Intertidal Environment (Littoral) 



145 



Figure 128. Some common 

 plants of rocky shores in south- 

 ern California. I, wave and 

 spray zone: A, Ralfsia sp. 

 (XO.04). 



II, high-tide zone: B, Pelvetia 

 fastigiata (J. Ag.) De Toni 

 (X0.09); C, Endocladia muri- 

 cata{?. &R.) J. Ag. (xO.5). 



III, midtide zone: D, Gigar- 

 tina canaliculata Harv. ( x 0. 1 5) ; 

 E, Gigartina leptorhynchos J. 

 Ag. (x0.15); F, Corallina van- 

 couverensis Yendo (x 1-5). 



IV, low- tide zone: G, Gigar- 

 tina spinosa (Kutz) Harv. 

 (xO.04); H, Gelidium cartila- 

 gineum var. robustum Gardn. 

 (X0.15); I, Phyllospadix torryi 

 S. Wat. (xO.02) (habit); J, 

 Egregia laevigata Setch. ( X 0. 1 ). 



IK 



zonations have been based on both plants 

 and animals, and some are on either one or 

 the other. A good discussion and compari- 

 son of several classifications used in Califor- 

 nia are given by Ricketts and Calvin (1952, 

 pp. 375-401). They concluded that a zona- 

 tion into four units is most practical, with 

 the top zone being above the 5.0-foot tide 

 level (spray and wave zone mostly above 

 high tide), the next between 5.0 and 2.5 feet 

 (high-tide zone), the next between 2.5 and 

 0.0 feet (midtide zone), and the lowest be- 

 low 0.0 tide, or mean lower low water (low- 

 tide zone exposed only during minus tides). 

 In the top zone, rarely covered by high 

 tides, the most obvious plant is the brown 

 alga, Ralfsia, which forms thin circular 

 patches on the rocks (Fig. 128); however. 



the microscopic blue-green algae are more 

 abundant although difficult to see. The ani- 

 mals of the zone are ones that can close their 

 shells or otherwise protect themselves from 

 drying out between high tides or between 

 visits to the water. Commonest is a peri- 

 winkle, Littorina planaxis, which has a tightly 

 fitting operculum or door (Fig. 129). This 

 snail wanders about grazing on blue-green 

 algae and other organic material present in 

 a thin film on the rocks; in the process of 

 feeding the snail is an active erosional agent, 

 rasping away the rock with its sharp radula 

 (Emery, 1946; North, 1954). Also common 

 a little lower in this zone is a limpet, Acmaea 

 digitalis, which can draw its cup-shaped shell 

 so tightly against the rock surface that it can 

 be pried off only with difficulty. Commonly, 



