Comparative growth rates and yields of ciliates and heterotrophic dinoflagellates

Growth rates, ingestion rates and grazer yields (grazer volumeproduced/prey volume consumed) were measured for six protozoanspecies (ciliates: Favella sp., Strombidinopsis acuminatum,Uronema sp.; heterotrophic dinoflagellates: Amphidinium sp.,Gymnodinium sp., Noctiluca scintillans) in laboratory batchculture experiments. Comparative growth data indicate that theprymnesiophyte Isochrysis galbana, the prasinophyte Mantoniellasquamata, two cryptophyte species and several autotrophic dinoflagellatespecies were suitable foods for these grazers. When grown onoptimized diets at 13C, maximum ciliate growth rates (range0.77–1.01 day^–1 uniformly exceeded maximum heterotrophicdioflagellate growth rates (range 0.41–0.48 day^–1).A compilation of published data demonstrates that this growthrate difference persists across a range of ciliate and dinoflagellatetaxa and cell sizes. Comparison of volume-specific ingestionrates and yields for the six species studied here showed thatthere was no single explanation for this growth rate disparity.Heterotrophic dinoflagellates exhibited both low ingestion ratesand, in one case, low yields; ciliates were able to achievehigher growth rates via either higher ingestion rates or higheryields, depending on ciliate species. Volume yield increasedover time throughout the exponential growth phase in nearlyall experiments, suggesting variation in response to changingfood concentrations or long-term acclimation to culture conditions.Higher maximum ciliate growth rates mean that these grazershave the potential to exercise tighter control over incipientblooms of their prey than do heterotrophic dinoflagellates.     

Feeding response of a benthic copepod to ciliate prey type,prey concentration and habitat complexity

1. Protozoans are important consumers within microbial food webs and, in turn, they represent potential prey for small metazoans. However, feeding interactions within these food webs are rarely characterised and this is especially true for freshwater sediments. 2. We aimed to quantify the feeding links between a freshwater meiofaunal copepod and ciliates in two laboratory experiments. The first experiment addressed the response of Eucyclops serrulatus towards ciliate density and type (two ciliate species of the same genus differing in terms of body size). A second experiment assessed the effect of habitat structure on feeding rates by introducing different structural complexity into the feeding arena. In contrast to the first experiment, which was run only for one time period, this experiment also tested three different total feeding times (4, 7 and 9 h). 3. Eucyclops serrulatus exhibited high ingestion rates, with 3–69 ciliates copepod^?1 h^?1 consumed depending on food concentration, food type and habitat complexity. Copepods exhibited a preference for the smaller ciliate when total ciliate concentration was low, but selected both ciliates equally when food concentrations were medium or high. However, at very high food concentration, Eucyclops preferred the larger ciliate (which was 1/3 of its own body size), suggesting that the longer handling times of the larger prey are rewarding when the large prey is present in high numbers. In terms of total numbers consumed, copepods fed on more small ciliates, but in terms of carbon units both ciliates were selected equally when total prey concentration was low or medium. However, copepods derived more carbon from the larger prey at high and very high prey concentrations (up to 0.7 μgC out of a maximum of 1.1 μgC copepod^?1 h^?1). Habitat complexity influenced the feeding of copepods when it was observed over time. 4. The copepod–ciliate link is well known from the pelagic zone of both marine and freshwater habitats. We have shown its potential importance within the benthos, where it can be influenced by food identity, food quantity and possibly by habitat complexity.     

Evaluation of the efficiency of metabolism of dinoflagellate phosphorus and carbon by a planktonic ciliate

