Ref ID : 2193
Roger Pourriot, Claude Rougier, and Anne Miquelis; Origin and development of river zooplankton: example of the Marne. Hydrobiologia 345:143-148, 1997
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Zooplankton composition and growth in the river Marne (France) were studied on a space scale of 300 km in July 1991. There were three distinct areas along the river: the immediate reservoir outlet (pK 652), the natural river called middle Marne (from pK 652 to pK 799 downstream) and the channeled river (from pK 799 to pK 975 downstream). A typical lake community, characterized both by an abundance of microcrustaceans and a high zooplankton concentration was found immediately downstream of the reservoir Marne (Der-Chantecocq Lake). Here, large microcrustaceans (copepods, daphnids), and large rotifers (Keratella cochlearis robusta and Polyarthra dolichoptera-vulgaris) rapidly disappeared, and small rotifer species (<120 µm) dominated the plankton. Their populations (specially Keratella c. cochlearis) proliferated in the middle Marne as far as 100 km downstream (up to 288 ind. l-1) but were considerably reduced (20 to 35 ind. l-1) where the river is channeled, algal resources decline and turbidity increases. The dominance of small organisms such as rotifers, in river plankton is assumed to be the result of fish predation on large zooplankton as well as of a short generation time which allows their in situ reproduction, in spite of a short residence time of the water.