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1.
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
2.
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
3.
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
4.
Fiala Michel; Kopczynska Elzbieta E.; Jeandel Catherine; Oriol Louise; Vetion Giles 《Journal of plankton research》1998,20(7):1341-1356
Time series of phytoplankton biomass and taxonomic compositionhave been obtained for the 3 years 1992, 1993 and 1994 in thenorthern part of the Southern Ocean (station Kerfix, 5040'S,6825;E) Autotrophic biomass was low throughout the year (<0.2mg m3 except during a short period in summer when a maximumof 1.2 mg chlorophyll (Chl) a m was reached. During winter,the integrated biomass was low (<10 mg m2) and associatedwith deeply mixed water, whereas the high summer biomass (>20mg m2) was associated with increased water column stability.During summer blooms, the >10 µ;m size fraction contributed60% to total integrated biomass. Large autotrophic dinoflagellates,mainly Prorocentrum spp., were associated with the summer phytoplankton maxima and accounted for >80% of the total autotrophcarbon biomass. In November and December, the presence of thelarge heterotrophic dinoflagellates Protoperidinium spp. andGyro dinium spp. contributed a high proportion of total carbonbiomass. During winter, the <10 µm size fraction contributed80% of total Chi a biomass with domination of the picoplanktonsize fraction. The natural assemblage included mainly nakedflagellates such as species of the Prasinophyceae, Cryptophyceaeand Prymnesiophyceae. During spring, picocyanobacteria occurredin sub-surface water with a maximum abundance in September of106 cells 11 相似文献
5.
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
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.
Calbet Albert; Alcaraz Miquel; Atienza Dacha; Broglio Elisabetta; Vaque Dolors 《Journal of plankton research》2005,27(11):1195-1203
The phytoplankton [chlorophyll a (Chl a)], microzooplankton,mesozooplankton and macrozooplankton biomass and distributionwere studied as part of a multidisciplinary project (Tempano)along the Antarctic Peninsula during December 2002. Even thoughthe summer phytoplankton bloom was not yet developed in thearea, autotrophs dominated the plankton biomass. Phytoplanktonvertical distribution was, in general, homogeneous in the upper4050 m of the water column, further decreasing with depth.Protozoans showed low biomass; their contribution to the totalplankton being one order of magnitude lower than that of autotrophs.The vertical distribution of protozoans was variable among stationswith marked peaks at depths ranging from 30 to 80 m. Mesozooplankton-integratedbiomass was generally low, although there was a notable increasesouthward near the ice marginal zone. Macrozooplankton distributionwas more variable without any clear zonal distribution pattern.The vertical distribution of meso- and macrozooplankton (>4mm) biomass showed clear peaks of abundance comprising differentspecies depending on the geographical area. Our biomass distributiondata suggest a food-web scenario in which macrozooplankton arepreying on mesozooplankton populations only in the northernerstations, and mesozooplankton are, in their turn, shaping theabundance of the emerging populations of microzooplankton. Phytoplankton,on the other hand, seem to be hardly controlled by grazing activity. 相似文献
8.
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
9.
The role of phosphorus on planktonic production of the Gironde plume waters in the Bay of Biscay 总被引:8,自引:0,他引:8
More and more studies emphasize the status of phosphorus (P)as the principal limiting nutrient of phytoplankton growth,especially in coastal waters under the influence of freshwaterdischarges. The purpose of the present paper is to investigatethe role of P on planktonic production in the waters influencedby the Gironde discharges; the Gironde being one of the twolargest rivers on the French Atlantic coast. The survey is basedon several cruises made in 1998 and 1999. Two different patternswere observed for waters with salinity below and above 34.5.For waters with salinity < 34.5, P was found to be the firstlimiting nutrient of winter and spring phytoplankton blooms,based on undetectable phosphate (< 20 nM), high NO3 : PO4ratios, typically > 100 : 1, short phosphate turnover time(1 to 2 h), high alkaline phosphatase activities (mean of 176nM h-1 in late May 1999) and ultimately great increases of chlorophylla (Chl a) and primary production in phosphate-enriched samplesrelative to controls. This limitation could be partly explainedby the Gironde nutrient supplies, which were phosphate deficientcompared with the mineral nitrogen(Nmin : PO4 was > 40 withina salinity range 1633). In summer, corresponding to theperiod of low influence of Gironde supplies (low runoff anda spreading effect of the plume), phytoplankton growth wouldbe controlled by both P and nitrogen (N), according to low nitrateand the major effect of combined P+N (NH4) enrichment on Chla and primary production