collected from sampling sites (SS) along the
entire coast of Galicia (NW Spain) in 5 sampling surveys carried out between 1990 and 2007, were
stored in an Environmental Specimen Bank (ESB). The ı15N was measured in the macroalgal tissues as
an indicator of eutrophication. A decrease in ı15N (p < 0.05) was observed in all species (except for F.
vesiculosus in 2007) in successive surveys. ı15N values were higher in macroalgae from interior zones of
the estuaries than in macroalgae collected from the open sea. The method was sensitive enough to detect
variations in ı15N signatures and SS with anomalous values, and to compare trends in contamination on a
regional scale. The method is therefore a useful tool for the establishment of environmental improvement
programmes (e.g. European Framework Directives) and monitoring surveys.