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1.
Grazing on bacteria by flagellates and cladocerans in lakes of contrasting food-web structure 总被引:4,自引:0,他引:4
We tested the hypothesis that grazing on bacteria would varybetween lakes with differing plankton community structures.Paul and Tuesday lakes (Gogebic County, MI) are respectivelydominated by piscivorous and planktivorous fish. Consequently,zooplankton in Paul are primarily large daphnids, while zooplanktonin Tuesday are primarily small cladocerans and copepods. Wemeasured flagellate grazing on bacteria using a fluorescentminicell method, while cladoceran grazing was estimated fromthe relationship between body length and filtering rate. Wepredicted that cladoceran grazing on bacteria would be higherin Paul, and flagellate grazing would be higher in Tuesday.Cladoceran grazing on bacteria was important in both lakes contraryto our initial expectation. Large populations of the small cladoceran,Bosmina longirostris, in Tuesday exerted a grazing pressure(0.1835x106 bacteria 11 h1) approximatelyequal to that of the large cladoceran, Daphnia pulex, in Paul(0.3430x106 bacteria 11 h1). Flagellategrazing was higher in Tuesday as predicted (range: Paul, 0.16x106bacteria 11 h1; Tuesday, 0.220x106 bacteria11 h1). However, there was not a simple relationshipbetween total abundance of flagellates and total grazing rates.High community grazing by flagellates occurred when attachedchoanoflagellates were present. These flagellates had higheringestion rates than free forms. We find no clear evidence thatdifferences in food-web structure between the two lakes influencethe process of grazing on bacteria. Instead, our results emphasizethe significance of cladocerans and attached flagellates asconsumers of bacteria in freshwater ecosystems. 相似文献
2.
Indirectly fluorescently labelled flagellates (IFLF): a tool to estimate the predation on free-living heterotrophic flagellates 总被引:2,自引:0,他引:2
A procedure was developed to estimate the direct grazing impacton free-living heterotrophic nanoflagellates (HNF). Culturedflagellates were labelled by feeding on brightly fluorescingbacteria (FLB) and then offered as indirectly fluorescentlylabelled flagellates (IFLF) to potential predators of HNF. Thenumber of FLB in the predators' food vacuoles could be convertedinto IFLF uptake and consumption of HNF. This new techniquewas used to study the HNF-ciliate relationship in the pelagiczone of Lake Constance. Three groups of ciliates were detectedas HNF grazers: small representatives of the genus Strobilidium.a small Haltena-like ciliate (probably Halteria grandinella)and a Codonella sp. Tintinnidium sp. group The ingestion ofHNF by these groups of ciliates ranged between 3 and 15, 3 and39, and 3 and 7 HNF ciliate1 h1; respectively.The IFLF method allows the direct determination of ingestedflagellate prey in the food vacuoles of their predators. Becauseindigenous living prey organisms were used, tracer discriminationcan be reduced. 相似文献
3.
Pigmented nanoflagellates in the coastal western subtropical Pacific are important grazers on Synechococcus populations 总被引:2,自引:0,他引:2
Tsai An-Yi; Chiang Kuo-Ping; Chan Ya-Fan; Lin Yun-Chi; Chang Jeng 《Journal of plankton research》2007,29(1):71-77
Although the key grazers on Synechococcus and other planktonicmarine bacteria are generally thought to be nanoflagellates(both non-pigmented and pigmented) as well as ciliates, we previouslyfound in our western subtropical Pacific coastal study sitethat ciliates exerted almost no grazing pressure. In this study,we used fluorescently labeled particles (FLP) as Synechococcus-sizedmimics to examine the contribution of pigmented (may includeautotrophic and mixotrophic spp.) versus non-pigmented (heterotrophic)nanoflagellate grazing to Synechococcus morality. During thewarm season from June to September, > 50% of the nanoflagellatepopulation was pigmented (1.82 x 103 versus 1.21.6x 103 cells mL1). Consumption, or clearance rates perpigmented nanoflagellate, varied considerably (0.5046.90nL cell1 h1), with the highest rates in June.Raw data showed pigmented nanoflagellate grazing to accountfor 294% (mean 43%) of Synechococcus production fromMay to October. Pigmented nanoflagellates consumed 12.5-foldmore Synechococcus than did ciliates. This study provides thefirst evidence that pigmented nanoflagellates are key grazersof Synechococcus populations in subtropical western Pacificcoastal waters. 相似文献
4.
