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1.
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
2.
The effect of detrital addition on the development of nanoflagellates and bacteria in Lake Kinneret 总被引:1,自引:0,他引:1
Hadas O.; Pinkas R.; Albert-Diez C.; Bloem J.; Cappenberg T.; Berman T. 《Journal of plankton research》1990,12(1):185-199
The effect of adding dissolved substrates derived from algalcells on the patterns of nutrient cycling and growth of bacteria,heterotrophic nanoflagellates (HNAN) and photoautotrophs wasdetermined in samples of near-surface waters from Lake Kinneret.Supplementation of substrates always resulted in an increasedpeak of HNAN numbers and had little effect on bacterial numbers.HNAN-mediated nutrient remineralization of nitrogen and phosphoruswas also stimulated. In light-incubated samples the remineralizednutrients were taken up by photoautotrophic cells. Maximum growthrates observed for HNAN ranged from 0.03 to 0.11 h1,clearance rates for bacteria 1.17.3 nl HNAN1 h1and remineralization rates 6.48.4 µg N mg dry wt1h1 and 0.370.99 µg P mg dry wt1 h1. 相似文献
3.
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
4.
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
5.
Fish-induced changes in zooplankton grazing on phytoplankton and bacterioplankton: a long-term study in shallow hypertrophic Lake Sobygaard 总被引:1,自引:0,他引:1
Jeppesen Erik; Sondergaard Martin; Jensen Jens Peder; Mortensen Erik; Sortkjaer Ole 《Journal of plankton research》1996,18(9):1605-1625
The impact of fish-mediated changes on the structure and grazingof zooplankton on phytoplankton and bacterioplankton was studiedin Lake Søbygaard during the period 198492 bymeans of in vitro grazing experiments (14C-labelled phytoplankton,3H-labelled bacterioplankton) and model predictions. Measuredzooplankton clearance rates ranged from 025 ml l1h1 on phytoplankton to 033 ml l1 h1on bacterioplankton.The highest rates were found during thesummer when Daphnia spp. were dominant. As the phytoplanktonbiomass was substantially greater than that of bacterioplanktonthroughout the study period, ingestion of phytoplankton was26-fold greater than that of bacterioplankton. Multiple regressionanalysis of the experimental data revealed that Daphnia spp.,Bosmina longirostris and Cyclops vicinus, which were the dominantzooplankton, all contributed significantly to the variationin ingestion of phytoplankton, while only Daphnia spp. contributedsignificantly to that of bacterioplankton. Using estimated meanvalues for clearance and ingestion rates for different zooplankters,we calculated zooplankton grazing on phytoplankton and bacterioplanktonon the basis of monitoring data of lake plankton obtained duringa 9 year study period. Summer mean grazing ranged from 2 to4% of phytoplankton production and 2% of bacterioplankton productionto maxima of 53 and 88%, respectively. The grazing percentagedecreased with increasing density of planktivorous fish caughtin August each year using gill nets and shore-line electrofishing.The changes along a gradient of planktivorous fish abundanceseemed highest for bacterioplankton. Accordingly, the percentagecontribution of bacterioplankton to the total ingestion of thetwo carbon sources decreased from a summer mean value of 8%in Daphnia-dominated communities at lower fish density to 0.71.1%at high fish density, when cyclopoid copepods or Bosmina androtifers dominated. Likewise, the percentage of phytoplanktonproduction channelled through the bacteria varied, it beinghighest (58%) at high fish densities. It is argued thatthe negative impact of zooplankton grazing on bacterioplanktonin shallow lakes is highest at intermediate phosphorus levels,under which conditions Daphnia dominate the zooplankton community. 相似文献
6.
