Daily and vertical dynamics of rotifers under the impact of diatom blooms in the Three Gorges Reservoir,China

The Three Gorges Dam was built in 2005 with a storage capacity of 39.3 billion m³, ranking 22nd in the world. However, since the impoundment of the reservoir, serious blooms of phytoplankton have occurred. Rotifers, having a key role in the freshwater aquatic food web, are important grazers of phytoplankton and an essential food resource to higher trophic consumers. To explore the impacts of phytoplankton blooms on the rotifer community, daily and vertical surveys of rotifers were conducted in a bay of the Three Gorges Reservoir (Xiangxi Bay). Altogether 46 rotifer species were registered, and Synchaeta tremula, Polyarthra vulgaris, and Brachionus calyciflorus were the most abundant species accounting for 36, 26, and 16% of the mean rotifer densities, respectively. Although these dominant species always prevailed in the rotifer community, their proportions changed significantly from non-bloom phase to bloom phase, e.g., the significance of S. tremula deceased from 46.8 to 33.2%, while P. vulgaris and B. calyciflorus increased from 23.9 and 13.9% to 26.2 and 16.2%, respectively. In the vertical water column, all the rotifer following phytoplankton displayed an aggregated distribution, concentrating at the upper layers (0.5–5 m), especially during the bloom phase. From the non-bloom phase to the bloom phase, rotifer densities, the dominant rotifers, Shannon–Wiener and Margalef’s diversity increased significantly, while the evenness displayed the opposite trend. Non-metric multidimensional scaling analysis (NMDS) revealed that the samples in the non-bloom phase were well separated from those in the bloom phase. This means that the outbreak of the diatom bloom in the Xiangxi Bay had significant impacts on the rotifer community. Further investigations are needed to address the impacts of the changes of rotifer community on higher trophic levels.     

Studies on Brachionus (Rotifera): an example of interaction between fundamental and applied research

The genus Brachionus has been the main subject of studies reported in about 1000 papers published since 1950. About three-fourths of these deal with Brachionus plicatilis and B. rotundiformis and are mainly related to their use as prey for aquatic organisms. Also abundant, but to a lesser extent, are studies on B. calyciflorus, many of which are concerned with aquatic ecotoxicology. These studies constitute an interesting interaction between fundamental and applied research. For example, advances in fundamental biology have been applied to improve the production of rotifer biomass. Alternatively, new perspectives in fundamental research on rotifers have emerged while solving technical and biological problems related to the rearing of aquatic animal larvae. This review describes some aspects that have shown a significant advance due to such interaction between fundamental and applied research on rotifers, e.g. growth conditions, biochemical composition and morphotypes.     

Rotifers as food in aquaculture

The rotifer Brachionus plicatilis (O.F. Muller) can be mass cultivated in large quantities and is an important live feed in aquaculture. This rotifer is commonly offered to larvae during the first 7–30 days of exogenous feeding. Variation in prey density affects larval fish feeding rates, rations, activity, evacuation time, growth rates and growth efficiencies. B. plicatilis can be supplied at the food concentrations required for meeting larval metabolic demands and yielding high survival rates. Live food may enhance the digestive processes of larval predators. A large range of genetically distinct B. plicatilis strains with a wide range of body size permit larval rearing of many fish species. Larvae are first fed on a small strain of rotifers, and as larvae increase in size, a larger strain of rotifers is introduced. Rotifers are regarded as living food capsules for transferring nutrients to fish larvae. These nutrients include highly unsaturated fatty acids (mainly 20: 5 n–3 and 22: 6 n–3) essential for survival of marine fish larvae. In addition, rotifers treated with antibiotics may promote higher survival rates. The possibility of preserving live rotifers at low temperatures or through their resting eggs has been investigated.     