Growth and grazing rates of Protoperidinium hirobis Abe, a thecate heterotrophic dinoflagellate 总被引:1,自引:0,他引:1
Growth and feeding rates of a laboratory-reared small thecateheterotrophic dinoflagellate, Protoperidinium hirobis Abè,grown on the diatom Leptocylindrus danicus, were measured inbatch cultures. Ingestion rates were determined directly bythe enumeration of empty diatom frustules produced by dinoflagellatefeeding. Both growth and feeding rates saturated at diatom concentrationsof {small tilde} 104 cells ml1, and reached maximum valuesof 1.7 divisions day1 and 23 diatoms grazer1 day1,respectively. This rate of cell division is notably high comparedto photosynthetic dinoflagellates, which seldom grow fasterthan 1 division day1. A maximal clearance rate of 0.5µl h1 was measured. Mean cell size varied proportionallywith food abundance, with food-saturated cells having doublethe mean volume of food-depleted cells. Tuning of cell divisionand grazing rate patterns were also examined; while mitosisoccurred chiefly during the dark period, no diel variationsin feeding rate were detected. These rates represent the firstdirect growth and ingestion measurements to be made for a thecateheterotrophic dinoflagellate. They serve to underscore one functionthese dinoflagellates perform within the microzooplanktonicfood web: that of transforming large diatoms into particlesmore easily ingested by microzooplankters. 相似文献
5.
The vertical distribution and abundance of microbial assemblagesand the grazing of nanoheterotrophs upon prokaryotes in oxicand suboxic waters were examined in two coastal upwelling areasoff northern Chile where a shallow Oxygen Minimum Zone (OMZ)is characteristic. Prokaryotic prey included bacterioplanktonand cyanobacteria (Synechococcus); both displayed a bimodaldistribution, with abundance maxima above and within the upperOMZ. Flagellates numerically dominated the nanoplankton andwere mostly concentrated in the oxic layer. Mean ingestion ratesof cyanobacteria by nanoflagellates (vacuole content method)ranged from 0.2 to 1.1 cells flagellate1 h1 andmean consumption rates (34160 cells mL1 h1)were four times higher in the oxic layer. With the selectiveinhibitors technique, specific grazing rates on bacteria werelow (<0.1 h1) and consumption did not control bacterialproduction in the surface layer but did so in the suboxic layer(accounting for >100% of bacterial production). With thesame method, the specific grazing rate on cyanobacteria rangedbetween zero and 0.23 h1 with no clear differences betweenoxygen conditions; prey growth and production were always higherthan the grazing pressure (accounting for <17% of cyanobacterialproduction). The impact of grazing by nanoheterotrophs in regulatingthe production of prokaryotes in oxic and suboxic waters inthis region is discussed. 相似文献
6.
The population abundances and rates of biomass production ofheterotrophic nanoplankton (HNAN) in Georgia coastal waterswere evaluated by epifluorescence microscopy. HNAN populations(mostly non-pigmented microflagellates <10 µm in diameter)ranged from 0.3 x 103 cells ml1 in shelf waters 15 kmoffshore to 6.3 x 103 cells ml1 in waters 0.25 km fromthe coast. There was a strong correlation (r = 0.83) betweenHNAN and free bacterioplankton population abundances, but noapparent relation (r = 0.38) between HNAN and phototrophic nanopLankton(PNAN) abundances. HNAN biomass production in estuarine andnearshore shelf waters, as estimated from increases in HNANpopulations during laboratory incubations of natural water samples,ranged from 0.10 to 0.79 mg C m3 h3, with populationgeneration times of 9.7 to 26.5 h. There was a significant linearrelation (r = 0.95) between HNAN biomass and HNAN productivity.We calculated that HNAN may graze at least 30% to 50% of dailybacterioplankton production in Georgia coastal waters. 相似文献
7.