Nutrient cycling through phytoplankton, bacteria and protozoa, in selectively filtered Lake Vechten water 总被引:2,自引:0,他引:2
Bloem Jaap; Albert Claudia; Bar-Gillissen Marie-Jose B.; Berman Thomas; Cappenberg Thomas E. 《Journal of plankton research》1989,11(1):119-131
The breakdown of organic carbon of dead Synechococcus cell walls,added to selectively filtered Lake Vechten water, was not acceleratedby protozoa. During 4 weeks of incubation at 15°C no significantdecrease of total organic carbon was observed. However, heterotrophicnanoflagel-lates (HNAN) and ciliates strongly increased theremineralization of N and especially P, from both cell wallsand cell extract. Bacterioplankton growth did not result innet P mineralization but in P uptake. P was remineralized onlyin the presence of protozoan grazers. Both HNAN and ciliatesgrazed on bacteria, with ingestion rates estimated at 2796bad HNAN1 h1 and 129 bact ciliate1 h1respectively. Grazers increased N mineralization too, althoughN was also mineralized in the absence of protozoa. The phytoplanktoncell walls yielded less P but more N remineralization than thecell extract. Thus, protozoa can strongly accelerate cyclingof specific nutrients through plankton. Nuclepore filters werefound to cause artificial DOC release during selective filtration. 相似文献
7.
Diurnal and seasonal variation in the contributions of autotrophic pico-, nano- and microplankton to the primary production of an upland lake 总被引:7,自引:0,他引:7
An investigation of the diurnal variation in productivity andcontribution to production of populations of autotrophic picoplankton(0.22.0 µm), nanoplankton (>2 <20 µm)and microplankton (>20 µm) was carried out at monthlyintervals, from May to October 1989, in Llyn Padarn a mesotrophicupland lake in North Wales. Maximum rates and contributionsto production of the lake by autotrophic picoplankton occurredduring mid-late summer, with the highest average daily contributionfrom picoplankton (64%) recorded in September at 4 m depth.Diurnal variation in contributions from picoplankton was pronounced,with greatest input, recorded at the end of the day, duringthe period of picoplankton dominance in mid-late summer. Maximumcontribution from picoplantkon (86% of total, 9.2 mg C m3h1) was recorded in September. Nanoplankton primary productionwas of greatest significance in June and July, although levelswere lower than for picoplankton in subsequent months. Contributionsvia nanoplankton increased with depth in the lake at this time,reaching a maximum of 78% of the total at the end of the dayat 9 m depth in early July. At this time, diurnal variationin contributions via nanoplankton was considerable, with maximumphotosynthesis generally at the end of the photoperiod at depthsof 4 and 9 m. Microplankton made the greatest impact on primaryproduction during the mixed water conditions of spring and autumn,and at these times did variation in production was less thanthose of both pico and nanoplankton during summer thermal stratification.Photosynthetic capacity was lower for picoplankton than fornanoplankton and microplankton; the highest values were 5, 33and 51 mg C (mg chl a)1) h1) for pico-, nano-and microplankton, respectively. The photosynthetic efficiencyof all three size categories of phytoplankton increased withdepth. Maximum values were similar for all phytoplankton groups,between 75 and 131 mg C (mg chl a)1) E1) m2 butmean levels of photosynthetic efficiency for the 6 months werelower for picoplankton than for nano- or microplankton. Ratesof carbon fixation per cell for picoplankton spanned three ordersof magnitude, varied considerably diurnally and reached maximumvalues of 484 fg C(cell)1) h1) in the afternoonin near-surface waters in the early stages of exponential populationgrowth in July. During the population maximum of picoplanktonin August and September, maximum daily values of carbon fixationper cell, assimilation number and photosynthetic efficiencywere all recorded at the end of the day. The seasonal and diurnalpatterns of production of the three size categories of planktonicalgae in Llyn Padarn were distinct. During spring, microplankton(mainly diatoms) were the dominant primary producers. As thermalstratification developed, nanoplankton were the major contributorsto phytoplanktonic production, particularly in the deeper regionsof the euphotic zone. Picoplankton made the greatest contributionto production in August and September, exhibiting maximum inputtowards the end of the light cycle. Diatoms became the majorphotosynthetic plankton in the mixed water conditions prevalentin Uyn Padarn in October. 相似文献
8.
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
9.