The trophic transfer of nutrients through the microbial food web is a key top-down control in aquatic ecosystems which is notoriously difficult to evaluate, particularly for planktonic protists. In this study, a sensitive dual-radioactive tracer technique was developed to simultaneously assess the ingestion rate, and carbon- and phosphorus-specific assimilation efficiencies, of the marine planktonic ciliate Strobilidium neptuni feeding on the autotrophic dinoflagellate Heterocapsa triquetra. Dinoflagellate prey were simultaneously 16 h pulse labelled with NaH¹⁴CO₃ and H₃³³PO₄ before being fed to the ciliate, and radioactive labels were traced into ciliate biomass and the experimental medium, as well as being monitored in the prey cells. Rates measured in short-term (10 min) incubations, as commonly used to estimate protist uptake of fluorescently labelled prey, were approximately 6 times higher and 3–6 times more variable than rates measured in longer 3–5 h incubations. The efficiency of accumulation of prey carbon (54±9%) by ciliates was lower than that of prey phosphorus (68±3%) suggesting that the phosphorus to carbon ratio in the ciliates was 1.3 times higher than in the labelled dinoflagellate biomass. Rates of phosphorus accumulation and release were combined to reveal that ciliates consumed 3.2±0.6 dinoflagellates cell^?1 h^?1. The assessment of carbon tracer release by ciliates was less reliable due to ¹⁴CO₂ exchange between the experimental media and air. The study concludes that the dual phosphorus–carbon radioactive tracer labelling of algal prey allowed the quantification of protist herbivory and nutrient remineralisation in laboratory experiments, thereby providing a potential technique for studying planktonic microbial trophic interactions in situ.     

Cyclopoids feed selectively on free-living stages of parasites

1. Many aquatic organisms can consume parasite larvae, thus hampering parasite transmission; however, information about feeding on them in the presence of an alternative prey remains scarce. When having a food choice, predators may decrease parasite consumption, therefore, it is important to assess the role of parasites in the diet of predators in natural communities with different types of prey available. Our study aims to test whether common freshwater cyclopoids feed on trematode free-living stages (cercariae) when an alternative food source is present.
2. We experimentally studied ingestion rates of cyclopoids Macrocyclops distinctus fed with cercariae of trematode Diplostomum pseudospathaceum, a common and harmful parasite of freshwater fishes, and ciliates Paramecium caudatum (an alternative prey, known as suitable food for copepods). First, the feeding response of cyclopoids to different densities of each prey was studied. Then, feeding selectivity in the mixtures of cercariae and ciliates was tested.
3. Feeding rates of cyclopoids increased with prey densities (both ciliates and cercariae) but almost stopped growing at high prey densities, which indicated saturation (Holling type II functional response). In most cases, cyclopoids consumed cercariae at higher rates than ciliates. Maximum ingestion rates estimated from the obtained curves were 37 cercariae ind⁻¹ hr⁻¹ and 17 ciliate ind⁻¹ hr⁻¹.
4. When exposed to prey mixtures, cyclopoids fed on cercariae selectively. When cercariae were offered to cyclopoids at concentrations exceeding the saturation level, the ingestion of ciliates remained constantly low at all ciliate densities. In contrast, the ingestion of cercariae increased with rising cercariae densities even when ciliates were presented ad libitum, decreasing only at very high prey densities. Possible reasons of such feeding preferences are discussed.
5. Our study demonstrated that cyclopoids may prefer to feed on cercariae when there is an alternative food choice and can ingest cercariae at high rates. These experimental results could be extended to natural communities, suggesting that cyclopoids can reduce the transmission of parasites and contribute to the incorporation of parasite production in food webs of lentic ecosystems.

     

Comparison of ciliate communities in the anoxic hypolimnia of three lakes: general features and the influence of lake characteristics

The ciliate communities and their food sources were investigatedin the anoxic hypolimnia of three lakes with differing waterchemistry. Bacterial biomass and, as a result, the biomass ofbactenvorous ciliates were correlated with lake trophy. Additionally,high sulfate and sulfide concentrations led to high bacterialbiomass of sulfate reducers and anaerobic phototrophic and heterotrophicbacteria, which in turn sustained large ciliate populations.The anaerobic ciliate communities of the lakes shared many characteristics.They were comprised of the same or closely related species;this was attributed to a low diversity of food sources. Ciliateto prey biomass ratios were 1.2–3.8% which is consistentwith a low theoretical growth efficiency of anaerobic metabolism.Grazing pressure on anaerobic ciliates by metazoa was insignificant.In all three lakes, ciliate populations showed distinct verticalnon-random distribution patterns which were often correlatedwith the distribution of the corresponding food sources. Itis suggested that the microbial communities in anoxic waterbodies are largely influenced by few common environmental conditionsand are therefore often inhabited by similarly structured ciliatecommunities.     

