Interannual changes in δ¹⁵N values in Fucus vesiculosus L

Highlights: • Isotopic values change along the thallus of F. vesiculosus. • δ¹⁵N values along the thallus are different between control and polluted sites. • δ¹⁵N values are temporally unstable at polluted sites. - Abstract: The natural abundance of ¹⁵N (δ¹⁵N) has been widely used to detect anthropogenically derived N loads in environmental impact studies. The present study involved retrospective analysis of subsamples of Fucus vesiculosus L. collected during a period of three years (2008–2010) from two sites: a control site, within a coastal reference area, and an area affected by the effluents of a marine land-based fish farm. The isotopic signal in different subsamples of the macroalgae thalli (tissue that has grown during the same period) varied depending on the age of the tissue. Moreover, the isotopic signal decreased significantly with the age of the frond to within a certain range. The δ¹⁵N of F. vesiculosus is temporally unstable; therefore, measurement of the δ¹⁵N of macroalgal tissues does not allow reliable retrospective biomonitoring of environmental pollution. Further knowledge about the growth and other biological aspects of this species is required