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1.
Autotrophic picoplankton in southern Lake Baikal: abundance, growth and grazing mortality during summer 总被引:5,自引:0,他引:5
Nagata Toshi; Takai Kenji; Kawanobe Kyoko; Kim Dong-Sup; Nakazato Ryoji; Guselnikova Nina; Bondarenko Nina; Mologawaya Oliga; Kostrnova Tatyana; Drucker Valentine; Satoh Yasuhiro; Watanabe Yasunori 《Journal of plankton research》1994,16(8):945-959
Autotrophic picoplankton were highly abundant during the thermalstratification period in late July in the pelagic area (waterdepth 5001300 m) of southern Lake Baikal; maximum numberswere 2 x 106 cells ml1 in the euphotic zone ({small tilde}15m). Unicellular cyanobacteria generally dominated the picoplanktoncommunity, although unidentified picoplankton that fluorescedred under blue excitation were also abundant (maximum numbers4 x 105 cells ml1) and contributed up to {small tilde}40%of the total autotrophic picoplankton on occasions. Carbon andnitrogen biomasses of autotrophic picoplankton estimated byconversion from biovolumes were 1484 µg C l1and 3.621 µg N l1. These were comparableto or exceeded the biomass of heterotrophic bacteria. Autotropicpicoplankton and bacteria accounted for as much as 33% of paniculateorganic carbon and 81% of nitrogen in the euphotic zone. Measurementsof the photosynthetic uptake of [l4C]bicarbonate and the growthof picoplankton in diluted or size-fractionated waters revealedthat 80% of total primary production was due to picoplankton,and that much of this production was consumed by grazers inthe <20 µ.m cell-size category. These results suggestthat picoplankton-protozoan trophic coupling is important inthe pelagic food web and biogeochemical cycling of Lake Baikalduring summer. 相似文献
2.
Pantoja Silvio; Gonzalez Humberto; Bernal Patricio A. 《Journal of plankton research》1989,11(3):599-604
Bacterial biomass (BB, acridine orange) and bacterial secondaryproduction (BSP, [3H]thymidine incubations) were measured forthe first time in Concepción Bay (37°35'S, 73°01'W).BB ranged from 1.8x106 to 22.5x106 cells ml1 (the lattervalue observed near to an industrial effluent), BSP from 0.27x106to 2.5x106 cell ml1 day1 and heterotrophic turnoverrates between 0.15 and 1.0 doublings day1. 相似文献
3.
Effects of Planktonic Copepods on Transparent Exopolymeric Particles (TEP) Abundance and Size Spectra 总被引:4,自引:0,他引:4
Prieto Laura; Sommer Frank; Stibor Herwig; Koeve Wolgang 《Journal of plankton research》2001,23(5):515-525
Diatoms exude considerable quantities of polymers, mainly polysaccharides,that play an important role in the process of sestonic particleaggregation in the sea. We investigated the impact of copepodson transparent exopolymeric particles (TEP) generated by thediatom Thalassiosira weissflogii. Grazing experiments with 14C-labelledalgae exudates demonstrated that copepods typical of the BalticSea were not actively filtering TEP. Control experiments showedthat uptake of radioactivity could be ascribedto passive uptake, such as adsorption of radioactively-labelledparticles to the body surface. Furthermore, we tested the effectof copepods on TEP size spectra. The abundance and size distributionof TEP (from 1.4 to 180 µm of Equivalent Spherical Diameter)were analysed in a 4 h incubation experiment. In the presenceof copepods, the proportion of larger TEP was higher. An increasein total volume of TEP in jars containing copepods (~2 x 107µm ml1) compared with control jars without copepods(~0.5 x 107 µm3 ml1) was also observed. The processof aggregation of TEP demonstrated in this work, whereby copepodsincrease downward particle flux without consuming carbon, canhave far-reaching consequences for carbon fluxes along the watercolumn and for copepods feeding dynamics. 相似文献
4.
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
5.
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
6.
