Heavy d15N in intertidal benthic algae and invertebrates in the Scheldt Estuary (The Netherlands): Effect of river nitrogen inputsd13C vs d15N of co-occurring molluscs within a community dominated by Crassostrea gigas and Crepidula fornicata (Oosterschelde, The Netherlands)Determination of food sources for benthic invertebrates in a salt marsh (Aiguillon Bay, France) by carbon and nitrogen stable isotopes: importance of locally produced sourcesUtilization of food sources by invertebrates in a man-made intertidal ecosystem (Westerschelde, the Netherlands a d13C and d15 N study