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1.
Pyrosoma atlanticum (Tunicata, Thaliacea): grazing impact on phytoplankton standing stock and role in organic carbon flux 总被引:2,自引:0,他引:2
Drits Alexander V.; Arashkevich Elena G.; Semenova Tatjana N. 《Journal of plankton research》1992,14(6):799-809
Pyrosomas are the large group of pelagic tunicates whose trophicrole in pelagic communities has not yet been sufficiently studied.We ran across a local area of high concentration of the mostwidespread and commonest species of pyrosomas, Pyrosoma atlanticum,450 miles off the Congo river mouth. The following was estimated:gut pigment content, defecation rate, organic carbon and pigmentcontent of fecal pellets, and sinking rate. Based on these dataand the measured number of pyrosomas colonies the grazing impacton phytoplankton and the fecal pellet flux were calculated.During the night swarms of 5065 mm P.atlanticum removed53% of phytoplankton standing stock in the 010 m layer;sparsely distributed pyrosomas consumed only 4%. The grazingimpact in the 050 m layer was only 12.5 and <1% respectively.The fecal pellet flux resulting from nocturnal feeding of P.atlanticumwhile swarming made up 1.41.6 x 106 pellets m210 h1 or 3051035 mg C m2 10 h1 and1.4 x 105 pellets m2 10 h1 or 87.4 mg C m210 h1 while non-swarming. Incubation experiments showedthe rapid degradation of fecal pellets at 23°C: the lossof pigment and carbon content was {small tilde}6070%after 45 h. We believe that given the sinking rate of 70 m day1the main part of fecal material does not leave the upper watercolumn and is retained in the trophic web of the epipelagiclayer. 相似文献
2.
Zooplankton fecal pellet fluxes and vertical transport of particulate organic material in the pelagic environment 总被引:3,自引:0,他引:3
Fecal pellet fluxes were determined using a series of multireplicatetraps set at 35, 65, 150, 500, 750 and 1500 m in the northeastPacific. Fecal pellets appear to be important contributors to total carbonfluxes. In near-surface waters (35150 m), pellet fluxesranged from 23 x 105 pellets m2 day1. Minimumpellet fluxes were observed at 500m({small tilde}0.4x 105 pelletsm2day1). In contrast, the 1500 m pellet flux valueincreased to approximately 0.8 x 105 pellets m2 day1relative to the 500 m depth, and is probably the result of insitu repackaging. Analyses of pellet content suggest multiplesources of "large" particle input throughout the water column.The implications of this phenomenon are discussed in terms ofthe detrital rain and ladder of migration theories. 相似文献
3.
The impact of short-term exposure to UV-B radiation on zooplankton communities in north temperate lakes 总被引:7,自引:0,他引:7
Williamson Craig E.; Zagarese Horacio E.; Schulze Peter C.; Hargreaves Bruce R.; Seva Jennifer 《Journal of plankton research》1994,16(3):205-218
We exposed natural zooplankton communities to in situ levelsof sunlight for 3 days at different depths in two north temperatelakes: one oligotrophic and one eutrophic. Natural fluxes ofUV-B radiation (280320 nm) were manipulated with cutofffilters (Mylar®). There was substantial mortality in someof the zooplankton exposed to UV-B in the oligotrophic lake,but not in the eutrophic lake. Reproduction of Diaptomus wassuppressed by UV-B down to 6 m in the oligotrophic lake. Thesedata suggest that natural levels of UV-B radiation in the oligotrophiclake may prevent some species of zooplankton from continuouslyexploiting the warm surface waters during summer stratification.In the more eutrophic lake, UV-B is a less important constraintin the vertical distribution of zooplankton. These differencesin the responses of zooplankton to natural UV-B radiation inlakes may alter their ecological interactions with food resources,predators and other environmental variables in the water column.
1Present address: Universidad Nacional del Comahue, Centro RegionalUniversitario Bariloche, CC 1336, (8400) Bariloche, Argentina
2Present address: National Academy of Engineering, 2101 ConstitutionAvenue, NW, Washington, DC 20418, USA 相似文献
4.
