罗非鱼对盐碱池塘围隔浮生物群落的影响

本文报道了单养尼罗罗非鱼（Ｏｒｅｃｏｈｒｏｍｉｓ ｎｉｌｏｔｉｃｕｓ）对施肥处理下盐碱池塘围隔生态系统浮游生物群落的影响。结果表明,罗非鱼的放养使浮游植物丰度、叶绿素ａ含量和初级生产力增大,浮游植物小型化,生物量以小型硅藻和绿藻占优势,裸藻占有相当比重;浮游动物生物量也增大,桡足类占优势,枝角类小型化,原生动物密度增大。施肥特别是施有机肥能显著提高浮游植物生物量,使透明度降低,但施无机肥对初级生产     

鲢放养和施肥对盐碱池塘围隔生态系统浮游生物群落的影响

报道了单养链（Hypophthalmichthys molitrix)和施肥对盐碱池塘围隔生态系统浮游生物群落的影响,链的放养使浮游植物丰度,叶绿素a 含量和和初组生产力增大,浮游植物小型化,生物量以小型硅藻和绿藻占优势,裸藻和金藻占有相当比重;浮游动物生物量减少,特别是枝角类的生物量无鱼围隔大于有鱼围隔,且多是较大型的种类,施肥特别是施无机肥能显著地提高浮游植物丰度和初级生产力,浮游动物生物量也增大,施有机肥围隔浮游植物和浮游动物生物量虽高于有鱼对照围隔,但其浮游植物初级生产力,叶绿素a含量,浮游生物多样性指数,P／R系数均较低,链鱼的生长最差,文中讨论了滤食性鱼类和施肥对浮游生物的影响。     

不同放养和管理模式下三角帆蚌养殖水体中的浮游生物和初级生产力

通过围隔实验研究了3种放养(单养三角帆蚌,蚌与鲢、鳙混养,蚌与银鲫混养)和2种管理(施肥、投饵兼施肥)模式下养殖水体的浮游生物和初级生产力.结果表明:围隔内浮游植物主要为＜20 μm粒级的种类,其中蓝藻、绿藻和裸藻占优势,硅藻、隐藻、黄藻和甲藻的数量和质量较低;实验期间,围隔内浮游植物数量和质量平均值分别为0.35×109～1.26×109 ind·L-1和32～86 mg·L-1,其中三角帆蚌与鲢、鳙混养的围隔内浮游植物数量和质量较高,蓝藻和硅藻数量和质量明显高于其它围隔;围隔内浮游动物数量以原生动物最多,其质量则以轮虫占优势,枝角类和桡足类等大型浮游动物的数量较少;单养蚌的围隔内浮游动物质量最高;与混养围隔相比,单养蚌的围隔内轮虫质量在浮游动物中的比例较低,桡足类的比例相对较高;蚌与鲢、鳙混养围隔内浮游动物数量最多,原生动物数量在浮游动物中的比例分别高于单养蚌和蚌、银鲫混养的围隔,而轮虫的比例低于后者;实验期间,围隔内初级生产力平均值为4.11～5.45 g O2·m-2·d-1,水呼吸为2.39～4.12 g O2·m-2·d-1,初级生产力与水呼吸的比值为1.25～1.99;单养蚌的围隔内初级生产力最高,蚌、银鲫混养的围隔内初级生产力最低.结果表明:三角帆蚌养殖水体内浮游植物和浮游动物均表现出小型化的趋势;较高的浮游植物数量和质量,特别是较高的硅藻数量和质量,可能是三角帆蚌与鲢、鳙混养围隔内二龄蚌生长较好的原因之一;浮游植物种类组成较初级生产力对蚌生长的影响更大.     

