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1.
The structure of ciliated cells from the siphon of Solen capensishas been studied by both scanning and transmission electronmicroscopy. Two types of ciliated cell, based on the numberand length of cilia have been described which resemble thosedescribed in Donax. Type I is characterized by having 2657({macron}= 43, n = 50) cilia which are 2.5 µm in length;Type II has fewer cilia (510; {macron}= 7) which are5 µn long. Both are primary receptors. Estimations ofabundance show that receptors are most numerous on the tipsof the siphon tentacles (8.8 x 103/mm2). (Received 15 January 1985; 相似文献
2.
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
3.
Limiting effect of abioseston on food ingestion, postembryonic development time and fecundity of daphnids in Lake Balaton (Hungary) 总被引:2,自引:0,他引:2
During ice-free periods, seston ranges from 10 to 600 and averages29.2 mg dry wt 11 in Lake Balaton, the largest shallowlake in Central Europe. Most (8099%) of the seston consistsof 110 µm sized mineral particles. The abiosestoncauses permanent food limitation in the ingestion of the ediblephytoplankton (122 µm fraction) by Daphnia cucullataand D.galeata. The postembryonic development time of D.galeataincreases and its fecundity decreases with increasing abioseston.The fecundity and the mortality of D.galeata are balanced atan abioseston concentration of 20.0 mg dry wt 11. 相似文献
4.
Photosynthetic 14C fixation by Characean cells in solutionsof high pH containing NaH14CO3 gave a measure of the abilityof these cells to take up bicarbonate (H14CO3). Whereascells of Nitella translucens from plants collected and thenstored in the laboratory absorbed bicarbonate at 11.5µµmoles cm2 sec1, rates of 38µµmoles cm2 sec1 were obtained withN. translucens cells from plants grown in the laboratory. Influxesof 56 µµmoles cm2 sec1 wereobtained with Chara australis, 38 µµmolescm2 sec1 with Nitellopsis obtusa, and 15µµmoles cm2 sec1 with Tolypella intricata.It is considered that these influxes represent the activityof a bicarbonate pump, which may be an electrogenic process. In solutions of lower pH, H14CO3 uptake would be maskedby rapid diffusion of 14CO2 into the cells: the four Characeanspecies fixed 14CO2 at maximum rates of 3040 µµmolescm2 sec1 (at 21° C). 相似文献
5.
The secondary gill of the pulmonate limpet Siphonaria capensisis located in the dorsal portion of the mantle cavity. Eachlamella of the gill is triangular in shape and bears ciliarytufts which have a density of about 400/mm2. The free ends ofsome of the cilia are enlarged biconcave discs. Each gill lamellais covered by a single layer of cuboidal (4x4 µm) epitheliumon each side, separated by a central haemocoelic space. Ciliatedand mucus secreting cells are interspersed amongst the epithelialcells. The haemocoelic space is spanned at intervals by trabeculaecontaining longitudinal and transverse muscle fibres. (Received 29 August 1986; 相似文献
6.
The ultrastructure of the pallial tentacles of seven speciesof patellid limpet is described. The tip of most of the tentaclesexamined bears a crown of long cilia, whereas the shaft of thetentacles has small tufts (510 µm diameter) ofshorter cilia. Sections through the ciliated tufts show themto be composed of several cells, each bearing cilia. The ciliacontain 57 central microtubules and therefore do nothave the conventional 9 + 2 arrangement of microtubules. Nerveprocesses run from the base of each ciliated cell to a nervebundle in the centre of the tentacle, suggesting a sensory function.Estimates of densities of ciliated tufts suggest that the territoriallimpets (Patella cochlear and P. longicosta) have the greaternumber of tufts. Electron dense plate-like structures are foundin the centre of the pallial tentacles of Patella cochlear,P. longicosta, P. granularis, P. barbara and Helcion pruinosus.Each plate is about 0.2 µm wide and is surrounded by adouble membrane. It is suggested that these may play a rolein scattering or reflecting light and thus form part of thedermal light sensing ability of these animals. (Received 26 January 1987; 相似文献
7.
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
8.