Laybourn-Parry Johanna; Ellis-Evans J.Cynan; Butler Helen 《Journal of plankton research》1996,18(4):495-511
The dynamics of bacterioplankton and protozooplankton in twomaritime Antarctic lakes (Heywood Lake and Sombre Lake, SignyIsland, South Orkneys) were studied during the phase of icebreak-out (December and early January 1994/95). The lakes aresuffering animal-induced (fur seal) eutrophication, though HeywoodLake is most severely affected. Both lakes had morphologicallydiverse bacterial communities which increased during the studyperiod, reaching maxima of 80 x 108 l1 in Heywood Lakeand 31.8 x 108 l1 in Sombre Lake. Heterotrophic nanoflagellates(HNAN) reached a peak in late December with maxima of 40.6 x108 l1 in Sombre Lake and 174 x 105 l1 in HeywoodLake. Phototrophic nanoflagellates (PNAN) peaked in late Decemberafter ice loss in Heywood Lake (63 x 105 l1), which coincidedwith a peak in a bloom of Chroomonas acuta which reached abundancesof 1.0 x 108 l1. In Sombre Lake, ice persisted for alonger period and here PNAN reached their highest density atthe end of the study period (around 70.0 x 105 l1). Ciliateabundance reached high levels in Heywood Lake (>600011),while in Sombre Lake maximum abundance was 568l1. Protozooplanktondiversity was greater in the less-enriched Sombre Lake. Grazingrates of ciliates averaged 70.6 bacteria indiv.1 h1in Heywood Lake and 119.3 bacteria indiv.1 h1in Sombre Lake. The difference was a reflection of the differenttaxonomic make-up of the community in the lakes. HNAN grazingrates varied between 0.51 and 0.83 bacteria indiv.1 h1in Sombre and Heywood Lakes, respectively. Specific growth rates(r) h1 in Sombre Lake were 0.028 for ciliates and 0.013for HNAN, and in Heywood Lake 0.010 for ciliates and HNAN 0.012.These growth rates result in doubling times ranging between38 and 69 h for ciliates and around 55 h for HNAN.HNAN grazingon bacteria was curtailed in Heywood Lake in early January asa result of predation by microcrustacean larvae feeding on theplankton. Thus, for a short phase top-down control was apparentin the dynamics of Heywood Lake, a feature uncommon in Antarcticlake ecosystems. The impact of natural eutrophication on thesesystems is discussed in relation to other unaffected Antarcticlakes. 相似文献
8.
Factors affecting the bacteria-heterotrophic nanoflagellate relationship in oligo-mesotrophic lakes 总被引:1,自引:0,他引:1
Tadonleke Remy D.; Pinel-Alloul B.; Bourbonnais N.; Pick F. R. 《Journal of plankton research》2004,26(6):681-695
The coupling between bacteria and heterotrophic nanoflagellates(HNF) was examined in nine lakes of low productivity for evidenceof the effects of various metazooplankton (i.e. rotifers, cladoceransand copepods) on this relationship. We considered the size ofcladocerans and, in contrast to most previous across-systemstudies, the three strata of the water column (i.e. epilimnion,metalimnion and hypolimnion). Rotifers were numerically dominantin all lakes and accounted for 4584% of total metazooplanktonabundance, while the abundance of large cladocerans was relativelylow, ranging from 0.066 to 15.2 ind. L1. The across-lakerelationship between bacteria and HNF was significant in thedeeper strata (meta- and hypolimnion) but not in the epilimnionand in the two groups of lakes separated on the basis of theiraverage number of large cladocerans (<5 and >5 ind. L1,respectively). The results confirmed the negative impacts oflarge cladocerans on HNF, but also showed that rotifers, probablythrough grazing on HNF, may be an important factor causing variationin the bacteriaHNF relationship in unproductive waters.Quadratic models best described the relationships between metazooplanktonand the ratio of bacteria to HNF. This ratio seemed to be aresult of complex interactions between several factors, includingthe zooplankton composition and abundance and the depth of thelake. Indeed, this ratio significantly decreased across lakes,with increase in depth. In addition, shallower lakes (having<5 large cladocerans L1 and fewer Polyarthra vulgaris)tended to have more bacteria and HNF and a higher ratio of bacteriato HNF than deeper lakes (which had >5 large cladoceransL1 and substantial proportions of P. vulgaris). We suggestthat the epilimnion, metalimnion and hypolimnion of lakes betaken into account when analysing the bacteriaHNF relationshipas well as the cascading effects of zooplankton on microbialcommunities. 相似文献
9.