鲤鱼种和鲢鳙对池塘浮游生物的影响

本文根据１９９０年－９月对９个鱼池的研究,报道鲤鱼种和鲢鳙对浮游生物的影响,结果表明：鲤鱼种使浮游植物和浮游动物生物量增加,浮游植物大型化,浮游动物小型化,并使浮游植物多样性增加,浮游动物多样性下降;鲢鳙密度增加,浮生物小型明显,微型藻类和超微在在浮植物中所占比重显著增加,小型浮游动物（原生动物和轮虫）在浮游动物中比重也明显增;鲢鳙密度对浮游生物多样性和浮游生物量的影响具有阶段性,当鲢鳙密度低时,     

罗非鱼对微型生态系统浮游生物群落和初级生产力的影响

本文报道罗非鱼不同放养密度对淡水微型生态系统结构与功能影响的部分研究结果。罗非鱼的捕食使微型生态系统中浮游动物密度下降,引起浮游植物密度、初级生产力和P/R系数的增长,同时使水柱透明度降低而pH值增高,以致于实验后期微型生态系统具有典型的富营养化水体的特征。就罗非鱼放养密度不同的微型生态系统而言,虽然其浮游生物密度和P/R系数存在显著的组(或部分组)间差异,但不同密度组的初级生产力水平和最终的理化状况相差不大,并且罗非鱼的收获量甚为接近。因此,实验条件下微型生态系统的群落结构和代谢的变化,按照营养级联假说不能很好地予以解释,表明微型生态系统是由捕食(下行影响)和理化因素(上行影响)共同调节或控制的。根据微型生态系统的实验结果推断,放养较大密度的罗非鱼,将会加速营养物负荷较高的天然水域富营养化的进程。     

鄱阳湖不同水文期浮游生物群落结构特征和影响因素及水质评价

为阐明鄱阳湖不同水文期浮游生物群落结构特征及其影响因素, 研究于2017年8月(丰水期)和12月(枯水期)在鄱阳湖湖区典型水域设置5个采样点进行浮游生物采样调查。研究期间共鉴定浮游植物8门75属186种, 丰水期与枯水期均以硅藻门和绿藻门为主。共鉴定浮游动物4类76种, 丰水期与枯水期均以原生动物和轮虫为主。方差分析显示: 浮游植物密度与生物量在不同水文期之间的差异均为极显著(P<0.01), 浮游动物丰水期密度高于枯水期, 但无显著差异(P>0.05), 浮游动物生物量(P<0.05)在不同水文期差异显著。冗余分析(RDA)显示: 丰水期透明度和浮游生物呈显著负相关关系, 电导率和浮游生物呈显著正相关。透明度、电导率与营养盐是影响丰水期浮游生物群落结构的主要环境因素, 枯水期水温和溶解氧是驱动鄱阳湖浮游生物群落生态分布的主要环境因素。基于Shannon-Wiener(H′)、Margalef(d)和Pielou(J)等生物多样性指数的水质评价结果表明: 鄱阳湖研究区域水质状态处于寡污-中污之间。研究揭示了2个水文期对通江湖泊浮游生物的影响: 季节变化不改变湖泊浮游生物的物种组成及优势种, 但显著影响浮游生物的丰度及多样性。     

放养鲢鱼(Hypophthalmichys molitrix C et V)对水库围隔浮游生物群落的影响

本文研究在水库围隔实验生态系统中鲢鱼对浮游生物群落的影响。结果表明,放养鲢鱼后,浮游动物生物量、浮游植物生物量、叶绿素a和浮游植物毛产量分别下降了58.7％、63.6％、52.5％和65.0％;透明度、浮游植物群落多样性指数分别提高了18.2％、32.5％;铜绿微囊藻数量减少了90.6％“水华”得到明显抑制。但小型绿藻(<20μm)数量未出现显著变化,因而其在藻类生物量中所占比例反而提高了82.3％。围隔内可被鲢鱼滤食的大型藻类(硅藻、甲藻、隐藻和绿藻(>20μm))占藻类生物量的85.8％,因此鲢鱼的存在能明显限制浮游植物的生物量。此外,放养鲢鱼还显著降低了水体中的COD,TP,DO和pH值,这表明鲢鱼对水质有净化作用。     