Water exchange, temperature tolerance and oxygen consumptionof the snail, Trigonephrus sp., from the southern Namib desertof Namibia were examined and related to activity. At 25°Cand 15% R.H. mean water loss and food and water uptake were5.95 mg. day1 and 630 mg.day1, respectively. Bodytemperature tracked sand temperature. Snails tolerated sandtemperatures as high as 45°C. Mean ± S.D. oxygenconsumption rates were 32.0 ± 2.94 µlO2.g totalbody mass1.h1 at 15°C, when the snails wereactive, and 11.27 µlO2.g total body mass1.h1at 25°C, when the snails were inactive. These values are2-6 times lower than those recorded for the similarly sizedmesic snail, Helix aspersa. Activity experiments indicated thatlow ambient temperatures and high humidities were favoured bythe snails. This, together with the burying behaviour of thesesnails during high temperatures, suggests that they limit stressby restricting activity to physiologically-favourable periods,even though more-extreme conditions may be tolerated. (Received 7 June 1990; accepted 20 November 1990) 相似文献
9.
Yield stress threshold (Y) and volumetric extensibility () arethe rheological properties that appear to control root growth.In this study they were measured in wheat roots by means ofparallel measurement of the growth rate (r) of intact wheatroots and of the turgor pressures (P) of individual cells withinthe expansion zone. Growth and turgor pressure were manipulatedby immersion in graded osmoticum (mannitol) solutions. Turgorwas measured with a pressure probe and growth rate by visualobservation. The influence of various growth conditions on Yand was investigated; (a) At 27 °C.In 0.5 mol m3 CaCl2 r, P, Y and were20.7±4.6 µm min1, 0.77±0.05 MPa,0.07±0.03 MPa and 26±1.9 µm min1MPa1 (expressed as increase in length), respectively.Following 24 h growth in 10 mol m3 KC1 these parametersbecame 12.3±3.5 µm min1, 0.72±0.04MPa, 0.13±0.01 MPa and 21±0.7 µm min1MPa1. After 24 h osmotic adjustment in 150 mol m3mannitol/0.5 mol m3 CaCl2 r= 19.6±4.2 µmmin1, P = 0.68±0.05 MPa and Y and were 0.07±0.04MPa and 30±0.2 µm min1 MPa01, respectively.After 24 h growth in 350 mol m3 mannitol/0.5 mol m3CaCl2 r= 13.3±4.1 µm min1, P= 0.58±0.07MPa, Y=0.12±0.01 MPa and ø 32±0.2 tim min1MPa1. During osmotic adjustment in 200 mol m3mannitol/0.5 mol m3 CaCl2, with or without KCl, the recoveryof growth rate corresponded to turgor pressure recovery (t1/2approximately 3 h). (b) At 15 °C. Lowered temperature dramatically influencedthe growth parameters which became r= 8.3±2.8 um min1,P=0.78 MPa, r=<0.2 MPa and =15±0.1 µm min1MPa1. Therefore, Y and are influenced by 10 mol m3 K+ ionsand low temperature. In each case the effective pressure forgrowth (P-Y) was large indicating that small fluctuations ofsoil water potential will not stop root elongation. Key words: Yield threshold, cell wall extensibility, wheat root growth, temperature, turgor pressur 相似文献
10.
Katechakis Alexis; Stibor Herwig; Sommer Ulrich; Hansen Thomas 《Journal of plankton research》2004,26(6):589-603
Selectivity-size spectra, clearance and ingestion rates andassimilation efficiencies of Acartia clausi (Copepoda), Peniliaavirostris (Cladocera) and Doliolum denticulatum (Doliolida)from Blanes Bay (Catalan Sea, NW Mediterranean) were evaluatedin grazing experiments over a wide range of food concentrations(0.028.8 mm3 L1 plankton assemblages from BlanesBay, grown in mesocosms at different nutrient levels). Acartiaclausi reached the highest grazing coefficients for large algae>70 µm (longest linear extension), P. avirostris forintermediate food sizes between 15 and 70 µm, and D. denticulatumfor small sizes from 2.5 to 15 µm. Penilia avirostrisand D. denticulatum acted as passive filter-feeders. Acartiaclausi gave some evidence for a supplementary raptorial feedingmode. Effective food concentration (EFC) decreased linearlywith increasing nutrient enrichment for D. denticulatum andfollowed domed curves for A. clausi and for P. avirostris withmaximum values at intermediate and high enrichment levels, respectively.Clearance rates of crustacean species showed curvilinear responseswith narrow modal ranges to increasing food concentration. Clearancerates of D. denticulatum increased abruptly and levelled intoa plateau at low food concentrations. Mean clearance rates were13.9, 25.5 and 64.1 mL ind.1 day1, respectively.No clearance could be detected for A. clausi at food concentrations<0.1 mm3 L1 and for P. avirostris at food concentrations 相似文献
11.
