Origin of carbon in organic matter in the Neva estuary

Analysis of the isotopic composition of tissues of representatives of zoobenthos and organic matter of seston have shown that the major part of carbon participating in the biological turnover in the ecosystem of the upper part of the Neva estuary is of terrestrial origin. Obviously, it is discharged from the lake drainage area to the Lake Ladoga–Neva–Neva estuary system. The results have revealed an important role in aquatic ecosystems of the humid zone of allochthonous humic substances creating a supplementary stock of nutrients and enhancing the productivity of ecosystems. Detailed investigations of the role of various forms of allochthonous organic compounds of terrestrial origin are necessary for elaboration of efficient measures for alleviation of eutrophication of the Neva estuary.     

长江口轮虫生物多样性特征分析

长江口径流在南北支分布不均导致北支盐度高于南支,因此南北支之间生物群落存在一定差异。2010年在长江口分支前的江段和南北支设置5个断面,开展轮虫生态研究。分支前的太海汽渡断面处共采集到轮虫9种,隶属6科8属,其中优势种为没尾无柄轮虫、暗小异尾轮虫、萼花臂尾轮虫等;长江口南支2个断面共采集轮虫20种,隶属于6科12属,南支优势种为暗小异尾轮虫、盘状鞍甲轮虫和蹄形腔轮虫;长江口北支2个断面共采集轮虫11种,隶属于7科10属,北支优势种为舞跃无柄轮虫、没尾无柄轮虫和盘状鞍甲轮虫。南支轮虫种类、密度、多样性都高于北支,南北支的轮虫群落相似度较低。轮虫与水域环境因子相关性分析显示,盐度的差别影响了轮虫种类组成、密度和空间分布。     

Oligochaete communities at the mouth of the Neva and their relationship to anthropogenic impact

Changes in the oligochaete community of the Neva Mouth for the period 1982–1993 are discussed in relation to anthropogenic impacts. A number of community parameters such as species composition, biomass and diversity were generally stable, although local changes were noted. Predominance of eutrophic species, i.e. L. hoffmeisteri, T. tubifex, P. hammoniensis was enhanced, whereas mesotrophic and oligotrophic species — L. isoporus, S. heringianus, T. newaensis disappeared or became less numerous at some stations. The reverse trend was observed at other stations. These phenomena were accompanied by a sharp increase in the variability of biomass and/or diversity, which is regarded as exceeding normal annual fluctuations. The oligochaete community is recognized as a promising indicator of the ecological situation in the Neva Mouth.     

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.     

The ecology of periphytic rotifers

The ecology of rotifer assemblages in the periphyton has received little attention relative to that of pelagic rotifers. This paper reviews the ecology of periphytic rotifers, with particular emphasis on the role of macrophytes in the structuring of rotifer assemblages spatially and temporally, and compares these aspects with the dynamics of better known pelagic rotifer communities. Littoral rotifer periphyton communities are typically diverse in lakes, and have composition dissimilar to that of the open water. In rivers, diversity and composition in the pelagic and littoral appear to be similar. Rotifers show preference for macrophyte species they associate with, probably through differences in physical structure or complexity, food concentration or composition, chemical factors, macrophyte age, and differences in the degree of protection from predation provided by macrophytes. These mechanisms are in general not well investigated in rotifers. Factors affecting the seasonal dynamics of periphytic communities appear to be similar to pelagic communities, with seasonal dynamics of substrates and disturbance by flooding or drying also being important.     

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.     

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。     

宁波市游览性湖泊浮游轮虫的群落结构及生物多样性

2006年10月至2007年7月,调查了宁波市东钱湖(Ⅰ、Ⅱ站)、月湖(Ⅲ、Ⅳ站)和日湖(Ⅴ、Ⅵ站)三个游览性湖泊浮游轮虫的群落结构及其生物多样性。共发现浮游轮虫21种,以月湖轮虫的密度(3287ind.·L^-1)和生物量(0.884mg·L^-1)为最高,日湖轮虫的Margalef多样性指数0.917为最高,东钱湖轮虫的群落指标均最低。东钱湖轮虫优势种为暗小异尾轮虫(Trichocerca pusilla);月湖和日湖轮虫第一优势种均为针簇多肢轮虫(Polyarthra trigla)。浮游轮虫生物多样性指数随着水体碱性环境的加剧而呈极显著地下降(r=-0.545,n=24,p<0.01),月湖和日湖的浮游轮虫生物多样性指数也随轮虫密度的增加而极显著地下降(r=-0.668,n=16,p<0.01)。     

Associations of planktonic and periphytic rotifers in a Malaysian estuary and two nearby ponds

