considerable spatial variation within the 

 forest, as is evident from a comparison of 

 the four transects surveyed by Turner et 

 al . (1968). This spatial variation will 

 be discussed in Section 3.4. Below we 

 describe an idealized transect (Figure 

 10), summarizing and combining the data 

 from all the transects surveyed. Surveys 

 have also been done in the nearby kelp 

 forest at La Jolla (Aleem 1956, 1973; 

 Neushul 1965), but are not discussed here. 



The kelp forest occurs on a broad, 

 gently-sloping mudstone-sandstone terrace 

 with pockets of sand, cobbles and 

 boulders. Macrocystis pyrifera was most 

 abundant between 6 and 25 m on rocky 

 substrata. Inshore of the giant kelp 

 forest, the surf grass Phyl lospadix 

 torreyi was particularly abundant, along 

 with the surface canopy brown algae 

 Egregia menziesii and Cystoseira 

 osmundacea . Articulated corallines were 

 also common, as were black perch and 

 senorita. 



When Turner et al . (1968) studied 

 Point Loma, giant kelp was sparse, 

 particularly on the more northerly 

 transects. Understory kelps were patchy 

 in occurrence but common, with 

 Pterygophora cal ifornica most abundant. 

 Common bottom cover algae included 

 articulated corallines and Rhodymenia spp. 

 The sea anemone Corynactis cal ifornica , 

 the solitary coral Balanophyllia eiegans , 

 the solitary tunicate Styela 

 montereyensis , and various sponges were 

 the most common sessile animals. The 

 whelk Kel letia kel leti i , bat stars, and 

 red and white sea urchins were the more 

 common mobile invertebrates. Red urchins 

 appeared to be keeping some areas clear of 

 foliose macroalgae. The most common fish 

 within the kelp forest were blacksmith, 

 senorita, California sheephead, kelp bass, 

 and the black-eyed goby. 



The terrace sloped more steeply 

 beyond 25 m depth, and in this deep region 

 outside the giant kelp canopy or 

 occasionally mixed with it, occurred the 

 elk kelp Pelagophycus porra . Beneath were 

 sparse stands of Laminaria farlowii , and a 

 reduced bottom cover of articulated 

 corallines, Rhodymenia spp. and Plocamium 

 cartilagineum . Invertebrates here were 

 similar to, but less diverse than, those 



at the outer edge of the giant kelp 

 forest; the gorgonian Lophogorgia 

 chi lensis was particularly abundant. Red 

 urchins were absent. The fishes, like the 

 invertebrates, were generally similar to 

 those found within the giant kelp forest. 



3.3.3 Other Geographic Areas 



With the exception of a number of 

 recent papers on South American kelp 

 forests, little information is available 

 on subtidal Macrocystis communities in 

 other parts of the world. Kuhnemann 

 (1970) described the vertical structure of 

 the vegetation in kelp forests in southern 

 Argentina. Canopy layering is similar to 

 forests in California but, with the 

 exception of Macrocystis pyrifera , the 

 species composition is very different. 

 Barrales and Lobban (1975) surveyed seven 

 sites on the coast of Argentina in March 

 1974, and found M^. pyrifera to occur from 

 the low intertidal to a depth of 15 m. 

 Plants were excluded from deeper water by 

 lack of hard substrata. The species 

 composition of associated organisms varied 

 with exposure to oceanic swells. Barrales 

 and Lobban (1975) suggested that 

 Macrocystis in this region goes through a 

 three- to four-year loss-replacement cycle 

 caused by holdfast deterioration and 

 storms. Older holdfasts are apparently 

 weakened by a boring isopod ( Phycol imnoria 

 sp.) and become susceptible to removal by 

 surge after three to four years of growth. 

 These authors also suggested that this 

 regular loss-replacement cycle contributes 

 to the low species diversity of these 

 forests relative to those in California. 

 However, some forests in California can 

 exhibit similar cycles (see Section 

 3.5.1). Sea urchins were not abundant at 

 these South American sites, and appeared 

 to have little impact on the community. 



Giant kelp forests in southern Chile 

 are also apparently limited to shallow 

 water by lack of suitable substrata, and 

 their inner margins can be determined by 

 competition with understory kelps 

 (Santelices and Ojeda 1984b). These 

 authors suggested that the Macrocystis 

 pyrifera loss-replacement cycle described 

 by Barrales and Lobban (1975) in Argentina 

 does not occur at their site. Two species 

 of the kelp, Lessonia , form understory 

 canopies in southern Chile, and foliose 



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