compared with the addition of N orP singly. In early October, after the first autumn gales, themixed layer was enriched with a sufficient supply of nutrientsto support exponential phytoplankton growth for 4 days in enclosures.The pattern was different for waters at the limit of the Girondeplume and Atlantic oceanic waters (within salinity range 34.535.4).P would not be the single limiting nutrient of winter bloomsand spring phytoplankton growth since low phosphate, and alsolow nitrate and silicate, availability were recorded and phosphateaddition alone had no effect on phytoplankton biomass and productionin bioassays. The early P limitation of winter blooms had consequencesfor the phytoplankton community structure in the Gironde plumewaters (salinity < 34.5). Whereas major cells of these bloomswere greater than 20 µm in size, phytoplankton growthin spring and autumn was dominated by 320 µm (e.g.53% of Chl a in late April 1999) and < 3 µm cells (e.g.29% of Chl a). The decreasing size of phytoplankton cells isemphasized by the severe competition between bacteria and algaefor phosphate, since bacteria dominated phosphate uptake inspring (e.g. 87% in late April, 77% in late May). Bacteria tendedto have greater affinity for phosphate and seemed also to beP limited at certain times in spring, according to results fromphosphate enrichment bioassays in late May 1999. The alternativemethod for phytoplankton to obtain P would be the use of thedissolved organic phosphorus pool by alkaline phosphatase activity.According to the movement of 33P after initial labelling ofmicrobial populations and a subsequent cold chase, the majortransfer of P occurred from the bacterial to the dissolved fraction.We hypothesize that algae obtain part of its dissolved organicphosphorus from bacteria-originated organic phosphorus compounds. 相似文献
10.
Chlorophyll (Chl) a was measured every 10 m from 0 to 150 min the Transition Domain (TD), located between 37 and 45°N,and from 160°E to 160°W, in May and June (Leg 1) andin June and July (Leg 2), 199396. Total Chl a standingstocks integrated from 0 to 150 m were mostly within the rangeof 20 and 50 mg m2. High standing stocks (>50 mg m2)were generally observed westof 180°, with the exceptionof the sporadic high values at the easternmost station. Thetotal Chl a standing stock tended to be higher in the westernTD (160°E172°30'E) than in the central (175°E175°W)and eastern (170°W160°W) TD on Leg 1, but thesame result was not observed on Leg 2. It was likely that largephytoplankton (210 and >10 µm fractions) contributedto the high total Chl a standing stock. We suggest that thehigh total Chl a standing stock on Leg 1, in late spring andearly summer, reflects the contribution of the spring bloomin the subarctic region of the northwestern Pacific Ocean. Thedistribution of total Chl a standing stock on Leg 2 was scarcelyaffected by the spring phytoplankton bloom, suggesting thattotal Chl a standing stock is basically nearly uniform in theTD in spring and summer. Moreover, year-to-year variation inthe total Chl a standing stock was observed in the western TDon Leg 1, suggesting that phytoplankton productivity and/orthe timing of the main period of the bloom exhibits interannualvariations. 相似文献
11.
George B. McManus Barbara A. Costas Hans G. Dam Rubens M. Lopes Salvador A. Gaeta Sylvia M. Susini Carol H. Rosetta 《Hydrobiologia》2007,575(1):69-81
We measured grazing by herbivorous zooplankton (<200 μm fraction) in coastal and slope regions of the South Brazil Bight.
Using the dilution technique, we performed nine experiments during the austral summer, when nutrient-rich South Atlantic Central
Water is present on the shelf, and five during winter. These experiments provide the first estimates of microzooplankton grazing
in the western South Atlantic Ocean. Model II regression showed a strong relationship between phytoplankton intrinsic growth
rates and grazing, with a slope of 0.64 (±0.28; 95% confidence interval) indicating that microzooplankton grazing could account
for the majority of phytoplankton mortality. Both phytoplankton growth and microzooplankton grazing were higher during the
summer upwelling season, compared to winter. For the two experiments that were conducted in oligotrophic slope water, grazing
accounted for >80% of phytoplankton production. A comparison of incubations with and without added inorganic nutrients showed
no consistent stimulation of phytoplankton growth (slope of enriched versus unenriched treatments not significantly different
from 1). Estimates from microscopic counts of heterotrophic organisms >10 μm indicated that copepod nauplii comprised the
largest share of the microzooplankton biomass (mean 62.4 ± 5.8% SE). Grazing estimates were not correlated with microzooplankton
biomass, whether or not nauplii were included, suggesting that most of the grazing was done by nano-sized zooplankton.
Electronic Supplementary Material Electronic supplementary material is available in the online version of this article at and is accessible for authorized users.
Handling editor: S. Wellekens 相似文献
12.
