全细胞多重PCR检测蓝藻、微囊藻及产毒微囊藻方法初探

选取三对分别针对微囊藻、蓝藻16S rDNA及微囊藻毒素合成酶基因mcyB的保守序列的特异性引物209F/409R、27F1/409R、MTR/MTF,其中409R为一条共用引物。设计并优化了一种可以同时检测蓝藻和微囊藻的两重全细胞PCR方法和一种可以同时检测蓝藻、微囊藻和可产毒微囊藻的三重全细胞PCR方法,并且测试了这两种PCR反应的灵敏度区间,分别为10⁵～10³cell·mL^-1、10⁵～10²cell·mL^-1。对采集水库水样检测结果表明双重全细胞PCR方法可以直接应用于对天然水样的检测,三重全细胞PCR方法可用于实验室培养藻细胞的筛查。全细胞多重PCR方法具有快速、简便、准确等特点,在水体微囊藻毒素检测预警方面具有应用价值。     

鹤地水库浮游生物与富营养化特征分析*

于2000年丰水期和枯水期调查分析了鹤地水库的营养状态及浮游生物特征。结果表明:鹤地水库营养盐含量很高,综合营养状态指数评价为中一富营养化水平。浮游植物丰水期和枯水期的细胞密度分别为1950.5～3509.7×10⁴cells·L^-1和130.5～231.3×10⁴cells·L^-1,蓝藻中的微囊藻和席藻数量占细胞总数的83%以上。在丰水期和枯水期,浮游植物的群落结构均为蓝藻-绿藻-硅藻型,优势种为微囊藻和席藻。次优势种由丰水期蓝藻中的粘球藻,颤藻,绿藻中的衣藻,和硅藻中的颗粒直链藻等转变为枯水期的蓝藻门的水华束丝藻和硅藻门的颗粒直链藻等富营养化指示种。鹤地水库的浮游动物种类不多,但数量很高。丰水期的无节幼体和桡足幼体数量很多,但从优势种类来说,轮虫以曲腿龟甲轮虫,纵长异尾轮虫,剪形臂尾轮虫为主,枝角类的优势种为长额象鼻蚤;枯水期时无节幼体的数量最多,桡足幼体数量急剧下降,优势种类则转变为枝角类的长额象鼻蚤和桡足类的广布中剑水蚤。两个水期浮游动物的优势种类均是以耐污种和广布性种类为主。     

浮游动物诱发藻类群体的形成

从研究蓝藻水华形成机理的需要出发,综述了浮游动物的牧食压力对藻类群体形成的诱发作用。指出诱发藻类群体形成的化合物来自牧食性浮游动物对藻类的有效牧食,是藻类群体形成的重要原因之一,而这些诱发性的化合物并不是有关生物体的组成成分,是种间相互作用的结果。藻类群体的形成方式有源于一个母细胞的分裂和业已存在的单细胞的聚合两种方式,栅藻的诱发性群体可能是来自一个母细胞的分裂,而在其它藻类的诱发性群体形成如铜绿微囊藻则可能是业已存在的单细胞的聚合。由于藻类形成群体后能显著降低浮游动物对其牧食速率,因此,这种诱发性群体形成的现象,可以解释为藻类对变化的牧食压力的一种有效的反牧食防御策略,也是两者协同进化的结果。浮游动物对藻类群体形成的重要作用,在研究模拟蓝藻群体及水华形成值得借鉴应用。作者还提出推测,水华蓝藻的群体形成,可能就是在富营养化条件下藻类快速生长,加上浮游动物的牧食压力共同作用下联合驱动的结果,而这种群体形成很可能在积累到一定程度后,结合特定的气象水文等理化因子,就会聚集于水表“爆发”出肉眼可见的水华。因此,开展浮游动物牧食作用对水华蓝藻早期群体形成诱发效应的研究不仅能加深对水华形成的全面认识,而且对于进一步认识藻类的诱发性反牧食防御适应机制、揭示生态系统中生物之间的复杂关系也具有重要的理论意义。     

