The effects of barley straw (Hordeum vulgare) on the growth of freshwater algae

Bioassays were conducted to determine the efficacy of barley straw liquor in controlling algal growth of 12 freshwater species of algae representing three divisions. Barley straw liquor inhibited the growth of three nuisance algae common in freshwater: Synura petersenii, Dinobyron sp., and Microcystis aeruginosa. However, Selenastrum capricornutum, Spirogyra sp., Oscillatoria lutea var. contorta, and Navicula sp. had significantly increased growth in the presence of straw liquor. The growth of the remainder, Ulothrix fimbriata, Scenedesmus quadricauda, Chlorella vulgaris, Anabaena flos-aquae, and Synedra sp. showed no significant difference from controls. In a related field study, we treated four of six ponds with barley straw and monitored their chlorophyll a levels for one growing season. While phytoplankton populations in all ponds decreased in midsummer, the phytoplankton biomass in treated ponds did not differ significantly from that of control ponds, suggesting that the application of barley straw had no effect on algal growth in these systems.     

东湖蓝藻水华毒性的研究 Ⅱ.季节变化及微囊藻的毒性

1984年至1986年间武汉东湖(包括湖边池塘)的水华有7种,即铜绿微囊藻、大型铜绿微囊藻、边缘微囊藻、水华鱼腥藻、卷曲鱼腥藻、美丽颤藻和束丝藻。经生物测定,除束丝藻未测、卷曲鱼腥藻和美丽颤藻未测出毒性外,其余4种皆为有毒水华。东湖的水华随着季节变化而有不同类型的更迭,其出现格局为:卷曲鱼腥藻、微囊藻、颤藻、微囊藻。微囊藻水华的毒性在不同季节也有较大差异,毒性最低在8—9月份,最高在12月份(LD_(50)=24mg/kg鼠重),随着温度的降低而提高。讨论了某些环境参数与微囊藻水华形成及其毒性变化的关系。此外,还用脑内注射和腹腔注射方法,研究了微囊藻毒素的毒性表现。     

食物种类对萼花臂尾轮虫种群增长率的影响

在短期慢性观测过程中,食物类型可能是造成萼花臂尾轮虫(Brachionuscalyciflorus)种群繁殖率变化的一种原因。共观测了分别单独投喂10种不同绿藻对轮虫种群增长率的影响。为验证藻青菌是藻类饵料(如绿藻Scenedesmus)有价值的佐剂这一假说,还用蓝细菌单独投喂或与斜生栅藻(Scenedesmusobliquus)混合投喂轮虫进行实验观测。结果发现食物种类对萼花臂尾轮虫种群增长率影响显著。斜生栅藻组获得最大种群增长(1.6/d),而Desmodesmus组增长率最低(0.3/d)。以占斜生栅藻组最大增长的百分率来表示,其它几种绿藻组种群增长由高到低依次为:Desmodesmussubspicatus88%,小球藻(Chlorellavulgaris)83%,单壳缝藻(Monoraphidiumminutum)77%,D.quadricauda74%,S.falcatus71%,S.acuminatus69%,S.pectinatus64%,莱茵衣藻(Chlamydomonasreinhardtii)57%,D.abundans19%。轮虫增长率的差异不能用藻类饵料的大小差异来解释。蓝细菌(Microcystisaeruginosa)和(Synechococcuselongates)不论是单独投喂还是与优良藻类饵料(斜生栅藻)混合投喂都对萼花臂尾轮虫种群增长有抑制作用。这种副作用似乎与微囊藻素无关。该结果不支持无毒蓝细菌可作为与其他绿藻饵料配合使用的优良佐剂这一假说。本研究所观察到的生长变化显示了饵料种类对萼花臂尾轮虫种群增长的影响,也预示了对毒性实验结果的影响     

The impact of small chironomid grazers on epiphytic algal abundance and dispersion

