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1.
The contribution of picophytoplankton to community structure in a Mediterranean brackish environment 总被引:3,自引:0,他引:3
The seasonal composition of phytoplankton communities was investigatedin a Mediterranean brackish area (Varano lagoon). Twelve stationswere sampled monthly from March 1997 to February 1998. Numbersof prokaryotic and eukaryotic picophytoplankton cells were estimatedby epifluorescence microscopy, while larger phytoplankton (nanoand micro fractions) were enumerated by the Utermöhl settlingtechnique. Picophytoplankton densities ranged from 0.7 to 448.6cells x 106 l1. Nano- and microphytoplankton abundancesvaried between 0.2 and 7.9 cells x 106 l1. The picoplanktonfraction was represented mainly by cyanobacteria and the Utermöhlfraction by nano-sized phytoflagellates (56.2%) and diatoms(20.1%). The phytoflagellates had a greater abundance over timewhile diatoms reached the highest densities in summer and fall.In Varano lagoon, phytoplankton development is related to nitrogen-poor'waters and to phosphorus availability. Suspension-feeding bivalves(Mytilus galloprovincialis) are sufficiently abundant to filtera volume equivalent to the volume of Varano lagoon at leastonce daily. These observations suggest that grazing exerts animportant influence on phytoplankton dynamics, mainly on themicro fraction, and that diatoms seem to play an important rolein the food web dynamics of this coastal fishery. 相似文献
2.
On the distribution and importance of picocyanobacteria in a boreal inshore area (Kiel Bight, Western Baltic) 总被引:5,自引:0,他引:5
From April to October 1986 abundance and vertical distributionof picocyanobacteria were studied at four stations in Kiel Fjordand Kiel Bight. Both picocyanobacteria and autotrophic, eukaryoticpicoplankton cell numbers were estimated by epifluorescencemicroscopy whereas larger phytoplankton (>3 µm) wasenumerated by the Utermöhi settling technique. Picocyanobactenacell numbers peaked in July and August near the water surface(1.42.6 x 108 cells l1). Although picocyanobacteriaabundance increased from the outer Kiel Bight to the more eutrophicinner stations of Kiel Fjord, their contribution to total phytoplanktonbiomass decreased. During summer up to 52% of phytoplanktoncarbon and up to 97% of autotrophic picoplankton carbon werecontributed by picocyanobacteria. Therefore picocyanobacteriaare an important component of the summer phytoplankton communityin boreal inshore waters, too. 相似文献
3.
Species-specific phytoplankton sedimentation in relation to primary production along an inshore--offshore gradient in the Baltic Sea 总被引:2,自引:0,他引:2
The temporal and spatial variability in the quality and quantityof settling phytoplankton material in relation to concurrentprimary production was studied using sediment traps at threecoastal stations from a semi-enclosed bay (Pojo Bay) throughthe outer archipelago to the open Gulf of Finland. The fluxof settling phytoplankton was high (9.3 g C m2period1)in Pojo Bay, especially in spring, and lower in the archipelago(8.1 g C m2 period1) and open-sea area (5.2 gC m"2 period"1), although the primary production followed theopposite pattern. A large influx of allochthonous material intoPojo Bay in spring brought allochthonous phytoplankton cellsinto the traps, but limited primary production. Diatoms werethe most abundant settled phytoplankton at all stations, butthe species composition varied between Pojo Bay (Aulacoseiraspp., Rhizosolenia minima) and the outer stations (Skeletonemacostatum, Chaetoceros spp.)At the outer stations, migratingdinoflagellates (Peridiniella catenate) comprised part of thesettling material in spring. The high settling flux of the cyanophyteAphanizomenon flos-aquae is discussed. The species compositionof the phytoplankton assemblage influenced the proportion ofthe total organic carbon sedimentation that consisted of phytoplanktoncarbon. 相似文献
4.
