Natural diet of herbivorous zooplankton in Lake Xolotlán (Managua)

The natural diet of herbivorous zooplankton was analyzed for a better understanding of the trophic relationships in Lake Xolotlán (Managua). Gut content of the most common zooplankton species (Arctodiaptomus dorsalis, Moina micrura andDiaphanosoma fluviatile) were analyzed. The quality and the relative abundance of ingested algae was studied. The most consumed algae during the dry season (February) wereCyclotella, Oocystis andLyngbya, and during the rainy season (November)Cyclotella, Oocystis andChroococcus. The kind of food ingested byA. dorsalis andM. micrura was similar in both periods. There was no similarity with the diet ofD. fluviatile. During the dry season, when algal biomass in the lake was high,A. dorsalis andM. micrura ingested a higher proportion of diatoms. During the rainy season, when food was scarce, the diet was more diverse and bluegreen algae (Chroococcus) were ingested in a larger proportion.Diaphanosoma fluviatile ingested predominantly tiny particles (bacteria and detritus) and algal food consisted mainly of green algae (Oocystis) and probably (not studied) nanoplanktonic algae. The results were consistent with those obtained in other lakes, indicating the importance of diatoms and green algae for zooplankton nutrition.     

Crustacean zooplankton species richness and associations in reservoirs and ponds of Aguascalientes State, Mexico

We report the species of crustacean zooplankton found in 19 resevoirs and ponds that were sampled at on at least two occasions in Aguascalientes State, Mexico, at a latitude of about 21°30 North Latitude. We collected a total of 33 cladoceran taxa, 15 calanoid and cyclopoid copepods, an Ergasilus copepod, 2 anostracans, one notostracan species and an amphipod. All these taxa had previously been reported in Mexico. As in more temperate areas, there was a significant correlation between the species richness and lake size. The species-area relationship for Aguascalientes was indistinguishable from that of more northerly lakes. The two most common associations of zooplankton species were (1) those small species that occurred with fish: Daphnia parvula, Diaphanosoma birgei, Leptodiaptomus siciloides, Mastigodiaptomus albuquerquensis, and Thermocyclops inversus, and (2) the large Daphnia schodleri that occurred with the predator Notonecta, in the absence of fish. With minor variations, these two associations also occur throughout temperate North America.     

An experimental demonstration of trophic interactions affecting water quality of Rice Lake, Ontario (Canada)

Eight cylindrical enclosures (3 m diameter, 2.7 m long, V = 20m³) were installed in eutrophic Rice Lake (Ontario, Canada) in late spring of 1987. Fish (yearling yellow perch (Perca flavescens) and macrophytes (Potamogeton crispus) presence and absence were set at the beginning of the experiment to yield four combinations of duplicate treatments. The purpose of the experiment was to determine if the phytoplankton, zooplankton, macrophytes and fish species resident in the lake interact to influence water quality (major ions, phosphorus, algal densities and water clarity).The presence of fish was associated with: (1) decreased biomass of total zooplankton, (2) decreased number of species in the zooplankton, (3) decreased average size of several zooplankton taxa, (4) higher total phosphorus concentrations, (5) higher phytoplankton and chlorophyll a concentrations, (6) lower water clarity, (7) lower potassium levels during macrophyte die-back, (8) lower pH and higher conductivity in the presence of macrophytes. Biomass of large Daphnia species (but not total zooplankton) was highly correlated with the algal response (r ² = 0.995) and was associated with reduced biomass of several algal taxa including some large forms (Mougeotia, Oedogonium) and several colonial blue-green algae. However, no significant control of late summer growth of the bloom-forming blue-green alga Anabaena planctonica Brun. was achieved by the Daphnia presence-fish absence treatment. Release of phosphorus to the water column during the die-back of P. crispus was not an important phenomenon.     

The ingestion and digestion of algae by Chloeon dipterum L. (Ephemeroptera)

Summary The ability of larvae of Chloeon dipterum L. to ingest various species of algae was investigated in the laboratory. There was a direct relationship between the size of an alga and the frequency with which it was ingested by different sizes of larva. The frequency of ingestion of Anabaena, Cladophora, and Hydrodictyon appeared to be governed by factors in addition to their size.Several species of algae were thoroughly and rapidly digested by C. dipterum in the laboratory.Cultures of the hind-gut contents of larvae collected in the field, and of those fed upon algae in the laboratory, showed that cells of several species of algae remained viable in the gut for periods of at least 20 hours. These were narrow filamentous forms or small cells with or without a gelatinous sheath. It is suggested that such species pass between the mouthparts without being damaged so that in the absence of a cellulase the digestive enzymes of the gut are unable to penetrate the cell walls.     

