Some physical and biological factors affecting a spring-summer phytoplankton dynamics in a shallow,temperate lake of South Andes (Argentina)

The phytoplankton dynamics of Laguna Ezquerra (Río Negro, Argentina) was analysed on the basis of high frequency sampling, each 3–4 days during a spring-summer period, in relation to physical factors and to the zooplankton community structure. The phytoplankton biomass presented a marked seasonality, accompanied by similar seasonal patterns in temperature and zooplankton dynamics. Community variations were reflected in the diversity, dominance and equitability values. The greatest change was associated during a short flooding period produced in late spring. The wind exposure was irregular during the whole study period, and was assumed to be a factor of stress for the phytoplankton growth. During spring and early summer, the phytoplankton community was dominated by nanoplanktonic forms like Rhodomonas lacustris, and the large sized Asterionella formosa presented an exponential increment at late summer. This Asterionella growth permitted to affirm that the community evolved towards plagioclimatic stages, attending the highly disturbed conditions of the shallow and wind exposed environment.     

Seasonal variations of size-fractionated phytoplankton along the salinity gradient in the York River estuary, Virginia (USA)

The dynamics of phytoplankton size structure were investigatedin the freshwater, transitional and estuarine zones of the YorkRiver over an annual cycle. The contribution of large cells(microplankton, >20 µm) to total concentrations ofchlorophyll a increased downstream during winter, whereas thatof small cells (nanoplankton, 3–20 µm; picoplankton,<3 µm) increased downstream during summer. In the freshwaterregion, the contribution of micro phytoplankton to total concentrationsof chlorophyll a was significant during warm seasons (springand summer) but not during colder seasons (winter), whereasthe contribution of small-sized cells (especially picoplankton)increased during cold seasons. Temperature, light and high flushingrate appear to control phytoplankton community structure inthe freshwater region. In the transitional region, nano-sizedcells dominated the phytoplankton population throughout allseasons except during the spring bloom (April) when the chlorophylla concentration of micro phytoplankton increased. Size structurein the transitional region is most likely regulated by lightavailability. In the mesohaline region, nano- and pico-sizedcells dominated the phytoplankton population during the summerbloom, whereas micro-sized cells dominated during the winterbloom. Factors controlling phytoplankton community size structurein the mesohaline zone may be riverine nitrogen input, temperatureand/or advective transport from up-river. Based on these results,the spatial and seasonal variations in size structure of phytoplanktonobserved on the estuarine scale may be determined both by thedifferent preferences for nutrients and by different light requirementsof micro-, nano- and picoplankton. The results suggest thatanalyses of phytoplankton size structure are necessary to betterunderstand controls on phytoplankton dynamics and to bettermanage water quality in river-dominated, estuarine systems.     

The recovery of a very shallow eutrophic lake, 20 years after the control of effluent derived phosphorus

1. Monitoring at fortnightly to monthly intervals of a very shallow, lowland lake over 24 years has enabled the time course of recovery from nutrient enrichment to be investigated after high external P loading of the lake (>10 g P m^?2 year^?1) was reduced between 1977 and 1980. 2. The lake showed a relatively rapid response during the spring and early summer, with a reduction in phytoplankton biomass occurring after 5 years when soluble reactive phosphorus concentration was <10 μg L^?1. 3. However, during the later summer the response was delayed for 15 years because of sustained remobilisation of phosphorus from the sediment. The greater water clarity in spring and a gradual shift from planktonic to benthic algal growth may be related to the reduction in internal loading after 15 years. 4. Changes in the phytoplankton community composition were also observed. Centric diatoms became less dominant in the spring, and the summer cyanobacteria populations originally dominated by non‐heterocystous species (Limnothrix/Planktothrix spp.) almost disappeared. Heterocystous species (Anabaena spp. and Aphanizomenon flos‐aquae) were slower to decline, but after 20 years the phytoplankton community was no longer dominated by cyanobacteria. 5. There were no substantial changes in food web structure following re‐oligotrophication. Total zooplankton biomass decreased but body size of Daphnia hyalina, the largest zooplankton species in the lake, remained unchanged, suggesting that the fish population remained dominated by planktivorous species. 6. Macrophyte growth was still largely absent after 20 years, although during the spring water clarity may have become sufficient for macrophytes to re‐establish.     

