鄱阳湖子湖“堑秋湖”过程中水位变化对浮游动物群落结构的影响

“堑秋湖”是鄱阳湖区渔民根据湖泊水位季节性涨退变化, 利用人工闸门控制子湖水位进行捕鱼的一种渔业方式。研究分析了“堑秋湖”过程中浮游动物群落结构的变化, 探讨水位变化对浮游动物群落结构的影响及其他可能的影响因素, 以期为合理管控鄱阳湖区“堑秋湖”渔业活动提供科学依据。鄱阳湖“堑秋湖”捕鱼期间(2014年11月9日至2015年1月4日), 在鄱阳湖国家级自然保护区内子湖——大湖池的敞水区设置了7个采样点进行了8次浮游动物定性、定量采集和分析。研究共发现浮游动物77种, 其中轮虫53种, 枝角类10种, 桡足类14种。在“堑秋湖”捕鱼过程中, 浮游动物物种数随水位的连续下降呈现逐渐减少趋势, 多样性指数也呈逐渐下降趋势, 密度和生物量呈现先增加后减少的变化趋势。浮游动物优势物种的密度变化具有明显的种属差异, 前节晶囊轮虫和中华窄腹剑水蚤的密度呈逐渐增加的趋势, 广布多肢轮虫、广布中剑水蚤、长额象鼻溞和桡足类无节幼体的密度呈逐渐减少的趋势。冗余分析表明: 水位、电导率、水温、溶氧、营养盐等环境因子均对浮游动物群落结构产生显著影响, 其中溶解氧是最强的影响因子。此外, 根据“堑秋湖”鱼类渔获量的变化情况推测, 捕鱼活动导致的浮游食性鱼类减少也对浮游动物的密度变化产生了影响。在“堑秋湖”过程中, 随着水位的持续下降水体理化因子发生了不同变化。浮游动物的种类和多样性指数逐渐降低, 浮游动物的密度呈现先升高后降低的变化趋势。浮游动物的群落结构主要受溶解氧、氨氮和水位的影响。捕鱼活动导致的浮游食性鱼类减少也对浮游动物的密度变化产生了影响。     

Mysis in the Okanagan Lake food web: a time-series analysis of interaction strengths in an invaded plankton community

Mysis introductions to the lakes of western North America have shown they are important predators on zooplankton, especially daphnids, and intercept energy flows that would otherwise be available to pelagic fishes. However, understanding of the ecological roles of Mysis within invaded communities following their establishment remains weak. We analyzed zooplankton and phytoplankton data collected from Okanagan Lake, British Columbia, within a time-series framework to evaluate the strength of ecological interactions between Mysis and the other dominant plankton. Top-down effects of Mysis in the plankton community were only detected on cyclopoid copepods and cyanophytes. Mysis dynamics were mostly driven by bottom-up effects from diatoms and from small cladocerans whose dynamics were driven primarily by the abundance of edible phytoplankton. This result supports the growing appreciation of the importance of omnivory in mysids and was consistent between the two main basins of the lake. We also analyzed published stable C and N isotope data from the plankton of Okanagan Lake with an isotope mixing model to estimate the relative importance of various potential energy sources to Mysis. This analysis supported the time-series results suggesting the importance of diatoms and small zooplankton to Mysis. However, the isotopes also suggested important resource flows from Daphnia to Mysis, an interaction not detected in the time-series analysis. Taken together, these results suggest that Mysis is a strong interactor in the Okanagan Lake food web, relying in part on energy flow through Daphnia. However, subsidies from diatoms likely decouple seasonal Mysis population dynamics from the seasonal population dynamics of Daphnia.     

Diel vertical distribution of zooplankton in Lake Naivasha,Kenya

Diurnal and diel vertical distribution of limnetic zooplankton species in relation to temperature and dissolved oxygen profiles was examined at a central station in Lake Naivasha. During calm days thermal stratification developed gradually from late morning to reach maximum formation at mid-day. Dissolved oxygen concentrations showed similar vertical profiles to temperature. These stratifications were, however, short lived and were broken up in late afternoons by the wind induced poly-holomictic nature of the lake. During the day most zooplankters aggregate at the top 3–4 metre zone of the water column coincident with maximum photosynthetic activity. The pattern of diel vertical distribution of zooplankton in Lake Naivasha is undefinedly even. The absence of significant diel changes in the distribution of the limnetic zooplankton may be related to the absence of permanent physico-chemical boundaries and lack of predation pressure in the open water.     