Effects of UV-B irradiated algae on zooplankton grazing

We tested the effects of UV-B stressed algae on grazing rates of zooplankton. Four algal species (Chlamydomonas reinhardtii, Cryptomonas sp., Scenedesmus obliquus and Microcystis aeruginosa) were used as food and fed to three zooplankton species (Daphnia galeata, Bosmina longirostris and Brachionus calyciflorus), representing different taxonomic groups. The phytoplankton species were cultured under PAR conditions, and under PAR supplemented with UV-B radiation at two intensities (0.3 W m^–2 and 0.7 W m^–2, 6 hours per day). Ingestion and incorporation experiments were performed at two food levels (0.1 and 1.0 mg C l^–1) using radiotracer techniques. The effect of food concentration on ingestion and incorporation rate was significant for all three zooplankton species, but the effect of UV-B radiation was more complex. The reactions of the zooplankton species to UV-B stressed algae were different. UV-B stressed algae did not affect Daphnia grazing rates. For Bosmina the rates increased when feeding on UV-B stressed Microcystis and decreased when feeding on UV-B stressed Chlamydomonas, compared with non-stressed algae. Brachionus grazing rates were increased when feeding on UV-B stressed Cryptomonas and UV-B stressed Scenedesmus, and decreased when feeding on UV-B stressed Microcystis, compared with non-stressed algae. These results suggest that on a short time scale UV-B radiation may result in increased grazing rates of zooplankton, but also in decreased grazing rates. Long term effects of UV-B radiation on phytoplankton and zooplankton communities are therefore difficult to predict.     

Effects of stoichiometric dietary mixing on<Emphasis Type="Italic"> Daphnia</Emphasis> growth and reproduction

Herbivores often encounter nutritional deficiencies in their diets because of low nutrient content of plant biomass. Consumption of various diet items with different nutrient contents can potentially alleviate these nutritional deficiencies. However, most laboratory studies and modeling of herbivorous animals have been done with diets in which all food has uniform nutrient content. It is not clear whether heterogeneous versus uniform food of equal overall nutrient content is of equivalent nutritional value. We tested the effects of dietary mixing on performance of a model organism, Daphnia. We fed two species of Daphnia ( D. galeata, D. pulicaria) with diets of equivalent bulk stoichiometric food quality (C:P) and studied whether they would produce equivalent performance when C:P was uniform among cells or when the diet involved a mixture of high C:P and low C:P cells. Daphnia were fed saturating and limiting concentrations of a uniform food of moderate C:P (UNI) or mixtures (MIX) of high C:P (LOP) and low C:P (HIP) algae prepared to match C:P in UNI. Daphnia were also fed HIP and LOP algae separately. Juvenile growth rate and adult fecundity were measured. D. galeata performance in UNI and MIX treatments did not differ, indicating that partitioning of C and P among particles did not affect dietary quality. Similarly, D. pulicarias performance was similar in the MIX and UNI treatments but only at low food abundance. In the high food treatment, both growth and reproduction were higher in the MIX treatment, indicating some benefit of a more heterogeneous diet. The mechanisms for this improvement are unclear. Also, food quality affected growth and reproduction even at low food levels for both D. pulicaria and D. galeata. Our results indicate that some species of zooplankton can benefit from stoichiometric heterogeneity on diet.     

