(2) Donax gouldi-l (Bean Clam} . The bean clam is noted for 

 its tremendous temporal variations in abundance (Coe, 1953). However, 

 this species appeared consistently at all intertidal stations for all 

 surveys except during beach replenishment (survey III, station B inter- 

 tidal). Densities found in ether surveys ranged from 2 to 36 per square 

 meter. This typically intertidal species was occasionally found off- 

 shore at the 3.7- and 6.1-meter stations. Beach replenishment may have 

 been responsible for the absence of donax intertidal ly during survey III 

 when they were possibly buried by silt, but later postdisposal densities 

 at impacted stations A and B were equal to or higher than those observed 

 at the beginning of this study. 



(3) Telling modesta . This small deposit-feeding bivalve is 

 considered a community dominant between depths of 9 and 27 meters 

 (Barnard, 1963) . At Imperial Beach it was consistently taken only at 

 the 6.1-meter stations where it ranked eighth in abundance (Table 11). 

 Densities varied from 13 to 769 per square meter (Table 15). Beach 

 replenishment appears to have had no discernible effect on the abundance 

 or persistence of this species. 



f. Vertebrates (Fish) . Leuresthes tenuis (Grunion)is the only 

 fish reported in this study because it spawns in the upper intertidal on 

 a series of receding high tides. Alterations of beach topographies and 

 sediment parameters caused by beach replenishment could conceivably 

 affect the spawning of this species. Grunion are known to spawn at 

 Imperial Beach. 



Eggs and larvae of this species were found in cores only at 

 the dredge impacted stations A and B for survey IV (postdredge dis- 

 posal) . Evidently, the beach replenishment which terminated 37 days 

 before survey IV did not prevent grunion spawning in the project area. 



VI. CONCLUSIONS 



Adverse effects of beach replenishment were few except for the 

 direct burial of less mobile organisms. There was an increase in di- 

 versity and abundance of organisms correlating with increased sediment 

 silt fractions which were increased significantly by beach replenish- 

 ment. However, this biological enhancement also correlated with the 

 summer low wave energy and the corresponding less physically disturbed 

 nearshore area. The relative individual contribution of these two 

 factors on diversity and abundance is difficult to discern. The posi- 

 tive response of organisms to beach replenishment was of short duration 

 (less than 2 months) and largely exhibited by the mobile crustaceans. A 

 longer lasting response of most organisms in the community appears to be 

 associated with the relatively stable bottom in the summer and fall. 

 With the onset of winter storms and the concomitant offshore movement of 

 sediments, abundances declined significantly and diversity was lower for 

 most of the 3.7- and 6.1-meter stations. 



99 