Feeding characteristics of two tintinnid ciliate species on phytoplankton including harmful species: effects of prey size on ingestion rates and selectivity

The feeding abilities of two tintinnid ciliates, Favella ehrenbergii and Favella taraikaensis, on 10 species of flagellates including harmful marine algae were examined under single prey conditions, and selective feeding of F. taraikaensis on two species of algae of different sizes was investigated under mixed prey conditions. Ingestion rates calculated from the rate of increases of auto-fluorescent particles inside food vacuoles in individuals ranged from 0.5 to 22.1 cells ind(-1) h(-1) for F. ehrenbergii and from 0.8 to 44.9 cells ind(-1) h(-1) for F. taraikaensis on nine species of prey algae. Significant ingestion rates of both Favella species could not be detected on Heterosigma akashiwo, although some individuals of both species were observed ingesting H. akashiwo in the initial incubation period. The relationship between prey cell volume and ingestion rate could be expressed mathematically for both Favella species, indicating that it is possible to estimate the potential feeding activity of each Favella species on specific algae using an equation, and may be applicable to evaluate the food value of prey alga for both Favella species. When F. taraikensis was fed mixtures of H. circularisquama and Pavlova lutheri, significant ingestion rates of H. circularisquama by F. taraikaensis could not be measured when H. circularisquama accounted for less than 20% of the other prey biomass. However, clear selectivity for H. circularisquama was observed when H. circularisquama reached and exceeded 34% of the other prey biomass. Under mixed prey conditions, it is likely that the selectivity of F. taraikaensis is stronger for larger prey compared to prey algae with a size near the lower limit on which F. taraikaensis can feed.     

Protozoan growth rates in Antarctic lakes

The growth rates of heterotrophic nanoflagellates (HNAN), mixotrophic cryptophytes, dinoflagellates and ciliates in field assemblages from Ace Lake in the Vestfold Hills (eastern Antarctica) and Lakes Fryxell and Hoare (McMurdo Dry Valleys, western Antarctica), were determined during the austral summers of 1996/1997 and 1997/1998. The response of the nanoflagellates to temperature differed between lakes in eastern and western Antarctica. In Ace Lake the available bacterial food resources had little impact on growth rate, while temperature imposed an impact, whereas in Lake Hoare increased bacterial food resources elicited an increase in growth rate. However, the incorporation of published data from across Antarctica showed that temperature had the greater effect, but that growth is probably controlled by a suite of factors not solely related to bacterial food resources and temperature. Dinoflagellates had relatively high specific growth rates (0.0057–0.384 h⁻¹), which were comparable to Antarctic lake ciliates and to dinoflagellates from warmer, lower latitude locations. Temperature did not appear to impose any significant impact on growth rates. Mixotrophic cryptophytes in Lake Hoare had lower specific growth rates than HNAN (0.0029–0.0059 h⁻¹ and 0.0056–0.0127 h⁻¹, respectively). They showed a marked seasonal variation in growth rate, which was probably related to photosynthetically active radiation under the ice at different depths in the water column. Ciliates' growth rates showed no relationship between food supply and mean cell volume, but did show a response to temperature. Specific growth rates ranged between 0.0033 and 0.150 h⁻¹ for heterotrophic ciliates, 0.0143 h⁻¹ for a mixotrophic Plagiocampa species and 0.0075 h⁻¹ for the entirely autotrophic ciliate, Mesodinium rubrum. The data indicated that the scope for growth among planktonic Protozoa living in oligotrophic, cold extreme lake ecosystems is limited. These organisms are likely to suffer prolonged physiological stress, which may account for the highly variable growth rates seen within and between Antarctic lakes. Accepted: 7 December 1999     

Growth kinetics of Colpoda steinii on Escherichia coli.

Colpoda steinii was grown in two-stage continuous cultures with Escherichia coli as prey species. The concentration of prey and the ciliate mean cell volume, dry weight, and number per milliliter were determined at known growth rates. Steady states were reached in the second-stage continuous cultures at all growth rates. Although changes occurred in mean cell size of the ciliates and in the number per milliliter at various growth rates, the yield of protozoan biomass per unit of prey consumed was constant at all growth rates. The data were compared with several equations proposed to describe the kinetics of protozoan growth as a function of prey density.     