• 1 A combination of field and laboratory experiments was used to assess the impact of chironomid grazers on taxonomic composition, abundance and dispersion of epiphytic algal assemblages.
• 2 In the laboratory, Psectrodadius sp. reduced the biovolume of algal species preferred as food and increased the degree of clumping of non-preferred species. Thienemanniella cf. fusca had both positive and negative effects (depending on the algal species) on the biovolumes of algal species preferred as food and increased the degree of clumping of non-preferred species.
• 3 In field exclosures, no effect of removal of chironomid larvae from the grazer assemblage could be detected in autumn or winter experiments. A third, longer removal experiment, conducted in summer, resulted in increased biovolumes of edible Cosmarium spp. and Aphanocapsa spp., preferred foods of chironomid larvae. Biovolumes of Lyngbya sp., Eulbochaete spp. and Oedogortium spp., filamentous taxa used extensively in larval case construction, also increased. Chironomid larvae had no effect on total algal biovolume or biovolume of large unicellular algae.
• 4 Chironomid larvae can influence epiphytic algal assemblages through selective grazing by reducing the biovolumes of preferred foods and through case-building activity by reducing the biovolumes of construction materials.

     

Spatio-temporal effects of selected physico-chemical variables of water, algae and sediment chemistry on the larval community of nuisance Chironomidae (Diptera) in a natural and a man-made lake in central Florida

Spatio-temporal distributions of Chironomus crassicaudatus, Chironomus decorus, Glyptotendipes paripes, Cryptochironomus fulvus and Tanypodinae midge larvae and selected associated environmental variables (physico-chemical variables of water, sediment chemistry and algal composition) were studied for one year in natural Lake Monroe and man-made Konomac Lake in central Florida. Ordination analysis (CCA with variation partitioning) showed that in each lake, sediment variables were the most important environmental variables. However, the most important proportion of species variability in pooled data from both lakes was explained by lake-specific combinations of water, sediment and algal variables. Chironomid larvae were ordinated with increasing depth as follows: G. paripes, C. fulvus, C. crassicaudatus, Tanypodinae, and C. decorus. This trend was similar for both lakes individually as well as for the pooled data. As water depth increased, organic matter content and associated metals concentrations in sediment increased. Glyptotendipes paripes displayed significant, negative correlation with water depth and sediment total carbon content, while C. decorus showed a significant positive correlation with these variables; C. crassicaudatus did not show any significant correlation with either of these variables. The algal composition in the pooled data from both lakes was another important factor affecting the larval distributions. The proportion of G. paripes and C. decorus larvae increased with filamentous algal density, and C. crassicaudatus larvae with increasing Cyanobacteria. Although both study lakes were very shallow, the effect of water depth (alone or shared with environmental variables) on chironomid larval community composition was substantially higher than the seasonality (sampling month) effect.     

鲢对藻类摄食效应的室内模拟研究

为研究鲢(Hypophthalmichthys molitrix)对藻类的摄食作用, 采用小环藻(Cyclotella)、小球藻(Chlorella)、微囊藻(Microcystis)和东湖原水开展了小规格鱼种的养殖试验, 对鲢摄食和排泄物进行了研究。结果显示: 在3 种纯培养藻种投喂下鲢存活率从高到低依次是小环藻组 小球藻组 微囊藻组;相应地, 鲢对藻的平均摄食率排序也是小环藻组 小球藻组 微囊藻组。在显微镜下观察粪便发现大部分小环藻为空壳, 一部分小球藻外部形态结构不完整, 外部形态完整的小球藻则色泽暗淡、内部结构紊乱, 微囊藻没有明显变化;3 种藻类细胞的受损率分别为20.04%、7.13%和1.97%。叶绿素荧光活性显示, 粪便中小环藻基本失去光合活性, 小球藻活性极显著降低(P0.01), 微囊藻活性明显降低(P0.05), 东湖原水处理组光合活性较对照极显著降低(P0.01)。对东湖水饲喂试验组排泄物的检测发现, 浮鞘丝藻Planktolyngya、鱼腥藻Anabeana(有破损)、假鱼腥藻Pseudoanabaena 和颤藻Oscillatoria 细胞受损严重;空星藻Coelastrum 和盘星藻Pediastrum 细胞部分破损;针杆藻Synedra、小环藻、桥弯藻Cymbella 和舟形藻Navicula 多为空壳。鱼粪中平裂藻Merismopedia、微囊藻、浮鞘丝藻、鱼腥藻、颤藻、卵囊藻Oocystis、栅藻Scenedesmus 和衣藻Chlamydomonas 在重新培养后恢复了生长。本研究显示硅藻尤其是小环藻、针杆藻和舟形藻对鲢摄食最敏感;栅藻、卵囊藻和平裂藻对摄食压力不敏感。研究表明鲢捕食对藻类群落结构有明显的改变效应, 利用鲢的滤食进行藻类群落调节和水华防控具有可行性。       

