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1.
During the spring of 1994, we determined the factors responsiblefor the decline of the seasonal diatom bloom in the Gullmarfjord, on the west coast of Sweden. Four species constituted>75% of the biomassDetonula confervacea, Chaetocerosdiadema, Skeletonema costatum and Thalassiosira nordenskioeldiireachingconcentrations of 4900, 350, 8200 and 270 cells ml1,respectively. Growth of phytoplankton was exponential (growthrate = 0.12 day1) from 3 to 21 March, after which a galewith winds >15 m s1 caused massive aggregation. Amaximum of 130 p.p.m. (v/v) of marine snow aggregates was observedby in situ video at the peak of the bloom. Critical concentrations(Jackson, Deep-Sea Res., 37, 11971211, 1990) were similarto observed showing that coagulation theory could explain thesudden decline of the bloom. The heterotrophic dinoflagellateGyrodinium cf. spirale increased exponentially after the peakof the bloom with maximum (temperature-adjusted) growth rates.After the rapid aggregation and sedimentation of the bloom,they were able to control any further growth of diatoms. Nitrateand silicate were never depleted, but phosphate may have beenlimiting by the end of the study period. We conclude that massaggregation during a gale marked the end of the bloom, and thatintense grazing by heterotrophic dinoflagellates prevented anysubsequent increase of diatoms. 相似文献
2.
Distribution, dynamics and in situ seeding potential of Scrippsiella hangoei (Dinophyceae) cyst populations from the Baltic Sea 总被引:2,自引:0,他引:2
The distribution and seasonal dynamics of cyst populations ofthe spring bloom dinoflagellate Scrippsiella hangoei were studiedin surface sediments on the southwest coast of Finland, BalticSea. In situ germination was assessed by monitoring the fractionof empty cysts and chlorophyll a fluorescence in cyst populationsat different coastal sites throughout the annual cycle. Scrippsiellahangoei resting cysts were widely distributed in the study areaand occurred in exceptionally large numbers (magnitudes of 104106cysts cm3) at all sampling locations between the innermostparts of the coastal archipelago and the open Gulf of Finland.The decreases in cyst number in winter and the increases occurringin late spring reflected the dynamics of germination and encystmentof the species. Chlorophyll fluorescence appeared in mid-winterin ~40% of cysts from well-aerated basins and 615% ofcysts from temporarily anoxic sediments. A generally low increasein the proportion of empty cysts indicated that only a partof the potentially germinable cysts actually germinates. Giventhe high cyst concentrations in the sediments, the potentialfor germination is considerable, despite the environmentallyand physiologically determined losses. In contrast, the sizeof the vegetative inoculum is very low, indicating that thesurvival of germlings is problematic under harsh winter conditions.This is an unusual life cycle strategy; however, the early releaseof cells into the water column provides a high probability forsuccessful bloom initiation under the unpredictable meteorologicalconditions in winter and early spring, which often lead to thesudden onset of favourable growth conditions. 相似文献
3.
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
4.
Dynamics of Copepod Faecal Pellets in Relation to a Phaeocystis Dominated Phytoplankton Bloom: Characteristics, Production and Flux 总被引:2,自引:0,他引:2
Frangoulis Constantin; Belkhiria Sami; Goffart Anne; Hecq Jean-Henri 《Journal of plankton research》2001,23(1):75-88
Copepod faecal pellet characteristics and production were measuredin spring 1995, 1996 and 1997 in the North Sea Southern Bightin order to define changes due to the development of the phytoplanktonbloom. Changes were related to the succession from diatomsto a Phaeocystis sp. bloom. Mean monthly pellet productiondecreased during the Phaeocystis bloom development to 0.27 pelletsind. 1 h 1, approximately 80% lower than beforeand after the bloom. Although phytoplanktonic pigments showedsignificant differences between inshore and offshore stations,there was no such significant difference for faecal pellet production.Faecal pellet sinking-rate decreased from 100 to 70 m day 1during the transition from a diatom- to a Phaeocystis-dominatedbloom. This was due to a decrease in pellet density and/or adecrease of the pellet volume. These results supported the ideaof lower feeding of copepods under Phaeocystis bloom conditions.As mean seasonal density of copepod faecal pellets was higher(1.37 g cm 3) than in other seas, accidental ingestionof sedimentary material as the cause of this high density isdiscussed. 相似文献
5.
