Comparative analysis of rotifer community structure in five subtropical shallow lakes in East China: role of physical and chemical conditions

Worldwide, there have been few comparative studies on rotifer communities in subtropical lakes. We studied changes in rotifer community structure over 1 year and its relationship to several physicochemical variables in five subtropical shallow lakes in East China, covering a nutrient gradient from mesotrophy to moderate eutrophy. In these lakes, the genera Brachionus, Lecane, and Trichocerca dominated the rotifer species composition, and Polyarthra dolichoptera, Keratella cochlearis, Filinia longiseta, T. pusilla, and Anuraeopsis fissa were the dominant species. With increased nutrient loading, total rotifer abundance and species dominance increased, indicating that rotifer abundance might be a more sensitive indicator of trophic state than species composition. Comparative analyses of the six rotifer community indices calculated in this study and redundancy analysis (RDA) revealed that the two slightly eutrophic lakes and the other two moderately eutrophic lakes exhibited a high degree similarity in community structure. This suggests that the trophic state of a lake determines the rotifer community structure. In contrast, in the two moderately eutrophic lakes, the mass ratios of TN:TP and the contents of TP suggested N-limitation and cyanobacteria dominance in phytoplankton communities might be possible. In these lakes TN played a more important role in shaping the rotifer community according to stepwise multiple regression and RDA. RDA analysis also suggested that rotifer species distribution was strongly associated with trophic state and water temperature, with water temperature being the most important factor in determining seasonality.     

Species composition,distribution and seasonal dynamics of Rotifera in a Rift Valley lake in Ethiopia (Lake Awasa)

The species composition of rotifers in Lake Awasa was studied and 40 species recorded. Seven species appeared in large numbers in the plankton seasonally. Brachionus and Keratella species made up more than 50% of the rotifer community by numbers during the observation period (1983–1987). The standing stock numbers of rotifer species are low with a maximum of 50 individuals L^–1, and some possible reasons for this observation are discussed. Most rotifer species are distributed randomly in the lake and show 3-fold fluctuations between consecutive days.The seasonal dynamics of most rotifer species are correlated with mixing periods in the lake, and the amplitude of seasonal fluctuation may be as high as 50-fold. Clear-cut seasonal succession of rotifer species was observed during the study period, but no consistent seasonal pattern for individual species was obvious. Also, observations indicate that rotifer biomass is partly sustained by availability of carbon through the bacterial pathway and that competitive exclusion for food by nauplii and ciliates probably keeps rotifer abundance low.     

Seasonal abundances of the psammic rotifers of a physically controlled stream

The psammic rotifer community inhabiting the bottom of a second order stream partially under the influence of acid mine drainage was studied from May, 1978 to November, 1979. Thirty-one species of rotifers were found, but abundances were very low (range 0.0 to 8.6 cm^-3). Total rotifer density and densities of major genera differed significantly over time, among sites and between depths in the sediment (P < .01). Highest densities occurred in the top 1 cm of sediment during periods of stream stability in the late summer and fall. Total rotifer density and densities of Lecane spp., Cephalodella spp. and Trichocerca spp. were positively correlated with alkalinity and negatively correlated with manganese (canonical correlation, p < .05). Densities of all taxa were negatively correlated with variability in water chemistry. Total rotifer density was found to be positively correlated with minimum monthly temperature (r = 0.6, P <. 05) and to lag behind the temperature cycle by 6 weeks. Rotifer species were found to be randomly distributed in time and space with no evidence which might suggest competitive exclusion. A highly variable and unpredictable environment is thought to keep density and diversity low in this community.     

Long-term changes in the rotifer fauna after biomanipulation in Haussee (Feldberg,Germany, Mecklenburg-Vorpommern) and its relationship to the crustacean and phytoplankton communities

In Feldberg Haussee, an anthropogenic eutrophicated lake, biomanipulation was executed for restoration. To increase the biomass of crustaceans, fish grazing on zooplankton was reduced by catching small fishes and introducing pike-perch. After biomanipulation rotifer biomass from a wide range of species decreased to a small spring maximum with three dominant species. The development of food in spring and food competition between crustaceans probably controlled the rotifer development.     