四种浮游生物的碎屑形成过程

本文就不同学者的观点,讨论了有机碎屑的具体定义问题。从有机碎屑产生的具体途径来看,细菌侵入已死亡的有机体这一时刻,就是碎屑形成的开始。根据Golterman的藻类矿化概念,以细菌侵入藻细胞这一时相作为有机碎屑的开始期;作者将隆线溞,水华束丝藻、螺旋鱼腥藻和铜绿微囊藻的碎屑开始期分别定为:心跳停止和细菌入侵(枝角类)、藻丝体断裂期(水华束丝藻及螺旋鱼腥藻)、灰蓝色细胞质显现期(铜绿微囊藻)。碎屑开始期及其后的各种形态均属碎屑范畴。       

Bioecology of Stenoma catenifer (Lepidoptera: Elachistidae) and associated larval parasitoids reared from Hass avocados in Guatemala

A 10-wk study of the avocado seed-feeding moth Stenoma catenifer Walsingham (Lepidoptera: Elachistidae), was conducted in a commercial 'Hass' avocado (Persea americana Miller [Lauraceae]) orchard in Guatemala. Up to 45% of fruit in the orchard were damaged by larval S. catenifer. Larval-to-adult survivorship for 1,881 S. catenifer larvae in Hass fruit was 37%, and adult sex ratio was 51% female. Four species of larval parasitoid were reared from field-collected S. catenifer larvae. The most common parasitoid reared was a gregarious Apanteles sp., which parasitized 53% of larvae and produced on average eight to nine cocoons per host. Apanteles sp. sex ratio was 47% female and 87% of parasitoids emerged successfully from cocoons. Apanteles sp. longevity was approximately equal to 1.5 d in the absence of food, and when provisioned with honey, parasitoids survived for 5-7 d. The mean number of cocoons produced by Apanteles sp. per host, and larval parasitism rates were not significantly affected by the number of S. catenifer larvae inhabiting seeds. Oviposition studies conducted with S. catenifer in the laboratory indicated that this moth lays significantly more eggs on the branch to which the fruit pedicel is attached than on avocado fruit. When given a choice between Hass and non-Hass avocados, S. catenifer lays up to 2.69 times more eggs on Hass.     

栅藻对水环境中镍的累积效应与机理分析

对不同Scenedesmus品种的藻细胞从含镍水溶液 (10mg/L)中累积金属镍的能力进行了分析 ,结果表明 :藻细胞对镍的生物累积量表现出明显的品种差异性。ScenedesmusquadricaudaFACHB 4 4和ScenedesmusquadricaudaFACHB 5 0 6表现出很强的累积能力 (累积量达到 5～ 6mgNi /g干重 ) ,而Scenedesmussp .FACHB 4 16和Scenedesmussp .FACHB 4 89在相同条件对金属镍累积量要少得多 (1～ 1.5mgNi /g干重 )。这种差异可能与不同品种藻细胞间的形态结构和生理特性是相关的。对S .quadricaudaFACHB 4 4重金属抗性和累积能力进一步的分析表明 ,S .quadricaudaFACHB 4 4用于含镍重金属废水处理是非常有效的 ,在高浓度 (10 0mg/L)的镍溶液中 ,藻细胞的最大累积量能达到 (2 6 .7mgNi/g干重 )。对该藻细胞镍累积动力学分析发现 :藻细胞对镍的生物累积包括一个快速的被动吸附过程 (5min ,结合 70 %的镍 )和一个缓慢的耗能累积过程 (2～ 3h时间内的累积量占总量的 2 0 %～ 30 % )。与其他藻类相比 ,S .quadricaudaFACHB 4 4对水溶液中镍的耗能累积量明显高于其他藻类。透射电子显微镜(TEM)和X射线能谱 (EDX)分析结果均表明 ,藻细胞耗能累积的镍主要集中在原生质体中 ,尤以淀粉粒和染色质中为多。     

