studies. Bernstein and Jung (1979) 

 recorded that Oxyjulis cal ifornica may 

 feed on the bryozoan, Membranipora , and 

 mobile invertebrates that inhabit the 

 laminae of Macrocystis . They suggested 

 that the removal of these invertebrates by 

 Oxyjul is may free the fronds from 

 extensive encrustation and grazing. 



Other anecdotal information (LOSL 

 1983) records that fish had a severe 

 grazing effect on large Macrocystis plants 

 that were moved to the Pendleton 

 Artificial Reef, off San Onofre. Large 

 numbers of halfmoon and opaleye were 

 attracted to these reefs, and they quickly 

 moved to the transplanted Macrocystis 

 plants moored on the reefs. Predation of 

 invertebrates and grazing of frond tissue 

 by these fish caused the demise of 

 Macrocystis within a few weeks. 



Other indirect effects of fish on 

 algal assemblages have been reported. 

 Cowen (1983) found in the San Nicolas 

 Island kelp forest that an alteration in 

 the abundance of the sheephead wrasse, 

 Semicossyphus pulcher , could affect local 

 populations of the sea urchin, S^. 

 f ranciscanus . When sheephead were removed 

 from a site, there was a slight increase 

 in the number of sea urchins. He also 

 recorded that in areas where sheephead 

 densities were low, echinoids were highly 

 exposed, whereas in areas with high 

 densities of the wrasse, echinoids tended 

 to be concealed in crevices. Nelson and 

 Vance (1979) and Tegner and Dayton (1981) 

 also reported that the densities of sea 

 urchins may be altered by Semicossyphus . 

 In all of these studies, however, the 

 effects of sea urchin removal on the algal 

 assemblages are not clear. 



It would be useful to do experiments 

 that assess the effects of fishes on 

 juvenile algae and of feeding on the 

 substrata where algae can recruit. 

 Exclusion of fishes by cages and shields 

 have been successful in some 

 circumstances. Of particular interest is 

 the variability of grazing effects and the 

 scales at which they occur. Are the 

 effects quite localized in some areas of 

 particular reefs, or are there broader 

 scale effects? A necessary part of such 

 studies is a record of the abundances of 

 each species of fish in experimental 



sites, and observations of their feeding 

 behavior to determine how selective 

 feeding is. Choat (1982) gives a thorough 

 review of the effects of fish feeding on 

 the biota of temperate shores. 



5.6.3 Sea Urchins 



If there is any generalization that 

 has made its way to prominence in the 

 literature dealing with kelp communities, 

 it is the dominating effect of sea urchins 

 on the distribution and abundance of large 

 brown algae. The words "control" and 

 "regulating" are frequently used when 

 discussing the effects of echinoids on 

 algae, and "overgrazing" is often 

 mentioned, evocative of an untoward shift 

 from a "natural" community dominated by 

 large macroalgae (e.g., Estes et al. 1978, 

 Kain 1979, Duggins 1980, Tegner and Dayton 

 1981). The general implication has been 

 that the grazing activities of sea urchins 

 have a comprehensive effect on the 

 character of the biotic assemblages on 

 rocky reefs. This argument has also been 

 expanded to an evolutionary context, 

 suggesting that the evolution of kelp life 

 histories and competitive abilities may be 

 the result of responses to echinoid 

 grazing activities (Vadas 1977, Steinberg 

 1984, Estes and Steinberg MS.). 



There is little argument that sea 

 urchins of many species may have dramatic 

 effects on kelp assemblages on most 

 temperate shores in both hemispheres 

 (Lawrence 1975). The relatively rapid 

 denudation of algal stands by mobile 

 aggregations of sea urchins have been the 

 focus of many investigations (e.g., 

 Leighton et al. 1966, North 1974, Lawrence 

 1975, Dean et al. 1984). It is also clear 

 that kelp can be abundant and persist in 

 close proximity to echinoids (Foster 

 1975b, Cowen et al. 1982, Dean et al . 

 1984, Dayton et al. 1984, Harrold and Reed 

 in press). Largely lacking, however, are 

 detailed distributional data which examine 

 the various spatial and temporal scales of 

 echinoid abundance. Within a site, for 

 example, the abundance of sea urchins is 

 not constant, and may change with depth 

 (Mann 1972a, Estes et al. 1978, Kain 1979, 

 Foster 1982a, Choat and Schiel 1982). 

 There may also be differences in 

 abundances between local sites, between 

 areas along a shoreline, and latitudinal 



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