Summer nutrient dynamics in the Middle Atlantic Bight: primary production and utilization of phytoplankton carbon 总被引:2,自引:0,他引:2
Falkowski P.G.; Vidal J.; Hopkins T.S.; Rowe G.T.; Whitledge T.E.; Harrison W.G. 《Journal of plankton research》1983,5(4):515-537
In late summer, production and utilization of carbon in thestratified water of the Middle Atlantic Bight appears to approachsteady-state conditions. In the euphotic zone there is a paniculateorganic carbon (POC) pool of {small tilde}6000 mg Cm2.Primary production adds {small tilde}350 mg C m2 d1,while zooplankton ingestion removes {small tilde}450 mg C m2d1, of which {small tilde}135 mg C m2 d1are returned to the POC pool as feces. Sinking of POC averages{small tilde}240 mg C m 2 d1. Thus, there is anet loss from the euphotic zone of {small tilde}200 mg C m2d1, which represents a removal rate from the POC poolof {small tilde}3%d1. However, sinking losses of phytoplanktoncarbon from the POC pool were small ({small tilde}12 mg C m2d1), which suggests that most of the primary productionenters the pelagic food chain. This is in sharp contrast tothe conditions in early spring, when the POC pool increasessubstantially, and the main loss is sinking rather than heterotrophicconsumption.
*This research was supported by the U.S. Department of Energyunder Contract No. DE-AC02-76CH000I6. 相似文献
5.
The importance of benthic recruitment to the population development of Aphanizomenon flos-aquae and internal loading in a shallow lake 总被引:7,自引:0,他引:7
The recruitment of Aphanizomenon flos-aquae out of the sedimentswas measured in the shallow, hypereutrophic Agency Lake, Oregon.There were two main episodes of recruitment, the latter of whichaccounted for 8.2% of the water column population increase duringits main growth phase. Phosphorus (P) content was higher innewly recruited cells than in water column cells. Recruitmentduring one weekly episode constituted an internal P load rateof 3.56 mg P m2 day1, accounting for 27% of thecorresponding increase in water column total phosphorus (TP).However, the majority of internal loading in the lake did notcoincide with, and therefore could not be explained by, biotranslocationdue to benthic recruitment of A.flos-aquae.
1Present address: WES-ES-P, USAE Waterways Experiment Station,3909 Halls Ferry Road, Vicksburg, MS 39180, USA 相似文献
6.
Bioluminescence of sound-scattering layers in the Gulf of Maine 总被引:2,自引:0,他引:2
Submersible-based investigations of bioluminescence were conductedin sound-scattering layers (SSLs) in the Gulf of Maine, usingintensified video and dual-beam acoustic methods. Stimulatedbioluminescence in the SSLs was high (341 µW sr1m3 while spontaneous bioluminescence was not detected.The average intensity of individual bioluminescent sources inthe SSLs was 30200 times greater than the intensity oflight emitters outside the SSLs. The two brightest sources ofbioluminescence were identified as the euphausiid, Meganyctiphanesnorvegica and the cydippid ctenophore, Euplokamis sp. Meganyctiphanesnorvegica formed a SSL within 50 m of the bottom during theday and migrated to the uppermost 30 m of the water column atnight, forming a near-surface SSL. Euplokamis sp., which producedexceptionally intense and long-lasting bioluminescent secretions,occurred within the near-bottom SSL in concentrations up to7 m3. Our findings indicate that traditional methodsof identifying the primary light emitters in a region, basedon light measurements from net- or pump-captured organisms,may have underestimated the significant in situ bioluminescencepotential of euphausiids and gelatinous zooplankton.
3 Present address: NOAA/NURP/R-OR2, Silver Spring, MD 20910,USA 相似文献
7.