Feeding electivity of two epiphytic chironomids in a subtropical lake

Summary Feeding electivity of two epiphytic orthoclad chironomid species, Psectrocladius sp. and Thienemanniella cf. fusca, was investigated using gut content analysis of larvae collected from Typha stems in Lake Padgett, Florida. Electivity values, computed using Strauss's Food Selection Index, were strongly positive for Cosmarium and negative for Oedogonium and Bulbochaete. Diatoms either were avoided or grazed in proportion to their abundance in the environment. Patterns of electivity were similar for both chrionomid species during all seasons studied. Pairwise food preference experiments were conducted in the laboratory using the algal species, Cosmarium impressulum, Navicula pelliculosa, Selenastrum capricornuatum, Oedogonium cardiacum, and Synedra sp. Preferences were hierarchical and consistent for both larval genera. Preference ranking for the algae offered were CosmariumSynedra>Navicula>Oedogonium>Selenastrum. Larvae seemed to be feeding electively based upon algal genus, size, position in the epiphytic community, and possibly extracellular chemistry.     

The effect of the quality of food patches on larval vertical distribution of the sea urchins Lytechinus variegatus (Lamarck) and Strongylocentrotus droebachiensis (Mueller)

Although most invertebrate larvae are weak swimmers and act as passive particles on horizontal scales, they may be able to regulate their vertical position in response to different factors, including increased food concentration. We examined the effect of the quality of food patches on larval vertical distribution for the sea urchins Lytechinus variegatus and Strongylocentrotus droebachiensis, and determined the effect of dietary conditioning on that response in the laboratory. We reared larvae on a mixed algal diet of Dunaliella tertiolecta and Isochrysis galbana under low (500 cells ml⁻¹) and high (5000 cells ml⁻¹) rations. Food patches were maintained in Plexiglas rectangular columns (30×10×10 cm) using a density gradient, where practical salinity in the bottom layer was 33, in the middle layer 30, and in the top layer 27. We examined the magnitude and mechanism of a behavioural response of larvae of L. variegatus in the four-arm stage, and on two developmental stages of S. droebachiensis (four- and six-arm), by manipulating patch quality. In the absence of a patch, larvae of both species and developmental stages swam through to the surface of the experimental columns. In the presence of algae, fewer larvae were present above the patch and more were at the patch than in control columns. More larvae swam through patches of “unflavoured” algal mimics than algal patches, and aggregated at the surface. Larval distribution relative to patches of algal filtrate without algal cells or of “flavoured” algal mimics in algal filtrate was not consistently different from that in either control or algal patches; thus, the magnitude of larval response to filtrate (with or without particles) was intermediate between that to control and algal patches. For L. variegatus, more larvae crossed the patches when reared on low than high rations, indicating that poorly conditioned larvae may be less responsive to environmental cues. Our results suggest that larvae can actively aggregate and maintain a vertical position in response to a food patch that depends on the quality and quantity of food. The response appears to be based mostly on a chemosensory rather than a mechanosensory mechanism.     

滇池中溶藻细菌的分离鉴定及其溶藻效应

【背景】藻类水华或赤潮在世界范围内频发,带来各种危害,亟需找到有效途径控制水华或赤潮。溶藻细菌具有杀死藻类控制藻类生物量的能力,可以作为防治水华和赤潮的有效工具。【目的】分离并鉴定滇池中的铜绿微囊藻(Microcystisaeruginosa)及其溶藻细菌,对溶藻菌作用于铜绿微囊藻的溶藻效应进行研究,初步了解其溶藻特性与溶藻机制。【方法】采用LB平板稀释涂布,再经多次划线分离纯化细菌,测定16SrRNA基因序列以鉴定细菌种类;采用毛细管分离的方法分离铜绿微囊藻,并测定其cpcBA基因序列以鉴定蓝藻种类;采用热乙醇法提取叶绿素a,从而计算溶藻效率;基于过氧化氢酶(CAT)、还原型谷胱甘肽(GSH)和丙二醛(MDA)探究藻细胞在溶藻菌处理下的抗氧化系统响应。【结果】共分离获得11株微囊藻和17株针对铜绿微囊藻的高效溶藻菌。选取其中一株生长速度最快的铜绿微囊藻DCM4和一株溶藻效果最好的溶藻菌Sp37 (Bacillus siamensis)进行后续研究。Sp37对DCM4的4 d溶藻率达到92.4%±1.5%,且对微囊藻属的水华微囊藻(M. flos-aquae)和惠氏微囊藻(M.wesenbergii)均有溶藻效果,而对绿藻没有溶藻效果。Sp37的原菌液和无菌滤液对DCM4的4d溶藻率分别为86.8%±4.3%和81.1%±2.2%,两者没有显著差异(P0.05)。Sp37菌体对DCM4的溶藻率为25.4%±7.3%。Sp37无菌滤液经不同温度和pH处理之后的溶藻率与未经处理的无菌滤液的溶藻率无明显差异。Sp37无菌滤液处理藻细胞会使藻细胞的CAT、GSH和MDA含量发生变化。【结论】菌株Sp37对铜绿微囊藻DCM4具有高效的溶藻作用,而且对微囊藻属具有一定的溶藻特异性。Sp37是通过分泌胞外物质间接溶藻,且溶藻物质具有热稳定性和酸碱稳定性。Sp37无菌滤液处理藻细胞会触发藻细胞抗氧化系统,并且会损伤藻细胞膜。Sp37无菌滤液很可能是通过对藻细胞造成氧化胁迫,最终导致藻细胞死亡的。     