Quantitative comparison of food niches in some freshwater zooplankton

Summary The abilities of some zooplankton (rotifers, cladocerans, copepods) to ingest different sizes and kinds of food cells were quantified by determining the relative efficiencies with which they ingested nine tracer-cell types, ranging from a coccoid bacterium (0.45 m³) to the alga Cryptomonas erosa (800–920 m³). These efficiencies were obtained by dividing the clearance rate of each zooplankton group (species population, developmental stage or size class of a species population) on each ³²P-labeled cell type by that of a simultaneously-offered, ³³P-labeled, standard cell type — Chlamydomonas reinhardtii. Similarities of efficiency patterns on these cell types (food niches) between all possible pairs of the 17 zooplankton groups from 4 ecosystems were determined by calculating correlation coefficients. Although the utilization of the tested cell types may vary greatly within a species, three feeding guilds could be distinguished — based primarily on the efficiencies with which the smallest cell types were ingested. Guild I (Poyarthra vulgaris, Keratella crassa, Diaptomus minutus nauplii) ate the smallest cells (<4 m diameter) (bacterium, Synechococcus, Nannochloris) and Ankistrodesmus very ineffifently but the three Cryptomonas species very efficiently. Guild II (Bosmina longirostris, D. minutus copepodites and Adults) had higher efficiencies on Synechococcus, Nannochloris, Ankistrodesmus, Stichococcus, and Stephanodiscus than guild I but similarly low ones on the bacterium and high ones on the Cryptomonas species. Guild III (Conochilus inicornis, Keratella cochlearis, Ceriodaphnia quadrangula, Diaphanosoma leuchtembergianum) differed from guilds I and II in having uniformly high efficiencies on all the small cells as well ad the larger ones. Principal component analysis of the matrix of correlation coefficients provided objective confirmation of the three guilds and provided a visual representation of the food niches of the 17 zooplankton groups in 3-dimensional space.     

A study of the zooplankton community of Billings Reservoir — São Paulo

The composition of the zooplankton of the Billings Reservoir and its variation in an eutrophic environment, subject to frequent blooms of algae (chiefly Cyanophyceae) was studied during one year (from October, 1977 to September, 1978) in two stations in the littoral and in the limnetic zone.The zooplankton community in the limnetic zone was dominated by cyclopoid copepods (Thermocyclops crassus and Metacyclops mendocinus) and by rotifers (Brachionus, Polyarthra and others) which represented, respectively 38.5 and 35.5% of the total zooplankton. At the littoral zone, cyclopoids were the most abundant (42.3%).The cladocerans were the least significant group at both stations, and calanoid copepods were found only at the littoral zone.A higher production of small filtrators, such as rotifers, cyclopoid nauplii and Bosmina sp was observed.     

Structure and dynamics of zooplankton communities in the littoral zone of some North Carolina lakes

Species composition and seasonal, dynamics of zooplankton in the littoral zone were studied in three piedmont North Carolina lakes for one year. Nygaard's compound index indicated oligotrophic conditions in Belews Lake and eutrophic conditions in Salem Lake and Lake 150. A total of 32 species of zooplankton were found in the samples. Significantly fewer species of truely littoral zooplankton were present in the oligotrophic lake regardless of season (P < 0.05). Eutrophication appears to favor increased diversity in zooplankton of the littoral zone. Habitat heterogeneity, provided by a well developed littoral zone containing aquatic macrophytes, may be the major factor contributing to the maintenance of more taxa of zooplankton in eutrophic systems.Distinct taxa of Cladocera and Copepoda are present in the littoral zone, exhibiting seasonal dynamics that are largely different from the limnetic fauna. Such dynamics may result from predation by characteristically limnetic species of cyclopoid copepods which seek prey in the littoral zone. The numerical and seasonal abundance of predators and prey are inversely related and the true littoral taxa, represented in the present study by the genera Alona, Chydorus, Pleuroxus, Sida, Simocephalus, and Eucyclops, contained no predaceous species. The seasonal dynamics of these genera are very similar even in widely separated geographical regions, indicating that the factor(s) responsible operate independently of climatic and chemical variables. Intrazooplankton predation appears to be a more plausable explanation than segregation along depth which, although consistent with data from studies of limnetic waters, cannot be related to populations of zooplankton in shallow littoral areas.     

Different Predation Impacts of Two Cyclopoid Species on a Small-sized Zooplankton Community: An Experimental Analysis with Mesocosms

We used mesocosms to analyze predation impacts on the prey populations and prey community structures by two cyclopoid copepod species, the larger Mesocyclops pehpeiensis and the smaller Thermocyclops taihokuensis, who coexist with small-sized herbivorous zooplankton species in a fish-abundant lake. The overall predation impact on the prey populations was stronger for Mesocyclops than for Thermocyclops. Mesocyclops had a strong and less selective impact on the rotifer community but a selective impact on the crustaceans. In contrast, Thermocyclops had a selective predation impact on rotifers but a weak and less selective impact on the crustacean community. As a result, the former predator reduced the diversity of the crustacean community but not the rotifer community, while the latter had an opposite impact on the diversities of the two communities. It has been suggested that fish induce development of a zooplankton community dominated by the small-sized zooplankton species in fish-abundant lakes. Our results demonstrated that cyclopoid copepods altered species composition and diversity of the small-sized zooplankton community in such lakes. Thus, the results have given an important suggestion on the role of the invertebrate predator cyclopoid copepods, which often coexist with fish, that they determine population dynamics and community structures of small-sized zooplankton in fish-abundant lakes.     

