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1.
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
2.
1. The occurrence and grazing activity of mixotrophic (phagotrophic) algae in three icecovered freshwater lakes of different trophic status were examined (oligotrophic Lake Giles, mesotrophic Lake Lacawac, eutrophic Lake Waynewood), Microbial population densities were low (4.1–7.2 × 105 bacteria ml?1 and 1.2–2.4 × 103 nanoplanktonic protists ml?1). All three nanoplankton communities were dominated by chloroplast-bearing forms (60–96%). 2. Mixotrophs formed up to 48% of the phototrophic nanoplankton in Lake Lacawac and were responsible for up to ~90% of the observed uptake of bacteria-sized particles. The abundance of mixotrophic algae in Lakes Giles and Waynewood were extremely low (3 and 2% of the phototrophic algae, respectively), and heterotrophs dominated nanoplankton bacterivory. 3. The overall impact of nanoplankton feeding activity on the bacterial assemblage was low under the ice in Lakes Giles and Waynewood. Removal rates of bacteria based on our particle uptake experiments were 1.0 and 4.0% of the bacterial standing stock day?1 in these lakes, respectively. Removal rates were higher in Lake Lacawac and ranged from 4.9 to 11% of the bacterial standing stock day?1 on 2 successive sampling days. 相似文献
3.
Carrias Jean-Francois; Amblard Christian; Bourdier Gilles 《Journal of plankton research》1994,16(5):471-485
Seasonal population dynamics and the vertical distribution ofciliates were studied in relation to the particular food resourcesoccurring in a humic and moderately acidic lake (Lake Vassivière).The abundance (1.4 x 10320.4 x 103 cells l1 mean= 4.8 x 103 cells l1) and biomass (0.534.6 µgC l1, mean = 6.0 µg C l1) of ciliated protozoawere low and close to values reported for oligotrophic environments.The species composition of the population varied greatly withdepth. Whereas large-sized species of oligotrichs, some of whichwere mixotrophic, dominated at the surface, haptorids were bestrepresented in deep waters. The spatial distribution of thevarious groups of ciliates was largely determined by light andthe vertical distribution of microbial food resources (detritus,bacteria, algae) within the water column of this brown-coloredlake. 相似文献
4.
Zubkov Mikhail V.; Sleigh Michael A.; Burkill Peter H.; Leakey Raymond J.G. 《Journal of plankton research》2000,22(4):685-711
Samples were collected from the top 200 m of the water columnat 50 stations during two cruises in different, near equinoctialseasons on an Atlantic transect near the 20°W meridian between50°N and 50°S. These samples were analysed to determinecharacteristics of the heterotrophic bacterial populations.Flow cytometry was used to enumerate these bacteria and determinetheir average size so as to calculate their biomass. Heterotrophicbacterial production, and the rate of grazing of these bacteriaby heterotrophic nanoplankton in the main depth layers, weredetermined using 3H thymidine and 14C leucine techniques. Thebiomass of heterotrophic nanoplankton in these layers was determinedusing a glucosaminidase assay. Five provinces were distinguishedalong the transect and characterized by average values of allmeasured parameters. The relative composition and activity ofthe microbial community in the water columns within each provincechanged little between the two cruises. Lowest heterotrophicbacterial biomass of 12 mg C m3 and productionof 0.10.2 mg C m3 day1 were found in thenorthern and southern Atlantic gyres, and were relatively similarin both seasons. Biomass and production were 24 timeshigher in the northern and southern temperate waters, and inequatorial waters, than in the gyres and tended to show moreseasonal variation. Production and biomass in the layer belowthe pycnocline were lower by 1030% and about 50%, respectively,than values determined in the surface mixed layer, and variedless with latitude. Depth-integrated values of these two parameterswere generally of similar size in the mixed water layer andthe layer of the chlorophyll maximum and pycnocline, and tendedto vary with season. The specific growth rate of heterotrophicbacteria was in the range 0.05 to 0.12 day1 in the topmixed layer at all latitudes. In spite of the elevated temperatures,bacterial growth appears to be restricted by a shortage of nutrientsso that the microbial community cycles very slowly, with a turnovertime of the order of 1 week or more. The depth-integrated biomassof heterotrophic nanoplankton was generally about 100% of theheterotrophic bacterial biomass in the same water. Grazing bythese nanoplankton at the rate measured could consume all ofthe new production of heterotrophic bacteria in all waters,and they probably control the populations of both heterotrophicand phototrophic bacteria. 相似文献
5.