A study of the phytoplankton community in the Faroe-ShetlandChannel was conducted in July 1999. Samples were collected atvarious depths in the photic zone along three transects (thenorthern entrance, the center and the southern entrance). Exceptfor a few easterly stations where nitrate and silicate werebelow 1 µM, all nutrients (phosphate, silicate, ammonium,nitrite and nitrate) were non-limiting for phytoplankton growth.HPLC pigment analysis revealed a pronounced (>50%) dominanceof Prymnesiophyceae at all stations. Their pigment ratio ofdiatoxanthin + diadinoxanthin/Chl a (DDX/Chl a) indicated thatthe phytoplankton community was controlled by light. Primaryproduction in the delayed spring bloom varied from 1.2 to 1.8g C m2 day1 along the northern transect. Alongthe other two transects, primary production ranged from 1.6to 3.8 g C m2 day1. Associated with the characteristicsindicating the establishment of a bloom, the relative contributionof diatoms and Prymnesiophyceae increased, whereas that of Prasinophyceae,Cryptophyceae, Chrysophyceae and Cyanobacteriaceae decreased.With respect to their vertical distribution, Cyanobacteriaceae,Chrysophyceae and Dinophyceae tended to have a higher abundance,relative to other taxonomic groups, in the surface layers. Therelative abundance of diatoms and Chlorophyceae increased withdepth. The DDX/Chl a ratio of the Prymnesiophyceae decreasedwith depth, indicating that vertical mixing in the upper 30m of the photic zone occurred less frequently than the timespan of physiological acclimation of cellular pigment composition. 相似文献
6.
Determining the mass density of marine copepods and their eggs with a critical focus on some of the previously used methods 总被引:3,自引:0,他引:3
We collected Calanus finmarchicus copepodites CIV, CV and CVIfemales in a deep fjord on the west coast of Norway during April1996, May 1997 and November 1998. Eggs of C. finmarchicus andCalanus glacialis were collected during May 1989 in the BarentsSea. The sinking speeds of animals and eggs were measured ina homogeneous column with seawater of known density, and Stokeslaw was applied to estimate their mass density. Also the densitycontrast between the organisms and seawater was calculated.The mean mass density of C. finmarchicus ranged from 1.0274to 1.0452 g cm3. During spring copepodite stage CV hada significantly lower mean mass density (1.0345 g cm3)compared to CIV (1.0381 g cm3) and CVI females (1.0408g cm3). Copepods collected during winter had a distinctlylower mass density. The sinking speed of C. glacialis eggs followeda unimodal distribution, with a mean of 25.9 m day1,while sinking speeds of C. finmarchicus eggs were bimodal, thetwo groups of eggs having a mean sinking speed of 23.3 m day1and 35.4 m day1 respectively. Correspondingly the meanmass density was 1.0556 g cm3 for C. glacialis eggs andfor the two groups of C. finmarchicus eggs 1.0639 g cm3and 1.0812 g cm3. Results of earlier work, particularlyusing density gradient methods to determine mass density ofzooplankton, are critically reviewed, and it is suggested thatthis method should not be used to determine the mass densityof small organisms the size of C. finmarchicus. 相似文献
7.