Predation pressure induced by seasonal fishing moratorium changes the dynamics of subtropical Cladocera populations

Seasonal fishing moratorium with selective fish harvesting is a common means of increasing fish production in Asia. Such manipulation might be expected to lead to a seasonal variation in abundance and composition of fish and predation pressure on zooplankton, and consequently a seasonal change in the Cladocera populations. In this study, we examined the seasonal dynamics of cladocerans in a subtropical plateau lake in southwestern China, Lake Erh, in which a fishing moratorium was implemented in spring and early summer. Cladocerans showed a bimodal seasonal distribution linked to variations in predation pressure induced by the seasonal fishing moratorium. When predation was low in winter because of cool water temperatures and decreasing fish density, Daphnia galeata appeared in the water column and increased towards spring. The cladoceran peaked in the middle of the fishing moratorium, coinciding with a clear water phase. The feeding rate increased with temperature in the late moratorium, allowing planktivorous fish to strongly suppress large daphnids. Small cladocerans benefited from the reduced competition with large daphnids by increasing their numbers rapidly, which resulted in a second peak of cladocerans in the fishing season.     

鄱阳湖丰水期水位波动对浮游动物群落演替的影响

为了解鄱阳湖夏季丰水期水位剧烈波动过程中浮游动物的群落演替特征,2012年夏季鄱阳湖水位剧烈波动期间,于6月24日、7月7日和8月27日当水位下降且接近17.6 m时,在江西鄱阳湖国家级自然保护区内的1个浅水碟形湖泊设置4个采样点进行采样调查。共发现浮游动物65种,其中轮虫52种,枝角类7种,桡足类6种,多为营浮游生活的广温性和嗜温性种类。单因子方差分析(one-way ANOVA)显示3个月之间浮游动物的密度和生物量均具有显著差异(P0.05),7月份浮游动物密度(1030.17±68.18个/L)显著高于6月份(325.16±41.60个/L)和8月份(203.79±24.91个/L);6月份浮游动物的生物量(0.56±0.04 mg/L)显著低于7月份(1.22±0.11 mg/L)和8月份(0.99±0.11 mg/L)。基于浮游动物多度的聚类分析和自组织映射神经网络图均揭示夏季3个月份的浮游动物可区分为明显的3个群落:6月群落、7月群落和8月群落。蒙特卡罗检验发现水温、电导率、浊度和溶氧与浮游动物群落结构变化显著相关(P0.05)。典型相关分析显示,6月份浮游动物群落与叶绿素a含量呈显著正相关关系,7月份浮游动物群落与水体温度呈显著正相关关系,8月份浮游动物群落与水深和电导率、浊度和溶氧呈显著正相关关系(P0.05)。在3个月均为优势物种的盖氏精囊轮虫与叶绿素a含量呈正相关关系(P0.05),与水温、pH、溶氧呈负相关(P0.05)。夏季水位波动过程中浮游动物的群落结构在时间上(月份之间)发生明显演替,呈现轮虫密度逐渐降低,枝角类和桡足类密度逐渐增加的变化规律。水位波动引起环境因子的改变,从而对浮游动物的群落演替产生了重要影响。     

Vertical distributions of zooplankton and population dynamics of Daphnia in a meromictic lake

Vertical distributions of zooplankton were studied in relation to profiles of temperature, oxygen and chlorophyll a in Roi Lake, a small meromictic lake in central Alberta. Zooplankton were distributed fairly evenly through the oxygenated part of the water column in early summer, but a gradual descent of several species became evident in June. The vertical distribution of chlorophyll was dominated by a huge peak at the 8- to 9-m-deep chemocline. the location of a plate of photosynthetic sulfur bacteria. Ambient concentration of chlorophyll was a poor predictor of the numbers of zooplankton and the fecundity of Daphnia pulicaria at different depths, and per capita birth rates of Daphnia were usually highest in the surface waters. The reproductively disadvantageous restriction of daphnids to deep water by late summer and their catastrophic decline in the face of high ambient concentrations of chlorophyll suggest that factors other than temperature and food supply are important in influencing the dynamics and distribution of zooplankton in this lake.     

