In northern Spain Sargassum muticum is abundant on sheltered shores an
d in tide pools on exposed shores, but is rare or absent at low-intert
idal levels on exposed shores. An experiment on two shores indicated t
hat S. muticum has an effective dispersal range of less than 5 m and t
hat the presence of fertile plants in the immediate vicinity were requ
ired for settlement of large numbers of S. muticum. Few recruits were
recorded in quadrats with a canopy of turfing and foliose algae. The r
esults suggest that the lack of free space and supply of propagules pl
ay important roles in Limiting the invasion of S. muticum at an expose
d shore in northern Spain. It therefore appears unlikely that S. mutic
um will significantly disrupt the ecology of the low-intertidal level
on exposed shores in northern Spain. (C) 1998 Elsevier Science B.V.