Differences of the protozoan biomass and grazing during spring and summer in the Indian sector of the Southern Ocean

The dynamics of protozoa were investigated during two cruises in the Indian sector of the Southern Ocean: the early spring ANTARES 3 cruise (28 September to 8 November 1995) and the late summer ANTARES 2 cruise (6 February to 8 March 1994). Biomass and feeding activity of protozoa were measured as well as the biomass of their potential prey – bacteria and phototrophic flagellates – along the 62°E meridian. The sampling grid extended from the Polar Frontal region to the Coastal and Continental Shelf Zone in late summer and to the ice edge in spring, crossing the Antarctic Divergence. Protozoan biomass, although low in absolute terms, contributed 30% and 20% to the total microbial biomass (bacteria, phytoplankton and protozoa) in early spring and late summer, respectively. Nanoprotozoa dominated the total protozoan biomass. The geographical and seasonal distribution of protozoan biomass was correlated with that of phototrophic flagellates. However, bacterial and phototrophic flagellate biomass were inversely correlated. Phototrophic flagellates dominated in the Sea Ice Zone whereas bacteria were predominant at the end of summer in the Polar Frontal region and Coastal and Continental Shelf Zone. Furthermore, bacteria were the most important component of the microbial community (57% of the total microbial biomass) in late summer. Phototrophic flagellates were ingested by both nano-and microprotozoa. In contrast, bacteria were only ingested by nanoprotozoa. Protozoa controlled up to 90% of the daily bacterial production over the period examined. The spring daily protozoan ingestion controlled more than 100% of daily phototrophic flagellate production. This control was less strong at the end of summer when protozoan grazing controlled 42% of the daily phototrophic flagellate production. Accepted: 30 October 1999     

Growth and production of heterotrophic nanoflagellates in a meso-eutrophic lake

The growth of heterotrophic nanoflagellates (HNF) in mesotrophicLake Constance was measured in situ during a 13 month period.Experiments were conducted with 10 µm pre-filtered lakewater incubated in diffusion chambers at 3 m water depth atthe sampling location for 24 h. Growth rates were calculatedfrom changes in cell numbers occurring during the period ofincubation. Growth rates of all dominant taxa showed pronouncedseasonal variation (–0.13 to 1.76 day^–1 and weregenerally highest in summer at high water temperatures. In situgrowth rates were well below maximum growth rates known forthe respective and similar species from laboratory experiments.While water temperature was a key parameter positively relatedto the growth of all HNF species, the effect of various potentialfood items was taxon specific and less clear. Bacterial abundancewas equally important as temperature for growth in the smallbactenvorous Spumella sp., but was insignificant for growthrates of the larger omnivorous Kathablepharis sp. In Spuniellasp., 84% of the observed seasonal variation of its growth ratecould be explained by temperature and bacterial food supply.Based on these results, a multiple linear regression equationwith temperature and bacterial concentration as dependent variableswas calculated for the growth rate of Spumella. Taxon-specificproduction rates were derived from growth rates and averagebiomass of these two species, and compared to total HNF productionestimated from previously measured community growth rates andbiomass in Lake Constance. Production peaks of Spumella sp.and Kathablepharis sp. alternated seasonally. Total HINF productionranged from –0.01 to 10 mg C m^–3 day^–1. Theaverage seasonal production varied between 1.4 and 33 mg C m^–3day^–1 over 6 consecutive years. These small protozoa thuscontribute a substantial amount to total zooplankton productionin Lake Constance.     

The significance of food web structure for the condition and tracer lipid content of juvenile snail fish (Pisces: Liparis spp.) along 65-72{deg}N off West Greenland