绿藻栅藻对微囊藻的抑制效应及评价

为筛选具有控制微囊藻水华潜力的绿藻, 研究基于藻类之间的化感作用, 对34株绿藻开展筛选及评价工作。结果发现, 栅藻FACHB-1229的抑制率最高, 其滤液对微囊藻FACHB-3550和FACHB-905的抑制率分别为53.95%和48.39%; 通过对滤液中的物质进行GC-MS检测, 推测该藻株的效应物质可能为邻苯二甲酸二(2-甲氧基乙基)酯。进一步对FACHB-1229生长和光合放氧、氨氮耐受等指标进行评价, 结果发现: 该藻株在孔板中的生长速率(0.38±0.06)/d高于微囊藻生长速率(0.13±0.03)/d; 栅藻FACHB-1229的光合放氧速率高于同期测定的其他绿藻光合放氧速率, 可达(229.91±10.49) μmol O₂/(mg Chl.a·h); 同时该藻株对氨氮的耐受能力最强, 在氨氮浓度为1888.60 mg/L时其生长速率可达(0.30±0.08)/d。此外, 在与微囊藻FACHB-3550进行共培养时, 栅藻FACHB-1229所占比例持续升高。综上, 栅藻FACHB-1229具备与微囊藻竞争的优势, 有望成为微囊藻水华生物控制的优选材料。     

Effects of food concentration and availability on the incidence of cloning in planktotrophic larvae of the sea star Pisaster ochraceus

A decade ago, cloning was first observed in the planktotrophic larvae of sea stars obtained from plankton tows. However, no controlled experimental studies have investigated what factors may regulate this remarkable phenomenon. In the present study we offer the first documentation of cloning in the planktotrophic larvae of Pisaster ochraceus from the northern Pacific coast. This species was used as a model system to investigate three factors that may influence the incidence of asexual reproduction (cloning) in planktotrophic sea star larvae. In an initial experiment, larvae were reared under nine combinations of three temperatures and three food (phytoplankton) concentrations. Larvae reared at 12-15 degrees C and fed the highest food concentrations grew larger than the other larvae and produced significantly more clones. In a second experiment, qualitatively different algal diets were fed to larvae reared under the conditions found to be optimal in the initial experiment. Up to 24% of the larvae consuming a mixed phytoplankton diet of Isochrysis galbana, Chaetocerous calcitrans, and Dunaliella tertiolecta cloned, and significantly more clones were produced by these larvae than by those fed monospecific diets. Our experiments indicate that cloning generally occurs after larvae have attained asymptotic body length and only when food is abundant and of high quality. Since larval mortality is considered to be extremely high for marine invertebrates with planktotrophic larvae, production of clones under optimal conditions of temperature and food may serve to increase larval populations when the environment is most conducive to larval growth.     