Photosynthetic capacity measured by DCMU-induced chlorophyll fluorescence in an oligotrophic lake

SUMMARY. Wastwater (English Lake District) was sampled at monthly intervals over 1 year to compare the seasonal and vertical extents of floristic and physiological variation in an oligotrophic phytoplankton assemblage. Cellular photochemical capacity (CPC) was measured by in vivo chlorophyll fluorescence before and after addition of the photosynthetic inhibitor 3(3,4-dichlorophenyl)-1,1-dimethyl urea (DCMU). The CPC index proved useful to define an activity coefficient for the chlorophyll levels measured in boiling methanol extracts. Large variations in CPC over time or depth were generally correlated with major shifts in phytoplankton species composition. Highest CPC values were recorded during autumnal mixing. Both CPC and floristic composition of the community demonstrated as great a variation over depth during a period of stratification as that recorded over time throughout the year. These observations emphasize the multi-canopy structure of the Wastwater phytoplankton community in summer.     

太湖金墅湾水源地浮游植物群落结构及其与环境因子的关系

利用典范相关分析方法(CCA),对太湖金墅湾水源地水体浮游植物群落结构及其与环境因子之间的关系进行了研究.共鉴定浮游植物7门58属,群落组成以蓝藻、硅藻和绿藻为主;夏季浮游植物的种类和数量均较多,平均密度为250×104ind.L-1,略高于春季(238×104ind.L-1).春、夏2季浮游植物群落结构差异较大,春季以蓝藻为最优势门类、鱼腥藻为最优势类群;夏季以绿藻为最优势门类,无最优势类群,但平裂面藻和栅藻在数量上较占优势.除受季节温度影响外,春季影响浮游植物分布的主要环境因子依次为铵态氮、总磷、总氮和磷酸盐,而总氮、铵态氮、磷酸盐、悬浮物、高等水生植物、总磷和透明度对夏季浮游植物分布的影响较大.     

Spatial and temporal variation in phytoplankton community structure in a southeastern U.S. reservoir determined by HPLC and light microscopy

Spatial and temporal variation in phytoplankton community structure within a large flood-control reservoir (Sardis Reservoir, MS, USA) was investigated in relation to variation in physicochemical properties, location within the reservoir, hydraulic residence time (HRT), nutrient concentrations, temperature, and light conditions over a 14-month period. During periods of short HRT, phytoplankton communities throughout the reservoir were homogeneous in biomass, composition, and production. With a gradual increase in HRT from spring to summer, spatially heterogeneous phytoplankton communities developed along the longitudinal axis of the reservoir. During this period of longer HRT, diatoms and chlorophytes were a larger proportion of total phytoplankton biomass at shallow and more turbid locations near the head of the reservoir, whereas cyanobacteria were a larger proportion of the community at deeper and less turbid locations closer to the outflow. Seasonal succession of the phytoplankton community was represented by high abundance of diatoms in spring, increasing biomass of cyanobacteria through summer, and a secondary bloom of diatoms in fall. Species of Cyclotella, Asterionella, Nitzschia, and Ankistrodesmus were among the first colonizers in the early growing season, closely followed by Aulacoseira, whereas species of Staurastrum and Tetraedron appeared later in the spring. Species of Synedra, Crucigenia, Selenastrum, Scenedesmus, and Merismopedia occurred throughout the sampling period. As the diatoms started to decrease during mid-spring, cryptophytes increased, prior to dominance of species of Pseudanabaena in summer. Reservoir management of HRT, in combination with spatial variation in reservoir morphology and seasonal variation in temperature and riverine nutrient inputs, creates seasonally variable yet distinct spatial patterns in phytoplankton community biomass, composition, and production. Handling editor: L. Naselli-Flores     

