red algae are common on the bottom. 

 Experiments by Castilla and Moreno (1982) 

 indicated that the four species of sea 

 urchins inhabiting this area feed on drift 

 algae and have little impact on 

 Macrocystis recruitment, growth, or 

 survivorship. The Macrocystis holdfast 

 fauna is less diverse than that in 

 California (Ojeda and Santelices 1984), as 

 are the fish associated with the forest 

 (Moreno and Jara 1984). 



More northerly Chilean kelp forests 

 studied by Moreno and Sutherland (1982) 

 are also often limited to shallow water by 

 lack of hard substrata, and giant kelp 

 abundance is regulated primarily by water 

 motion and not herbivorous urchins or 

 mol luscs. 



3.4 DISTRIBUTIONAL VARIATION WITHIN SITES 

 3.4.1 Between Depths 



Although considerable variation in 

 distribution with depth exists both 

 between and within sites (see Section 3.3; 

 Turner et al . 1968), a general pattern of 

 algal distribution emerges from the 

 California sites above. If rocky 

 substratum is available from the low 

 intertidal to depths where light is 

 insufficient for macroalgal growth, three 

 subtidal zones can be recognized, similar 

 to those proposed by Neushul (1965; Figure 

 6). 



Zone 1, inshore of Macrocystis , is 

 commonly inhabited by Phyllospadix spp. 

 (surf grass), feather boa kelp ( Tgregia 

 menziesii ) , and Cystoseira osmundacea . 

 Depending on geographic location and 

 exposure to swell, Eisenia arborea , 

 Pterygophora cal ifornica , Laminaria spp. , 

 various species of Sargassum , and 

 articulated corallines may be present. 

 Macrocystis is most abundant in Zone 2, 

 may be mixed with C. osmundacea throughout 

 California, and may be mixed with, or 

 replaced by, Nereocystis luetkeana in 

 central California. Various understory 

 kelps (particularly _P. cal ifornica and J.. 

 farlowii ) occur in patches under 

 Macrocystis , and articulated (especially 

 Calliarthron spp.) and encrusting 

 corallines are most common on the bottom. 

 Zone 3, seaward of the Macrocystis canopy, 

 may be inhabited by Pelagophycus porra in 



southern California, or more commonly by 

 sparse stands of understory kelps such as 

 Agarum fimbriatum and JL. farlowii , 

 encrusting corallines, and small foliose 

 red algae. 



Invertebrate zonation is not as 

 distinct, although broad changes along a 

 depth gradient in the distribution of sea 

 urchins have been noted (purple urchins in 

 shallow water, red urchins at mid-depths, 

 and in southern California, white urchins 

 and Centrostephanus coronatus in deeper 

 water). But there are numerous excep- 

 tions: e.g., Sandhill Bluff above, and 

 other areas where red urchins are most 

 abundant at the outer edge of giant kelp 

 distribution (Yellin et al . 1977, Pearse 

 and Hines 1979). Three common species of 

 turban snails ( Tegula ) in central 

 California also occur in different depth 

 zones subtidally: T. brunnea at 0-6 m, T. 

 montereyi at 3-9 m, T. poll i go at 7-12 m 

 (Riedman et al . 1981, Watanabe 1984a). 

 In general, sessile invertebrate abundance 

 increases with depth (Aleem 1973), perhaps 

 in part due to reduced competition for 

 space with algae (Foster 1975b). 



The distribution and abundance of 

 fish species are often not clearly zoned 

 along a depth gradient. Distribution 

 appears most strongly related to vertical 

 relief, including that due to vegetation, 

 rather than depth (Quast 1971a, Ebeling et 

 al. 1980a, Moreno and Jara 1984, Larson 

 and DeMartini in press; see Section 4.5). 

 Within continuous reef habitats, however, 

 closely related species may segregate with 

 depth (Hixon 1980, Larson 1980a). 



3.4.2 Within Depths 



Few published surveys discuss the 

 distributional variation of plants or 

 animals within depths, but qualitative 

 observations and the high variances 

 associated with abundance estimates at any 

 particular depth (Rosenthal et al. 1974, 

 Foster et al . 1979a, Pearse and Hines 

 1979) suggest that distributions are 

 generally clumped at fairly small scales. 

 This variability can result from a number 

 of processes, including variability in 

 distribution of many abiotic factors 

 discussed in Chapter 2, as well as 

 environmental changes created by the 



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