流溪河水库敞水区轮虫多样性与群落的动态特征

流溪河水库是位于北回归线上的大型峡谷型供水水库,于2013—2014年对该水库敞水区轮虫群落及其环境因子进行观测,分析敞水区轮虫多样性与群落动态特征。流溪河水库介于贫营养到中营养水平之间,丰水期(5月—9月)的总磷、透明度均高于枯水期(10月—4月),两年的总磷的平均值为0.019mg/L,透明度为2.55m。两年共检出轮虫40种,单月检出物种数波动范围为8—19种,月均检出轮虫13种。螺形龟甲轮虫、真翅多肢轮虫、沟痕泡轮虫和胶鞘轮虫是主要优势轮虫。2013、2014年轮虫年均总丰度分别为68.9、66.9个/L,两年物种丰富度在丰水期大于枯水期,但枯水期轮虫群落Simpson多样性指数均大于丰水期。采用Bray-Curtis距离测度群落之间的相异性,计算表明两年的枯水期轮虫群落之间的平均距离均大于丰水期,即丰水期时轮虫群落相似性较高,枯水期时轮虫群落变异较大。丰水期的水温和水质参数的变化相对稳定,种类的优势度更为明显,导致丰水期群落之间更为相似。主成分分析表明,无柄轮属、胶鞘轮属、多肢轮属、异尾轮属、泡轮属、晶囊轮属和皱甲轮属的主要种类的全年分布有较大的差异,而其余多数轮虫种类全年分布差异较小,反映了我国南亚热带地区水温全年变幅小,可维持较多的全年性种类共存。群落的方差解析与RDA分析表明,相对于生物与化学变量,物理环境变量主导了流溪河水库敞水区轮虫群落的变异,就单个变量而言,水温和食物是影响流溪河水库敞水区轮虫群落结构的重要因素,降雨则是影响轮虫群落结构变异的宏观因素。绝大多数轮虫为滤食性的,处于食物链底端,个体小、生活史短,轮虫群落在对环境因子变化的响应上与浮游植物具有相似性。     

Rotifer sampling — a complete species list from one visit?

This paper describes a possible method of compiling a rotifer species list for any site from a single visit. Sediment samples collected from Loch Leven on one occasion in winter were exposed to light and a range of temperature conditions in the laboratory. Resting eggs in the sediment were induced to hatch. The resultant species list was very similar to that obtained from regular plankton collections over the previous six year period.     

上海崇明岛明珠湖轮虫群落结构

根据2008年1-12月上海市崇明岛明珠湖的综合调查资料,分析了明珠湖轮虫的数量分布、群落特征、种类组成、优势种及物种多样性.结果表明：本次调查共鉴定出轮虫27种,隶属于8科11属,优势种包括刺簇多肢轮虫、暗小异尾轮虫、萼花臂尾轮虫、未定名的旋轮属1种和剪形臂尾轮虫;轮虫生物密度的年均值为（1505.42±1304.63） ind·L^-1,生物量年均值为（2.012±2.146） mg·L^-1;明珠湖轮虫的Shannon-Wiener多样性指数、丰富度指数和均匀度指数均较低,优势种的优势度指数较大,反映出明珠湖轮虫群落结构不稳定;其富营养种数/贫营养种数（E/O）的比值为1.61±1.46,臂尾轮虫属（B）种数和异尾轮虫属（T）种数的比值（Q_B/T）为1.23±0.84.影响明珠湖轮虫生态特征分布的主要因子是水温;目前明珠湖水质呈轻度富营养化.     

Rotifer distribution in relation to temperature and oxygen content

Lunzer Obersee, a small lake located at an altitude of 1100 m above sea level, was investigated from July 1985 to October 1987. The rotifer community consists of 7 dominant species, 7 subdominant species and 34 species which occasionally occurred in the plankton. The dominant species show rather different demands in relation to temperature and oxygen content; e.g.: Filinia hofmanni was found at a wide range of oxygen concentrations (0.6–13.3 mg O₂l^–1) and low temperatures (4–6 °O, living in the upper water layers (1–7 m) during spring and in the deeper, anoxic zone in summer. In contrast, Asplanchna priodonta was found at rather high oxygen contents (> 9 mg O₂ l^–1), ), and showed a wide range of temperature tolerance (4–15 °C).On the basis of field data the temperature and oxygen requirements of several species are described and discussed.     