Feeding convergence in South American and African zooplanktivorous cichlids Geophagus brasiliensis and Tilapia rendalli

Synopsis Acará, Geophagus brasiliensis, and red-breasted bream, Tilapia rendalli, are important planktivorous cichlids in southern Brazilian lakes and reservoirs. In laboratory experiments, I quantified behavior and selectivity of different sizes of these two fish feeding on lake zooplankton. Feeding behavior depended on fish size. Fish < 30 mm were visual feeders. Fish 30–50 mm either visually fed or pump-filter fed depending on zooplankton size. Fish > 70 mm were pump-filter feeders. Replicate 1 h feeding trials revealed that, as the relative proportions of prey changed during an experiment, acará (30–42 mm, standard length) and tilapia (29–42 mm) shifted from visual feeding on large evasive copepods to filter feeding on small cladocerans and rotifers. Electivity and feeding rate increased with prey length, but were distinct for similar-sized cladocerans and copepods. Visual/filter-feeding fish had lowest electivities for small and poorly evasive rotifers and cyclopoid nauplii. They fed non-selectively on cyclopoid copepodites, had intermediate electivities for calanoid nauplii and small cladocerans, and had highest electivities for large cladocerans, cyclopoid adults, and calanoid copepodites and adults. Although belonging to different cichlid genera and native to South America and Africa, respectively, acará and red-breasted bream (= congo tilapia) exhibited similar selectivity for zooplankton. Apparently, few stereotyped feeding behaviors have evolved during the acquisition of microphagy in fish. Shift in feeding modes allows these two species to optimally exploit the variable and dynamic patchy distribution of planktonic resources.     

Feeding behaviour of major 0 + fish species in a shallow, eutrophic lake (Tjeukemeer, The Netherlands)

The forage base and the food selectivity of 0+ representatives of six abundant freshwater fish species were studied in a shallow, eutrophic Dutch lake. Most species relied on the zooplankton; the size-selective predation in early summer was directed to the smaller copepods and in late summer to larger cladocerans and copepods than concurrently present in the lake. Daphnia spp. and cyclopoid copepods were the main zooplankton taxa for smelt, perch and pikeperch. Energetically, the large cladoceran, Leptodora kindtii, was especially important for pikeperch. Bream and roach preyed upon smaller zooplankton than the other fish species. The influence of the zooplankton predation by abundant 0+ fish was clear from a small mean Daphnia size in September; this size is to be used as an indicator in fishery management. Neomysis integer, the most important macrofauna species, was consumed by perch, pikeperch and ruffe; pikeperch was most size-selective in this respect. The 0+ ruffe was à typically benthivorous fish. Only the 0+ pikeperch became piscivorous, especially in years when smelt was abundant.     

Diatom–salinity relationships in wetlands: assessing the influence of salinity variability on the development of inference models

We determined in situ feeding rates of three co-occurring coastal mysid species using [methyl-³H]-thymidine-labelled algal detritus (Lessonia corrugata), NaH¹⁴CO₃-labelled phytoplankton (Isochrysis galbana) and zooplankton (Artemia sp. nauplii). All three species showed a wide and overlapping range of feeding rates on the three food types, suggesting they were broadly omnivorous. However, selectivity studies often showed a strong preference for animal prey. Although there was an overlap in the types of food the mysids ingested, some degree of feeding niche partitioning was demonstrated. Paramesopodopsis rufa tended to be more carnivorous, Tenagomysis tasmaniae fed least on zooplankton and phytoplankton, and largely on algal detritus, and Anisomysis mixta australis ingested few zooplankters, and moderate amounts of algal detritus and phytoplankton. Handling editor: P. Viaroli     

