was reported for N. lapillus. Furthermore, comparisons between mean FST values between island and mainland populations of S. balanoides (Fig. 2) for each island locality showed significant differences (F3,15 = 8.6, P < 0.001) between the islands located close to the mainland (Skomer and Inishbofin Islands), compared with those located further offshore (Lundy and Inishmaen Islands). No such significant difference was reported for N. lapillus (F3,15 = 1.32, P = 0.30). There was strong