The Potential of Genomic Approaches to Rotifer Ecology

Rotifers are a key component of many freshwater ecosystems, but surveys of the composition of rotifer communities are limited by the labor-intensiveness of sample processing, particularly of non-planktonic taxa, and by the shortage of investigators qualified to identify a broad range of rotifer species. Additional problems are posed by species that must be identified from living specimens, and by members of cryptic species complexes. As DNA sequencing becomes easier and cheaper, it has become practical to obtain representative DNA sequences from identified rotifer species for use in genome-based surveys to determine which rotifers are present in a new sample, avoiding the difficulties of traditional surveys. Here we discuss two genome-based tools used in surveys of microbial communities: serial analysis of gene tags (SAGT) and microarray hybridization. SAGT is a method for inexpensively obtaining characteristic short DNA sequences from a sample that can both identify taxa for which the tag sequence is known and signal the presence of additional uncharacterized species. Microarray hybridization allows detection of DNA sequences in the sample that are identical or similar to sequences present on the microarray. We also report the construction and hybridization of a small microarray of rotifer sequences, demonstrating that this method can discriminate among bdelloid families, and is likely to make much finer discriminations if appropriate sequences are present on the microarray. These techniques are most powerful when combined with traditional systematics in collaborative efforts, which may be fostered through the data base of rotifer biology, WheelBase (http://jbpc.mbl.edu/wheelbase).     

Associations of zooplankton in six crater lakes in Arizona, Mexico and New Mexico

Zooplankton associations in six crater lakes have been compared by means of indices of similarity and diversity, and by k -dominance curves. The lakes covered a wide range of salinities and vegetational characteristics.
The total number of species identified were: Protozoa, 34; Rotifera, 48; Gastrotricha, 7; Crustacea, 24; and Chaoborus larvae, 2; giving an overall total of 115. The numbers of zooplankton species in each lake varied from 68, in a richly vegetated fresh crater lake in Arizona, to one in a highly saline lake in New Mexico.
Testate rhizopods and gastrotrichs were not found in the more saline lakes. A comparison of the rotifer associations with those of crater lakes in other parts of the world shows that there is a general tendency for a reduction in the total number of species when the conductivity rises above 400 μS cm⁻¹ 20°C, and when the conductivity reaches 10,000 μS cm⁻¹ 20°C the number of rotifer species is usually reduced to two. The two species found at high salinities show some variation in different parts of the world, but generally include species of Brachionus and Hexarthra.
There is a general tendency for the number of rotifer species in a crater lake to increase with increasing vegetation, at least up to the stage where there is a dense, zoned vegetation, and before a complete mosaic of vegetation covers the lake.     

广东典型小型供水水——-契爷石水库浮游生物与富营养化特征分析

于2000年丰、枯水期对契爷石水库的理化因子,浮游生物种类组成,细胞密度等进行了调查研究,并利用有关评价指数对该水库水体的营养水平进行了评价。结果表明,契爷石水库目前已进入富营养化状态,且枯水期较丰水期富营养化程度更为严重,另外,全年有机污染也比较严重。浮游植物丰水期以蓝藻、绿藻为主,枯水期以蓝藻、硅藻为主,该水库属于典型的蓝藻-绿藻-硅藻型水库,且有较高丰度的耐有机污染的裸藻所在。浮游动物以轮虫和桡足类为主,轮虫主要以耐有机、喜富营养的萼花臂尾轮虫（Rrachionus calyciflorus）、前节晶囊轮虫（Asplanchna priodonta）、螺形龟甲轮虫（Keratella cochearis）为主,挠足类主要以无节幼体,桡足幼体为主,成体很少,且主要以剑水蚤为主,喜寡营养的哲水蚤在该水库中没有出现,枝角类种类,数量都很少,多为广温型、嗜暖型种类,其中长额象鼻蚤（Bosmina longirostris）和微型裸腹蚤（Moina micrura）习居于富营养型水体中。     

Rotifer Population Dynamics in Two Coupled Habitats: Invasion of Chaos

We study the role of interactions between habitats in rotifer dynamics. We use a simple discrete-time model to simulate the interactions between neighboring habitats with different intrinsic dynamics. Being uncoupled, one habitat shows periodical oscillations of the rotifer biomass while the other one demonstrates chaotic oscillations. As a result of the exchange of rotifer biomass, chaos replaces regular oscillations. As a result, the rotifer dynamics becomes chaotic in both habitats. We show that the invasion of chaos is followed by the synchronization of the chaotic regimes of both habitats, and this synchronization increases as coupling between the habitats is increased. We also demonstrate that the biological invasion of the rotifer species, which show chaotic dynamics, to a neighboring habitat with intrinsically regular plankton dynamics leads to the invasion of chaos and the synchronization of chaotic oscillations of the plankton biomass in both the habitats.     

