144 



Life 



Calvin (1952, p. 196). Where not so inten- 

 sively hunted in Baja California, it is still 

 common, some older specimens being 15 cm 

 long. Another common inhabitant of sandy 

 beaches is a small, 2-mm-diameter, red 

 worm, Thoracophelia mucronata, whose activ- 

 ities leave a telltale rough surface on the 

 sand, and which along with the sand crabs 

 and sand hoppers is of considerable interest 

 to shore birds. 



Perhaps most interesting is the occasional 

 visitor, the grunion Leuresthes tenuis, a fish 

 that flops up on the beach at night-time 

 spring tides between March and August (Fig. 

 127). The female digs a hole and lays her 

 eggs, which are immediately fertilized by the 

 male and left to incubate in the warm sand 

 for two weeks and be re-exposed and hatched 

 at the next spring tide (Walker, 1947, 1952). 

 These fishes are known only in southern Cali- 

 fornia and the adjacent part of Mexico 

 (Roedel, 1953). A reference in Vizcaino's 

 log (Bolton, 1916, p. 56) to "sardines" 

 washed ashore at Cape San Lucas during the 

 night of June 8, 1602, probably refers to 

 grunion, since this date would be 4 days 

 after a spring tide. Sea lions also are tem- 

 porary visitors to beaches, especially beaches 

 of islands where they are not likely to be dis- 

 turbed by man or beast. On several islands 

 they form large colonies whose incessant 

 barking may be heard for a mile or more 

 away. 



Sand beaches are rare in the geological 

 column because of the ease by which they 



are eroded when exposed; nevertheless, sev- 

 eral ancient sand beaches are exposed in 

 southern California. One example of Pleis- 

 tocene age forms part of a sea cliff" beside 

 Highway 101 at Newport Beach. In it are 

 many valves of Donax and Pismo clam 

 (Bruff", 1946), and below it are fine-grained 

 sediments that probably represent a marsh 

 buried by migrating beach sands (Emery, 

 1950c). 



Rocky Shores 



The favorite collecting grounds of biolo- 

 gists are along rocky shores because of the 

 abundance and wide variety of both plants 

 and animals. Vertical variations in flora and 

 fauna are produced within the intertidal 

 area and the wave and spray zone above it 

 by vertical differences in exposure, drying, 

 light intensity, temperature change, and 

 probably other factors. Similarly, horizon- 

 tal variations are produced by differences in 

 water temperature, exposure to waves, hours 

 of shade, kind of rock, and other factors. 

 Thus wide differences of organisms may be 

 noted between rocky intertidal areas of 

 caves, cliffs facing the open sea, rocks in the 

 lee of projecting shore points, and boulders 

 surrounded by sand. These horizontal and 

 vertical variations of flora and fauna have 

 given rise to many schemes of zonation that 

 are largely related to a particular worker's 

 chief site of work or to the kinds of organ- 

 isms in which he is most interested. Some 



Figure 127. Grunion [Leures- 

 thes tenuis (Ayres)] on beach 

 at La Jolla in 1937. At lower 

 right note females dug into 

 sand to lay eggs. Photograph 

 by E. C. LaFond. 