Dynamics of phytoplankton in the Great Barrier Reef Lagoon 总被引:1,自引:0,他引:1
The characteristics of the phytoplankton crop in the centralregion of the Great Barrier Reef were analyzed through two annualcycles together with basic oceanographic parameters. Chlorophylla standing crop and primary production were size fractionatedinto nanoplankton and microplankton components. Community compositionwas determined using the Utermöhl settling technique andcommunity diversities estimated by the Shannon-Weaver equation.The data and analysis are the most comprehensive in existencefor the region, and the first detailed study since the 192829Great Barrier Reef expedition. A marked seasonal cycle was identified,contrary to most assumptions, closely associated with precipitationpatterns and nutrients introduced by land drainage. The regionwould rank as mesotrophic with some eutrophic areas in the innerreaches of the Lagoon. Oscillatoria spp. accounted for a largefraction of the majority of phytoplankton maxima and were inverselyrelated to diatom crop densities even under conditions favoringdiatom growth. Microplankton crop species diversities usuallydecreased during extended Oscillatoria blooms. The reduced diversitypersisted after the bloom suggesting that Oscillatoria spp.were the source of extracellular metabolites and/or decompositionproducts adversely influencing diatom microplankton. 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.
Gocke Klaus; Hernandez Carlos; Giesenhagen Hanna; Hoppe Hans-Georg 《Journal of plankton research》2004,26(12):1429-1439
The seasonal development of bacteria was studied in the hypertrophiccoastal lagoon Ciénaga Grande de Santa Marta (Caribbeancoast of Colombia). This large but only 1.5 m deep lagoon issubject to strong seasonal variations of salinity from almostfully marine (April/May) to brackish conditions in October/November.Chlorophyll ranged from 6 to 182 µg L1, and grossprimary production amounted to 1690 g C m2 per year.Total bacterial number (TBN) ranged from 6.5 to 90.5 x 109 cellsL1 and bacterial biomass (BBM) from 77 to 1542 µgC L1, which are among the highest ever reported for naturalcoastal waters. Neither TBN nor BBM varied significantly withsalinity, phytoplankton or seston concentrations. Only the bacterialmean cell volume showed a significant relation to salinity,being highest (0.066 µm3) during the period of increasingand lowest (0.032 µm3) during decreasing salinity. Bacterialprotein accounted for 24% (1926%) and phytoplankton proteinfor 57% (5371%) of total seston protein. The ratio (annualmean) of bacterial carbon to phytoplankton carbon was 0.44 (range0.041.43). At low phytoplankton abundance [chlorophylla (Chl a) < 25 µg L1], bacterial carbon wasalmost equal to phytoplankton biomass (i.e. the mean ratio was1.04). In contrast, at Chl a > 100 µg L1, BBMwas low compared to phytoplankton biomass (the mean ratio was0.16). In general, BBM varied less than phytoplankton biomass.Most probably, the missing correlation between bacterial andphytoplankton variables was due to (i) organic material partlyderived from allochthonous sources serving as food resourcefor bacteria and (ii) a strong resuspension of bacteria fromthe sediment caused by frequent wind-induced mixing of the veryshallow lagoon. 相似文献
7.
The longitudinal and seasonal patterns of plankton developmentwere examined over 2 years in a lowland, temperate river: theRideau River (Ontario, Canada). Following an initial decreasein phytoplankton and zooplankton biomass as water flowed fromthe headwaters into the Rideau River proper, there was an increasein chlorophyll a (chl a) and zooplankton biomass with downstreamtravel. At approximately river km 60, both phytoplankton andzooplankton reached their maximum biomass of 27 µg l1(chl a) and 470 µg l1 (dry mass), respectively.Downstream of river km 60, the biomass of both planktonic communitiesdeclined significantly despite increasing nutrient concentrationsand favorable light conditions. These downstream declines maybe due to the feeding activity of the exotic zebra mussel (Dreissenapolymorpha) which was at high density in downstream reaches(>1000 individuals m2). There was no evidence forlongitudinal phasing of phytoplankton and zooplankton, as increasesand decreases in chl a and zooplankton biomass appeared to coincide.Overall, chl a was best predicted by total phosphorus (R2=0.43),whereas zooplankton biomass was best predicted by chl a (R2=0.20).There was no evidence for significant grazing effects of zooplanktonon phytoplankton biomass. 相似文献
8.
A study of the phytoplankton in Concarneau Bay (Bretagne, France)was carried out on 68 June, 1978. Autotrophy was measuredby the 14C method and heterotrophic activity was estimated by14C labelled glucose and protein hydrolysate uptake. The measurementswere made on the whole of the sample as well as on the bacterialfraction, isolated by size-fractionation on Nuclepore 3 µmfilters. Moreover, a study of the relationships between naturalphytoplanktonic and bacterial populations was possible becauseof cell counts. The phytoplankton shows coastal characteristicsand diatoms are dominant. The distribution of the genus Chaetoceros,Nitzschia and Leptocylindrus seems to have an influence on therelationship between algae and bacteria so that environmentalconditions not only interfere directly at the bacterial levelon heterotrophic activity, but also through the specific compositionand abundance of the phytoplankton. 相似文献
9.