盐碱池塘围隔生态系统的悬浮物结构及有机碳库储量

1 998年 4～ 7月对高青盐碱池塘单养鲢和罗非鱼围隔生态系统颗粒悬浮物构成和各有机碳库储量及动态进行了研究。结果表明 ,浮游生物的干重 (PZ)占总颗粒悬浮物干物质 (TS)的 4.2 6%～ 2 5 .97% ,平均 1 2 %。各围隔浮游植物干重(DWP)平均值变化范围为 0 .1 6～ 0 .70 mg/L,有鱼围隔均比无鱼围隔的大。浮游动物干重 (DWZ)平均值变化范围为0 .3 2～ 2 .81 mg/L,养鲢围隔中最小 ,小于无鱼对照围隔 ,养罗非鱼围隔明显高于养鲢围隔。颗粒悬浮物的灰分含量平均值为 42 .3 8%。溶解有机碳 (DOC)、颗粒有机碳 (POC)库储量平均值分别为 5 .40± 1 .61 mg C/L和 1 .96± 0 .96mg/L。各处理围隔间颗粒有机物的 C/N比的平均值比较接近 ,总平均值为 6.97± 0 .2 4。 TOC、DOC和 POC比例为 1∶ 0 .73∶0 .2 7。浮游生物碳和腐质颗粒碳占 POC的比例的平均值分别为 3 4.65 %和 65 .3 5 %。腐质颗粒碳、浮游动物碳与浮游植物碳的比例为 9.2 9∶ 3 .71∶ 1。浮游生物碳中浮游动物碳占 78.8% ,浮游植物碳占 2 1 .2 %。浮游动物碳比浮游植物碳高 ,这可能是内陆盐水的通性。盐碱池塘围隔生态系统颗粒有机碳 (POC,mg C/L)与浮游植物叶绿素 a(Chla,μg/L)和悬浮颗粒有机物 (SO,mg/L)之间存在显著的正相关关系 ,其回归方程分别为     

发酵有机肥对主养草鱼池塘水质调控效果研究

在草鱼(Ctenopharyngodon idellus)主养池塘中,对比检测了发酵有机肥实验塘与未施肥对照塘水质理化指标、浮游生物及微生物群落结构差异,以分析发酵有机肥肥效及其对池塘水环境产生的影响。结果如下:发酵有机肥显著提高了浮游生物种类数、生物量和细菌丰度,增加了浮游植物多样性;实验期间,实验塘浮游植物、浮游动物平均生物量和细菌平均丰度分别为(68.21±25.13)mg/L、(9.83±5.74)mg/L和(6.53±2.13)×10~6 ind./mL,分别是对照塘的2.78倍、4.35倍和1.29倍;发酵有机肥促进有益菌增殖作用显著,施肥后期,实验塘乳酸菌、芽孢杆菌和节杆菌属相对比例分别为(0.61±0.17)%、(0.89±0.29)%和(0.04±0.0082)%,分别是对照塘的3倍、3倍和4倍;发酵有机肥平抑NH_4~+-N、NO_2-N效果显著,在NH_4~+-N、NO_2~--N快速积累季节,实验塘NH_4~+-N、NO_2~--N浓度均显著低于对照塘(P0.05);发酵有机肥增氧效果显著,而对pH、TN、TP、NO_3~--N、PO_4~(3-)-P等无显著影响。研究结果表明,发酵有机肥肥效突出,具有显著改善池塘水环境作用。     

基于围隔实验研究鳙在亚热带贫-中营养水库的下行效应

为了解鳙在低营养水体中的下行效应,于秋冬季节在流溪河水库开展了原位围隔实验。该实验在水库原水中进行,并根据鳙的生物量(0 g·m^–3和3 g·m^–3)设置了对照组和有鱼组。研究结果显示:总氮(TN)、总磷(TP)、氮磷质量比(TN:TP)和叶绿素(Chl a)在加入鳙后均未发生显著变化。所有围隔中浮游动物群落均是以小个体种类为主,缺少大型枝角类。鳙的存在促进了轮虫和剑水蚤丰度的增加,但降低了枝角类和哲水蚤的丰度,并导致枝角类、桡足类及浮游动物的生物量显著下降。有鱼围隔中甲壳类的平均体长(352—396μm)显著低于对照组(547—592μm)。添加鳙使浮游植物优势门类绿藻与大型浮游植物(最大轴直径≥30μm)的生物量显著升高,但对优势门类硅藻、金藻和甲藻、小型浮游植物(最大轴直径<30μm)以及浮游植物的生物量无显著影响。这些结果显示,鳙对浮游动物群落产生了强烈的下行效应,对浮游植物群落则未产生明显的级联效应。我们的结果表明,在缺少大型牧食性枝角类的低营养水体中,鳙在低温季节对水质的影响可能相对有限。     

Studies on the Effects of Silver Carp (Hypophthalmichthys molitrix) on the Phytoplankton in a Shallow Hypereutrophic Lake through an Enclosure Experiment

