Trophic variations in the Bin El Ouidane oligotrophic reservoir (Morocco)
The study of the flood transport, plankton and the stomach contents of Cladoceran species and some planktivorous and omnivorous fish of the reservoir-lake Bin El Ouidane has allowed to extract the following conclusions: - flood transport of dissolved and suspended matters during the period 1995-1997 has a net influence on the seasonal dynamics of the zooplancton via changes in the dynamics of the phytoplanktonic populations; - during the same period, the peak of zooplanktonic biomass appeared generally just after spring and summer phytoplanktonic peaks showing the importance of the herbivorous zooplankton in the food chain; - the study of algal stomach contents of Cladocerans Daphnia longispina, Daphnia lumholtzi, Diaphanosoma brachyurum, Ceriodaphnia dubia, Ceriodaphnia reticulata and Bosmina longirostris showed that all species are herbivorous filter-feeders that adopt a variable diet behavior linked to the availability of the phytoplankton in the lake, to their age and biotic and abiotic characteristics of the ecosystem; - the preliminary study of the stomach contents of three omnivorous and herbivorous fish Tinca tinca, Eupomotis gibbosus and Cyprinus carpio species showed also that their food spectre was clearly dominated by the plankton. The animal fraction in their digestive tube was represented by large Cladoceran species and Chironomes showing the importance of these fish, essentially planktivorous, in the regulation of planktonic populations in the reservoir-lake Bin El Ouidane.