Relationship between vegetative cells and cyst production during Alexandrium minutum bloom in Arenys de Mar harbour (NW Mediterranean) 总被引:2,自引:0,他引:2
Garces Esther; Bravo Isabel; Vila Magda; Figueroa Rosa Isabel; Maso Mercedes; Sampedro Nagore 《Journal of plankton research》2004,26(6):637-645
A recurrent Alexandrium minutum bloom in the Arenys de Mar harbour(Catalan coast, North Western Mediterranean) was monitored inorder to establish the relationship between vegetative cellsand cyst production. The bloom lasted from January 21 to February24, 2002 and reached cell concentrations of up to 47 x 106 cellL1. Two aspects related to the resting cysts depositionwere studied: (i) production of resting cysts during the bloomperiod (by means of sediment traps) and (ii) distribution ofresting cysts in the sediment after the bloom (May 2002). Cystformation in Arenys clearly started in a period with high vegetativecell densities in the water column. Once production was initiatedencystment fluxes remained constant for two weeks, and coveringthe periods of maintenance and decline of the bloom. High cystfluxes (up to 6000 cysts cm2 day1) were quantifiedas a result of the high vegetative cell concentration. Moreover,encystment occurring in less than 1% of the total populationindicates that most of the cells are not involved in restingcysts formation. A comparison of the resting cyst flux valuesobtained from the sediment traps and the resting cyst concentrationsin surface sediment (6283270 cysts cm3) threemonths later, revealed that the number of cysts in the sedimentdecreased during that time. The studies of excystment showeda high germination percentage (91%) and germling viability (100%).These data, together with the resting cyst distribution in thesediment, are important in assessing the role of resting cystsin the bloom dynamics of A. minutum in confined waters. 相似文献
8.
Abundance, size distribution and bacterial colonization of transparent exopolymeric particles (TEP) during spring in the Kattegat 总被引:3,自引:0,他引:3
The abundance, size distribution and bacterial colonizationof transparent exopolymeric particles (TEP) were monitored inthe Kattegat (Denmark) at weekly intervals throughout the spring(February-May) encompassing the spring diatom bloom. These recentlydiscovered particles are believed to be formed from colloidalorganic material exuded by phytoplankton and bacteria, and mayhave significant implications for pelagic flux processes. Duringthis study, the number concentration of TEP (>1 µm)ranged from 3 x 103 to 6 x 104 ml1 and the volume concentrationbetween 0.3 and 9.0 p.p.m.; they were most abundant in the surfacewaters subsequent to the spring phytoplankton bloom. The rangeof TEP (encased) volume concentration was similar to that ofthe phytoplankton, although at times TEP volume concentrationexceeded that of the phytoplankton by two orders of magnitude.The TEP size distribution followed a power law, with the abundanceof particles scaling with particle diameter(ß+1).The seasonal average estimate of ß (2.3) was not significantlydifferent from three, consistent with TEP being formed by shearcoagulation from smaller particles. However, date-specific estimatesof ß differed significantly from three, probably becauseTEP are fractal. All TEP were colonized by bacteria, and bacteriawere both attached to the surface of and embedded in TEP. Yetthe number of attached bacteria per TEP was related neitherto the surface area nor the volume, but rather scaled with TEPsize raised to an exponent of 相似文献
9.
Dinoflagellate bloom development and collapse in Lake Kinneret: a sediment trap study 总被引:1,自引:0,他引:1
Warm monomictic Lake Kinneret, Israel, is characterized by awinterspring water bloom of the large (~50 µm diameter)dinoflagellate Peridinium gatunense Nygaard. Usually the P.gatunense bloom declines in MayJune and a less prominentbloom of smaller dinoflagellates (mostly Peridiniopsis spp.of ~2030 µm diameter) develops. Water column abundancesand sedimentation losses to those dinoflagellates were followedthroughout 1994 and 1995. The objective was to quantify thevariables that describe population dynamics, that in turn willshed more light on the seasonal patterns of bloom dynamics.Sedimentation losses were measured by means of sediment trapswith and without a preservative (formaldehyde) that were exposedfor 24 h once every 23 weeks. Annual sedimentation lossesof Peridinium (hypolimnetic trap catches) were 209 g wet wtm-2 year-1 in 1994 and 187 g wet wt m-2 year-1 in 1995, whichconstituted 16 and 23% of Peridinium production in those years,respectively. This study revealed that increased death ratespreceded a mass sedimentation flux of Peridinium and causedthe decline of the bloom in Lake Kinneret. Annual sedimentationlosses of Peridiniopsis were 55 g wet wt m-2 year-1 in 1994and 34 g wet wt m-2 year-1 in 1995. In contrast to live Peridiniumcells, Peridiniopsis cells continued to swim to the lower trapafter the onset of thermal stratification, possibly taking advantageof the higher nutrient concentrations below the thermocline,at a time when the lake is already stratified and the epilimnionis nutrient depleted. This could be an important factor allowingPeridiniopsis spp. to peak after the decline of Peridinium. 相似文献
10.
