organisms themselves, particularly by the 

 large kelps. Kelps in dense stands can 

 effectively exclude many other algae (Reed 

 and Foster 1984, Dayton et al. 1984). 

 Moreover, the dispersal range of many 

 large kelps is probably only several 

 meters from attached adults (Anderson and 

 North 1966, Schiel 1981) contributing to 

 the maintenance of local stands. 

 Dispersal distances for invertebrates can 

 also be quite short (Ostarello 1976, 

 Gerrodette 1981). Inhibition of 

 settlement by established sessile 

 organisms (Breitburg 1984), local grazing 

 by sea urchins (Turner et al. 1968, Vance 

 1979, Cowen et al. 1982, Dean et al. 1984, 

 Harrold and Reed in press) predator-prey 

 interactions (Bernstein and Jung 1979, 

 Schmitt 1982), territorial behavior and 

 competitive interactions among fish 

 (Clarke 1970, Hixon 1980, Larson 1980a), 

 physical disturbance (Cowen et al. 1982, 

 Wells 1983) and competition among algae 

 (Kastendiek 1982, Reed and Foster 1984, 

 Dayton et al. 1984) also contribute to 

 variations in distribution. Stochastic 

 events are probably also important, but 

 detailed descriptions necessary to detect 

 them have not been done. However, in 

 these diverse and structurally complex 

 communities, most of the patterns of 

 within-depth distribution remain 

 undescribed, and the mechanisms creating 

 these patterns are unknown -- a fruitful 

 area for further research. 



3.5 TEMPORAL VARIATION IN COMMUNITY 

 STRUCTURE 



3.5.1 Long-Term (> 5 years) 



The best records of long-term (> 5 

 years) changes in California kelp forests 

 come from maps of kelp canopy distribu- 

 tion, the first of which were made in 

 1910, 1911, and 1912 (McFarland 1912, 

 Crandall 1915). Comparisons with recent 

 surveys indicate an overall 30%-70% 

 decline in the area of giant kelp canopies 

 in southern California since these early 

 surveys (Hodder and Mel 1978, Neushul 

 1981). Hodder and Mel (1978), however, 

 suggested that the magnitude of the 

 decline may be, in part, an artifact of 

 differences in canopy-mapping techniques. 

 Sewage pollution (Leighton et al . 1966, 



Grigg and Kiwala 1970, Wilson 1982, 

 Meistrell and Montagne 1983), abnormal 

 oceanographic conditions ("El Nino" years: 

 warm water, low nutrients; Jackson 1977), 

 and sea urchin grazing (Leighton et al. 

 1966, North 1974) stimulated by sewage 

 (North 1974) and/or removal of sea urchin 

 predators by man (North 1974, Tegner and 

 Dayton 1981) have all been implicated as 

 causative agents. As these factors may 

 all affect canopy distribution, and 

 because information about organisms in the 

 community other than Macrocystis and 

 Nereocystis is almost non-existent prior 

 to the 1950's, we will probably never know 

 what did happen. However, Macrocystis has 

 begun to return to the Palos Verdes Penin- 

 sula coincident with reduction in sludge 

 and DDT discharge from the White's Point 

 sewer outfall (Wilson 1982). This 

 suggests that sewage pollution, and 

 particularly increased turbidity 

 (Meistrell and Montagne 1983) and sludge 

 accumulation on the bottom (Grigg and 

 Kiwala 1970), had important direct effects 

 on the decline of giant kelp around 

 southern California sewer outfalls. 



Long-term changes in central 

 California may be associated with changes 

 in the abundance and distribution of sea 

 otter populations. Van Blaricom (in 

 press) has compared canopy distribution 

 data from the early 1900' s (when sea 

 otters were essentially absent) with 

 recent surveys (sea otters present). He 

 suggests that the Macrocystis canopy area 

 has recently increased and Nereocystis 

 luetkeana has decreased as an indirect 

 result of sea urchin removal by sea 

 otters. 



The production, dispersal, and 

 recruitment of larvae can be periodic 

 phenomena. Little is known of the 

 relationship of production and dispersal 

 to recruitment because little is known 

 about larval mortality, particularly for 

 planktonic larvae. Large-scale temporal 

 patterns of some invertebrate (Dayton and 

 Tegner 1984a) and fish distributions 

 (Miller and Geibel 1973) in kelp forests 

 have been correlated with recruitment. 

 Small scale patterns in sea urchin (North 

 1983a), Tegula spp. (Watanabe 1984a), and 

 spider crab (Hines 1982) recruitment have 

 been shown or suggested as important to 

 the population dynamics of these species. 



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