Samples were taken from a Malaysian estuary along a salinity gradient from full strength sea water down to a conductivity of 27 µS cm^–1. In a region where the conductivity fluctuated between 6500 and 14000 µS only empty loricas of Keratella cochlearis and Lecane bulla were found. Where the salinity reached a maximum of 3800 µS Lecane bulla was the dominant rotifer, and 17 other species were found. Where the conductivity remained below 1000 µS at all stages of the tidal cycle there were more species of rotifers, up to 33 at one station.The rotifer fauna of the estuary was compared to the assemblage found in two local ponds. Of the 63 species found in the estuary only 29 were also found in the ponds. Compared to the total known rotifer fauna of Malaysia the estuary has a higher proportion of Lecane species (40%), and the genera Brachionus and Trichocerca are under-represented.Species associated with inland saline waters, such as Brachionus plicatilis, B. dimidiatus and Hexarthra jenkinae were not found in the estuary.     

Schistosoma mansoni: Effect of rotifers on cercarial output,motility and infect1vity

Spontaneous colonization of rotifers on the shells of schistosome-infected Biomphalaria glabrata reduced the cercarial output of these snails and the motility and infectivity of the cercariae which did emerge. The rotifer effect was observed not only in the actual presence of rotifers, but also in rotifer-conditioned water from which the rotifers themselves had been removed by nitration. The significance of the rotifer effect to laboratory maintenance of S. mansoni is considerable. It may be one of many factors which reduce the infective index under field conditions.     

Composition and distributional patterns in arctic rotifers

Based on collections of rotifers from 212 localities in arctic North America, the patterns of distribution and composition are evaluated. An attempt is made to discern the dominant components of the rotifer community in arctic habitats. One hundred and sixty five species of rotifers are reported, three of which represent new records for North America. With increasing latitude and decreasing summer temperatures, a decline in species richness and change in species composition is observed. Some rotifers that previously were not adequately described are redescribed and illustrated. The significance of the dispersal capacity of rotifers in the arctic is discussed.     

Notes on the rotifers of coal mine water in Eastern Poland

The species composition and quantitative structure of the rotifer fauna was investigated in a reservoir containing coal mine water. Only nine mainly planktonic species of rotifers, were found. Two of these were dominating: Brachionus angularis and B. rubens. They are typical indicators of eutrophic waters. Chlorides and sulphates may have an influence on the occurrence and quantitative structure of rotifer assemblages in the investigated reservoir.     

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.     

Some rotifers from coastal lakes of Brazil,with description of a new rotifer,Lepadella (Xenolepadella) curvicaudata n. sp.

Four relatively rare, two common rotifers and one rotifer new to science are described from some coastal lakes near Rio de Janeiro, Brazil. Each rotifer is described in detail, and several are accompanied by illustrations and mensuration data. Geographic distribution and individual habitats of the rotifers are also discussed. Several species show a larger geographic distribution than previously known.     

Spring-Summer Succession of Planktonic Rotifers in a South Andes Lake

The dynamics of planktonic rotifer in Laguna Ezquerra (Rio Negro, Argentina) was studied from October 1988 to March 1989, in relation to food resources and cladoceran populations. During the spring and summer period, total rotifer density differed markedly. In spring rotifer populations remained at low density and an inverse relationship with cladoceran biomass was found. In contrast, in summer, the rotifer densities increased greatly and a positive relationship with cladoceran biomass was observed. Food resources decreased during mid January and this seemed to give rotifers a competitive advantage over cladocerans. Bosmina longirostris and Ceriodaphnia dubia were both present during the spring, but only Bosmina prevailed in summer. The composition of cladoceran assemblages together with food resources seem to be an important factor in rotifer dynamics.     

Zooplankton community structure along a trophic gradient in a canyon-shaped dam reservoir

The zooplankton community was surveyed along the longitudinalaxis of Rimov Reservoir (Czech Republic) on seven occasionsduring the vegetative season of 1996. The dimictic Rimov Reservoirhas a pronounced trophic gradient along its axis. In nearlyall samples, rotifers were dominant by numbers and formed onaverage 60–95% of the total zooplankton (including copepodnauplii). There was a consistent pattern of increasing relativeabundance of rotifers in the upper regions of the reservoircompared with the downstream parts. Very large rotifer populationscould develop in the upper regions, often associated with floodevents, but also coinciding with reduced abundance of crustaceansassociated with stronger wash-out effects and the advent ofturbid conditions. There was a greater similarity between twoadjacent sites in the proportions of crustacean species thanof rotifer species. This is partially due to the greater speciesdiversity of rotifers than of crustaceans. The timing of theseasonal succession of zooplankton species showed a coherentpattern along the whole longitudinal profile. The site-specificzooplankton patchiness seems to be reduced as there was no sitedependence if average data on zooplankton composition from downstreamlacustrine sites were compared.     