Dynamics of ice algae and phytoplankton in Frobisher Bay

Summary Vertical and seasonal variations of ice algae and phytoplankton were studied in relation to their physico-chemical environments in Frobisher Bay from 1979 to 1986. The biomass, estimated by both chlorophyll a concentrations and cell counts, was greater in the ice algae than in the phytoplankton in the underlying sea-water during winter and spring. Algal distribution in the sea ice varied vertically and seasonally, while in the underlying water column the phytoplankton distribution was much less variable. The ice algal bloom occurred at the bottom of the ice, particularly in the lower 5 cm during late spring, while the phytoplankton bloom took place at depths between 1 and 10 m during early summer after the ice bloom was over. The community structure of the ice algae changed from pennate to centric diatoms as the ice melted. The centrics dominated through the fall, and then decreased as the pennates increased in dominance when the ice formed again in winter. Species diversity and number were greater in the sea ice than in the seawater, but they were similar vertically within each habitat. The evenness of the species distribution did not vary with ice thickness or water depth. Species composition, abundance and dominance of ice algae and phytoplankton continually change both vertically and seasonally. The differential abilities of the species to attain maximal growth rates under various environmental conditions may result in species succession. Evidence is given for the major role of environmental factors regulating the dynamics of ice algae and phytoplankton.     

Bacterioplankton composition of the coastal upwelling system of 'Ría de Vigo', NW Spain

Catalysed reported deposition-FISH and clone libraries indicated that Roseobacter , followed by Bacteroidetes , and some gammaproteobacterial groups such as SAR86, dominated the composition of bacterioplankton in Ría de Vigo, NW Spain, in detriment to SAR11 (almost absent in this upwelling ecosystem). Since we sampled four times during the year, we observed pronounced changes in the structure of each bacterioplankton component, particularly for the Roseobacter lineage. We suggest that such variations in the coastal upwelling ecosystem of Ría de Vigo were associated with the characteristic phytoplankton communities of the four different hydrographical situations: winter mixing, spring bloom, summer stratification, and autumn upwelling. We retrieved new sequences among the major marine bacterial lineages, particularly among Roseobacter , SAR11, and especially SAR86. The spring community was dominated by two Roseobacter clades that had previously been related to phytoplankton blooms. In the other seasons, communities with higher diversity than the spring one were detected.     

Association between temporal and spatial beta diversity in phytoplankton

The rates of temporal and spatial species turnover have been compared in different organisms and scales, revealing that both are not independent but, rather, associated. However, the knowledge is limited for the association between spatial turnover and temporal turnover. Here, we performed two investigations of the phytoplankton composition in the lakes of the Yangtze River catchment in China in the spring and summer of 2012, which covered regional spatial scale and two‐season temporal scale. We analysed the association between temporal and spatial species turnover in phytoplankton. The results showed that 1) the two‐season temporal turnover of phytoplankton varied based on the mean values and the coefficient of variance of environmental variables, and pH was the most important variable negatively affecting the temporal turnover; 2) the spatial beta diversity of phytoplankton in summer was higher than that in spring, and the distance decay pattern was significant in summer, but not in spring; 3) the variation in spatial turnover in spring and summer was attributed to the primary environmental variables (nitrogen, phosphorus and underwater available light) and broader‐scale spatial variables; 4) the proportion of jointly explained variation of spatial Bray–Curtis dissimilarity by the environment and space increased from ~38% (spring) to ~55% (summer), which was mainly due to the variation in spatially structured environmental variables during the two‐season temporal turnover, such as pH and ion concentrations; 5) the community compositions in summer were more similar between the lakes with similar two‐season temporal turnover. These results indicate that the spatial turnover of phytoplankton composition in summer was partially predetermined by the variation in environmental variables and phytoplankton composition during the process of two‐season temporal turnover, and highlight the understanding of temporal variations in spatial beta diversity as well as the underlying assembly mechanisms in phytoplankton.     

