Ecological limits to the invasion of Sargassum muticum in northern Spain

In northern Spain Sargassum muticum is abundant on sheltered shores and in tide pools on exposed shores, but is rare or absent at low-intertidal levels on exposed shores. An experiment on two shores indicated that S. muticum has an effective dispersal range of less than 5 m and that the presence of fertile plants in the immediate vicinity were required for settlement of large numbers of S. muticum. Few recruits were recorded in quadrats with a canopy of turfing and foliose algae. The results suggest that the lack of free space and supply of propagules play important roles in limiting the invasion of S. muticum at an exposed shore in northern Spain. It therefore appears unlikely that S. muticum will significantly disrupt the ecology of the low-intertidal level on exposed shores in northern Spain. q 1998 Elsevier Science B.V.