Mesure de l'intensité et de la sélectivité du bronzage zooplanctonique diurne et nocturne sur le peuplement physoplanctonique de la retenue Al Massira (Maroc) ; Measurement of the intensity and selectivity of the diurn and night zooplanktonic bronzage on the physoplanktonic population of Al Massira (Morocco)
In: oai:erudit.org:705186ar ; 705186ar ; 10.7202/705186ar ; 2097097742 ; 10|opendoar____::16e6a3326dd7d868cbc926602a61e4d0 ; 10|openaire____::081b82f96300b6a6e3d282bad31cb6e2, 2005
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Zugriff:
The Al Massira reservoir, located in the district of Settat 120 km south-east of Casablanca, is of great importance notably at the level of the management of the Oum Er Rbia River-catchment basin.Several grazing experiments were performed to assess the intensity of phytoplankton predation by zooplankton species, on 20 March l992, 27 and 28 May 1992, respectively, over the day and the night. Two enclosures were used and incubated in situ at 5 and 15 m over 8 hours, The first enclosure consisted of a mixture of several phytoplankton and zooplankton species. The second was free of zooplancton.The results clearly demonstrated that the technique used in this work seemed to be effective in that a signifïcant difference between the initial and final numbers of phytoplankton species incubated in the enclosure was detected. In addition, we confirmed several literature reports relative to the selective characteristics of herbivore predation on algae: large phytoplankton (e.g., Peridinium cinctum, Ceratium hirundinellaand Staurastrum pingue) were not affected. The grazing pressure depended on the size of preys and on the exudates released by the physiofogically active small phytoplankton species (e.g., Oocystis crassa, Cyclotella sp.) evolving in the enclosures. Among small preys, only species with high growth rate (estimed in the control flask, e.g., Cosmarium sp. and Tetraedron sp.) were subjected to the zooplankton predation. The copepod nightgrazing was lower than that recorder during the day, probably due to a decrease in their ability to detect preys in the dark.Our result contradict several results obtained by the method of NANEY (1971) according to which grazing increases during the night.Two assumptions may be proposed to explain such a discrepancy:- The zooplankton community of the Al Massira Reservoir was quantitatively dominated by the Calanoid Neolovenula alluaudi.Yet, according to HANEY and HALL (1975), these Copepods showed a slight diel grazing change compared to that of Cladocera. It seemed likely that ...
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Mesure de l'intensité et de la sélectivité du bronzage zooplanctonique diurne et nocturne sur le peuplement physoplanctonique de la retenue Al Massira (Maroc) ; Measurement of the intensity and selectivity of the diurn and night zooplanktonic bronzage on the physoplanktonic population of Al Massira (Morocco)
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Autor/in / Beteiligte Person: | Moncef, M. ; Fahde, A. ; Devaux, J. ; Malki, M. |
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Zeitschrift: | oai:erudit.org:705186ar ; 705186ar ; 10.7202/705186ar ; 2097097742 ; 10|opendoar____::16e6a3326dd7d868cbc926602a61e4d0 ; 10|openaire____::081b82f96300b6a6e3d282bad31cb6e2, 2005 |
Veröffentlichung: | Université du Québec - INRS-Eau, Terre et Environnement (INRS-ETE), 2005 |
Medientyp: | academicJournal |
DOI: | 10.7202/705186ar |
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