Dynamic analysis of phytoplankton community characteristics in Daya Bay, China

Daya Bay is a large bay along the southern coast of China. The composition, abundance, community structure and diversity of phytoplankton in Daya Bay were investigated to assess its status in different seasons in 2002, and a total of 48 genera and 114 species of phytoplankton were identified. The cell abundance of phytoplankton varied from 5.79 × 10⁴ cells/m³ to 5.37 × 10⁶ cells/m³ with an average of 1.14×10⁶ cells/m³. The largest community was Bacillariophyta containing 84 taxa, and its average abundance was 1.08 × 10⁶ cells/m³. Annual abundance variations show a typical one-peak cycle, with the highest peak recorded during summer and the lowest recorded during autumn. The ecotypes of phytoplankton were mostly alongshore warm-water species; however, marine warm-water species and eurytopic species during winter and autumn are more abundant than during the other seasons. The dominant species were diverse and varied with seasons. The species diversity index of phytoplankton in Daya Bay was low during summer, especially near the nuclear power station (NPS) and the aquaculture farms during summer and autumn. Community structure and cell abundance were categorized in relation to monsoon, current and anthropological activities. It is presented that the temperature and hydrodynamics in conjunction with the pattern of nutrients (DIN, DIP and N/P) availability and depletion affect the composition, abundance, community structure, community succession and diversity of phytoplankton.     

Trophic relationships in the pelagic zone of Mondsee,Austria

Data are presented on nutrient concentrations, phytoplankton biovolume development, zooplankton composition and population dynamics, and fish from a deep, stratifying, alpine lake (Mondsee, Austria) during a three-year period between 1982 and 1984. Development of the phytoplankton is closely related to structuring events of the physico-chemical environment. Dissolved silicate and phosphorus concentrations are critical for the summer situation. During summer algal abundance is largely affected by grazing of zooplankton, but no clear-water phase was observed at the end of the spring peak of phytoplankton.Temperature and food are factors responsible for the timing and growth of the zooplankton populations. Because of close overlap in the epilimnion, exploitative and mechanical interference competition and predation by invertebrate and vertebrate predators are the main structuring forces acting on the zooplankton community, and hence influence phytoplankton indirectly.     

Seasonal and annual variability in the phytoplankton community of the Raunefjord,west coast of Norway from 2001–2006

Changes in phytoplankton community composition potentially affect the entire marine food web. Because of seasonal cycles and inter-annual variations in species composition, long-term monitoring, covering many sequential years, is required to establish a baseline study and to reveal long-term trends. The current study describes the phytoplankton biomass variations and species composition in relation to hydrographic and meteorological conditions in the Raunefjord, western Norway, over a 6-year period from 2001 to 2006. The extent of inflow or upwelling in the fjord varied from year to year and resulted in pronounced differences in water column stability. The annual phytoplankton community succession showed some repeated seasonal patterns, but also high variability between years. Two to four diatom blooms were observed per year, and the spring blooms occurring before water column stratification in March were dominated by Skeletonema marinoi and Chaetoceros socialis, and other Chaetoceros and Thalassiosira spp. Blooms of the haptophytes Phaeocystis pouchetii and Emiliania huxleyi were irregular and in some years totally absent. Although E. huxleyi was present all year round it appeared in bloom concentrations only in 2003, when the summer was warm and the water column characterized by high surface temperatures and pronounced stratification. The annual average abundance of both diatoms and flagellates increased during the six years. Despite the high variation from year to year, our investigation provides valuable knowledge about annual phytoplankton community patterns in the region, and can be used as a reference to detect possible future changes.     

The phytoplankton community of a eutrophic reservoir

The dynamics of the phytoplankton community of a eutrophic reservoir are described for a two year period. Fifty-eight species were recorded, 25 of them common. Bacillariophyta dominated during the winter and early spring and Chlorophyta during late spring, to be replaced by a bloom of Cyanophyta. The mean and peak biomass of phytoplankton was 8.6 mg 1^–1 and 40.8 mg 1^–1 in 1981, and 8.3 mg 1^–1 and 37.6 mg 1^–1 in 1982. Temperature accounted for 67.3% and pH for 8% of the variation in total phytoplankton biomass over the two year period, using a multiple regression technique.Both horizontal and vertical patchiness, measured as an index of mean crowding, were recorded in the reservoir. Horizontal aggregations were associated with spring blooms of Chlorophyta and summer blooms of Cyanophyta, while vertical aggregations were most marked during the summer bloom of Cyanophyta. Concentrations of phytoplankton were influenced by wind, the prevailing southwesterly wind accumulating algae in the northeasterly arm of the reservoir during much of the year.     

