400-fold. There was a temporary increase in the number of active ciliates, followed by a rapid decline, although the size of the bacterial prey populations remained high. During this initial burst of ciliate growth, the population of cystic ciliates increased 100-fold. We suggest that internal population regulation is the major factor governing ciliate encystment and that the rate of encystment depends on ciliate density. This model provides a quantitative explanation of ciliatostasis and can explain why protozoan growth in soil is less than that in aquatic systems. Internally governed encystment may be an essential adaptation to an unpredictable environment in which individual protozoa cannot predict when the soil will dry out and will survive desiccation only if they have encysted in time.

Effect of elevated cobalt intake on fermentative parameters and protozoan population in RUSITEC

The effects of 2, 4 and 8 mg cobalt per kg dry matter (DM) of feed ration consisting of 11.5 g hay, 2.8 g barley and 1.6 g molasses (10% of the DM feeding ration) were examined in an artificial rumen simulation technique (RUSITEC) as affecting fermentation and protozoan population. The cobalt content of the feed ration was 0.2 mg kg −1 DM (control value). The 2, 4 and 8 mg kg −1 DM intake level of cobalt was achieved by CoSO 4 supplementation. The results of the experiment showed no changes in the degradability of DM, organic matter, neutral detergent fiber, acid detergent fiber, production of total gas and methane. The cobalt level of 8 mg kg −1 DM significantly increased the degradability of cellulose by approximately 10% as contrasted to 0.2 mg level. Total production and molar proportion of volatile fatty acids were not significantly affected by increased cobalt intake except for an increased molar proportion of iso-butyric acid at 4 mg cobalt intake. Other parameters of rumen fermentation — glucose utilization, adenosine-triphosphate production, fermented hexose, fermented organic matter, hydrogen recovery and nitrogen utilization — were not influenced by the higher level of cobalt intake. Major ciliate groups in RUSITEC were Entodinium spp. and Dasytricha ruminantium. Minor groups were Isotricha spp., Ophryoscolex caudatus tricoronatus, Polyplastron multivesiculatum, Enoploplastron triloricatum, and Diploplastron affine. A cobalt level of 8 mg significantly decreased the total number of rumen ciliates, but only the number of Isotricha spp. was significantly decreased at all cobalt levels examined. The cobalt accumulation in the protozoan and bacterial fractions of the two vessels were measured. At the cobalt intake level of 0.2 mg kg −1 DM of feed the 24 and 33% of the Co was recovered in the protozoan and bacterial fraction, respectively, after a 12-day operation of RUSITEC. At the cobalt intake level of 2 mg, the values for the protozoan and bacterial fractions were 49 and 51%, respectively.

Trophic interactions between ciliates and nematodes from an intertidal flat

The present study investigated the possibility of a trophic link between ciliates and nematodes in fine sandy sediments of the Molenplaat intertidal flat (Schelde estuary, SW Nether- lands). Grazing experiments were conducted under controlled laboratory conditions, with ciliate spe- cies isolated from enrichment cultures and nematodes collected directly from the field. Significant reductions in ciliate numbers were found in the presence of the predatory nematode Enoploides longispiculosus, a prominent species (and genus) in fine to medium sandy sediments of the North Sea and adjacent estuaries. No such effects were found when ciliates were inoculated with a mix of mainly deposit-feeding nematodes from the same sampling site. On the basis of these results, ciliate predation by E. longispiculosus was tested for several benthic ciliate species and abundances, at a range of predator abundances and temperatures, and in the presence of alternative prey (in casu nematodes). E. longispiculosus significantly reduced the densities of 5 out of 6 ciliate species offered as prey. Depending on the experimental conditions and the prey species, predation rates ranged from 0.19 to 10.8 ciliates predator -1 h -1 , corresponding to a biomass consumption of 0.001 to 0.33 µg C predator -1 d -1 . An overall positive relation between available ciliate biomass and predation rate was found. Comparison of experimental data with field conditions suggests that a considerable part of the ciliate production in fine sandy sediments of the Molenplaat is likely to be consumed by E. longispiculosus, which largely dominates meiofaunal biomass there. Estimated carbon requirements for the predator and production estimates of ciliate and nematode prey at the study site strongly sug- gest that ciliates are probably a far more important carbon source for E. longispiculosus than nema- tode prey, at least between late spring and autumn. This implies that carbon transfer from primary producers and bacteria to predatory nematodes may to a large extent be mediated through the micro- bial food web. In view of the generally high densities and biomasses of ciliates as well as predacious nematodes in fine sandy sediments, similar patterns are to be expected in many other estuarine and marine sediments.

