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Résumé :
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Estimation of benthic macrofauna consumption by water birds in the bay of,Saint-Brieuc (France). - The biomass and productivity of benthic invertebrates were studied in the bay of Saint-Brieue in connection with the consumption by the nine most numerous wader and duck species present on the site. This consumption is about 1.9 g ash free dry weight/m(2)/year, it is similar to that obtained in the bay of Mont-Saint-Michel but very lower to results from Wadden Sea. Eutrophication generally induces an increase in overall productivity of the intertidal coastal ecosystem, as it has been observed in the German part of the Wadden Sea since the 1950s. Consequently, the bird populations grow very significantly in eutrophic systems. But this is not the case in the bay of Saint-brieuc where macrozoobentic biomass produced and consumed by birds is comparable to what was observed in the bay of Mont-Saint-Michel, an oligotrophic marine site characterized by relatively low biomass and productivity. In the bay of Saint-Brieuc excessive inputs of nutrients induce an important development of Ulva armocicana. responsible for the spectacular green tides which greatly impact this bay each summer. The proliferation of Ulva brings the nutrient flows to a standstill and by the way regulates the production of microphytoplankton and so, indirectly, the abundance of higher trophic levels.
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