活体微藻吸附水体中Cd2+的性能特征

【目的】藻类对重金属吸附和吸收是重金属进入食物链的重要渠道之一。研究活体微藻对水体中Cd~(2+)的吸附性能和吸附机理,旨在为Cd~(2+)等重金属离子进入水体后的去向及去除提供理论依据。【方法】选取地表水普遍存在的4种微藻:钝顶螺旋藻(Spirulina platensis)、铜绿微囊藻(Microcystis aeruginosa)、四尾栅藻(Scenedesmus quadricauda)和小球衣藻(Chlamydomonas microsphaera)作为试验材料,通过室内模拟实验,利用Langmuir、Freundlich和Dubinin-Radushkevich(D-R)3种等温吸附模型,研究4种活体微藻对Cd~(2+)的吸附规律及吸附参数。【结果】4种微藻对水体Cd~(2+)吸附均可以用Langmuir、Freundlich和D-R模型描述,其中用Langmuir模型拟合钝顶螺旋藻、Freundlich模型拟合小球衣藻、D-R模型拟合铜绿微囊藻和四尾栅藻的吸附效果最佳。四尾栅藻对Cd~(2+)的吸附量最高,而钝顶螺旋藻对Cd~(2+)的吸附量最低,但与Cd~(2+)的亲和力最强,4种微藻吸附Cd~(2+)主要是以离子代换为主的化学吸附。【结论】微藻对Cd~(2+)均有较强的吸附能力,会引起以微藻为食的水生动物Cd~(2+)富集;微藻也是去除水体Cd~(2+)的潜在吸附剂原料。     

Temporal variation in plankton assemblages and physicochemistry of Devils Lake, North Dakota

Seasonal and annual variation in biomass and structure of algal assemblages of hyposaline Devils Lake were examined in relation to turbidity, ambient concentrations of major ions, trace elements and nutrients, and the standing crop of herbivores. Lake level declined during the early years of study, but rose markedly in subsequent years as historically large volumes of water flowed into this hydrologically-closed basin. Winter algal assemblages were dominated (in biomass) most years by small, non-motile chlorophytes ( Choricystis minor, Kirchneriella lunaris or Dunaliella sp.), or Euglena sp. in the most saline sub-basin. Spring assemblages were dominated by diatoms (Stephanodiscus cf. minutulus, Surirella peisonis, Cyclotella meneghiniana and Entomoneis paludosa were especially prominent) or chlorophytes ( C. minor) until the lake level rose. C. minor abundances then declined in spring assemblages and diatoms ( Stephanodiscus cf. agassizensis and S. niagarae; E. paludosa in the more saline sub-basins) dominated. The potential for nitrogen-deficient conditions for phytoplankton growth was evidenced most summers and early autumns by consistently high concentrations of reactive-P relative to inorganic-N and blooms of the N-fixing cyanophyte Aphanizomenon flos-aquae; Microcystis aeruginosa typically was a co-dominant (>30% of biomass) in these assemblages. Pulses of diatoms ( S. cf. agassizensis and C. meneghiniana) occurred in summers following unusually prolonged periods of calm weather or large water inflows. Physical (irradiance, turbulence) and chemical (major nutrients) variables were the primary factors associated with phytoplankton growth. Transparency and major nutrient concentrations accounted for more of the annual variation in phytoplankton structure than did salinity. Seasonal abundance patterns of the dominant zooplankton (the copepod Diaptomus sicilis; the cladocerans Ceriodaphnia quadrangula, Chydorus sphaericus, Daphnia pulex and Diaphanosoma birgei; and the rotifers Brachionus spp., Filinia longiseta, Keratella cochlearis and K. quadrata) also indicated variation in algal populations related to grazing. This revised version was published online in July 2006 with corrections to the Cover Date.     

Occurrence of isopropylthio compounds in the aquatic ecosystem (Lake Neusiedl, Austria) as a chemical marker for Microcystis flos-aquae

Abstract Volatile organic sulfur compounds occuring during a bloom of different species of Microcystis in Lake Neusiedl, Austria, were analyzed by gas chromatography and mass spectrometry. In open water diisopropyl disulfide and diisopropyl tri-sulfide were the only sulphur compounds to be found. It was shown that Microcystis flos-aquae was the causative agent for the generation of these sulphur compounds, since high concentrations of these substances were found both in the floating scum of cyanobacteria taken from open lake and in axenic cultures of five isolated strains of M. flos-aquae . Strains isolated from colonies of Microcystis aeruginosa were not able to synthesize isopropylthio compounds. Alternatively, methylthio compounds were released. The rather unusual formation of the isopropylthio group can be used as a chemical marker to differentiate between M. flos-aquae and M. aeruginosa as two separate species which hitherto have been regarded as formae. In a canal passing through the reed belt of Lake Neusiedl where Microcystis was missing, these compounds were not detected. Different sulfur compounds (dimethyl disulfide, dimethyl trisulfide, dibutyl sulfide and bis(methylthio) methane) which in part have not yet been reported for freshwater ecosystems occurred at this site. Their origin, however, remains obscure.     