Tufa deposition and periphyton overgrowth as factors affecting the ciliate community on travertine barriers in different current velocity conditions

A characteristic of aquatic systems in karstic region is the formation of tufa – the product of calcium carbonate precipitation. Artificial substrata (glass slides) were used to investigate the influence of tufa deposits at two different current velocities (5 cm s−1 and 50 cm s−1) on the ciliate assemblages in periphyton. After two-month exposure periods, periphyton biomass and tufa deposit were c. three times greater at 50 cm s−1 than at 5 cm s−1. Ciliate population density was also higher on artificial substrata exposed in a lotic than in a lentic microhabitat (the overall mean number of ciliates at 5 cm s−1 was 122 ind. cm−2, and at 50 cm s−1 497 ind. cm−2). At each of the two observed current velocities, a Principal Components (PCA) ordination of the colonized ciliate associations showed a spatial separation of the associations that developed under two different conditions of tufa deposition. During the period of greater tufa deposit, associated with greater periphyton overgrowth rate, the ciliate communities had higher species diversity (a higher number of species and a lower number of individuals). Species diversity of ciliates had a positive nonlinear relation to tufa deposition rate. These results suggest that artificial surfaces covered by a rough tufa layer associated with greater periphyton biomass offer diverse conditions for colonization by ciliates.

Soil microbiota in two annual grasslands: responses to elevated atmospheric CO2.

We measured soil bacteria, fungi, protozoa, nematodes, and biological activity in serpentine and sandstone annual grasslands after 4 years of exposure to elevated atmospheric CO2. Measurements were made during the early part of the season, when plants were in vegetative growth, and later in the season, when plants were approaching their maximum biomass. In general, under ambient CO2, bacterial biomass, total protozoan numbers, and numbers of bactivorous nematodes were similar in the two grasslands. Active and total fungal biomasses were higher on the more productive sandstone grassland compared to the serpentine. However, serpentine soils contained nearly twice the number of fungivorous nematodes compared to the sandstone, perhaps explaining the lower standing crop of fungal biomass in the serpentine and suggesting higher rates of energy flow through the fungal-based soil food web. Furthermore, root biomass in the surface soils of these grasslands is comparable, but the serpentine contains 6 times more phytophagous nematodes compared to the sandstone, indicating greater below-ground grazing pressure on plants in stressful serpentine soils. Elevated CO2 increased the biomass of active fungi and the numbers of flagellates in both grasslands during the early part of the season and increased the number of phytophagous nematodes in the serpentine. Elevated CO2 had no effect on the total numbers of bactivorous or fungivorous nematodes, but decreased the diversity of the nematode assemblage in the serpentine at both sampling dates. Excepting this reduction in nematode diversity, the effects of elevated CO2 disappeared later in the season as plants approached their maximum biomass. Elevated CO2 had no effect on total and active bacterial biomass, total fungal biomass, or the total numbers of amoebae and ciliates in either grassland during either sampling period. However, soil metabolic activity was higher in the sandstone grassland in the early season under elevated CO2, and elevated CO2 altered the patterns of use of individual carbon substrates in both grasslands at this time. Rates of substrate use were also significantly higher in the sandstone, indicating increased bacterial metabolic activity. These changes in soil microbiota are likely due to an increase in the flux of carbon from roots to soil in elevated CO2, as has been previously reported for these grasslands. Results presented here suggest that some of the carbon distributed below ground in response to elevated CO2 affects the soil microbial food web, but that these effects may be more pronounced during the early part of the growing season.