Effects of temperature, sulfide, and food abundance on growth and feeding of anaerobic ciliates

The trophic role of ciliates in anaerobic food webs has not been assessed experimentally. In order to obtain basic information necessary to interpret field situations, we studied the effects of temperature, sulfide concentration, and food abundance on the growth and feeding activities of two anaerobic ciliates, Plagiopyla nasuta and Metopus es. The growth rate of P. nasuta increased with temperature from 8 to 18 degrees C (Q(10) = 2.0) and remained constant in the range between 18 and 24 degrees C (0.22 day). Sulfide concentrations of between 0 and 1 mM did not affect the feeding activities, but concentrations greater than 2 mM were inhibitory. The functional response of P. nasuta feeding on fluorescently labeled heterotrophic and phototrophic bacteria was investigated. In both cases, the parameters of the functional response were almost identical when expressed in terms of biovolume: the maximal uptake rate (U(m)) was 1,800 mum ciliate h and the half-saturation constant for ingestion (k) was 1.5 x 10 mum ml. The functional response of M. es feeding on heterotrophic bacteria was found to be similar to that of P. nasuta. These ciliates needed high bacterial abundances in order to maintain their growth (k of about 4 x 10 bacteria ml), implying that they will frequently be food limited in planktonic environments. Both the maximal uptake rates and the maximal clearance rates were comparable to those of aerobic ciliates. By combining the growth and feeding data, we estimated gross growth efficiencies of 12 and 13% for P. nasuta and M. es, respectively. These results indicate that the feeding rates of anaerobic ciliates are similar to those of aerobic ciliates. Their slower growth must, therefore, be due to the lower gross growth efficiency (likely due to anaerobic metabolism).     

Growth kinetics of Colpoda steinii on Escherichia coli.

Colpoda steinii was grown in two-stage continuous cultures with Escherichia coli as prey species. The concentration of prey and the ciliate mean cell volume, dry weight, and number per milliliter were determined at known growth rates. Steady states were reached in the second-stage continuous cultures at all growth rates. Although changes occurred in mean cell size of the ciliates and in the number per milliliter at various growth rates, the yield of protozoan biomass per unit of prey consumed was constant at all growth rates. The data were compared with several equations proposed to describe the kinetics of protozoan growth as a function of prey density.     

Predator–prey interactions between a planktonic ciliate Strombidium sp. (Ciliophora, Oligotrichida) and the dinoflagellate Pfiesteria piscicida (Dinamoebiales, Pyrrophyta)

The functional response of a planktonic ciliate, Strombidium sp. feeding on the dinoflagellate Pfiesteria piscicida non-toxic zoospores (NTZ) was experimentally studied with four different prey concentrations (43–3153 cells ml⁻¹). Data from direct observations (NTZ inside individual Strombidium sp.) was used to calculate predator–prey specific ingestion and clearance rates. The ingestion rates varied between 0.68 and 14.26 NTZ ind⁻¹ h⁻¹, and with the predator–prey specific handling time of 2.83 min the U_max was 21.18 NTZ ind⁻¹ h⁻¹. The increase in the prey concentration between approximately 700 and 3000 NTZ ml⁻¹ did not increase the uptake of prey, and at the lowest Pfiesteria NTZ concentrations the feeding efficiency of Strombidium sp. was lowered, possibly indicating a situation of threshold feeding. When data from direct observations of ingested Pfiesteria NTZ were compared with values of total NTZ loss from the experimental water during the experiment, ingestion was found to represent only a fraction of the total NTZ loss in the presence of ciliates. This discrepancy was concluded to be due to other grazer related factors than actual ciliate grazing. The control of the initial growth of Pfiesteria community, in a pre-bloom situation, would require only a small ciliate abundance (less than 5 ml⁻¹), but when the Pfiesteria NTZ are scarce, relatively more ciliates are needed to limit the population growth of the dinoflagellate community because of the apparent feeding threshold. It is concluded that the formation of non-toxic P. piscicida blooms require periods of low grazing pressure or a means to escape grazing.     

