EFFECTS OF WAVE EXPOSURE AND INTRASPECIFIC DENSITY ON THE GROWTH AND SURVIVORSHIP OF SARGASSUM-MUTICUM (SARGASSACEAE, PHAEOPHYTA)

In this paper we quantify the interactive effects of wave exposure and intraspecific density on the survivorship and growth of Sargassum mut icum in northern Spain. Juveniles settled onto slate plates were exper imentally thinned to two densities and transplanted to exposed and she ltered shores. Initially, plants grew faster at the exposed sites but final lengths were similar between exposures after 5 months, largely b ecause of breakages at the top of the main primary lateral of plants a t exposed sites. Mean weights of plants did not significantly differ b etween exposures. The results indicate that S. muticum juveniles growi ng at high density were longer and thinner but similar in weight to th ose at low density. Patterns of growth of larger plants transplanted b etween sheltered sites similarly suggested changes in morphology of S. muticum in response to differences in density. Survivorship of juveni les did not differ between exposures but was significantly poorer at t he higher density irrespective of wave exposure. The results of this a nd previous studies suggest that the abundance of S. muticum in the lo w intertidal area of exposed shores in northern Spain is limited at se veral life-history stages. The relative importance of these potential bottlenecks compared with the availability of propagules remains unkno wn.