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
6.
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
7.
The seasonal abundance of the phototrophic ciliate Mesodinium rubrum in Southampton Water, England 总被引:1,自引:0,他引:1
The abundance of the marine phototrophic planktonic ciliateMesodinium rubrum was monitored throughout an annual cycle attwo stations in the Southampton Water estuary. Seasonal changesin the concentration of nitrate, ammonia and phosphate weremonitored both at the inner estuary station (NW Netley) andouter estuary station (Calshot). Nutrient levels in the winterwere similar at both stations, and were diminished during sequentialdiatom blooms dominated initially by Sketetonema costatum andthen by Rhizosolenia dclicatula. Nitrate was reduced to a seasonalminimum in the outer estuary following these spring diatom blooms,but in the inner estuary was sustained >500 µg I1until the onset of the M.rubrum bloom. During the developmentof a visible red tide of M.rubrum in June/July at NW Netley,nutrient concentrations were considerably reduced. Cell numbersof M.rubrum varied between 2 and 3 cells ml during winterto >400 cells ml1 during the bloom at NW Netley, whereasat Calshot cell abundance did not increase above 25 cells ml1at any time of the year. At NW Netley, dense accumulations ofthe ciliate occurred over restricted depth intervals duringthe bloom and possible factors influencing the observed verticaldistribution of cells are considered.
1Present address: Biology Department, Faculty of Science, AddisAbaba University, PO Box 1176, Addis Ababa, Ethiopia 相似文献
8.
Photo- and heterotrophic pico- and nanoplankton in the Mississippi River plume: distribution and grazing activity 总被引:3,自引:0,他引:3
The abundance of pico- and nanophytoplankton, bacteria and heterotrophicnanoflagellates, and grazing rates on phototrophic pico- andnanoplankton and bacterioplankton were assessed along a salinitygradient (0.234.4) in the Mississippi River plume inMay 2000. Grazing rates were established by serial dilutionexperiments, and analysis by flow cytometry allowed differentiationof grazing rates for different phytoplankton subpopulations(eukaryotes, Synechococcus spp., Prochlorococcus spp.). Grazingrates on phytoplankton tended to increase along the salinitygradient and often approached or exceeded 1 day-1. Phytoplanktonnet growth rates (growth grazing) were mostly negative,except for positive values for eukaryotic nanoplankton in thelow-salinity, high-chlorophyll region. Grazing pressure on bacteriawas moderate ( 相似文献
9.
Description of phytoplankton and nutrient in spring in the western North Atlantic Ocean 总被引:2,自引:0,他引:2
Abundance of diatoms in the northern Sargasso Sea in springhas been observed in a 4-year period between 1981 and 1985 andthen again in 1987. A theory is presented that if stratificationblocks get-through of deep nutrients to the surface, as in thesouthern Sargasso, then in-situ cycling via non-diatoms andammonia dominates. The theory is that if in-situ cycling doesnot dominate, as northward, then stratification does not blockget-through of deep nutrients to the surface, which, in combinationwith the marked growth capacity of diatoms, produce an abundanceof cells. This abundance consumes nitrate, phosphate and silicateat the surface and ultimately this nutrient-depleted water arrivesin the southern Sargasso via the gyre circulation. Thus thenutrient-depleted water of the western Atlantic gyre is consideredto be primarily achieved only by diatoms, in spring and in thenorthern Sargasso. A transect during April 1316, 1985,north from the Virgin Islands along 63°64°W showsa great change in the diatom species plus Emiliania huxleyifrom negligible concentrations in the southern half of the sectionto large concentrations in the northern half. This unevennessof distribution can be rephrased by indicating that these speciesare narrow-niched with regard to nutrient availability. Theother species, coccolithophores and dinoflagellates, are evenlydistributed at low concentrations south-north (though some diminishslightly) and so they are broad-niched with respect to nutrient.High species diversity depends on broadness of nutrient nicheand equilibrium conditions of hydrographically stable water(i), implying that when non-equilibrium conditions occur (ii),when niche breadth is less (iii) or both (iv), then diversityis less marked, (i) is confirmed by broad-niched species southward,(ii) is confirmed by broad-niched species northward, (iii) isconfirmed by narrow-niched species southward and (iv) by narrow-nichedspecies northward. 相似文献
10.