Plankton community structure was analysed during summer along 65-72N off West Greenland, The south-north transect mimics a time span of months in the phytoplankton and zooplankton succession during the Arctic summer. In the south, the mixing depth was below the photic zone and the phytoplankton community was dominated by flagellates. North of Disko Bay (69°N), the water column was stratified due to melt water, and the phytoplankton dominated by flagellates and a small amount of diatoms, but with higher biomass and primary production. The copepod community was dominated by Calanus spp. and was more progressed in terms of developmental stage composition in the south. The biochemical lipid finger printing in the food chain phytoplankton-mesozooplankton-juvenile planktivorous snail fish (Liparis spp.) confirmed the qualitative composition of the phytoplankton, and revealed that the mesozooplankton >400 m in body size contained lipids originating from a non-diatom diet in the south, whereas it showed mesozooplankton lipids originating from a diatom diet in the north. The C16:1 (n-7)/C16:0 ratio increased from 0.63 to 3 for mesozooplankton along the transect, indicating feeding based on diatoms in the north. This ratio was reflected in Liparis spp. along the transect. The condition of the juvenile snail fish was generally good (high b exponent) along the entire transect based on the relationship: total fatty acids (mg) = 0.0008 x standard length (mm)²³⁵. However, the relationship triacylglycerol:cholesterol was much higher north of Disko Bay, indicating a much better condition and thereby potential starvation tolerance and survival in the north. We conclude that the plankton structure along the south-north transect reflected the yearly succession in phytoplankton with respect to tracer lipids and that juvenile Liparis spp. were in a better condition when foraging on wax ester-rich mesozooplankton, which in turn developed ontogenetically during a diatom-based spring bloom in the north.      

Size and species-specific primary productivity and community structure of phytoplankton in Tokyo Bay

Combined methods of size fractionation and single-cell isolationwere used to investigate the seasonal variation of phytoplanktondynamics in Tokyo Bay with an emphasis on primary productivity.Red tides occurred in Tokyo Bay from spring to autumn; a diatom,Skeletonema costatum, and a raphidophycean, Heterosigma akashiwo,were the most important primary producers. Small diatoms andflagellates, including these species, were dominant and showedrapid changes of phytoplankton community structure within severaldays in summer. The nanoplankton (3–20 µm) fractioncontributed most to chlorophyll a concentration and primaryproductivity during spring to autumn, whereas the microplankton(>20 µm) contribution was remarkable in winter. Picoplankton(<3 µm phytoplankton) remained relatively constantthroughout the year. A significant reverse relationship wasobtained between assimilation rate and chlorophyll a contentfor the total and nanoplankton population; the assimilationrate was high at the initial phase of the bloom, then decreasedto a minimum level at the peak of the bloom. Factors controllingthe reduction of assimilation rates at the peak, and changesin phytoplankton community structure, are discussed.     

Summer feeding activities of zooplankton in Prydz Bay, Antarctica

Grazing of dominant zooplankton copepods (Calanoides acutus, and Metridia gerlachei), salps (Salpa thompsoni) and microzooplankton was determined during the austral summer of 1998/1999 at the seasonal ice zone of the Prydz Bay region. The objective was to measure the ingestion rates of zooplankton at the seasonal ice zone, so as to evaluate the importance of different groups of zooplankton in their grazing impact on phytoplankton standing stock and primary production. Grazing by copepods was low, and accounted for <1% of phytoplankton standing stocks and 3.8-12.5% of primary production for both species during this study; even the ingestion rates of individuals were at a high level compared with previous reports. S. thompsoni exhibited a relatively high grazing impact on primary production (72%) in the north of our investigation area. The highest grazing impact on phytoplankton was exerted by microzooplankton during this investigation, and accounted for 10-65% of the standing stock of phytoplankton and 34-100% of potential daily primary production. We concluded that microzooplankton was the dominant phytoplankton consumer in this study area. Salps also played an important role in control of phytoplankton where swarming occurred. The grazing of copepods had a relatively small effect on phytoplankton biomass development.     

Phytoplankton population dynamics in perennially ice-covered Lake Fryxell, Antarctica