Small-sized invertebrates in a gravel stream: community structure and variability of benthic rotifers

1. The Rotifera assemblage inhabiting the streambed surface and the hyporheic zone of a gravel stream was investigated between October 1991 and October 1992. Forty-two species of Monogononta and 27 of Bdelloidea were identified. Within these two classes, dominant species differed between the surface and the hyporheic zone. At the streambed surface, the abundance of monogonont rotifers showed a seasonal pattern with significantly higher densities in pools, whereas bdelloids showed no clear temporal trend and did not differ significantly among sites. In the hyporheic zone, the depth distribution differed among the two rotifer groups, bdelloids occurred in highest densities between 0 and 30 cm sediment depth, while monogononts were most abundant at greater depths.
2. Species composition differed greatly between successive sampling dates (min. 5 to max. 26 days) at both the streambed surface and the hyporheos. At the streambed surface and in the shallow hyporheos a significantly higher percentage of species was replaced in riffles than in pools.
3. Few measured hydrophysical variables were associated with the Rotifera assemblage structure. At the streambed surface, species richness was negatively correlated with water temperature and substratum heterogeneity, and Monogononta rotifer densities declined with water depth and substratum roughness.
4. Permutation tests carried out on temporal serial correlations showed that, at riffle sites at the streambed surface, bdelloid rotifer densities, rotifer species richness and diversity did not differ significantly from a temporal, near-random pattern. The hyporheic rotifer assemblage followed similar near-random patterns.     

Local adaptation in rotifer populations

The adaptation of organisms to their environment has been a subject of study for a long time. One method to study adaptations in populations involves comparing contemporary populations of the same species under different selective regimes, in what is known as a ??local adaptation?? study. A previous study of the cyclically parthenogenetic rotifer Brachionus plicatilis found high heritabilities for some life-history traits. Some of these life-history traits significantly differed among six populations from Eastern Spain and data suggested some traits to have higher evolutionary rates than neutral genetic markers. Here, by studying the same B. plicatilis populations, we examine the variation and possible local adaptation of their main life-history traits, closely related to fitness, in relation to habitat salinity and temperature. These environmental factors have been shown to play a key role in the ecological differentiation among co-generic species of B. plicatilis. The results obtained in this study show that: (1) the seasonality of rotifer populations from Eastern Spain has profoundly influenced sexual reproduction strategies; (2) salinity is probably a key factor in the ecological specialization of some populations; and (3) rotifer populations harbour high variability in their fitness components.     

南方某水库轮虫群落特征及其对环境因子的响应

于2006年8月至2007年8月,对广东省某水库4个站点轮虫群落的周年变化进行了调查分析,同时测定了浑浊度、叶绿素、总氮、总磷等理化因子。调查期间,共记录轮虫41种,以臂尾轮属和异尾轮属种类居多,全年以广布多肢轮虫(Polyarthravulgaris)和尖尾疣毛轮虫(Synchaetastylata)为主要优势种;轮虫丰度范围为6-1966ind./L,以库心和大坝处的轮虫丰度较高,高峰期出现在夏秋季。相关分析显示叶绿素浓度对轮虫群落有重要影响。典范对应分析(CCA)表明,采样站点具有明显的空间异质性。CCA分析还表明浑浊度和透明度是影响轮虫空间分布的重要因子,水温和叶绿素浓度是影响轮虫群落结构季节变化的主要因子。CCA排序可将轮虫分为3个类群,优势种广布多肢轮虫位于CCA坐标轴的原点附近,表明其所受环境因子影响较小。根据相关加权营养状态指数(TLI),该水库处于中营养型。     

Predatory interactions between a cyclopoid copepod and three sibling rotifer species

SUMMARY 1. Cyclopoid copepod predation on rotifers affects the dynamics and structure of zooplankton communities. We address the differential vulnerability of three sympatric rotifer sibling species belonging to the Brachionus plicatilis species complex. These co-occur with their cyclopoid predator, Diacyclops bicuspidatus odessanus .
2. Using video recording and tracking, we analysed the steps in predation including attack distance, attack angle, and rotifer species swimming in the presence and absence of the predator. Our results show the greater vulnerability of B. rotundiformis (the smallest species) to D. b. odessanus predation, which is associated with a high percentage of attacks after contact. Brachionus plicatilis (the biggest species) is the less vulnerable prey, with low percentage of attacks after contact and captures after attacks. Branchionus ibericus , the intermediate sized species, had also intermediate vulnerability.
3. The differential vulnerability provides insight into the coexistence and seasonal succession of these competing rotifer species. Our results show that the competitive superiority of B. rotundiformis may be balanced by its greater vulnerability to copepod predation.     