Particulate and dissolved phytoplankton production of the Patos Lagoon estuary, southern Brazil: comparison of methods and influencing factors 总被引:3,自引:0,他引:3
Abreu Paulo C.; Odebrecht Clarisse; Gonzlez Adriana 《Journal of plankton research》1994,16(7):737-753
Uptake rates of 14C (filtration and the acidification-bubblingmethodABM) were measured weekly in a shallow region ofthe Patos Lagoon estuary (3207'S, 5206'W) between March 1989and March 1990. Phytoplankton production varied seasonally,the lowest values occurring in the austral winter (JuneAugust1989) and the highest rates during spring and summer (March1989; September 1989March 1990). Particulate carbon productionvaried between 0.65 and 70.6 mg C m3 h1 and wasmostly associated with organisms <20 µm (mean = 73.4%).Dissolved organic carbon (DOC) released by phytoplankton variedbetween 0.1 and 89.3 mg C m3 h1 representing 相似文献
10.
Biomass, feeding and production of Noctiluca scintillans in the Seto Inland Sea, Japan 总被引:1,自引:0,他引:1
The abundance and biomass of the large heterotrophic dinoflagellateNoctiluca scintillans, together with the changes in its potentialprey items, were monitored in the Seto Inland Sea, Japan, duringsummer 1997 (17 July-11 August). Growth and grazing rates ofNscintillans fed natural plankton populations were also measuredeight and seven times, respectively, during the survey period.The abundance and biomass of N scintillans averaged over thewater column (19 m) were in the range 1345 cells 11(temporalaverage = 93 cell11) and 0.149.6 µg C l1(temporalaverage = 13.8 µg C l1; three times higher thanthat of calanoid copepods during the same period). Noctilucascintillans populations followed the changes in phytoplankton:N.scintillans biomass was increasing during the period of diatomblooms and was at a plateau or decreasing during periods oflow chlorophyll a. The growth rates of N.scintillans (µ)were also consistent with the wax and wane of the N.scintillanspopulation: N.scintillans showed highest growth rates duringdiatom blooms. A simple relationship between µ and chlorophylla concentration was established, and the production of N.scintillanswas estimated using this relationship and the measured biomass.The estimated production averaged over the water column wasin the range >0.15.2 µg C l1 day1(temporalaverage = 1.4 µg C l1 day1; 64% of the productionof calanoid copepods during the same period). Diatom clearancerates by N.scintillans were in the range 0.100.35 mlcell1 day1, and the phytoplankton population clearanceby N.scintillans was >12% day1. Thus, although thefeeding pressure of N.scintillans on phytoplankton standingstock was low, N.scintillans was an important member of themesozooplank-ton in terms of biomass and production in the SetoInland Sea during summer. 相似文献
11.
Palomares-Garcia Ricardo; Bustillos-Guzman J. J.; Lopez-Cortes D. 《Journal of plankton research》2006,28(12):1217-1232
Phytoplankton growth and microzooplankton grazing rates wereevaluated in one station in Bahía Concepción,located in the middle region of the Gulf of California, México.We used high-performance liquid chromatography (HPLC) estimationsof phytoplankton pigment signatures to evaluate the annual variationof taxon-specific grazing and growth rates obtained with thedilution technique. Chlorophyll-a (Chl-a) concentrations variedwidely (0.343.32 µg L1) and showed two maxima,during late spring and autumn, associated with the transitionbetween mixed and stratified conditions. Phytoplankton growthrates varied seasonally with the lowest rates during summer(range: 0.012.55 day1 for Chl-a; 0.003.84day1 for Chl-b; 0.263.29 day1 for fucoxanthin;0.006.27 day1 for peridinin; 0.004.35 day1for zeaxanthin). Microzooplankton grazing was an important lossprocess (range: 0.01.89 day1 for Chl-a; 0.003.12day1 for Chl-b; 0.263.29 day1 for fucoxanthin;0.002.03 day1 for peridinin; 0.003.51 day1for zeaxanthin). Average grazing rates accounted 6889%of estimated average phytoplankton pigment-specific growth rates.The analysis of pigment signatures indicates that diatoms anddinoflagellates were the dominant groups, and contrary to expectationfor typical subtropical lagoons, the specific growth rates inBahía Concepción showed a pronounced seasonalvariability, linked to transitional hydrographic conditions.Our results indicate a close coupling between the communitymicrozooplankton grazing and phytoplankton growth rates, withoutselective feeding behavior. These results suggest that microzooplanktonplay a critical role and may significantly modify the availabilityand efficiency of transfer of energy to higher trophic levels. 相似文献
12.