Phytoplankton were collected over five austral summers (1987–88through 1991–92) to examine seasonal and annual fluctuationsin species composition and biovolume in Lake Fryxell, a perenniallyice-covered lake located in the Dry Valleys of South VictoriaLand, Antarctica. Lake Fryxell has perennial gradients of salinity,dissolved oxygen and nutrients. We found that algal speciesdiversity was low (56 taxa were collected), confirming the resultsof previous short-term studies. The phytoplankton consistedprimarily of cryptophyte and chlorophyte flagellates, and filamentouscyanobacteria. The presence of filamentous cyanobacteria, whichhave not been reported as abundant in this lake by previousworkers, may represent a significant ecological change. Eachaustral summer, one dominant species contributed >70% ofthe total biovolume; Chroomonas lacustris was dominant in 1987–88,while Cryptomonas sp. dominated the phytoplankton in the remaining4 years. No species succession occurred during the austral summer.Some common taxa were vertically stratified (Oscillatoria limnetica,Phormidium angustissimum, Pyramimonas sp., Oscillatoria sp.),while others showed no distinct vertical stratification (Chlamydomonassubcaudata, Cryptomonas sp.). The stratification of the phytoplanktonreflects the gradients of nutrients and light, and the stabilityof the water column.     

Dynamics of protozoan and metazoan communities in a full scale wastewater treatment plant by rotating biological contactors

Performance of a full-scale wastewater treatment plant by rotating biological contactors (RBC) system was monitored during a year by physico-chemical and microbial characterisation. Six points along wastewater treatment were selected in the plant: three points along the water line (influent, sedimentation tank and effluent) and three points along RBC system (RBC1, RBC2 and RBC3). Although a large seasonal change in the values of physico-chemical parameters was observed, operation of the plant was optimal during all year (90% of removal in BOD5 and SS influent content). Microbial characterisation was approached by determining the structure and dynamics of protozoan and metazoan communities. Protozoa were the most abundant in all stages in the plant, heterotrophic flagellates being the most representative group in the water line and ciliates in the RBC system. The same seasonal preference was only observed for heterotrophic flagellates in the water line and green flagellates in the RBC system, both groups having highest abundances in summer and spring, respectively. Identification of ciliated protozoa populations rendered 58 species of ciliates in the plant. Most of these species are typical of aerobic wastewater treatment systems except three of them, which are cited for the first time in this type of ecosystems: Chaenea stricta, Holosticha mancoidea and Oxytricha lanceolata. Along the water line 34 species were identified, and half of them only appeared occasionally (once in all the study), while along the RBC system biofilms 55 species were observed, and the majority appeared permanently in this system. Our results indicate that the type of habitat, rather than the physico-chemical water parameters, was the primary factor in determining the different distribution of protozoan and metazoan communities in the plant. In RBC biofilms, the structure of ciliate protozoa community was found to be quite sensitive to changes in physico-chemical parameters, mainly to organic loading (BOD5) variations.     

Factors influencing geographic patterns in diversity of forest bird communities of eastern Connecticut,USA

At regional scales, the most important variables associated with diversity are latitudinally‐based temperature and net primary productivity, although diversity is also influenced by habitat. We examined bird species richness, community density and community evenness in forests of eastern Connecticut to determine whether: 1) spatial and seasonal patterns exist in diversity, 2) energy explains the greatest proportion of variation in diversity parameters, 3) variation in habitat explains remaining diversity variance, and 4) seasonal shifts in diversity provide clues about how environmental variables shape communities. We sought to discover if our data supported predictions of the species–energy hypothesis. We used the variable circular plot technique to estimate bird populations and quantified the location, elevation, forest type, vegetation type, canopy cover, moisture regime, understory density and primary production for the study sites. We found that 1) summer richness and population densities are roughly equal in northeastern and southeastern Connecticut, whereas in winter both concentrate toward the coast, 2) variables linked with temperature explained much of the patterns in winter diversity, but energy‐related variables showed little relationship to summer diversity, 3) the effect of habitat variables on diversity parameters predominated in summer, although their effect was weak, 4) contrary to theory, evenness increased from summer to winter, and 5) support for predictions of species–energy theory was primarily restricted to winter data. Although energy and habitat played a role in explaining community patterns, they left much of the variance in regional diversity unexplained, suggesting that a large stochastic component to diversity also may exist.     

