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Ephyra larvae and small medusae (1.795 mm diameter, 0.01350mg ash-free dry wt, AFDW) of the scyphozoan jellyfish Aureliaaurita were used in predation experiments with phytoplankton(the flagellate Isochrysis galbana, 4 µm diameter, {smalltilde}6 x 106 µg AFDW cell1), ciliates (theoligotrich Strombidium sulcatum, 28 µm diameter, {smalltilde}2 x 103 µg AFDW), rotifers (Synchaeta sp.,0.5 µg AFDW individual1) and mixed zooplankton(mainly copepods and cladocerans, 2.13.1 µg AFDWindividual1). Phytoplankton in natural concentrations(50200 µg C I1) were not utilized by largemedusae (4495 mm diameter). Ciliates in concentrationsfrom 0.5 to 50 individuals ml"1 were consumed by ephyra larvaeand small medusae (314 mm diameter) at a maximum predationrate of 171 prey day1, corresponding to a daily rationof 0.42%. The rotifer Synchaeta sp., offered in concentrationsof 100600 prey I1, resulted in daily rations ofephyra larvae (25 mm diameter) between 1 and 13%. Mixedzooplankton allowed the highest daily rations, usually in therange 540%. Large medusae (>45 mm diameter) consumedbetween 2000 and 3500 prey organisms day"1 in prey concentrationsexceeding 100 I1. Predation rate and daily ration werepositively correlated with prey abundance. Seen over a broadsize spectrum, the daily ration decreased with increased medusasize. The daily rations observed in high abundance of mixedzooplankton suggest a potential scope for growththat exceeds the growth rate observed in field populations,and this, in turn, suggests that the natural populations areusually food limited. The predicted predation rate at averageprey concentrations that are characteristic of neritic environmentscannot explain the maximum growth rates observed in field populations.It is therefore suggested that exploitation of patches of preyin high abundance is an important component in the trophodynamicsof this species.
1Present address: University of Bergen, Department of MarineBiology, N-5065 Blomsterdalen, Norway 相似文献
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We monitored the hatching frequencies and clutch sizes of Eurytemoraaffinis, and environmental variables in the Gulf of Bothnia,between May and October 2003. We tested the hypothesis thatthe hatching frequency of the copepod would be negatively affectedduring time periods with high diatom concentrations. Resultsfrom two stations showed significant differences between thedifferent sampling occasions, with the lowest observed hatchingfrequency during the spring diatom bloom. The reverse was truefor clutch size, with the highest average egg number duringthe diatom bloom. These results were not correlated to ambienttemperature, salinity or chlorophyll a (Chl a). In a separatelaboratory experiment, nine different local clones of the diatomSkeletonema costatum were used as food for adult E. affinisfemales, in order to screen for possible differences in toxicitywithin the Skeletonema community. The resulting average copepodhatching frequency varied between 5 and 75% for the differentclones, indicating that there can be large within-species variationin the toxic properties of diatoms. The significance of suchvariations in natural communities remains to be tested in futurestudies. 相似文献
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Sornes Tom A.; Aksnes Dag L.; Bamstedt Ulf; Youngbluth Marsh J. 《Journal of plankton research》2007,29(2):157-167
The mesopelagic coronate medusa Periphylla periphylla has beenvery abundant (20320 individuals m2), with asmany as 2.5 individuals m3, for more than a decade incertain Norwegian fjords. These abundances are two to threeorders of magnitude higher than reported from open ocean environments.Comparisons of the size, density and behavior of this jellyfishin three fjords (Lurefjorden, Sognefjorden and Halsafjorden)support the hypothesis that retention of P. periphylla is relatedto basin topography, light attenuation and photosensitivity.Furthermore, we hypothesize that the abundances of P. periphyllain Lurefjorden and Halsafjorden, but not in Sognefjorden, havebeen stimulated by increased light absorbance of water massesformed in the North Sea. 相似文献
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An evaluation of acoustic and video methods to estimate the abundance and vertical distribution of jellyfish 总被引:5,自引:1,他引:4
Four non-invasive methods (three acoustic and one video) werecompared to estimate the abundance and vertical distributionof scyphomedusae, using the locally abundant coronate speciesPeriphylla periphylla in Lurefjorden, north of Bergen, Norway,as the test organism. The acoustic methods included single-targetquantification by, respectively, a hull-mounted 38 kHz split-beamecho sounder and a 675 kHz scanning sonar mounted on a remotelyoperated vehicle (ROV). Data from acoustic backscattering providedestimates of abundance and changes in the vertical positionof scattering (= aggregation) layers. Vertical migration wasalso studied by acoustic target tracking, following single individualsas they ascended in the afternoon. The ROV-mounted scanningsonar missed an unidentified part in the lower size distributionof the target population. Vertical video profiles, conductedduring ROV dives, provided the most detailed information onabundance and distribution, although uncertainties remainedregarding the size distribution in the population. 相似文献
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