Freshwater Copepods and Rotifers: Predators and their Prey

Three main groups of planktonic animals inhabit the limnetic zone of inland waters and compete for common food resources: rotifers, cladocerans and copepods. In addition to competition, their mutual relationships are strongly influenced by the variable, herbivorous and carnivorous feeding modes of the copepods. Most copepod species, at least in their later developmental stages, are efficient predators. They exhibit various hunting and feeding techniques, which enable them to prey on a wide range of planktonic animals from protozoans to small cladocerans. The rotifers are often the most preferred prey. The scope of this paper is limited to predation of freshwater copepods on rotifer prey. Both cyclopoid and calanoid copepods (genera Cyclops, Acanthocyclops, Mesocyclops, Diacyclops, Tropocyclops, Diaptomus, Eudiaptomus, Boeckella, Epischura and others) as predators and several rotifer species (genera Synchaeta, Polyarthra, Filinia, Conochilus, Conochiloides, Brachionus, Keratella, Asplanchna and others) as prey are reported in various studies on the feeding relationships in limnetic communities. Generally, soft-bodied species are more vulnerable to predation than species possessing spines or external structures or loricate species. However, not only morphological but also behavioural characteristics, e.g., movements and escape reactions, and temporal and spatial distribution of rotifer species are important in regulating the impact of copepod predation. The reported predation rates are high enough to produce top-down control and often achieve or even exceed the reproductive rates of the rotifer populations. These findings are discussed and related to the differences between the life history strategies of limnetic rotifer species, with their ability to quickly utilize seasonally changing food resources, and adjust to the more complicated life strategies of copepods.     

Characterization of the bacterial flora of mass cultivated Brachionus plicatilis

Bacterial density and composition in association of mass cultivated rotifers (Brachionus plicatilis, SINTEF-strain) was investigated, during experimental conditions identical to the procedures used for preparing rotifers as live food for marine cold water fish larvae. These procedures include cultivation, enrichment with squid meal and acclimation to low temperature by storage of the rotifer culture at 6 °C. Large variations were observed in the number of rotifer associated (1.8–7.6 · 10³ colony forming units per rotifer^–1) and free-living (0.6–25 10⁷ cells·ml^–1) bacteria. An increase of 50–150% in the bacterial number was normally observed after feeding the rotifer with squid meal, but after three days of acclimation at 6 °C, the bacterial numbers decreased to the initial level.After enrichment of the cultures with squid meal, the similarity in the composition of the bacterial flora between the rotifers and water was reduced. However, acclimation of the culture at 6 °C resulted in better agreement of the rotifer associated flora and that in water. Enrichment of the cultures induced a shift in the bacterial composition from Cytophaga/Flavobacterium dominance to Pseudomonas/Alcaligenes dominance. The bacterial flora of the rotifer cultures are dominated by presumably opportunistic species after enrichment, which may have detrimental effects when rotifers are fed as live food to marine fish larvae.     

On relation to substrate in sessile rotifers

Information on the distribution of 45 sessile rotifers from diverse freshwaters in south and central Sweden was analyzed to reveal possible relationships to their substrates. Almost all of them showed an exclusively periphytic occurrence. The highest number of species was found on Utricularia, but otherwise it was not possible to correlate rotifer presence to any special macrophyte or category of plants (e.g., fine-leaved or floating-leaved species).     

Social parasites among African allodapine bees (Hymenoptera,Anthophoridae, Ceratinini)*

Among the numerous nonparasitic allodapine bees there are 11 known species with parasitic or probably parasitic habits. These species live in nests of their close relatives, the female parasite replacing an egg-layer of the host. Seven of the parasitic species are distributed among four otherwise nonparasitic genera, while four species of parasites are placed in three exclusively parasitic genera. The parasites have mostly arisen independently from different nonparasitic forms. There is much convergence among the parasitic forms involving such characters as the flattened or concave face, reduced eyes, reduced mouthparts, reduced wing venation, and reduced pollen-carrying scopa. In the most specialized parasitic genera the mouthparts are so small as to be almost surely useless for obtaining food from flowers. Such bees must feed in the host nest, and are not found on flowers. Their wings must be adequate to take them to a new host nest but the reduced venation and eyes must reflect the reduced locomotary and sensory needs of a bee that does not visit flowers. In this paper a new, presumably parasitic Allodapula is described as is a parasitic Braunsapis, a parasitic Allodape, and a Eucondylops. A previously described Macrogalea is recognized as a parasite for the first time. A new genus and species of parasites Nasutapsis straussorum, allied to Braunsapis, is also described. All these forms are from Africa.     

