Therefore we also investigated the variability in nitrogen isotope composition within the individual organisms in our study. Limpets from two locations (7 and 14) were dissected, and different tissues of the body (muscle, digestive organs, head, mantle) were analysed separately. The variations in nitrogen isotope composition of the tissues are presented in Fig. 4. The results of the mean 15N values show fractionation in the following way: head (7.05‰), muscle(6.74‰), digestive organs (6.72‰) and mantle (6.41‰). Differences in mean 15N values between tissues within a single organism were below 0.7‰.