Summer nutrient dynamics of the Middle Atlantic Bight: nitrogen uptake and regeneration 总被引:4,自引:0,他引:4
Harrison W.G.; Douglas D.; Falkowski P.; Rowe G.; Vidal J. 《Journal of plankton research》1983,5(4):539-556
Nitrate and ammonium uptake and ammonium regeneration rates(by zooplankton, microplankton and benthos) were measured onthe Atlantic continental shelf (Middle Atlantic Bight) duringsummer, 1980. Euphotic zone profiles of NO3 and NH4+uptake rates were similar in magnitude and vertical structureover a large geographical area. Microplankton NH4+ regenerationrates, although measured less frequently, also showed a relativelyconsistent vertical structure; rates were positively correlatedwith uptake rates. Nitrate assimilation (new production)was used to estimate vertical eddy diffusivity and paniculatesinking rates. Eddy diffusion estimates ranged from <0.1to >2.0 cm2 s1 and were positively related to arealprimary production. Estimated particulate sinking rates averaged5 mg at Nm2d1 and compared favorably with sedimentationrates measured from free-floating and moored sediment traps.Benthic nitrogen regeneration rates represented <10% of thispaniculate nitrogen flux. Within the mixed layer, NH4+ assimilation(regenerated production) represented 5080%of the total (NO3 + NH4+ ) nitrogen productivity and33% for the euphotic zone. Of this, 30% was attributed to zooplankton,63% to microplankton (<100 µm) and 7% to benthos. Onthe average, 74% of the microplankton NH4+ regeneration wasassociated with organisms passing 1 µm filters. 相似文献
8.
The number, size (mm3 pellet 1) and total volume of fecalpellets produced (mm3 h1) by Boeckella titicacae increasedwith concentration of Chlorella and natural seston in threedifferent lakewaters from Bahia de Puno and Lago Grande of LakeTiticaca and nearby Laguna Arapa. The three lakewaters differedin the size and number of fecal pellets produced at seston concentrations>0.5 mg dry wt l1. However, the total volume of fecalpellets egested varied little. Large-sized food (>10 µg)resulted in larger pellets but smaller total fecal production.Food concentration had parallel effects on the production offeces and on feeding rates. Both fecal production and feedingincreased linearly with food concentration with saturation between5 and 7.5 x 105 Chlorella ml1 (3.75.6 mg dry wtl1). Varied responses in fecal production when fed differentsize fractions of lake seston suggest Boeckella has a complexand flexible feeding behavior. Feeding preferences of B.titicacaeand B.occidentalis (Ivlev index) for two seston size fractionsare generally reflected by fecal production. 相似文献
9.
A paralytic shellfish poisoning (PSP) incident caused by consumptionof the mussel Mytilus edulis occurred for the first time inKorea in April 1986. Weekly water samplings were carried Outduring the period from 7 March to 21 April 1989 in Chinhae Bay,Korea, in order to identify the causative organism. The temperaturecharacteristics of the water column indicated three differenthydrological regimes: well mixed (up to 7 March), weakly stratified(1731 March) and stratified (721 April). Toxicityof the phytoplankton was detected during the weakly stratifiedperiod, but only in the 1050 p.m phytoplankton size fraction.This study presents the occurrence of the toxigenic dinoflagellateAlexandrium tamarense, which is a causative organism of PSP,in Korean coastal waters. Its biomass varied at different depthsin the water column, ranging from 200 to 8000 cells 11in the water column. The weekly fluctuation of A.tamarense toxicitywas similar to that of mussel toxicity.
1 Present address: Department of Biology, College of NaturalSciences, Hanyang University, Seoul 133-791, Korea 相似文献
10.
The relationship between chlorophyll a (Chl a) and primary productivity(PP) in the uppermost water layer and the water column-based(015 m) integral values of those variables were examinedusing measurements taken in Lake Kinneret (Israel) from 1990to 2003. In 81% of all Chl a profiles examined, the distributionwas fairly uniform within the entire 015 m water column,and 12.3% of instances showed a prominent subsurface maximum,when the lake phytoplankton was dominated by the dinoflagellatePeridinium gatunense. Chl a can be reliably estimated by remotesensing techniques in the productive and turbid water of LakeKinneret, since Chl a concentration at surface layers can beextrapolated to the entire water column. Light vertical attenuationcoefficient average for wavelengths from 400 to 700 nm, Kd,ranged from 0.203 to 1.954 m1 and showed high degreeof temporal variation. The maximal rate of photosynthetic efficiency,PBopt [average 3.16 (±1.50)], ranged from 0.25 to 8.85mg C m3 h1 mg Chl a1. Using measured dataof Chl a, PBopt, and light as an input, a simple depth-integratedPP model allowed plausible simulation of PP. However, a lackof correlation between photosynthetic activity and temperature(or other variable with remotely sensed potential) renders theuse of models that require input of photosynthetic efficiencyto calculate integrated PP of little value in the case of productiveand turbid Lake Kinneret. 相似文献
11.