Bulk-phase viscoelastic properties of seawater relationship with plankton components 总被引:5,自引:0,他引:5
The viscous and elastic moduli at different shear rates, togetherwith various biological oceanographic properties, were determinedin seawater from different hydrological layers in the southernNorth Sea in June. The biological oceanographic parameters includedPhaeocystis and Noctiluca abundances, chlorophyll a level (Chl),bacteria. HNAN and aggregate volume fraction. The plankton wasjointly dominated by Phaeocyslis sp. and Noctiluca scinullans.Noctiluca abundance showed no correlation with any other biologicalor viscoelastic parameter, but Phaeocystis abundance correlatedstrongly. The other biological parameters correlated with Phaeocystisand with each other positively and mostly significantly. Overall,viscoelasticity correlated more strongly with Chl than withany other biological parameter. For non-microlayer samples,the excess complex (viscoelastic) modulus (µ.Pa) G*E =2.0 x Ch113 (Chl in mg m3). Viscous and elasticmoduli also correlated closely with each other. For a givenvalue of Chl. the microlayer samples were 6.5 or 14 times (dependingon the estimation method) more viscoelastic than in bulk-phasesamples. Viscoelasticity in samples of settled benthic fluffwere lower even than bulk-phase samples, but this differencewas not significant. Comparison with Mediterranean data on viscoelasticity(Jenkinson. Oceanol. Acta, 16, 317334, 1993), using publishedvalues for phytoplankton biomass (Wiadnyana, J. Rech. Océanogr.,17, 16, 1992), suggests that the relationship betweenChl (or phytoplankton biomass) and viscoelasticity might begeneral. This apparent biomodification of the viscosity andelasticity of seawater is discussed in relation to its likelyimpact on turbulence and plankton ecology. 相似文献
13.
The dynamics of heterotrophic nanoflagellates and bacterioplankton in a large ultra-oligotrophic Antarctic lake 总被引:4,自引:0,他引:4
Laybourn-Parry Johanna; Bayliss Peter; Ellis-Evans J.Cynan 《Journal of plankton research》1995,17(9):1835-1850
The abundance of both heterotrophic nanoflagellates (HNAN) andbacterioplankton in a large (9km2) ultraoligotrophic Antarcticlake (Crooked Lake) were investigated from December 1992 untilNovember 1993. HNAN abundance peaked in spring, summer and autumn,falling to lowest numbers during the winter. Numbers rangedbetween 0 and 50.9x104 l1. Bacterioplankton abundancewas highest during the late summer and then fell progressivelytowards winter and autumn (range 1.194.46x106 l1)In contrast to numbers, mean cell volumes (MCV) of the bacteriareached their highest in spring, and consequently highest bacterialbiomass occurred at this time. MCV ranged between 0.052 and0.224µm3. Bacterial production measurements followingthe incorporation of [3H] thymidine into DNA and [14C] leucineinto protein using a doubling-labelling procedure were undertakenin January, June, August, October and November. Rates variedbetween 2.8 and 52 ng C l1 h1. On occasions, a significant differencein production rates based on the uptake of leucine and thymidinewas observed, suggesting unbalanced growth. Highest rates ofproduction coincided with times of high dissolved organic carbonlevels in the water column and lowest production with low levelsof DOC. HNAN grazing rates were measured by following the uptakeof fluorescently labelled bacteria and averaged 4.8 bacterialcells individual1 day1 at 2 and 4°C. Specific growth rates(h1) ranged around 0.000700.00077 in both the field andlaboratory, giving doubling times of 37.3 and 41.0 days, respectively.These low rates of grazing and growth indicate that there isno adaptation to low temperatures in these freshwater protists.Based on these data, the gross production efficiency is 24%.HNAN removed between 0.1 and 9.7% of bacterial production perday. 相似文献
14.
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
15.
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
16.
Ramirez Teodoro; Liger Esperanza; Mercado Jesus M.; Cortes Dolores; Vargas-Yanez Manuel; Sebastian Marta; Reul Andreas; Aguilera Jose; Bautista Begona 《Journal of plankton research》2006,28(7):629-641
Respiratory electron transport system (ETS) activity was measuredin plankton samples (<200 µm) collected in the NW AlboranSea. Sampling was carried out during seasonal cruises (summerand autumn 2003 and winter and spring 2004) in 12 stations locatedin transects off the coast of Malaga (southern Spain). Thiswork reports for the first time seasonal variations of the Arrheniusactivation energy (Ea) as well as being the first study to addressCO2 balance in the NW Alboran Sea. These variations were relatedto changes in the phytoplankton community assemblage, whichcould ultimately be caused by the seasonal variability of hydrologicalconditions. ETS activity was significantly higher in summer,coinciding with a higher chlorophyll a (Chl a) concentrationand relatively high levels of particulate organic matter. TheETS:Chl atotal ratios were low during the four seasons, suggestinga high contribution of autotrophic phytoplankton to the respiratoryactivity of planktonic community. Respiratory CO2 production(RCP) calculated from ETS activity ranged from 4.6 to 28.1 mgC m3 day1 during the four cruises. Chl a-specificRCP was lower than the maximum photosynthetic rates reportedin the literature for the studied area, suggesting that primaryproduction (PP) and respiration in the water column might beunbalanced. 相似文献
17.