Rees A.P.; Owens N.J.P.; Heath M.R.; Plummer D.H.; Bellerby R.S. 《Journal of plankton research》1995,17(6):1307-1324
Carbon (C) fixation and nitrogen (N) assimilation rates havebeen estimated from 14C and 15N techniques for a 12 month periodin a Scottish sea loch. The maximum rate of nitrogen assimilated(29.92 mmol N m2 day1) was in April at the mostseaward station; similar high rates were experienced duringMay at the other stations. Carbon fixation rates were maximal(4884047 mg C m2day1) at the time of highphytoplankton biomass (maximum 8.3 mg m3 chlorophylla) during May, whilst nitrate concentrations remained >0.7µ.mol l1. C:N assimilation ratios suggest nitrogenlimitation only during the peak of the spring bloom, althoughat times nitrogen (nitrate and ammonium) concentration fellto 0.2 µmol l1 in the following months. The verticalstability of the water column, influenced by tidal and riverineflushing, varied along the axis of the loch, resulting in markeddifferences between sampling stations. Although ammonium waspreferentially assimilated by phytoplankton, >50% of productionwas supported by nitrate uptake and only during the summer monthswas the assimilation of ammonium quantitatively important. 相似文献
11.
'St Martin's Summer': the case of an autumn phytoplankton bloom in the Gulf of Naples (Mediterranean Sea) 总被引:2,自引:0,他引:2
Zingone Adriana; Casotti Raffaella; d'Alcal Maurizio Ribera; Scardi Michele; Marino Donato 《Journal of plankton research》1995,17(3):575-593
Phytopiankton abundance. species composition and primary productionof the Gulf of Naples were investigated during an autumn bloomin November 1985. Hydrographic data and surface phytoplanktonsamples were collected during a 3 day cruise, whereas investigationson in situ primary production and phytoplankton vertical distributionwere conducted from a second boat on three different dates.A coast-offshore gradient was recorded for most of the chemicaland biological parameters analysed. At stations closer to thecoast, which were affected by land run-off, phytoplankton populationsattained concentrations of 2.5 106 cells l1 with amarked dominance of diatoms belonging to the genera Thalassiosiraand Chaetoceros. The most striking character of the system wasa remarkably high carbon assimilation rate (up to 1.04 g C m2day2) at stations closer to the coast. The causativemechanism for this bloom appeared to be land-derived nutrientenrichment, possibly enhanced by autumn rains, followed by aperiod of favourable meteorological conditions, which occursrecurrently in the region for a brief period around November,known locally as St Martin's Summer. We hypothesizethat a similar mechanism can stimulate phytoplankton growthmore than once every year. since high-stability penods followingmeteoro logical perturbations can occur several times in temperateregions of the northern hemisphere in autumn. 相似文献
12.
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
13.
Halsband-Lenk C.; Nival S.; Carlotti F.; Hirche H.-J. 《Journal of plankton research》2001,23(6):597-609
Reproduction of the dominant copepods Centropages typicus andTemora stylifera was studied at a permanent station in the LigurianSea (north-western Mediterranean). Seasonal patterns of eggproduction, clutch size, egg size and female prosome lengthwere followed from January 1998 to December 1999. Female carboncontent and weight-specific egg production were compared inautumn 1998 and spring 1999. Reproductive patterns of C. typicusand T. stylifera were very similar, indicating that reproductionwas affected by the same environmental factors. Reproductiveactivity was highest in autumn in both species and years. Asecond peak of egg production was observed in early summer,which was less intense in 1999 after a bloom of salps. Egg productionrates reached maximal values of 33.5 and 33.3 eggs female1day1 and annual means of 10.8 and 11.7 eggs female1day1 in Centropages and Temora, respectively. Maximalweight-specific egg production was 0.21 day1 in bothspecies in November 1998, when female carbon contents were 6.7(C. typicus) and 12.0 µg (T. stylifera). No statisticalrelationship between egg production and food availability ortemperature was detected. Reproductive activity did not reflectthe seasonal abundance patterns, with C. typicus dominatingin spring and T. stylifera in autumn. 相似文献
14.