Recurrent response patterns of a zooplankton community to whole-lake fish manipulation

1. In a series of whole-lake manipulations conducted from 1984 to 1991, planktivorous fishes were alternately removed and restocked in a small mesotrophic lake, resulting in dramatic changes in the zooplankton community. 2. Response patterns in the zooplankton community, which include species and size structure, and within-year community variability, were examined. Variation in the zooplankton community in unmanipulated years was much lower than that in manipulated years, regardless of direction of the manipulation (i.e. decreasing or increasing planktivory). 3. The succession of zooplankton species abundance was repeated in the second removal of planktivorous fishes. The community shifted from small-bodied cladocerans, copepods and rotifers, through an intermediate state with high abundance of Holopedium, to an assemblage dominated by large-bodied daphnids.     

Bacterial epibionts of Daphnia: a potential route for the transfer of dissolved organic carbon in freshwater food webs

The identification of interacting species and elucidation of their mode of interaction may be crucial to understand ecosystem-level processes. We analysed the activity and identity of bacterial epibionts in cultures of Daphnia galeata and of natural daphnid populations. Epibiotic bacteria incorporated considerable amounts of dissolved organic carbon (DOC), as estimated via uptake of tritiated leucine: three times more tracer was consumed by microbes on a single Daphnia than in 1 ml of lake water. However, there was virtually no incorporation if daphnids were anaesthetised, suggesting that their filtration activity was essential for this process. Microbial DOC uptake could predominantly be assigned to microbes that were located on the filter combs of daphnids, where the passage of water would ensure a continuously high DOC supply. Most of these bacteria were Betaproteobacteria from the genus Limnohabitans. Specifically, we identified a monophyletic cluster harbouring Limnohabitans planktonicus that encompassed sequence types from D. galeata cultures, from the gut of Daphnia magna and from daphnids of Lake Zurich. Our results suggest that the epibiotic growth of bacteria related to Limnohabitans on Daphnia spp. may be a widespread and rather common phenomenon. Moreover, most of the observed DOC flux to Daphnia in fact does not seem to be associated with the crustacean biomass itself but with its epibiotic microflora. The unexplored physical association of daphnids with heterotrophic bacteria may have considerable implications for our understanding of carbon transfer in freshwater food webs, that is, a trophic ‘shortcut'' between microbial DOC uptake and predation by fish.     

Zooplankton response to flooding of a drought refuge and implications for the endangered fish species Craterocephalus fluviatilis cohabiting with alien Gambusia holbrooki

Disruption to a river’s natural flow regime changes its ecological character, which becomes unfavourable for previously adapted biota. The zooplankton particularly are affected, and survival of larval and juvenile fish is largely determined by their availability. Alien fishes can also impact on recruitment in native fishes, sometimes through competition. In this regard, the invasive eastern Gambusia Gambusia holbrooki is linked to the decline of several fish species. It can have a substantial influence in shaping plankton communities, which implies that it competes with native fish that rely on the microfauna. The effects of river regulation and over abstraction of water in the Murray–Darling Basin, south-eastern Australia, were exacerbated by drought from 1997 to 2010. Consequently, the endangered Murray hardyhead Craterocephalus fluviatilis underwent substantial population decline and extirpations. The purpose of this study is to determine if a link exists between zooplankton response to flooding of a drought refuge and the recruitment success of C. fluviatilis in the presence of G. holbrooki. Flooding triggered sharp and substantial increases in the zooplankton and their eggs, which was the sole food of C. fluviatilis. This apparently benefitted the recruitment of C. fluviatilis, and sometimes alleviated diet overlap with G. holbrooki. Conversely, the zooplankton in a nearby non-flooded refuge was low in abundance and diversity, and all fish species were extirpated. The findings indicate that the flooding of drought refugia with relatively small volumes of water can be timed with ecological cues that would otherwise be desynchronized in highly regulated rivers, particularly during drought.     