Seasonal dynamics of phytoplankton in two warm temperate reservoirs: association of taxonomic composition with temperature

Variations in phytoplankton composition were observed over 2.7years in two warm temperate reservoirs in north central Texas,Joe Pool Lake (JPL) and Eagle Mountain Lake (EML), and analysedin relation to temperature, light, dissolved nutrients, sestonnutrient ratios and hydrological variables. The dominant variationsin both phytoplankton composition and environmental variableswere seasonal and strongly related to the annual temperaturecycle. Phytoplankton composition was annually periodic, withfilamentous cyanobacteria, pennate diatoms and chlorophytesdominant in summer, while other chlorophytes, centric diatoms,cryptophytes, dinoflagellates and other flagellates either dominatedin other seasons or remained abundant year round. The seasonaldynamics of several major taxa could be represented by a nicheresponse model based on temperature alone, although seasonalvariations in many environmental variables likely contributedto variation in phytoplankton composition. Such seasonal variationsdominated these data, but interannual variation in phytoplanktoncomposition and environmental variables also appeared to resultfrom dry weather late in the study.     

Large-bodied Crustacea and rainbow smelt in Lake George, New York: trophic interactions and phytoplankton community composition

The phytoplankton community of south Lake George, New York,has recently undergone a dramatic shift in composition; froma community dominated by Chrysophytes, Cryptomonads, and Chlorophyta(1975–1976) to one currently dominated by blue-green algae,i.e.Anacystis incerta and Aphanothece nidulans. No increasesin nutrient concentrations or inputs have been documented beforeor during this period. This shift in dominance can be relatedto changes in higher trophic levels, i.e. grazers and planktivores.Standing crop and abundance of the small-bodied filter feeders,Bosmina longirostris, Daphnia galeata, D. dubia, Holopediumgibberum, Diaptomus minutus and D. sicilis are significantlygreater in the south basin. Standing crop and abundance of thelarge-bodied Crustacea, Daphnia pulicaria, Epishura lacustrisand Mysis relicta, are significantly greater in the north basin.The clutch sizes of all herbivorous species except D. minutuswere significantly greater in the south basin populations. Thesedifferences are consistent with greater productivity and sizeslective planktivory in the south basin. Stomach analysis ofthe recently introduced rainbow smelt, Osmerus mordax indicatesa marked selection for the large-bodied Crustacea. The establishmentof large populations of rainbow smelt in the south basin ofLake George is responsible for significant basin differencesin the abundance of large-bodied Crustacea and appears to havecontributed to the changes in phytoplankton community composition.The shift to small-bodied Crustacea in the south basin has resultedin significantly lower grazing rates but generally higher Prelease rates in the south basin. These factors contribute togreater springtime phytoplankton production and silica depletionin the south basin. Coccoid blue-green algae are able to dominatewaters with low phosphorus and silica concentrations, i.e. LakeGeorge. Thus, the establishment of rainbow smelt in Lake Georgecoincides with, and appears to be responsible for, changes inphytoplankton community composition.     

镇江长江豚类省级自然保护区浮游动物群落结构特征及影响因素

江苏镇江长江豚类省级自然保护区是长江下游江段长江江豚的最主要的栖息地之一。为了解江豚主要栖息地的浮游动物群落结构,于2016年1月至2018年10月对保护区水域浮游动物进行了现状调查,分析了浮游动物群落时空结构变化特征及其与环境因子的关系。研究共发现浮游动物4门41属90种,其中原生动物种类数最多,为40种,其次为桡足类和枝角类,而轮虫类较少。三年共确定优势种8种,以食藻类原生动物为主要优势类群。保护区浮游动物群落小型化趋势明显。浮游动物密度和生物量季节性差异显著（P<0.05）,总体上呈现夏、秋季较春、冬季高的现象。Pearson相关性和RDA分析结果显示,水温、溶氧、pH和氮营养盐是造成浮游动物群落显著差异的主要环境因子。根据浮游动物群落结构特征及渔产潜力综合评估结果显示,与历史资料相比,保护区水生态环境有所改善,但渔业资源匮乏的局面没有得到根本性的改变,江豚的食物资源状况依然不容乐观。本研究结果为镇江保护区江豚栖息地生态环境的监测和保护研究提供了数据资料和理论依据。     