Short‐term temperature change may impact freshwater carbon flux: a microbial perspective

Small freshwater bodies are abundant and economically and ecologically important on a global scale. Within these, protozoa play an important role in structuring planktonic food webs and sequestering CO₂. We hypothesized that short‐term (～20 days) fluctuations, of 2–10 °C, will significantly alter carbon flux associated with predator–prey interactions within the microbial planktonic food web. We examined the model ciliate, Urotricha farcta, which is abundant and common; it was fed the autotrophic flagellate Cryptomonas sp., which is also common. Laboratory experiments were conducted over relevant ranges: 8–24 °C; 0–2 × 10⁵ prey mL^?1. Mechanistic‐phenomenological multiple regressions were developed and fit to the data to obtain relationships for (1) growth rate and volume changes of the flagellate vs. temperature and (2) growth rates, grazing, and cell volume change of the ciliate vs. temperature and prey concentration. Responses revealed interaction between temperature and prey levels on all ciliate parameters, indicating it is inappropriate to apply simple temperature corrections (e.g. Q₁₀) to such functions. The potential impact of such temperature changes on carbon flux was illustrated using a simple ciliate–flagellate predator–prey model, with and without the top grazer, Daphnia, added. The model indicated that predator–prey pulses occurred over 20 days, with the ciliate controlling the prey population. For ciliates and prey, carbon production peaked at 20 °C and rapidly decreased above and below this maximum; differences between minimum and maximum were approximately fourfold, for both prey and ciliate, with low levels at 25–30 °C and 10–15 °C. Including literature data to parameterize, the influence of the grazer Daphnia did not alter the prediction that the ciliate may control short‐term flagellate pulses and temperature will influence these in a nonintuitive fashion.     

Predation on ciliates by freshwater calanoid copepods: rates of predation and relative vulnerabilities of prey

• 1 The susceptibility of ciliates in a mesotrophic lake to predation by Epischura lacustris, Diaptomus minutus and D. pygmaeus was assessed during summer. Oligotrichs, particularly Strobilidium velox (c. 43 μm), were removed efficiently by adult copepods and contributed substantially to the diet of female D. minutus. The presence of approximately 1,6 adult Epischura 1-^?1, or sixteen adult female Diaptomus 1-^?1, could halt the growth of S. vechx populations in summer.
• 2 Factors affecting the rate at which copepods prey on ciliates were examined in experiments with D. pygmaeus and cultured ciliates. Rate of predation on S. velox, the preferred species, became saturated at 5 S. velox ml^?1 (45ngCml^?1) and did not change with a 10-fold increase in alternative algal food.
• 3 Behavioural differences among ciliates, and the presence of other ciliates, contributed to differences in ciliate susceptibility to predation and suggest reasons why rates of removal of ciliates are not related to ciliate size.
• 4 By feeding selectively, at high rates, calanoids may suppress populations of some ciliates and thereby influence microzooplankton community structure.

     

Feeding, respiration and life history of the hyperiid amphipod Themisto libellula in the Arctic marginal ice zone of the Greenland Sea

Daily ingestion rates of the pelagic hyperiid amphipod Themisto libellula were studied in the marginal ice zone of the Arctic Fram Strait by feeding experiments, respiration measurements and an allometric approach based on body mass. Amphipods were collected by stratified multiple opening/closing net hauls and Rectangular Midwater Trawl (RMT 8) in August 2000 during the expedition ARK XVI/2 of R/V “Polarstern”. T. libellula occurred with abundances of 0.043 and 0.015 ind. m⁻³ in the upper 30 m of the water column at two RMT 8 stations. Based on respiration data, the daily ingestion necessary to cover metabolic energy demands measured 1.9±0.6% of body carbon per day. Actual prey consumption during feeding experiments with Calanus copepodids as prey was very similar and accounted for 1.9±1.5% day⁻¹, indicating that feeding on Calanus can meet the energy demands of T. libellula. In general, experimental results were slightly lower than the maximum potential ingestion (2% day⁻¹ for an individual of median body dry mass of 32 mg) estimated by an allometric equation based on body mass, but feeding experiments showed a strong variability. Reduced metabolism and low ingestion rates of T. libellula are consistent with low ambient temperature, large body size, slow growth and long life span of this polar species. The effect of the active pelagic life style of T. libellula on metabolism and ingestion rate is discussed in comparison to the sympagic (i.e. ice-associated) amphipod Gammarus wilkitzkii of similar body size living in the same environment. In relation to the mesozooplankton biomass in the investigation area, the predation impact by T. libellula was low. However, high-Arctic conditions also limit the secondary production of principal prey species, such as Calanus glacialis and Calanus hyperboreus, so that even low predation rates may affect the growth of prey populations.     