Microzooplankton grazing in the surface water of the Southern Ocean during an austral summer 总被引:1,自引:0,他引:1
Microzooplankton grazing was investigated in surface waters of the Indo-Pacific and Atlantic sectors of the Southern Ocean
by the dilution method. Phytoplankton growth varied mainly between 0.1 and 0.4 day−1, and microzooplankton grazing between 0.0 and 0.3 day−1. Great fluctuations in phytoplankton growth rate were observed at one station within 3 weeks and between closely spaced stations.
Microzooplankton grazing rates were similar to phytoplankton growth rate despite the variation of phytoplankton growth rates,
although in some cases, phytoplankton growth overwhelmed microzooplankton grazing. These observations suggest that microzooplankton
are the main consumers of primary producers, and that steady state between phytoplankton growth and microzooplankton grazing
is usually established in the Southern Ocean in austral summer.
Received: 5 November 1996 / Accepted: 4 March 1997 相似文献
18.
Recent studies indicate that Oithona spp. contribute significantlyto total copepod biomass. Little is known, however, about theirecological significance, particularly in the case of the estuarineOithona nana. A study comprising three sites within SouthamptonWater was conducted to evaluate the late-stage copepodite/adult(stages IVVI) O. nana community, using 120-µm meshnets. Although present throughout the estuary, there was a strikingspatial gradient with O. nana most common in the upper estuary.A clear seasonal pattern was observed with O. nana as the mostabundant copepod species from late summer until early winter.It comprised 61% of all copepods recorded, with a biomass of757.22 mg C m3. Production estimates of O. nana werederived from the instantaneous-growth approach,using appropriate growth equations. The estimated productionof O. nana ranged from 1.50 mg C m3 year1 withinthe lower estuary to 146.77 mg C m3 year1 in theupper estuary. In the upper estuary, this compares with productionrates of 187.47 mg C m3 year1 for all Acartiacongeners (excluding nauplii), the most common calanoid genus.Throughout the estuary, O. nana annual production represented18% of total copepod production clearly indicating that, atleast in the upper estuary, O. nana production may be directlycomparable with calanoid production. 相似文献
19.
Seasonal variations of size-fractionated phytoplankton along the salinity gradient in the York River estuary, Virginia (USA) 总被引:5,自引:0,他引:5
Sin Yongsik; Wetzel Richard L.; Anderson Iris C. 《Journal of plankton research》2000,22(10):1945-1960
The dynamics of phytoplankton size structure were investigatedin the freshwater, transitional and estuarine zones of the YorkRiver over an annual cycle. The contribution of large cells(microplankton, >20 µm) to total concentrations ofchlorophyll a increased downstream during winter, whereas thatof small cells (nanoplankton, 320 µm; picoplankton,<3 µm) increased downstream during summer. In the freshwaterregion, the contribution of micro phytoplankton to total concentrationsof chlorophyll a was significant during warm seasons (springand summer) but not during colder seasons (winter), whereasthe contribution of small-sized cells (especially picoplankton)increased during cold seasons. Temperature, light and high flushingrate appear to control phytoplankton community structure inthe freshwater region. In the transitional region, nano-sizedcells dominated the phytoplankton population throughout allseasons except during the spring bloom (April) when the chlorophylla concentration of micro phytoplankton increased. Size structurein the transitional region is most likely regulated by lightavailability. In the mesohaline region, nano- and pico-sizedcells dominated the phytoplankton population during the summerbloom, whereas micro-sized cells dominated during the winterbloom. Factors controlling phytoplankton community size structurein the mesohaline zone may be riverine nitrogen input, temperatureand/or advective transport from up-river. Based on these results,the spatial and seasonal variations in size structure of phytoplanktonobserved on the estuarine scale may be determined both by thedifferent preferences for nutrients and by different light requirementsof micro-, nano- and picoplankton. The results suggest thatanalyses of phytoplankton size structure are necessary to betterunderstand controls on phytoplankton dynamics and to bettermanage water quality in river-dominated, estuarine systems. 相似文献
20.
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