微囊藻和栅列藻的垂直迁移及生态学意义

本研究在自制沉降柱中,检测铜绿微囊藻(Microcystis aeroginosa)和斜生栅列藻(Scenedesmus obliquus)不同生长时期的细胞群体在不同光照条件下的垂直迁移。本文首次提出藻密度衰减系数(K)的概念、拟合方法和生态学意义,并根据等细胞密度沉降面的沉降速率来计算细胞沉降速率(Vc),以这两个参数来衡量细胞的沉降特性,对细胞垂直迁移研究的方法进行了的探索。结果表明,两种藻细胞群体在三个生长时期和四种光照条件的沉降特性表现已定的差异。栅列藻细胞密度的衰减系数(K)最小值为-0.0021cm^-1(上浮),最大值为0.0065cm^-1(下沉);微囊藻的K最小值为-0.0029cm^-1(上浮),最大值为0.0036cm^-1(下沉)。两种藻沉降曲线的指数拟合的R²大多在0.6以上,说明K值是一个较好的衡量细胞群体沉降特性的参数,细胞密度与深度的关系较好地服从指数规律。细胞沉降速度V的最大值(4.681cm·h^-1,下沉)出现在栅列藻的指数期,最大上浮速率-1.790cm·h^-1,出现在微囊藻的稳定期。本文得到的活体藻细胞群体的垂直迁移特性差异的实验数据,说明该实验方法的适用性和两种藻沉降特性差异的可检测性。本文讨论了水华优势种形成与藻细胞群体迁移特性之间的关系。     

Climate change and the phytoplankton spring bloom: warming and overwintering zooplankton have similar effects on phytoplankton

Indoor mesocosms were used to study the combined effect of warming and of different densities of overwintering mesozooplankton (mainly copepods) on the spring development of phytoplankton in shallow, coastal waters. Similar to previous studies, warming accelerated the spring phytoplankton peak by ca. 1 day °C^?1 whereas zooplankton did not significantly influence timing. Phytoplankton biomass during the experimental period decreased with warming and with higher densities of overwintering zooplankton. Similarly, average cell size and average effective particle size (here: colony size) decreased both with zooplankton density and warming. A decrease in phytoplankton particle size is generally considered at typical footprint of copepod grazing. We conclude that warming induced changes in the magnitude and structure of the phytoplankton spring bloom cannot be understood without considering grazing by overwintering zooplankton.     

浙江水源地河流浮游动物多样性与环境因子的通径分析

为探明水源地河流浮游动物多样性及与水环境因子的关系, 利用浮游动物多样性参数监测水质, 2010-2014年间, 我们于每年的冬季(1月)、春季(4月)、夏季(7月)和秋季(10月), 对浙江2个水源地河流采样站(H1站和H2站)展开浮游动物种类组成、丰度和多样性指数的季节性调查, 同时测定水环境因子。结果表明, H1站和H2站浮游动物平均丰度分别为1,387.4 ind./L和873.0 ind./L, 小型浮游动物(轮虫 + 桡足类无节幼体)丰度分别占92.8% (H1站)和91.5% (H2站)。两采样站轮虫、枝角类和桡足类的优势种均为针簇多肢轮虫(Polyarthra trigla)、短尾秀体溞(Diaphanosoma brachyurum)和温剑水蚤(Thermocyclops sp.)。多元逐步回归与通径分析结果表明: 冬季氮磷比是轮虫类Shannon-Wiener多样性指数(H′)波动的限制因子, 主要通过总磷含量对轮虫类H′指数产生较大的间接正向作用; 春季氮磷比是轮虫类H′指数发展的决策因子; 秋季氮磷比可通过总氮含量对轮虫类H′指数产生较大的间接正向作用。冬季氨氮、总氮含量分别是甲壳动物体积多样性指数(Hs)的决策因子和限制因子。夏季溶解氧含量是总浮游动物物种丰富度(d)波动的限制因子, 主要通过pH值对d指数产生较大的间接正向作用, 作用机制表现为轮虫类H′指数随着夏季溶解氧含量的升高呈极显著上升(P < 0.01), 而甲壳动物Hs指数则显著下降(P < 0.05)。水源地河流环境因子与浮游动物多样性之间的相互关系为浙江水源地生态学监测提供了可能性。     