Review of rotifers and crustaceans in highly acidic environments of pH values ≤3

A review of the literature on rotifers and crustacean zooplankton in highly acidic environments revealed that data from eleven aquatic environments on three continents (America, Europe, Japan) with a pH 3 are available. Seven sites are influenced by volcanism or weathering processes in the catchment area, four others originated from human mining activities. Species richness was generally low. Only 16 species are found and 1–11 species are reported for each area. These studies clearly show that small littoral or benthic rotifers predominate over crustaceans under highly acidic conditions. In the Lusatian mining area (Germany), all lakes are colonized by zooplankton, even the most acidic one with a pH of 2.3. The core community consists of the rotifers Cephalodella hoodi, C. gibba, Elosa worallii and Rotaria rotatoria, with C. hoodi and E. worallii the most abundant. Larger species, such as the rotifer Brachionus sericus or the cladoceran Chydorus sphaericus, occur at a pH close to 3. A similar pattern is reported from acidic mining lakes in Illinois, U.S.A. Many of these species can also be found in less acidic softwater or even alkaline environments due to the tolerance of a broad range of pH values. Elosa worallii and Brachionus sericus are probably the most acidophilic rotifer species, though at least the latter can also grow at neutral pH in the laboratory. Clear understanding of the pH limits of B. sericus in nature may also have been complicated by the fact that it has probably in the past been wrongly named as B. urceolaris (phenotype `sericus'). The typical B. urceolaris cannot tolerate extremely low pH. Overall, generalist species with a worldwide distribution seem to play the major role in the colonization of anthropogenic highly acidic lakes.     

Environmental Predictors of Rotifer Community Structure in Two Types of Small Water Bodies

The species diversity and distribution of rotifers between different habitats (elodeids, helophytes and open water) of 34 field and 31 forest ponds, differing in regard to origin, size, depth, macrophyte cover, overshading and the presence of fish were examined (N = 381). 197 taxa were found in both types of ponds with 32 species being rare, endangered or new to Polish fauna. The species composition and Shannon‐Wiener index distribution reflected heterogeinity of the habitats, while rotifer mean densities revealed a reverse pattern in both types of water bodies. The great variability of limnological features contributed to a lack of significant differences in rotifer abundance between both types of water bodies. Although some rotifers preferred one specific type of water body (forest vs. field), the type of habitat was a much stronger predictor of their distribution, which reflects a necessity to examine ponds in relation to their microhabitats created by various macrophytes. Rotifers revealed a strict division into two groups – of pelagic origin (e.g., Polyarthra vulgaris), which were attributed to the open water and helophytes, and of littoral origin (e.g., Lepadella patella), which were associated with elodeids, biomass of a plant habitat and a lack of fish. The selective choice of the most complex habitat (elodeids) by only littoral species suggests the weak impact of fish in the studied ponds and the most advantageous conditions for littoral rotifers among such a habitat. The first group comprised species characteristic of field ponds, while the second was characteristic of forest ponds. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of the epizoic rotifer Brachionus rubens on the population growth of three cladoceran species