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
12.
Microzooplankton herbivory and bacterivory in Newfoundland coastal waters during spring, summer and winter 总被引:8,自引:0,他引:8
Grazing by microzooplankton on autotrophic and heterotrophicpicoplankton as well as >0.7 µm phytoplankton (as measuredby chlorophyll a) was quantified during July, August, October,January and April in the surface layer of Logy Bay, Newfoundland(47°38'14'N, 52°39'36'W). Rates of growth and grazingmortality of bacteria, Synechococcus and >0.7 µm phytoplanktonwere measured using the sea water dilution technique. Microzooplanktoningested 83184, 96366 and 64118% of bacterial,Synechococcus and >0.7 µm phytoplankton daily potentialproduction, respectively and 34111, 2530 and 16131%of bacterial, Synechococcus and >0.7 µm phytoplanktonstanding stocks, respectively. The trends in prey net growthrates followed the seasonal cycles of prey biomass, suggestingthat microzooplankton are important grazers in Newfoundlandcoastal waters. Ingestion was lowest during January and October(~2 µg C l1 day1) and highest in August(~20 µg C l1 day1). Aside from April when>0.7 µm phytoplankton represented the majority (~80%)of carbon ingested, bacterioplankton and <1 µm phytoplanktonrepresented most of the carbon ingested (~40100%). Althoughmicrozooplankton have here-to-fore been unrecognized as an importantgrazer population in Newfoundland coastal waters, these resultssuggest that they play an important role in carbon flow withinthe pelagic food web, even at low temperatures in Logy Bay. 相似文献
13.
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
14.
Three marine phytoplankton species (Skeletonema costatum, Olisthodiscusluteus andGonyaulax tamarensis) were grown in batch culturesat 15°C and a 14:10 L:D cycle at irradiance levels rangingfrom 5 to 450 µEinst m2 s1. At each irradiance,during exponential growth, concurrent measurements were madeof cell division, carbon-specific growth rate, photosyntheticperformance (both O2 and POC production), dark respiration,and cellular composition in terms of C, N and chlorophyll a.The results indicate that the three species were similar withrespect to chemical composition, C:N (atomic) = 6.9 ±0.4, photo-synthetic quotient, 1.43 ± 0.09, and photosyntheticefficiency, 2.3 ±0.1 x 103 µmol O2 (µgChl a)1 h1 (µEinst m2 s1)1.Differences in maximum growth rate varied as the 0.24power of cell carbon. Differences in growth efficiency, werebest explained by a power function of Chl a:C at µ = 0.Compensation intensities, ranged from 1.1 µEinst m2s1 for S. costatum to 35 forG. tamarensis and were foundto be a linear function of the maintenance respiration rate.The results indicate that interspecific differences in the µIrelationship can be adequately explained in terms of just threeparameters: cell carbon at maximum growth rate, the C:Chl aratio (at the limit as growth approaches zero) and the respirationrate at zero growth rate. A light-limited algal growth modelbased on these results gave an excellent fit to the experimentalµI curves and explained 97% of the observed interspecificvariability.
1Present address: Lamont-Doherty Geological Observatory Columbiaof University, Palisades, NY 10964, USA 相似文献
15.
Photoadaptation in Antarctic phytopfankton: variations in growth rate, chemical composition and P versus I curves 总被引:1,自引:0,他引:1
The response of phytoplankton to variations in the light regimewas studied during the VULCAN and ACDA cruises in the Antarctic.Unenriched batch cultures of 1219 days' duration reachedchl concentrations of 1050 µg1 and exhibitedexponential growth rates, with the maximal rate being 0.41 doubl,day1. Ice edge algae exhibited maximum growth rates atphoton flux densities (PFD) of 30100 µE m2S1and the growth rate was reduced by about 30% at 5001000µE m2S1 The chl/C ratio ranged between 0.004and 0.018, with the lowest ratios at PFDs above 500 µEm2S1 chl/C ratios were also below maximum at PFDsbelow 4050 µE m2S1 The C:N:P ratioswere close to the Redfield ratios; the Si/C ratio averaged 0.16(atoms), and the ATP/C ratio averaged from 0.0024 to 0.0050in different culture senes. When thawed after having been frozenfor 10 days, shade-adapted cultures were in a much better conditionthan sun-adapted ones. P versus I data showed that the maximumassimilation number varied from 0.75 to 4.4 µg C (µgchl)1h1. It varied inversely with the chl/C ratio;therefore the maximum carbon turnover rate varied little betweensamples (0.024/0.035 h1). Low biomass communities exhibitedrelatively high values for (the initial slope of P versus Icurves), low values for 1sat (160330 µE m2S1),and they were susceptible to photoinhibition. In contrast, communitiesdominated by Odontella weissflogii exhibited low values for, a high value for Isat (560 µE m2S1 andthey tolerated high PFDs. The photo-adaptational status of thephytoplankton in natural water samples is discussed relativeto the profile of water column stability and mixing processes. 相似文献
16.
