MEPS 358:13-25 (2008)  -  DOI: https://doi.org/10.3354/meps07294

ABSTRACT: Estuarine areas provide highly valuable ecosystem benefits for human populations, despite being under intense demographic, economic and ecological pressures. Hence, an understanding of the structure and function of estuarine ecosystems is essential for understanding the persistence and stability of these ecosystems and their response to perturbations. This study synthesises available data and knowledge about the Gironde estuary (SW France) in a mass-balanced trophic model to illustrate potential key patterns in the functioning of the estuarine ecosystem and key elements of its stability. In order to evaluate the total direct and indirect impact on the whole community of the 2 main sources of anthropogenic perturbations in the estuarine area, mortalities induced by fishing and the Blayais nuclear power plant were included in the model. The results suggest that in the Gironde, a typical heterotrophic estuary, there is an asymmetrical flow between distinct and complementary energy channels that enhances the stability of the food web. This dynamic process is illustrated by differential trophic flows in the water column according to the seasons. The succession of species in the environment indicates an optimisation of the use of the available carbon resources over a typical year by the estuarine biological communities. Finally, it seems that an increase in human impacts could significantly affect the topology and functioning of the food web by altering stabilizing elements of the network and decreasing the diversity of trophic flows that insures resilience of the trophic structure.

KEY WORDS: Estuarine ecosystem · Food web · Network analysis · Stability · Diversity · Ecopath · Gironde estuary