Inter-species variability in the consumption of algae by oligochaetes

The importance of algae in the diet of the oligochaetesArcteonais lomondi, Uncinais uncinata andLimnodrilus claparedeianus was determined from May 1978 to April 1979 in two lakes located in northern Canada. The lakes were small (130–157 ha), shallow, (<15 m) and mesotrophic. During summer, algae accounted for up to 57–75% by volume of ingested matter inA. lomondi andU. uncinata depending on lake whereas in winter the corresponding range was 10–22%. Dominant algae found in the gut included the diatomsSurirella robusta, Diploneis puella, Amphora ovalis, Stephanodiscus astraea, Fragilaria construens andAchnanthes minutissima. Although the same taxa were ingested byL. claparedeianus, algae always represented <5% by volume of the gut contents. This possibly reflects subsurface feeding in an area where algae were rare. The length distribution of ingested diatoms, ranging from 9 to 250 m, was similar regardless of species in both lakes. Hence, there was no partitioning of algal food resources among oligochaetes.     

Linking herbivore-induced defences to population dynamics

1. Theoretical studies have shown that inducible defences have the potential to affect population stability and persistence in bi‐ and tritrophic food chains. Experimental studies on such effects of prey defence strategies on the dynamics of predator–prey systems are still rare. We performed replicated population dynamics experiments using the herbivorous rotifer Brachionus calyciflorus and four strains of closely related algae that show different defence responses to this herbivore. 2. We observed herbivore populations to fluctuate at a higher frequency when feeding on small undefended algae. During these fluctuations minimum rotifer densities remained sufficiently high to ensure population persistence in all the replicates. The initial growth of rotifer populations in this treatment coincided with a sharp drop in algal density. Such a suppression of algae by herbivores was not observed in the other treatments, where algae were larger due to induced or permanent defences. In these treatments we observed rotifer population densities to first rise and then decline. The herbivore went extinct in all replicates with large permanently defended algae. The frequency of herbivore extinctions was intermediate when algae had inducible defences. 3. A variety of alternative mechanisms could explain differential herbivore persistence in the different defence treatments. Our analysis showed the density and fraction of highly edible algal particles to better explain herbivore persistence and extinctions than total algal density, the fraction of highly inedible food particles or the accumulation of herbivore waste products or autotoxins. 4. We argue that the rotifers require a minimum fraction and density of edible food particles for maintenance and reproduction. We conjecture that induced defences in algae may thus favour larger zooplankton species such as Daphnia spp. that are less sensitive to shifts in their food size spectrum, relative to smaller zooplankton species, such as rotifers and in this way contributes to the structuring of planktonic communities.     

Zooplankton as a compound mineralising and synthesizing system: phosphorus excretion

Data on phosphate excretion rates of zooplankton are based on measurements using the pelagic crustacean zooplankton of Lake Vechten and laboratory-cultured Daphnia galeata. In case of Daphnia sp we measured the effects of feeding on P-rich algae and P-poor algae (Scenedesmus) as food on the P-excretion rates at 20°C. The excretion rates of the natural zooplankton community, irrespective of the influence of the factors mentioned, varied by an order of magnitude: 0.025–0.275µg PO₄-Pmg^–1C in zooplankton (C _zp ) h^–1. The temperature accounted for about half the observed variation in excretion rates. The mean excretion rates in the lake, computed for 20°C, varied between 0.141 and 0.260 µg Pmg^–1C _zp h^–1. Based on data of zooplankton biomass in the lake the P-regeneration rates by zooplankton covered between 22 and 239% of the P-demand of phytoplankton during the different months of the study period.In D. galeata, whereas the C/P ratios of the Scenedesmus used as food differed by a factor 5 in the experiments, the excretion rates differed by factor 3 only. Despite the higher P-excretion rates (0.258± 0.022 µg PO₄-P mg^–1 C h^–1) of the daphnids fed with P-rich food than those fed with P-poor food (0.105 ± 0.047 µg PO₄-P mg^–1 C h^p–1), both the categories of the animals were apparently conserving P. A survey of the literature on zooplankton excretion shows that in Daphnia the excretion rates vary by a factor 30, irrespective of the species and size of animals and method of estimation and temperature used.About two-thirds of this variation can be explained by size and temperature. A major problem of comparability of studies on P-regeneration by zooplankton relates to the existing techniques of P determination, which necessitates concentrating the animals several times above the in situ concentration (crowding) and prolonged experimental duration (starving), both of which manifest in marked changes that probably lead to underestimation of the real rates.     

