large patches which could reasonably be labeled as a distinct associ- 

 ation was limited to a few areas on the southeast and northeast 

 "wings" of the island. 



d. Macrophytic Algae Association . The macrophytic algae 

 association (association D in Figs. 9 to 12), extends around the 

 island in a continuous band except on the east side under the wharf, 

 where light is presumably the limiting factor. Its composition is 

 variable from side to side. Statistical comparisons between associ- 

 ation D in various parts of the island and association E on the north 

 side (the type Lithothamnium association) generally showed no signifi- 

 cant differences for the three taxa selected as characteristic domi- 

 nants for association E (Lithothamnium complex, Veleroa complex, and 

 Dodecaceria fewkesi) . The only exceptions were the south side, 

 which had significantly less Veleroa and Dodecaceria than association 

 E, and the southeast wing, which had significantly less Veleroa. 

 Thus, it appears reasonable to consider association D as an extension 

 of association E, overgrown by macrophytes to depths where physical 

 conditions (including illumination) are favorable. 



Lithothamnium dominates algal biomass on all sides of the island. 

 The macrophytic algae zone on the south side is unusual in that 

 Lithothamnium complex there is composed of much thicker and irregular 

 patches than elsewhere on the island. The south side also supports 

 the densest growths of a coralline alga [Corallina officinalis) and a 

 green alga [Codium fragile). Other common species on the south side 

 include feather boa kelp (Egregia menziesii) , Gelidium rohustum, and 

 Gigartina canaliculata. The north side also supports substantial 

 beds of Egregia. Other north-side macrophytic dominants include 

 Prionitis lanceolata and Gelidium robustum. Cystoseira osmundacea 

 and coralline algae are abundant in some areas of the north side. 

 Quantitative data for the west side are of limited value in character- 

 izing the macrophytic algae because none occurred in any of the ran- 

 dom west-side quadrats. Qualitative observations and results of the 

 seasonal surveys suggest that this zone is dominated by Egregia, 

 Cystoseira, coralline algae, and Gigartina canaliculata. A bed of 

 giant kelp (Macrocystis sp.) is located at the south end of the west 

 side of the island. Judging from earlier air photos, however, the 

 present kelp bed is small compared to the extensive beds that have 

 existed in the past. Large numbers of sea urchins now exist on the 

 island and may account for this phenomenon. It is possible that kelp 

 and urchins alternate in cycles of abundance on the island. The in- 

 verse relationship between urchin and algae abundance has been dis- 

 cussed, for example, by North (1962). 



e. Lithothamnium-Veleroa Association . 



The Lithothamnium association (association E in Figs. 9 to 

 12) is characterized by high concentrations of Lithothamnium complex. 



53 