The total and heterotrophic bacterial microflora of gut andfecal pellets of the copepod Temora stylifera was studied inthe coastal zone of the northwestern Mediterranean basin. Digestivetracts and feces were always found to contain bacteria. Withmean values close to 1011 cells ml1and 1010 colony-formingunits (CFU) ml1, both total and heterotrophic communitiesfound in fecal pellets largely exceeded the corresponding bacterialmicroflora observed in surrounding seawater (105 cells ml1 and103 CFU ml). In the same way, the frequency of dividingcells and mean cell volumes increased, respectively, from 3%and 0.12µm3 in seawater to >6% and 0.24 µm3 infecal pellets. The bacterial community structure was investigatedby carrying out 29 morphological and biochemical tests on 147isolated strains. Although Pseudomonas was always the most frequentlyencountered genus, the bacterial communities found in copepodfecal pellets clearly differ from those inhabiting seawater.Vibrio species, which were not detected in seawater microflora,were always present in fecal pellet communities. The close correspondenceobserved between the potential metabolic characteristics ofthe fecal bacterial communities isolated from a subantarcticdeposit feeder (Mytilus edulis) and from zooplankton in thisMediterranean study suggests that the fecal community differentiationis an even more general feature. 相似文献
12.
The contribution of ammonia excreted by zooplankton to phytoplankton production in Narragansett Bay 总被引:1,自引:0,他引:1
Ammonia excreted by mixed zooplankton populations over an annual(19721973) cycle in Narragansett Bay varied from 0.04to 3.21 µg at NH3-N dry wt1 day1, exclusiveof two exceptional rates measured one year apart: 11.74 and18.39 µg at NH3-N mg dry wt1 day1. Grossphytoplankton production integrated over the year (19721973)averaged 151 mg C m3 day1 for an 8 m water column;peaks of 332 and 905 mg C m3 day1 occurred duringthe winter-spring and summer blooms, respectively. Excretedammonia, integrated seasonally and annually, contributed only0.2% and 4.9% of the nitrogen required for observed gross productionduring the winter-spring and summer blooms, respectively, and4.4% annually. However, excreted ammonia may be an importantsource of the nitrogen required by Skeletonema costatum, thedominant diatom in Narragansett Bay, during the post-bloom periodwhen 186% of the nitrogen required for its net production wasmet by ammonia excretion. A combination of zooplankton ammoniaexcretion and benthic ammonia flux contributed 22% of the nitrogenrequired for the annual gross production (440 g C m2)while 51% of the nitrogen required for the net production ofSkeletonema was accounted for by regenerated nitrogen.
1This research was supported by NSF grant GA 31319X awardedto Dr.T.J.Smayda. 相似文献
13.
Nodulated 1-1.5-year-old plants of Acacia littorea grown inminus nitrogen culture were each partnered with a single seedlingof the root hemiparasite Olax phyllanthi. Partitioning of fixedN between plant organs of the host and parasite was studiedfor the period 48 months after introducing the parasite.N fluxes through nodules of Acacia and xylem-tapping haustoriaof Olax were compared using measured xylem flows of fixed Nand anatomical information for the two organs. N2 fixation duringthe study interval (635 µg N g FW nodules1 d1)corresponded to a xylem loading flux of 0.20 µg N mm2d1 across the secretory membranes of the pencycle parenchymaof the nodule vascular strands. A much higher flux of N (4891µg mm2 d1) exited through xylem at the junctionof nodule and root. The corresponding flux of N from host xylemacross absorptive membranes of the endophyte parenchyma of Olaxhaustorium was 1.15 µg N mm1 d1, six timesthe loading flux in nodules. The exit flux from haustorium toparasite rootlet was 20.0 pg N mm1 d1, 200-foldless than that passing through xylem elements of the nodule.Fluxes of individual amino compounds in xylem of nodule andhaustorium were assessed on a molar and N basis. N flux valuesare related to data for transpiration and partitioning of Cand N of the association recorded in a companion paper. Key words: Olax phyllanthi, host-parasite relationships, N flux, Acacia, N2 fixation 相似文献
14.