Post-embryonic development time, egg production rate and adultbody size of calanoid copepod Eurytemora affinis from Lake Ohnuma,Japan, were determined under six temperature-food conditions(103,5 x 103, 104 and 5 x 104 cells ml1 at 15°C,5 x 104 cells ml1 at 10and20°C) in the laboratory.The measured parameters varied with both temperature and foodconcentration. Development time from hatching to adult femalewas 9.2, 11.4 and 22.8 days at 20, 15 and 10°C respectively,at the highest food concentration. The males developed to adultat one to two days earlier than the females. An effect of foodshortage on development time occurred at the lowest food concentration.This development time was 24.8 days even at 15°C, beingtwice as long as that at the highest food concentration. Prosomelength of these food-limited females was approximately 75% ofwell-fed ones, which reduced by only 10% with increasing temperaturefrom 10 to 20°C. Clutch size (C, eggs clutch1) ofwell-fed individuals depended on prosome length of the adultfemale (L, mm), and was expressed as an equation: C = 65.2 L383. Clutch size of individuals reared at less than 104 cellsml1, however, mostly laid below the estimated curve,especially at the lowest food concentration being only 10% ofthat at the highest food concentration. These results suggestthat food availability is a more important factor affectingpopulation growth of E.affinis in Lake Ohnuma than variationof temperature. 相似文献
7.
Contribution of Picocyanobacteria to total primary production and community respiratory losses in a backwater system 总被引:2,自引:0,他引:2
The contribution of autotrophic picoplankton (APP) to phytoplanktonicprimary production, investigated during the phytoplankton growingseason (MarchSeptember) in a macrophyte-dominated backwatersystem near Vienna, showed that APP mainly consisted of rod-shapedand coccoid cyanobacteria. Two stations were examined, exhibitingsimilar seasonal patterns in the development of picocyanobacteria,although the two sites differed in picocyanobacterial cell numbersand biomass by a factor of 1.5. Cell numbers determined by epifluorescencemicroscopy varied between 0.29 x 104 and 34.5 x 104 cells ml1at Station 1, and between 0.23 x 104 and 19.1 x 104 cells ml1at Station 2. At both sites, the mean cell volume of picocyanobacteriawas 0.5 µm3. Carbon fixation in the planktonic communityof the Kühwörter Wasser was dominated primarily bylarger phytoplankton, although the picoplankton community sometimessupplied up to 74% (mean: 35%) of total primary production.Distinct differences in chlorophyll a concentrations and primaryproduction between the two sites refer to a greater competitionbetween phytoplankton and macrophytes at Station 2. Communityrespiration deviated greatly in time and in level at the twostations, showing a higher dynamic in community metabolism atStation 1. At this site, community respiration losses rangedbetween 12 and 100% of gross production. Hence, community metabolismcomprised net autotrophic, balanced, and net heterotrophic situationsover the investigation period, whereas at Station 2, only netautotrophic situations could be determined. 相似文献
8.
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
9.
Sato Riki; Ishibashi Yukiko; Tanaka Yuji; Ishimaru Takashi; Dagg Michael J. 《Journal of plankton research》2008,30(3):299-309
To estimate the productivity and grazing impact of a commonappendicularian species Oikopleura dioica in Tokyo Bay, monthlyobservations on its abundance and vertical distribution wereconducted during 2000. The abundance peaked in February andOctober, but was low during summer. Seasonal fluctuations inproductivity were similar to those of the abundance, with maximumvalues of 92, 134 and 508 mg C m–2 day–1 for somatic,new house and discarded house productivity in October and 206mg C m–2 day–1 for fecal pellet productivity inFebruary, respectively. The averaged biomass of O. dioica wasonly 2.5% of that of copepods; however, the secondary productivityof the former corresponded to 12.4% of the latter. Daily grazingimpact on particulate organic carbon ranged from 0.05% to 5%,which is close to the impact by copepods. These results implythat in Tokyo Bay, where small copepods and jellyfish are abundant,O. dioica is an important component of the ecosystem becauseit bridges between small primary producers and higher consumers. 相似文献
10.
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
11.
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
12.