Using population densities and growth rates as criteria, we studied interactions between the epizoic rotifer Brachionus rubens and each of three cladoceran species differing in size and reproductive rates — Daphnia carinata, Moina macrocopa and Ceriodaphnia rigaudi. In all mixed — species experiments, B. rubens existed in both the epizoic mode, attached to the cladoceran host, and in the free-swimming mode. Rotifer population growth rates were significantly depressed in the presence of M. macrocopa, presumably as a consequence of exploitative and interference competition. The largest cladoceran, D. carinata probably did not suppress B. rubens, because the epizoic component of the rotifer population escaped from the deleterious effects of mechanical interference. Peak population numbers and initial population growth rates reached by all three cladocerans were lower in the presence of B. rubens, probably because of the adverse effects of the epizoic infestation, which was maximal on D. carinata and least on C. rigaudi. In mixed-species cultures of D. carinata and M. macrocopa, the presence of B. rubens helped D. carinata coexist with M. macrocopa, which otherwise would have suppressed the Daphnia.     

Neuromuscular organization of the freshwater colonial rotifer, Sinantherina socialis, and its implications for understanding the evolution of coloniality in Rotifera

Coloniality among rotifers is rare, and while the adaptive significance of the lifestyle has been explored previously, there are few details about how it may have influenced the morphology of colony members. In this study, we use confocal laser scanning microscopy combined with cyto- and immunohistochemistry to determine if the colonial rotifer, Sinantherina socialis, differs in neuromuscular organization relative to other colonial and solitary forms. Our observations indicate that the patterns of serotonergic neurons and somatic muscles in S. socialis are broadly similar to other rotifers. At the neuronal level, the distribution of serotonergic (5HT-IR) neurons in S. socialis is most similar to colony-forming species of Conochilus: (1) paired nerve cords extend the length of the body; (2) the cerebral ganglion innervates the corona with paired neurites that form a neuronal ring; and (3) a single pair of neurites innervates the ventral sensory antennae. Unique to S. socialis is the presence of two additional neuronal rings that supply the corona and may function to modulate ciliary beat. At the muscular level, S. socialis displays a typical pattern of somatic muscle organization similar to other rotifers, but diverges from the pattern in three significant ways: (1) somatic circular muscles form complete rings; (2) circular muscles are distinguishable based on their size and position in the body; and (3) transverse muscles are present within the corona and presumably function to modify its shape for feeding and defensive purposes. These differences in neuromuscular organization may be adaptations to the colonial and/or sessile lifestyle, both of which are characteristic of S. socialis.     

Diversity of Rotifera (Monogononta) in wetlands of Río Pilcomayo National Park, Ramsar Site (Formosa, Argentina)

The rotifers at this Ramsar site were inventoried for the first time. A total of 114 taxa, belonging 30 genera were found in samples collected from four aquatic habitats in the Río Paraguay basin, in northern Argentina. The rotifer fauna is characterized by a large proportion of cosmopolitan and tropicopolitan species and few species endemic to the Neotropical Region (5%). In the list, 22% of the taxa are new to the Argentine fauna. Colurella sinistra Carlin is a new record to the Neotropical fauna. Ecological and distributional notes on selected species are included.     

Fish and nutrient enrichment effects on rotifers in a Mediterranean shallow lake: a mesocosm experiment