大沙河水库冬季浮游植物群落结构与水华分析

于2009年12月、2010年1月和2月对广东省大沙河水库湖泊区距水表层0.5m、5m和10m三个水层的浮游植物进行了定性与定量分析,同时对环境变量进行了测定.采样期间三个月的总降雨量为263mm,水温范围在15.5～19.4℃之间,水体处于混合状态.三次采样中,共检测出浮游植物69种(属),隶属于6个门,浮游植物丰度范围在4.1×10⁶～14.8×10⁶cells·L^-1之间.三个水层的浮游植物优势种类差异不显著(p>0.05),丰度的主要优势种为蓝藻门的卷曲鱼腥藻(Anabaena circinalis)、铜绿微囊藻(Microcystis aeruginosa),这两个种的丰度之和占总丰度的70%以上,在2009年12月和2010年2月的表层出现了轻度鱼腥藻和微囊藻水华.蓝藻自身的浮力调节机制和适应低磷的生活策略是其成为优势种的重要原因,相对稳定的外部条件、水体混合与富营养共同导致的光的可获得性的减少是形成蓝藻水华的关键外部因子.     

宁波港典型海域浮游动物种类组成及数量分布特点

根据2009年秋～2010年夏每季采样调查,分析和研究了浙江省宁波港海区浮游动物种类组成和数量分布的四季变化特征。结果表明: 经鉴定浮游动物共有70种,隶属3门35属。其中桡足类的种类最多,占总种数的73.54%; 优势种主要有中华异水蚤、矩形龟甲轮虫、伪长腹剑水蚤、挪威小星猛水蚤、小星猛水蚤属、驼背隆哲水蚤、短角长腹剑水蚤等。浮游动物群体丰度呈现出夏季>秋季>春季>冬季的现象,四季平均丰度分别为2.50×10³ ind/m³、40.16×10³ ind/m³、3.72×10³ ind/m³、1.20×10³ ind /m³。生物量呈现出夏季>春季>秋季>冬季的现象,四季平均生物量分别为88.94 mg/m³、931.22 mg/m³、58.74 mg/m³、24.49 mg/m³。与历史资料以及邻近海域比较发现,浮游动物丰度和生物量小于或接近于东海各海域。生物多样性分析显示,夏季与春秋冬三季生物多样性(H')有显著性差异(P<0.05),夏季具有较高的生物多样性,Shannon-Wiener多样性指数(H')、种类丰富度(D)、Pielou均匀度指数(J)、最大多样性指数(H'max)基本呈现出夏季>春季>秋季>冬季。与邻近海域相比,多样性指数(H')、种类丰富度(D)、最大多样性指数(H'max)呈下降趋势。     

Biotic interactions may overrule direct climate effects on spring phytoplankton dynamics

To improve our mechanistic understanding and predictive capacities with respect to climate change effects on the spring phytoplankton bloom in temperate marine systems, we used a process‐driven dynamical model to disentangle the impact of potentially relevant factors which are often correlated in the field. The model was based on comprehensive indoor mesocosm experiments run at four temperature and three light regimes. It was driven by time‐series of water temperature and irradiance, considered edible and less edible phytoplankton separately, and accounted for density‐dependent grazing losses. It successfully reproduced the observed dynamics of well edible phytoplankton in the different temperature and light treatments. Four major factors influenced spring phytoplankton dynamics: temperature, light (cloudiness), grazing, and the success of overwintering phyto‐ and zooplankton providing the starting biomasses for spring growth. Our study predicts that increasing cloudiness as anticipated for warmer winters for the Baltic Sea region will retard phytoplankton net growth and reduce peak heights. Light had a strong direct effect in contrast to temperature. However, edible phytoplankton was indirectly strongly temperature‐sensitive via grazing which was already important in early spring at moderately high algal biomasses and counter‐intuitively provoked lower and later algal peaks at higher temperatures. Initial phyto‐ and zooplankton composition and biomass also had a strong effect on spring algal dynamics indicating a memory effect via the broadly under‐sampled overwintering plankton community. Unexpectedly, increased initial phytoplankton biomass did not necessarily lead to earlier or higher spring blooms since the effect was counteracted by subsequently enhanced grazing. Increasing temperature will likely exhibit complex indirect effects via changes in overwintering phytoplankton and grazer biomasses and current grazing pressure. Additionally, effects on the phytoplankton composition due to the species‐specific susceptibility to grazing are expected. Hence, we need to consider not only direct but also indirect effects, e.g. biotic interactions, when addressing climate change impacts.     

