competition for space with other species. 

 Even within sites of similar depth at one 

 locality, other factors such as amounts of 

 sediment covering the substratum and the 

 presence of grazers may differ on a small 

 spatial scale, resulting in a small-scale 

 variation in the presence and abundance of 

 algae. Each of these factors may act on a 

 different life history stage of a species. 

 Because both biotic and abiotic factors 

 may change over small distances, the 

 pattern of algal distribution and abun- 

 dance may change from locality to locality 

 (see Chapter 3). Moreover, some of this 

 pattern may result from stochastic pro- 

 cesses, large scale phenomena (Dayton and 

 Tegner 1984a), and historical events that 

 are difficult to study. 



We have generally taken a functional 

 approach in discussing the organisms in 

 Macrocystis communities, as floristic and 

 faunistic species checklists may be found 

 in other sources (see Chapters 3 and 4). 

 We discuss many species and environmental 

 factors, assessing their interactions with 

 Macrocystis and, where possible, their 

 influence on some phase or phases of the 

 life cycle of Macrocystis . It is our 

 intention to influence the direction of 

 future field-based studies involving 

 Macrocystis . Research to date has gone 

 through qualitative and descriptive 

 phases, with a relatively small amount of 

 experimental work. We hope to see more 

 carefully conceived sampling and experi- 

 mental research featuring specific 

 hypotheses with replication and proper 

 controls. We synthesize the extant liter- 

 ature and technical reports with this in 

 mind, and include accounts of work in 

 progress in several California localities. 



1.1. TAXONOMY, DEFINITIONS, AND 

 DESCRIPTIONS 



The taxonomy of Macrocystis has been 

 argued since the genus was first named by 

 C.A. Agardh (1820, 1839), and has been 

 reviewed by Womersley (1954), Neushul 

 (1971a), and Brostoff (1977). C.A. Agardh 

 recognized six species, based on blade and 

 float characteristics of what were proba- 

 bly drift specimens (Agardh 1839). Hooker 

 (1847) decided that only one species 

 existed, M. pyrifera . Howe (1914) was the 

 first to use the now commonly accepted 

 system of holdfast characteristics to 



separate another species, H. integrifol ia 

 (Howe 1914, Setchell 1932, Womersley 

 1954). Womersley (1954) used holdfast 

 characteristics to decide that a third 

 species, M. angustifol ia , existed in 

 Australia and Africa. The holdfasts of 

 these currently recognized species are 

 illustrated in Figure IA. Neushul (1971a) 

 mapped the distribution' of the three 

 species in the northern hemisphere, with 

 M. integrifol ia occurring north from 

 Monterey, California to Sitka, Alaska; M. 

 angustifol ia occurring in central 

 California and perhaps southern 

 California; while M. pyrifera was distri- 

 buted in southern Cal ifornia. Brostoff 

 (1977) concluded, based on detailed mor- 

 phological comparisons and transplant 

 experiments, that the California M. 

 angustifolia described by Neushul (1971a) 

 should be designated _M. pyrifera var. 

 cal ifornica , with M. pyrifera becoming M. 

 pyrifera var. pyrifera . Abbott and 

 Hollenberg (1976), however, recognize only 

 two species of Macrocystis from 

 California, M. pyrifera in the subtidal 

 zone and M. integrifol ia in the low 

 intertidal-shal low subtidal zone. For the 

 purposes of this profile, we will abide by 

 the Abbott and Hollenberg (1976) classifi- 

 cation; references to "giant kelp forests" 

 mean subtidal M_. pyrifera communities 

 found on the west coast of North America. 



A few other terms are used throughout 

 this book, so it would be useful to define 

 them here. Almost every paper concerning 

 Macrocystis mentions the rapid growth 

 rates of individual fronds. Early des- 

 criptions also noted the great sizes of 

 plants. The name "giant kelp" has 

 remained the common designation of the 

 species of Macrocystis . Because of the 

 great sizes of individual plants, their 

 trunk-like appearance in the water column 

 (see cover photo), and the surface 

 canopies which can be extensive along 

 coastlines, these areas of subtidal 

 habitat have been called "forests" and we 

 will use this term. A "stand" refers to 

 any localized group of plants. "Community 

 structure" is used as a general term that 

 includes the species composition, abun- 

 dance, and three-dimensional distribution 

 of organisms in a kelp forest. "Community 

 dynamics" refers to change in structure 

 with time. 



