326 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 19 



SUBMERGED SEA MOUNTS IN THE 

 SAN PEDRO CHANNEL 



Two sea mounts (LS) in the San Pedro Channel have been biologi- 

 cally explored. 1 he larger Lasuen sea mount is on the eastern and the 

 smaller Sixmile bank on the western side of the channel (see Map 1). 



The Lasuen sea mount is located 13 nautical miles west of Newport 

 and beyond the outer end of Newport Canyon ; its base is in depths of 

 about 250 fms and it rises to 40 to 68 fms at its top. It measures about 

 3.25 by 5.33 miles and covers more than 16 square miles. Six samples 

 were recovered and analyzed. The sediments at the top are rocky, calca- 

 reous, with much debris ; downward the sediments contain much shelly 

 debris, mucoid stringy masses, Hocculent debris ; this gives way farther 

 down to gravelly debris and then sandy green mud. Siliceous sponge 

 occurs at its deepest perimeter. Ihe faunal components are richly diversi- 

 fied ; the most abundant and largest are echinoderms, coelenterates, mol- 

 lusks, polychaetes and crustaceans. 



1. Sta. 2298 (no. 235). SW end of sea mount, in 68 fms. OPG took 

 0.37 cuft of shelly sand and a few rocks. In addition to the species listed 

 on the chart, there were single individuals of anemone, nemertean, sipun- 

 culid (2), oligochaete (1), and crustaceans (amphipods and isopods) in 

 sparse numbers. Largest individual was Lanice conchi/ega, and most 

 abundant species were Spio punctata (148), and (Jhloeia pinnata (16). 



Numbers of species and specimens totalled : 

 polychaetes 33 species, 254 specimens 



echinoderms 4 12 



mollusks 3 3 



crustaceans 2* 2"^ 



others 4 14 



Total: 46* species, 285* specimens 



2. Sta. 2297 (no. 236). Southeast end of Lasuen sea mount, in 181 

 fms. OP(i took 0.68 cuft of large and small rocks, mud, gravelly debris, 

 with many small animals and a large brown, coarse sponge measuring 

 3 by 5 cm. In addition to those named on the chart, there were also a 

 sipunculid (2), an amphipod (2), a caprellid (1), and a tanaid (3). 

 None was abundant, and most were under-developed. Total number of 

 species was estimated at less than 30, and specimens numbered about 50. 