The abundance, frequency of dividing cells and growth ratesof the planktonic cyano bacteria Synechococcus sp. during thesummer of 1995 and 1996 were estimated in the Northwest MediterraneanSea to test whether depth-dependent growth rates of this speciesexplain its dominance in the deep chlorophyll maximum (DCM)layer formed during summer thermal stratification in the NWMediterranean, compared to the surface layer. Abundance at theDCM layer (5070 m) was up to two orders of magnitudegreater than that at the surface, with values ranging from 1.7to 13x106 cells I-1 and from 4 to 175 x 106 cells I-1 at thesurface and in DCM waters, respectively. Gross growth rates,however, were much higher at the surface than in the DCM layer(surface: 0.761.07 day DCM: 0.300.47 day-1 Thehigher gross growth rates at the surface layer were supportedby a higher frequency of dividing cells (surface: 0.090.24;DCM: 0.010.12). The negative correlation between theabundance or standing stock and growth rates of these planktonicpicocyanobacteria points to losses, and not growth rate, asthe main control on the abundance of Synechococcus. Althoughwe provide some evidence that grazing alone may be able to accountfor these losses, further, direct determinations are clearlyneeded to elucidate the regulation of the abundance of Synechococcusin the NW Mediterranean. 相似文献
11.
Composition and distribution of the pelagic and sympagic algal assemblages in the Laptev Sea during autumnal freeze-up 总被引:5,自引:0,他引:5
Tuschling Kirsten; Juterzenka Karen v.; Okolodkov Yuri B.; Anoshkin Andrej 《Journal of plankton research》2000,22(5):843-864
The phytoplankton and ice algal assemblages in the SiberianLaptev Sea during the autumnal freeze-up period of 1995 aredescribed. The spatial distribution of algal taxa (diatoms,dinoflagellates, chrysophytes, chlorophytes) in the newly formedice and waters at the surface and at 5 m depth differed considerablybetween regions. This was also true for algal biomass measuredby in situ fluorescence, chlorophyll (Chl) a and taxon-specificcarbon content. Highest in situ fluorescence and Chl a concentrations(ranging from 0.1 to 3.2 µg l1) occurred in surfacewaters with maxima in Buor Khaya Bay east of Lena Delta. Thealgal standing stock on the shelf consisted mainly of diatoms,dinoflagellates, chrysophytes and chlorophytes with a totalabundance (excluding unidentified flagellates <10 µm)in surface waters of 35133 660 cells l1. Highestalgal abundance occurred close to the Lena Delta. Phytoplanktonbiomass (phytoplankton carbon; PPC) ranged from 0.1 to 5.3 µgC l1 in surface waters and from 0.3 to 2.1 µg Cl1 at 5 m depth, and followed the distribution patternof abundances. However, the distribution of Chl a differed considerablyfrom the distribution pattern shown by PPC. The algal assemblagein the sea ice, which could not be quantified due to high sedimentload, was dominated by diatom species, accompanied by dinoflagellates.Thus, already during the early stage of autumnal freeze-up,incorporation processes, selective enrichment and subsequentgrowth lead to differences between surface water and sea icealgal assemblages. 相似文献
12.