Impact of fish predation on cladoceran body weight distribution and zooplankton grazing in lakes during winter

1. It is well accepted that fish, if abundant, can have a major impact on the zooplankton community structure during summer, which, particularly in eutrophic lakes, may cascade to phytoplankton and ultimately influence water clarity. Fish predation affects mean size of cladocerans and the zooplankton grazing pressure on phytoplankton. Little is, however, known about the role of fish during winter. 2. We analysed data from 34 lakes studied for 8–9 years divided into three seasons: summer, autumn/spring and winter, and four lake classes: all lakes, shallow lakes without submerged plants, shallow lakes with submerged plants and deep lakes. We recorded how body weight of Daphnia and then cladocerans varied among the three seasons. For all lake types there was a significant positive correlation in the mean body weight of Daphnia and all cladocerans between the different seasons, and only in lakes with macrophytes did the slope differ significantly from one (winter versus summer for Daphnia). 3. These results suggest that the fish predation pressure during autumn/spring and winter is as high as during summer, and maybe even higher during winter in macrophyte‐rich lakes. It could be argued that the winter zooplankton community structure resembles that of the summer community because of low specimen turnover during winter mediated by low fecundity, which, in turn, reflects food shortage, low temperatures and low winter hatching from resting eggs. However, we found frequent major changes in mean body weight of Daphnia and cladocerans in three fish‐biomanipulated lakes during the winter season. 4. The seasonal pattern of zooplankton : phytoplankton biomass ratio showed no correlation between summer and winter for shallow lakes with abundant vegetation or for deep lakes. For the shallow lakes, the ratio was substantially higher during summer than in winter and autumn/spring, suggesting a higher zooplankton grazing potential during summer, while the ratio was often higher in winter in deep lakes. Direct and indirect effects of macrophytes, and internal P loading and mixing, all varying over the season, might weaken the fish signal on this ratio. 5. Overall, our data indicate that release of fish predation may have strong cascading effects on zooplankton grazing on phytoplankton and water clarity in temperate, coastal situated eutrophic lakes, not only during summer but also during winter.     

Influence of overwinteringDaphnia on spring zooplankton communities: An experimental study

To evaluate the influence of overwintering individuals of zooplankton on spring zooplankton communities, the dynamics of zooplankton communities with or without overwintering individuals were observed in experimental ponds from fall to spring. An insecticide, carbaryl, was used to regulate the overwintering individuals. In ponds which received insecticide applications in November or January, all cladoceran and rotiferan species were eliminated by the treatments and did not reappear until late March or early April, even when the chemical disappeared rapidly. The low water temperature may delayed the establishment of the populations from resting eggs. In these ponds, populations of various cladoceran and rotiferan species, which seemed to be originated from resting eggs, were built up in the spring. In control ponds,Daphnia ambigua orD. longispina overwintered as juveniles and adults and established a large spring population earlier than other cladocerans and rotifers overwintering as resting eggs. The latter zooplankters did not increase in the spring probably because their growth was suppressed by the precedingDaphnia species through competition. In nature, even if the number of overwintering individuals is small, they may have a potential to build up a large population earlier than the individuals hatching from resting eggs. As a result, the species which have overwintered as individuals seem to predominate in the spring and have a large influence on the spring zooplankton community.     

Winter ecology of shallow lakes: strongest effect of fish on water clarity at high nutrient levels