Short-term changes of protozoan control on autotrophic picoplankton in an oligo-mesotrophic lake 总被引:3,自引:0,他引:3
Pernthaler Jakob; Simek Karel; Sattler Birgit; Schwarzenbacher Angela; Bobkova Jitka; Psenner Roland 《Journal of plankton research》1996,18(3):443-462
In May 1994, we investigated the short-term development of theplanktonic community in the epi- and metalimnion of an oligo-mesotrophiclake (Piburger See, Tyrol), focusing on trophic links betweenprotists and picoplankton, but also including phyto- and zooplankton.Uptake experiments with fluorescently labelled bacteria (FLB)and picocyanobacteria (FIC) were performed in order to comparethe importance of both prey types as carbon sources for bacterivorousprotists. Heterotrophic nanoflagellates (HNF) were responsiblefor {small tilde}90% of total protozoan picoplanktivory (FLB+ FLC); ciliates accounted for {small tilde}10%. A selectivityindex related to prey density showed that both HNF and ciliatesclearly preferred FLC over FLB. The mean cell size of autotrophic(prokaryotic) picoplankton (APP) was nearly three times larger(0.323 µm3) and much less variable than mean bacterialcell volume (0.122 µm3). Although APP biomass was on averageonly 8.6% of total picoplankton biomass, pico-cyanobacteriaaccounted for a mean 15.9% of total HNF carbon uptake. We calculatedthat total HNF grazing could match potential APP maximum growthrates at the beginning of the study period. A strong decreasein HNF individual clearance rate (CR) on APP was clearly relatedto a fall in the percentage of choanofiagellates (from 75 to{small tilde}10% of the HNF community). A simultaneous decreasein HNF biomass and CR was followed by a steep increase in APPabundance; APP abundance and HNF biomass were highly negativelycorrelated both in the epi- and the metalimnion (r1 EM = 0.879,r1 META = =0.907; P = 0.001). Total rotifer abundance increasedby a factor of 50 within 2 weeks and was also negatively correlatedwith HNF biomass (r1 EM = 0.852, P < 0.001; r1 META= 0.659, P < 0.05). HNF grazing was found to exerta strong short-term control on picocyanobacteria and this linkwas probably broken by an increase in metazooplankton, especiallydue to rotifer predation on HNF. 相似文献
10.
Pyrosoma atlanticum (Tunicata, Thaliacea): grazing impact on phytoplankton standing stock and role in organic carbon flux 总被引:2,自引:0,他引:2
Drits Alexander V.; Arashkevich Elena G.; Semenova Tatjana N. 《Journal of plankton research》1992,14(6):799-809
Pyrosomas are the large group of pelagic tunicates whose trophicrole in pelagic communities has not yet been sufficiently studied.We ran across a local area of high concentration of the mostwidespread and commonest species of pyrosomas, Pyrosoma atlanticum,450 miles off the Congo river mouth. The following was estimated:gut pigment content, defecation rate, organic carbon and pigmentcontent of fecal pellets, and sinking rate. Based on these dataand the measured number of pyrosomas colonies the grazing impacton phytoplankton and the fecal pellet flux were calculated.During the night swarms of 5065 mm P.atlanticum removed53% of phytoplankton standing stock in the 010 m layer;sparsely distributed pyrosomas consumed only 4%. The grazingimpact in the 050 m layer was only 12.5 and <1% respectively.The fecal pellet flux resulting from nocturnal feeding of P.atlanticumwhile swarming made up 1.41.6 x 106 pellets m210 h1 or 3051035 mg C m2 10 h1 and1.4 x 105 pellets m2 10 h1 or 87.4 mg C m210 h1 while non-swarming. Incubation experiments showedthe rapid degradation of fecal pellets at 23°C: the lossof pigment and carbon content was {small tilde}6070%after 45 h. We believe that given the sinking rate of 70 m day1the main part of fecal material does not leave the upper watercolumn and is retained in the trophic web of the epipelagiclayer. 相似文献
11.
