The intertidal macrofauna of the inner part of the Baie de Somme, cons
tituting the estuary of the Somme has been investigated. The condition
s in the area range from tidal freshwater into virtually marine condit
ions over a short distance of 4 km. The fauna comprised a compressed e
stuarine sequence. In such a situation salinity is the controlling eco
logical factor although sedimentary conditions are also of importance.