Herbivory in the tilapia Oreochromis niloticus: a comparison of feeding rates on phytoplankton and periphyton

A quantitative comparison of the grazing behaviour of young Oreochromis niloticus feeding on the planktonic cyanobacterium Microcystis aeruginosa and a periphytic community dominated by the cyanobacterium Oscillatoria sp., determined that biomass ingestion rates of fish filter-feeding on planktonic cyanobacteria were significantly lower than those surface-grazing on periphyton. Comparisons of published laboratory data on filter-feeding with field data on algal ingestion rates suggest that filter-feeding may be a relatively unimportant method of ingesting algae.     

The effect of a predatory leech,Nephelopsis obscura,on mortality,growth, and production of chironomid larvae in a small pond

Summary The effect of a predatory leech, Nephelopsis obscura, on survivorship, growth, and production of chronomid larvae was studied by enclosure experiments carried out in a small pond. The prey population was composed almost entirely of the tubiculous, microphagous chironomid larvae, Chironomus riparius and Glyptotendipes paripes. Nephelopsis significantly reduced chironomid survivorship within the enclosures, and accounted for most of the measured mortality of fourth instar larvae. The cropping by Nephelopsis was not significantly biased toward either prey species. In long-term experiments (66 d) chironomid biomass in enclosures without leeches reached much higher levels than in enclosures containing Nephelopsis. This increase in biomass was due to growth of surviving larvae, rather than recruitment, since emergence and oviposition were not going on during the course of the experiments. The enhanced survivorship of larvae within leech-free enclosures was eventually accompanied by reduced growth and specific production (daily production/biomass) for C. riparius, which made up about 90% of the larval population. Growth and specific production of G. paripes (10% of larval population) was not affected. Short-term experiments (25 d) involving manipulation of densities and species ratio (9:1 CR:GP and 1:9 CR:GP) of larvae revealed that growth of the majority species was strongly influenced by larval density, whereas growth of the minority species was not. The same pattern was observed both in the presence and in the absence of Nephelopsis and was a result of differences in resource utilization between the two species. In the shortterm experiments, growth rates estimated for larvae exposed to leeches were significantly less than those for larvae in leech-free enclosures. This could be due either to size-biased consumption of larvae by Nephelopsis, or possibly a disturbance factor leading to reduced larval food intake and/or increased metabolic costs.     

溶藻细菌筛选及溶藻活性物质对铜绿微囊藻生理活性的影响

从太湖水华水体中分离纯化细菌, 再将细菌的LB液体和固体斜面纯培养物分别收集后感染铜绿微囊藻(Microcystis aeruginosa)细胞, 从中筛选出7株具有溶藻活性的细菌, 并对其中一株溶藻细菌THW7的溶藻方式及溶藻活性物质对铜绿微囊藻生理活性的影响进行了初步研究。结果表明: 仅采用细菌的LB液体纯培养物进行溶藻细菌筛选会存在误筛或高估溶藻效率的风险, 而采用细菌的固体斜面纯培养物进行筛选则可避免以上风险; 溶藻细菌THW7通过分泌胞外活性物质的方式间接溶藻; 在THW7无菌滤液胁迫下, 铜绿微囊藻的生长受到显著抑制(P<0.01), 10d溶藻效率可达94.38%, 光合系统活性也显著降低(P<0.01), MDA含量积累, SOD、POD、CAT活性整体呈现先升高后降低的趋势且显著高于对照组(P<0.01)。推测菌株THW7分泌的溶藻活性物质可能作用于铜绿微囊藻细胞的光合系统Ⅱ, 阻碍电子传递, 抑制其光合作用过程, 并对藻细胞产生氧化损伤, 破坏藻细胞细胞膜的完整性, 从而实现溶藻作用。