The relationships between photosynthesis and photosyntheticphoton flux densities (PPFD, P-l) were studied during a red-tideof Dinophysis norvegica (July-August 1990) in Bedford Basin.Dinophysis norvegica, together with other dinoflagellates suchas Gonyaulax digitate, Ceratium tripos, contributed {small tilde}50%of the phytoplankton biomass that attained a maximum of 16.7µg Chla 1 and 11.93 106 total cells I1.The atomic ratios of carbon to nitrogen for D.norvegica rangedfrom 8.7 to 10.0. The photosynthetic characteristics of fractionatedphytoplankton (>30 µm) dominated by D.norvegica weresimilar to natural bloom assemblages: o (the initial slope ofthe P-l curves) ranged between 0.013 and 0.047 µg C [µgChla]1 h1 [µmol m s1]1the maximum photosynthetic rate, pBm, between 0.66 and 1.85µg C [µghla]1 h1; lk (the photoadaptationindex) from 14 to 69 µ,mol m2 s1. Carbonuptake rates of the isolated cells of D.norvegica (at 780 µmolm2 s1) ranged from 16 to 25 pg C cell1h and were lower than those for C.tripos, G.digitaleand some other dinoflagellates. The variation in carbon uptakerates of isolated cells of D.norvegica corresponded with PBmof the red-tide phytoplankton assemblages in the P-l experiments.Our study showed that D.norvegica, a toxigenic dinoflagellate,was the main contributor to the primary production in the bloom. 相似文献
10.
Studies were conducted over a 13 month period at four pelagicsites in eutrophic Lake Okeechobee, Florida (USA), in orderto quantify carbon (C) uptake rates by size-fractionated phytoplankton,and subsequent transfers of C to zooplankton. This was accomplishedusing laboratory 14C tracer methods and natural plankton assemblages.The annual biomass of picoplankton (<2 µm), nanoplankton(220 µm) and microplankton (<20 µm averaged60, 389 and 100 µg C 11 respectively, while correspondingrates of C uptake averaged 7, 51 and 13 µg C11h1. The biomass of microzooplankton (40200 µm)and macrozooplankton (<200 µm averaged 18 and 60 µgC 11, respectively, while C uptake rates by these herbivoregroups averaged 2 and 3 µg C 11 h1. Therewere no strong seasonal patterns in any of the plankton metrics.The ratio of zooplankton to phytoplankton C uptake averaged7% over the course of the study. This low value is typical ofthat observed in eutrophic temperate lakes with small zooplanktonand large inedible phytoplankton, and indicates ineffectiveC transfer in the grazing food chain. On a single occasion,there was a high density (<40 11) of Daphnia lumholrzii,a large-bodied exotic cladoceran. At that time, zooplanktoncommunity C uptake was <20 µg C 11 h1and the ratio of zooplankton to phytoplankton C uptake was near30%. If D.lumholrzii proliferates in Lake Okeechobee and theother Florida lakes where it has recently been observed, itmay substantially alter planktonic C dynamics. 相似文献
11.
The impact of grazing by natural assemblages of microzooplanktonwas estimated in an upwelling area (Concepción, Chile)during the non-upwelling season in 2003 and 2004. Seawater dilutionexperiments using chlorophyll a (Chl a) as a tracer were usedto estimate daily rates of phytoplankton growth and microzooplanktongrazing. Initial Chl a concentrations ranged from 0.4 to 1.4mg Chl a m3 and phytoplankton prey biomass and abundancewere numerically dominated by components <20 µm. Phytoplanktongrowth and microzooplankton grazing rates were 0.190.25day1 and 0.260.52 day 1, respectively.These results suggest that microzooplankton exert a significantremoval of primary production (>100%) during the non-upwellingperiod. 相似文献
12.
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
13.
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
14.