A mesocosm experiment was conducted “in situ” in a Chara dominated shallow lake near Valencia (Spain) to study top–down and bottom–up effects on rotifers by means of nutrient and fish additions. Both processes were important in determining rotifer abundance, biomass and diversity. A total of 36 mesocoms were established with triplicate treatment combinations of three fish levels (from no fish to 45 individuals of Gambusia holbrooki males) and four nutrient enrichment levels (from no additions to 10 mg l⁻¹ nitrate-N and 1 mg l⁻¹ phosphate-P). The main effect was a notable increase of planktonic and plant associated rotifers densities with fish. Rotifers benefited from mosquitofish predation on microcrustaceans and chironomids. The results showed a marked negative relationship between rotifer and cyclopoid abundances, indicating the importance of the predatory pressure of cyclopoids on rotifers. Effects on rotifer diversity were also evident, in general rotifer diversity decreased with nutrients and increased with fish. The effects of nutrients analysed at species level showed two contrasting density responses: an increase or a decrease with nutrients, which levelled off at high nutrient concentrations. High-level nutrient additions (from 5 mg l⁻¹ nitrate-N and 0.5 mg l⁻¹ phosphate-P) induced a switch to a turbid state with macrophyte disappearance. Most planktonic rotifer species, as well as plant associated ones, diminished when the turbid state was well established, especially in the mesocosms without fish. In the turbid mesocosms, relative abundance of plant-associated rotifers (as a whole) was higher than that of planktonic rotifers. The changes in rotifer species composition after the switch from a clear to a turbid water state are also described. Species of the genus Anuraeopsis, Trichocerca and Hexarthra, dominant in the clear water state, practically disappeared in the turbid water state, in which Proalides tentaculatus and Lecane nana were the main species. Guest editors: S. S. S. Sarma, R. D. Gulati, R. L. Wallace, S. Nandini, H. J. Dumont & R. Rico-Martínez Advances in Rotifer Research     

Patterns of prey selectivity in the cyclopoid copepod Mesocyclops thermocyclopoides

In the shallow and eutrophic subtropical aquatic ecosystems, which it generally inhabits, the omnivorous copepod Mesocyclops thermocyclopoides encounters a wide variety of animal prey types including ciliates, rotifers, and cladocerans. We studied prey selectivity in laboratory-reared adult females of this species given a choice of (i) prey types belonging to different taxa (ciliates, rotifers, cladocerans, and cyclopoid nauplii), and (ii) different prey species within a taxonomic group differing in body size, morphology or behaviour. We also tested the effect of different proportions of prey species on its selectivity. Prey type proportion had no significant effect on selectivity of the copepod, nor was there any evidence of switching based on the relative abundance of prey. Among the ciliate prey species tested, the largest species, Stylonychia mytilus was positively selected regardless of its relative abundance, while the smallest, S. notophora was selected only when its density was higher. Offered a choice of three species of a brachionid rotifer differing in size, the copepod selected the largest of them, Brachionus calyciflorus, and avoided the smallest B. angularis. The evasive rotifer Hexarthra mira was also avoided. When prey choice included three cladoceran species Daphnia similoides, Moina macrocopa and Ceriodaphnia cornuta, the copepod selected the intermediate-sized M. macrocopa regardless of the abundance of the other two species. Although it fed on Mesocyclops nauplii when there was no choice, M. thermocyclopoides avoided them when alternative food was available. In a multispecies prey choice test, the copepod selected predominantly the rotifer B. calyciflorus and the cladoceran M. macrocopa. We suggest that the prey selectivity patterns shown by M. thermocyclopoides are adaptive in that they lead to ingestion of the most profitable prey.     

Species‐specific separation of lake plankton reveals divergent food assimilation patterns in rotifers

相似文献   

Rotifers as predators on components of the microbial web (bacteria,heterotrophic flagellates,ciliates) — a review

Recent investigations have shown that processes within the planktonic microbial web are of great significance for the functioning of limnetic ecosystems. However, the general importance of protozoans and bacteria as food sources for rotifers, a major component of planktonic habitats, has seldom been evaluated. Results of feeding experiments and the analysis of the food size spectrum of rotifers suggest that larger bacteria, heterotrophic flagellates and small ciliates should be a common part of the food of most rotifer species. About 10–40 per cent of rotifers' food can consist of heterotrophic organisms of the microbial web. Field experiments have indicated that rotifer grazing should generally play a minor role in bacteria consumption compared to feeding by coexisting protozoans. However, according to recent experiments regarding food selection, rotifers should be efficient predators on protozoans. Laboratory experiments have revealed that even nanophagous rotifers can feed on ciliates. Preliminary microcosm and chemostat experiments have indicated that rotifers, due to their relatively low community grazing rates compared to the growth rates of bacteria and protozoans, should generally not be able (in contrast to some cladocerans) to suppress the microbial web via grazing, though they may structure it. Filter-feeding nanophagous rotifers (e.g. brachionids) seem to be significant feeders on the smaller organisms of the microbial web (bacteria, flagellates, small ciliates), whereas grasping species (e.g. synchaetids and asplanchnids) seem to be efficient predators on larger organisms (esp. ciliates). Another important role of rotifers is their feedback effect on the microbial web. Rotifers provide degraded algae, bacteria and protozoans to the microbial web and may promote microbial activity. Additional experimental work is necessary for a better understanding of the function of rotifers in aquatic ecosystems.     