PERIODICITY OF EPIPELIC UNICELLULAR VOLVOCALES (CHLOROPHYCEAE) IN A SHALLOW ACID POOL1

The occurrence, periodicity and growth of twenty species of unicellular Volvocales on sediments in an acidic pool are described. Minimum populations were recorded in winter, but during the rest of the year standing crops fluctuated rapidly. The greatest species diversity and primary productivity occurred in late spring-early summer and in autumn, when maximum numbers of Chlamydomonas spp. and Chloromonas spp. increased exponentially on the sediments. The chlamydomonads were more numerous in the epipelon than other major algal components such as diatoms, euglenoids, bluegreen algae and desmids. Growth of the chlamydomonad population occurred after the period of maximum diatom standing crop. Evidence shows that rates of primary production were greater in late spring and late summer when species diversity and standing crop or apparent growth rates of unicellular Volvocales were high. Thus these algae which are normally neglected may be more important in primary productivity than previously believed since they grow during periods when larger algae are scarce. Analysis of the data using the multivariate technique of Reciprocal Averaging confirmed seasonal periodicity in this community of epipelic flagellates. It also identified species with distinctive ecological requirements. A relationship between the bicarbonate-alkalinity of the overlying water and the chlamydomonad population was demonstrated by ordination analysis.     

Seasonal variations in copepod size: effects of temperature, food abundance, and vertebrate predation

Seasonal dry weights of female and male Cyclops bicuspidatusthomasi, Diaptomus ashlandi and Diaptomus minutus were studiedin southeastern Lake Michigan during 1975–1981. Smallestanimals occurred during summer and early fall, and largest animalsin winter and spring, a pattern reported for other copepods.The range of weights for the species and sexes decreased fromwinter to summer, and converged in summer to a value of approximately2 µg/animal. Surface water temperature and abundancesof young-of-the-year (YOY) fish were inversely correlated withweights of males and females of the three copepod species. Standingstocks of important phytoplankton groups, especially pennatediatoms and flagellates, were positively correlated with copepodweight. Seasonal change of copepod body size appears to be morethan simply a function of temperature; seasonal predation byYOY fish may be a factor influencing sizes of adult copepods.     

Seasonal pattern of zooplankton communities and their environmental response in subtropical maritime channels systems in the Bay of Bengal,Bangladesh

Zooplankton are a primary component of aquatic food chain and play an important role in the functioning of aquatic food webs. Seasonal variation in community structures of zooplankton and potential environmental drivers were studied, during a 1-year cycle (summer 2015 – spring 2016) in subtropical maritime channels systems in the Bay of Bengal, coastal waters in Bangladesh. A total of 32 species representing 25 families, 13 orders and 15 taxonomic groups were identified. Of these species, 23 distributed in all four season of which 8 were dominant species with high contributions of the total communities. Species number was peaked in autumn and fell in summer while maximum abundance was in the winter and minimum in summer. Multivariate analyses showed that there was a clear seasonal shift in zooplankton community structures in relation with environmental conditions. Species diversity and evenness peaked in summer while the high value of species richness was found in autumn. Multivariate correlation (RELATE) and BIO-ENV analysis demonstrated that seasonal variation in community patterns was significantly correlated with temporal shift of environmental conditions and that variation mainly driven by water transparency, salinity, DO, TSS and nutrients. Thus, this finding implies that the zooplankton community represented a clear seasonal shift shaped by environmental drivers in subtropical channels systems.     

Seasonal Patterns of Planktonic Production in McMurdo Sound, Antarctica

The prolonged periods of continuous darkness and light in polarregions have resulted in a unique seasonal partitioning of primaryand heterotrophic production. In McMurdo Sound for example,the biomass, size distribution and production by phytoplanktonand bacterioplankton undergo distinct seasonal cycles. The seasonalpattern of primary production appeared to be regulated by lightwhereas the three order of magnitude change in phytoplanktonbiomass during mid- to late December was largely controlledby the advection of planktonic algae from the Ross Sea intoMcMurdo Sound. The size distribution of phytoplankton was highlyseasonal; nano- and picoplankton were dominant from August throughNovember while netplankton were more abundant in December andJanuary. Seasonal variations of bacterial biomass and productionwere smaller than those of phytoplankton. During the late australwinter and spring, bacterial biomass and production exceededthose of phytoplankton. This implies that during this period,organic material from allochthonous sources sustained bacterialgrowth. During the late spring and summer, however, the patternwas reversed and autochthonous primary production was sufficientto support concurrent bacterioplankton production. The apparenttemporal disequilibrium in autochthonous bacterioplankton andphytoplankton production was maintained by the seasonal inputof allochthonous organic material into McMurdo Sound. The factsthat a) bacteria were both abundant and highly active, b) bacterivorywas common among many of the endemic protozoa and some planktonicmetazoa and c) these bacterivores consumed >95% of the bacterialproduction strongly suggest that bacteria are a crucial componentin the transfer of energy and material to metazoans in polarregions.     

