Measurement of δ15N in macroalgae stored in an environmental specimen bank for regional scale monitoring of eutrophication in coastal areas

The use of stored samples of macroalgae (Fucus ceranoides, Fucus spiralis and Fucus vesiculosus) to monitor contamination of coastal areas was evaluated. The samples, 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 δ15N was measured in the macroalgal tissues as an indicator of eutrophication. A decrease in δ15N (p < 0.05) was observed in all species (except for F. vesiculosus in 2007) in successive surveys. δ15N 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 δ15N 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.