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Ponsero A.,Reserve Naturelle Nationale de la baie de Saint Brieuc | Lemao P.,French Research Institute for Exploitation of the Sea
Revue d'Ecologie (La Terre et la Vie) | Year: 2011

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-Brieuc 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/m2/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 Viva 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.

Le Luherne E.,Agrocampus Ouest | Reveillac E.,Agrocampus Ouest | Ponsero A.,Reserve Naturelle Nationale de la baie de Saint Brieuc | Sturbois A.,Reserve Naturelle Nationale de la baie de Saint Brieuc | And 3 more authors.
Estuarine, Coastal and Shelf Science | Year: 2016

All over the world, numerous bays and estuarine systems that are known to shelter essential fish habitats are experiencing proliferations of green macroalgae known as green tides. Although the processes that enhance green tides in response to nutrient enrichment are well known, their consequences for ecological communities -especially for ichthyofauna- remain poorly studied. To estimate these consequences, this analysis focused on the two types of shallow systems that are experiencing green tides: sandy beaches and estuarine mudflats. In these two systems, macroalgae proliferation and fish community were surveyed along seasonal cycles at control and impacted sites that shared similar physico-chemical parameters and sediment structure. To analyse the consequences of green tides on the fish community, a Before-After Control-Impact approach was used. This approach reveals no difference between fish communities at the control and impacted sites before the macroalgal bloom. Then, it underlines an influence of green tides on the fish community, and this influence varies according to the composition, density and duration of the macroalgal bloom. Indeed, when intertidal systems experienced short proliferation and/or weak density, green tides did not seem to impact the fish community. However, when green macroalgae proliferated in large quantities and/or when the proliferation lasted for long periods, the fish community was significantly affected. These modifications in the fish community led to a significant decrease in fish species diversity and density until fish disappeared from impacted sites at high proliferations. Furthermore, the response of fish species to green tides differed according to their functional guilds. Negative consequences for benthic and marine juvenile fish species were beginning at low proliferations, whereas for pelagic fish species they occurred only at high proliferations. Thus, green tides significantly affect fish habitat suitability because they lead to changes in the composition of the fish community and eventually to the local disappearance of fish at high proliferations. © 2016 Elsevier Ltd.

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