A dual radioactive-labelled bacteria technique using Vibrio(DRLV), developed for laboratory studies on bacterivory, hasbeen refined for use at the concentrations of prey and predatorstypcially found at sea. Experiments with estuarine water collectedin spring and in autumn showed that bacterivorous nanoflagellates(HNF) (concentration 1.38±0.35x103 HNF ml1) ingested2.7±0.96 DRLV flagellate11 h1 at concentrationsof 0.82.2x106 DRLV ml1 in the presence of 2.04±0.68x106natural bacteria ml1. The method was also applied tosamples collected in October in the Celtic Sea, when on average1 ml of water from the surface layer contained 1.41±0.16x106natural bacteria, 14.6x103 cyanobacteria, 530±170 HNF,7.3±3.0x103 phototrophic nanoflagellates (1.54µm), 49.0±26.5 phototrophic dinoflagellates, 36.3±12.6heterotrophic dinoflagellates and 21.3±9.5 Leucocryptosmarina. Under these conditions the grazing rate in most samplesdid not exceed the coefficient of variation of the method (2%),although we estimate the grazing rate was -1.6 DRLV HNF1h1 and on one occasion a rate of 2.45 was recorded. Thegross growth efficiency for protein of -30% displayed by naturalHNF means that they could release about 相似文献
13.
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
14.
Malinsky-Rushansky Nechama Z.; Berman T.; Dubinsky Z. 《Journal of plankton research》1997,19(8):979-993
Autotrophic picoplankton populations in Lake Kinneret are composedof picocyanobacteria and picoeukaryotes. Overall, the ratesof photosynthetic carbon fixed by autotrophic picoplankton duringthis study were low (0.011.5 mg Cm3 h1).The highest chlorophyll photosynthetic activity of the <3µm cell-size fraction was found in spring, when picoeukaryotespredominated and in addition small nanoplankton passed throughthe filters. The maximum cell-specific photosynthetic rate ofcarbon fixation by picocyanobacteria and picoeukaryotes was2.5 and 63 fg C cell1 h1, respectively. The highestspecific carbon fixation rate of autotrophic picoplankton was11 µg C µg1 Chl h1 The proportionalcontribution of autotrophic picoplankton to total photosynthesisusually increased with depth. Picocyanobacteria collected fromthe dark, anaerobic hypolimnion were viable and capable of activephotosynthesis when incubated at water depths within the euphoticzone. Maximum rates of photosynthesis (Pmax) for picocyanobacteriaranged from 5.4 to 31.4 fg C cell1 h1 with thehighest values in hypolimnetic samples exposed to irradiance.Photosynthetic efficiency ( 相似文献
15.
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
16.
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
17.
The uptake of bacteria and picoplankton sized fluorescentlylabelled beads was measured off the west coast of the SouthIsland of New Zealand in winter. Phytoflagellates and heterotrophicflagellates showed similar grazing rates on 0.49 µm beads,with mean clearance rates of 1.1 and 1.8 nl ind.1 h1,respectively. Clearance rates for 1.09 µm beads were 0.9nl ind.1 h1 for heterotrophic flagellates and0.5 nl ind.1 h1 for phytoflagellates. Non-loricateciliates had clearance rates of 1.5 µl ind.1 h1for the picoplankton sized particles. The heterotrophic flagellatesshowed no significant difference between clearance rates of0.49 and 1.09 µm particles. Phytoflagellates, however,showed an apparent preference for the smaller particles. Themeasurement of significant grazing by phytoflagellate populationsin the marine environment is important and indicates that weneed to reassess our concepts of food web structure. 相似文献
18.