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
15.
Bacterial dynamics and distribution during a spring diatom bloom in the Hudson River plume, USA 总被引:6,自引:0,他引:6
Bacterial abundance and [3H]thymidine incorporation rates wereused to characterize bacterial distributions and dynamics duringa spring diatom bloom in the coastal plume of the Hudson Riverduring March, 1981. Bacterial abundance did not decline significantlyaway from the plume or across the continental shelf. However,a pronounced gradient was observed for [3H]thymidine incorporation. Following a northeast gale, a bloom of Skeletonema costatumdeveloped in response to coastal upwelling. As the plume becamesaltier, warmer and larger, bacterial abundance averaged 1.3x 109 cells 11. Bacterial incorporation of [3H]thymidineinto cold 5% TCA insoluble materials, bacterial production andspecific growth rates averaged 80120 pmol 11 d1,1.42.0 x 109 cells 11 and 1.21.5 d1.respectively. The mean density of bacteria in the plume didnot change even though growth rates were higher than expectedlosses from sinking, mixing and export. The abundance and production levels of attached bacteria inthe plume were significantly higher than they were in coastalwater outside the plume. In contrast, free bacterial levelswere similar in all regions of the shelf and plume. Bacterialparameters in the plume were not correlated with phytoplanktonpigment concentrations, while significant positive correlationswere found in shelf waters >33 salinity. Thus bacteria werecoupled to phytoplankton in shelf waters but not in the plumewhere allochthonous dissolved matter was probably supportingthe bacteria.
*Lamont-Doherty Geological Observatory Contribution No. 3459
2Present address: Department of Microbiology, University ofGeorgia, Athens, GA 30602, USA. 相似文献
16.
The chain-forming dinoflagellate Gynmodinium catenatum Grahamcauses recurrent outbreaks of paralytic shellfish poisoning(PSP) in the Galician Rias Bajas (northwest Spain). A sedimentsurvey in Ria de Vigo in April 1986 indicated that the highestconcentrations of cysts of this species were located in themiddle sections of the ria, with maximum abundance of 310 cystscm3. The effects of temperature, growth medium compositionand irradiance on the germination of laboratory-produced restingcysts were investigated. Newly formed cysts required very littletime for maturation, as excystment was possible within 2 weeksof encystment. Growth media did not affect germination success.In contrast, the excystment rate was retarded signifiantly indarkness. Germination was also strongly affected by temperature,with {small tilde}75% excystment success at 2228°Cand little or no germination below 11°C after 1 month ofincubation. In culture, the optimum growth rate of vegetativecells was between 22 and 28°C, the highest rate being 0.53divisions day1 at 24°C. Growth did not occur at temperatures< 11°C or >30°C. These results are important withrespect to the different hypotheses proposed to explain theinitiation of G.catenatum blooms in the Galician Rias Bajasand Northern Portugal. The pattern of G.catenatum bloom developmentalong this coast has been related to seasonal upwelling in thearea, with major blooms occurring during the autumn as warmeroffshore surface water is transported towards the coast whenupwelling relaxes. The landward transport of established offshorepopulations of G.catenatum with the warm surface layer remainsa viable explanation for the observed blooms within the rias,but alternatively, our data suggest that cysts within the riascan provide the inoculum population at times conducive to growthand bloom formation. Even though newly formed G.catenatum cystshave a very short maturation time and can germinate in darknessacross a wide temperature range, bloom development will be significantonly during the late summer and early autumn, since in othermonths light levels at the sediment surface and temperaturesthroughout the water column are too low for significant germinationor growth. 相似文献
17.
The productivity of a stand of Salix glauca at 68° N inArctic Norway was investigated. The biomass was 18.4 t ha1and the annual production was 1.341.56 t ha1 year1.These low values are attributed to the short growing season.The mean age of the stems was 23.4 years. The prostrate-ascendinggrowth form of the plants is regarded as an adaptation to thesevere winter climate. 相似文献
18.
