The relationship between oceanographic distances (Table 2) and genetic differentiation between the populations of S.
balanoides and N. lapillus are shown in Fig. 2. A strong positive correlation was reported for S. balanoides (Mantel test r = 0.82, P < 0.001, 10,000 permutations), while a weaker, insignificant correlation (Mantel test r = 0.42, P = 0.10, 10,000 permutations)