Pelagic Ciliates in a Large Mesotrophic Lake: Seasonal Succession and Taxon‐Specific Bacterivory in Lake Constance

The taxonomic composition of the ciliate assemblage and their taxon‐specific bacterial grazing rates in Lake Constance were investigated over the course of one year. Bacterial grazing rates were measured using natural fluorescently labelled bacteria (FLB) and compared to bacterial production. Small species such as Balanion planctonicum/Urotricha furcata and Rimostrombidium spp./Halteria sp. were the most numerous ciliates on the annual average. Larger ciliates such as Rimostrombidium lacustris and Limnostrombidium spp. contributed significantly to total ciliate biomass, but were relatively unimportant as bacterial grazers. Per capita ingestion rates ranged from 0–194 bacteria ciliate⁻¹ h⁻¹ and changed seasonally up to a hundredfold within a given taxon. Approximately 1% of the bacterial production were removed by the ciliate community on the annual average. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Direct and indirect impact of two common rotifer species (Keratella spp.) on two abundant ciliate species (Urotricha furcata, Balanion planctonicum)

1. We investigated the potential competition and feeding impact of the common rotifer species, Keratella cochlearis and K. quadrata , on the abundant prostomatid ciliates, Urotricha furcata and Balanion planctonicum, in laboratory batch culture experiments. All four species have similar feeding preferences, co-occur in many freshwater environments, and are thus potential competitors for the same algal food.
2. Two small Cryptomonas species served as food for the ciliates and the rotifers in the experiments. Growth rates of each ciliate species were measured when they grew alone and when they were paired with one of the rotifer species.
3. Both rotifer species reduced the growth rate of U. furcata , probably primarily by direct feeding on the ciliates. Growth rate of B. planctonicum was unaffected by K. cochlearis , but was drastically reduced by grazing and/or mechanical interference of K. quadrata .
4. These results suggest niche partitioning of the sympatric ciliates with respect to their rotifer competitors/predators.     

Cyclops predation on ciliates: species.specific differences and functional responses

Experiments were conducted to measure to what extent cyclopoidcopepods ingest ciliated protists. Five freshwater ciliate species,ranging in size from 22 to 120 µm diameter, were testedwith two species of cyclopoids: Cyclops abyssorum and Cyclopskolensis. Ingestion rates were measured by radiolabeling ciliateswith ¹⁴C, and from these, functional response curves (the changein ingestion rate with changing cell densities) were constructed.Cyclopoids ingest ciliates with very high estimated maximalrates of >200 cells cyclopoid^–1 h^–1 However,there are large differences in ingestion rates that are notpredictable by the size of predator or prey. One ciliate speciesof intermediate size, Coleps hirtus, is nearly immune from cyclopoidpredation at all measured ciliate densities. Three other smallciliate species that move in rapid jumps elicit Honing type3 functional responses, with very little change in ingestionrates at low ciliate densities. Thus, while cyclopoids are capableof having a very considerable impact on ciliate populations,some ciliate species appear to have behavioral, morphologicalor chemical defenses to reduce their vulnerability. This callsinto question the practice of considering ciliates a homogeneousgroup when constructing food web models.     

Participation of a Specific Substrate Degrading Strain in a Mixed Bacteria Culture as a Result of Ciliate Grazing

Participation of nitrilotriacetic acid degrading bacterial strain NTA-1 in the continuous-cultivated mixed culture was studied under different conditions including predation pressure of the ciliate Dexiostoma campyla (STOKES , 1886). From the viewpoint of dispersed/flocculated biomass distribution, significant relationships between NTA-1 and total bacteria ratio, and dispersed and total biomass ratio were proved in the systems without high concentrations of ciliates. The ciliate concentrations reaching 10⁴ ml⁻¹ stabilized flocculated biomass growth without directly affecting NTA-1 portion. Using fluorescently labelled NTA-1 bacteria, filter feeding rates of ciliates were evaluated (maximum individual uptake rate upon NTA-1 bacteria as a number of bacteria per ciliate per hour being 120 h⁻¹ and 260 h⁻¹ under ciliate division rate of 0.3 day⁻¹ and 1 day⁻¹, respectively). Biomass balance showed that dispersed NTA-1 bacteria should not serve as the sole feeding source for these free-swimming ciliates. The role of diversity of mixed bacterial diet in ciliate growth and the role of ciliate predation in stabilizing bacterial assemblage structure was proved.     

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.