(4) Triohophoxus epistomus (Amphipod) . Four species of this 

 genus were collected at Imperial Beach, but only T. epistomus was abun- 

 dant. This species ranked 6th in abundance intertidally, 5th at 3.7 

 meters, and 11th at 6.1 meters (Table 11). The geographic range of 



T. epistomus extends from California to Panama. 



Abundances of this species were highest at the 3.7- 

 meter depth. The average was from 200 to 550 per square meter (Fig. 34); 

 the pattern of abundance agrees well with Barnard (1963) who reported 55 

 per square meter from inshore depths of 2 to 5 meters with numbers 

 decreasing offshore. However, abundance was 4 to 10 times that found 

 by Barnard (1963) and probably reflects different sampling methods 

 (diver core samples versus remote grab samples) . Intertidal zone 

 abundances were. 10 to 91 per square meter and were highest during beach 

 replenishment (91 per square meter. Table 10, Fig. 35). At the 3.7- 

 meter depths, abundances fluctuated greatly with maximum estimated 

 densities of 1,127 per square meter being encountered at station B, 

 survey II (6 April 1977). As this survey was conducted 15 days after 

 the start of beach replenishment, this response by a mobile species such 

 as T. epistomus might be expected. No response was noted at station A 

 during survey II, and this impacted station did not differ from the 

 control station. At this time dredge disposal of sediments was local- 

 ized near station A (1.2 kilometers north from station B) and station B 

 had not been impacted by this operation. Consequently, it appears that 

 the large increase in density at station B was unrelated to beach re- 

 plenishment and may have resulted from changes brought about by the 

 severe erosion of intertidal station B between surveys I and II. The 

 large decrease observed at station B, 3.7 meters, for survey III (con- 

 current with beach replenishment) may have been due to beach replenish- 

 ment, but abundances were not significantly different (p<.05) than 

 station C. 



(5) Mandibulophoxus cilesi (Amphipod) . This species ranked 

 seventh in abundance at the 3.7-meter stations and reached densities in 

 excess of 600 per square meter (Table 11, Fig. 36). This species was 

 also more abundant at that depth than intertidally or at 6.1 meters. 

 Beach replenishment had no discernible effect on this species. 



(6) Cumaceans . Three species of cumaceans were common in 

 nearshore sediments at Imperial Beach. These showed strong depth 

 preferences. Leptocwna forsmani ranked 12th and 14th in abundance at 

 3.7- and 6.1-meter depths, respectively, and was not found intertidally. 

 This species was found consistently at all offshore stations during all 

 surveys except survey V when only three specimens were collected at 

 station B, 6.1 meters. 



Diastytopsis tenuis was common only at the 6.1-meter 

 stations ranking sixth in abundance. Densities reached over 800 per 

 square meter (Table 15) but populations fluctuated greatly. Barnard 

 (1963) reported 100 per square meter in southern California inshore 

 sands. Cyclaspis sp, B, an undescribed species, ranked third in 



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