Dynamic analysis of phytoplankton community characteristics in Daya Bay, China

Daya Bay is a large bay along the southern coast of China. The composition, abundance, community structure and diversity of phytoplankton in Daya Bay were investigated to assess its status in different seasons in 2002, and a total of 48 genera and 114 species of phytoplankton were identified. The cell abundance of phytoplankton varied from 5.79 × 10⁴ cells/m³ to 5.37 × 10⁶ cells/m³ with an average of 1.14×10⁶ cells/m³. The largest community was Bacillariophyta containing 84 taxa, and its average abundance was 1.08 × 10⁶ cells/m³. Annual abundance variations show a typical one-peak cycle, with the highest peak recorded during summer and the lowest recorded during autumn. The ecotypes of phytoplankton were mostly alongshore warm-water species; however, marine warm-water species and eurytopic species during winter and autumn are more abundant than during the other seasons. The dominant species were diverse and varied with seasons. The species diversity index of phytoplankton in Daya Bay was low during summer, especially near the nuclear power station (NPS) and the aquaculture farms during summer and autumn. Community structure and cell abundance were categorized in relation to monsoon, current and anthropological activities. It is presented that the temperature and hydrodynamics in conjunction with the pattern of nutrients (DIN, DIP and N/P) availability and depletion affect the composition, abundance, community structure, community succession and diversity of phytoplankton.     

Seasonal abundance, reproduction and development of four key copepod species on the Faroe shelf

The copepod community on the Faroe shelf is dominated by Calanus finmarchicus, Temora longicornis, Acartia longiremis and Pseudocalanus spp. The species composition, abundance and development of the copepod community varied considerably during the season 2004. These variations reflected to a large extent the different life strategies of the copepods. Both nauplii and copepodites of C. finmarchicus were most abundant during spring and early summer. The two neritic copepods T. longicornis and A. longiremis were present in low numbers during spring but dominated the copepod community later during the productive period. Pseudocalanus spp., on the other hand, occurred throughout the year, but showed no clear numerical response in abundance to the spring bloom. The egg production measurements of C. finmarchicus and T. longicornis showed some pre-bloom egg production, but as the spring bloom started the egg production rate increased significantly, especially for C. finmarchicus. There seemed to be a substantial loss of nauplii and copepods from the shelf ecosystem during the productive season. It was, however, not possible to determine whether this was mainly due to mortality or advective loss.     

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.     

Recurrent seasonal variations in abundance and composition of filamentous SOL cluster bacteria (Saprospiraceae, Bacteroidetes) in oligomesotrophic Lake Mondsee (Austria)

The spatial and temporal variation of SOL cluster bacteria was assessed in oligomesotrophic Lake Mondsee and adjacent lakes by fluorescence in situ hybridization over two annual cycles. The filamentous SOL bacteria were present in Lake Mondsee throughout the study period, and the seasonal dynamics of the SOL community were remarkably similar with respect to both abundance and composition in the two consecutive years. Only two of the three SOL subclusters were detected in Lake Mondsee and four connected lakes. These two populations significantly differed in size distribution and demonstrated pronounced but recurrent differences in seasonality and length of period of appearance in Lake Mondsee. Extensive sampling of the lakes in September 2003 revealed low horizontal variation in the composition of the SOL community within Lake Mondsee but marked variations with depth. Between connected habitats pronounced differences in the composition and abundance of the SOL community were detected. The interaction of SOL bacteria with bacterivorous protists, mesozooplankton, and phytoplankton was investigated in order to reveal variables controlling the structure and dynamics of SOL communities. No strong indication for a bottom-up influence of phytoplankton was found, while the estimated community grazing rates of mesozooplankton on SOL bacteria indicated a top-down control of SOL abundance during mesozooplankton peaks in spring and early autumn. Furthermore, species-specific differences in grazing of mesozooplankton on SOL bacteria were observed. In general, the overall composition of SOL communities was controlled by abiotic factors (water chemistry), while their dynamics seemed to be controlled by abiotic and biotic interactions.     

