obs.) now suggest that growth rings are 

 annual . Maximum ages for Pterygophora 

 plants have been estimated to be 18 years 

 in central California (Reed and Foster 

 1984), 11 years in southern California 

 (Dayton et al . 1984), and 10 years in 

 British Columbia (DeWreede 1984). 



All of the understory kelp species 

 have been described morphologically, but 

 little is known about most of them from 

 field studies on the west coast. Each may 

 form dense aggregations locally, but their 

 individual effects on the remainder of the 

 community are generally not known. Some 

 of these species can have a fairly long 

 (80+ cm), erect stipe, placing the blades 

 and canopy over a meter above the 

 substratum (for example, Laminaria 

 setchelli i [Figure 3], Pterygophora 

 cal ifornica , and Eisenia arborea [Figure 

 3 J ) . Many others have short stipes and 

 long blades. This type of morphology 

 results in plants being draped over the 

 substratum and flopping back and forth 

 with water motion. Laminaria farlowii , 

 Agarum f imbriatum , and Costaria costata 

 are examples. Besides shading substrata 

 near plants, abrasion by blades could also 

 have local effects. Dayton et al. (1984) 

 calculated life tables for some understory 

 species in southern California. They 

 estimated that Eisenia arborea plants can 

 live for 11 years and Laminaria farlowii 

 for 6 years. By selectively removing the 

 understory kelps, they found that the 

 stipitate species ( Eisenia , L_. setchell i 

 and Pterygophora ) inhibited the successful 

 recruitment of Macrocystis , Pterygophora , 

 Nereocystis , and Desmarestia . 



Extreme water motion may be the 

 primary cause of adult Pterygophora 

 cal ifornica mortality in central 

 California, as drift plants are commonly 

 observed on beaches after storms. At more 

 protected locations such as Stillwater 

 Cove (see Section 3.3.1) other factors 

 such as occasional damage to the meristem 

 by turban snails (Section 4.4.3.2), or 

 destruction of the medulla in the stipe by 

 burrowing amphipods (Foster pers. obs.) 

 may cause a slow attrition of old 

 individual s. 



4.3.3.2 Species in other areas . 

 There has been extensive research on the 

 biology of Laminariales in many areas of 



the world. We will not review that work 

 here, but will mention a few species that 

 have either been well-studied in the 

 field, or whose effects on other species 

 have been demonstrated. Kain (1979) 

 provides a review of the biology and field 

 research on Laminaria and related species. 



Various species of Laminaria and 

 Agarum have been studied in northern areas 

 of the eastern Pacific. Demographic 

 studies on these species are lacking, but 

 some studies have selectively removed 

 canopies or have prevented sea urchins 

 from access to areas of substratum. Paine 

 and Vadas (1969) reported that Nereocystis 

 became the dominant alga in the first year 

 on subtidal rocks kept free of sea 

 urchins, forming some 90% of the biomass. 

 In the following year, L_. groenlandica 

 became the dominant alga. 



Dayton (1975) worked with three 

 species of Laminaria and Agarum cribosum 

 in Alaska. Laminaria longipes was able to 

 re-establish in areas after its canopy was 

 removed. It has a rhizome-like holdfast 

 with multiple meristems, and can quickly 

 regrow stipes and fronds after they are 

 removed. When the canopies of three 

 laminarian species, I. groenlandica , I. 

 dentigera , and I. yezoensis , were removed 

 in a shallow site, the percentage cover 

 and density of Agarum increased. The 

 long-term consequences of these invasions 

 were not known. 



Duggins (1980) removed Laminaria 

 groenlandica from several small plots in 

 Torch Bay, Alaska. In the first year 

 after removal, there was a high 

 recruitment of annual kelp. By the second 

 year, however, Laminaria was once again 

 dominant (mean ± S.D.: 53 + 27 plants/m 2 

 vs. 8 ± 7/m 2 for other species). There 

 was no successful recruitment of any 

 species in the control plot where the 

 canopy was left intact. 



Understory Laminariales and Fucales 

 are very abundant in many other boreal and 

 temperate areas of the world. In northern 

 New Zealand, for example, Fucales are 

 usually dominant in shallow subtidal areas 

 (< 5 m depth), while a single kelp, 

 Ecklonia radiata , dominates deeper areas. 

 In most cases, the substratum beneath 

 dense stands of these algae is covered 



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