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
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.
Rates of ingestion and their variability between individual calanoid copepods: direct observations 总被引:1,自引:0,他引:1
Paffenhofer G.-A.; Bundy M.H.; Lewis K.D.; Metz C. 《Journal of plankton research》1995,17(7):1573-1585
The goals of this study were to determine rates of ingestionand fecal pellet release, and their variability, for individualplanktonic copepods over extended periods of time (>20 min).Ingestions and rejections of individual cells of the diatomThalassiosira eccentrica by adult females of the calanoid Paracalanusaculeatus were directly quantified by observing individual copepodscontinuously at cell concentrations ranging from 0.1 toli mm3l1.Average ingestion rates increased with increasing food concentration,but were not significantly different between 0.3 and 1.0 mm3l1(9.8 and 32.7 µg Cl1) of T.eccentrica. Rates ofcell rejections were low and similar at 0.1 and 0.3, but weresignificantly higher at 1.0 mm3 l1. The coefficientsof variation for average ingestion rates of individual copepodshardly differed between food concentrations, ranging from 17to 22%, and were close to those for average fecal pellet releaseintervals which ranged from 15 to 21%. A comparison betweenindividuals at each food concentration found no significantdifferences at 1.0; at 0.1 and 0.3 mm3l1, respectively,ingestion rates of four out of five females did not differ significantlyfrom each other. Average intervals between fecal pellet releaseswere similar at 0.3 and 1.0 mm3l1 of T.eccentrica, butsignificantly longer at 0.1 mm3 l1. Fecal pellet releaseintervals between individuals were significantly different ateach food concentration; these significant differences wereattributed to rather narrow ranges of pellet release intervalsof each individual female. Potential sources/causes of variabilityin the sizes and rates of copepods in the ocean are evaluated.
3Present address: Great Lakes Environmental Research Laboratory,2205 Commonwealth Boulevard, Ann Arbor, Ml 48105, USA 相似文献
17.
Miralto A.; Ianora A.; Guglielmo L; Zagami G.; Buttino I. 《Journal of plankton research》1998,20(12):2369-2378
In situ rates of egg production and hatching success are reportedfor Calanus simillimus, one of the most abundant calanoid speciesin peri-Antarctic regions, during the Italian Italicscruise in the Straits of Magellan in March-April 1995. Low fecundity(8.6 eggs female1 day1) and fecal pellet production(0.8 fecal pellets female1 day1) in this periodindicate that the species was feeding very poorly. Sixty-sixof the 126 females sampled did not produce eggs and 80 of thesedid not produce any fecal pellets during the 24 h period ofincubation. Striking abnormal naupliar and embryonic developmentwas recorded in 81.8% of the eggs spawned. Aberrant eggs didnot undergo normal cleavage, and failed to develop to hatching.Deformed nauplii were asymmetrical and presented strong anatomicalanomalies in the total body length and number of swimming appendages.These results are discussed in the light of recent findingson the causes of low hatching success in copepods. 相似文献
18.
The predatory copepod Mesocyclops edax is an important componentof many zooplankton communities where it typically makes extensivedid vertical migrations. To describe the effect of light onadults we measured their photoresponses in the laboratory. Theresponse spectrum is characterized by a wide plateau of greatestsensitivity from about 480 580 nm. These animals areadapted to perceive light during the day since their regionof maximum sensitivity overlaps the spectral region of highestquantal intensity underwater (575 700 nm). The thresholdintensity for positive phototaxis by dark adapted animals wasabout 5 x 101 Wm2 at 540 nm, and they were positivelyphototactic up to an intensity of 5 x 101 Wm2.Above this intensity phototaxis is no longer observed. Light-adaptedanimals were less sensitive than dark-adapted, but their generalpattern of response to light intensity did not differ. Thereis no rhythm in phototaxis. Their photoresponses may providea mechanism for controlling vertical migration so as to minimizeexposure to planktivorous fish.