Dillon PF Root-Bernstein RS Lieder CM 《American journal of physiology. Cell physiology》2006,291(5):C977-C984
Ascorbate has previously been shown to enhance both 1- and 2-adrenergic activity. This activity is mediated by ascorbate binding to the extracellular domain of the adrenergic receptor, which also decreases the oxidation rate of ascorbate. H1 histamine receptors have extracellular agonist or ascorbate binding sites with strong similarities to 1- and 2-adrenergic receptors. Physiological concentrations of ascorbate (50 µM) significantly enhanced histamine contractions of rabbit aorta on the lower half of the histamine dose-response curve, increasing contractions of 0.1, 0.2, and 0.3 µM histamine by two- to threefold. Increases in ascorbate concentration significantly enhanced 0.2 µM histamine (5500 µM ascorbate) and 0.3 µM histamine (15500 µM ascorbate) in a dose-dependent manner. Histamine does not measurably oxidize over 20 h in oxygenated PSS at 37°C. Thus the ascorbate enhancement is independent of ascorbate's antioxidant effects. Ascorbate in solution oxidizes rapidly. Transfected histamine receptor membrane suspension with protein concentration at >3.1 µg/ml (56 nM maximum histamine receptor) decreases the oxidation rate of 392 µM ascorbate, and virtually no ascorbate oxidation occurs at >0.0004 mol histamine receptor/mol ascorbate. Histamine receptor membrane had an initial ascorbate oxidation inhibition rate of 0.094 min·µg protein1·ml1, compared with rates for transfected ANG II membrane (0.055 min·µg protein1·ml1), untransfected membrane (0.052 min·µg protein1·ml1), creatine kinase (0.0082 min·µg protein1·ml1), keyhole limpet hemocyanin (0.00092 min·µg protein1·ml1), and osmotically lysed aortic rings (0.00057 min·µg wet weight1·ml1). Ascorbate enhancement of seven-transmembrane-spanning membrane receptor activity occurs in both adrenergic and histaminergic receptors. These receptors may play a significant role in maintaining extracellular ascorbate in a reduced state. molecular complementarity; vitamin C; seven-transmembrane-spanning membrane receptors 相似文献
13.
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
14.
The spawning rate of laboratory-reared Centropages typicus fedHymenomonas elongala increases with food concentration, up toa value of {small tilde}2800 µg C (16 500 cells) ml1.An alternation of a low food (1000 cells ml1) and highfood concentration (16 500 cells ml1) is not favourableto egg release when its periodicity is 1 or 2 days, whereasit may be of advantage if it is longer (36 days). Inthe latter case, Centropages typicus will benefit best fromthe rich food diet if this coincides with (or just follows)the last moult. 相似文献
15.
The standard synthetic culture medium (Stuart and Street, 1969)has been modified by adjustment of its initial pH to 6.4 andby the addition of gibberellic acid (0.25 mg/l) and of a mixtureof 15 L-amino acids formulated from an analysis of the conditionedmedium. The minimum effective density for the growth of sycamorecell suspensions in the standard medium is 915 x 103cells ml1, for the modified synthetic medium it is 2.0x 103 cells ml1, and for conditioned medium 1.01.25x 103 cells ml1. Using either conditioned medium (Stuart and Street, 1969) orthe modified synthetic medium it is demonstrated that the growthof cultures initiated at low density is enhanced by a volatilefactor released from actively growing cell suspensions. In presenceof conditioned medium and this volatile factor cultures canbe established from stationary-phase cells at a density of 6x 102 cells ml1. The volatile factor can be absorbedin 40 per cent w/v KOH but attempts to replace the factor byair containing carbon dioxide at concentrations up to 5 percent have so far been unsuccessful. 相似文献
16.
Temporal variability of diversity and biomass of tintinnids (Ciliophora) in a southwestern Atlantic temperate estuary 总被引:2,自引:0,他引:2
Seasonal variations in diversity and biomass of tintinnids (Ciliophora:Tintinnida) were investigated at two fixed stations in the innerpart of the Bahía Blanca Estuary (38°42' S, 61°50'W) during an annual cycle. The variations were analysed in relationto surface temperature, salinity, transparency, solar radiationand chlorophyll a (Chl a)concentration. Biomass was calculatedin terms of biovolume and carbon units. Diversity was estimatedas the number of species and the Shannon Index (H', ln based).Density of tintinnids ranged from 100 to 7800 individuals L1H' ranged from 0 to 1.81. The biomass varied from 0.3 to 127.78x 106 µm3 L1 (0.0239.4 µg C L1).Density was significantly related to temperature, solar radiationand Secchi distance (P < 0.01); diversity was significantlyrelated to temperature (P < 0.01) and solar radiation (P< 0.05). Biomass was significantly related only to temperature(P < 0.01) in one of the stations. According to principalcomponents analysis (PCA) tintinnids exhibited a segregationof three groups: winter, springsummer and autumn forthe most internal station and winter, spring and summerautumnfor the most external station. H' values were lower than thoseobserved in other coastal systems found at about the same latitudein the northern hemisphere. 相似文献
17.