While the structuring role of fish in lakes is well studied for the summer season in North temperate lakes, little is known about their role in winter when fish activity and light irradiance potentially are lower. This is unfortunate as the progressing climate change may have strong effects on lake winter temperature and possibly on trophic dynamics too. We conducted an enclosure experiment with and without the presence of fish throughout winter in two shallow lakes with contrasting phosphorus concentrations. In hypertrophic Lake Søbygård, absence of fish led to higher biomass of zooplankton, higher grazing potential (zooplankton:phytoplankton ratio) and, accordingly, lower biomass of phytoplankton and chlorophyll a (Chl a), while the concentrations of total nitrogen (TN), total phosphorus (TP), oxygen and pH decreased. The average size of egg-bearing Daphnia and Bosmina and the minimum size of egg-bearing specimens of the two genera rose. In the less eutrophic Lake Stigsholm, zooplankton and their grazing potential were also markedly affected by fish. However, the decrease in Chl a was slight, and phytoplankton biovolume, pH and the oxygen concentration were not affected. TN was higher when fish were absent. Our results indicate that: (i) there is a notable effect of fish on zooplankton community structure and size during winter in both eutrophic and hypertrophic North temperate lakes, (ii) Chl a can be high in winter in such lakes, despite low light irradiance, if fish are abundant, and (iii) the cascading effects on phytoplankton and nutrients in winter may be more pronounced in hypertrophic lakes. Climate warming supposedly leading to reduced winter mortality and dominance of small fish may enhance the risk of turbid state conditions in nutrient-enriched shallow lakes, not only during the summer season, but also during winter.     

Sequence of the E. coli O104 antigen gene cluster and identification of O104 specific genes

The Escherichia coli O104 polysaccharide is an important antigen, which contains sialic acid and is often associated with EHEC clones. Sialic acid is a component of many animal tissues, and its presence in bacterial polysaccharides may contribute to bacterial pathogenicity. We sequenced the genes responsible for O104 antigen synthesis and have found genes which from their sequences are identified as an O antigen polymerase gene, an O antigen flippase gene, three CMP-sialic acid synthesis genes, and three potential glycosyl transferase genes. The E. coli K9 group IB capsular antigen has the same structure as the O104 O antigen, and we find using gene by gene PCR that the K9 gene cluster is essentially the same as that for O104. It appears that the distinction between presence as group IB capsule or O antigen for this structure does not involve any difference in genes present in the O antigen gene cluster. By PCR testing against representative strains for the 166 E. coli O antigens and some randomly selected Gram-negative bacteria, we identified three O antigen genes which are highly specific to O104/K9. This work provides the basis for a sensitive test for rapid detection of O104 E. coli. This is important both for decisions on patient care as early treatment may reduce the risk of life-threatening complications and for a faster response in control of food borne outbreaks.     

Relative effects of elevated grazing pressure and competition from a red algal turf on two post-settlement stages of Fucusevanescens C. Ag.

In Nova Scotia, Canada, the lower shore of wave-exposed and semi-sheltered portions of the coast is dominated by a dense turf of the red alga Chondrus crispus C. Ag. The mid shore is dominated by three species of rockweed belonging to the genus Fucus, which are also physiologically competent in the low zone, but may be inhibited by pre-emptive competitive exclusion by red algal turf and/or increased grazing pressure from abundant mesoherbivores. A grazer assay showed that herbivore pressure is >50% higher in the Chondrus zone than in the rockweed zone. Fucus can colonize the low shore only through microrecruits which develop from planktonic zygotes. A main objective of this study was to test the hypothesis that early post-settlement stages represent a critical phase for successful recruitment. We, therefore, tested the relative effects of competitive pressure from Chondrus and grazing on small (2 mm) and larger (6 cm) Fucus evanescens plants in a three-way factorial experiment. Red algal turf and grazers independently depressed F. evanescens growth, but only a combination of factors resulted in a significant weight loss in the rockweeds. The effect size of grazing was more than double that of competition from the turf. Small and larger individuals of F. evanescens were equally affected by grazing and competition. The results showed that colonization by rockweeds may only occur where there are gaps in the Chondrus canopy. We hypothesized that grazer effects may decrease with increasing gap size. However, a controlled experiment showed no differences in Fucus recruitment among the range of naturally occurring gap sizes. That is, larger gaps do not promote rockweed recruitment. In concordance with this observation, we found that grazer abundances were similar among gap sizes. Chondrus was shown to be highly resistant to intense physical and herbivore-induced disturbance. This combination ensures the persistence of a dense canopy which largely excludes rockweed recruitment from zygotes. Competitive dominance of Chondrus on the low shore is not obviously related to individual growth rates or canopy height. A positive correlation between growth rate and competitive ability may be expressed only in morphologically similar species which are likely to compete as germlings.     

