NO. 3541 BENTHIC AMPHIPODA — BARNARD 3 



Geographic Positions and Environments 



The region of southern California, with a median latitude of 33° 

 N, extends from Point Conception on the north to the international 

 border between California amd Mexico on the south. The coastal 

 length is approximately 300 km. Monterey Bay, with a latitude of 

 approximately 36.5° N, Hes 275 km north of Point Conception. The 

 bay occurs near the southern end of the cold-temperate Oregonian 

 zoogeographic province and is within the Montereyan subprovince. 

 Monterey Bay is broad, semilunar, and about 30 km wide. Its 

 shelf is narrow and cut by the shoreward ends of the Monterey Canyon 

 complex occurring just north of the area shown in figure 1. The 

 benthic envu-oment, except for intertidal areas, has been scarcely 

 explored, but several known envu-onmental differences between 

 Monterey Bay and southern Cahfornia are explained below. 



Surface waters of Monterey Bay are dominated by the upwelling 

 of cool subsm-face layers (California Cooperative Fishery Investi- 

 gations, 1952-1964). Sea-sm-face temperatiu-es vary between 10° 

 and 14° C. The average sea-surface temperature of southern Cali- 

 fornia, at 33° N during 1957-1960, was about 17.5°, and the range 

 was 14° to 23° C (Jones and Barnard, 1963). Upwelling occurs from 

 place to place and is especially prominent in the Gulf of Santa Bar- 

 bara, where waters are entrained by the California cm-rent. 



The shelf of the southern part of Monterey Bay lies in greater 

 water depths than do Santa Monica Bay (Hartman, 1956) and San 

 Pedro Bay (Barnard and Ziesenhenne, 1961) of southern Cahfornia. 

 Very little of Monterey Bay is shallower than 37 m (20 fms). Those 

 southern bays have a large share of benthic area in the 27-46 m 

 (15-25 fms) depth interval. As a result, the benthic fauna of Mon- 

 terey Bay is dominated by deep-water ophiuroid communities, whereas 

 the southern bays are dominated by shaUow-water ophiuroid com- 

 munities or nonophiuroid communities. The distribution of the 

 communities in Monterey Bay is shown in figure 1. Contoiu-s are 

 necessarily diagrammatic because of low sampling frequencies. The 

 principal ophiuroids are Amphioda urtica (Lyman), Amphipholis 

 squamata (Delle Chiaje), Amphiura arcystata H. L. Clark, and 

 Amphioplus strongyloplax (H. L. Clark). The southern bays are domi- 

 nated principally by the Amphioplus hexacanthus H. L. Clark com- 

 munity (Barnard and Ziesenhenne, 1961), which occurs only on the 

 inshore margins of Monterey Bay. The deep-water Amphiodia urtica 

 is the common dominant of the outer shelf of southern California. 

 The prevalence of A. strongyloplax, A. amphacantha, and A. arcystata 

 in depths of less than 100 m in Monterey Bay is a reflection of the 

 northern emergence of communities occm-ring in southern California 