Occurrence of mixotrophic flagellates in relation to bacterioplankton production, light regime and availability of inorganic nutrients in unproductive lakes with differing humic contents

1. Field data from five unproductive Swedish lakes were used to investigate the occurrence of mixotrophic flagellates in relation to bacterioplankton, autotrophic phytoplankton, heterotrophic flagellates and abiotic environmental factors. Three different sources of data were used: (i) a 3‐year study (1995–97) of the humic Lake Örträsket, (ii) seasonal measurements from five lakes with widely varying dissolved organic carbon (DOC) concentrations, and (iii) whole lake enrichment experiments with inorganic nutrients and organic carbon. 2. Mixotrophic flagellates usually dominated over autotrophic phytoplankton in Lake Örträsket in early summer, when both bacterial production and light levels were high. Comparative data from the five lakes demonstrated that the ratio between the biomasses of mixotrophic flagellates and autotrophic phytoplankton (the M/A‐ratio) was positively correlated to bacterioplankton production, but not to the light regime. Whole lake carbon addition (white sugar) increased bacterial biomass, and production, reduced the biomass of autotrophs by a factor of 16, and increased the M/A‐ratio from 0.03 to 3.4. Collectively, the results indicate that the dominance of mixotrophs among phytoplankton was positively related to bacterioplankton production. 3. Whole lake fertilisation with nitrogen (N) and phosphorus (P) demonstrated that the obligate autotrophic phytoplankton was limited by N. N‐addition increased the biomass of the autotrophic phytoplankton but had no effect on mixotrophic flagellates or bacteria, and the M/A‐ratio decreased from 1.2 to 0.6 after N‐enrichment. Therefore, we suggest that bacteria under natural conditions, by utilising allochthonous DOC as an energy and carbon source, are able to outcompete autotrophs for available inorganic nutrients. Consequently, mixotrophic flagellates can become the dominant phytoplankters when phagotrophy permits them to use nutrients stored in bacterial biomass. 4. In Lake Örträsket, the biomass of mixotrophs was usually higher than the biomass of heterotrophs during the summer. This dominance could not be explained by higher grazing rates among the mixotrophs. Instead, ratios between mixotrophic and heterotrophic biomass (the M/H‐ratio) were positively related to light availability. Therefore, we suggest that photosynthesis can enable mixotrophic flagellates to outcompete heterotrophic flagellates.     

Predation impact of ciliated and flagellated protozoa during a summer bloom of brown sulfur bacteria in a meromictic coastal lake

Anaerobic phagotrophic protozoa may play an important role in the carbon flux of chemically stratified environments, especially when phototrophic sulfur bacteria account for a high proportion of the primary production. To test this assumption, we investigated the vertical and temporal distribution of microbial heterotrophs and of autotrophic picoplankton throughout the water column of the meromictic coastal lake Faro (Sicily, Italy), in the summer of 2004, coinciding with a bloom of brown-colored green sulfur bacteria. We also assessed the grazing impact of ciliated and flagellated protozoa within the sulfur bacteria plate using a modification of the fluorescently labeled bacteria uptake approach, attempting to minimize the biases intrinsic to the technique and to preserve the in situ anoxic conditions. Significant correlations were observed between ciliate biomass and bacteriochlorophyll e concentration, and between heterotrophic nanoflagellate biomass and chlorophyll a concentration in the water column. The major predators of anaerobic picoplankton were pleuronematine ciliates and cryptomonad flagellates, with clearances of 26.6 and 9.5 nL per cell h⁻¹, respectively, and a cumulative impact on the picoplankton gross growth rate ranging between 36% and 72%. We concluded that protozoan grazing channels a large proportion of anaerobic picoplankton production to higher trophic levels without restraining photosynthetic bacteria productivity.     

