Experimental removal of various types of dominant canopies have resulted in predictable patterns of competitive hierarchies among algae in intertidal and subtidal communities. However, few attempts have been made to distinguish functionally different groups of algae in these communities. The intertidal/subtidal boundary of exposed rocky habitats in central Chile is numerically dominated by the kelp Lessonia nigrescens. When the kelp is absent, 2 other algal formations can be found at this intertidal level. In vegetational openings surrounded by individuals of L. nigrescensand in the absence of large grazers, large patches of Gelidium chilenseoccur. In vegetational openings with abundance of grazers, patches of calcareous algae and bare rock are normally found. Through experimental manipulation we evaluate the ecological changes of the understory algal assemblages following removal of the numerically dominant L. nigrescens and confirm that, with minor differences the 3 functional groups of algae distinguished elsewhere ('canopy forming', 'fugitive' and 'obligated understory') also occur here. By experimental removal at different seasons and in presence or absence of sea urchins we explain the occurrence of the 2 algal formations found in areas devoid of kelp.
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Ojeda et al. (1984) studied this question.