Cobelas M.Alvarez; Haering F.J.; Velasco J.L.; Rubio A. 《Journal of plankton research》1992,14(7):979-996
The seasonal time course of phytoplankton primary productivitywas studied weekly in a hypertrophic, gravel-pit lake closeto Madrid, Spain. Chlorophyll a ranged 22445 mg m2.Gross primary productivity attained 0.28±0.14 g C m2h1 (range: 0.060.60), its yearly value being 900g C m2, but the shallow euphotic depths and the highplankton respiration ensured that net productivity was generallylow. Respiration losses amounted to 0.31±0.24 g O2 m2h1, with phytoplankton respiration roughly attainingone-half of overall plankton respiration. Areal phytoplanktonproductivity and plankton respiration followed a seasonal trendbut this was not the case for photosynthetic capacity. Surfacephotoinhibition was evenly distributed throughout the study.Quantum yields showed an increasing depth trend, but no seasonaltrend. Both Pmax and Ik were both temperature- and irradiance-dependent.As compared with lakes of lesser trophic degree, phytoplanktonprimary production in hypertrophic lakes might be increasednot only by higher nutrient contents but also by low chlorophyll-specificattenuation coefficients and low background, non-algal attenuation,thereby allowing for higher areal chlorophyll contents and hencehigher areal productivity. Our study suggests that physical(irradiance and water column stability) as well as chemicalfeatures (dissolved inorganic carbon and soluble reactive phosphorus)may control seasonality of phytoplankton primary productionin this lake despite recent claims that only physical factorsare of significance in hypertrophic lakes. However, this doesnot explain all the variability observed and so a food web controlis also likely to be operating. 相似文献
15.
Cyanobacteria and cyanobacterial toxins in three alkaline Rift Valley lakes of Kenya--Lakes Bogoria, Nakuru and Elmenteita 总被引:4,自引:0,他引:4
Ballot Andreas; Krienitz Lothar; Kotut Kiplagat; Wiegand Claudia; Metcalf James S.; Codd Geoffrey A.; Pflugmacher Stephan 《Journal of plankton research》2004,26(8):925-935
For decades frequent mass mortalities of Lesser Flamingos (Phoeniconaiasminor Geoffroy) have been observed at alkaline-saline KenyanRift Valley lakes. To estimate the potential influence of toxiccyanobacteria on these mass deaths, the phytoplankton communitieswere investigated in Lakes Bogoria, Nakuru and Elmenteita. Cyanobacterialtoxins were analyzed both in the phytoplankton from the threelakes and in isolated monocyanobacterial strains of Arthrospirafusiformis, Anabaenopsis abijatae, Spirulina subsalsa and Phormidiumterebriformis. Lake Bogoria was dominated by the cyanobacteriumA. fusiformis. In L. Nakuru and L. Elmenteita the phytoplanktonmainly consisted of A. fusiformis, A. abijatae and Anabaenopsisarnoldii, and in L. Nakuru an unknown Anabaena sp. was alsofound. Furthermore, this is the first time A. abijatae and theunknown Anabaena sp. have been found in Kenyan lakes. Phytoplanktonwet weight biomass was found to be high, reaching 777 mg L1in L. Bogoria, 104 mg L1 in L. Nakuru and 202 mg L1in L. Elmenteita. Using HPLC, the cyanobacterial hepatotoxinsmicrocystin-LR, -RR -YR, -LF and -LA and the neurotoxin anatoxin-awere detected in phytoplankton samples from L. Bogoria and L.Nakuru. Total microcystin concentrations amounted to 155 µgmicrocystin-LR equivalents g1 DW in L. Bogoria, and 4593µg microcystin-LR equivalents g1 DW in L. Nakuru,with anatoxin-a concentrations at 9 µg g1 DW inL. Bogoria and 223 µg g1 DW in L. Nakuru. In L.Elmenteita phytoplankton, no cyanobacterial toxins were found.A. fusiformis was identified as one source of the toxins. Theisolated strain of A. fusiformis from L. Bogoria was found toproduce both microcystin-YR (15.0 µg g1 DW) andanatoxin-a (10.4 µg g1 DW), whilst the A. fusiformisstrain from L. Nakuru was found to produce anatoxin-a (0.14µg g1 DW). Since A. fusiformis mass developmentsare characteristic of alkaline-saline lakes, health risks towildlife, especially the Arthrospira-consuming Lesser Flamingo,may be expected. 相似文献
16.