Seasonal dynamics in the abundance of Micromonas pusilla (Prasinophyceae) and its viruses in the Gulf of Naples (Mediterranean Sea) 总被引:2,自引:0,他引:2
To assess the role of viruses in the bloom dynamics of Micromonaspusilla in the Gulf of Naples (Mediterranean Sea), variationsof host and virus abundance were followed over one annual cycleand in late winterspring of three consecutive years.Micromonas pusilla was recorded from autumn to spring, withpeak values up to 6.6 x 103 cells ml1, but was undetectablein summer. Free M.pusilla viruses were detectable in all seasons,with concentrations from 0.02 viruses ml1 to 1.9 x 103viruses ml1, exceeding host abundances only in one case.We found a great intraspecific variability in host susceptibilityto viruses present in natural samples, with viral titres rangingover one or two orders of magnitude for the same samples incubatedon different M.pusilla strains. Over the winterspringperiods, a highly dynamic situation was evident, with wide fluctuationsfor both host and virus abundances from one week to another.In some cases, peak host concentrations were accompanied byan increase in viral numbers, whereas in other cases the respectivefluctuations were uncoupled. Although fluctuations of M.pusillaabundance could be influenced by viral infection, there wasno evidence that viruses were able to terminate host blooms.The summer decline of M.pusilla populations did not appear tobe related to the impact of viral infection. 相似文献
19.
Changes in the elemental composition of Asterionella formosa during the diatom spring bloom 总被引:1,自引:0,他引:1
Changes in the elemental composition of the diatom Asterionellaformosa within mixed phytoplankton samples were determined overthe spring bloom period using energy dispersive X-ray microanalysis.Using a 10 kV electron microprobe, X-ray information from thetop 12 µm of the cell revealed overall mean concentrationsof: Si (4636 mmol kg1 dry wt), P (82), S (54), Cl (71)K (94) and Ca (90). Concentrations of all elements showed widevariation within each date sample, with unimodal frequency distributionsapproximating to a Normal distribution. Correlation of the entiredata set demonstrated clear statistical associations betweenelements, including Si, P and K. Uptake of Si during the courseof the diatom bloom led to a major fall in lake water concentration(1.0 to 0.07 mg l1), which correlated with a decreasein the mean cell Si concentration (6735 to 3107 mmol kg1dry wt) during the final phase of the bloom. Mean cell concentrationsof P and K also showed marked decreases with time, in closeparallel with cell Si. These changes in P and K were attributedto the high level of internal correlation with Si and not toany significant decrease in P and K availability in the environment. 相似文献
20.
Uptake and regeneration of inorganic nitrogen in coastal waters influenced by the Mississippi River spatial and seasonal variations 总被引:1,自引:0,他引:1
The Mississippi and Atchafalaya Rivers introduce large amountsof nutrients to surface waters of the northern Gulf of Mexico.This paper reports the most complete data to date on inorganicnitrogen uptake and regeneration in a broad range of coastalenvironments influenced by the river water, along with informationon nutrient concentrations and including pico-, nano-, and microplanktonspecies composition. Nitrate in surface waters is greatly reducednear the river plume, at salinities between 5 and 25 PSU, wherethe largest variance in uptake rates was observed, and was coincidentwith peaks in surface chlorophyll. Despite the depletion ofnitrate, nitrogen limitation was a rare event during the study,because of relatively high ammonium concentrations (>1 µmolNH4+ I1 and regeneration rates. Two contrasting situationscharacterize the seasonal nitrogen dynamics in surface shelfwaters. High nitrate input during the spring caused a largebloom in which the cells were well adapted to use nitrate.Thedominant phytoplankton species were chain forming diatoms, alsoreported in sediment-trap studies in the area. Ammonium regenerationonly accounted for a small fraction of the nitrogen requirementsduring the bloom. In contrast, the low flow of river water duringsummer resulted in low nitrate concentrations in surface water.In this case phytoplankton productivity was highly reduced andmay depend greatly on in sita ammonium regeneration. 相似文献