The responses of nutrients, water transparency, zooplankton and phytoplankton to a gradient of silver carp biomass were assessed using enclosure methods. The gradient of four silver carp biomass levels was set as follows: 0, 116, 176 and 316 g m^—2. Nutrients did not show any statistically significant differences among the treatments. An outburst of Daphnia only occurred in fishless enclosures where phytoplankton biomass was the lowest and water clarity significantly increased. While among fish enclosures, the small‐sized Moina micrura dominated throughout the experiment and both zooplankton and phytoplankton biomasses decreased with increased fish biomass. No large colonial cyanobacterial blooms occurred in the fishless enclosures as predicted. This might be due to low water temperature, short experiment time and the occurrence of large bodied Daphnia in our experiment. Cryptophyta was the most dominant group in most of the enclosures and the lake water throughout the experiment. The fishless enclosure had much lower proportion of Cyanophyta but higher proportion of Trachelomonas sp.     

Plankton community of a polyhumic lake with and without Daphnia longispina (Cladocera)

The impact of Daphnia longispina (Cladocera) on the plankton food web was studied in a polyhumic lake where this species comprised almost all zooplankton biomass. Plastic enclosures (volume 7 m³) were inserted into the lake retaining the initial water stratification except that in one enclosure zooplankton was removed. After the removal of Daphniaa rotifer, Keratella cochlearis, ciliates and heterotrophic nanoflagellates increased markedly and the density and biomass of bacteria decreased. Edible algal species, Cryptomonas rostratiformisand three small chrysophytes,Ochromonas, Pedinella and Spinifermonas, took advantage of the removal of Daphnia, while more grazing-resistant species declined. In spite of the changes in the species composition of phytoplankton, the removal of Daphnia did not affect the biomass, primary production or respiration of plankton. The results implied that the density of heterotrophic flagellates and ciliates was controlled by Daphnia, but in its absence the former took its role as the bacterial grazers.     

A cyanobacterial bloom prevents fish trophic cascades

1. We experimentally compared the impacts of visually feeding zooplanktivorous fish and filter‐feeding omnivorous fish in shallow tropical Dakar Bango reservoir, Senegal. We provoked a cyanobacterial Anabaena bloom under mesotrophic to eutrophic N‐limited conditions in 18 enclosures assigned to six Nile tilapia life‐stage treatments, at typical biomasses: fishless control (C), zooplanktivorous fry (Z), omnivorous juveniles (O), herbivorous fingerlings (H) and two combinations (OZ, OH). 2. All fish grew well, but as prevalent inedible phytoplankton dampened fish effects, community‐level trophic cascades did not occur. Planktivore types acted independently and affected differentially the biomasses of total zooplankton, cyclopoids, nauplii, cladocerans, invertebrate carnivores, large herbivores, colonial cyanobacteria and Chlorophyta. They neither influenced the total biomass of phytoplankton, nor most water chemistry characteristics. Responses were apparently not fish‐biomass related. The bloom collapsed synchronously in all enclosures, coinciding with enrichment ending, with a return to clear water within 12 days. 3. Our results support the hypothesis that excess nutrients and prevalent inedible cyanobacteria inhibit the cascading effects of natural biomass levels of both visually feeding zooplanktivores and filter‐feeding omnivores. In N‐limited meso‐eutrophic shallow tropical lakes with predominantly small herbivorous zooplankton, neither the type nor the biomass of planktivorous fish present seems likely to prevent the transient outburst of cyanobacterial blooms. Such fragile ecosystems may thus not sustain a trophic state suitable for drinking water production, unless human impacts are restricted. The generality of restoration approaches based on ecological engineering should be further explored.     