Limnology of a desertic terminal lake,Walker Lake,Nevada, U.S.A.

Walker Lake, a large terminal lake in west-central Nevada, is rapidly desiccating and becoming more saline. From 1937 to 1977, total dissolved solids increased from 5 650 to 10 650 mg l^–1. Ionically, the lake is a chlorocarbonate one; however, as desiccation continues it should eventually have about equal amounts of chloride, sulfate and carbonate. With regard to algal nutrients, the lake appears to be nitrogen limited. The phytoplankton is currently dominated by Nodularia spumigena; at times this produces noxious blooms. The zooplankton community is depauperate and composed of three species. The fish fauna is limited to three endemic fishes, with tui chub, Gila bicolor, dominant. Lahontan cutthroat trout, Salmo clarki henshawi, is restricted during summer to a narrow mid-water zone low enough in temperature and high enough in dissolved oxygen to meet physiological requirements.Dr. Koch passed away in October 1983.     

有关彩色真菌培养基的应用

彩色真菌培养基具有选择性强、分辨率高、易生长、易观察的特点。在真菌培养方面优于其它培养基,其主要作用机理在于应用了化学生物效应促进真菌生长。     

Diel microdistribution of physical and chemical parameters within the dense <Emphasis Type="Italic">Chara</Emphasis> bed and their impact on zooplankton

Research on the diurnal distribution of physical and chemical parameters within a single macrophyte bed was carried out on the shallow Wielkowiejskie Lake (Poland). A non-parametric statistical analysis was used to compare the water quality features in different parts of a Chara hispida habitat including the middle, both edge (vertical and horizontal) parts of a macrophyte plant, and the open water next to-and above the stonewort stand. The obtained results showed a differentiation in the physical-chemical parameters of the environmental conditions within the Chara hispida stand. The greatest variability was found for dissolved oxygen. Its lowest concentrations were noted in the central part of the macrophyte stand, irrespective of the sampling time. The zooplankton communities within the examined Chara bed were strongly influenced by the concentration of dissolved oxygen. It was also found that two main components of zooplankton communities (rotifers and cladocerans) had a similar trend in their spatial and diurnal distribution within the stonewort stand.     

Temperature sensitivity of vertical distributions of zooplankton and planktivorous fish in a stratified lake

Recent studies have indicated that temporal mismatches between interacting populations may be caused by consequences of global warming, for example rising spring temperatures. However, little is known about the impact of spatial temperature gradients, their vulnerability to global warming, and their importance for interacting populations. Here, we studied the vertical distribution of two planktivorous fish species (Coregonus spp.) and their zooplankton prey in the deep, oligotrophic Lake Stechlin (Germany). The night-time vertical centre of gravity both of the fish populations and of two of their prey groups, daphnids and copepods, were significantly correlated to the seasonally varying water temperature between March and December 2005. During the warmer months, fish and zooplankton occurred closer to the surface of the lake and experienced higher temperatures. The Coregonus populations differed significantly in their centre of gravity; hence, also, the temperature experienced by the populations was different. Likewise, daphnids and copepods occurred in different water depths and hence experienced different temperatures at least during the summer months. We conclude that any changes in the vertical temperature gradient of the lake as a result of potential future global warming may impact the two fish populations differently, and may shape interaction strength and timing between fish and their zooplankton prey. Priority programme of the German Research Foundation—contribution 9.     

Specialized morphology for a generalist diet: evidence for Liem's Paradox in a cichlid fish

The stable isotope ratio and seasonal changes in diet of Alluaud's haplo Astatoreochromis alluaudi, a cichlid fish with massive pharyngeal jaws well known for its ability to process hard‐bodied prey, are described. The diet of A. alluaudi was quantified in Lake Saka, Uganda, over a period of 30 months. Variation in physico‐chemical variables (mean monthly rainfall, water temperature, turbidity and dissolved oxygen), as well as potential competitor density and food abundance, was measured throughout the second half of the study (14 months). Stomach contents and isotope analysis revealed a diet comprised mainly of fishes and insects, with a low contribution of molluscs (0–33%) in any given month. No correlation was detected between diet and either macroinvertebrate abundance or competitor abundance. The running average rainfall was positively related to the percentage of fish consumed per month. Although A. alluaudi exhibits an apparent molluscivorous trophic morphology in Lake Saka, molluscs did not appear to compose a major portion of its diet. Gradients of rainfall seemed to be the most important environmental predictor of diet choice in Lake Saka. These results are discussed with reference to Liem's Paradox that apparently morphologically specialized fishes often function as generalist feeders in the wild.     