1Contribution No. 1375-AEL from UM-CEES, Appalachian EnvironmentalLaboratory. 相似文献
19.
Bradford-Grieve J. M.; Nodder S. D.; Jillett J. B.; Currie K.; Lassey K. R. 《Journal of plankton research》2001,23(9):963-975
We estimate that Neocalanus tonsus makes a contribution to downwardscarbon flux of 1.79.3 g C m2 year1, insubantarctic waters, the Subtropical Front and waters immediatelyto the north, based on its ontogenetic vertical migration minusthe biomass of eggs, the products of which are returned to thesurface the following season. This flux is an order of magnitudegreater than that estimated (0.27 g C m2 year1)for vertical migration of large copepods in the North Atlantic.Over the total 55.6 x 106 km2 where N. tonsus is distributed,0.17 Gt C year1 are estimated to be lost annually tothe ocean interior. In subantarctic water, this loss represents1.4% of primary production and is 14% greater than the measuredsedimented particulate organic carbon (POC) at 300 m. Similarly,in subtropical water, carbon loss to the ocean interior fromN. tonsus seasonal migration is estimated to be 13% lower thanmeasured POC flux. Nevertheless, N. tonsus was never found intime-incremental sediment trap samples. We hypothesize thatthe apparently proportionally different role of downwards seasonalmigration of large copepods relative to sedimented POC in theNorth Atlantic compared with the subarctic North Pacific andSouthern Ocean arises because of a combination of differencesin the nutrient status of these oceans, differences in the rateof development of grazer populations in spring, and differencesin life history characteristics of large copepods. The fluxdue to the behaviour of N. tonsus in different parts of itsrange, put into the context of the estimated global-mean netflux of 1.73.7 g C m2 year1 taken up bythe ocean, may be a regionally significant amount. The summerdownward migration of N. tonsus, however, does not entirelyexplain the observed seasonal variation in regional measurementsof pCO2 off New Zealand. 相似文献
20.
Peterson William T.; Painting Suzanne J.; Hutchings Laurence 《Journal of plankton research》1990,12(2):259-281
The gut fluorescence technique was used to estimate ingestionand filtration rates of the adult female copepods Paracalanusparvus, Cenlropages brachiatus and Calanus austrails, and copepoditestages 3, 4 and 5 of C.australis in the southern Benguela upwellingregion. During the study period chlorophyll concentrations withinthe upper 20 m of the water column were high, 5 µg I1in mid-shelf waters and 1530 µg I1 in innershelf waters. Copepod gut pigment content was low and constantduring the day then increased sharply during the first 2 h aftersunset. Gut pigment content was 26 times higher duringthe night compared with daytime values. Small non-migratingcopepods (Paracalanus parvus) showed the smallest diel differencein gut pigment content and large migrating copepods (Centropagesbrachiatus and Calanus australis) the largest difference. Eggproduction rates were 20 and 50% of maximum at the mid-shelfand inner shelf stations respectively, suggesting food-limitation.Comparison of ingestion rates calculated from egg productiondata with ingestion rates calculated from gut pigment data suggestedthat the copepods were feeding omnivorously at the inner shelfstations but herbivorously at the mid-shelf stations. Assumingthat all of the phytoplankton was available as food, the nearshorecopepod assemblage grazed {small tilde}1% of the standing cropeach day, and the mid-shelf assemblage grazed 5% day1.Because of errors and uncertainties associated with the gutfluorescence technique, the feeding impact could be underestimatedby 24-fold. We discuss several approaches which couldlead to more precise estimates of feeding rates.
3Present address: Marine Sciences, SUNY, Stony Brook, NY, 11794-5000,USA 相似文献