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Etude des crustacés planctoniques d'une retenue soumise à des rejets thermiques : description, dynamique et relations avec le peuplement pisciaire

Abstract : The zooplanktonic community of the Mirgenbach reservoir has progressively evolued towards a steady state since its creation in 1985. Between 1986 and 1989, a tropic explosion occurred with great quantities of zooplankton and a large proliferation algae. After this period the zooplankton showed a reduction of its stock and a characteristics species established in the reservoir with a dominance of cladocerans. The water salinity, one of the characteristics of this reservoir, permits the installation of typically euryhalines species : erytemora velox for the zooplankton and actinocylus normanii for the phytoplankton. Similarly the temperature, main characteristic of the reservoir, allowed the development of Ceriodaphnia dubia (not common in France) and the display of the cycle of the summer species. Relatively high winter temperatures also allowed the maintien of some cladoceran populations during this season and an early development of the zooplankton early spring. The spatial distribution of planktonic crustaceans showed a predominate influence of physical phenomena (water movements). Two different area can be distinguished : the first, located between the input and the output works of the water, is characterized by weak densities and a less important seasonal variability. The second area is located in part of the reservoir which is not subjected to the water flow were. The community is characterized by raised densities and strong seasonal variability. The structure of the fish community showed strong variation with time. In 1990 and 1991, the roach (Rutilus rutilus) and the common bream (Abramis brama) were the dominant species. At the end of 1992 and 1993 the abundance of these species regressed, while white bream (blicca bjoerkna), until here present in low number, increased in abundance. These very rapid modifications in the community structure were caused by a strong individual growth and a reduction of life-span. In consequence, the population become very sensitive to recruitment. An absence or a poor rate of recruitment of one year can cause a modification of the community structure during several years. This case was specifically observed for the roach in 1992. The impact of fish predation on the seasonal cycle of crustacean populations was clearly observed only in the case of Daphnia longispina notably in the pelagic area. This impact is particularly important during the summer. Copepods are less subjected to predation by fish than the cladocerans. Inthe case of the cyclopoïds only copepodit stages are eaten, whereas for the calanoïds, no predation was observed
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Rachid Marzou. Etude des crustacés planctoniques d'une retenue soumise à des rejets thermiques : description, dynamique et relations avec le peuplement pisciaire. Sciences agricoles. Université Paul Verlaine - Metz, 1996. Français. ⟨NNT : 1996METZ027S⟩. ⟨tel-01777139⟩



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