CHAPTER 7 



SUMMARY 



Usually it seems to be true that when even the most definitely 

 apparent cause-effect situations are examined in the light of 

 wider knowledge, the cause-effect aspect comes to be seen as 

 less rather than more significant, and the statistical or relational 

 aspects acquire larger importance. Steinbeck (1962). 



7.1 OVERVIEW AND GENERALIZATIONS 



Darwin's (1860) early observations 

 and subsequent studies by others all agree 

 that giant kelp forests are exceptional 

 biological entities; the abundance and 

 diversity of life associated with struc- 

 turally complex and highly productive 

 Macrocystis populations are obvious to 

 anyone who swims through one of these 

 stands on a clear day. In the preceding 

 chapters, we described the composition, 

 distribution, and abundance of organisms 

 in giant kelp forests, the factors that 

 affect community composition, what we 

 consider to be lacking in our under- 

 standing of the ecology of these 

 communities, and necessary approaches for 

 future studies. 



Kelp forest communities are found 

 relatively close to shore along the open 

 coast, and are influenced by local coastal 

 processes as well as large-scale oceano- 

 graphic events. Thus, a large number of 

 factors can affect community structure and 

 dynamics at a variety of spatial and 

 temporal scales. Changing currents and 

 water masses affect temperature, nutrient 

 availability, and dispersal of spores, 

 larvae, and adults. Large-scale 

 (geographic) changes in temperature (and 

 perhaps other factors; see Chapter 5) and 

 the late 1950' s and recent "El Nino" warm- 

 water events (see Sections 2.2.3 and 

 2.2.5) are examples of phenomena that may 

 affect the community over a large area 



(i.e., the entire range of Macrocystis 

 pyrifera ). Regional differences in 

 current patterns, exposure to swell, and 

 even degree of pollution due to sewage, 

 can affect the community on a smaller 

 scale (e.g., southern California). At a 

 third level, very local differences in 

 terrestrial runoff, substrata, exposure to 

 swell, etc. result in great differences 

 among and within stands over time. 

 Finally, a variety of abiotic factors, 

 some of which are influenced by the 

 organisms themselves (e.g., shading by 

 Pterygophora cal ifornica ) , and biotic 

 factors affect distribution and abundance 

 within a particular stand. 



The influence of large-scale pheno- 

 mena are most difficult to determine 

 because they are difficult or impossible 

 to examine experimentally (Chapter 5). 

 Moreover, processes at all levels may 

 affect population characteristics on a 

 very local scale. The current warm 

 oceanographic period that coincided with 

 record winter storms in 1982-83 is an 

 example of the problem. Numerous changes 

 in kelp forests are now commonly being 

 attributed to changes in water character- 

 istics associated with "El Nino" 

 conditions, but prior to and during these 

 changes, associated storms drastically 

 reduced Macrocystis abundance in 

 California. Therefore, without site- 

 specific demographic studies, the relative 

 importance of these events to the present 



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