博斯腾湖浮游植物群落结构特征及其影响因子分析

2011年对博斯腾湖大湖区17个采样站位的浮游植物及水体主要理化因子进行了4次系统调查。结果表明, 在17个站位共鉴定出浮游植物127种（属）, 其中优势种（属）9种。浮游植物群落全年均以硅藻为主导, 冬、春季节, 浮游植物组成呈硅藻-甲藻型, 优势类群主要为贫-中营养型浮游藻类, 到夏、秋季节逐渐形成硅藻-绿藻型, 以富营养型的浮游藻类为优势类群。浮游植物总平均生物量为（2.512.95） mg/L, 生物量季节变动显著, 峰值出现在夏季, 冬季最低。基于Canoco的多变量分析表明: 环境变量共解释了浮游植物群落总变异的54.5%, 水温是影响浮游植物分布最重要的环境因子, 其次为枝角类丰度。水中氮含量是影响浮游植物丰度的主要因子, 同时浮游植物对水体有机物含量也有较大的影响。       

Recurrent Seasonal Variations in Abundance and Composition of Filamentous SOL Cluster Bacteria (Saprospiraceae, Bacteroidetes) in Oligomesotrophic Lake Mondsee (Austria)

The spatial and temporal variation of SOL cluster bacteria was assessed in oligomesotrophic Lake Mondsee and adjacent lakes by fluorescence in situ hybridization over two annual cycles. The filamentous SOL bacteria were present in Lake Mondsee throughout the study period, and the seasonal dynamics of the SOL community were remarkably similar with respect to both abundance and composition in the two consecutive years. Only two of the three SOL subclusters were detected in Lake Mondsee and four connected lakes. These two populations significantly differed in size distribution and demonstrated pronounced but recurrent differences in seasonality and length of period of appearance in Lake Mondsee. Extensive sampling of the lakes in September 2003 revealed low horizontal variation in the composition of the SOL community within Lake Mondsee but marked variations with depth. Between connected habitats pronounced differences in the composition and abundance of the SOL community were detected. The interaction of SOL bacteria with bacterivorous protists, mesozooplankton, and phytoplankton was investigated in order to reveal variables controlling the structure and dynamics of SOL communities. No strong indication for a bottom-up influence of phytoplankton was found, while the estimated community grazing rates of mesozooplankton on SOL bacteria indicated a top-down control of SOL abundance during mesozooplankton peaks in spring and early autumn. Furthermore, species-specific differences in grazing of mesozooplankton on SOL bacteria were observed. In general, the overall composition of SOL communities was controlled by abiotic factors (water chemistry), while their dynamics seemed to be controlled by abiotic and biotic interactions.     

Seasonal succession of ciliates in lake constance

We found a recurrent seasonal pattern in abundance and composition of planktonic ciliates in Lake Constance, FRG, over a three-year period. Abundance peaks occurred in early spring and summer/autumn, while ciliate numbers were low in late spring (clear-water phase) and winter. Prostomatida and Oligotrichida dominated in early spring. They responded immediately to the phytoplankton spring bloom, while Haptorida, Peritrichida, and large Scuticociliatida (Histiobalantium) were delayed by 1 to 2 weeks. The spring community broke down at the onset of the clear-water phase.Pelagohalteria viridis containing symbiontic algae appeared shortly after this event. A highly diverse community was recorded in summer/autumn. Peritrichida, small Oligotrichida, and large Scuticociliatida reached their maxima during this season. Small Scuticociliatida were rare throughout the year and contributed moderately to total ciliate numbers only during the cold season. The observed seasonal sequence of pelagic ciliates in Lake Constance is discussed in relation to simultaneously collected data on potential food organisms and grazers.