Grazing and ingestion rates of laboratory-born Thalia democraticaaggregates and Dolioletta gegenbauri gonozooids, phorozooidsand oozooids were determined while fed Isochrysis galbana (45µm diameter) alone or in combination with Peridinium trochoideum(1618 µm diameter) at concentrations of 0.150.70mm3 x 11. Grazing rates (ml x zooid1 x 24 h 1)ranged from 10 to 355, and at zooid weights greater than 5 µgcarbon were in order oozooid > gonozooid > aggregate.Grazing rates increased exponentially with increasing zooidweight. Weight-specific grazing rates (ml x µgC1x 24 h1) were independent of the four-fold initial foodconcentration. Mean weight-specific grazing rates increasedlinearly with increasing zooid weight for the aggregates andoozooids, but gonozooid mean rates were independent of zooidweight. Aggregate and gonozooid ingestion rates (106 µm3x zooid1 x 24 h1) ranged from 4 to 134 while oozooidrates ranged from 3 to 67. All ingestion rates were independentof the initial food concentration but increased linearly withincreasing zooid weight at similar rates. All mean weight-specificingestion rates (ml x µgC1 x 24 h1) wereindependent of zooid weight. The mean aggregate daily ration(µgC ingested x µg body C1) was 59% and themean doliolid ration was 132%. Field studies indicate that normalconcentrations of D. gegenbauri in the Georgia Bight clear theirresident water volume (1 m3) in about 4 months, but that highlyconcentrated, swarm populations which occur along thermohalinefronts clear their resident water volume in less than 1 day.
1Current address: MacLaren Plansearch Ltd., P.O.Box 13250, sta.A.,St.John's, Nfld. A1B 4A5 相似文献
12.
Dynamics of autotrophic picoplankton in Lake Constance 总被引:7,自引:0,他引:7
The vertical distribution, biomass concentrations and growthrates of autotrophic picoplankton (APP) were investigated duringthe growing season (March-October) in Lake Constance in differentdepths. Cell numbers determined by epifluorescence microscopyvaried between 1.0 x 103 and 1.6 times; 105 cells ml1depending on season and water depth. Highest concentrationswere recorded above the thermodine in late summer. Numerically,APP consisted almost exclusively of chroococcoid cyanobactena.During lake stratification several peaks of biomass concentrationsoccurred in epilimsietic waters at intervals of 68 weeks.In-situ experiments using a dilution technique and dialysisbags revealed that during summer APP population dynamics wereprimarily driven by combined changes of their growth and grazingrates, whereas temperature was less important. Gross growthrates varied between 0.006 and 0.051 h1, grazing ratesbetween 0.002 and 0.053 h1. On average APP productionwas completely removed by grazing within the microbial community.Ciliates, heterotrophic nanoflagellates and rotifers have beenidentified as the major consumers of APP cells. APP biomassis small compared to larger phytoplankton, ranging from ito5% of total phytoplankton biovolume. Due to its high gross growthrates, which are on the same level as those of free-living pelagicbacteria, APP contributes slightly more to overall primary productionwith maximum percentages of {small tilde}15% in late summer. 相似文献
13.
Density and distribution of bacterioplankton and planktonic ciliates in the Bering Sea and North Pacific 总被引:3,自引:0,他引:3
The total number of planktonic bacteria in the upper mixed layerof the Bering Sea during the late spring-early summer periodranged between 1 and {small tilde}4 x 106 ml1 (biomass1040mg C m3). In the northern Pacific, along 47526N,the corresponding characteristics of the bacterioplankton densityin the upper mixed water layer were: total number 12x 106 cells ml1 and biomass 1546mg C m3Below the thermocline at 50100 m, the density of bacterioplanktonrapidly decreased. At 300 m depth, it stabilized at 0.10.2x 106 cells ml1. The integrated biomass of bacterioplanktonin the open Bering Sea ranged between 1.2 and 3.6 g C m2(wet biomass 618 g m2) Its production per dayvaried from 2 to 23 mg C m3 days1 in the upper0100 m. The numerical abundance of planktonic ciliatesin this layer was estimated to be from 3 to l0 x 103 cells l1,and in the northern Pacific from 0.4 to 4.5 x 103 l2.Their populations were dominated by naked forms of Strombidium,Strombilidium and Tontonia. In some shelf areas, up to 40% ofthe total ciliate population was represented by the symbioticciliate Mesodinium rubrum. The data on the integrated biomassof basic groups of planktonic microheterotrophs are also presented,and their importance in the trophic relationships in pelagiccommunities of subarctic seas is discussed. 相似文献
14.