湖北四湖泊营养类型与轮虫群落的关系

对湖北梁子湖水系不同营养类型(中营养型、富营养型)4个湖泊中轮虫的群落结构和物种多样性进行了周年研究,分析比较了不同营养类型湖泊的轮虫种类组成、分布、优势种组成、密度、生物量和多样性指数。结果表明：轮虫的种类数、物种多样性与营养水平呈负相关关系,轮虫密度大体上随营养水平提高而增大,富营养化引起轮虫空间异质性降低,受污染湖泊与非污染湖泊轮虫种类数、寡污性种类数及分布差异尤为明显。用多样性指数评价湖泊营养状态与TLIc方法一致。     

Steady-state rotifer growth in a two-stage, computer-controlled turbidostat

Steady-state populations of rotifers (Brachionus calyciflorus)were maintained in twostage, continuous-flow turbidostatic cultureon the green alga Chlorella pyrenoidosa. In this system, themaximum specific growth rate,µ^max of the rotifers wasmaintained by using a computer to control the concentrationof algae, as rotifer food, in the rotifer culture. As rotifersconsumed algae, the turbidity decreased until a set-point wasreached. Then fresh algal suspension (supplied from a steady-statealgal chemostat) was metered into the rotifer culture, whichwas held in the dark. Rotifer and algal populations, as wellas rotifer µ^max entered steady states. These steady-stateresults were consistent with previous data from chemostat studies,but growth transients indicated that the of the µ^maxrotifersmay be subject to selection. The system is unique in providinga means to explore population dynamics of a metazoan maintainednear its µ^max.     

水蕹菜浮床对草鱼主养池塘轮虫群落结构的影响

研究了水蕹菜浮床对草鱼主养池塘轮虫群落结构的影响,共检出轮虫38种,隶属于2纲14属,其中浮床池塘出现轮虫36种,而非浮床池塘28种。浮床池塘与非浮床池塘的优势种组成基本类似,萼花臂尾轮虫（Brachionus calyciflorus）、裂足臂尾轮虫（Brachionus diversicornis）、裂痕龟纹轮虫（Anuraeopsis fissa）、暗小异尾轮虫（Trichocerca pusilla）以及长肢多肢轮虫（Polyarthra dolichoptera）为共有优势种;浮床池塘与非浮床池塘的轮虫平均密度分别为1892和2255 ind./L,差异极显著（p0.01）;浮床池塘与非浮床池塘轮虫平均生物量分别为1.535和1.405 mg/L,差异不显著（p0.05）。结果表明,水蕹菜浮床显著促进了轮虫种类数增加,提高了轮虫多样性和均匀度,并在一定程度上减缓了轮虫小型化。       

Differences in rotifer communities in two freshwater bodies of different trophic degree (Lake Ohrid and Lake Dojran,Macedonia)

We investigated monogonont rotifers in two natural Macedonian lakes that greatly differ in age, size and trophic state: Lake Ohrid and Lake Dojran. A main characteristic of Lake Ohrid is the scarcity of nutrients and consequently a low level of primary production. Lake Dojran represents a typical eutrophic lake. Results clearly indicate that species numbers are negatively correlated with trophic degree. Qualitative analyses of rotifer compositions in Lakes Ohrid and Dojran showed the presence of 70 and 55 taxa, respectively. Rotifer assemblages differed in their community structure, population densities, and the occurrence pattern of dominant species. The density of rotifers increased with increasing nutrient concentration, varying from min. 0.67 ind. L⁻¹ in June, 2006 to max. 8.2 ind. L⁻¹ in July, 2004 in Lake Ohrid, whereas min. 28.8 ind. L⁻¹ (in December, 2005) and max. 442.5 ind. L⁻¹ (in September, 2005) were recorded in Lake Dojran. Gastropus stylifer and Keratella cochlearis were the most abundant species in the pelagic zone of Lake Ohrid, averaging monthly densities of 1.2 ind. L⁻¹ and 0.6 ind. L⁻¹, respectively, thereby contributing 29% and 15% to rotifer abundance. In contrast, Lake Dojran rotifers were dominated by Brachionus spp. Brachionus diversicornis and Brachionus calyciflorus f. amphiceros were most abundant, comprising 40% and 25% of the total rotifer density. These results corroborate our idea, that the trophic state is an important factor in determining the composition of rotifer communities.