Zooplankton abundance and evidence for its reduction by macrophyte mats in two Orinoco floodplain lakes

Zooplankton populations were sampled over one annual cycle intwo floodplain lakes of the Orinoco River, Venezuela, in anattempt to establish the relationship between abundance patternsand the hydrology and morphometry of the lakes. One of the lakes(Tineo) is relatively large with a gently sloping basin; theother one (Aguilera) is smaller and channel-shaped. The hydraulicresidence time of Lake Aguilera during inundation by the riveris shorter (<1 day) than the minimum generation times ofcrustacean (4–12 days) and rotiferan (2.5 days) zooplankton.For Lake Tineo, residence time during inundation (7 days) islonger than generation times for all taxa except copepods. AlthoughLake Aguilera receives water from Lake Tineo during inundation,zooplankton densities were greatly reduced during passage througha large bed of the floating aquatic grass Paspalum repens locatednear the outlet of Lake Tineo. This retention was not size-selectiveand affected phytoplankton as well as zooplankton. In the Orinocofloodplain zooplankton densities are affected not only by hydraulicresidence times but also by passage of water between lakes,which exposes populations to large losses within macrophytebeds. Retention of plankton by floating macrophyte beds is potentiallyimportant to the trophic ecology of tropical floodplain lakesbecause it results in the concentration of planktonic productionin epiphytic and benthic habitats, where it can readily supportfood webs consisting of macroinvertebrates and fishes. Exportof plankton from floodplain waterbodies to the river is alsoreduced by this mechanism. ¹Present address: Department of Biological Sciences, Universityof California, Santa Barbara, CA 93106, USA     

A fish-kill in Heart Lake, Ontario, associated with the collapse of a massive population of Ceratium hirundinella (Dinophyceae)

SUMMARY. A massive population of the common dinoflagellate Ceratium hirundinella developed in Heart Lake. Ontario, Canada during the summer of 1976 and its sudden collapse and subsequent decomposition depleted dissolved oxygen and resulted in a fish-kill in the lake. The lake was being artificially mixed at the time by supplying compressed air to the bottom waters and the limnological events contributing to the development of the Ceratium population and its collapse appear to be closely related to the artificial destratification process. Artificial destratification during 1976 precluded the development of blue-green algue. The process also led to an increase in the density of herbivorous zooplankters which controlled the development of smaller planktonic algae. Ceratium flourished in Heart Lake because there was little competition for nutrients from other algae and because Ceratium cells are too large to be grazed by the zooplankton. The maximum size of the Ceratium population (53 mm³ 1⁻¹) is apparently the highest biomass reported in the literature and its collapse may have been related to a depletion of inorganic nitrogen. There is apparently no previously published record of a Ceratium -induced fish-kill in a freshwater lake.     

<Emphasis Type="Italic">Limnocnida tanganyicae</Emphasis> medusae (Cnidaria: Hydrozoa): a semiautonomous microcosm in the food web of Lake Tanganyika

Medusae are important members of marine food webs, but are rare in lakes. In one of the largest lakes in the world, Lake Tanganyika, a small medusa (Limnocnida tanganyicae) is a prominent component of zooplankton. We used field and laboratory methods to study the ecological role of Lake Tanganyika medusae, which occasionally reached high local densities in the whole epilimnion. The largest individuals showed low amplitude, diel vertical migration which minimized their exposure to harmful UV radiation and also may be important for picocyanobacteria regularly present in the medusae. The endosymbiotic picocyanobacteria differed morphologically among medusae and were predominantly one Lake Biwa type Cyanobium sp. that typically was abundant in the water column. Under light, some medusae were net primary producers. Although nitrogen stable isotopic ratios indicated that the free-living cyanobacteria were nitrogen-fixers, the picocyanobacteria in medusae obtained nitrogen predominantly from their host. Stable isotopic ratios of carbon and nitrogen further suggested that copepods were the most likely prey for the medusae. Lake Tanganyika medusae apparently base their metabolism both on animal and plant sources, with possible internal cycling of nutrients; however, the role of picocyanobacteria gardening in the Lake Tanganyika ecosystem and its medusae requires quantification.     