A strain of Coleps hirtus (Ciliophora, Prorodontida) was isolatedfrom the epilimnion of monomictic Lake Kinneret. Growth of thisciliate was tested in response to 12 species of planktonic algaeand seven species of cultured bacteria from lake isolates whichwere offered as food. Eight species of algae (one Cryptophyceaeand seven Chlorophyceae) and four bacteria supported good toexcellent growth of C.hirtus. Growth rates (µ) and doublingtimes (DT) ranged from 0.008 to 0.029 h1 and from 23.9to 90.8 h respectively. C.hirtus was able to grow on bacteriaat concentration levels as low as 28 x 105 cells ml1.No correlation was observed between growth rate of C.hirtusand cell volume of the prey.
aPresent address: Istituto di Ecologia, Universita di Parma,43100 Parma, Italy 相似文献
15.
Bacterial secondary production and rates of bacterivory weredetermined from samples collected from mesotrophic Lake Arlington.Bacterial production and losses were determined by comparingthe growth of natural bacterial assemblages in the presenceof predators (unfiltered samples) to growth in the absence ofpredators (water filtered through 1.0 (im porosity filters).Growth rates of heterotrophic nanoflagellates (HNF) were estimatedfrom growth in the absence of predators (water filtered through5.0 µm porojity filters). Bacterial growth rates rangedbetween 0.002 and 0.069 h1 and averaged 0.026 h1.HNF grew at rates ranging between 0.003 and 0.107 h1and averaged 0.028 h Grazing rates ranged between 0.002and 0.043 h1, and averaged 0.018 h. The annual averagerate of bacterial biomass synthesis was 3.2 g Clh1 and {small tilde}69% of this production was grazed.Temporal changes in growth and grazing rates suggest a tightlycoupled predator-prey linkage in this lake.
1Present address: Hydrobiological Institute, Czech Academy ofSciences, Na sddkach 7, 370 05 teski Budjovice, Czech Republic 相似文献
16.
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 day1 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 m3 day1. Theaverage seasonal production varied between 1.4 and 33 mg C m3day1 over 6 consecutive years. These small protozoa thuscontribute a substantial amount to total zooplankton productionin Lake Constance. 相似文献
17.
Annual variation in the abundance and size of heterotrophic nanoflagellates on the SW coast of Finland, the Baltic Sea 总被引:3,自引:0,他引:3
Annual variation and vertical distribution in the abundanceand cell volume of heterotrophic nanoflagellates (HNF) was studiedon the SW coast of Finland, the Baltic Sea. HNF cell numbersand mean cell volume varied annually from 90 to 104 cells ml1,and from 3 to 32 µm3, respectively, with maxima in earlysummer. The proportion of choanoflagellates in the HNF communitywas 023%. Statistical analysis revealed the verticaldifferences in HNF abundance to be insignificant, but verticaldifferences in the size structure of HNF communities were found,especially during thermal stratification. The majority (>80%)of HNF were small (maximum dimension 24 µm); theproportion of large (>7 µm) cells were only 24%of the HNF abundance. An empirical equation for the relationshipbetween HNF cell length and volume is presented, and the measurementof flagellate volume by epifluorescence microscopy is discussed. 相似文献
18.
