Analysis of the trophic network of a macrotidal ecosystem: the Bay of Somme (Eastern Channel)

A steady state mass-balance trophic model with Ecopath II was constructed to determine the flow of energy in the trophic network of the Bay of Somme. Parameters were taken or estimated from field and laboratory studies or from literature for fishes and birds. Particulate organic carbon flux has been described in relation to freshwater and tidal inputs. Results of Network Analysis indicate that only 1/8 of the input is from the benthic and pelagic primary production (589 gCm 2 yr 1) and that herbivores use only 6% of this production. An important part of this production is exported and recycled to detritus with a detritivory/herbivory ratio of 8.5. The trophic network of the Bay of Somme has a low level of recycling ðFCI ¼ 12:2%Þ and a low level of organization as indicated by several indices like Ascendancy, Capacity, Redundancy and Ascendancy/Capacity. All of these results show an ecosystem with a low maturity, a great production of energy and a low diversity of resources. These results confirm that the Bay of Somme is an ecosystem where detrital flow appears to be the most important input of energy and which exports a significant part of energy (27.9%).