Regulation of rotifer densities by crustacean zooplankton in an oligotrophic montane lake in British Columbia

Summary To examine the relative demographic effects of predation and competition for food in rotifers during spring and summer in an oligotrophic lake, predator and competitor densities and food supplies were experimentally altered inside large enclosures. Abundances of rotifer species were positively correlated with experimental densities of fourth instar Chaoborus trivittatus larvae, a major crustacean predator in 1976. Experimental alteration of the densities of Daphnia rosea and Diaptomus leptopus and D. kenai in 1978 produced highly significant increases in rotifer biomass only under Daphnia removal, but not under copepod removal. Inorganic fertilizer additions to enclosures in 1978 and 1979 revealed minimal rotifer increases unless pulsed additions were large or Daphnia were also excluded. Large demographic reponses of rotifers to low fertilizer loadings in the absence of Daphnia confirmed the pre-eminence of competitive food limitation in producing rotifer scarcity in summer.     

Swimming speed and Reynolds numbers of eleven freshwater rotifer species

We obtained data on the swimming speed of 11 freshwater rotifer species. These data were analyzed in terms of Reynolds numbers given the fact that rotifers are in the evolutionary boundary between the use of cilia and swimming appendages. Swimming speed ranged from 0.174 to 0.542 mm ^–1. Philodina acuticornis odiosa was the fastest rotifer in terms of absolute speed. However, Gastropus hyptopus, the smallest of the rotifers analyzed, was the fastest (2.849) in terms of body-lengths s^–1. Reynolds numbers (Re) among the 11 species analyzed varied from 0.023 to 0.301. Lecane furcata had the smallest Re, while Epiphanes senta had the highest Re. The two bdelloid rotifers analyzed in this work swam five times faster than they crept. The importance of Reynolds numbers and drag coefficients are discussed in view of the present results and data found in the literature.     

Molecular Ecology of Rotifers: From Population Differentiation to Speciation

The development of cost-effective molecular tools allowing the amplification of minute amounts of DNA effectively opened the field of molecular ecology for rotifers. Here I review these techniques and the advances they have provided in the understanding of sibling species complexes, clonal structure, resting egg banks, population structure, phylogeographic patterns and phylogenetic relationships in rotifers. Most of the research to date has focused on the rotifer species complex Brachionus plicatilis. The use of DNA sequence and microsatellite variation, in the context of the background knowledge of life history, mating behaviour, and temporal population dynamics in these organisms have revolutionised our views into the processes shaping the genetic diversity in aquatic invertebrates. Rotifers have populations with a very high number of clones in genetic equilibrium. In temporary populations clonal selection is effective in eroding the number of clones. Rotifer populations are strongly differentiated genetically for neutral markers, even at small geographical scales, and exhibit deep phylogeographic structure which might reflect the impact of Pleistocene glaciations. Despite the high potential for dispersal afforded by resting eggs, rotifers display persistent historical colonisation effects, with gene flow effective only at a local scale and with marked isolation by distance. Instances of long-distance transcontinental migration resulting in successful colonisation have also been revealed. B. plicatilis is composed of a group of several ancient species and sympatry is common. Despite this, the presence of cosmopolitan species in this species complex cannot be discounted. I discuss future priorities and point out the main areas where our knowledge is still insufficient.