The plastochron index (PI) has been compared with leaf growthand biomass accumulation in young soya bean plants of severalcultivars that were grown in controlled environments with differentirradiance levels and durations, temperatures, and nitrogen(N) regimes. Increasing the photoperiod from 10 to 16 h day1 increasedthe plastochron rate (PR) and the proportion of axillary growth.Doubling the photosynthetic photon flux density (PPFD) to 1000µmol m2S1, increased PR and the proportionof roots to total plant weight, but decreased the proportionof stems plus petioles to total. In a series of experiments,the plants were grown in an 8 h photoperiod at constant temperaturesof 17, 20, 26 or 32 °C. As temperature increased, PR increased,but the duration of leaf expansion decreased. Leaves were largestat 20 and progressively smaller at 26, 32 and 17 °C. Biomasswas greatest for a given PI at 20 °C and decreased in theorder of 26, 32, and 17 °C. The proportion of axillary growthalso was greatest at 20 °C. When plants were grown in a15 h photoperiod at temperatures from 17.1 to 26.6 °C, leafsize continued to increase up to the highest temperature. At17 °C, the PR in the 15 h photoperiod (PPFD 390 µmol;m2S1) was about threefold greater than in 8 h(500 µmol m2 S1); biomass accumulation perday was about fivefold greater. Increasing N from 3 to 36 mMincreased PR about 10 per cent, altered biomass partitioningamong plant parts, and increased the biomass of the plants.The NO2 form of N markedly stimulated axillary growth as comparedwith the NH4+ form. Environment or cultivar had little influenceon the duration of leaf expansion in terms of PI. Cultivarsdid not differ consistently in biomass production and allocationin the different environments. Glycine max (L.) Merrill, soybean, soya bean, plastochron index, leaf development, growth analysis, partitioning, light, nitrogen, temperature 相似文献
18.
During the 1983 el Niño, filter fractionationshowed that over 80% of the chlorophyll-based phytoplanktonbiomass in the Santa Barbara Channel was <5 µm. Largernanoplankton (530 µm) accounted for the chlorophyllin the remaining fraction but, unlike other years, no significantquantities of net plankton <30 µm were detected. Thepopulation as a whole was dominated by chroococcalean cyanobacteriawhich were two times were abundant (123±24x103 cellsml1 than previously reported for the California CurrentSystem (Krempin and Sullivan, 1981). Numbers of other typesof bacteria were uniformly low (277±44x103 cells ml1Cyanobacteria and larger nanoplankton exhibited similar diurnalpatterns of photosynthesis, i.e., maximal rates of light-saturatedphotosynthesis (Pmax) occurred mid-day and day-night amplitudeswere >2.0. In both size fractions the onset of the rise andfall in Pmax preceded sunrise and sunset, respectively, andthe photosynthetic periodicity was independent of both chlorophyllcontent and dark fixation of inorganic carbon. Unlike previousstudies on diel periodicity in phytoplankton, no significantoscillations in light-limited rates of photosynthesis ( 相似文献
19.
Koski Marja; Moller Eva F.; Maar Marie; Visser Andre W. 《Journal of plankton research》2007,29(7):641-654
Despite the potential importance of zooplankton in degradationof marine snow, the association of colonising zooplankton withdiscarded appendicularian houses has not been investigated innorthern areas. We sampled the vertical distributions of appendicularians,houses and potential zooplankton colonisers at two stationsin the central North Sea during late summer. In addition, grazingexperiments were performed with the copepod Microsetella norvegica,which was assumed to be the main contributor to house degradation.The results were used in (i) inverse modelling, to estimatethe factors which were significant in shaping the vertical distributionof houses and (ii) calculations to estimate potential housedegradation rates. M. Norvegica was able to feed on appendicularianhouses, with feeding rates up to 0.42 g C (g C)1 day1(0.14 µg C ind.1 day1). The model resultssuggested that the vertical distribution of houses was shapedby sinking of houses, bacterial degradation and feeding of M.norvegica and invertebrate larvae. The estimated community degradationrate by M. norvegica was low, whereas invertebrate larvae haddegradation rates close to bacterial degradation. We concludethat at the typical concentrations of M. norvegica in the NorthSea (104 ind. m2), its role in marine snow degradationis likely to be small. Degradation by other zooplankton groups,such as invertebrate larvae, can, however, be substantial. 相似文献
20.
Growth rates of two freshwater diatoms and three chlorophyteswere compared under 3 h days at 10 µmol m2 s1.Specific growth rates ranged between µ=0.03 day1and µ=0.055 day1 for the different species andwere in every species independent of temperature between 8 and16°C. 相似文献