Characterisation of Pseudomonas aeruginosa isolated from freshwater culture systems

Members of the genus Pseudomonas are important phytopathogens and agents of human infections, while other strains and species exhibit bioremediation and biocontrol activities. Species-specific detection of Pseudomonas species in the environment may help to gain a more complete understanding of the ecological significance of these microorganisms. The objective of present study was comparative analysis of biochemically and PCR based confirmed 10 isolates of Pseudomonas aeruginosa (6 from fish intestine and 4 from pond sediment). PCR-ribotyping and PAGE revealed that there was extensive heterogeneity at the genetic and protein levels. Both genetic and phenotypic heterogeneity were more in the sediment isolates compared to the fish isolates. SDS-PAGE clearly demonstrated the differences between fish and sediment isolates as evident from the higher range of protein profiling. In antibiotic sentivity test no habitat specific antibiogram was obtained. Zinc adversely affected the DNA of all the isolates to be amplified by PCR as DNA banding pattern was different from normal DNA in stressed DNA. Thus stress, particularly, zinc may interfere monitoring of Pseudomonas by PCR.     

Overwintering colonies of German (Vespula germanica) and common wasps (Vespula vulgaris) (Hymenoptera: Vespidae) in New Zealand

Abstract

Nests of both common (Vespula vulgaris) and German wasps (V. germanica) sometimes overwinter in New Zealand. Three overwintering common wasp colonies were found in low-altitude honeydew beech forest; about 2% of the colonies initiated there in 1988 survived the winter. Wasp traffic rates from nests in Nelson city and a nation wide survey of wasp abundance, showed that more German wasp than common wasp workers were on the wing in winter and spring. German wasp colonies in Nelson city were more likely to overwinter than were common wasp colonies. Of the active German wasp colonies recorded in Nelson in January and February 1989, only two (4%) had previously overwintered, but these two nests accounted for 38% of all German wasp workers estimated to leave nests in the area. Had other overwintering colonies not been poisoned, overwintering colonies might have accounted for up to 11 % of nests and produced up to 64% of German wasp workers on the wing in January and February 1989.

Overwintering common wasp colonies did not produce queens or drones in their first year or second spring, but all 10 overwintering German wasp colonies examined produced sexuals at both times. German wasp queens produced in winter and spring may influence the number of colonies successfully initiated and affect the population dynamics of German wasps in New Zealand.     

陕北黄土丘陵沟壑区坡沟立地环境下幼苗的存活特征

幼苗是植被恢复演替的基础, 在生态系统中具有非常重要的作用。为了探索黄土丘陵沟壑区坡沟立地环境下幼苗的存活特征, 在陕西省安塞县宋家沟和纸坊沟流域设置15个固定样地进行定点动态监测, 运用单因素方差分析法和系统聚类分析法对不同立地环境下的幼苗密度和幼苗存活率进行了分析。结果表明: 1)不同坡沟立地环境下, 幼苗存活特征差异明显, 整体表现为阳坡幼苗密度较小而存活率较高, 阴坡幼苗密度较大但存活率较低。2)细裂叶莲蒿(Artemisia gmelinii)、菊叶委陵菜(Potentilla tanacetifolia)、阿尔泰狗娃花(Heteropappus altaicus)等物种具有较高的幼苗存活率, 在生存竞争中幼苗是以“质”取胜; 而猪毛蒿(Artemisia scoparia)、中华苦荬菜(Ixeris chinensis)、阴行草(Siphonostegia chinensis)等物种具有较高的幼苗密度, 在生存竞争中是以“量”取胜。3)同一物种在坡沟立地环境下表现出不同的存活曲线, 不同物种在不同立地环境下也可呈现同一存活曲线; 细裂叶莲蒿、菊叶委陵菜、长芒草(Stipa bungeana)、阿尔泰狗娃花、兴安胡枝子(Lespedeza davurica)等物种, 幼苗不仅在雨季存活能力强且具有较强的越冬能力; 猪毛蒿、香青兰(Dracocephalum moldavica)、臭蒿(Artemisia hedinii)等物种在雨季前幼苗存活能力较强, 但冬季存活能力弱。4)坡面不同微环境下幼苗存活特征也存在差异, 即微环境的改变在一定程度上影响着幼苗的生长、存活和越冬。因此, 在黄土丘陵沟壑区应根据物种幼苗存活特性对幼苗进行适当的抚育管理, 这将有利于幼苗的建植和植被更新。     

