On a shorter time scale (1-5 years), 

 changes have been associated with year- 

 to-year variations in storm-swell 

 intensity. Ebeling et al. (MS.) has made 

 long-term observations of a kelp forest on 

 an isolated reef near Santa Barbara. 

 Large waves in 1980-81 removed most of the 

 Macrocystis from the reef. Sea urchins 

 then came out of cracks and crevices and 

 actively grazed over the substratum. This 

 grazing not only removed most of the 

 remaining non-encrusting algae, but also 

 prevented the re-establishment of these 

 plants. The more severe storms of 1982-83 

 reduced the abundance of these exposed sea 

 urchins, and macroalgae, including 

 Macrocystis , have subsequently recolonized 

 the area. Ebeling et al. (MS.) found that 

 these changes also affect fishes, particu- 

 larly surfperch, as the juveniles use 

 Pterygophora cal ifornica as shelter from 

 predators, and the adults forage for 

 invertebrate food among the algae that 

 cover the bottom. Abnormally stormy years 

 can also have dramatic long-term effects 

 in central California, altering understory 

 abundance both by direct removal, and via 

 increased light from surface canopy 

 removal (Foster 1982a). 



There have been historical changes in 

 the relative abundance and distribution of 

 M. pyrifera and Nereocystis luetkeana in 

 central California, with particular sites 

 changing completely or partially from 

 giant to bull kelp and vice versa (Yellin 

 et al. 1977, Van Blaricom in press). 

 Numerous causes are possible. Storms 

 appear to affect surface canopy type, with 

 Nereocystis replacing Macrocystis after 

 the latter has been removed by severe 

 water motion (Foster 1982a, Van Blaricom 

 in press). In addition, variations in sea 

 urchin grazing may affect species 

 composition (Van Blaricom in press) and 

 kelp forest size (Pearse and Hines 1979). 

 Storms can also indirectly affect entire 

 forests, as storm-induced sand movement 

 can change kelp forests into soft-bottom 

 communities (North 1971b, Grant et al. 

 1982, LOSL 1983). 



3.5.2 Short-Term (< 1 year) 



The relative lack of large seasonal 

 changes in the local ocean climate, 

 particularly storms, appears to result in 

 reduced seasonal variability in kelp 



forest communities in southern California 

 (Rosenthal et al. 1974, SCE 1978). These 

 and other studies (North 1971b, Dean pers. 

 comrn. ) suggest that many southern 

 California kelp canopies go through a 

 three- to five-year cycle of abundance and 

 decline, perhaps associated with holdfast 

 deterioration in older plants. However, 

 even without unusually high water motion, 

 mortality of adult plants is about 40% per 

 year in the kelp forest at San Onofre 

 (Dean pers. comm. ) . 



In central California, the larger and 

 more frequent winter swells produce a 

 regular seasonal canopy cycle with a 

 maximum canopy size in summer, and a 

 minimum in winter (Miller and Geibel 1973, 

 Gerard 1976, Foster 1982a, Reed and Foster 

 1984, Kimura and Foster in press). These 

 storms can also influence understory algal 

 abundance (Foster 1982a). Productivity, 

 growth rate, and recruitment of understory 

 algae also change seasonally in response 

 to climatic conditions and cover of 

 surface canopies (Johansen and Austin 

 1970, Breda 1982, Heine 1983, Reed and 

 Foster 1984, Kimura and Foster in press). 

 Seasonal changes in sand cover can also be 

 important (Breda 1982). In addition, 

 juvenile rockfish commonly recruit into 

 central California kelp forests during the 

 strong upwelling period in late 

 spring-early summer (Miller and Geibel 

 1973). The effects of seasonal climatic 

 changes appear to increase with latitude, 

 as shown in the distinct summer-winter 

 differences in Nereocystis luetkeana 

 forests in Washington (Neushul 1967). 



3.5.3 Succession 



The causes of both long- and 

 short-term changes in community 

 composition, such as spatial patterns, are 

 a complex of interacting factors of which 

 only the extremes of storms and grazing 

 have been clearly documented in particular 

 forests. These disturbances initiate 

 successional changes that remain largely 

 unexplored. Foster (1975a) found that 

 successional events on small concrete 

 blocks placed within a kelp forest were 

 largely determined by the availability of 

 larvae or spores in the water, and 

 differences in growth rates and 

 competitive abilities among colonizing 

 species. Aside from a possible initial 



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