the effects of other urchin predators, and 

 the influence of man (aboriginal and 

 modern). 



8. Man may have had a profound 

 impact on kelp forests through the 

 historical hunting of mammals, and has had 

 a recent impact by discharging wastes in 

 southern California (Chapters 4 and 6). 



The above generalizations are a 

 subset of the factors listed in Table 1, 

 and cover a subset of possible scales of 

 effects outlined in Figure 26; their 

 relative importance varies locally and on 

 different spatial and temporal scales. 

 This suggests that single factors and 

 simple cause-effect relationships will 

 never explain or predict kelp forest 

 community structure. What seems probable 

 are typologies where the relative influ- 

 ence of various factors are assigned to 

 different "types" of forests at different 

 spatial and temporal scales. Thus, water 

 motion may be most important to the 

 structure of giant kelp communities 

 growing on relatively soft rock and 

 exposed to extreme water motion (e.g., 

 Sandhill Bluff, Section 3.3.1 and Figure 

 5). Sites under these conditions may form 

 one site type. Dispersal and light 

 reduction may be important on the scale of 

 meters, but not tens of meters, to the 

 ecology of stands of understory kelps. 

 Extreme water motion is important on the 

 scale of tens of years but not years. 



Such a classification scheme, 

 emphasizing the relationships between 

 sites, scales and factors, is similar to 

 that in an analysis of variance, and would 

 help remove some of the confusion that 

 results from mixing different scales and 

 from generalizing about "kelp forests" 

 from one "kelp forest." It would also 

 provide a more rigorous context for future 

 investigations (for a general discussion 

 of this kind of organization see Bateson 

 1972, pages 279-308, and 1979, Chapter 7). 

 More thorough descriptive studies at a 

 variety of different sites and spatial 

 scales are needed for development of such 

 a system, but it may be worthwhile to 

 attempt a tentative classification based 

 on our present information. 



There appear to be three main dif- 

 ferences between temperate subtidal reefs 



with and without Macrocystis : giant kelp 

 increases three-dimensional structure by 

 providing living microhabitats such as 

 holdfasts and surface canopy that are 

 reduced or unavailable where giant kelp is 

 absent. Macrocystis also provides 

 increased productivity and, thirdly, the 

 majority of this production is used as 

 detritus (Chapters 3 and 4). 



The quantities of drift kelp, both 

 within kelp forests and in other communi- 

 ties such as sandy beaches, and the high 

 abundances and diversity of organisms 

 within forests that can use this drift and 

 detrital material (perhaps directly with 

 little or no prior degradation and energy 

 loss through microbial decomposition), all 

 suggest that Macrocystis stimulates the 

 development of food webs based on detritus 

 (Chapter 3). Further studies of the 

 effects of habitats created by Macrocystis 

 on the remainder of the community, and of 

 differences in detritus versus plankton 

 feeding among assemblages in areas with 

 and without giant kelp, may thus reveal 

 important structural and functional 

 differences between Macrocystis and other 

 nearshore reef communities. 



7.2 MANAGEMENT RECOMMENDATIONS 



Management of kelp forests is 

 hampered by site-specific community 

 differences, lack of information about the 

 causes of these differences, conflicting 

 uses of the community, and pressures from 

 special-interest groups (Chapter 6). Even 

 if the latter three problems are solved, 

 it is clear that evaluations of the 

 effects of proposed activities such as new 

 sewer outfalls will still have to be based 

 on local studies of the particular forest 

 likely to be impacted (Foster et al. 

 1983). Even with thorough studies, 

 uncertainties about effects will remain. 



Kelp forests have recovered where the 

 quality of discharged sewage has improved, 

 or when the locations of outfalls have 

 been changed (Section 6.5.5). It is also 

 true that many direct and probably 

 indirect changes in kelp forest popula- 

 tions are caused by overfishing (Section 

 6.6.2). On the other hand, although kelp 

 forest restoration attempts are still in 

 the research phase, it appears that this 

 form of management is, and will continue 



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