Planktonic ciliates in the northwestern Indian Ocean: their abundance and biomass in waters of contrasting productivity 总被引:4,自引:0,他引:4
The abundance and biomass of planktonic ciliates in the northwesternIndian Ocean ranged from 31 l1 and 0.1 µg C l1in oligotrophic open-ocean waters to 823 l1 and 1.2 µgC l1 in more productive waters of the equator, northernArabian Sea and Gulf of Oman.
3Present address: British Antarctic Survey, High Cross, MadingleyRoad, Cambridge, CB3 OET, UK 相似文献
13.
Tintinnids and other microzooplankton -- seasonal distributions and relationships to resources and hydrography in a Maine estuary 总被引:3,自引:0,他引:3
Species composition and abundance of tintinnids and other microzooplanktonwere studied in the Damariscotta River estuary, Maine, USA duringthe period March 1981 to May 1982. Peak tintinnid abundancesoccurred during spring and summer and exceeded 7 x 103 I1.Spearman rank correlation coefficients indicated that temperature,nanoplankton chlorophyll and phaeopigments passing a 20 µnfilter were important factors correlating with total tintinniddensity. Species composition of tintinnids changed seasonallyand was similar in the spring of both years. Non-loricate ciliateswere also most abundant in the spring, reaching peak densitiesof 4.5 x 104 I1 in April 1982. Rotifers were most commonupestuary in the spring.
Present address: Department of Zoology, University of Georgia,Athens, GA 30602, USA 相似文献
14.
Howell-Kubler Alexis N.; Lessard Evelyn J.; Napp Jeffrey M. 《Journal of plankton research》1996,18(5):731-745
We surveyed springtime biomass and abundance of the >20 µmmicroprotozoa in surface waters of the SE Bering Sea and Shelikof Strait, Alaska. This study was part of the Fisheries OceanographyCoordinated Investigations (FOCI) program examining processeswhich affect the recruitment variability of walleye pollock(Theragra chalcogramma). Microprotozoa are a potential preyresource for larval pollock which has not been previously examined.In both areas, the >20 µm microprotozoa were predominantlydinoflagellates and ciliates. At the time of sampling (May 1990in Shelikof Strait and April 1992 in the SE Bering Sea), thespring diatom bloom was under way in Shelik of Strait, but notin the SE Bering Sea. Heterotrophic dinoflagellates dominatedthe microprotozoan assemblage in Shelik of Strait, but not inthe SE Bering Sea. In the SE Bering Sea. total microprotozoanabundances ranged from 300 to 6233 organisms 11 and biomassfrom 0.58 to 9.73 µg C 11. In Shelik of Strait,abundance and biomass were higher, ranging from 850 to 14 960organisms 11 and from 1.29 to 70.73 µg C 11,respectively. These biomass levels are comparable to those reportedfrom other coastal and oceanic regions. Microprotozoan biomasslevels were sufficient to support the estimated metabolic needsof first-feeding larval walleye pollock. It remains to be shownwhether larval pollock use this resource. 相似文献
15.
Nitrogen dynamics in lower Narragansett Bay, Rhode Island. I. Uptake by size-fractionated phytoplankton populations 总被引:1,自引:0,他引:1
The contribution of nanoplankton (< 10 µm fraction)to winter spring (1977 78) and summer (1978,1979) phytoplankton nitrogen dynamics in lower NarragansettBay was estimated from ammonium, nitrate and urea uptake ratesmeasured by 15N tracer methods. During the winter spring,an average of 80% of chlorophyll a and nitrogen uptake was associatedwith phytoplankton retained by a 10 µm screen. In contrast,means of 51 58% of the summer chlorophyll a standingcrops and 64 70% of nitrogen uptake were associatedwith cells passing a 10 µm screen. Specific uptake ratesof winter spring nanoplankton populations were consistentlylower than those of the total population. Specific uptake ratesof fractionated and unfractionated summer populations were notsignificantly different. Ammonium uptake averaged between 50and 67% of the total nitrogen uptake for both the total populationand the < 10µm fraction. The total population and the10 µm fraction displayed similar preferences for individualnitrogen species. Though composed of smaller cells, flagellatedominated nanoplankton assemblages may not necessarily takeup nitrogen at faster rates than diatom dominated assemblagesof larger phytoplankters in natural populations.
