enhancement of colonization by microalgal 

 or bacterial films, there was no evidence 

 for facilitative interactions ( sensu 

 Connel 1 and Slatyer 1977). Macrocystis 

 can be among the first organisms to settle 

 and grow if spores, space, and light are 

 adequate. Similar patterns were noted by 

 Fager (1971) on isolated structures placed 

 some distance from a kelp forest, while 

 Kennelly (1983) has shown on a microscopic 

 scale that most species associated with an 

 Ecklonia radiata bed in Australia have the 

 potential of quickly recruiting on 

 artificial substrata. 



The above examples mimic extreme 

 disturbances where small patches of 

 natural substratum are completely cleared. 

 All organisms are not generally removed 

 during normal disturbances in kelp 

 forests, and the processes involved in 

 succession after more natural disturbances 

 remain generally uninvestigated (see 

 review in Foster and Sousa in press). 

 Reed and Foster (1984) demonstrated that, 

 with less extreme disturbance, changes in 

 overstory canopies are particularly 

 important to subsequent successional 

 events. Van Blaricom (in press) suggested 

 that in central California Nereocystis 

 luetkeana first colonizes areas where sea 

 otters remove sea urchins because this 

 annual kelp is more common than 

 Macrocystis (i.e., more spores available 

 for colonization). Macrocystis then 

 gradually invades these areas, and in the 

 absence of storms which seem to have a 

 greater impact on Macrocystis , the 

 perennial giant kelp eventually replaces 

 bull kelp, as the canopy of the former 

 reduces light and thereby restricts 

 recruitment of the latter. This sequence 

 may be altered if perennial understory 

 kelps ( Laminaria , Pterygophora ) invade 

 after the initial disturbance (storms, 

 grazer removal), and inhibit further 

 recruitment (Van Blaricom in press). An 

 increase in understory foliose red algae 

 could also inhibit recruitment of all 

 kelps (Kimura pers. comm.). 



Various other interactions may also 

 alter succession. Predators may directly 

 alter sessile invertebrate abundance 

 (Foster 1975b, Neushul et al. 1976) and 

 species composition (Day and Osman 1981), 

 and these changes may indirectly affect 

 algal succession by reducing competition 



for space (Foster 1975b). Grazing 

 (probably by fish) may alter algal species 

 composition (Foster 1975b), and small 

 algal turf species may facilitate the 

 survivorship of young kelp sporophytes by 

 providing a refuge from fish grazing 

 (Harris et al . 1984). Small herbivores 

 may alter early successional patterns in 

 Ecklonia radiata beds (Kennelly 1983, 

 pers. commTT After incomplete removal of 

 sessile organisms, remaining encrusting 

 corallines can inhibit recruitment of 

 numerous sessile invertebrates (Breitburg 

 1984), and encrusting and articulated 

 corallines may inhibit Macrocystis 

 recruitment (Wells 1983). 



Additional effects associated with 

 the magnitude and extent of disturbance, 

 micrograzers and predators, sedimentation, 

 etc., as well as competition for light, 

 dispersal, and basic life history 

 characteristics of the organisms involved 

 are no doubt also important to kelp forest 

 succession (Foster and Sousa in press), 

 but remain to be investigated in detail. 



3.6 BIOMASS, PRODUCTIVITY, AND ENERGY 

 FLOW 



3.6.1 Introduction 



Not surprisingly, giant kelp 

 communities are highly productive; 

 nutrients are generally high in nearshore 

 waters, and Macrocystis can form a dense, 

 light-absorbing canopy at the water's 

 surface. The production of Macrocystis , 

 understory kelps, and bottom-cover algae, 

 together with energy imported from the 

 plankton, support consumers in giant kelp 

 forests as well as in nearby communities 

 receiving drift from forests. These 

 processes, as well as food webs within the 

 Macrocystis community, are reviewed in 

 detail in this section. 



3.6.2 Biomass (Standing Stocks) 



Coon (1982) recently compiled the 

 available information on biomass and 

 productivity of eastern north Pacific 

 Macrocystis . Table 4 summarizes these 

 values for Macrocystis , and includes 

 additional estimates for understory algae, 

 sessile invertebrates, and fishes. Other 

 than the few quadrats sampled by Aleem 



35 



