Again, this study suggests the 

 importance of light to successful algal 

 recruitment, but suffers from having only 

 one experimental plot and one control , and 

 the lack of separating other factors such 

 as the effects of understory species. 



A different result occurred in a kelp 

 forest in southern Chile. Santelices and 

 Ojeda (1984a) cleared a Macrocystis canopy 

 from a 5 x 50 m transect. The dominant 

 understory plant, Lessonia flavicans , 

 increased in biomass in the non-removal 

 area but most other permanent members of 

 the community did not change in 

 distribution. The method of removing the 

 canopy, however, was different than in 

 other studies. Plants were cut 1 m below 

 the sea surface, rather than immediately 

 above the holdfast. The senescence of cut 

 fronds could have had an adverse effect on 

 Lessonia in the removal area. Recruitment 

 was not specifically recorded in this 

 study, but there appeared to be a 

 qualitatively different response to canopy 

 removal in this southern kelp forest 

 depauperate in laminarian species. 



Kastendiek (1982) examined some 

 interactions among three algal species in 

 a shallow portion of a Macrocystis - 

 dominated community at Santa Catalina 

 Island in southern California. He found 

 that two species were narrowly zoned with 

 depth: Halidrys dioeca (Fucales) occurred 

 abundantly at 0.5 m and 1.9 m below MLLW, 

 with Eisenia arborea (Laminariales) 

 occupying three intermediate depths (0.8, 

 1.2 and 1.5 m). The third species, the 

 red alga Pterocladia capil lacea , was most 

 abundant beneath Eisenia canopies. By 

 selectively removing each species, 

 Kastendiek (1982) found that if Eisenia 

 was removed, Halidrys could invade 

 intermediate depths by growing 

 adventitiously and preempting space. If 

 both Hal idrys and Eisenia were removed, 

 Pterocladia was able to occupy free space. 

 Thus, Eisenia appeared to be the 

 competitive dominant at intermediate 

 depths because its dense canopy excluded 

 Halidrys . This, in turn, allowed 

 Pterocladia to occupy the space beneath. 

 Two other factors were cited as important 

 to the coexistence of these species. 

 Large storms had a differential effect on 

 the species, removing most Eisenia plants 

 in some areas while leaving Hal idrys 



intact. Differential recruitment was also 

 important. Eisenia was able to recruit 

 beneath Hal idrys , yet even when free space 

 was available at all depths, Eisenia had 

 few recruits above and below the zone (1.2 

 m) where adult plants were most abundant. 

 The relative recruitment failure in the 

 lower area was probably not due to 

 physiological restrictions because Eisenia 

 adults are very abundant at depths to 25 

 m. In this case, the limited dispersal of 

 algal spores or the differential survival 

 of spores could be important factors. 



5.5.2 Density of Macrocystis Stands 



Hypothesis: Recruitment and growth 

 at high densities has an adverse effect on 

 the growth, reproduction, and survival of 

 Macrocystis plants. 



Evidence from many terrestrial 

 studies suggests that individual plants in 

 dense stands should exhibit lower growth, 

 reproduction, and survivorship relative to 

 plants in similar environments at lower 

 density (Harper 1977). The fact that 

 large, essentially monospecific 

 aggregations of large brown algae commonly 

 occur worldwide suggests that there might 

 be advantages to plants in denser stands, 

 in some situations. There is evidence 

 both for and against adverse effects to 

 plants in high density algal populations. 

 Schiel and Choat (1980) found that two 

 subtidal species in New Zealand, Ecklonia 

 radiata and Sargassum sinclairii , had the 

 largest plants in dense, single-species 

 stands on one semi-exposed reef. These 

 plants were of the same age and in an 

 apparently similar habitat, although 

 differences among local sites (boulders) 

 may have been important. Cousens and 

 Hutchings (1983) reached different 

 conclusions for stands of brown algae in 

 Nova Scotia. They found that large plants 

 could occur at low density, and concluded 

 that water motion was the most important 

 factor determining size and morphology. 

 Their evidence is equivocal, however, 

 because ages of plants were not known, and 

 plants were in different habitats on the 

 shore. Black (1974) found that 

 survivorship was density-dependent for 

 recruits of Egregia laevigata 

 (= menziesii ) , but that this was not the 

 case after plants were three months old. 



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