Correlations between nutrient concentrations and zooplankton populations in a mesotrophic reservoir

1. A year-round study was conducted in a mesotrophic reservoir to determine the dynamics of zooplankton populations as a function of food availability (edible phytoplankton), nutrient concentration, temperature and hydraulic regime.
2. Rotifer biomass was correlated with soluble reactive phosphorus (SRP) concentration. The abundance of the rotifers Keratella cochlearis and Anuraeopsis fissa were not correlated with food availability (measured by chlorophyll and cell counts) but showed a strong dependence on P availability. Another rotifer, Synchaeta oblonga , and crustacean species were not related to nutrient availability but seemed to be dependent on food concentrations, especially of some phytoplankton taxa.
3. In this field study, rotifers seemed more susceptible than Daphnia or copepods to P-limitation. Among rotifer species, Keratella seemed to be more susceptible than Anuraeopsis to P limitation. Different susceptibilities of zooplankton species to nutrient limitation may be important in explaining the dynamics of these organisms in natural situations. Further analyses are warranted to clarify the interactions between nutrient limitation and energy limitation among zooplankton.     

Regulation of rotifer species by invertebrate predators in a hypertrophic lake: selective predation on egg-bearing females and induction of morphological defences

Temporal changes in the biomass of rotifer plankton were examinedin a shallow hyper trophic lake during 1 month (April/May),when the predatory rotifer Asplanchna brightwelli develops.The abundance of herbivorous rotifers was regulated by predationfrom A.brightwelli and from the copepod Acanthocyclops robustus.The densities and fecundity rates of Keratella cochlearis andKeratella quadrata were negatively related with the biomassof predators. Stomach analyses showed that Asplanchna fed selectivelyon reproductive females of K.cochlearis, reducing the fecundityof this species. Predators induced longer caudal spines in K.quadrata,which were negatively related to the fecundity of this rotifer,suggesting a reproductive cost associated with spine production.In contrast, spine length of K.cochlearis was not related topredators, but to temperature. These results showed that predatorscan reduce rotifer densities through increasing mortality andthrough decreasing rotifer fecundity rates regardless of phytoplanktonbiomass. We also show that morphological defences of K.cochlearisand K.quadrata are induced in different ways.     

淡水轮虫休眠卵的研究进展

本文综述了温度、休眠卵形态、光照条件和休眠卵贮存条件等因子对轮虫休眠卵萌发的影响, 以及休眠卵萌发型式差异的生态学意义。温度骤变可以诱导休眠卵萌发, 光照条件对休眠卵萌发率的影响存在种间差异, 母体轮虫的食物和休眠卵贮存条件影响其萌发率。     

Differentiated macrophyte types as a habitat for rotifers in small mid-forest water bodies

The rotifer community structure may be shaped by a variety of environmental factors, including biological parameters, such as predation or competition, as well as by physical-chemical factors, among which the kind of macrophyte substratum and parameters relating to the trophic state and to the catchment area conditions are of great importance. Another impact on rotifer composition, abundance and frequency may be expected when considering differentiated macrophyte types (including helophytes, nymphaeids and elodeids) within a group of eight ponds located within a mid-forest catchment area, which was the main aim of the present study. Detailed analysis on the participation of indicator eutrophic rotifer species provided an additional goal of this investigation in order to qualify the trophic state of this kind of water body located within the Wielkopolska region, in the central western part of Poland. The presence of 117 taxa, including 7 species that are rare or infrequently distributed in the Polish fauna was recorded. The number of taxa and rotifer abundance differed greatly in respect to the specific water body and to the type of substratum. The vegetated zones dominated by elodeids were characterised by the most various and most abundant rotifer communities as well as by the highest values of the Shannon-Weaver index. This reflects a positive relationship between the heterogeneity of habitat and the structure of rotifer communities. It was also found that helophytes and the open water zone possessed the highest, while elodeids the lowest percentage of eutrophic species.