Community structure, biomass and productivity of size-fractionated summer phytoplankton populations in lower Narragansett Bay, Rhode Island 总被引:1,自引:0,他引:1
Seventeen size-fractionation experiments were carried out duringthe summer of 1979 to compare biomass and productivity in the< 10, <8 and <5 µm size fractions with that ofthe total phytoplankton community in surface waters of NarragansettBay. Flagellates and non-motile ultra-plankton passing 8 µmpolycarbonate filters dominated early summer phytoplankton populations,while diatoms and dinoflagellates retained by 10 µm nylonnetting dominated during the late summer. A significant numberof small diatoms and dinoflagellates were found in the 108µm size fraction. The > 10 µm size fraction accountedfor 50% of the chlorophyll a standing crop and 38% of surfaceproduction. The <8 µm fraction accounted for 39 and18% of the surface biomass and production. Production by the< 8 µm fraction exceeded half of the total communityproduction only during a mid-summer bloom of microflagellates.Mean assimilation numbers and calculated carbon doubling ratesin the <8 µm (2.8 g C g Chl a1 h1; 0.9day1)and<5 µm(1.7 g C g Chl a1h1; 0.5day1)size fractions were consistently lower than those of the totalpopulation (4.8 g C g Chl a1 h1; 1.3 day1)and the <10 µm size fraction (5.8 g C g Chl a1h1; 1.4 day 1). The results indicate that smalldiatoms and dinoflagellates in fractionated phytoplankton populationscan influence productivity out of proportion to their numbersor biomass.
1Present address: Australian Institute of Marine Science, P.M.B.No. 3, Townsville M.S.O., Qld. 4810, Australia. 相似文献
19.
Food size selectivity was examined in Artemia franciscana metanaupliiat three different developmental stages. Clearance rates weredetermined in short-term experiments either by measuring thedecrease in concentration of live particles and plastic beads,or by measuring the radioactivity accumulated in animals thatgrazed 14C-labelled live particles. The maximum clearance rateofA.franciscana metanauplii increased during development andwas measured at 5063 µl ind.1 h1,254 µl ind.1 h1 and 1.482.10 ml ind.1h1 in 2-, 4- and 7-day-old metanauplii, respectively.A preference for particles with a diameter of 48 µmwas observed at all three developmental stages. The abilityof A.franciscana metanauplii to graze bacterial particles wasalso demonstrated, although the efficiency in grazing such smallparticles was low compared to microalgae (28, 20 and 9% of themaximum clearance rate in 2-, 4- and 7-day-old metanauplii,respectively). Electron microscopy showed that the inter-setulardistance in antennae and thoracopods was 0.20 ± 0.07,0.16 ± 0.05 and 0.18 ± 0.04 µm in 2-, 4-and 7-day-old metanauplii, respectively, and accordingly independentof stage. 相似文献
20.
Loliun perenne L. (cv.S. 23) was grown on vermiculite in winterin a heated greenhouse for 8 weeks under factorial combinationsof two potassium regimes (nominally 6 parts/106 and 156 parts/106in Hewitt's solution) and three densities of artificially supplementedvisible radiation flux (36.1, 7.3, and 2.2 W m2). Growthand potassium uptake were studied through the calculation ofvarious growth functions from fitted curves. There was little effect of potassium treatment but the experimentalmaterial responded markedly to light. Leaf-area ratio in thethree treatments showed extreme plasticity in increasing from23 x 102 through 6 x 102 to 89 x102 m2 g1 as light intensity decreased. Correspondingdecreases in unit leaf rate, however, caused over-all reductionsin relative growth rate. Specific absorption rates for potassium (AK, dry-weight basis)were strongly reduced at the lower light intensities but alsodisplayed complex ontogenetic drifts. Values of the allometricconstant, k (the ratio of root and shoot relative growth rates),decreased from c. 0.7 at 36.1 W m2 through c. 0.3 at7.3 W m2 to a value not significantly different fromzero (P < 0.05) at 2.2 W m2. In material grown under the two higher light intensities a constantinverse relationship was found between the mass ratio of rootand shoot and the corresponding activity ratio. The resultsconform to this model: Mass ratio = 0.001+45.0 (1/activityratio) where activity ratio is expressed as specific absorptionrate for potassium (in µg g root1 h1)/unitshoot rate (rate of increase of whole-plant dry weight per unitshoot dry weight, in mg g shoot1 h1). The implicationsof this relationship are discussed. 相似文献