Effects of omnivorous filter‐feeding fish and nutrient enrichment on the plankton community and water transparency of a tropical reservoir

1. The major aim of this study was to test the hypothesis that nutrient enrichment and the introduction of the Nile tilapia (Oreochromis niloticus), an exotic omnivorous filter‐feeding fish, operate interdependently to regulate plankton communities and water transparency of a tropical reservoir in the semi‐arid northeastern Brazil. 2. A field experiment was performed for 5 weeks in 20 enclosures (9.8 m³) to which four treatments were randomly allocated: tilapia addition (F), nutrient addition (N), tilapia and nutrient addition (F + N) and a control treatment with no tilapia or nutrient addition (C). A two‐way repeated measures anova was undertaken to test for time, tilapia and nutrient effects and their interactions on water transparency, total phosphorus and total nitrogen concentrations, phytoplankton biovolume and zooplankton biomass. 3. Nutrient addition had no effect except on rotifer biomass, but there were significant fish effects on the biomass of total zooplankton, copepod nauplii, rotifers, cladocerans and calanoid copepods and on the biovolume of total phytoplankton, large algae (GALD ≥ 50 μm), Bacillariophyta and Zygnemaphyceae and on Secchi depth. In addition, we found significant interaction effects between tilapia and nutrients on Secchi depth and rotifers. Overall, tilapia decreased the biomass of most zooplankton taxa and large algae (diatoms) and decreased water transparency, while nutrient enrichment increased the biomass of rotifers, but only in the absence of tilapia. 4. In conclusion, the influence of fish on the reservoir plankton community and water transparency was significant and even greater than that of nutrient loading. This suggests that biomanipulation of filter‐feeding tilapias may be of importance for water quality management of eutrophic reservoirs in tropical semi‐arid regions.     

Calanoid copepod grazing on phytoplankton: seasonal experiments on natural communities

Calanoid copepods are major components of most lacustrine ecosystems and their grazing activities may influence both phytoplankton biomass and species composition. To assess this we conducted four seasonal, in situ, grazing experiments in eutrophic Lake Rotomanuka, New Zealand. Ambient concentrations of late stage copepodites and adults of calanoid copepods (predominantly Calamoecia lucasi, but with small numbers of Boeckella delicata) were allowed to feed for nine days on natural phytoplankton assemblages suspended in the lake within 1160 litre polyethylene enclosures. The copepods reduced the total phytoplankton biomass of the dominant species in all experiments but were most effective in summer (the time of highest grazer biomass) followed by spring and autumn. In response to grazing pressure the density of individual algal species showed either no change or a decline. There were no taxa which increased in density in the presence of the copepods. The calanoid copepods suppressed the smallest phytoplankton species (especially those with GALD (Greatest Axial Linear Dimension) < µm) and there appeared to be no selection of algae on the basis of biovolume. Algal taxa which showed strong declines in abundance in the presence of the copepods include Cyclotella stelligera, Coelastrum spp., Trachelomonas spp., Cryptomonas spp., and Mallomonas akrokomos. Calanoid copepods are considered important grazers of phytoplankton biomass in this lake. The study supports the view that high phytoplankton:zooplankton biomass ratios and large average algal sizes characteristic of New Zealand lake plankton may, at least partly, be caused by year round grazing pressure on small algae shifting the competitive balance in favour of larger algal species.     

Effects of silver carp (Hypophthalmichthys molitrix) and nutrients on the plankton community of a deep,tropical reservoir: an enclosure experiment

1. An in situ enclosure experiment was conducted in a deep reservoir of southern China to examine (i) the effects of a low biomass (4 g wet weight m^?3) of silver carp (Hypophthalmichthys molitrix) and nutrients on the plankton community and (ii) the response of Daphnia to eutrophication. 2. In the absence of fish, Daphnia galeata dominated the zooplankton community, whereas calanoids were dominant in the fish treatments, followed by D. galeata. Silver carp stocking significantly reduced total zooplankton biomass, and that of D. galeata and Leptodorarichardi, but markedly increased the biomass of smaller cladocerans, copepod nauplii and rotifers. In contrast, nutrient enrichment had no significant effect on the plankton community except for cyclopoids. 3. Chlorophyta, Cryptophyta and Bacillariophyta were dominant phytoplankton groups during the experiment. Chlorophyta with high growth rates (mainly Chlorella vulgaris in the fish enclosures and Ankyra sp. in the fishless enclosures) eventually dominated the phytoplankton community. Total phytoplankton biomass and the biomass of edible phytoplankton [greatest axial linear dimension (GALD) < 30 μm], Chlorophyta, Cryptophyta, Bacillariophyta and Cyanobacteria showed positive responses to fish stocking, while inedible phytoplankton (GALD ≥ 30 μm) was significantly reduced in the fish enclosures. However, there was no significant effect on the plankton community from the interaction of fish and nutrients. 4. Overall, the impact of fish on the plankton community was much greater than that of nutrients. High total phosphorus concentrations in the control treatment and relatively low temperatures may reduce the importance of nutrient enrichment. These results suggest it is not appropriate to use a low biomass of silver carp to control phytoplankton biomass in warmer, eutrophic fresh waters containing large herbivorous cladocerans.     