Uptake of 13C and 15N (ammonium, nitrate and urea) by Microcystis in Lake Kasumigaura 总被引:1,自引:0,他引:1
The uptake rate of carbon and nitrogen (ammonium, nitrate andurea) by the Microcystis predominating among phytoplankton wasinvestigated in the summer of 1984 in Takahamaira Bay of LakeKasumigaura. The Vmax values of Microcystis for nitrate (0.0250.046h1) and ammonium (0.150.17 h1) were considerablyhigher than other natural phytoplankton. The ammonium, nitrateand urea uptake by Microcystis was light dependent and was notinhibited with nigh light intensity. The K1 values were farlower than the Ik values. The carbon uptake was not influencedby nitrogen enrichment. Microcystis accelerated the uptake rateby changing Vmax/K s value when nitrogen versus carbon contentin cells declined. Nitrate was scarcely existent in TakahamairiBay during the summer, when Microcystis usually used ammoniumas the nitrogen source. However, the standing stock of ammoniumin the water was far lower than the daily ammonium uptake rates.Therefore, the ammonium in this water had to be supplied becauseof its rapid turn-over time (0.72.6 h). 相似文献
17.
Shiomoto Akihiro; Tadokoro Kazuaki; Monaka Kojo; Nanba Masaaki 《Journal of plankton research》1997,19(7):907-916
We determined the productivity (µg C µg1Chi a h1) of size-fractionated phytoplankton in the northernNorth Pacific and the Bering Sea in summer and winter. Picoplankton(<2 µm) were more productive than larger sized phytoplankton(210 and 10200 µm) in the subtropical region,where the in situ temperature was >10°C; whereas picoplanktonin the subarctic region were similar in productivity or lessproductive than larger sized plankton, where the in situ temperaturewas <10°C. The result from the subtropical region inthis study agrees with previous results from tropical and subtropical waters, which indicate that phytoplankton productivitytends to decrease with increasing cell size. The result fromthe subarctic region, however, differs from previous results.We observed a positive linear regression for in situ temperatureand picoplankton productivity, but this trend was not seen inthe larger sized phytoplankton. The results show that the productivityof picoplankton is markedly influenced by in situ temperaturecompared with that of larger sized plankton. Low tem peratureappears to account largely for the observation that the productivityof picoplankton is not significantly higher than that of largersized phytoplankton in the subarctic region. 相似文献
18.
Estimation of the biomass of some components of the marine nano-and picoplankton is made for several locations using the Utermohlsettling technique. The importance of these small cells in thephytoplankton biomass is confirmed. The proportion of cellsof 212 µm diameter in the total phytoplankton biomassis usually lower than the proportion of primary productivityattributed to a similar size fraction in the literature. Dataare presented on geographical and vertical distributions ofsome <2 µm and 212 µm organisms. At theoceanic stations and at offshore sites the latter make up ahigher percentage of the total biomass than in the coastal areasbut their numerical abundance is lower. Depth distributionsare variable but oceanic profiles show a decrease in abundancewith depth. The Utermöhl technique is evaluated as a continuingmethod for biomass estimation. 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.
Contribution of Picocyanobacteria to total primary production and community respiratory losses in a backwater system 总被引:2,自引:0,他引:2
The contribution of autotrophic picoplankton (APP) to phytoplanktonicprimary production, investigated during the phytoplankton growingseason (MarchSeptember) in a macrophyte-dominated backwatersystem near Vienna, showed that APP mainly consisted of rod-shapedand coccoid cyanobacteria. Two stations were examined, exhibitingsimilar seasonal patterns in the development of picocyanobacteria,although the two sites differed in picocyanobacterial cell numbersand biomass by a factor of 1.5. Cell numbers determined by epifluorescencemicroscopy varied between 0.29 x 104 and 34.5 x 104 cells ml1at Station 1, and between 0.23 x 104 and 19.1 x 104 cells ml1at Station 2. At both sites, the mean cell volume of picocyanobacteriawas 0.5 µm3. Carbon fixation in the planktonic communityof the Kühwörter Wasser was dominated primarily bylarger phytoplankton, although the picoplankton community sometimessupplied up to 74% (mean: 35%) of total primary production.Distinct differences in chlorophyll a concentrations and primaryproduction between the two sites refer to a greater competitionbetween phytoplankton and macrophytes at Station 2. Communityrespiration deviated greatly in time and in level at the twostations, showing a higher dynamic in community metabolism atStation 1. At this site, community respiration losses rangedbetween 12 and 100% of gross production. Hence, community metabolismcomprised net autotrophic, balanced, and net heterotrophic situationsover the investigation period, whereas at Station 2, only netautotrophic situations could be determined. 相似文献