1Present address: Australian Institute of Marine Science, P.M.B.No. 3, Townsville M.S.O., Qld. 4810, Australia 相似文献
16.
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
17.
Chlorophyll standing crop and phytoplankton production in the western Irish Sea during 1992 and 1993
Chlorophyll standing crop and phytoplankton production werestudied in the western Irish Sea over a 21 month period during1992 and 1993. For both years, the start of the production seasonwas first observed in Dundalk Bay and occurred progressivelylater in more northerly coastal and offshore waters. Standingcrop and production exhibited marked spatial heterogeneity with12.5- to 19-fold differences in crop observed over distancesof 2030 km. Distinct regional differences in the lengthof the production season were apparent. The longest season,67 months with a production of 194 g C m2, occurredin Dundalk Bay. The season lasted 34 months in the summerstratified region with a production of 140 g C m2. Northerly,offshore mixed waters and coastal waters of Northern Irelandsupported a short (23 months) season and production of194 and 140 g C m2, respectively. The similarity in seasonalproduction between Dundalk Bay and coastal waters of NorthernIreland, and between the summer stratified and northern mixedregions, is attributed to the intensity of production duringthe summer. Between 59 and 79% of seasonal production in thenorthern mixed region and coastal waters of Northern Irelandtook place during June and July, compared to 2940% inDundalk Bay and the summer stratified region. Lower summer productionin the latter two may be due to nutrient limitation and thishas implications for the sensitivity of these two regions toanthropogenic nutrient enrichment. 相似文献
18.
Fine-scale vertical (5 40 m) and horizontal (50 500 m) patterns of temperature, chlorophyll and abundance ofzooplankton species were sampled with a pump filtration systemin the surface waters offshore of San Diego in May and October,1978. Intense and consistent patterns were most apparent invertical profiles. Herbivorous zooplankton were more consistentlyassociated with the estimated primary productivity maximum thanwith the deeper chlorophyll maximum layer, which representeda phytoplankton biomass maximum. Predators were positively correlatedwith abundant potential prey species. Variations in body lengthwith depth suggest that these fine-scale patterns were sufficientlystable to influence zooplankton growth. Consequences for grazingand predator prey interactions in pelagic ecosystemsare discussed.
1Present address: NOAA/NMFS Southwest Fisheries Center, PO Box271, La Jolla, CA 92038, USA 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.
Annual pattern of micro- and mesozooplankton abundance and biomass in a subtropical estuary 总被引:7,自引:0,他引:7
The pattern of biomass and abundance of microzooplankton andmesozooplankton were studied over an annual cycle in the NuecesEstuary, Texas. Zooplankton samples and associated hydrographicdata were collected at four locations at biweekly intervalsfrom September 1987 through October 1988. This is a broad, shallowbay system with an average depth of 2.4 m. The concentrationof chlorophyll a in the surface waters averaged 7.4 µgl1with 85% passing through a 20 µ mesh. Microzooplankton(20200 µ in length) were extremely abundant throughoutthis study. Abundances of ciliates (including both aloricateciliates and tintinnids) ranged from 5000 to 400 000 l,with a mean of 38 000 l1 of seawater over the entirecourse of the study. Mesozooplankton (2002000 µmin length) abundance averaged 6100 m3 for samples collectedduring the day and 10 100 m3 for samples collected atnight. Mesozooplankton were dominated by Acartia tonsa whichmade up {small tilde}50% of the total. Biomass estimates formicrozooplankton (based on volume estimates) were often higherthan measured biomass of mesozooplankton. Given the shortergeneration times and higher metabolic rate of microzooplanktoncompared to mesozooplankton, microzooplankton should have agreater effect on the trophic dynamics of the Nueces Estuarythan mesozooplankton. 相似文献