仙女湖及入湖河流浮游植物功能类群与环境因子的相互关系

文章分析了仙女湖及入湖河流浮游植物群落结构和功能类群的时空分布特征, 探讨了影响其时空分布规律的关键环境因子。调查期间共鉴定表层水体中浮游植物82种(属), 包括蓝藻15种(属), 绿藻33种(属), 硅藻23种(属), 甲藻3种(属), 裸藻5种(属), 隐藻2种(属), 金藻1种(属)。各季节平均密度和生物量分别在7.95×106—2.19×109 cells/L和10.52—792.91 mg/L变化。群落功能类群的结果表明, 冬、春河流生境中具硅质结构的无鞭毛个体浮游植物(硅藻门)占据主导地位(Ⅵ功能群), 而湖区生境中具鞭毛、中等到大型的单细胞或群体浮游植物(如隐藻和甲藻)具有明显优势(Ⅴ功能群); 而夏秋季节不同生境中虽然Ⅵ型浮游植物数量仍然相对较高, 但是具伪空胞的、较大表面积/体积比的丝状个体浮游植物(Ⅲ型)以及具胶质鞘、小的表面积/体积比的群体类的浮游植物(如蓝藻, Ⅶ功能群)在某些河流和湖泊生境中的比重有显著增长。功能类群与环境因子的相关分析表明: 冬、春季Ⅴ与Ⅵ功能群浮游植物生物量主要受到总氮和总磷水平影响; 而夏、秋季节Ⅲ与Ⅶ功能群浮游植物受到水温、浊度、总氮和总磷水平的多重影响。     

Phytoplankton composition and cell carbon distribution in Prydz Bay, Antarctica: relation to organic particulate matter and its {delta}13C values

In January-February 1991, in Prydz Bay, phytoplankton bloomwas evident in the inner shelf area with the dominant diatomsbeing represented mainly by pennate species of the Nitzschia-Fragilariopsisgroup. Dinoflagellates and naked flagellates were most abundantin the centre of the bay; however, larger heterotrophic speciesprevailed at the southern stations. Cell carbon values (average317 µg l^–1; range 92-1048 µg l^–1) foundin the bloom in the south were chiefly due to pennate diatomsand larger heterotrophic dinoflagellates. Much lower carbonvalues (average 51 µg l^–1; range 7-147 µgl^–1) in the outer shelf region were mainly contributedby large centric diatoms (70-110 mu;m) and small dinoflagellates(5-25 µm). Wide ranges of algal cell sizes were observedin both southern and northern communities; the overlapping ofsizes of diatoms and flagellates, the latter containing heterotrophs,suggested complex trophic relationships within the planktonand an enhanced heterotrophic activity in the south. North-to-southvariations in surface     

三峡水库运行期间原生动物群落的时空异质性

于2010年10月—2011年6月三峡水库正常运行周期内对库区干流原生动物进行调查,研究其空间分布及水库周期排蓄期间的变化。共检测到原生动物99种,蓄水后纤毛虫有增多的趋势。水库运行的不同阶段优势种不同,大致演变为:砂壳纤毛虫(蓄水期)—非砂壳类纤毛虫(高位运行期间)—有壳肉足虫(低位运行期间)。不同水域优势种也存在差异,从上游到下游特征指示种变化为:有壳肉足虫(变动回水区)—纤毛虫(湖泊区)。结果表明,三峡水库原生动物的分布具有明显的时空异质性(P0.05),影响原生动物时空分布的主要因素有透明度、温度、电导率和叶绿素a。原生动物平均密度为952.19个/L,平均生物量为8.14μg/L。蓄水期上游现存量高于下游,低位运行期间则低于下游。原生动物Marglef和Shannonn-Weiver多样性指数平均值分别为3.78和2.18,1月份最低,6月份最高。蓄水175 m后上游变动回水区原生动物具有较高的丰度。水库冬蓄夏排的运行模式模糊了河流本身的季节变化,使原生动物的种类和现存量更多的受水库水动力学的影响,使水体理化因子和水文特征呈现明显的时空差异,最终形成原生动物种群的时空异质性分布。