Collos Y.; Vaquer A.; Johnston A. M.; Pons V.; Bibent B.; Richard S. 《Journal of plankton research》2001,23(3):263-270
Ammonium uptake and regeneration were measured in the euphoticzone of Petit Saut Lake, French Guyana, to examine nitrogencycling in this recently flooded equatorial forest environment.Am-monium regeneration rates were extremely high (mostly inthe range 16 µmol N l1 h1), and aredue to the very high grazing rates of the microzooplankton,which consumed between 56 and 95% of the phytoplankton productionin any given incubation. These regeneration rates were aboutan order of magnitude higher than the net ammonium uptake rates.This imbalance is probably due to dissolved organic nitrogenrelease during grazing. At the bottom of the euphotic zone (45m), photosynthetic bacteria are responsible for ammonium uptake.Diffusion-driven ammonium fluxes are an order of magnitude lowerthan biologically driven fluxes. Therefore, ammonium fluxesare dominated by biology rather than by physics in this lake. 相似文献
19.
Copepod abundance in the western Irish Sea: relationship to physical regime, phytoplankton production and standing stock 总被引:1,自引:0,他引:1
Gowen R.J.; McCullough G.; Dickey-Collas M.; Kleppel G.S. 《Journal of plankton research》1998,20(2):315-330
The distinct patterns of stratification in the North Channeland stratified region of the western Irish Sea influence theseasonal abundance of phytoplankton. The 34 month productionseason in the stratified region was characterized by productionand biomass peaks in the spring (up to 2378 mg C m2 day1and 178.4 mg chlorophyll m2) and autumn (up to 1280 mgC m2 day1 and 101.9 mg chlorophyll m2).Phytoplankton in the North Channel exhibited a short, late productionseason with a single summer (June/July) peak in production (4483mg Cm2 day1) and biomass (160.6 mg chlorophyllm2). These differences have little influence on copepoddynamics. Both regions supported recurrent annual cycles ofcopepod abundance with similar seasonal maxima (182.8241.8103ind. m2) and dominant species (Pseudocalanus elongatusand Acartia clausi). Specific rates of population increase inthe spring were 0.071 and 0.048 day1 for the North Channel andstratified region, respectively. Increased copepod abundancein the stratified region coincided with the spring bloom, andwas significantly correlated with chlorophyll standing stock.Increased copepod abundance preceded the summer production peakin the North Channel. This increase was not correlated withchlorophyll standing crop, suggesting that a food resource otherthan phytoplankton may be responsible for the onset of copepodproduction prior to the spring bloom. Hetero-trophic microplanktonas an alternative food source, and advection of copepods fromthe stratified region, are proposed as possible explanationsfor copepod abundance increasing in advance of the summer peakin primary production. 相似文献
20.
Conspicuous Peak of Oligotrichous Ciliates Following Winter Stratification in a Bog Lake 总被引:2,自引:0,他引:2
We analysed early spring protozooplankton peaks following winterstratification in two different basins (northeast, NE; southwest,SW) of an artificially-divided bog lake Große Fuchskuhle(Brandenburg,Germany). The maximum ciliate biomass and numbers (660 and 990µg l1 of organic carbon, and 290 and 260 cellsml1 in NE and SW, respectively) were reached in the surfacelayer during the ice melting and then continuously decreased.The surface layers were numerically dominated by species ofthe genus Urotricha, while in the ciliate biomass during thefirst part of the study, a mixotrophic oligotrich, Pelagostrombidiummirabile prevailed (Corg up to 940 µg l1). We observeda conspicuous ciliate peak that could not be related to thefeeding activity of the dominant ciliate species upon picoplankton.Seemingly, the peak was related to the specific conditions resultingfrom the ice melting where these ciliates could be concentrated.Additionally, the mixotrophy of oligo-trichous species allowedthem to penetrate below the oxycline, although feeding on nanoplanktonsuch as flagellates was also very likely. Our direct measurementsof uptake rates of bacteria showed that the abundant strombidiidswere not nutritionally dependent on bacterivory. However, theciliate uptake rate (up to 670 bacteria ciliate1 h1)contributed significantly to the overall bacteria mortalityrate. The maximum (community average) cell-specific ciliatefeeding rate of over 200 bacteria ciliates1 h1was reached, along with an increasing contribution of scuticociliates,paralleled by a drop in large oligotrichs. 相似文献