An experimental study of the effects of nutrient supply and Chaoborus predation on zooplankton communities of a shallow tropical reservoir (Lake Brobo, Côte d'Ivoire)

1. Based on two mesocosm experiments and 10 in vitro predation experiments, this work aimed to evaluate the impact of nutrient supply and Chaoborus predation on the structure of the zooplankton community in a small reservoir in Côte d'Ivoire. 2. During the first mesocosm experiment (M1), P enrichment had no effect on phytoplankton biomass (chlorophyll a) but significantly increased the biomass of some herbivorous zooplankton species (Filinia sp, Ceriodaphnia affinis). During the second experiment (M2), N and P enrichment greatly increased phytoplankton biomass, rotifers and cladocerans (C. affinis, C. cornuta, Moina micrura and Diaphanosoma excisum). In both experiments, nutrient addition had a negative impact on cyclopoid copepods. 3. Larger zooplankton, such as cladocerans or copepodites and adults of Thermocyclops sp., were significantly reduced in enclosures with Chaoborus in both mesocosm experiments, whereas there was no significant reduction of rotifers and copepod nauplii. This selective predation by Chaoborus shaped the zooplankton community and modified its size structure. In addition, a significant Chaoborus effect on chlorophyll a was shown in both experiments. 4. The preference of Chaoborus for larger prey was confirmed in the predation experiments. Cladocerans D. excisum and M. micrura were the most selected prey. Rotifer abundance was not significantly reduced in any of the 10 experiments performed. 5. In conclusion, both bottom‐up and top‐down factors may exert a structuring control on the zooplankton community. Nutrients favoured more strictly herbivorous taxa and disadvantaged the cyclopoid copepods. Chaoborus predation had a strong direct negative impact on larger crustaceans, favoured small herbivores (rotifer, nauplii) and seemed to cascade down to phytoplankton.     

Response of algae and zooplankton to C18 fatty acids of Chlamydomonas reinhardtii

Three C₁₈ fatty acids were assayed for their activity against a number of algae and zooplankton. The three acids, lenolenic, lenoleic, and oleic, reduced the growth of Haematococcus lacustris, Synechococcus leopoliensis, and Botrydiopsis alpina by 50% of control growth in concentrations below 7 ppm. Calanoid and cyclopoid copepods in mixed cultures inoculated with lenolenic and lenoleic acid had LD₅₀ values below 10 ppm. An increase in copepod mortality was observed with increases in cyclopoid density and decreased with increases in calanoid density. Eucyclops agilis inoculated with lenolenic acid had a LD₅₀ value of 4 ppm.     

The influence of prey hardness on Daphnia's selectivity for large prey

Two comparable methods were used to study the feeding of four species of Daphnia on large spherical particles which differed in size and hardness. The first method used gut analysis to estimate the selectivities of daphnids feeding in a broad size range of a single particle type, including polystyrene beads (4–60 µm diameter) in the laboratory and Eudorina colonies (10–90 µm) in the field. In the second method, Daphnia of different sizes fed in a mixture of 6.5 µm Chlamydomonas and one of eight test particles. Smaller daphnids were less effective in feeding on large test particles. Nonlinear regression was therefore used to estimate the Daphnia body size at which the clearance rate on a test particle was reduced to 50% of that for Chlamydomonas. The results of both methods show that prey size and hardness are both very important in determining daphnid feeding selectivity. For a given particle size, soft algae (naked and gelatinous flagellates) are more readily ingested than hard algae (diatoms and dinoflagellates), and hard algae are more readily ingested than polystyrene beads. Daphnia can feed effectively on algae that are 2–5 times larger than the largest ingestible bead.     

Carnivorous planktonic Difflugia (Protista, Amoebina Testacea) and their predators

Four planktonic species of Difflugia co-occurring in a south Chinese reservoir were found to be carnivorous, but the diet was widest in the largest species (D. tuberspinifera) and narrowest in the smallest (D. hydrostatica). It included rotifers, ciliates, dinoflagellates, floating eggs, and small particles associated with organic debris. Scavenging and cannibalism were also observed. Species with a collared test (D. biwae, D. mulanensis) showed a form of suction-feeding, while species with teeth on the pseudostome used these, together with their pseudopods, as “inverted crown corks”, providing leverage for opening the lorica of their (rotifer) prey. Predators of Difflugia included cyclopoid copepods. In addition, the rotifers Asplanchna priodonta, Ploesoma hudsoni and, occasionally, big ciliates (Stentor sp.) all ingested their prey as a whole.