Whipple Stuart J.; Patten Bernard C.; Verity Peter G. 《Journal of plankton research》2005,27(5):495-501
Using well plates of Phaeocystis pouchetii colonies isolatedfrom experimental mesocosms in western Norway, increases incolony size and division were documented. Median longest lineardimensions increased 07 µm h1; literaturePhaeocystis globosa values are 0.94.7 µm h1.Ten to twelve percent of colonies divided at rates of 0.210.28divisions day1. Daughter colonies were 100 µm smallerthan mother colonies. Colonies delayed 3.54.9 days tofirst division, compared with literature values of 45days for P. globosa. This study provides the first experimentalevidence for colony division of wild P. pouchetii. 相似文献
17.
THE RATIO OF CALCAREOUS AND ORGANIC SHELL COMPONENTS OF FRESHWATER SPHAERIID CLAMS IN RELATION TO WATER HARDNESS AND TROPHIC CONDITIONS 总被引:1,自引:0,他引:1
BURKY ALBERT J.; BENJAMIN MICHELE A.; CATALANO DENNIS M.; HORNBACH DANIEL J. 《Journal of Molluscan Studies》1979,45(3):312-321
Shells from 14 populations of sphaeriid clams including Sphaeriumstriatinum, S. simile, Pisidium walkeri, Musculim partumeiumand M. iransversum were analyzed for organic carbon (µgCmg1 shell), nitrogen (µg,N mg1 shell) andCaCOs (%CaCO3 of total clam dry weight). Habitat waters wereassessed for total hardness (expressed as ppm CaCo3), ppm Ca,ppm Mg, conductivity (µmho) and suspended organic Carbon(µgCl1). For all populations, shell organic C andN are positively correlated and there is an inverse relationshipbetween the amounts of shell CaCO3 and shell organic carbon.Trophic considerations give the best correlation with shelltype at the generic level of consideration since species ofMusculium are found at the opposite end of the trophic scale(eutrophic) from all other populations studied. For S. striatinum,the most extensively studied species, the amount of shell CaCO3is inversely related to water hardness. The selection of shellsin the Sphaeriidae is discussed in relation to structural-functionalneeds and habitat conditions
1 Present Address: Department of Biology, Syracuse University,Syracuse, New York 13210, U.S.A.
2 Present Address: Department of Zoology, Miami University,Oxford, Ohio 45056, U.S.A. (Received 5 December 1978; 相似文献
18.
The nutritional value of different sized fractions of naturalplankton was investigated for the growth of Eodiaptomus japonicusBurckhardt by comparing the development of its naupliar andcopepodid stages fed on differentially fractionated planktonicassemblages of a eutrophic pond, at 20°C. Water filteredthrough a 0.8 µm Nuclepore filter, containing mainly smallcoccoid bacteria (0.450.6 µm in cell diameter),at a concentration of 82.7 µg C 11 could not supportthe development of E.japonicus. The 3 µm filtered water,containing bacteria and picoalgae. at a total concentrationof 259 µg C 11, supported development but not eggproduction. The 20 µm filtered water, containing bacteria,picoalgae and large algae, at a total concentration of 2600µg C 11, supported rapid development of the juvenilesand continuous egg production by the adults. The separated 320µm fraction, containing only large algae, could not supportthe development at concentrations of 131 and 196 µg C11. However, the same rapid development of the juvenilesand continuous egg production by adults occurred at all of thetested concentrations between 261 and 3920 µg C11of the large algae. The results suggest that E.japonicus favoursalgae larger than 3 µm during its complete lifespan, andthat the threshold food concentration for its development variesbetween 200 and 250 µg C 11. 相似文献
19.
