Estimation de la consommation de la macro-faune invertébrée benthique par les oiseaux d'eau en baie de Saint-Brieuc

The biomass and the productivity of benthic invertebrates were studied in the Bay of Saint-Brieuc in connection with the consumption by the nine most numerous species of limicoles and ducks present on the site. This consumption is about 1,9 g ash free dry weight/m²/year, this is similar to what was obtained in Mont-Saint-Michel bay, but is very lower to the results from Wadden Sea.Eutrophication generally induces an increase in overall productivity of the intertidal coastal ecosystem, as it has been observed in the Dutch Wadden Sea since the 50s. Consequently the birds' population grows very significantly in eutrophic systems. But this is not the case in the Bay of Saint-Brieuc where macro-zoobentic biomass produced and consumed by birds is comparable to what was observed in the Mont-Saint-Michel bay, an oligotrophic site characterized by a relatively low biomass and productivity. In the Saint-Brieuc bay excessive intakes of nutrients induced a significant development of Ulva armocicana, responsible for the spectacular green tides which greatly impacts this bay each summer. The proliferation of Ulva bring to a standstill the nutrient flows and by the way regulates the production of microphytoplankton so, indirectly, the abundance of higher trophic levels.