The impact of planktivorous flsh on the structure of a plankton community

SUMMARY. 1. The abundance of pianktivorous juvenile yellow perch, Perca flavescens , was manipulated in three 750 m³ enclosures in a eutrophic lake.
2. There was a significant negative relationship between fish and zoopiankton biomasses. At high fish densities the zooplankton community was dominated by small filter-feeding cladocera. primarily bosmi- nids. At low fish densities the zooplankton community was dominated by large filter-feeding cladocera, primarily daphnids.
3. There was no significant relationship between zooplankton and phytoplankton biomasses when considered over the whole experiment but there was a trend towards lower phytoplankton biomass in the enclosure dominated by daphnids during mid-summer.
4. We conclude that although planktivorous fish have a strong negative impact on zooplankton community biomass and size structure, the relationship at the next lower trophic level, zooplankton and phytoplankton, is much weaker. Therefore, the biomanipulation of planktivorous fish populations as a management technique to control phytoplankton abundance is largely ineffective.     

Effects of water-column mixing on bacteria,phytoplankton, and rotifers under different levels of herbivory in a shallow eutrophic lake

Water-column mixing is known to have a decisive impact on plankton communities. The underlying mechanisms depend on the size and depth of the water body, nutrient status and the plankton community structure, and they are well understood for shallow polymictic and deep stratified lakes. Two consecutive mixing events of similar intensity under different levels of herbivory were performed in enclosures in a shallow, but periodically stratified, eutrophic lake, in order to investigate the effects of water-column mixing on bacteria abundance, phytoplankton abundance and diversity, and rotifer abundance and fecundity. When herbivory by filter-feeding zooplankton was low, water-column mixing that provoked a substantial nutrient input into the euphotic zone led to a strong net increase of bacteria and phytoplankton biomass. Phytoplankton diversity was lower in the mixed enclosures than in the undisturbed ones because of the greater contribution of a few fast-growing species. After the second mixing event, at a high biomass of filter-feeding crustaceans, the increase of phytoplankton biomass was lower than after the first mixing, and diversity remained unchanged because enhanced growth of small fast-growing phytoplankton was prevented by zooplankton grazing. Bacterial abundance did not increase after the second mixing, when cladoceran biomass was high. Changes in rotifer fecundity indicated a transmission of the phytoplankton response to the next trophic level. Our results suggest that water-column mixing in shallow eutrophic lakes with periodic stratification has a strong effect on the plankton community via enhanced nutrient availability rather than resuspension or reduced light availability. This fuels the basis of the classic and microbial food chain via enhanced phytoplankton and bacterial growth, but the effects on biomass may be damped by high levels of herbivory. Received: 3 May 1999 / Accepted: 13 April 2000     

Water level and fish-mediated cascading effects on the microbial community in eutrophic warm shallow lakes: a mesocosm experiment

Information on the effects of water level changes on microbial planktonic communities in lakes is limited but vital for understanding ecosystem dynamics in Mediterranean lakes subjected to major intra- and inter-annual variations in water level. We performed an in situ mesocosm experiment in an eutrophic Turkish lake at two different depths crossed with presence/absence of fish in order to explore the effects of water level variations and the role of top-down regulation at contrasting depths. Strong effects of fish were found on zooplankton, weakening through the food chain to ciliates, HNF and bacterioplankton, whereas the effect of water level variations was overall modest. Presence of fish resulted in lower biomass of zooplankton and higher biomasses of phytoplankton, ciliates and total plankton. The cascading effects of fish were strongest in the shallow mesocosms as evidenced by a lower zooplankton contribution to total plankton biomass and lower zooplankton:ciliate and HNF:bacteria biomass ratios. Our results suggest that a lowering of the water level in warm shallow lakes will enhance the contribution of bacteria, HNF and ciliates to the plankton biomass, likely due to increased density of submerged macrophytes (less phytoplankton); this effect will, however, be less pronounced in the presence of fish.