Ephyra larvae and small medusae (1.795 mm diameter, 0.01350mg ash-free dry wt, AFDW) of the scyphozoan jellyfish Aureliaaurita were used in predation experiments with phytoplankton(the flagellate Isochrysis galbana, 4 µm diameter, {smalltilde}6 x 106 µg AFDW cell1), ciliates (theoligotrich Strombidium sulcatum, 28 µm diameter, {smalltilde}2 x 103 µg AFDW), rotifers (Synchaeta sp.,0.5 µg AFDW individual1) and mixed zooplankton(mainly copepods and cladocerans, 2.13.1 µg AFDWindividual1). Phytoplankton in natural concentrations(50200 µg C I1) were not utilized by largemedusae (4495 mm diameter). Ciliates in concentrationsfrom 0.5 to 50 individuals ml"1 were consumed by ephyra larvaeand small medusae (314 mm diameter) at a maximum predationrate of 171 prey day1, corresponding to a daily rationof 0.42%. The rotifer Synchaeta sp., offered in concentrationsof 100600 prey I1, resulted in daily rations ofephyra larvae (25 mm diameter) between 1 and 13%. Mixedzooplankton allowed the highest daily rations, usually in therange 540%. Large medusae (>45 mm diameter) consumedbetween 2000 and 3500 prey organisms day"1 in prey concentrationsexceeding 100 I1. Predation rate and daily ration werepositively correlated with prey abundance. Seen over a broadsize spectrum, the daily ration decreased with increased medusasize. The daily rations observed in high abundance of mixedzooplankton suggest a potential scope for growththat exceeds the growth rate observed in field populations,and this, in turn, suggests that the natural populations areusually food limited. The predicted predation rate at averageprey concentrations that are characteristic of neritic environmentscannot explain the maximum growth rates observed in field populations.It is therefore suggested that exploitation of patches of preyin high abundance is an important component in the trophodynamicsof this species.
1Present address: University of Bergen, Department of MarineBiology, N-5065 Blomsterdalen, Norway 相似文献
20.
Dynamics of microplankton communities at the ice-edge zone of the Lazarev Sea during a summer drogue study 总被引:2,自引:0,他引:2
Microzooplankton grazing and community structure were investigatedin the austral summer of 1995 during a Southern Ocean Drogueand Ocean Flux Study (SODOFS) at the ice-edge zone of the LazarevSea. Grazing was estimated at the surface chlorophyll maximum(510 m) by employing the sequential dilution technique.Chlorophyll a concentrations were dominated by chainformingmicrophytoplankton (>20 µm) of the genera Chaetocerosand Nitzschia. Microzooplankton were numerically dominated byaloricate ciliates and dinoflagellates (Protoperidinium sp.,Amphisoleta sp. and Gymnodinium sp.). Instantaneous growth ratesof nanophytoplankton (<20 µm) varied between 0.019and 0.080 day1, equivalent to between 0.03 and 0.12 chlorophylldoublings day1. Instantaneous grazing rates of microzooplanktonon nanophytoplankton varied from 0.012 to 0.052 day1.This corresponds to a nanophytoplankton daily loss of between1.3 and 7.0% (mean = 3.76%) of the initial standing stock, andbetween 45 and 97% (mean = 70.37%) of the daily potential production.Growth rates of microphytoplankton (>20 µm) were lower,varying between 0.011 and 0.070 day1, equivalent to 0.0150.097chlorophyll doublings day1. At only three of the 10 stationsdid grazing by microzooplankton result in a decrease in microphytoplanktonconcentration. At these stations instantaneous grazing ratesof microzooplankton on microphytoplankton ranged between 0.009and 0.015 day1, equivalent to a daily loss of <1.56%(mean = 1.11%) of initial standing stock and <40% (mean =28.55%) of the potential production. Time series grazing experimentsconducted at 6 h intervals did not show any diel patterns ofgrazing by microzooplankton. Our data show that microzooplanktongrazing at the ice edge were not sufficient to prevent chlorophylla accumulation in regions dominated by rnicrophytoplankton.Here, the major biological routes for the uptake of carbon thereforeappear to be grazing by metazoans or the sedimentation of phytoplanktoncells. Under these conditions, the biological pump will be relativelyefficient in the drawdown of atmospheric CO2. 相似文献