CHAPTER 1 



INTRODUCTION 



/ know few things more surprising than to see this plant grow- 

 ing and flourishing amidst those breakers of the western ocean, 

 which no mass of rock, let it be ever so hard, can long resist. 

 Darwin (1860). 



This profile is about large brown 

 algae of the genus Macrocystis and 

 organisms associated with them in subtidal 

 habitats along the west coast of North 

 America. Historical interest in giant 

 kelp was stimulated by its wide geographic 

 distribution, particularly in the southern 

 hemisphere, and by the immense size of the 

 plants. As early as the 1600's, European 

 mariners used Macrocystis as a naviga- 

 tional aid: the presence of a floating 

 canopy of attached plants indicated 

 shallow reefs, while floating bundles of 

 drift plants indicated that the coast was 

 not far off (North 1971b). 



The relatively easy harvesting of 

 plants made them the basis of the potash 

 industry in the United States during the 

 First World War. At present, some 150,000 

 wet tons are harvested annually, mostly 

 for the extraction of algin, a hydro- 

 colloid (Frey 1971). The recreational and 

 aesthetic value of these plants is also 

 recognized now because of the association 

 between them and many desirable food 

 species of fish and shellfish. Mammals 

 such as sea otters and harbor seals, as 

 well as numerous birds, also commonly 

 occur in these habitats. The disappear- 

 ance of a large tract of Macrocystis off 

 the Palos Verdes Peninsula (Los Angeles 

 County) and from other areas of southern 

 California in the 1950's brought an aware- 

 ness that these stands may be ephemeral in 

 nature and particularly disturbed by 

 pollution associated with large centers of 

 population. This spawned a series of 



research programs to study life history 

 features of giant kelp and its associated 

 organisms. It became apparent that many 

 factors were responsible for the variation 

 in kelp abundance. Variation through time 

 was assessed by estimates of the cover of 

 the surface canopy of Macrocystis in 

 several localities (North 1967, 19691. 



Differences in coverage between 

 surveys were ascribed to human pertur- 

 bation such as sewage outfalls (Wilson 

 1982), to warm water (North 1971b), and to 

 grazers such as sea urchins (Leighton 

 1971; see Foster et al. 1983 for review). 

 It was also clear that the temporal and 

 spatial variation in Macrocystis abundance 

 was controlled not by a single factor but 

 by numerous factors, some acting in 

 concert. 



It is our aim to describe the giant 

 kelp forest environment and to discuss the 

 sources of variability in the distribution 

 and abundance of the organisms in it, 

 especially Macrocystis (see Preface). Be- 

 sides geographic and temporal differences 

 in plant abundance, great spatial differ- 

 ences in distribution are also evident at 

 any one locality. Even in areas where 

 hard substratum is available, any particu- 

 lar alga is usually restricted to a 

 relatively narrow range of depths (e.g., 

 McLean 1962, Neushul 1967). This sort of 

 distribution can be the result of the 

 interactions of many abiotic factors such 

 as light and temperature change with 

 depth, and biological factors such as 