Seasonal variation in abundance and diversity of zooplankton in Asu River,Ebonyi state,Nigeria

The Physicochemical variables and Zooplankton of Asu River, Ebonyi State, Nigeria were studied monthly between October 2013 and June 2014 which covered the wet and dry seasons. The study was carried out monthly in two selected sites by collecting water samples for physiochemical analysis and zooplankton identification. Shannon-Weiner diversity and Margalef's indices were used to determine the zooplankton composition. Investigation on the physiochemical variables showed that water temperature, dissolved oxygen, total dissolved solids, pH, conductivity and carbon (iv) oxide all recorded maximum values in the dry season. The present result also showed that the river is not seriously polluted. However, only carbon (iv) oxide and nitrate varied significantly between seasons (p < 0.05). Forty two (42) zooplankton species comprising Rotifera (7 families; 23 species), Copepoda (2 families; 8 species) and Cladoceran (6 families; 11 species) were identified. Rotifera spp. were numerically dominant and the most diverse group but the crustacean, Thermocyclops oithonoides dominated the total zooplankton biomass during the study. Species abundance showed inverse relationship with species richness, Shannon-Weiner diversity and Evenness. Zooplankton abundance was at its peak in the dry season while species richness, Shannon- Weiner diversity and evenness increased from dry season to wet season.     

Leptodora kindtii survival in the laboratory

Leptodora kindtii, a pelagic predatory cladoceran, suffers high mortality on transfer to laboratory, which makes the experimental work difficult. We investigated the causes of high mortality, using four variables: water volume, animal density, light intensity, and origin of water for culturing, i.e., water from native or a non-native lake. For the experiments we used Leptodora and water from Lake Loosdrecht and Lake Maarsseveen (The Netherlands). Water was found to be the most important factor; the animals did not necessarily do better in lake water from which they were collected. Water volume and animal density were of limited importance, and light intensity did not affect survival.     

太平湖浮游动物动态演替与环境因子的相关性研究

2012年11月至2014年10月, 对太平湖浮游动物群落进行了为期两年的调查研究。共鉴定出浮游动物45属89种, 其中轮虫 29属69种、枝角类5属7种、桡足类2属4种和原生动物9属9种; 优势种主要来自于轮虫异尾轮虫属(Trichocereca)和龟甲轮虫属(Keratella)。浮游动物的丰度值存在明显的季节变化, 表现为夏季最大, 平均达1326 ind./L, 秋季春季次之, 分别为608和605 ind./L, 冬季最小为216 ind./L; 垂直分布表现为春夏季太平湖表层浮游动物丰度最高, 中间层次之, 底层最小, 秋冬季则表现为中间层最高。浮游动物群落Shannon-Wiener多样性指数和Margalef丰富度指数中间层普遍高于表层和底层, Pielou均匀度指数表现为底层要高于表层和中间层, 季节变化表现为夏秋季显著高于冬春季的现象, 水质评价表明夏秋季水质好于春冬季。聚类和多维尺度分析表明: 太平湖浮游动物可分为夏秋季类群与春冬季类群, 两类群均表现为湖心与上下游区域群落结构差异较大, 其中春冬季类群差异较明显; 相关和逐步回归分析表明: 透明度和水温为太平湖浮游动物群落结构变化的主要环境影响因子; 依据结构方程模型(SEM)和冗余分析(RDA)的结果显示, 在溶解氧和水温较高的水环境中浮游动物丰度值表现为较大, 其中水温对轮虫的影响高于对枝角类和桡足类的影响。