however, in its abundance and in the sizes 

 of plants. Below depths of ^ 10 m, plant 

 numbers become lower, and a decreasing 

 proportion have thai 1 i that extend more 

 than a few meters from the bottom. This 

 sort of depth distribution is similar to 

 that found for most of the abundant 

 Fucales found in austral areas (Schiel 

 1981, Choat and Schiel 1982). 



Sargassum muticum is another Fucales 

 that co-occurs with Macrocystis in some 

 areas of southern California, especially 

 Catalina Island. An experiment by Ambrose 

 and Nelson (1982) at Santa Catalina Island 

 indicated that a dense recruitment of S_. 

 muticum can preempt the space for other 

 species to settle and grow, and this 

 species may be able to keep Macrocystis 

 from localized sites. 



Sargassum muticum has caused some 

 excitement since ' its accidental 

 introduction and dramatic spread along the 

 west coast of North America, and its 

 recent arrival on the south coast of 

 England (Fletcher and Fletcher 1975, 

 Norton 1977). Deysher and Norton (1982) 

 found experimentally that the majority of 

 recruits appeared within 2-3 m of parent 

 plants, although some recruits could be 

 found at distances to 30 m. It was 

 proposed that this species may have spread 

 long distances by detachment of vegetative 

 fronds which continue to grow and develop 

 while adrift and swept along by wind and 

 currents (Deysher and Norton 1982). As 

 this species is monoecious and 

 self-fertile, populations could become 

 established at considerable distances by 

 propagules dispersed from one adult plant. 



4.3.2.3 Surface canopy species in 

 other areas . Alaria f istulosa is a large 

 kelp that is particularly abundant in 

 Alaska. This species has a short stipe 

 with sporophylls concentrated near the 

 bottom of each plant. The vegetative 

 blade, however, has a gas-filled mid-rib, 

 and may reach a length of 25 m and a width 

 of 2 m. At most localities, this species 

 is largely confined to depths of < 5 m. 

 Dayton (1975) did selective canopy 

 removals of A. fistulosa , species of 

 Laminaria and Agarum cribosum at a site 

 near Amchitka Island, Alaska. He found 

 that when Laminaria spp. were removed from 

 quadrats at 5-m depths, the quadrats were 



colonized by Alaria , but that this species 

 did not invade other quadrats where the 

 Laminaria canopy was left intact. At 

 depths of 9.1 m and 16.8 m, Alaria 

 colonized only the quadrats from which 

 both Laminaria and Agarum were removed. 

 As few Alaria were found naturally at 

 these depths, Dayton (1975) concluded that 

 this is a fugitive species, which may take 

 advantage of free space but which is 

 normally prevented from doing so by the 

 presence of other species. He concluded 

 that the lower distribution of Alaria 

 appeared to be restricted primarily by the 

 grazing activities of sea urchins. 



4.3.3 Understory Canopy Species: Kelp 

 Beds 



4.3.3.1 Species in California and 

 Mexico . Many members of the Laminariales 

 and Fucales form a canopy 0.5 to 2.5 m off 

 the bottom, and dense stands of single 

 species may completely or partially 

 exclude other species of large brown algae 

 (see Section 2.4). Pterygophora 

 cal ifornica (Figure 3, Plate IE) is a 

 perennial species abundant along the west 

 coast (Abbott and Hollenberg 1976). This 

 species can grow to maturity in 6 months 

 in central California (Foster pers. obs.). 

 At sites in Stillwater Cove, Carmel Bay, 

 sporophylls and terminal blades may be 

 almost entirely removed during periods of 

 intense water motion in winter. New 

 growth of fronds occurs in spring and, by 

 summer, frond growth is great enough that 

 plants at 4-8/m 2 can form a closed canopy 

 over the substratum. This species has 

 been transplanted to the Pendleton 

 Artificial Reef near San Onofre in 

 southern California (LOSL 1983). It was 

 believed to be more resistant to fish 

 grazing (thicker blades, meristem at base 

 of blade) than Macrocystis , and that it 

 would modify the populations of encrusting 

 organisms prevalent on the reef so that 

 other brown algae might naturally 

 establish. Storms and fish grazing, 

 however, removed almost all blades after 

 transplantation (LOSL 1983). 



Growth rings and sporophyll scars 

 have been used to estimate the age of 

 individual plants thought to live over 15 

 years (Frye 1918). Although Frye's data 

 are indecipherable, field studies by 

 DeWreede (1984) and Reed and Foster (pers. 



49 