Zooplankton grazing on Phaeocystis: a quantitative review and future challenges

The worldwide colony-forming haptophyte phytoplankton Phaeocystis spp. are key organisms in trophic and biogeochemical processes in the ocean. Many organisms from protists to fish ingest cells and/or colonies of Phaeocystis. Reports on specific mortality of Phaeocystis in natural plankton or mixed prey due to grazing by zooplankton, especially protozooplankton, are still limited. Reported feeding rates vary widely for both crustaceans and protists feeding on even the same Phaeocystis types and sizes. Quantitative analysis of available data showed that: (1) laboratory-derived crustacean grazing rates on monocultures of Phaeocystis may have been overestimated compared to feeding in natural plankton communities, and should be treated with caution; (2) formation of colonies by P. globosa appeared to reduce predation by small copepods (e.g., Acartia, Pseudocalanus, Temora and Centropages), whereas large copepods (e.g., Calanus spp.) were able to feed on colonies of Phaeocystis pouchetii; (3) physiological differences between different growth states, species, strains, cell types, and laboratory culture versus natural assemblages may explain most of the variations in reported feeding rates; (4) chemical signaling between predator and prey may be a major factor controlling grazing on Phaeocystis; (5) it is unclear to what extent different zooplankton, especially protozooplankton, feed on the different life forms of Phaeocystis in situ. To better understand the mechanisms controlling zooplankton grazing in situ, future studies should aim at quantifying specific feeding rates on different Phaeocystis species, strains, cell types, prey sizes and growth states, and account for chemical signaling between the predator and prey. Recently developed molecular tools are promising approaches to achieve this goal in the future.     

Macrophyte-associated macroinvertebrates as an important food source for wintering waterbirds at Lake Constance

In many lake ecosystems, waterbirds rate among the top consumers. Lake Constance is an important overwintering site for waterbirds in Central Europe because it provides sufficient food sources to meet energy demands during the winter months. In this study we focussed on the submerged vegetation and its associated macroinvertebrate fauna as a food source. We conducted experiments with exclosure cages which protected evergreen charophytes from bird grazing and compared the mass decline throughout the winter to unprotected grazed sites. Furthermore, we assessed the change in macrophyte-associated macroinvertebrates during the course of winter. We found that wintering waterbirds caused a significant decline of charophytes and their associated macroinvertebrates down to a depth of 4 m. We determined the taxa and abundance of macroinvertebrates associated with charophytes and predominantly found Dreissena polymorpha. At sites protected from bird grazing, the biomass of the macroinvertebrate fauna increased relative to the plant biomass during the course of winter. This might also have affected the foraging behaviour of diving waterbirds.     

Autodissemination of Beauveria bassiana by Sap Beetles (Coleoptera: Nitidulidae) to Overwintering Sites

An autoinoculative device was used to test the ability of sap beetles (Coleoptera: Nitidulidae) to carry a specific strain of Beauveria bassiana (Balsamo) Vuillemin to overwintering sites in a multiyear field study. The device was baited with the pheromone and coattractants for the dusky sap beetle (Carpophilus lugubris Murray) and placed in the field in the fall of each year. The introduced strain occurred at high frequency among the B. bassiana isolated in the fall of all four years tested (100% of all isolates from 21 of 22 collection dates). The introduced strain of B. bassiana was isolated at high frequency from all the B. bassiana-contaminated sap beetles recovered from the overwintering traps (100% of all isolates from 13 of 23 trap/beetle species combinations) and was highest after the longest fall exposure. The introduced strain was primarily isolated from C. lugubris and C. antiquus, but species distribution was also dependent on the overwintering trap design used. Few non-sap beetles species of insects were recovered from the artificial overwintering sites. Although B. bassiana was isolated from free flying sap beetles caught in traps in the spring of each year, none were infected with the introduced strain. The autoinoculating device provides selective contamination of sap beetles in overwintering sites when used in the fall. It may be useful in providing some control of sap beetles or other insects where limited numbers of mass overwintering sites (such as tree holes) occur.